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Water-related Diseases of People using Municipal Wastewater: Risks, Exposure, Control Approaches and Effects on Health in Tanzania.

Authors:

Abstract and Figures

The amount of available freshwater in most low- and middle-income countries is not sufficient to meet increasing demand. Treated municipal wastewater often becomes a significant source of irrigation water. Wastewater is valuable and its reuse has many potential benefits: flow is reliable even where water is scarce, nutrients increase agriculture production, and it can be used in many income-producing enterprises. Wastewater use also provides low cost reduction of a pollution hazard from direct release to the environment. Wastewater use is a health risk to people and animals. Contaminants can include pathogenic microorganisms and industrial pollutants. Some pathogens cause harm in smallest numbers, and wastewater may spread diseases to sewage systems workers, farmers, their families, downstream communities and consumers of irrigated produce. Common wastewater pathogens include helminths like roundworms, tapeworms, whipworms, hookworms and schistosomes. Perhaps half of Tanzanians have urinary or intestinal schistosomiasis; likewise, about half the population are infected with soil-transmitted helminths. Diseases caused by these worms are exacerbated by inaccessible health care and mediocre treatments. Data includes operational parameters from the Iringa wastewater treatment plant, a field survey of effluent use, observations, and a helminth assessment of four wastewater treatment plants. Effluent from Arusha, Iringa and Moshi met WHO standards for agricultural use; in Morogoro, the effluent included hookworm eggs. Many soil-transmitted helminth eggs settle into the sludge and are viable for years, making the sludge infectious. Schistosoma eggs hatch when they come into contact with water. The resulting miracidae must find snails, their obligatory host, within 48 hours. Without snails, the life cycle of the schistosome will end. Prevention, where actions are taken to prevent the occurrence of disease, is the most equitable way to deal with disease threats. Environmental modifications are generally more sustainable than treatment, and have longer-term impact. Environmental modifications that prevent disease include sewage treatment systems like waste stabilization ponds and constructed wetlands. Recommendations for wastewater reuse are divided into five categories: planning, design, construction, implementation, and monitoring. During planning, disease prevalence of humans and other animals must be evaluated. High background disease levels show that risk management procedures should be improved. Multisectoralism is crucial: the health sector and the engineering sector must work together. For effective disease control, engineering designs must consider the biological aspects of pathogens and their diseases; likewise, disease control will not be effective if health workers depend on drugs and health education without the preventive aspects inherent to well-engineered sewage treatment systems. Educational campaigns should improve knowledge and actions over the long term. Waste stabilization ponds should include fish to eat the mosquito larvae; constructed wetlands should generally be subsurface to decrease habitat for mosquito larvae. To protect workers and their families from wastewater pathogens, staff should wear clothing that can be cleaned in boiling water and rubber boots to protect their feet, and treatment plants should have a place to shower and disinfect after work. Agricultural practices and crops can be changed to reduce pathogen transmission from wastewater irrigation; sludge can be stored or composted to reduce ova content before land application. Regular monitoring should be site specific. Data on local disease incidence and prevalence should be collected periodically. Pond monitoring should include periodic checks for snails that are Schistosoma hosts. Influent should be tested for total petroleum hydrocarbons, heavy metals, pharmaceutics, and other pollutants; effluent should be monitored for coliforms and helminth eggs. We need continued research to reduce the disease-carrying potential of wastewater while utilizing its fertilizer value, and on the role of natural systems like mangrove forests and marshes in cleaning sewage-laden streams and rivers.
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DisseminationofthesustainablewastewatertechnologyofconstructedwetlandsinTanzania
ZEIN2011Z097
IR3
WaterrelatedDiseasesofPeopleusingMunicipal
Wastewater:
Risks,Exposure,EffectsonHealthandControlAp
proachesinTanzania
TeamMembers:
Outwater,AnneH.
Pamba,Siajali
Outwater,AliceB.
VLIRUOSSouthInitiatives20112013
Promoter:ThomasMoreKempenUniversityCollege
LocalPartner:UniversityofDarEsSalaam,WSPandCWResearchGroup
Dissemination of Sustainable Wastewater
Technology of Constructed Wetlands in Tanzania
Water-related Diseases of People
using Municipal Wastewater:
Risks, Exposure, Effects on Health
and Control Approaches
in Tanzania
Team Members
Outwater, Anne H.
Pamba, Siajali
Outwater, Alice B.
October 2013
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ii | Page
Water-related Diseases of People using Municipal Wastewater: Risks, Exposure,
Control Approaches and Effects on Health in Tanzania
(VLIR3 Research Project)
AH Outwater, S Pamba, AB Outwater
Summary
October 2013
The amount of available freshwater in most low- and middle-income countries is not
sufficient to meet increasing demand. Treated municipal wastewater often becomes a
significant source of irrigation water.
Wastewater is valuable and its reuse has many potential benefits: flow is reliable
even where water is scarce, nutrients increase agriculture production, and it can be
used in many income-producing enterprises. Wastewater use also provides low cost
reduction of a pollution hazard from direct release to the environment.
Wastewater use is a health risk to people and animals. Contaminants can include
pathogenic microorganisms and industrial pollutants. Some pathogens cause harm in
smallest numbers, and wastewater may spread diseases to sewage systems workers,
farmers, their families, downstream communities and consumers of irrigated produce.
Common wastewater pathogens include helminths like roundworms, tapeworms,
whipworms, hookworms and schistosomes. Perhaps half of Tanzanians have urinary or
intestinal schistosomiasis; likewise, about half the population are infected with soil-
transmitted helminths. Diseases caused by these worms are exacerbated by
inaccessible health care and mediocre treatments.
Data includes operational parameters from the Iringa wastewater treatment plant, a
field survey of effluent use, observations, and a helminth assessment of four
wastewater treatment plants. Effluent from Arusha, Iringa and Moshi met WHO
standards for agricultural use; in Morogoro, the effluent included hookworm eggs.
Many soil-transmitted helminth eggs settle into the sludge and are viable for years,
making the sludge infectious. Schistosoma eggs hatch when they come into contact
with water. The resulting miracidae must find snails, their obligatory host, within 48
hours. Without snails, the life cycle of the schistosome will end.
iii | Page
Prevention, where actions are taken to prevent the occurrence of disease, is the most
equitable way to deal with disease threats. Environmental modifications are generally
more sustainable than treatment, and have longer-term impact. Environmental
modifications that prevent disease include sewage treatment systems like waste
stabilization ponds and constructed wetlands.
Recommendations for wastewater reuse are divided into five categories: planning,
design, construction, implementation, and monitoring.
During planning, disease prevalence of humans and other animals must be evaluated.
High background disease levels show that risk management procedures should be
improved. Multisectoralism is crucial: the health sector and the engineering sector
must work together. For effective disease control, engineering designs must consider
the biological aspects of pathogens and their diseases; likewise, disease control will
not be effective if health workers depend on drugs and health education without the
preventive aspects inherent to well-engineered sewage treatment systems.
Educational campaigns should improve knowledge and actions over the long term.
Waste stabilization ponds should include fish to eat the mosquito larvae; constructed
wetlands should generally be subsurface to decrease habitat for mosquito larvae.
To protect workers and their families from wastewater pathogens, staff should wear
clothing that can be cleaned in boiling water and rubber boots to protect their feet,
and treatment plants should have a place to shower and disinfect after work.
Agricultural practices and crops can be changed to reduce pathogen transmission from
wastewater irrigation; sludge can be stored or composted to reduce ova content
before land application.
Regular monitoring should be site specific. Data on local disease incidence and
prevalence should be collected periodically. Pond monitoring should include periodic
checks for snails that are Schistosoma hosts. Influent should be tested for total
petroleum hydrocarbons, heavy metals, pharmaceutics, and other pollutants; effluent
should be monitored for coliforms and helminth eggs.
We need continued research to reduce the disease-carrying potential of wastewater
while utilizing its fertilizer value, and on the role of natural systems like mangrove
forests and marshes in cleaning sewage-laden streams and rivers.
iv | Page
CONTENTS
Summary
LIST OF FIGURES AND PLATES ................................................................... VI
LIST OF TABLES .................................................................................. VIII
ABBREVIATIONS AND ACRONYMS ................................................................ IX
CHAPTER ONE ...................................................................................... 1
1.1 Introduction / Background .................................................................. 1
1.2 Conceptual Framework ...................................................................... 3
1.3 Methodology .................................................................................. 4
1.3.1 Setting ........................................................................................ 4
1.3.2 Data collection methods ................................................................... 5
1.3.3 Data analysis ................................................................................ 6
CHAPTER TWO ...................................................................................... 9
2.0 Assessment of health risks of water-related diseases related to waste
sedimentation ponds and constructed ......................................................... 9
2.1 Introduction ................................................................................... 9
2.2 Helminths in Tanzania ...................................................................... 11
2.3 Schistosomiasis in Tanzania ............................................................... 14
2.4 Gaps ........................................................................................... 20
2.4.1 Challenges Affecting Prevalence ....................................................... 20
2.4.2 Challenges Preventing Treatment ...................................................... 21
2.5 Conclusion ................................................................................. 22
CHAPTER THREE .................................................................................. 24
3.0 Assessment of Exposures ................................................................... 24
3.1 Theoretical Assessment of Exposures .................................................... 24
3.2 Parameters for Assessments to Exposures ............................................... 26
3.3 Assessment of Socio-economic and Water Quality Exposures. Case Study Iringa.
........ ……………………………………………………………………………………………………………………………29
3.3.1 Iringa Municipal wastewater treatment plant ........................................ 29
3.3.2 Reuse of Municipal Wastewater Treatment effluent ................................ 31
3.3.3 The Perfomance of Iringa Municipal Wastewater Treatment plant ............... 32
3.3.4 Kleruu Teachers’ College Constructed Wetland ..................................... 38
3.4 Assessment of exposure to workers downstream of Kleruu constructed wetland..42
3.4.1 Exposure time of Workers to effluent from the constructed wetlands ........... 43
3.4.2 Assessment of Exposure Arusha: Wastewater Helminths ........................... 44
3.4.3 Rapid Assessment of Pathogen Exposure in four Municipal Waste Stabilization
Ponds ....................................................................................... 48
3.5 Diseases Associated with the Exposure risk ........................................... 51
v | Page
CHAPTER FOUR ................................................................................... 53
4.0 The use of Constructed wetlands for wastewater treatment......................... 53
4.1 Prevention .................................................................................... 53
4.2 Interventions ………………………………………………………………………………………………………….54
4.2.1 Reducing helminth ova in wastewater effluent………………………………………………….54
4.3 Waste Stabilization Ponds………………………………………………………......…..54
4.4 Constructed wetlands…………………………………………………………………….55
4.4.1 Reduce Helminth Ova in Sludge …………………………………………………………………………57
4.4.2 Long-Term Sludge Storage ………………………………………………………………………………… 58
4.4.3 Thermophilic composting of sludge …………………………………………………………………. 59
4.5 Changing agricultural practices to reduce helminth infections…………………………….60
CHAPTER FIVE ................................................................................... 62
5.0 Effects of Sewage Treatment on the Health of the People ........................... 62
CHAPTER SIX
6.0 Recommendations ........................................................................... 69
REFERENCES ...................................................................................... 75
APPENDICES ....................................................................................... 87
Appendix A. Millennium Development Goals and Targets ................................. 87
Appendix B. MKUKUTA Goals and Targets ................................................. 89
Appendix C. Parameters for Assessments of Water Quality through BOD, COD, TSS,
Nitrogen and Phosphorus ....................................................................... 97
Appendix D. Review of Water-borne Diseases in Tanzania ............................... 99
Appendix E. The median prevalence of helminth species infection (inter-quartile
range, minimum and maximum) (n) by region for Tanzania, 1980-2009.. ............ 118
vi | Page
LIST OF FIGURES AND PLATES
Figure 2.1The known geographical distribution of soil-transmitted helminths in
East Africa. ........... …………………………………………………………….12
Figure 2.3 Mwamgongo village landing site ................................................................ 16
Figure 2.4. Raw prevalence of self-reported schistosomiasis ...................................... 19
Figure 3.1 The layout of Iringa Municipal wastewater treatment plant ...................... 30
Figure 3.2 Free surface constructed wetland (a) at Iringa Municipal wastewater
treatment plant polishes effluent used for irrigation (b). .............. ........... 31
Figure 3.4 The influent to the Iringa Municipal wastewater treatment plant has
unusually high BOD5, plotted on a logarithmic scale ................................. 32
Figure 3.5 Iringa Municipal wastewater treatment plant, BOD5 in the influent and
effluent plotted on a logarithmic scale ..................................................... 33
Figure 3.6 Iringa Municipal wastewater treatment plant effluent BOD5 (mg O2/liter)
from the wastewater treatment plant and the constructed wetlands
plotted on a linear scale ............................................................................ 34
Figure 3.7 Iringa Municipal wastewater treatment plant chemical oxygen demand
(mg O2/liter) in influent and effluent plotted on a logarithmic scale ....... 35
Figure 3.8 Iringa Municipal wastewater treatment plant Total Dissolved Solids
(mg/liter) in influent and effluent .................................................. ........... 35
Figure 3.9 Iringa Municipal wastewater treatment plant Nitrogen levels (mg/liter) in
influent and effluent, plotted on a linear scale. ....................................... 36
Figure 3.10 Iringa Municipal wastewater treatment plant Phosphate levels (mg/liter)
in influent and effluent plotted on a linear scale. .................................... 36
Figure 3.11Iringa Municipal wastewater treatment plant coliform counts
(coliforms/100ml) in influent and effluent .............................................. .. 37
Figure 3.12 The pretreatment facility (a) and (b) the constructed wetland at Klerruu
Teachers’ College in December 2012. ........................................................ 38
Figure 3.13 The pie chart illustrates the reuse of effluent downstream of Klerruu
Teachers’ College constructed wetlands .................... Fout! Bladwijzer niet
gedefinieerd.
vii | Page
Figure 3.14 Wastewater concentration by month in 2012, and average monthly
rainfall in Tanzania 1901 to 2009. ............................................................ 40
Figure 3.15 Different types of crops irrigated by the effluent from constructed
wetlands at Klerruu Teachers’ College observed December 2012. ............ 40
Figure 3.16 Some students from Lugalo Secondary Schools near stream (a) fishing
while others are (b) playing in the garden irrigated with effluent
downstream from the constructed wetland. ............................................. 42
Figure 3.17 Helminth eggs found in wastewater in Arusha, Tanzania ......................... 45
Figure 3.18 Percentage removal of helminth eggs and BOD5 in waste stabilization
ponds; log removal of bacteria and viruses ............................................... 46
Figure 3.19 Reduction in helminth ova in wastewater before, during and after
treatment in a waste stabilization pond ........................ ............................ 48
Figure 3.20 Photos taken in August 2013 at the Arusha Municipal Sewage Treatment
System showing evidence of industrial effluent. ....................................... 49
Figure 3.21. Reduction in worm eggs by waste stabilization ponds and constructed
wetlands in Morogoro ................................................................................. 49
Figure 3.22. Wastewater Samples from Morogoro, focusing on possible Schistoma
molts/shells. .............................................................................................. 50
Figure 5.1 Freshwater withdrawals for agricultural use in the year 2000 and countries
reporting the use of wastewater or polluted water for irrigation ............. 62
Figure 5.2 Soil parameters in Nagpur, India after irrigation with freshwater and
wastewater .................................................................................................. 63
Figure 5.3 Crop Yields in Nagpur, India after irrigating with fresh water, untreated
sewage, and sewage after primary treatment .................................. ......... 64
Figure 5.4 Crop Yields in Nagpur, India after irrigating with fresh water, untreated
sewage, and sewage after primary treatment .................................. ......... 65
Figure 5.5 Nutrients in Chinese Cabbage irrigated with clean water and wastewater,
Iringa, Tanzania ....................................... .................................................... 66
Figure 5.6 Iringa Municipal wastewater treatment plant, BOD5 removal .................... 67
Figure (Appendix D1) Entamoeba coli cyst, center, found in Morogoro Municipal
Sewage System. Photo by Abdallah Zachariah .......................................... 103
viii | Page
Figure (Appendix D2) Number of cases of cholera reported to WHO by region (Africa,
Asia, Latin America) and year, 1960–2005 .................... .................. ........... 105
Figure (Appendix D3)Trachoma distribution in Tanzania ............. ............................. 107
Figure (Appendix D4)Ascaris lumbricoides egg found in Morogoro Municipal Sewage
Treatment System ..................................................................................... 108
Figure (Appendix D5)Hymenolepis diminuta egg found in Morogoro Municipal Sewage
System. ...................................................................................................... 109
Figure (Appendix D6) Hookworm ova found in the Morogoro Municipal Sewage System
.................................................................................................................................... 110
Figure (Appendix D7) P.falciparum rates. ................................................................ 115
Figure 2.9 The Spatial Limits of Plasmodium falciparum in Tanzania 2010 ............. 117
LIST OF TABLES
Table 2.1 Description of Important Water-related Diseases Important in Tanzania .... 9
Table 2.2Lake Tanganyika villages by Population, S. Mansoni prevalence, and snails
infected .............................. ....................................................... ................. 17
Table 2.3 Treatment of humans living in villages around Gombe National Park, for S.
mansoni treated with praziquantel ................................................. ........... 18
Table 2.4 Population using improved drinking water sources and sanitation facilities
...................................................................................................................................... 20
Table 3.1 Effluent limits for water discharged from a wastewater treatment plant .. 25
Table 3.2: Different categories, reuse conditions, exposure groups and wastewater
treatment expected to achieve required quality. ....................................... 27
Table 3.3 WHO guidelines for wastewater used to irrigate crops .............................. 28
Table 3.4 Exposure time for worker using wastewater for irrigation at different stage
of cultivation ............................................................................................... 44
Table 4.1 Helminth ova in sludge from waste stabilization ponds .............................. 57
Table 4.2 The reduction of the viability of helminth eggs in sludge stored for
different periods ................... .................................................... .................... 58
Table 4.3 Pathogen reductions achievable by selected health-protection measures 60
Table 2.2 Death rate per 100,000 for Diarrhoea and percent among all deaths among
people aged 15-59 years by sex, selected sites, Tanzania 1992-1998 ...... 101
ix | Page
ABBREVIATIONS AND ACRONYMS
CW Constructed Wetland
FSCW Free Surface Constructed Wetlands
IRUWASA Iringa Urban Water Supply & Sanitation Authority
MDG Millennium Development Goals
MKUKUTA Mkakati wa Kukuza Uchumi na Kupunguza Umaskini
Tanzania (National Strategy for Growth and Reduction of
Poverty)
MPN most probably number
SCI Schistosomiasis Control Initiative
WHO World Health Organization
WSP&CW Wastewater Stabilization Ponds & Constructed Wetlands
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CHAPTER ONE
1.1 Introduction / Background
The amount of available freshwater in most low- and middle-income countries is not
sufficient to meet the increasing demand.
Taking into account that 80% of water consumption leads to wastewater generation
(Qadir et al., 2010; Meneses et al., 2010), treated municipal wastewater can be a
significant source of irrigation water. In addition, urban expansion and increasing
population and industrial use has led to remarkable production of wastewater and
growing water scarcity for agricultural use.
The use of industrial or municipal wastewater in agriculture and aquaculture is a
common practice in many parts of the world (Blumenthal et al., 2000; Ensink et al.,
2002; WHO, 2006). The reuse of wastewater in these regions has grown rapidly and
has become a recommended practice (Agrafioti and Diamadopoulos, 2012).
Wastewater is valuable and its reuse has many potential benefits. It is often a reliable
supply of water to farmers for crop production, even in places of water scarcity
(Lubello et al., 2004; Oron et al., 1999; Pedrero et al., 2010). A major objective of
wastewater reuse is effective utilization of its nutrients, thereby reducing the need
for artificial fertilizers, increasing crops’ yields and returns from farming (Lubello et
al., 2004; Oron et al., 1999). In addition, wastewater provides sources of income
through its uses in other enterprises such as aquaculture or construction. Irrigating
with wastewater diminishes a pollution hazard from direct release to environment. It
can reduce the volume of wastewater being discharged to the environment (Pedrero
et al., 2010) and it is a low cost method for sanitary disposal of municipal wastewater
(IMWI, 2001).
Despite its many benefits, wastewater harbors potential dangers. Long-term
wastewater use can have negative impacts on soil resources – buildup of salts and
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heavy metals in the soils, which may reduce the productive capacity of the soil in the
long run (IWMI, 2001). The most serious danger of wastewater use is the risks to
people. Wastewater may contain contaminants, like heavy metals and industrial
pollutants. Most commonly, wastewater harbors dangerous levels of pathogenic
microorganisms such as bacteria, viruses, parasitic worms and protozoa that can lead
to disease. Some of these pathogens can cause harm in smallest numbers (Blumenthal
et al. 2000). The reuse of domestic wastewater for agriculture and aquaculture
increases exposure of sewage treatment system workers farmers, their families,
neighboring communities and even consumers of agricultural produce to infectious
diseases.
The World Health Organization (WHO) has estimated that 24% of the global disease
burden, and 23% of all deaths can be attributed to environmental factors (Prüss-Üstün
and Corvalán, 2006); among children 0–14 years of age, the proportion of deaths
attributed to environment factors is as high as 36%. There are more than 4 million
environmentally caused deaths among children every year, mostly in low- and middle-
income countries.
How much disease can be prevented with modification of the environment?
The definition of "modifiable" environmental risk factors include those reasonably
amenable to management or change (Prüss-Üstün and Corvalán, 2006). Examples
of modifiable waterborne environmental factors include:
• Pollution of air, water, or soil with chemical or biological agents
• Occupational risks
• Built environments including housing, land use patterns, roads, latrines,
sewage systems
• Agricultural methods and irrigation schemes
• Behavior related to the availability of safe water and sanitation facilities.
If any of these factors is sub-optimal, the result is a decrease in the health of the
environment and an increase in waterborne diseases.
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Decreasing this disease burden can make an important contribution to meeting the
Millennium Development Goals (MDGs) (see Appendix A). Environmental factors are
integral to all the MDGs, Goal 7 explicitly.
MDG 7. Ensure environmental stability
Providing sustainable sources of safe water and clean energy are key environmental
interventions that contribute to this MDG. The potential health gains from these
interventions can be appreciated from the global statistics for 2002: 1.1 billion
people, mostly in low- and middle-income countries, were still using potentially
harmful sources of water, and 2.6 billion people lacked even a simple improved
latrine. Billions of people are ill with diseases that could be prevented by improved
sanitation and hygiene.
Decreasing disease burden through increased access to sanitation is also an important
contribution to the Tanzanian National Strategy for Growth and Reduction of Poverty,
known as MKUKUTA (Mkakati wa Kukuza Uchumi na Kupunguza Umaskini Tanzania),
which was approved by Cabinet in 2005 for implementation over five years. The
MKUKUTA is informed by Vision 2025 and committed to the achievement of the
Millennium Development Goals (MDGs) (see Appendix B). Although the time span of
the plan is completed, the work continues.
The strategy identified three clusters of broad outcomes: (I) growth and reduction of
income poverty; (II) improvement of quality of life and social well-being, and (III)
good governance. Each cluster has a set of goals and targets. Within Cluster II is a
goal including increased access to sanitation and a sustainable environment, with the
aim of reducing vulnerability from environmental risks.
1.2 Conceptual Framework
This report focuses on waterborne diseases that can be transmitted through municipal
sewage systems, modifiable environmental risk factors, and the expected impact of
VLIR3. 2013. Outwater, Pamba, Outwater
4 | Page
waste management through waste sedimentation ponds and constructed wetlands. To
answer the question of how people can safely use waste water, we need to think of
how specific diseases and injuries are impacted by environmental risks.
Following an expert meeting in Stockholm, Sweden, the World Health Organization
published Guidelines, Standards, and Health: Assessment of Risk and Risk
Management for Water-related Infectious Disease (Bartram, Fewtrell & Stenström,
2001). This document creates a harmonized framework for the development of
guidelines and standards, in terms of water-related microbiological hazards.
What became known as the Stockholm Framework provides the conceptual framework
for WHO water-related guidelines. The Stockholm Framework involves:
1/ Assessment of health risks prior to the setting of health-based targets
2/ Development of guideline values
3/ Definition of basic control approaches
4/ Evaluation of the impact of these combined approaches on public health.
This Framework has been adapted for the present report.
The overall aim of this paper is to provide a holistic picture of risks and benefits of
urban wastewater use in agriculture. The objective of this paper is to provide a
framework for the analysis of socioeconomic, health, and environmental aspects of
urban wastewater use in the agricultural sector. The specific objectives of this paper
are to: 1) identify various impacts (short-term and long-term) of urban wastewater
use in agriculture, and 2) identify/develop approaches and methods for assessing,
valuing and analyzing these impacts.
1.3 Methodology
1.3.1 Setting
The setting is Tanzania. Data are presented from four municipalities which have
constructed wetlands and/or waste sedimentation ponds for municipal sewage
VLIR3. 2013. Outwater, Pamba, Outwater
5 | Page
treatment: Arusha, Iringa, Morogoro, and Moshi. Iringa, used as a case study, is in the
Southern Highlands of Tanzania.
1.3.2 Data collection methods
Assessment of Health Risks
1/ Literature Review
Data about health risks were identified and collected using electronic databases
including Google Scholar and PubMed. Members of the Wastewater Stabilization Ponds
& Constructed Wetlands (WSP&CW) Research Group provided relevant student
dissertations.
2/ Case study
i. Government monitoring parameters for Iringa Municipal wastewater
treatment plant
Data from the Iringa Municipal wastewater treatment plant was obtained from Iringa
Urban Water Supply and Sewerage Authority (IRUWASA). Samples were collected on a
monthly basis from May to November 2012 by IRUWASA from the inlet strainer partial
flume, outlet anaerobic pond 1 and anaerobic pond 2, outlet of the maturation pond
and at the outlet of the constructed wetland (Fig 1.2).
ii. On-site field survey
An on-site field survey during 5th to 7th December 2012 focused on agricultural workers
and people living near the Klerruu Teachers College constructed wetland. The survey
questionnaire focused on assessment of health risk, water sanitation and hygiene.
Respondents were requested to describe their reuse of the wastewater from Klerruu
constructed wetland.
Box 1: Questions for assessing health risk from effluent from Iringa Municipal
wastewater treatment plant
How is the effluent used?
VLIR3. 2013. Outwater, Pamba, Outwater
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Do you catch or eat fish from the ponds? How often? How much?
How much time do you spend in the water? What do you do in the water?
Do you feel any concern about the water?
For families and community members:
Where do you get your drinking and household water?
Where do you defecate and urinate?
In the last month, have you experienced ear infections, skin infections, skin
rashes, diarrhoea?
iii. Observation
On-site observation was conducted and a photographic record was made. Types of
effluent re-use were identified and the duration of time spent in contact with
wastewater due to farming practices was recorded. Identification of crops and
irrigation use of wastewater downstream of Klerruu Teachers College and the
municipal wastewater treatment system were observed.
iv. Assessment of pathogen exposures
In August 2013 data were collected from the Arusha, Iringa, Morogoro and Moshi
municipal sewage systems. Water samples were collected from four municipal sewage
systems. Five to six samples were collected from consecutive points in each sewage
system as follows: i/ influent to Pond 2 – a facultative pond, ii/center of Pond 2, iii/
effluent from Pond 2, iv/ influent to constructed wetland, v/ effluent from
constructed wetland, and vi/ effluent from fishpond if there is one. For each sample
ten liters of water were collected and allowed to settle for 2-3 hours. One liter of
sediment was fixed with 10% formalin, then transported to the WHO supported
laboratory at Muhimbili University of Health and Allied Sciences in Dar es Salaam.
1.3.3 Data analysis
1/ Literature for the review was gathered and organized by relevant
categories.
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2/ The case study presented in Chapter Three is comprised of
i. The parameters measured during the government monitoring of the
Iringa Municipal wastewater treatment plant which include Biochemical
Oxygen Demand (BOD), Chemical Oxidation Demand (COD), Nitrate (NO3-
N), Nitrite (NO2-N), Phosphate (PO4), Faecal Coliforms, Total Dissolved
Solid (TDS), Ammonia (NH4-N) and pH (see Appendix C).
The performance of the system for BOD and ammonia removal is a good
indicator for the reuse of effluent for aquaculture, while a level of
ammonia, nitrate and phosphate provides information pertaining to the
beneficial reuse of effluent for irrigation. The level of faecal coliform
was mainly used in the present study to assess possible health risk
associated with exposure to the wastewater.
ii. A socioeconomic survey about Klerruu constructed wetland wastewater
reuse was completed. The answers were categorized and represented in
percentages in pie charts and graphs.
iii. Observations and photographs were organized into the categories of the
on-site questionnaire.
iv. To assess pathogen exposures, data from an unpublished student
dissertation (Marwa, 2011) were re-analyzed. Data that had been
presented on a linear scale was replotted on a log scale.
v. Each newly collected sample was centrifuged and in the laboratory WHO
techniques were followed (Ayres & Mara, 1996). Each sample was
examined for: Faecal coliforms, Ascaris lumbricoides, Trichuris
trichuira, Nector americanus, Hymenolepsis nana, Taenia, Schistosoma
haematobium, Schistosoma mansonii, Entamoeba histoylica, and
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Entamoeba coli. When the laboratory scientist had questions about
anything he was seeing, he consulted with other experts nearby.
vi. Chapter Five data of conductivity, pH, nitrate, ammonia, phosphate,
calcium, magnesium and iron content in vegetables irrigated with
effluents from Iringa Municipal wastewater treatment plant was
obtained from a 2012 water quality laboratory report. The report was
mainly based on investigation of pollution accumulation in vegetables
irrigated with wastewater effluent by Kahwa.
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CHAPTER TWO
2.0 Assessment of health risks of water-related diseases related to waste
stabilization ponds and constructed wetlands
2.1 Introduction
There is a long list of human diseases related to water, sanitation and hygiene as
described in Appendix D. The failure to properly treat and manage wastewater and
excreta worldwide is directly responsible for many adverse health and environment
effects. Bacterial diseases and health problems include salmonellosis, shigellosis,
cholera, trachoma, skin rashes and infections, ear infections; viral diseases include
infectious hepatitis and gastroenteritis; protozoans and amoebas cause health
problems such as giardiasis, amoebic dysentery and cryptosporidiosis; and parasitic
helminths including nematodes (roundworms), cestodes (tapeworms) and trematodes
(flukes) are involved with ascariasis, trichuriasis, hookworm infection and
schistosomiasis. Malaria is not usually considered a waterborne disease but is a
concern in water and sanitation treatment if systems provide sites where mosquitos
breed.
Table 2.1 Description of Important Water-related Diseases Important in Tanzania
Disease Cause Type of
pathogen Common Mode
of
transmission
% of disease
attributable
environment
(% to water,
sanitation
and
hygiene)*
Notes
Diarrhoea
Salmonella spp
Shigella spp
Giardia lambia
Antamoeba
histolityca
Rotavirus
Norwalk
Bacteria
Protozoa
Faecal-oral
94 (88)
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Gastroenteritis
Virus
Cholera Vibrio cholera Bacteria
Faecal-oral
usually 2o
to
contaminated
water
Trachoma Chlamydia
trachomatis Bacteria
Hygiene e.g.
flies, clothing
100
Ascariasis
Roundworm
Ascaris
lumbricoides Helminth
(Nematode)
Ingestion of
eggs
100 (100)
Trichuriasis
Whipworm
Trichuris
trichiura Helminth
(Nematode)
Ingestion of
eggs
100 (100)
Hookworm
infection Necator
americanus Helminth
(Nematode)
Larval
penetration of
the skin,
Ingestion of
eggs
100 (100)
Schistosomiasis:
(Bilharzia)
Urinary
Intestinal
Schistosoma
haematobium
Schistosoma
mansoni
Helminth
(Trematode)
Larval
penetration of
the skin
100 (100) Intermediate
host = snails
Malaria Plasmodium
falciparum,
ovale, malariae,
vivax
Protozoa
Anopheles
mosquito bite.
42
Eggs and
larvae are
aquatic
*estimates by Prüss-Üstün and Corvalán, 2006.
According to Prüss-Üstün and colleagues, 13% of all deaths in Tanzania are water
related. For children under five, the proportion is even higher (2008, p.52). Deaths
attributable to water sanitation and hygiene in Tanzania in 2004 (the most recent
year for which WHO statistics are available) were 32,665 over all, of which 21,499
were children.
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However, not all these diseases strongly affect people who work in sewage treatment
plants and constructed wetlands or users of effluent per se. Diarrhoea and cholera are
primarily associated with untreated drinking water. Trachoma is generally associated
with flies and with personal hygiene between mother and child, for example when the
mother cleans the eyes of her child with an infected cloth. Malaria is a theoretical
risk and certainly poses many societal and economic burdens in Tanzania, ranging
from school absenteeism to low productivity in the workplace. However, it seems that
sewage treatment plants are not usually important contributors to the disease. The
waste stabilization ponds have fish and other predators that eat mosquito larvae, and
most constructed wetlands in Tanzania are sub-surface.
In this chapter, waterborne diseases prevalent in Tanzania that are directly related to
workers at waste stabilization ponds and constructed wetlands and effluent users are
examined through the current literature. These include ascariasis, trichuriasis,
hookworm infection, and both urinary and intestinal schistosomiasis. Special focus is
placed on Arusha, Iringa, Morogoro, and Moshi regions where the WSP&CW Research
Group has projects.
2.2 Helminths in Tanzania
The atlas of human helminth infections in East Africa was recently updated by Brooker
and colleagues (2009). As shown on the following maps, East Africa is described as
Burundi, Rwanda, Tanzania, Kenya, and Uganda. To construct these maps, empirical
data collected between 1980 and 2008 were used. Details of survey population,
diagnostic methods, sample size and numbers infected with schistosomes and soil-
transmitted helminths were recorded. The authors attempted to identify the
geographical location of each record and then assembled the data into a geographical
information system.
For Tanzania alone they assembled 410 studies, 91.5% of which were published. Most
of the surveys in Tanzania were conducted post-2000. As can be seen on the maps,
most of the records from Tanzania were data collected in the northeast and from
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around Lake Victoria. There were big gaps in the data set as no studies had been
conducted in many regions, including Arusha, Dodoma, Iringa, Kigoma, Lindi, Mara,
Rukwa, Ruvuma and Singida (see Appendix E).
Figure 2.1 The known geographical distribution of soil-transmitted helminths in
East Africa. The geographical distribution of (A) hookworm (B) Ascaris lumbricoides
(C) Trichuris trichuira, based on available survey collected between 1980 and 2009
and categorized according to WHO prevalence thresholds (n=1,948)
From Brooker et al., 2009.
As shown in Appendix D, hookworm, roundworm and whipworm were found in human
beings in 13 of Tanzania’s 26 regions. That is, they were found in 13 of the 17 regions
for which there is data. These parasites are widespread, but not everywhere.
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Of these soil-transmitted helminths, hookworm was the most common. Hookworm in
Tanzania has been found to be widespread along coastal Tanzania since the early
twentieth century, particularly in the farms and plantations around Tanga and Dar es
Salaam. It was believed to be spread chiefly among large congregations of workers
and to have become widespread with the development of the plantation economy
(Kopenen, 1994). In many plantation areas, 30 to 60% of Africans were carriers of
the parasite. The number defined as “sick” was smaller – about 1% to 4% of the
carriers. The definition of “sick” was “incapable of work as a result of hookworm”.
Those who complained of “paleness of skin, pain, constipation, etc.” did not qualify.
Considering studies since 1980, the prevalence of hookworm ranged from 3.5% in
Kilimanjaro to 81% to 95% in South and North Pemba, respectively. The median
presence of hookworm, considering all the studies in Tanzania, was almost 50%.
Whipworm and Ascaris share similar prevalence and regional patterns, with high
prevalence in Pemba and North Zanzibar and low prevalence in continental Tanzania.
Their ranges are more restricted. In Tanzania their highest prevalence is in Pemba,
where over 90% of the people are infected. On the mainland prevalence is
insignificant in many places, with a high of about 7% for both worms in populations in
Kilimanjaro.
The rates for helminth infection were found to be low in Ifakara, where a matched
case control study focusing on diarrhoea also tested the stools of the 309 children for
parasites (Gascon et al. 2000). Few children in Ifakara tested positive for parasites:
5 tested positive for hookworm, 2 for Strongyloides stercoralis, and one each tested
positive for Ascaris lumbricoides, Cryptosporidium, and Antamoeba histolyca.
Intestinal nematodes do not seem to play a role in diarrhoeal diseases in Ifakara. Low
rates of nematodes in both patients and controls suggest a low incidence of these
health problems in the Ifakara region for patients of this age (Gascon et al., 2000).
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2.3 Schistosomiasis in Tanzania
Schistosomiasis was first reported in Tanzania decades ago (Mallya, 1988) and since
then cases of its occurrence in other parts of the country have been confirmed. The
two most common species of the blood fluke are Schistosoma haematobium and
Schistosoma mansoni, both of which are endemic to East Africa. In 1988 it was
estimated that 38% of the general population was infected with schistosomiasis
(Mallya, 1988).
Brooker and colleagues also mapped the prevalence of Schistosoma haematobium
and S. mansoni in Tanzania by using data gathered by research studies from 1980-
2009.
Figure 2.2: The known geographical distribution of schistosomiasis in East Africa. The
geographical distribution (A) Schistosoma haematobius and (B) S. mansoni infection,
based on available survey collected between 1980 and 2009 and categorized according
to WHO prevalence thresholds (Brooker et al., 2009).
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As shown in the above figure, many areas of Tanzania, including most of the southern
regions, have not been sufficiently surveyed for schistosomiasis. Urinary
schistosomiasis (S. haematobium) appears to be much more prevalent than intestinal
schistosomiasis (S. mansoni). S. haematobium was found in 14 of Tanzania’s regions
with a national median prevalence of over 30%. Urinary schistosomiasis is distributed
along the Indian Ocean coast and Lake Victoria. The highest mean prevalence was in
Mwanza (58.3%). Interestingly Kagera had a very low prevalence recorded for both S.
haematobium and S. mansoni. S. mansoni was found in nine of Tanzania’s 26 regions
but the prevalence generally appears to be comparatively low. In three regions none
was found. The highest rates were found in Kilimanjaro and North Unguja.
Jared Bakuza of the Dar es Salaam University College of Education, addressed a gap in
the atlas with data from his PhD dissertation. Bakuza and colleagues from Glasgow
University mapped the epidemiology of intestinal schistosomiasis along the shores of
Lake Tanganyika. Between January and September 2010, stool samples were collected
from 235 children and 171 adults at Gombe National Park and four neighboring
villages. The stools were examined for parasite ova using the Kato-Katz technique.
Baboon and vervet monkey stools were also examined. High rates of S. mansoni were
found in Kigoma region.
As shown in Table 2.2, S. mansoni infection was recorded at an overall prevalence of
47% across study sites.
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Figure 2.3 Mwamgongo village landing site. Photo by J. Bakuza.
Two villages (Gombe and Mtanga) had adult schistosomiasis rates of 44% whilst the
others had rates of 50%. The difference of a few percentage points in the adult rates
of schistosomiasis infection was reflected as dramatic differences in the prevalence of
schisotosomiasis among children. The children living in a village where the adults had
the lower rate of S. mansoni infection had childhood prevalence rates of about 10%.
Where the adults had rates of 50%, the children prevalence of schistosomiasis ran
from 38% in Kiziba to almost 90% in Mwamgongo.
The important questions of what are the differences between villages of high and low
child schistosomiasis prevalence is not yet explained. Childcare practices, hygiene
practices, latrine siting, water usage, and previous exposure to praziquantel could all
be partial answers and need to be urgently sorted out.
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Table 2.2 Lake Tanganyika villages by Population, S. Mansoni prevalence, and
snails infected (Bakuza, 2012).
Site N
Adults
N Child
<18 yrs
N
Snails S.mansoni
Prevalence
Adult
S.mansoni
Prevalence
Child
S.mansoni
Prevalence
Snails
Bugamba 28 57 23
50
70
30
Gombe 45 10 47
44
10
0
Kiziba 16 64 27
50
38
63
Mtanga 35 49 44
11
?
Mwamgongo 46 54 96
50
89
57
Total/Average
170 234 220
47
43
47
Snails known to harbor schistosomes were also analyzed for infection. The rate of
snail infection paralleled that of human adult infection so that the lowest proportion
was at Gombe (zero) and the highest percentage of infected snails were at Kiziba,
where 57% were infected.
While none of the 16 vervet monkeys appeared to be infected with S. haematobium,
the stools of 13% of 136 baboons harbored S. mansoni. Moreover the DNA tests imply
that the baboons were probably becoming infected with schistosomiasis through
closer interaction with humans and their waste. Baboons spend more time than
vervets on the ground. Baboons are also more willing to cavort in the water giving the
Schistosoma cercariae time to burrow into their skin.
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Table 2.3 Treatment of humans living in villages around Gombe National Park, for S.
mansoni treated with praziquantel (Bakuza, 2012).
S. mansoni Before
Treatment After treatment
Prevalence (%) 79.10 19.40
Intensity (epg) 574 22.22
Praziquantel, the standard and recommended drug of choice, as part of their ethical
obligations was given to people in villages in which more than half the population was
infected with schistosomiasis. The praziquantel showed itself to be an effective drug,
yet also it cleared only about 75% of the infections and heavily reduced egg intensity
by 96%. It needs to be noted that treatment is not 100% effective and a significant
minority of the treated population were left harboring schistosomes.
Tanzania is one of the initial six focal countries for the international Schistosomiasis
Control Project. To make baseline data for use in this project, answers were
obtained from 2,586,140 schoolchildren, between 7 and 14 years old, in 12,399
schools located in 2373 wards in 116 districts (Clements, Brooker, Nyandindi, Fenwick,
Blair, 2008). They were asked if they have schistosomiasis, and/or if they had blood
in their urine (a common symptom in urinary schistosomiasis).
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Figure 2.4. Raw prevalence of self-reported schistosomiasis (a) and blood in urine (b)
in Tanzanian wards.
Overall, the prevalence of self-reported schistosomiasis was 24.8% and prevalence of
self-reported blood in the urine was 20.5%. Maps based on the children’s answers and
maps based on geostatistical prediction from other data show a lot of similarity.
These maps will be used to prioritize praziquantel distribution.
The SCI in Tanzania will be treating seven neglected tropical diseases with this
program: schistosomiasis, lymphatic filarial, onchoceriasis, trachoma, hookworm
infection, ascariasis, and trichuriasis. Although they state that the problem is due to
poor sanitation and lack of water, and they expect high re-infection rates, the
approach is primarily pharmaceutic including Praziquantel for the schistosomiasis and
albendazole for the other helminths.
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2.4 Gaps
Many of the disease study sites were chosen to be generally illustrative of the
condition of many Tanzanian citizens. But geographic disease data from many regions
in Tanzania is sparse or absent, especially in the southeast part of the country. There
is also a lack of data on urban and peri-urban populations. None of the studies
reported here included communities or individuals connected to municipal sewage
systems or constructed wetlands.
2.4.1 Challenges Affecting Prevalence
Access to safe drinking water and improved sanitation
The table below based on WHO data shows that the proportion of the population with
access to improved drinking water sources has decreased overall since 1995. Slightly
more than half of Tanzanians had improved drinking water in both 1995 and 2010.
The proportion of the population with improved sanitation facilities has increased
slightly, but the total by year 2010 was only 10% of the population overall and 20% in
urban areas.
Table 2.4 Population using improved drinking water sources and sanitation facilities
Population using
improved drinking-water
sources (%)i Population using improved
sanitation facilities (%)i
Rural Urban
Total
Rural
Urban Total
United
Republic
of
Tanzania
2010 44 79
53
7
20 10
2005 45 83
54
7
18 10
2000 45 86
54
7
15 9
1995 46 90
55
7
13 8
Source: World Health Organization, n.d
While the population has increased, the proportion of people with improved drinking
water sources has decreased and the fraction of the population connected to a sewer
system has very minimally increased. During this period, bottled water became widely
available, especially in urban areas. Corporations including Coca Cola (Kilimanjaro
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brand) and Pepsi (Dasani brand) have participated in increasing access to drinking
water for those who can afford it even as public access has fallen. In the case of
water connections especially, perhaps project-provided hardware broke and could not
be repaired, or the projects were built poorly and could not be fixed.
It is important to note that in the last fifteen years, the proportion of people with
access to clean water has decreased and improved sanitation has barely increased,
and then only in urban areas. These data may also be pointing to the fragility of the
existing systems and incomplete planning for follow-up and maintenance.
2.4.2 Challenges Preventing Treatment
The persistently high case fatality rate in the WHO Africa Region reflects general
problems in access to effective health care.
Infrastructure
Access to health facilities is often difficult. There is often no readily available
transportation for patients too ill to walk. In 1999, a median of only 12% of roads in
Africa were paved (Gaffga, Tauxe, Mintz, 2007).
Access to health care
The average health care bed/population ratio in the WHO Africa Region was one tenth
the average for high-income countries and half the average seen in other low- and
middle-income countries. With only 2.3 health workers per 100,000 people, Africa
also has a smaller health workforce than any other region (WHO, n.d.).
Access to proper treatment
A patient can arrive at the hospital only to meet inadequate care. For example, use
of oral rehydration therapy and proper case management of diarrhoea in Africa is
suboptimal. Recent data from Demographic and Health Surveys conducted in Africa
from 1988–2003 indicate that the proportion of children under 5 years old with
diarrhoea who did not receive oral rehydration solution or increased fluids during
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diarrhoea episodes actually rose in nine of ten African countries during this period
(Gaffga et al., 2007).
Assessment of health risks
Water borne diseases in Tanzania are common and widespread. There also appears to
be wide variability in community prevalence of these diseases. Overall in the short
term, widespread morbidity reduces agricultural production and other economic
outputs. In the long-term, the accumulated effect certainly decreases national
economic capacity and development. The burden of one or more of these diseases
downgrades the quality of life.
There are many collateral effects of waterborne diseases. For example, all these
diseases can lead to malnutrition and anaemia. Individual nutritional status depends
on the food that an individual eats, his or her general health, and the physical
environment. In all three aspects, poor water and sanitation play an important role
and diseases caused by intestinal parasites are related to poor water, sanitation,
hygiene and food safety (Martorell, Mendoza and Castillo, 1988; Prüss-Üstün et al.,
2006). It has also been shown that the levels of water and sanitation services
significantly affect weight gain in infants (Esrey, Habicht and Casella, 1992; Esrey,
1996).
2.5 Conclusion
Overwhelmingly, while there is geographic variability in prevalence for reasons that
are not always clear, the overall high rates of these diseases in Tanzania highlight
that the environment is conducive to diseases related to water, sanitation, and
hygiene. In every city, town, and almost every village, Tanzanians are at high risk for
ill health due to infectious disease. Due to deficiencies in basic sewerage and
hygiene, waterborne diseases including helminths are leading causes of morbidity and
mortality among all age groups in Tanzania. This has profound results in terms of
quality of life, and weighs heavily on the health system.
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How people are exposed to those diseases in Tanzania is the focus of the next
chapter.
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CHAPTER THREE
3.0 Assessment of Exposures
3.1 Theoretical Assessment of Exposures
The process of microbiological risk assessment was considered to comprise three
phases, namely problem formulation, analysis, and risk characterization (ILSI, 2000).
The analysis phase consisted of two elements: the characterization of exposure and
characterization of human health effects (ILSI, 2000). The characterization of
exposure requires an evaluation of the interaction between the pathogen, the
environment and the human population.
Generally, the major health risks for people in direct contact with wastewater are
diarrhoeal diseases, skin problems and worm infections. The most affected groups are
those who are work in fields irrigated with wastewater and consumers of wastewater-
irrigated produce. Quantitative microbial risk assessment studies indicate that this is
a significant threat for farmers and consumers (Seidu et al. 2008). In Ouagadougou,
the capital of Burkina Faso in West Africa, soil, crop leaves and vegetables including
carrots, lettuce, and tomatoes were found to be heavily contaminated by faecal
coliforms and helminth eggs (Cissé et al. 2002). The authors also reported that family
members of market gardeners were often ill. Similar vegetable contamination was
reported in other areas including Ghana (Amoah et al., 2006), Turkey (Erdogrul and
Sener, 2005), and Morocco (Amahmid et al., 1999).
For unrestricted crop irrigation, it is very important to remove the pathogens from
the wastewater. As recently as the 1970s, wastewater reuse standards were based on
a "zero-risk" concept with the intent of achieving a pathogen- or microbial-free
effluent without accounting for pathogen-host relationships or epidemiological
evidence of disease transmission caused by using wastewater for irrigation (Hespanhol
and Proust, 1994). These zero-risk technology-based standards could be met, so
countries with this advanced level of technology set extremely rigorous standards for
wastewater reuse. In the United States, for example, the California State Health
Department adopted a bacterial standard for unrestricted wastewater irrigation of
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less than 2.2 total coliforms/100 ml, close to the existing drinking water standard
(FAO, 1997). The prohibitively high costs of treating wastewater to this level prior to
reuse for crop irrigation may not be justified on economic, social, or political
grounds. Nevertheless, valuation of public health risk should be an important decision
variable in wastewater irrigation policy analysis.
Effluent limits represent the maximum allowable concentrations of pollutants in
wastewater. These limits vary between countries due to geography, climate and
socio-economic differences. They also vary depending on the final destination of the
wastewater: effluent limits for wastewater discharged to the ocean are less stringent
than effluent limits for wastewater used for agriculture. Effluent limits define the
quality of the discharged wastewater, so these limits are used as water quality
objectives when designing local wastewater treatment plants.
Table 3.1 Effluent limits for water discharged from a wastewater treatment plant
E.U.
(mg/l) India
(mg/l)
Tanzania
(mg/l)
BOD5 25
30
30
COD 125
250
60
Total suspended solids (TSS)
150
100
100
Total Nitrogen
15 (10)*
100
15**
Total Phosphorus
2 (1)*
5
6
*If city population exceeds 100,000.
**Total Kjeldahl Nitrogen (as N) including organic nitrogen, ammoniacal
nitrogen – not including nitrate and nitrite nitrogen and not necessarily
including all organically bound nitrogen.
Fecal coliform limits are highly variable. The EU standards are as follows: "Depending
on the water quality standards, the fecal coliform limits for municipal wastewater
range from less than 2.2 colonies/100ml up to 5000 colonies/100 ml, with 200
colonies/100ml being the most common limit." In India, "the standard for fecal
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coliforms in the effluent from sewage treatment plants are 1000 MPN /100 ml
(desirable) and 10, 000 MPN/100 ml (permissible)." In Tanzania, the limits are 10,000
MPN/100 ml.
The European Union effluent standards are for wastewater discharged into surface
and coastal waters; in India, the effluent standards for the discharge of treated
wastewaters into inland surface waters are given in the Environment Protection Rules
(CPCB, 1996, Ramadan and Ponce, 2013). In Tanzania, the effluent standards are for
wastewater discharged into water receiving bodies (Tanzania Bureau of Standards,
2005). Parameters to assess these limits are discussed in Appendix C.
3.2 Parameters for Assessments to Exposures
Since it is expensive and time consuming to detect different types of microbial
pollutants in wastewater, faecal coliforms are used as an indicator organism to
determine if other contaminants associated with faeces, like parasitic protozoa or
bacteria, are likely to be present in wastewater (Paillard et al., 2005). In Ifakara,
Tanzania Escherichia coli was found more than any other enteropathogen. However
none of the many strains of E. coli were an absolute measure of the presence of
pathogenic microbes, but rather a measure of the potential for the presence of
pathogens that might be associated with faecal material (Cooper, 1991).
There are benefits to using effluent for irrigation, but there are real risks as well.
Effluent quality is a critical factor, but since effluent limits are typically set to
protect the health of the waterways, most of the parameters used to characterize
wastewater address the impacts of effluent on the waterways rather than on human
health.
The World Health Organization recommended microbiological quality guidelines for
wastewater used for irrigating crops in 1989. These irrigation standards require that
effluent contain less than 1 intestinal nematode per liter, and less than 1,000 faecal
coliforms per 100ml.
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Table 3.2: Different categories, reuse conditions, exposure groups and wastewater
treatment expected to achieve required quality Source: Westcot, 1997.
Cat Reuse
Conditions Exposed
Group Intestinal
Nematodes1
(/liter*)
Faecal
coliforms
(/100ml**)
Wastewater
treatment expected
to achieve required
quality
A Irrigation of
crops likely to
be eaten
uncooked,
sports fields,
public parks2
Workers,
consumers,
public
<1
<1000
A series of
stabilization ponds
designed to achieve
the microbial quality
indicated, or
equivalent
B Irrigation of
cereal crops,
industrial
crops, fodder
crops, pasture
and trees3
Workers <1
None set
Retention in
stabilization ponds for
8-10 days or
equivalent helminth
removal
C Localised
irrigation of
crops if
category B
exposure of
workers and
the public
does not occur
None n/a
n/a
Pretreatment as
required by irrigation
technology, but not
less than primary
sedimentation
In 2006, the WHO revised their guidelines for the safe use of wastewater, faecal
material and sludge in agriculture and aquaculture. Rather than setting absolute
limits on the number of helminth ova allowed in water used for irrigation, the revised
1Inspecificcases,localepidemiological,socioculturalandenvironmentalfactorsshouldbetakenintoaccount,andthe
guidelinesmodifiedaccordingly.
2AscarisandTrichurisspeciesandhookworms
3Amorestringentguideline(<200faecalcoliforms/100ml)isappropriateforpubliclawnswithwhichthepublicmaycomeinto
directcontact
4Inthecaseoffruittrees,irrigationshouldceasetwoweeksbeforethefruitispickedandnoneshouldbepickedoffthe
ground.
*ArithmeticMeanduringtheirrigationperiod
**Geometricmeanduringtheirrigationperiod
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WHO effluent limits are based on the fraction of helminth ova that are removed
during the wastewater treatment process. For example, if the influent to a
wastewater treatment plant has 1000 helminth ova and the effluent has 100 helminth
ova, then wastewater treatment has resulted in a 90% reduction of the contaminant
or a 1-log removal. With an influent containing 1000 helminth eggs per liter and an
effluent with 10 helminth eggs per liter, the reduction is 99% or a 2-log removal. With
an influent containing 1000 helminth ova per liter and an effluent containing 1
helminth ovum per liter, the wastewater treatment process has removed 99.9% of the
contaminant, a 3-log removal. In low and middle income countries, the WHO
recommends treatment methods with 1-3 log removal for acceptable helminth ova
content in effluent used for irrigation.
Table 3.3 WHO guidelines for wastewater used to irrigate crops, 2006
Some countries apply raw or partially treated wastewater without regulations or
guidelines, while others have either implemented their own regulations/guidelines or
have adopted quality criteria based on international regulations (Carr, 2005).
According to the World Health Organization, most countries have adopted the WHO
guidelines for wastewater reuse (WHO, 1989).
Effluent for Use in Helminth Eggs
(#/liter) E. Coli
(#/100 ml)
Restricted irrigation
<1/liter
<105
Relaxed to <106 when
exposure is limited or
re-growth is likely
Unrestricted irrigation
<1/liter
<1000
Relaxed to <104 for high-
growing leaf crops or drip
irrigation
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According to the assistant director of the Ministry of Health and Social Welfare, Elias
B. M. Chinamo, “Tanzania has no guidelines or standards for the use of wastewater in
agriculture … While the WHO standards are somewhat flexible, the capability of
Tanzania to attain them is limited by cost, knowledge and skills.”
In many low- and middle-income areas, non-built up urban lands – especially those
lying along the courses of urban drainage systems – are seen as ideal locations for the
production of agricultural products that are in high demand by urban dwellers, such
as vegetables. Several researchers have shown that a significant proportion of a city’s
food requirements in low- and middle-income countries are supplied from within the
urban boundaries, because within those areas substantial amounts of wastewater from
homes and industries is available to irrigate lands along the urban drainage courses,
and the markets are close (WHO 2006).
The following sections of this chapter will use complementary data to bring insight as
to how these ideas translate to Tanzania. Data from Iringa Municipal wastewater
treatment plant describes important parameters of wastewater (see Appendix C), and
data from the Kleruu constructed wetland show behaviors of people that may put
them at risk for becoming infected with waterborne diseases. Data from Arusha
describes pathogen pathways through the municipal sewage systems, while additional
data from Arusha, Iringa, Morogoro, and Moshi give insight into the current ability of
sedimentation ponds and constructed wetlands to clear pathogens from the
wastewater.
3.3 Assessment of Socio-economic and Water Quality Exposures. Case Study
Iringa.
3.3.1 Iringa Municipal wastewater treatment plant
The main wastewater production in Iringa is from domestic and municipal sources;
there is very little industrial wastewater production in the collection area. The most
commonly used sanitary facilities in Iringa are traditional pit latrines, septic tanks and
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central sewers. Septic tanks and soak away pits are used to treat wastewater at the
household level. Waste stabilization ponds and constructed wetland systems are used
at the institution and municipal levels.
There is only one set of waste stabilization ponds at the Iringa Municipal wastewater
treatment plant, which is mainly used to treat the wastewater collected through the
sewers and septic tank sludge. The Iringa Municipal wastewater treatment plant
receives septage from the local septage haulers. During some months, much of the
flow is composed of septage.
As can be seen in Figure 3.1, the treatment plant is comprised of anaerobic ponds,
facultative ponds and maturation ponds.
A
B
C
Anaerobic 1
Anaerobic 2
Facultative 1
Facultative 2
Maturation
Maturation
Free
Surface
Constructed
Wetlands
D
CULTIVATION AREA FOR VEGETABLES AND MAIZES
Figure 3.1 The layout of Iringa Municipal wastewater treatment plant comprises
sampling points (A) inlet strainer partial flume (B) outlet of anaerobic pond 1 and 2,
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(C) outlet of the maturation ponds and (D) the outlet of constructed wetlands (On-site
survey, 2012)
The Iringa Municipal wastewater treatment plant receives a huge amount of
wastewater and effluent from septic tanks. Due to the low quality of the effluent
from the maturation ponds, a free surface constructed wetland was added to the end
of the maturation pond in 2012 to polish the effluent from the maturation ponds.
3.3.2 Reuse of Municipal Wastewater Treatment plant effluent
The effluent from free surface constructed wetland is discharged at Hoho Street.
People use effluent from the Iringa Municipal wastewater treatment plant
downstream to irrigate several crops (Figure 3.2)
(a) Free surface constructed wetland
(b) Cultivation of vegetables downstream of
free surface constructed wetland
Figure 3.2 Free surface constructed wetland (a) at Iringa Municipal wastewater
treatment plant polishes effluent used for irrigation (b).
Downstream of the Iringa Municipal wastewater treatment plant, leafy vegetables like
lettuce, matembele, and spinach are usually irrigated even on the day of harvest,
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resulting in high risk to consumers. Each day without watering allows natural
pathogen die-off, especially for bacteria and viruses.
3.3.3 The Performance of Iringa Municipal Wastewater Treatment Plant
According to Metcalf and Eddy (1991), typical values for the five-day biological oxygen
demand (BOD5) of untreated domestic wastewater are between 110 mg O2/L and 400
mg O2/L for weak to strong wastewater, while the BOD5 of typical septage varies
between 2,000 mg O2/liter and 30,000 mg O2/liter. The influent to the Iringa
Municipal wastewater treatment plant has BOD5 levels that vary from 700 mg O2/L to
3600 mg O2/L. The influent to the Iringa Municipal WWTP contains unusually high
levels of organic matter, and during some months could be classified as septage
rather than untreated wastewater influent.
Figure 3.4 The influent to the Iringa Municipal wastewater treatment plant has
unusually high BOD5, plotted on a logarithmic scale
As shown in Figure 3.4, the waste stabilization ponds at the Iringa Municipal
wastewater treatment plant are responsible for a large reduction in BOD5, while
constructed wetlands do not significantly reduce the BOD5. Influent is more
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concentrated in May, and more dilute in October. In order to analyze data with such a
large variation in BOD5, it is necessary to plot the influent and effluent on a
logarithmic scale.
Figure 3.5 Iringa Municipal wastewater treatment plant, BOD5 in the influent and
effluent plotted on a logarithmic scale
The reduction in the five-day biological oxygen demand in the effluent as it passes
through the constructed wetlands is so slight that it is necessary to plot the effluent
data on a linear scale, as shown in Figure 3.5. Replotting the effluent data shows
that most months the constructed wetlands cause some reduction in the BOD5 of the
effluent. Averaging the results for all months shows that the constructed wetlands
reduce the BOD5 of the effluent by an average of 5% during this period. According to
Professor K. Njau (personal communication, 2013) this is attributed to wrong
placement of the CW which is receiving effluent from the last maturation pond. This
pond is full of algae and the algae tend to decompose as it travels through the CW
releasing BOD in the system. The sampling is also a problem because the water
samples for analysis of BOD are not filtered. This will contain both the dissolved
organic and the suspended organic particles in form of algae. During BOD
determination the algae will tend to decompose again releasing BOD5 into the sample.
The net reduction observed is therefore very low.
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Figure 3.6 Iringa Municipal wastewater treatment plant effluent BOD5 (mg O2/liter)
from the wastewater treatment plant and the constructed wetlands plotted on a
linear scale
By comparing Figure 3.7 with Figure 3.5, we can see that the chemical oxygen
demand (COD) of the influent appears to be barely higher than the BOD5, indicating
that nearly all of the organic matter in the influent flow is biologically active.
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Figure 3.7 Iringa Municipal wastewater treatment plant chemical oxygen demand
(mg O2/liter) in influent and effluent plotted on a logarithmic scale
As shown in Figure 3.7, the waste stabilization ponds in Iringa are responsible for a
one-log reduction in chemical oxygen demand, while the constructed wetlands do not
significantly reduce the chemical oxygen demand of the effluent.
Figure 3.8 Iringa Municipal wastewater treatment plant Total Dissolved Solids
(mg/liter) in influent and effluent
According to Metcalf and Eddy (1991), the influent total dissolved solids (TDS) for
wastewater ranges from 250 mg/L to 850 mg/L, depending on whether the influent is
weak or strong. We can see in Figure 3.8 that the level of total dissolved solids in the
influent to the Iringa Municipal wastewater treatment plant is comparable to a
medium strength wastewater. Referring back to Figure 3.4, where the five-day
biological oxygen demand of the influent flows is shown to be comparable to low
strength septage, we can see that the total dissolved solids of this influent is
surprisingly modest, and usually increases as the wastewater makes its way through
the waste stabilization ponds and the constructed wetlands.
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Figure 3.9 Iringa Municipal wastewater treatment plant Nitrogen levels (mg/liter) in
influent and effluent, plotted on a linear scale.
As shown in Figure 3.9, most months the total nitrogen content of the Iringa
wastewater is reduced by wastewater treatment and the constructed wetlands.
Figure 3.10 Iringa Municipal wastewater treatment plant Phosphate levels (mg/liter)
in influent and effluent plotted on a linear scale.
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The phosphates in the Iringa wastewater are shown in Figure 3.10. Like the total
nitrogen, another fertilizer, the phosphate levels are modestly reduced by the
wastewater treatment plant and the constructed wetlands.
Figure 3.11 Iringa Municipal wastewater treatment plant coliform counts
(coliforms/100ml) in influent and effluent
As shown in Figure 3.11, faecal coliform counts at the Iringa Municipal wastewater
treatment plant are far above the 1,000 coliforms/100ml allowed by the WHO
standards. However, we can also see that the coliform counts have been reduced by
roughly 99%, or 2-logs. In addition, we see the constructed wetlands are particularly
helpful in reducing the faecal coliform count. Some months, the effluent from the
constructed wetlands is substantially cleaner than the effluent from the waste
stabilization ponds.
Generally the reuse of the wastewater in Iringa can be widely viewed as an
agricultural source of water supply and fertilizer. According to FAO (1992), the
estimated typical wastewater effluent from domestic sources could supply all of the
nitrogen and much of phosphorus and potassium that are normally required for
agriculture production. However, there are disadvantages and risks related to
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wastewater reuse: irrigation workers and food consumer are exposed to faecal borne
pathogens. The use of partially treated of wastewater from the Iringa Municipal
wastewater treatment plant can pose health risks even though the gross contaminants
have been removed by wastewater processing and the effluent appears to be
relatively clean. If the water users and consumers are unaware of the pollution
content of the effluent, they are less likely to protect themselves from possible
adverse effects.
3.3.4 Kleruu Teachers’ College Constructed Wetland
Kleruu Teachers’ College is one of two schools in Iringa treating typical domestic
water using constructed wetlands. The Klerruu constructed wetlands system is
comprised of a pretreatment unit and constructed wetland units planted with
phragmites (Figure 3.12).
(a) Pretreatment of wastewater before
the constructed wetland system at
Klerruu Teachers’ College
(b) Constructed wetland at Klerruu
Teachers’ College
Figure 3.12 The pretreatment facility (a) and (b) the constructed wetland at Klerruu
Teachers’ College in December 2012. The phragmites are healthy, implying the
possibility of good performance of the system.
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The effluent from the Klerruu constructed wetland system is directed downstream
into the receiving body, which is a storm drain that connects with a stream.
According to data collection and observations, there are multiple uses of the effluent
downstream of the constructed wetland in Klerruu Teachers’ College as shown in
Figure 3.13. The wastewater from the wetlands was mostly used for agricultural
irrigation (58.8%), followed by illegal recreation for children (23.5%) and brickwork
construction (11.8%). Other uses included watering flowers and drinking water for
cattle weighted by 5.8%. Reuse of effluent for domestic uses and for aquaculture
were not observed (0%).
5.88%
11.8%
0%
23.5%
58.8% 0%0%
Drinking Water
Household water
Irrigation
Children playing
Aquaculture
Brickworks
other
Figure 3.13 Reuse of effluent downstream of Klerruu Teachers’ College (On-site
survey, 2012).
The reuse of effluent for irrigating vegetables downstream of the Klerruu constructed
wetland varies between the dry and rainy seasons. In the dry season, the irrigation
practices were mainly depending on the wastewater, while in the rainy season the
effluent was diluted by rain, reducing the concentration of wastewater and hence the
associated health risk. As can be seen in Figure 3.14, the effluent from the
wastewater treatment plant has a higher BOD5 in the dry season than in the rainy
season.
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Figure 3.14 Wastewater concentration by month in 2012, and average monthly
rainfall in Tanzania 1901 to 2009. (Source: World Bank Climate Change Knowledge
Portal, Climate Research Unit, University of East Anglia; IRUWASA effluent data.)
(a) Some tomatoes irrigated with effluent
downstream of Klerruu Teachers’ College
constructed wetlands
(b) The mixture of maize and vegetables
downstream of the Klerruu Teachers’
College constructed wetlands
Figure 3.15 Crops irrigated by the effluent from constructed wetlands at Klerruu
Teachers’ College observed December 2012.
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There is a diversity of crops irrigated with effluent downstream of the Kleruu
constructed wetlands. The most common crops were tomatoes, maize, bananas, taro,
potatoes, onions, cabbage, eggplant, and spinach (Fig. 3.13).
Another considerable use of the effluent observed was the manufacture of bricks
(11.8%). A local construction company has been established downstream, and it uses
the effluent from the constructed wetland for construction activities. According the
manager of the company, the reuse of the effluent for the construction work has
saved a lot of money. The workers in this company are not using any protective gear.
Although the reuse of wastewater for aquaculture is not common in this region, some
fish species were found in the effluent downstream of Klerruu constructed wetland,
and children from nearby schools like to catch the fish by using local nets and the
mosquito nets. During the survey done in the present study, the children from Lugalo
Secondary School were found fishing in the effluent without protective gear (Figure
3.16). It is a normal tendency for students close to the stream to practice fishing
during the tea break and lunchtime, which accounts for 23.5% of the effluent reuse
from the constructed wetland. This practice exposes schoolchildren to wastewater.
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(a) Students fishing in effluent stream
(b) Students playing in the garden
Figure 3.16 Some students from Lugalo Secondary Schools near stream (a) fishing
while others are (b) playing in the garden irrigated with effluent downstream from
the constructed wetland.
Other reuse of effluent includes drinking water for cattle and construction works. (Fig
3.13).
3.4 Assessment of exposure to workers downstream of Kleruu constructed
wetland
There is no regular monitoring of the performance of Kleruu constructed wetland.
Since wetlands have not been proved to remove all pathogens in wastewater, there is
a possibility that the effluent poses health risks to consumers. The irrigation practices
and types of crops cultivated were examined downstream of Kleruu constructed
wetlands.
The present study revealed that the reuse of effluent varies between rainy season and
dry season. During the dry season, the effluent from the constructed wetlands is used
as irrigation water. In this period the vegetables are more valuable to farmers and
consumers. Generally, in dry season the availability of the vegetables is very low
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resulting in high prices. Therefore most of the farmers shift to vegetable cultivation
in the dry season. The intensive cultivation of vegetables in the dry season increases
the health risk to farmers from exposure to wastewater since they are in contact with
wastewater from farm preparation to harvest.
During the rainy season, the water availability is high and the price of vegetables is
lower. This situation encourages the farmers downstream to grow maize instead of
vegetables. This implies that in the dry season, the health risk is higher to farmers
due to the exposure to wastewater, and to the consumer since the crops are directly
consumed as salads. The exposure risk to the farmer is minimal during the rainy
season. The effluent from the wetland is weaker since it is highly diluted with the
storm water. The consumer risk also is very minimal due to the type of crops
produced: maize is not consumed directly until it has been processed.
Apart from workers and consumers, the students and children playing in the effluent
and gardens downstream of the constructed wetlands may be at high risk of
contracting diseases associated with wastewater.
3.4.1 Exposure time of Workers to effluent from the constructed wetlands
Exposure time in the present study is defined as the duration of time workers spend in
contact with wastewater during the reuse of wastewater. The exposure time depends
on how the wastewater is reused. For instance in aquaculture, the worker spends
more time in contact with the effluent than during fishing. When effluent is used for
irrigation, the exposure time depends on the type of crops and the stage of
cultivation, while in the brick works the exposure time depends on the production of
bricks per day. From the questionnaire conducted downstream at Kleruu Teachers’
College constructed wetlands, the workers spend between 2 and 5 hours per day in
the preparation of their farms. However during this time they do not effectively
utilize the effluent from the constructed wetlands (Table 3.4). The most vulnerable
time for the workers is during irrigation where the effluent is used to water the
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plants. During irrigation, the workers spend between 2 and 4 hours in contact with the
wastewater.
Table 3.4 Exposure time for workers using wastewater for irrigation at different
stages of cultivation
Cultivation Stages
Exposure time
(Hrs/day/person)
Preparation of farms
2-5
Planting 1-3
Irrigation 2-4
Weeding 1-3
Harvesting 2-4
In general people living downstream of the Iringa Municipal wastewater treatment
plant and Klerruu Teachers’ College constructed wetlands benefit economically from
reuse of wastewater effluent in irrigation. Availability of water is the most important
determining factor for whether the farmer cultivates seasonally or year round.
Downstream from the wastewater treatment plant, the effluent is available
throughout the year. This explains why vegetable growers in Iringa are mostly located
downstream of the Iringa Municipal wastewater treatment plant and constructed
wetlands. The greatest benefit of using wastewater for irrigation, apart from its
nutrient load, is that effluent flows are reliable and easily accessed. Cultivating
vegetables downstream from constructed wetlands and wastewater treatment plant
makes it easier for the farmer to obtain much needed water for irrigation.
3.4.2 Assessment of Exposure Arusha: Wastewater Helminths
A primary exposure route for urban populations in general is the consumption of raw
vegetables that have been irrigated with urban wastewater (Scott et al., 2004).
Therefore, factors needing to be considered include survival of the pathogens in the
environment and numbers of pathogens present before wastewater reuse.
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If wastewater has a high faecal coliform count, there is the possibility that this
wastewater carries disease associated with human faeces. While the faecal coliform
count is an indirect marker for the health risk associated with wastewater, the
number of helminth eggs in a wastewater sample is a direct marker for the level of
helminth infestation in the sewered population (Seidu, 2011).
In Arusha, Tanzania, wastewater samples were analyzed for the presence of helminth
eggs (Marwa, 2011). A rich and varied assortment of thousands of helminth eggs was
found in wastewater samples taken in Arusha (Figure 3.17).
Helminth eggs resist chlorine disinfection and are relatively large (Metcalf and Eddy,
2003). Helminth ova measure between 20 and 80 μm, and their gelatinous outer layer
makes them sticky. The size and stickiness of the helminth eggs determines how they
behave during wastewater treatment.
Figure 3.17 Helminth eggs found in municipal wastewater treatment plant in Arusha,
Tanzania
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The helminth egg has multiple layers of protection. The outer one or two layers are
made of mucopolysacharides and proteins. The middle chitinous layers provide
structure and mechanical support to the eggs, while the inner layer of lipids and
proteins maintain the egg’s moisture content while physically protecting the
protoplasm. These combined layers protect the eggs in many environmental
conditions, including strong acids and bases, oxidants and reductive agents as well as
detergent and proteolytic compounds (Jimenez-Cisneros, 2007). Helminth eggs are
unaffected by lime (calcium carbonate), mesophilic digestion or vermi-composting
(composting with earthworms).
All of the commonly used wastewater treatment processes have been analyzed with
respect to their removal rates for bacteria, helminths, protozoa and bacteria. Some
processes are more effective than others at pathogen removal, and the waste
stabilization ponds are particularly efficient at removing all kinds of pathogens.
According to Feachem et al. (1983), waste stabilization ponds remove up to 6 log
units of helminths ova and bacteria compared to 1 to 4 log units removal of virusesand
five-day biological oxygen demand. Helminth ova settle out through sedimentation.
Removing helminth ova requires a minimum retention time of 5–20 days, depending on
the initial content.
Figure 3.18 Percentage removal of helminth eggs and BOD5 in waste stabilization
ponds; log removal of bacteria and viruses (Feacham, 1983)
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When a helminth egg enters the waste stabilization pond, its sticky surface attracts
other suspended solids and the clump sinks to the bottom of the pond. The reduction
in total suspended solids is the best proxy for helminth removal, and the reduction in
BOD5 is another stand-in for direct measurement of helminth removal from the
effluent. When it comes to waste stabilization ponds, helminth eggs come in, and
they don’t come out.
Schistosoma eggs on the other hand hatch as soon as they find fresh water. The
miracidia which emerge from the egg are viable for about 48 hours (IARC, n.d.). If
they cannot find Bulinus, Biomphalaria, or Oncomelaria snails, the life cycle ends.
Wastewater from Arusha, Tanzania was tested as influent at two points during
wastewater treatment, and at the exit of the waste stabilization pond system (Marwa,
2011). We find the reduction of helminth eggs in wastewater to be more complicated
than the simple theoretical curve sketched above.
The whipworm eggs from Trichuris trichuira were completely eradicated. The dwarf
tape worm and the tapeworm eggs from Hymenolepis nana and Taenia were very
responsive to treatment, and well within WHO standards for unlimited irrigation.
Likewise, the giant roundworm eggs and hookworm eggs were initially exceedingly
plentiful, and were reduced to levels that met the WHO standards for unlimited
irrigation. But all helminth eggs are not the same. Of the six type of worm eggs that
were tested for, two types of worm eggs appeared particularly persistent:
Schistosoma haematobium and Schistosoma mansoni eggs. While all of the other
worm eggs experienced reduction from 99.3% to 100%, the eggs associated with
schistosomiasis seemed to show a reduction of roughly 82%.
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Figure 3.19 Reduction in helminth ova in wastewater before, during and after
treatment in waste stabilization ponds
It is important to note that this effluent meets the WHO standards for unrestricted
irrigation used for every type of worm eggs that were tested for. However,
Schistosoma eggs appeared to be the least common worm eggs in the influent, and
seemed to be the most common worm eggs found in the effluent. Processing the
wastewater through waste stabilization ponds seemed to effectively select for the
eggs of worms associated with schistosomiasis.
3.4.3 Rapid Assessment of Pathogen Exposure in four Municipal Waste
Stabilization Ponds
In order to understand the implications of Marwa’s data better, a rapid assessment of
the four municipal sewer systems of Arusha, Iringa, Moshi, and Morogoro was
conducted. No pathogens were found in the samples of Arusha, Iringa, and Moshi.
This may because the samples were only ten litres and/or the parasite load is not
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heavy. In Arusha, the same site as Marwa reported from, the influent now includes
industrial wastewater with foam as shown in the photos below.
Figure 3.20 Photos taken in August 2013 at the Arusha Municipal Sewage Treatment
System showing evidence of industrial effluent.
This may have affected the biological residents of the sewage treatment ponds.
Figure 3.21. Reduction in worm eggs by waste stabilization ponds and constructed
wetlands in Morogoro
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The figures above shows that the samples from Morogoro contained the same
pathogens, and in the same order of frequency as were observed by Marwa in her
study with larger samples (1000 liters) from Arusha.
Also reported in Morogoro were E.histolytica, rat tapeworm, Isospora belli, as well as
E. coli. Hookworm eggs were the most plentiful and most persistent. That they
survived passage all through the constructed wetland is discouraging. This may
partially be attributed to the fact that the wetland was only planted three months
earlier and is not working efficiently yet.
Intact Schistosoma eggs were not found in Morogoro sewage treatment system. The
MUHAS laboratory scientist A. Zachariah reported seeing numerous “things” that
resembled Schistosoma haemotobium eggs as shown in the photos below.
Figure 3.22. Wastewater Samples from Morogoro, focusing on possible Schistoma
molts/shells. Photo by Abdallah Zachariah.
Zachariah reported, and as can be seen in the above photo, that:
1. They were seen to be small in size under the Microscope compared to the
normal Schistosoma haemotobium eggs
2. Their shape and size are not uniform
3. They lack internal structures of the normal Schistosoma haemotobium eggs.
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For the life cycle of the schistosome to continue, the eggs in the stool or urine must
find fresh water. The eggs hatch when they come into contact with water. Could
these irregular “egg shapes” be molts left behind when the eggs hatched and the
miracidia swam off to find a snail host?
Miracidia are viable for about 48 hours. If they do not find an appropriate snail host,
the life cycle ends. This demonstrates the importance of identifying if there are snail
hosts living in the sewage treatment ponds. If there are no Biomphalaria, Bulinus, or
Oncomelaria snails (Mazigo et al., 2012), wastewater treatment ponds could be an
effective way of ending the Schistosoma life cycle. Unfortunately we do not know if
there are snails in the sedimentation ponds at any of the municipal sites.
3.5 Diseases Associated with the Exposure risk
These data sets confirm that people are exposed to potential harm as a result of
contact with wastewater. The major concerns are helminths including schistosomiasis.
It seems that wastewater treatment workers, users of the effluent such as farmers,
their families, children, brick makers, fishermen and the consumers of vegetables
irrigated with effluent are at risk for becoming infected with helminths, either
through people ingesting helminth eggs or through the hookworm larvae or
Schistosoma cercariae penetrating the skin.
They also confirm that danger is mitigated through the treatment system in Iringa. In
Iringa, irrigators watered their fields through diversions or by carrying buckets to the
fields, so their exposure was probably minimal.
Despite the potential risk and ignorance of potential danger, the wastewater from
Iringa and Arusha Municipal wastewater treatment plants offer a livelihood to many of
the urban poor, and fields irrigated with this nutrient-rich water are an important
source of fresh produce.
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Limitations
Unfortunately we have no records of the health status of the people exposed to these
specific risks. The updated atlas for helminth infections also has no data recorded
from Iringa or Arusha regions. In addition, sludge was not measured for helminth ova.
It is not known if Bulinus or Biomphalaria snails are in any of the sewage treatment
ponds.
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CHAPTER FOUR
4.0 Defining control approaches
4.1 Prevention
Amidst all the data and studies reported in Chapter 2, the practical experience in
Chapter 3 provides an urgent message towards prevention of disease. Prevention,
where actions are taken to prevent the occurrence of disease, is the most just and
equitable way of dealing with disease threats (Prüss-Üstün and Corvalán, 2006).
Primary prevention seeks to prevent the onset of disease by altering behaviors or
exposures that can lead to disease, or by enhancing resistance to the effects of
exposure to a disease agent (AFMC, 2013). Preventing disease before it arises
diminishes the health burden borne by the population and eliminates associated
health-care treatment costs. Prevention is the most humane and cost effective
approach to care.
Environmental modification to improve human health has many advantages over
attempting to “cure” people once they become ill (Prüss-Üstün and Corvalán, 2006).
Diseases (including most of Tanzania’s top killers) can be prevented before they arise,
saving on treatment costs. In addition, such interventions are generally more
sustainable than treatment, and have longer-term impact. Environmental
modification is often the most equitable option, with benefits felt across broad groups
and populations.
Communicable diseases and toxins are especially susceptible to community standards.
For example in Egypt, level of schistosomiasis infection has been shown to be related
to the proportion of households with sewage connections, but sewage connection
cannot be correlated to non-infection at the household level (El Katsha and Watts,
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1997). In other words, schistosomiasis was shown to be a social disease that
correlated to the number of people in the community who were connected to
sewerage, but not to actions taken at the individual or household level.
The prevalence of helminth infections in the world correlates clearly with sanitation
coverage. The infection rates of the population, particularly children, in low-income
countries can be very high. The primary objective of wastewater treatment in low-
income countries such as Tanzania is to remove pathogens--disease-causing organisms
including bacteria, viruses, fungi, protozoans, and helminths--from the effluent.
Wastewater treatment systems can be effective as preventive environmental
modifications that protect human health.
4.2 Interventions
4.2.1 Reducing helminth ova in wastewater effluent
One method of reducing helminthiasis in Tanzania is to reduce the concentration of
helminth ova in wastewater effluent used for irrigation. Waste stabilization ponds and
constructed wetlands are two methods of wastewater treatment that remove
helminth ova from the effluent.
4.3 Waste Stabilization Ponds
Waste stabilization ponds are large manmade water bodies that are filled with
wastewater that is then treated by naturally occurring processes. The ponds can be
used individually, or they can be linked in a series for improved treatment. There are
three types of ponds: anaerobic, facultative and aerobic, each with a different
treatment modality and design characteristics. Anaerobic ponds are two to five
meters deep with detention times of one to seven days. Anaerobic bacteria convert
organic carbon in the wastewater into methane and remove up to 60% of the
biological oxygen demand in the process; they are capable of treating strong
wastewater. The second pond is typically a facultative pond of one to two and a half
meters with detention times of five to thirty days. Both aerobic and anaerobic
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processes occur: the top layer of the pond receives oxygen from wind mixing, natural
diffusion, and algae-driven photosynthesis, while the lower layer is anaerobic. Solids
settle out and accumulate in the bottom of the pool, and the biological oxygen
demand of the wastewater is decreased up to 75%. A third aerobic pond is the
shallowest pond in the series with a depth of one half to one and a half meters. This
ensures that sunlight penetrates the full depth of the pond, driving photosynthesis.
The first two ponds are designed to reduce BOD while the third pond, or polishing
pond, reduces pathogens in the effluent (von Sperlin and de Lemos, 2005; Crites and
Tchobanoglous, 1998).
The use of waste stabilization ponds to recycle wastewater for agriculture is
recommended in low and middle income countries with warm climates if land is
available at a reasonable price (Jimenez-Cisneros, 2007). The pond system is
characterized by minimal energy requirements, and functions well during changes in
wastewater volumes and load. Waste stabilization ponds have been used for the
treatment of various kinds of wastewaters, including industrial and domestic, in low-
income as well as high-income countries (Kouraa et al., 2002).
Waste stabilization ponds can be very efficient at removing all kinds of pathogens.
They remove up to 6 bacteria log, up to 5 viruses log and almost all the protozoa and
helminth ova. These performances are higher than those observed in conventional
processes (12 bacteria log and 70-99% of protozoa and helminth ova) without
disinfection, as is the case of the activated sludge process. Several factors contribute
to producing this efficiency, including sedimentation, temperature, sunlight, pH,
microorganism predation, adsorption and absorption. Helminth ova are typically
removed by sedimentation. To effectively remove helminth ova in waste stabilization
ponds requires a minimum retention time of 5 to 20 days, depending on the initial
content.
4.4 The use of Constructed wetlands for Wastewater treatment
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In the 1950s, Dr. Seidel in Germany was the first researcher to experiment with using
wetland plants to treat wastewater, and the first full-scale systems were built in the
late 1960s. Since then, subsurface systems have become common in Europe while free
water surface systems are more popular in Australia and North America. Constructed
wetland technology spread slowly, but since the 1990s the technology has become
international. Today, constructed wetlands are recognized as a reliable wastewater
treatment technology and are used to treat many types of wastewater (Vymazal,
2010).
Constructed wetlands can successfully remove a variety of pollutants from the water
that passes through them, including pathogenic bacteria, viruses, and protozoa (Stott
et al., 2002). Constructed wetlands have medium bacterial and viral removal efficacy,
and pathogen removal is variable, depending upon a variety of factors. Removal rates
for faecal coliforms (commonly greater than 99%) generally equal or exceed those
described for conventional biological wastewater treatment processes (Nuttall et al.,
1998). According to WHO Guidelines (2006), constructed wetlands may not be as
effective in cleaning wastewater as waste stabilization ponds; instead, constructed
wetlands have an added effect or polishing effect on the effluent from waste
stabilization ponds. Subsurface flow wetlands are more effective than free-surface
flow wetlands at removing human pathogens.
A variety of processes are involved in removing pathogens and parasites from
wastewater in constructed wetlands. According to Stott et al. (2002) these include:
mechanical filtration through the substrate and attached biofilm, sedimentation,
aggregation, oxidation, exposure to natural biocides, antibiosis, predation,
attachment by lytic bacteria and viruses, natural die-off and competition for limiting
nutrients or trace elements. One of the main capacity limitations of horizontal
subsurface flow constructed wetlands systems is their tendency to clog when
subjected to high levels of organics and suspended solids (Winter and Goetz, 2003).
Since most important degradation processes require aerobic conditions, clogging of
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the substrate matrix hinders oxygen transport and can result in failure of the
performance of the system (Harbel et al., 2002).
4.4.1 Reduce Helminth Ova in Sludge
Using a series of waste stabilization ponds followed by filtration in constructed
wetlands can provide high quality effluent that is suitable for reuse as irrigation
water. However, the helminth ova removed from the effluent are transferred to the
biosolids that settle at the bottom of the waste stabilization ponds. These biosolids
are a high quality soil amendment and are sought by farmers for land application to
improve soil structure and crop yields. Unless the sludge is treated before land
application, it will serve as a pathway for helminth transmission to farmers and to
people who purchase crops grown on sludge-amended soil (Strauss, 2000).
Table 4.1 Helminth ova in sludge from waste stabilization ponds
Country Source of sludge
Helminth eggs/gram total solids
(% viable)
Campina Grande, Brazil
Waste stabilization ponds
in series
1400-40000 eggs/gram total solids
(2% to 8%)
Toluca, Mexico Waste stabilization pond
48-136 eggs/gram total solids
(0% - 50%)
Bangkok, Thailand Waste stabilization ponds
in series
170 eggs/gram total solids
(0.2% to 3.1%) after 3.5 years
Chiclayo, Peru Primary facultative ponds
60-260 eggs/gram total solids
(1% to 5%) after 4-5 years
(Source: Modified from Jimenez-Cisneros and Maya-Rendon, 2007.)
As we can see in Table 4.1, sludge from waste stabilization ponds typically contains
large numbers of helminth ova that remain viable after years of underwater storage.
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Without further processing, land application of this sludge will allow these helminth
ova to contaminate the soil. The farmer hoping to increase crop yields by amending
fields with this sludge is probably not considering the probability of increased
helminth infections as well.
4.4.2 Long-Term Sludge Storage
Possible treatment methods to inactivate helminth eggs in sludge include long-term
dry storage and thermophilic composting (WHO, 2006, volume 4).
Table 4.2 The reduction of the viability of helminth eggs in sludge stored for
different periods
Type of Sample Treatment
Reduction of
helminth egg viability
Sludge artificially infected with
Toxocara canis, Trichuris
vulpis, Trichuris suis, Ascaris
suum and Hymenolepis
diminuta
Storage for 3 month at 25°C
5% -40%
Storage for 1 year at 25°C 70%-100%
Ascaris eggs in sludge 7 months of storage at 0 to
20°C 10%
Ascaris eggs in sludge
storage for 1 year
50%
storage for 3 years
100%
(Source: Modified from Gallizzi, 2003.)
As shown in Table 4.2, storing the sludge at temperatures ranging from 0°C to 20°C
for three years or at 25°C for over one year can completely eradicate the viable
helminth eggs in sewage sludge. If there is sufficient land area to stockpile sludge
for an extended period of time, the rate of helminth infection caused by the land
application of sludge can be reduced to zero.
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4.4.3 Thermophilic composting of sludge
To inactivate helminth eggs in less than a year, it is recommended to either compost
or dry the sludge. More specifically, the sludge temperature must exceed 40ºC, or
sludge moisture must be reduced to below 5% (Jiménez, 2008). In parts of the world
with a regular rainy season, including Tanzania, it may be impractical to dry sewage
sludge. Therefore we will look more closely at sludge composting.
The most commonly used method of composting is the windrow process, where
sewage sludge is mixed with organic wastes and stacked into long windrows that are
regularly turned. Windrows should be 3 to 5 feet tall and have a base width of about
10 to 15 feet. Air moves through the porous composting material from the bottom up
through the top, removing released moisture and excess heat.
To promote aeration, composting materials need to have enough pore space to allow
air to flow freely through the matrix, and they need added carbon to help
microorganisms break down the organic matter. Bulking agents are used to increase
the porosity of fine-textured sewage sludge and to absorb excess moisture. Suitable
bulking agents include sawdust, peanut hulls, corncobs, wood chips, rice hulls and
brush trimmings. Depending on the particle size and the initial moisture content of
the sludge, the amount of bulking agent can range from less than 1:1 by volume to
more than 5:1 (Outwater, 1994).
Aerobic, thermophilic composting is said to begin when the temperature reaches 45
degrees C. After that, the temperature usually rises rapidly as heat is released by the
breakdown of complex molecules or organic matter to simpler compounds. The peak
temperature may exceed 65 degrees C. As pile temperatures approach 70 degrees C
the piles should be turned, cooled the composting sludge and increasing the aeration.
The windrows should be turned several times per week initially, and less often later in
the composting process. The compost is then stockpiled for curing, during which final
degradation occurs. During composting, susceptible pathogens are almost completely
destroyed by high temperatures and competition with thermophilic organisms. The
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U.S. Environmental Protection Agency regards composting temperatures of 40 degrees
C for 5 days as a “process to significantly reduce pathogens” in sewage sludge. To be
classified as a “process to further reduce pathogens,” which is considered equivalent
to pasteurization, a temperature of 55 degrees C must be attained for 15 days within
windrows being turned at least five times (USEPA, 2002).
A 2007 study in Ghana examined the effects of windrow composting on helminth eggs
in sewage sludge (Koné et al., 2007). Public toilet sludge and septage were mixed at
a 1:2 ratio and dewatered on a drying bed. The biosolids had initial loads of 25-83
helminth eggs per gram of total solids. This material was mixed with solid waste as a
bulking agent at a 1:2 volume ratio. Two sets of windrows were created, with one
being turned every 3 days during the active composting process, and one turned every
10 days. Turning frequency had no effect on the helminth egg removal efficiency,
and in both cases the helminth eggs were reduced to less than 1 viable egg per gram
total solids, meeting the 2006 WHO guidelines for safe reuse of sewage sludge.
4.5 Changing agricultural practices to reduce helminth infections
When effluent from a wastewater treatment plant is used for irrigation and when
wastewater sludge is used as a soil amendment, it is inevitable that some helminth
eggs will come in contact with the farmers growing the crops, and with the crops
themselves. Helminth eggs are sticky, and can adhere to fruit, vegetables, fingers,
money, door handles, furniture and utensils (Kagei, 1983). The routes of transmission
can be reduced by the measures listed in Table 4.3.
Table 4.3 Pathogen reductions achievable by selected health-protection measures
Control measures Reduction
(log units) Comments
Drip irrigation for
Low growing crops
2 Root crops and crops such as lettuce that
grow just above, but partially in contact
with, the soil
High growing crops 4 Crops such as tomatoes that grow above, but
partially in contact with the soil
Pathogen die-off 0.5-2
per day
Die off on crop surfaces that occurs between
last irrigation and consumption. The log unit
reduction achieved depends on climate
(temperature, sunlight intensity, humidity)
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time, crop type, etc.
Produce-washing with
water
1 Washing salad crops, vegetables and fruit
with clean water
Produce-washing with
disinfection
2-3
Washing salad crops, vegetables and fruit
with a weak chlorine solution and rinsing with
fresh water
Produce peeling
1-2
Fruits, cabbage, root crops
Produce cooking
6-7
Immersion in boiling or close-to-boiling water
until the food is cooked
Source: Adapted and modified from WHO (2006)
Drip irrigation is a method of irrigation where water is delivered directly to the plants
through a series of valves, pipes, tubing and emitters. Using drip irrigation instead of
flood irrigation can reduce the transmission of helminth eggs by two log units for root
crops and lettuce or other crops that grow directly above the soil. For crops like
tomatoes, using drip irrigation instead of flood irrigation can reduce the transmission
of helminth eggs by four log units. Although it is a very efficient method of irrigation
and is well suited to delivering effluent to crops, it is expensive to set up drip
irrigation systems. Furrow irrigation can also protect crops from direct exposure to
wastewater, and is a less costly to install than drip irrigation.
Some pathogens will start to die off as soon as the surface dries out. Many bacteria
can see reductions of 0.5 to 2 log per day of drying time. However, helminth ova are
well protected, and their transmission rate is unlikely to be affected by stopping
irrigation a few days before harvest.
Washing produce with clean water can reduce pathogen transmission by up to one log,
but helminth eggs are sticky and are not likely to be affected by washing. Likewise,
produce washing with disinfectant can reduce pathogens by 2 to 3 log, but helminth
eggs are notoriously impervious to weak solutions of disinfectant.
Peeling fruits, vegetables and root crops can reduce pathogen transmission by 2 to 3
log, and may reduce the number of helminth eggs that are consumed.
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Cooking produce reduces the transmission of pathogens by 6 to 7 log, and will
certainly inactivate helminth ova. This is the gold standard for crops that are
irrigated with effluent: if there are possibly helminth ova on a crop, it should be
cooked before it is consumed.
CHAPTER FIVE
5.0 Effects of Sewage Treatment on the Health of the People
Wastewater is a complex resource, with both risks and benefits to its use. In most
high-income countries, wastewater is treated before reuse. Many low- and middle-
income countries use wastewater with and without treatment; if the wastewater is
untreated, it may be used undiluted or diluted (Raschid-Sally & Jayakody, 2008).
Rough estimates indicate that at least 20 million hectares in 50 countries are irrigated
with raw or partially treated wastewater (Hussain, Raschid, Hanjra, Marikar, van der
Hoek, 2001).
Figure 5.1 Freshwater withdrawals for agricultural use in the year 2000 and countries
reporting the use of wastewater or polluted water for irrigation
Source: Lenntech BV, Rotterdamseweg 402 M, 2629 HH Delft, The Netherlands
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As described in the previous chapters, waste water treatment has profound effects on
human health in terms of disease burden, accompanying malnutrition and anemia, as
well as overall quality of life. In addition, when treated, wastewater used for
irrigation can safely improve soil structure, increase crop yields, and increase food
nutrients that improves health indirectly.
Soil structure
Over time, irrigating with wastewater increases the capacity of a field to absorb and
retain water.
Figure 5.2 Soil parameters in Nagpur, India after irrigation with freshwater and
wastewater. Source: Modied from Jayaraman et al. (1983); Minhas and Samra (2004)
In Nagpur, India, the soil structure in farm plots irrigated with wastewater for 15 and
25 years, respectively, was compared to soil structure in a nearby plot that had been
irrigated with fresh water. The total porosity, hydraulic conductivity and water-
holding capacity of the soil was enhanced by wastewater irrigation.
Crop yields
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Wastewater is a rich source of plant food nutrients. Wastewater contains nitrogen and
phosphates as well as a complex of micronutrients. The organic matter in effluent
improves the tilth of the soil and the complexity of the soil microflora. If crops have
been undersupplied with essential plant food nutrients, wastewater irrigation will act
as a complex fertilizer (Ul-Hassan and Ali, 2002). Higher than average crop yields are
possible with wastewater irrigation.
Figure 5.3 Crop Yields in Nagpur, India after irrigating with fresh water, untreated
sewage, and sewage after primary treatment
As soil structure improves, so do crop yields. In Nagpur, India, fields irrigated with
untreated wastewater produced more food per hectare than land irrigated with clean
water. Fields that were irrigated with effluent that had undergone primary treatment
were even more productive.
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Figure 5.4 Crop Yields in Nagpur, India after irrigating with fresh water, untreated
sewage, and sewage after primary treatment
For most crops, there was more than 10% increase in crop yields when irrigating with
treated wastewater. As a rule these farmers were able to increase crop yields while
using lower value water that reduced their need for purchased fertilizer (Ul-Hassan
2002; Ul-Hassan and Ali 2002).
In Tanzania most agriculture is rain-fed. Therefore wastewater in Tanzania, as
illustrated in the case study of Iringa, can allow a farmer two crops per year rather
than one. In addition, a steady supply of wastewater can allow farmers to produce
water-loving crops in the dry season that can fetch a higher price. Therefore access to
wastewater can easily double a farmers’ income.
Food nutrients
Many wastewaters have significant value as a source of plant nutrients. FAO (1992)
estimated that typical wastewater effluent from domestic sources could supply all of
the nitrogen and much of the phosphorus and potassium normally required for crop
production, while micronutrients and organic matter provide additional benefits (FAO,
1997). When effluent is land applied instead of discharged into the receiving waters,
the nitrogen, phosphates and organic matter in the effluent improve crop yields
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rather than fueling algae blooms. Given the options, irrigating with wastewater is
likely to result in healthier waterways and soils.
Figure 5.5 Nutrients in Chinese Cabbage irrigated with clean water and wastewater,
Iringa, Tanzania
In Iringa, Tanzania, the nutrient content of Chinese cabbage irrigated with
wastewater was compared to Chinese cabbage irrigated with clean water. The
calcium and iron content of the Chinese cabbage grown on land irrigated with
wastewater increased by more than 10%, while the magnesium content went from 0.0
to 4.4 mg/liter.
Diseases
Besides being productive of the health benefits discussed above, widespread use of
untreated wastewater for irrigation may increase the incidence of the waterborne
diseases described in Chapter Two.
The Iringa Municipal wastewater treatment plant, where waste stabilization ponds are
followed by constructed wetlands, is well designed to meet the revised WHO
guidelines for irrigation water.
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Figure 5.6 Iringa Municipal wastewater treatment plant, BOD5 removal
We see that the treatment process has 1-3 log removal of faecal coliforms. Using BOD5
reduction as a proxy for helminth removal, we see that the reduction of BOD5 in the
wastewater treatment process exceeds 1 log, meeting the WHO requirements of 1-3
log reduction.
Good elimination of helminth eggs can be achieved by sedimentation in a pond with a
long residence time as pre-treatment, followed by filtration in constructed wetlands
(WHO, 2006, volume 4). However, the helminth eggs that are removed from the
effluent are not destroyed. When waste stabilization ponds are followed by
constructed wetlands, the helminth eggs are sequestered in the biosolids that build
up at the bottom of the ponds. The eggs can survive for more than 10 years in the
sludge of waste stabilization ponds and other sedimentation processes (Metcalf and
Eddy, 2003).
Sewage biosolids are regularly land applied by farmers who value it as a soil
amendment. This rich source of organic matter is not appropriate for agricultural
application without long-term storage or careful thermophilic composting.
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Finally, crops that are eaten raw are more likely to transmit helminth eggs than crops
that are cooked, and crops that grow close to the ground are more likely to serve as
vectors than crops that grow well above the ground.
In conclusion, wastewater is potentially dangerous. However, to a large extent the
the IRUWASA system is effectively treating wastewater to WHO irrigation standards.
Because of this, the farmers’ use of this effluent is increasing crop yields, increasing
food nutrients, and improving soil structure. Further research needs to be conducted
on the sludge of the wastewater treatment system. If the sludge contains helminth
eggs, (and it may be heavily laden), it is improper to give it to farmers for application
to their fields without storage or thermophilic composting.
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CHAPTER SIX
6.0 Recommendations
Reclaimed water is an increasingly important water source. Even if it is polluted, it is
not practically possible to prohibit people from using the water. Therefore it is
important to work with sewage treatment workers, farmers and end-users so that
they and their products are protected from contamination.
People should be encouraged to use wastewater, and to use it sensibly and carefully.
Effective technologies such as waste stabilization ponds and constructed wetlands are
needed to decrease disease burden. Recommendations are divided into five
categories to be implemented during planning, design, construction, implementation,
and monitoring.
Planning
Emphasize prevention
Amidst all these data and studies is an urgent message towards prevention. If a person
gets infected with a waterborne disease it is problematic. It is often difficult to get to
health care centres. Even when the patient arrives, the centre may be understaffed,
or the staff untrained for the roles they need to take (Gaffga, Tauxe, Mintz, 2007). In
some cases the disease cannot be well identified (Gascon et al., 2000). And then
after all that the patient may get the correct drug, but it does not work (Bakuza,
2013).
Evaluate disease prevalence
It is important to evaluate local disease prevalence of human beings and other
animals. High background disease levels indicate that risk management procedures
have not been adequately implemented and need to be strengthened.
Geographically targeted control programmes
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There is considerable geographical variation in the occurrence of waterborne diseases
in Tanzania. The maps presented in this report are of fine enough quality that they
can contribute to a rational basis for geographically targeted control programmes and
in some sites can serve as baseline assessments. These particular maps describe an
urgent need for surveillance in southern Tanzania, especially in the east, which is not
mountainous. They also demonstrate an urgent need for improved sewage control,
pharmaceutical intervention, and health education in Pemba and North Zanzibar. Our
own data points to the need for intervention in Morogoro.
Use broad based multisectorial approach and multidisciplinary teams
Emphasis on multisectoralism is crucial (see King, 2009). The experience in Brazil
demonstrates that besides the environment, the context of the prevailing
demographic, health and social systems need to be considered in order to address
health concerns effectively (Utzinger et al, 2009).
In terms of ecosystem health, it is particularly important that the health sector is
integrated with the engineering sector and vice versa. Engineering designs will be
incomplete and even detrimental if they do not take into consideration the biological
aspects of pathogens and their diseases. Likewise, if health workers depend on drugs
alone and miss out on the preventive aspects inherent to well-engineered sewage
treatment systems, these diseases will not be controlled.
The experiences shown in Bakuza’s study (2012) of villages around Gombe National
Park show a wide range in childhood disease prevalence. The reasons for this range
are unknown, and it is important to understand the differences between the low and
high prevalence villages. Moreover, human beings are infecting baboons and vervets.
Effective research to solve the problem will need a multisectorial team of health
workers, engineers, architects, wildlife ecologists, and water/land use planners.
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A health component should be injected into all sewage treatment projects by testing
people, water and sludge for faecal coliforms, helminth eggs, and the snail hosts of
Schistosoma.
Evaluate the need for pre-treatment
Some institutions such as hospitals and industries may need to pre-treat their effluent
before releasing it into the municipal sewage treatment system.
Plan an educational campaign
Educational campaigns must be built with the aim of improving knowledge and actions
over the long term. Health education campaigns need to be long lasting. Permanent
exhibits for schools and natural history museums, for example, would be preferable to
posters.
Design
Constructed wetlands in Tanzania should generally be subsurface to decrease the
possibility of providing habitat for mosquito larvae that as adults could carry malaria
and other diseases.
Fish should be encouraged in waste stabilization ponds as predators in case
mosquitoes lay eggs there.
Sludge needs long-term storage or composting before it is applied to farmland. A site
needs to be designated for sludge composting or storage.
Workers working in direct contact with sludge and effluent are at highest risk for
coming into contact with pathogens and bringing them to their families. Therefore a
place to shower and disinfect after work should be incorporated into the design.
Construction
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Local construction workers, especially in remote settings, should be trained on the
job about building and maintaining constructed wetlands.
Implementation
Proper handling of sewage and sludge
People directly handling biosolids are at high risk because the sludge is loaded with
helminth eggs. Therefore, clothing that can be cleaned in boiling water should be
worn by people who are in direct contact with the sludge, and their feet should be
protected by rubber boots.
Proper treatment of sludge from waste sedimentation ponds
Since the helminth eggs are partitioned into the sludge, sludge must be appropriately
and effectively treated before being given to farmers for land application. Storage
and thermophilic composting are effective and appropriate treatments.
Education
Farmers also need education. Recommendations to farmers should be data based and
tailored to their situation. If the effluent fails to meet standards, then different crops
should be grown, or crops should be grown in different ways. For example, if the
crops grown are cooked then the presence of helminth eggs may not affect the
consumer. Therefore if the water is not clean, irrigated crops should include maize,
rice that is eaten cooked or tree crops that are not in direct contact with irrigation
water rather than greens like lettuce that are eaten raw. Crops can be grown on
raised beds with furrow irrigation, so that the polluted water does not come in direct
contact with the leaves.
Income generation
It is possible that farmers would buy sludge that has been properly treated. It is
possible that crops grown with effluent have higher value than those grown with fresh
water since it has been shown that the crops absorb the effluent nutrients.
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Monitoring
Periodic data collection
Data on the levels of disease incidence and prevalence need to be collected
periodically. Otherwise it is not possible to know where to focus activities or to know
if risk management actions were effective.
Government testing of sewage treatment systems is a positive development but the
testing should be tailored to the site. For example in Iringa where the effluent is
almost completely used for irrigation, emphasis on BOD is not as important as in
Mwanza where the effluent is discharged into Lake Victoria. In Iringa it is important to
test faecal coliforms.
Pond monitoring should include periodic checks for the Biomphalaria, Bulinus and
Oncomelaria snails needed to complete the Schistosoma life cycle.
All systems discharging into the environment should be moni