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This is the authors version of the chapter. The original publication is available at www.Springerlink.com.
Bunting SW, Edwards P, 2018. Global prospects for safe wastewater reuse through aquaculture. In: Jana BB,
Mandal RN, Jayasankar P (eds), Wastewater Management Through Aquaculture. Springer, Singapore, pp. 55–
72. https://doi.org/10.1007/978-981-10-7248-2_3
Global prospects for safe wastewater reuse through aquaculture
Authors: Stuart W Bunting1, Peter Edwards2
Affiliations: 1Bunting Aquaculture, Agriculture and Aquatic Resources Conservation Services,
Glemsford, Suffolk CO10 7SS, UK, Email: stuartwbunting@gmail.com; 2Emeritus Professor, Asian
Institute of Technology, Bangkok, Thailand.
Content
1. Introduction
2. Prospects for rational design and participatory and integrated planning
3. Alternative reuses paradigms to mitigate health risks and concerns
4. Value addition through cutting-edge biorefinery approaches
5. Enhancing prospects for wastewater-fed aquaculture
6. Conclusions
7. References
Abstract
Given the parlous provision of basic sanitation and wastewater treatment globally the rationale for
safe wastewater reuse through aquaculture is presented. Wastewater-fed aquaculture related
Responses to counteract negative Driving forces, Pressures and Impacts associated with inadequate
sanitation and wastewater treatment and to enhance the State of systems are systematically
reviewed with the DPSIR framework. Prospects for a rational design-based approach to safe
wastewater reuse using treatment lagoons are discussed. A SWOT (Strengths, Weaknesses,
Opportunities and Threats) assessment is presented concerning the future development of safe
wastewater reuse through aquaculture. Specific opportunities for value addition to products through
cutting-edge biorefinery approaches are reviewed and the need for appropriate hazard barriers is
highlighted. Conditions required to support and promote safe wastewater-fed aquaculture are
assessed using the STEPS (Social, Technical, Environmental, Political/Institutional and Sustainability)
framework. It is concluded that reuse using intermediaries and biorefinery approaches holds great
promise. Widespread adoption of wastewater reuse through aquaculture could contribute to
achieving targets specified for sanitation and safe wastewater reuse by 2030 in accordance with the
United Nations’ Sustainable Development Goals.
Keywords: aquaculture; DPSIR; reuse; safe; STEPS; SWOT; UN SDGs, wastewater
1. Introduction
Globally 2.4 billion people do not have basic sanitation (toilets or latrines) and ‘up to 90% of
wastewater in developing countries is discharged partially treated or untreated directly into rivers,
lakes or the ocean’ (WHO 2015). Safe reuse to reduce the proportion of wastewater discharged
untreated is a global priority highlighted in the Sustainable Development Goals (SDGs) adopted
2
under the United Nations’ 2030 Agenda for Sustainable Development (UN 2016). In support of Goal
6 ‘Ensure availability and sustainable management of water and sanitation for all’ Target 6.3
specifies that ‘By 2030, improve water quality by reducing pollution, eliminating dumping and
minimizing release of hazardous chemicals and materials, halving the proportion of untreated
wastewater and substantially increasing recycling and safe reuse globally’ (UN 2015, p18).
The practice of wastewater reuse through aquaculture was widespread in the first half of the 20th
century, with notable examples from China, India, Indonesia and Vietnam in Asia and Germany and
the Soviet Union in Europe (Edwards and Pullin 1990; Edwards 1992; Prein 1996). Towards the end
of the last century, traditional systems of reuse through aquaculture, often devised by local
entrepreneurs, were in decline or lost with rapid urbanisation in many developing countries
(Edwards 2005a, b). Conversion of large peri-urban wetland areas used for wastewater-fed
aquaculture to more valuable housing and industrial development was common. Other reuse
systems were abandoned owing to pollution or were outlawed based on perceived public health
risks and the desire to portray a more ‘developed’ image on the world stage (Rigg and Salamanca
2005). Furthermore, unreliable wastewater flows attributed to either the deliberate neglect or poor
maintenance of delivery channels and infrastructure, and prioritising direct discharges to natural
waterways to avoid urban flooding, contributed to the demise of wastewater-fed aquaculture.
Adopting conventional wastewater treatment plant designs, with fixed packages of technology,
effectively eliminated any chance of wastewater reuse.
Provision of new wastewater treatment has been wholly inadequate to meet the needs of
burgeoning urban populations and this has caused widespread environmental degradation and
exacerbated public health problems (WHO 2015). The pressing need to address these issues was
again highlighted in the SDGs (UN 2015). Under Goal 3 ‘Ensure healthy lives and promote well-being
for all at all ages’, Target 3.1 specifies that ‘By 2030, substantially reduce the number of deaths and
illness from hazardous chemicals and air, water and soil pollution and contamination’ (p16). Under
Goal 6, Target 6.2 specifies that ‘By 2030, achieve access to adequate and equitable sanitation and
hygiene for all and end open defecation, paying special attention to the needs of women and girls
and those in vulnerable situations’ (p18). Against this backdrop, it is reasonable to ask whether
wastewater reuse through aquaculture has a role to play in meeting the UN SDGs by 2030?
An assessment of wastewater-fed aquaculture related Responses needed to counter negative
Driving forces, Pressures and Impacts and enhance the State of the system using the DPSIR
framework is presented in Figure 1. This analysis builds on the DPSIR-based reviews of threats to
wastewater reuse through aquaculture in the East Kolkata Wetlands (EKW) in Kolkata, West Bengal,
India (Bunting et al. 2010) and future potential of urban aquaculture to contribute to resilient food
systems (Bunting and Little 2015). The assessment benefitted further from the addition of cultural
and administrative factors identified by Rigg and Salamanca (2005) concerning the ‘drivers of
periurban change’ affecting peri-urban aquatic food production systems in Southeast Asia.
3
Driving forces
- population growth and economic
development
- rapid urbanisation and industrialisation
- poor planning and inadequate planning
control and enforcement locally
- urban expansion and rural-urban migration
- cultural change and changing labour markets
Responses
- responsible authorities must meet their
international obligations, notably SDGs
specifying safe wastewater reuse
- policy and planning must stipulate safe
wastewater reuse if feasible
- legislation must be enacted to legitimise
wastewater reuse and safeguards
introduced to protect and reassure
consumers and others
Pressures
- rapid increase in wastewater flows owing to
population growth, industrialisation and
urbanisation
- increased industrial effluents lead to pollution,
environmental degradation, contamination and
adverse public health impacts
- mixing of industrial and domestic wastewater
heightens risks associated with wastewater
reuse practices for producers and their families,
local communities and consumers
- rapid expansion of urban areas leads to land
conversion from agricultural and peri-urban
settlements and natural areas, including
wetlands, to high density housing for more
affluent people and industrial developments
- low-lying areas, including lakes and ponds, are
in-filled so that the land could be sold for
development at a much greater price
- with supportive policies and enabling
institutional environment, entrepreneurs
could initiate safe wastewater reuse
through aquaculture that capitalises on
nutrient and water resources
- safe wastewater reuse through
aquaculture could reduce pollution of
receiving waterways and enhance health
outcomes for local communities
- aquaculture as one element of
multifunctional treatment and water
storage strategies could prompt greater
vigilance and action in response to
potential contamination of wastewater
resources
- policies should ensure operators of
systems reusing wastewater safely through
aquaculture have security of tenure and
that there is a strategy for ‘managed
retreat’ in anticipation of urban expansion
State
- share of global population living in urban areas
exceeded 50% in 2007 and this trend continues
with many hundreds of millions or poor people
suffering as they lack access to basic services,
- wastewater reuse could aid cost recovery
to subsidise appropriate collection and
treatment and provide income
opportunities for poor and marginal groups
4
such as sanitation, and have to live in insecure
and polluted environments
- surface water quality in many urban settings
and downstream environments is below
acceptable international standards (impacts -
adversely affects human health)
- vast amounts of nutrients are discharged to
receiving waters (impacts - causing
eutrophication and the loss of a valuable
resource)
- extent of low-lying areas that could previously
accommodate runoff and flood water has
declined significantly (impacts – substantial
financial costs associated with need to build
drainage infrastructure and heightened risk of
flooding in established and newly urbanised
areas)
- appropriate reuse systems could avoid
capital and O&M costs for conventional
sewage treatment systems
- wastewater reuse could achieve better
environmental protection and biodiversity
conservation and restoration of ecosystem
services that sustain economic and socio-
cultural activities
- wastewater reuse could facilitate nutrient
recycling and added value from water
appropriated for human use
- production of affordable aquatic plants
and animals could enhance nutrition and
food security amongst poor communities
- water-bodies established for wastewater
reuse could provide additional capacity to
store urban runoff and floodwater
Impacts
- poor and marginal groups suffer owing to limited employment and income, insecure living
conditions and food supplies, absence of health care and sanitation, air and water pollution, and
flooding
- population pressure leads to informal settlements on accessible areas that are not served by
sewers and consequently discharge wastewater indiscriminately and lead to open defecation and
overhung latrines along canals and over ponds
- discharge of untreated wastewater negatively impacts biodiversity, undermines stocks and flows of
ecosystems services, and increases animal and public health risks associated with direct and
unintentional wastewater reuse through aquaculture
- conflicts between land use activities, with poor communities and agriculture and aquaculture
generating modest financial returns displaced or further marginalised
- financial costs associated with living in urban settings force younger generation to avoid farm work
and seek urban employment
Figure 1. DPSIR framework assessment for wastewater-fed aquaculture globally1
1 As noted by Bunting et al. (2015, p22) ‘solid arrows indicate the typical cause-and-effect interpretation of the
DPSIR framework and scope for Responses across this continuum; broken arrows indicate that Responses must
be moderated in light of prevailing conditions’
5
Considering the situation in India, wastewater reuse through aquaculture is still practiced, notably in
the EKW (EKWMA 2016). Globally, the practice of irrigation with wastewater for food production is
more common in terrestrial farming (Strauss 2003) and ‘at least 10% of the world’s population is
thought to consume food irrigated by wastewater’ (WHO 2015, p1). Large volumes of processed
sludge from sewage treatment plants are currently applied to agricultural land in Europe. The
practice is not generally challenged as it is not very visible, occurring sporadically in rural areas, and
no adverse effects have been reported. Furthermore, the separation of waste inputs to the soil
earlier in the growing season, and the harvest of grains that undergo processing, may psychologically
allay any concerns. There is a degree of trust in the regulatory authorities, whom the public expect
would prevent any unhygienic or unsafe practices.
2. Prospects for rational design and participatory and integrated planning
Prominent practitioners and scientists advocated an ecological engineering approach to wastewater
treatment using lagoons and fishponds recalling the example set by indigenous reuse practices
developed and refined by producers, as with the EKW, and Mudialy Fishermen’s Cooperative Society
also in West Bengal, India (Ghosh 1999; Jana 1998a, 1998b, 2000; Mara 1997; Pye-Smith et al. 1994).
Lagoon-based wastewater treatment and reuse systems were established at Bally (North Howrah),
Nabadwip, Panihati and Titagarh (Mara 1997) in West Bengal, under the Ganges Action Plan (GAP)
initiative. Fish were grown in batch culture in maturation ponds established as part of a waste
stabilization pond system at the Kalyani Sewage Treatment Plant (STP) (Jana 1998; Ganguly et al.
2015). A demonstration system was commissioned to reuse sewage from treatment ponds in San
Juan, Lima, Peru to test and promote the technology in South America (Moscoso 2006). A lagoon-
based treatment system was established to treat polluted water extracted from the Kam Tin River,
Hong Kong and trials were conducted growing fish in the water following sedimentation and
aeration (Liang et al. 1999).
Treatment lagoons are routinely designed to produce water that meets international standards for
safe reuse. This level of treatment, however, removes significant quantities of nutrients, thus
limiting the productivity of the receiving fishponds. Cognisant of this limitation, a rational design
approach was formulated that capitalises on the rapid die-off of bacteria in aerobic and alkaline
fishponds to compensate for a more moderate treatment phase (Mara et al. 1993). Anaerobic ponds
with a depth of 2 m and retention time of 1 day are followed by facultative ponds, 1.5 m deep and
with a retention time of 5 days. To validate the design the volumetric and areal BOD5 loading should
not exceed 300 g m-3 d-1 or 350 kg ha-1 d-1 for the anaerobic and facultative ponds, respectively.
Fishponds are then designed based on the optimal nitrogen loading of 4 kg ha-1 d-1 (Edwards 1992);
this necessitates calculating the removal of nitrogen in the facultative ponds but no loss of nitrogen
is expected from the anaerobic ponds.
Faecal coliform (FC) concentrations in the fishponds are estimated using the relationship established
for a continuous stirred reactor (CSTR) defined by Mara et al. (1993) and based on the earlier work
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of Marais (1974) thus: Np = Ni/(1 + kTOa)(1 + kTOf)(1 + kTOp), where Np is the number of FCs in 100 ml
of fishpond water, Ni is the number of FCs in 100 ml of untreated wastewater, kT is the rate constant
for FC removal per day (2.6(1.19)T-20) and Oa, Of and Op are the retention times (days) in the
anaerobic pond, facultative pond and fishponds, respectively. Subsequent evaluation deemed the
CSTR model safer as compared to the alternative dispersed flow (DF) model proposed by Oakley
(1997) as the DF model tends to overestimate faecal coliform removal rates in ponds with plug-flow
conditions and higher retention times (Buchauer 2006).
Assuming that the rational design approach was adopted to enhance the reuse of 550,000 m3 d-1 of
wastewater in the EKW, it was indicated that fish production could be increased to 45,000 t annually
(Bunting 2007). This would, however, require extensive and costly reconfiguration of the existing
pond system and the creation of 27.5 ha of anaerobic ponds and 182 ha of facultative ponds. Water
entering the fishponds in this case would contain 2.2 x 105 FC per 100 ml, thus exceeding WHO
(2006c) guideline targets for wastewater for aquaculture reuse. If the fishponds were reconfigured
so that they were small (1 ha), infrequently loaded with wastewater and well mixed, then rapid
pathogen die-off in the ponds would ensure the safety of producers, local communities and
consumers (Mara et al. 1993).
Hybrid waste stabilization pond and storage and treatment reservoirs have been proposed to store
treated water for unrestricted irrigation whilst simultaneously producing water for restricted
irrigation (Mara and Pearson 1999). The authors calculated that to treat 10,000 m3 of wastewater
daily and store water for five months of unrestricted irrigation would require a storage reservoir of
15.75 ha. Following a one month rest phase the faecal coliform count would be below 1000 per 100
ml of water (p591). At this concentration, the reservoir water meets the microbial quality target for
wastewater-fed aquaculture to safeguard ‘aquacultural workers and local communities’ (WHO
2006c, p41) and within four months a crop of 200 g tilapia could be produced (Mara et al. 1993).
Cages could be used to culture fish in wastewater treatment ponds to facilitate harvesting and to
avoid predation of farmed stock by larger wild carnivorous fish (Gaigher and Krause 1983).
Opportunistic fish culture in wastewater treatment lagoons has been reported from several
countries including Bangladesh and India in Asia and Ghana, Kenya and South Africa in Africa
(Ampofo and Clerk 2003; Bunting 1998; Kumar et al. 2014; Letema 2012; Prinsloo and Schoonbee
1992). Fish ponds were constructed downstream of the Keshopur wastewater treatment plant, Delhi
to make use of treated wastewater (Spatial Decisions and Winrock International India 2006). Whilst
these authors also noted that untreated wastewater was used for aquaculture in large slums, such
as Yamuna Pushta, Delhi to produce food and income for the local community. An urgent need for
‘policy-makers and authorities … as well as donors and the private sector’ to confront ‘the realities of
wastewater use in agriculture [and aquaculture]’ was highlighted by the signatories to ‘The
Hyderabad Declaration on Wastewater Use in Agriculture’ (IWMI 2002). The declaration specified
the need to adopt appropriate policies and commit financial resources for implementation and apply
‘cost-effective and appropriate treatment suited to the end use of wastewater, supplemented by
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guidelines and their application’. As with formal wastewater-fed aquaculture, the international
guidelines for safe reuse published by WHO (2006c) present a sound starting point for responsible
authorities to devise appropriate risk management strategies and implement hazard barriers that
safeguard the health of consumers, as well as producers, their families and local communities.
3. Alternative reuses paradigms to mitigate health risks and concerns
Ten years on from the publication of revised guidelines by the World Health Organisation for the
‘Safe Use Wastewater, Excreta and Greywater’ (WHO 2006a, b, c, d) the impact of this major policy
development on public health still demands assessment. A central tenet of the guidelines for
‘wastewater and excreta use in aquaculture’ (WHO 2006c) was ‘to ensure that waste-fed
aquacultural activities are made as safe as possible so that the nutritional and household food
security benefits can be shared widely in affected communities’ (pxiii). The urgent need to tackle
untreated wastewater discharges to protect the Ganges River and the communities it sustains was
highlighted by the recent call for innovative solutions (NMCG 2016). The call identified 144 drains
across four states (Uttar Pradesh, Uttarakhand, Bihar and West Bengal) discharging 6,614 mld-1 of
untreated wastewater to the Ganges (Annexure VI). A further 853 mld-1 is discharged to two of the
rivers’ major tributaries and the situation is made worse by non-point source pollution and open
defecation along the river banks.
Wastewater interception and treatment schemes established over 20 years under the auspices of
the GAP cost many hundreds of millions of dollars but did not result in the ecological restoration of
the Ganges owing to ‘bad planning, poor execution, extensive corruption, absence of coordination ...
delay ... cost escalation ... inadequate treatment of effluents, especially in tackling ... bacterial load ...
deficient public awareness and participation’ (Dayal 2016, p58-59). A comprehensive review of 152
wastewater treatment plants established under the National River Conservation Plan (NRCP) in India
noted that the cumulative design capacity was 4716 mld-1 but that only 3126 mld-1 (66%) was
operational (CPCB 2013). Of the 152 plants surveyed, 31 were WSP systems and it was noted that
associated average capital costs of Rs. 2.3 million per mld-1 of capacity to achieve secondary
treatment were significantly lower than conventional treatment technologies (p10).
Nationally the flow of wastewater from class I cities (population above 100,000 in 2001) was
estimated at 35,558 mld-1, but the treatment capacity was only 11,554 mld-1 or 32.5% of the total.
For class II cities (population 50,000 to 99,999 in 2001) a flow of 2697 mld-1 was estimated but the
treatment capacity was only 234 mld-1 or 8.7% of the total. It was noted that inadequate wastewater
collection meant the limited treatment capacity that was available was not fully utilised. Focusing on
West Bengal, 34 treatment plants with a design capacity of 457 mld-1 were surveyed, but the actual
treatment level was 214 mld-1 (46.8% of the total). It was observed that 13 plants were not
operational. One facility operating at its design capacity of 6 mld-1 and effectively treating
wastewater was the Baidyabati plant (CPCB 2013). This WSP-based system consists of an anaerobic
8
pond, a facultative pond, an aerobic pond and five fishponds. Revenue generated from fish culture
could provide an incentive to ensure the correct functioning of the plant.
Key to meeting the SDG to ensure sanitation for all by 2030 will be the adoption of appropriate
technologies given the prevailing environmental, social and economic setting (Mara 2001).
Supporting policies and institutional arrangements are required to legitimise wastewater reuse
through aquaculture. Considering Vietnam, with its history of wastewater-fed aquaculture in and
around Hanoi, it was noted that ‘although policies, strategies, laws and guidelines support the use of
wastewater in agriculture and aquaculture’ there is a lack of implementation and enforcement
(Evans et al. 2014, p5). The need for reciprocal arrangements within agriculture, aquaculture and
irrigation policies and regulation concerning health impacts was highlighted. Consequently, it was
noted that ‘small changes could lead to safe, cost effective planned reuse which would protect the
environment and provide Hanoi with a much needed water supply in the future’ (p1).
Cost effective and easy-to-operate strategies are required as opposed to conventional energy
intensive technological packages. Fundamental to the WHO guidelines for safe use of wastewater
and excreta in aquaculture is that ‘minimum good practices or health-based targets should be based
on local social, cultural, environmental and economic conditions and be progressively implemented
over time depending on the existing reality and resources of each individual country or region,
leading to steady public health improvements’ (WHO 2008, p2). Innovative financing and
management arrangements should be devised that are efficient, effective and accountable. Waste
Enterprisers Ltd signed a public-private partnership agreement with Kumasi Metropolitan Assembly,
Ghana to operate and maintain the waste stabilization ponds at Ahensan Estate and Chirapatre
Estate in return for access to the maturation ponds to culture catfish (Murray and Yeboah-Agyepong
2012). Water conditions in the maturation ponds were suboptimal for fish growth and survival. Poor
design, short-circuiting and siltation led to poor treatment performance; in response stocking
advanced fingerlings that had been acclimatised to wastewater was recommended.
The crux of the matter is finding a balance between wastewater treatment to make it safe and
acceptable to use and optimising the reuse strategy to maximise the benefits. A distinction is made
between safe and acceptable, as practices that conform to international standards for safe reuse,
may still be regarded as unacceptable by consumers and authorities from a psychological or socio-
cultural perspective. Fish raised using wastewater in Egypt were deemed safe for human
consumption based on international guidelines, but were not accepted by consumers owing to
cultural barriers (Mancy et al. 2000). To allay concerns over the reuse of sewage sludge in terrestrial
agriculture in the UK a consortium of wastewater operators and major food retailers produced the
‘Safe Sludge Matrix’ (ADAS 2001). The matrix summarises what level of sludge processing is
appropriate for different crop categories and what harvest interval post sludge application is
required. A safe wastewater reuse matrix for aquaculture within the local context could be
developed jointly by authorities, producers and consumer representatives adopting these principles.
9
Prospects for wastewater-fed aquaculture are critically reviewed here using the SWOT (Strengths,
Weaknesses, Opportunities, Threats) framework to structure the assessment (Table 1).
Table 1 SWOT assessment of wastewater-fed aquaculture (adapted from Bunting and Little 2015)
Strengths: existing or potential resources or
capability
Weaknesses: existing or potential internal
force that could be a barrier to achieving
objectives/results
- demand for aquaculture products amongst
burgeoning urban populations and more
affluent middle-class consumers is strong
and increasing
- wastewater reuse through aquaculture is
recognised in national and international
policy and supported by aid agencies and
development banks
- optimal production strategies have been
devised through local innovation by farmers
and extensive programmes of scientific
research
- productive wastewater-fed aquaculture
systems can act as a bio-indicator for good
environmental health, conserve biodiversity,
restore ecosystem services, and notably
open spaces for flood retention and
infiltration
- wastewater reuse through aquaculture can
provide income and employment
opportunities for poor and marginal groups
and produce aquatic plants and fish that are
affordable and contribute to the nutrition
and food security of poor communities
- responsible authorities do not widely
recognise wastewater reuse through
aquaculture as a legitimate urban/peri-urban
activity or effective and efficient option for
wastewater treatment and management
- widespread discharges of partially and
untreated wastewater from rapidly expanding
urban populations are not safe for reuse
through aquaculture, contaminate surface-
waters and cause environmental degradation
- lack of supportive and coherent policies and
legislation across different sectors, combined
with weak enforcement and insecurity of
tenure dissuade entrepreneurs from investing
in aquaculture businesses that could reuse
wastewater
- poor urban planning and inertia that
perpetuates the selection of inappropriate
wastewater treatment options means that
wastewater reuse through aquaculture is not
given equal consideration with regards to
cost-benefit analysis (CBA) or comparative
health impact assessments
Opportunities: existing or potential factors
in the external environment that, if
exploited, could provide a competitive
advantage
Threats: existing or potential force in the
external environment that could inhibit
maintenance or attainment of unique
advantage
- perfect storm of population growth,
urbanisation, untreated wastewater flows,
water scarcity, food insecurity and rising
energy costs make the rationale for safe
reuse through aquaculture undeniable
- international agreements stipulating the
need for far greater wastewater reuse and
supporting policies and guidelines should
legitimise and encourage adoption of reuse
- wastewater reuse through aquaculture
requires more extensive use of land than
conventional wastewater treatment systems,
a major constraint in peri-urban areas of
rapidly expanding cities where available land
at reasonable cost may be limited
- concerns amongst consumers regarding
wastewater reuse practices may be
exacerbated or made insurmountable through
10
through aquaculture
- growing awareness of environmental and
public health impacts of discharging
untreated wastewater and the reality of
unintended and unsafe use for aquatic food
production should shift public opinion
favourably towards appropriate treatment
and safe reuse through aquaculture
- abstraction of water from waterways
receiving wastewater for use in aquaculture
(with appropriate precautions) could
promote ecological restoration, whilst
mitigating cultural and psychological
aversions to direct wastewater reuse
- innovative community members and
entrepreneurs exploit opportunities to
appropriate wastewater (raw and partially
treated) flows and access treatment lagoons
to culture aquatic plants and fish to meet
demand from expanding urban populations
adverse media coverage of practices and
adverse public health outcomes
- advocates for conventional treatment
practices, notably engineers and those with
commercial interests may promote
inappropriate technological packages given
prevailing environmental, social and economic
conditions
- contamination with industrial effluents and
chemical pollutants and the occurrence of
pathogens, notably trematodes, within the
general population, may make risks associated
with wastewater reuse through aquaculture
unacceptable
- products cultured using wastewater (directly
or indirectly) must compete with products
from elsewhere, and costs of treating and
conditioning wastewater and elevated land
and labour costs in urban and peri-urban
areas may mean reuse strategies are not
financially viable
- limited information on extent and nature of
wastewater reuse (intentional and
unintentional) in aquaculture means that
authorities do not appreciate the contribution
to livelihoods, nutrition and food security and
economic development and health risks are
not assessed and managed
When an additional degree of separation, whether temporally, spatially or psychologically, is
deemed necessary to allay the concerns of potential consumers and others an intermediate
production phase could be included. Aquatic plants could be grown on wastewater-fed lagoons and
harvested and processed to feed to livestock or herbivorous fish in ponds not receiving wastewater
(Alaerts et al. 1996; Edwards et al. 1992). Comprehensive trials growing duckweed on wastewater
have been undertaken and the optimal conditions to maximise the yield and composition of the
biomass produced are well defined (Iqbal 1999). Tilapia and small carp species could be cultured in
wastewater-fed ponds for processing to make feed for other aquatic animals (Edwards 1990).
Wastewater could be used to cultivate aquatic animals, plants and phytoplankton for use as
feedstock for industrial processes and bio-energy production (see Section 4).
The non-use or intrinsic values of ecologically-based treatment systems may justify their
establishment when productive reuse of wastewater is not possible. Treatment wetlands could
sustain a broad range of ecosystem services, in addition to regulating waste discharges, and could
provide a valuable habitat for aquatic species. Reuse through aquaculture of waste not originating
from humans, such as manure from animals, waste streams from agro-industrial processes and food
11
and drink production is well established (Little and Edwards 2003). Promotion of such practices to
reuse wastewater, capture nutrients and safeguard the environment should be less controversial.
Ecologically-based wastewater treatment should be integrated with other uses as part of
multifunctional floodplains or landscapes to maximise synergistic effects, but associated public
health risks would demand assessment and appropriate safeguards.
4. Value addition through cutting-edge biorefinery approaches
Biorefinery approaches have the potential to add substantial value to plants and animals cultured in
wastewater reuse systems. Plants such as microalgae and seaweeds and animals such as crustaceans
and molluscs could be transformed through extraction and purification processes to higher value
products. Microalgae are cultured to produce a range of chemicals, fatty acids and bioactive
compounds (Borowitzka 1993). Harvesting microalgae represents a major constraint to
commercialisation of pond-based culture. Culturing fish on algae derived from high rate algae ponds
may be a viable alternative that could add value to microalgae production using wastewater
(Edwards and Sinchumpasak 1981; de la Noue et al. 1992). Seaweed biomass can be degraded by
bacteria (Alteromonas espejiana) to produce single cell detritus that can be fed to suspension
feeding animals in hatcheries or to Artemia nauplii for use as fish feed (Uchida et al. 1997).
By-products from seafood processing, notably crustacean shell material, has been highlighted as a
potential source of nitrogen rich chemicals and the development of appropriate biorefinery practices
could help protect the environment and generate substantial economic benefits (Yan and Chen
2015). Calcium carbonate derived from shells can be used in agriculture, construction, paper
manufacture and pharmaceuticals. Protein from shrimp shell could be processed to produce
livestock feed as it contains essential amino acids and is nutritionally comparable to soya bean meal.
Chitin from shells can be used in biomedicine, cosmetics, textile manufacture and water treatment.
Composed of a linear polymer containing nitrogen, chitin could be a significant new feedstock for
ethanolamine (ETA). Two million tonnes of ETA, with a value of $3.5 billion, are used annually for
carbon sequestration, household cleaning products, soap and surfactants (Yan and Chen 2015).
According to these authors the refinery of shell-derived industrial feedstock materials is constrained
as extraction methods are ‘destructive, wasteful and expensive’ (p156). Innovative methods using
ionic liquids are being developed to extract long-chain and high-molecular weight chitin polymers,
that can be spun into fibres and used to produce films, both with excellent potential for
commercialisation.
Prospects for reusing wastewater to culture zooplankton (Daphnia magna) in aerated waste
stabilisation ponds were assessed in the Grand-Duchy of Luxembourg (Cauchie et al. 2002). The
chitin content of the zooplankton biomass was between 3% and 7% on a dry weight basis.
Depending on the processing mechanism the average molecular weight ranged from 600,000 to
2,600,000 and had a low nitrogen content ‘indicating a high degree of acetylation’ (p103).
Wastewater from the Iztacalco treatment plant in Mexico City, Mexico was used to culture four
12
cladoceran species and population growth rates comparable to those achieved with green algae
were obtained (Nandini et al. 2004). Comparing different organic wastes to produce zooplankton
(Moina micrura) it was found that diluted human urine was the best media (Golder et al. 2007).
Feeding by zooplankton species can reduce the bacterial load in wastewater. But prior to using
cladocerans grown using wastewater to feed fish larvae it was noted that the risks from transferring
bacterial diseases and the bioaccumulation of toxins must be evaluated. Zooplankton (Daphnia
carinata) from wastewater treatment lagoons at Werribee, Melbourne, Australia had a protein
content of 54.8% and when fed to silver perch (Bidyanus bidyanus) resulted in better growth and
feed conversion ratios than a control diet (Kibria et al. 1999). The authors also noted that heavy
metal concentrations in fish fed zooplankton were very low.
Biorefinery approaches are being devised to add value to small mussels cultured in sub-optimal
conditions and low-trophic level species biomass produced from integrated multi-trophic
aquaculture (IMTA) systems. Opportunities to produce biomass as an industrial feedstock from
wastewater reuse through aquaculture could avoid problems with reuse to produce food for people.
Considerable investment in research and development is required, however, to devise processing
pipelines that are efficient and suitably refined to produce high quality and high value products.
Appropriate hazard barriers to safeguard the health of operators, their families, local communities
and those working in biorefinery pipelines will still be needed.
5. Enhancing prospects for wastewater-fed aquaculture
Problems encountered by operators of wastewater-fed aquaculture systems have been widely
reported and media coverage has borne witness to the demise of iconic systems such as Boeng
Tompun Lake in Phnom Penh, Cambodia (The Cambodia Daily 2014) and the EKW, West Bengal,
India (The Times of India 2015). Critical reflection on such experiences can, however, help clarify the
conditions required to successfully implement and sustain the safe reuse of wastewater through
aquaculture (Bunting et al. 2010). The STEPS (Social, Technical, Environmental, Political,
Sustainability) framework that cuts across disciplines and sectors is used to structure such an
assessment (Table 2).
Table 2 STEPS assessment of conditions needed to support and promote wastewater-fed aquaculture
(adapted from Bunting and Little 2015)
STEPS
element
Conditions
Social
- acceptance and support for safe wastewater reuse through aquaculture as a
legitimate and worthwhile activity
- demand exists for animals and plants grown safely using wastewater or
appropriate intermediaries and refined materials could be produced
13
- aquaculture reusing wastewater generates sufficient revenue to provide
attractive employment and income generating opportunities
Technical
- wastewater treatment and conditioning facilities, whether conventional or
ecologically-based systems, produce water that is safe and of sufficient quality to
stimulate natural productivity in culture ponds and promote good aquatic animal
or plant growth
- practices in which indirect or unintentional wastewater reuse through
aquaculture is occurring identified using appropriate tests and safeguards
implemented to manage health risks
- monitoring programmes implemented to ensure that systems function correctly
and within permissible limits
- quality inputs e.g. healthy fish and nutritious supplementary feed are available
and employees sufficiently trained to effectively operate and maintain the system
(including wastewater treatment facilities where necessary)
- arrangements across product value chains are implemented to safeguard the
health of workers, the general public and consumers
Environmental
- wastewater reuse through aquaculture recognised as an effective and legitimate
element in managing wastewater to protect receiving waterways and facilitate
recycling of resources
- wastewater treatment system components and aquaculture facilities are
designed appropriately given prevailing climatic conditions and safeguards
included to mitigate against extreme weather events, flooding and climate change
- authorities enforce laws to prevent pollution to safeguard wastewater reuse
through aquaculture practices and products
- city planning includes provision for green infrastructure, including space for
appropriate wastewater treatment and reuse through aquaculture, as this will help
dissipate adverse impacts of urbanisation such as the urban heat island effect and
flooding (within urban areas and downstream) and provide habitat for biodiversity
Political
(Institutional)
- national and international polices explicitly support wastewater reuse through
aquaculture for increased sanitation coverage, public health and environmental
protection, ecosystem services enhancement, resource recovery and food security
- signatories to the UN 2030 Agenda for Sustainable Development adhere to their
commitments, notably improve water quality and reduced pollution through safe
reuse of wastewater for aquaculture
- municipal authorities and engineers recognise and encourage wastewater reuse
14
through aquaculture as a legitimate and desirable activity
- land-use planning policy and tenure arrangements provide security for operators
and enable them to access credit and justify investment in ongoing operation and
maintenance
- government agencies and extension services and private sector support providers
cover aquaculture using wastewater (intentionally and unintentionally)
- operators of systems reusing wastewater for aquaculture cooperate, share
knowledge and pool resources to lobby for greater support and recognition within
wastewater management and urban planning processes
Sustainable
(long-term
viability)
- policies supporting appropriate wastewater treatment strategies and wastewater
reuse through aquaculture continue and remain consistent with developments in
other sectors
- management plans and the design and location of treatment and reuse systems
are adaptable to changing circumstances
- investment in wastewater collection and treatment infrastructure continues so
that wastewater flows are maintained and the quality of aquaculture products is
safeguarded
- minimum good practices and health protection targets should be appropriate to
local conditions and progressively implemented given the reality of the situation
and availability of resources
6. Conclusions
Prospects for wastewater-fed aquaculture have been critically reviewed from a global perspective.
Technologies and processes to enable the safe reuse of wastewater through aquaculture have been
established although they require more extensive use of land than conventional wastewater
treatment systems, a major constraint in peri-urban areas of rapidly expanding cities where available
land at reasonable cost may be limited. Problems concerning the acceptance of food products from
wastewater reuse systems may constitute a fundamental barrier to future development. Reuse
through intermediaries and for biorefinery feedstocks appears to hold the greatest promise.
Research and development must focus on such strategies to ensure that they are cost effective and
appropriate. Responsible authorities have a key role to play in ensuring that safe reuse through
wastewater-fed aquaculture is regarded not only as a legitimate practice, but is championed as a
practical means towards protecting the environment, safeguarding public health and contributing to
food security. Awareness must be raised regarding the risks of practicing aquaculture (either
intentionally or inadvertently) in faecally polluted surface waters and appropriate safeguards
15
implemented to protect the health of producers, local communities and consumers (WHO 2006c).
Widespread adoption of wastewater reuse through aquaculture is an appropriate strategy for small-
and medium-sized settlements in low- and middle-income countries with tropical climates and could
make a significant contribution to achieving the United Nations’ SDGs by 2030.
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