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<International Source Book On Environmentally Sound Technologies
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9.3 Case studies

3.1 Case Study 1 - Hanoi wastewater-fed aquaculture system

Hanoi, the capital of Vietnam has a major system of wastewater reuse involving vegetables, rice as well as fish in low lying Tranh Tri district which lies to the south of the city (Photo 7). Produce from the reuse system provides a significant part of the diet of the city’s people (Vo, 1996).

Photo 7: Raw wastewater being pumped into wastewater-fed fish ponds in Hanoi, Vietnam

Construction of sewers began in the colonial era in the last century and continued following independence in 1954. Wastewater and stormwater are discharged untreated, about 320,000 m3/day, to four small rivers which play a dual role: drainage of wastewater from the city; and wastewater supply for reuse in agriculture and aquaculture. Conventional wastewater treatment plants have been constructed but lie idle due to lack of budget for operational and maintenance costs. About one-third of the city is sewered. The wastewater is 75-80% domestic and 20-25% industrial.

The system has largely been developed by the district farmers and local community over the past 30 years. Before 1960 the area was a sparsely populated swamp where rice was grown but with low yields and frequent flooding. Aquaculture began to develop in the early 1960s with the construction of an extensive irrigation and drainage system to facilitate rice cultivation. Farmers began to stock seed of wild fish collected from the river in rice fields as they perceived the benefits of wastewater-fed aquaculture. Following the formation of cooperatives in 1967, land use stabilized into vegetable cultivation on higher land, rice/fish cultivation on medium level land, and year-round pond fish culture on deeper land adjacent to the main irrigation and drainage canals. Wastewater-fed aquaculture became the major occupation of 6 cooperatives with easy access to wastewater and a minor occupation of 10 others out of the total of 25 district communes.

The local aquaculture research institute provided seed of exotic fish species, and fish hatcheries and nurseries were developed by farmers. Farmers also learned how to regulate the introduction of wastewater to produce fish. The major species are silver carp, rohu, and tilapia. Rohu has been the most popular species in recent years following its introduction in the late 1980s, displacing silver carp. However, tilapia is growing rapidly in popularity with the recent introduction of improved strains. Yields of fish of 3-8 tonnes/ha are harvested annually, lower yields from rice/fish and higher from pond culture.

The district will retain the same land use pattern of agriculture and aquaculture according to the Master Plan for the development of Hanoi city to 2010. This should diminish the threat of urban encroachment. An on-going project to improve the wastewater and drainage system of Hanoi has had only marginal impact on the wastewater-fed fish ponds through loss of a small area to construct a reservoir. The reservoir constructed to reduce flooding by storing wastewater and stormwater during heavy rain, is located downstream from the wastewater-fed pond system. A new industrial development area is being established outside the drainage area of the district so fish being cultured on city wastewater should be relatively free of contamination. However, the change in land use policy since the 1980s from cooperative to individual household management has adversely affected wastewater fed aquaculture. Over the decade since 1985 the area of wastewater fed aquaculture (essentially the rice/fish system) has declined in area by 36% from a total of 750 to 480 ha. In contrast to wastewater-fed fish ponds which are located adjacent to the main wastewater canals, rice/fish farms are unable to obtain sufficient wastewater. This is because of the breakdown in the wastewater distribution system which was previously operated by the communes.

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