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Integrated Wastewater Treatment System
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This research project was designed to demonstrate that wastewater that has been adequately treated in constructed wetland system can be safely used in irrigation of crops and in fish farming. The general objective of this research project was to improve the productivity of urban / peri-urban agriculture by making use or recycling of wastewater treated in constructed wetlands. The research activity involved Designing and Construction of a Horizontal Subsurface Flow CW (21m x 14m x 1m ) and a Fish Pond (16m x 8m x 1.5m); Application of wastewater in crop irrigation – where suitable quality of wastewater (microbial, nutrients), agronomical application, types of crops, optimum yields, quality and quantity of agricultural of agricultural produce, risk assessment were assessed; studies on the application of wastewater in aquaculture – suitable quality of wastewater (microbial), types of fish species, yields, and quality and quantity of aquaculture produce and finally the studies on value Chain Analysis/ Cost Benefit Analysis/ Attitude and Perception - related to urban / peri urban agriculture.
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Since 1999, the University of Dar es Salaam and partner institutions have been conducting research, mainly in Tanzania, East Africa on various topics with the main objective of developing constructed wetlands (CW) technology as a wastewater treatment system that is effective in costs, sustainability and performance. The research involved both pilot and full-scale CW and the following topics have been covered: design based on mass transfer processes and pathogen removal, substrate and macrophyte selection, coupling of CW with other treatment systems, agricultural reuse of wastewater, and wildlife habitat services. This chapter presents a summary of the results obtained from some of these studies. The results show that improved design and configuration by increasing flow velocity improves mass transfer coefficients. Novel substrates such pumice and use of indigenous macrophytes greatly improve the performance and sustainability of the treatment system. Coupling with other treatment systems such as waste stabilization ponds can improve the overall performance. CW have the potential to remove pathogens, including helminth eggs or larvae and protozoa cysts or oocysts. Inclusion of pathogen removal in the design equation greatly improves the accuracy of the design procedure to predict the hygienic quality of the effluent. Treated effluent has acceptable quality for reuse in, for example, paddy farming. CW improve general aesthetics and support biodiversity such as birds. For this technology to continue performing sustainably, more robust operations and management programs must be in place.
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.
The unabated urbanization and industrialization process in many arid and semi-arid countries leads to increasing demand for municipal and industrial water supply, often in direct competition with irrigation demand. In such cases wastewater reclamation and reuse should be an integral component of water resources management strategies. National reuse policies should be developed and implemented taking into account local conditions and based on affordable approaches that ensure safe reuse practice. This paper describes research and development carried out in several developing countries on appropriate technologies for implementing reuse, as well as coordinated international efforts to provide recommended guidelines and policies for safe wastewater reuse in agriculture and aquaculture.
Artificial wetlands have not yet been used in Uganda for wastewater purification. The feasibility of using artificial wetlands to improve presettled wastewater quality was tested using 40 1 experimental buckets (mesocosms) at Kirinya sewage works, Jinja, Uganda. These mesocosms were operated in an intermittent, vertical flow mode. They were synoptic experiments to a pilot constructed wetland project in which the utility of Phragmites mauritianus to treat presettled wastewater for P and N was examined. Results showed that the laterite-gravel rooted Phragmites reactors improved the wastewater quality significantly, possibly to advanced secondary or tertiary water quality levels. These reactors achieved reduction efficiency of over 90% for P and over 60% for N after a 5-day water retention time. The mass balances of N and P over the reactors, indicated a higher uptake rate for P by the plant than for N. Laterite-gravel rooted Phragmites mesocosms were more efficient than the floating Phragmites mesocosms for the wastewater treatment.
The primary goal of this study has been to carry out a rigorous, critical review and evaluation of all available documented epidemiological evidence with the aim of determining the significant, quantifiable, health effects on population groups directly or indirectly exposed to wastewater irrigation: through occupation; by residing in continguous communities or by consuming the sewage irrigated crops. Based on these findings, we have developed an epidemiological model predicting the degree of risk associated with various groups of pathogens.
Based on theoretical consideration of the model and confirmation by the empirical evidence collected and analyzed in this study, we have concluded that the risk of pathogen transmission by irrigation with raw wastewater for most developing countries is according to the following descending order: high - helminths (Ascaris, Trichuris, Ankalostoma and Taenia), lower - bacteria (Typhoid and Cholera); and lowest - viruses.
In general, it can be stated that based on both the theoretical and empirical findings of this study, there appears to be a basis for relaxing the conventional effluent quality standards for unrestricted crop irrigation. A guideline of no helmiths in 1 liter and a log mean of 1000 fecal coliforms/100 ml is proposed.
A review of some water quality management principles in culture Fisheries was carried out to provide fish culturist and environmental manager adequate knowledge to manage our fishery resources. Optimum fish production can be achieved only when the water quality is effectively managed. The required levels of physical and chemical characteristics of the culture medium, is necessary for fish culture. Some variables influence also water quality. Interactions between these variables can become complex and would require much more explanation. Salinity, conductivity, sediment, turbidity, dissolved oxygen, carbon (iv) oxide, pH, alkalinity, com compounds in water, estimation of nitrogenous compound, plankton, algae, light and dark method, plankton collection, plankton bloom and fish kill, pond productivity, harvest methods, carbon (iv) assimilation, carbon-14-fixation, nutrient uptake and chlorophyll are some water quality parameter reviewed to provide fish culturist and environmental manager adequate knowledge to manage our fishery resources.
It is known that pathogenic bacteria are sensitive to changes in environmental conditions.
This applies to Enterobacteriaeeae, as well, where optimum temperature is 37°C. Wastewater of various qualities are also hostile environments to these bacteria. The aim of the present study was to investigate the influence of temperature on the die-off of enteric bacteria in waste stabilization ponds at the temperature range 40-60°C. Survival of indicator microorganisms at the control pond effluent was higher than at increased temperature pond effluent (40°C, 50°C, 60°C). Survival percentages of the indicators at the elevated temperature pond compared to the control pond were 0.12% to 73.33%. The pathogenic bacteria Salmonella typhimurium and Shigella sonnei were introduced in dialysis bags placed in the ponds. The number of the pathogenic bacteria decreased by a few orders of magnitude within days, depending on the temperature and the strain. Following certain periods of time, the bacteria held in the heated pond and in some instances in the control pond, lost their ability to agglutinate with specific antibody. The phenomenon of bacteria showing negative specific agglutination requires further research. It is thought that this phenomenon might indicate an unknown heat survival mechanism of the pathogenic bacteria in adverse environment.
