Posted on 01 March 2012
Wastewater aquaculture closes ecosystem loop
Wastewater aquaculture closes ecosystem loopWastewater-fed aquaculture systems, such as in Hanoi, Vietnam, can act as an integrating mechanism to create closed-loop ecosystems, where wastewater becomes a key resource for urban environmental sustainability. This can be crucial given water scarcity, nutrient provision, and food production in rapidly growing urban populations. Fish, rice, and vegetables from Hanoi’s wastewater-fed aquaculture provide an important source of nutrition, especially protein.
Keywords: wastewater, aquaculture, urban planning, closed-loop ecosystems, food security
Aquaculture in Hanoi, Vietnam, fed by wastewater, is a multi-dimensional human-ecological system with a range of benefits, yet also creates problems like industrial effluents in wastewater. Fish, rice, and vegetables are cultivated through aquaculture (see also Havana, Lubumbashi and Shanghai). Its major benefits are providing an important source of food nutrition, especially protein, aiding water-treatment of Hanoi’s wastewater, and poverty alleviation. Also, aquaculture preserves water infrastructure in and around the city, thereby supporting ecosystem services like micro-climate control, flood control, and irrigation. These services raise the resilience of multiple city systems, not only the food system. When aquaculture is practised there are also tourism and leisure benefits from preserving water bodies near the city.
Solving key problems
The significance of wastewater-fed aquaculture for urban sustainability is considered to be high, given a handful of critical problems that it helps to solve. These are, for example, the treatment of urban wastewater in developing-countries and the local provision of a high-demand food, i.e. fish. Urbanisation is most rapid in developing countries, and it is seen as unlikely that wastewater-treatment services will keep pace. Therefore wastewater-based aquaculture is increasing in global significance (see also Hyderabad). With climate change, the rivers and other water-infrastructure around cities that aquaculture supports become more important for adaptation and resilience.
Experiences in Hanoi
Hanoi provides a learning case where aquaculture systems have developed over several decades with various phases of design and operation, such that today they are a combination of public structures (e.g. infrastructure, regulation) and private structures (e.g. private farm ownership and open markets). Since the 1980s, the total area under aquaculture has decreased by nearly half, but both the yield per hectare and the total annual yield of fish have more than doubled in Hanoi.
The cultivation of aquatic vegetables by utilising the city’s wastewater has an important role in providing incomes and livelihoods, poverty alleviation, improved diet, and in particular, greater protein availability. In Hanoi, more than half of fish production occurs in a single district to the south (Thanh Tri district), and is often integrated with rice and/or vegetable production (e.g. water spinach, mimosa, dropwort and cress). Wastewater-fed aquaculture provides around a third of Hanoi’s fish production, with other sources such as fish ponds, urban lakes, etc.
Hanoi also shows that controls are required. A key challenge for any wastewater-fed aquaculture system is to control changes in the quality of the wastewater. In Hanoi, increasing levels of effluents from industry, hospitals, and residential areas have caused problems. Yet there are important efforts to control quality. Along with increased overall wastewater treatment by the city, a 2002 regulation stipulates that industry, laboratories and hospitals should have their own treatment procedures at least for the most harmful wastes. But the regulation is criticized for lack of systematic checking for compliance. However, a 2007 study on Hanoi’s wastewater-fed fish concluded that consumption of common carp, silver carp and tilapia from wastewater-fed ponds posed limited or no food safety risk with respect to the studied toxins – arsenic, cadmium, and lead.
Major challenges to meet
Research on urban and peri-urban wastewater-fed aquaculture gives prominent attention to the need to go beyond controls of wastewater quality. Urban planning can use wastewater-fed aquaculture as an integrating mechanism for a range of human-environmental systems to create ‘closed loop’ ecosystems. Thus wastewater becomes a key asset, instead of a ‘waste’ and a problem for cities. Education and research are seen as vitally important, to enable the support and planning steps required for sustainable wastewater-fed urban aquaculture.
Other challenges are that as societies become wealthier, there is a tendency to shun wastewater-based food products, and simultaneously, with economic development there is often increased industrial/medical pollution of wastewater. Yet closed-loop wastewater systems may be crucial for environmental sustainability. For example, with larger populations, the increased wastewater discharges by urban areas increases nutrient inputs to coastal waters, additionally stressing and degrading coastal ecosystems. Researchers therefore propose that urban societies need to “turn the ‘wastewater pipes’ inland away from the coasts”, i.e. by developing innovative systems such as aquaculture wetland ecosystems (AWEs) for nutrient cycling, food production, habitat sustainability, and urban ecosystem health.
More widespread recognition of the threats and opportunities of wastewater and wastewater-fed aquaculture is necessary. For example, research points out that while the World Health Organisation has developed guidelines for the use of wastewater in aquaculture, these guidelines focus on microbiological safety, and more researh is needed on the human health aspects of potentially toxic elements.
Helle Marcussen, Peter E. Holm, Le Thai Ha, Anders Dalsgaard, 2007, “Food safety aspects of toxic element accumulation in fish from wastewater-fed ponds in Hanoi, Vietnam”, Tropical Medicine and International Health, volume 12 suppl. 2 pp 34–39
Vo Quy Hoan, Peter Edwards, 2005, “Wastewater Reuse through Urban Aquaculture in Hanoi, Vietnam: Status and Prospects”, Urban Aquaculture, eds B Costa-Pierce, A Desbonnet, P Edwards & D Baker, CABI Publishing, Wallingford, pp. 45–59. 2005
Alan Desbonnet, Barry Costa-Pierce, 2005, “Aquaculture in Future Urban Ecosystems”, Urban Aquaculture, eds B Costa-Pierce, A Desbonnet, P Edwards & D Baker, CABI Publishing, Wallingford, pp. 45–59
Nguyen Thi Dieu Phuong, Pham Anh Tuan, 2005, “Current Status of Periurban Aquatic Production in Hanoi”, Urban Agriculture (UA) Magazine, http://www.ruaf.org/sites/default/files/uam14_article3.pdf
Key data are retrieved from the UN World Urbanization Prospects: The 2011 Revision, http://esa.un.org/unup/unup/index_panel2.html
Text by: Aaron Thomas