SEWAGE BASED AQUACULTURE

By Christine Harris

Domestic wastewater has been traditionally used for aquaculture in China for six centuries (Ruddle & Zhong 1988). More recently George Chan, an engineer from Mauritius has been replicating these traditional systems in a number of places around the world, including Denmark and Vietnam. The result is commercially viable levels of fish production from wastewater: the dyke ponds in China produce up to fifteen tonnes of fish per hectare annually (Bodlovich 1994). The ponds in China are 2.5 to 3 metres deep, this allows for the growth of heterotrophic organisms, which increases available food for fish and also increases available niches. Six varieties of carp live in the Chinese dyke ponds, all having specific niches in which they live and feed.

Sewage is often viewed as a resource in developing countries and aquaculture is one of the traditional methods used for treating sewage throughout many countries in Asia.

Sewage based aquaculture Malang, East Java, Indonesia.

Plate 1. Sewage based aquaculture system in Malang.

Photo: Christine Harris

In Malang, East Java, there have been positive health benefits from the installation of a sewage based aquaculture system. The impetus for building this system was that five children in the community died from diarrhoea. A group of women in the community banded together and pushed for some form of sanitation system to be installed. Over a period of two years Agus Guntaro, the neighbourhood head led the community in the building of a simple sewerage network and treatment system. There are currently 67 houses in the community connected to this system. The treatment system consists of a septic tank followed by a series of seven tanks through which the water passes (see plate 1). The first two tanks are desludged every three months, the sludge from these tanks is then dried and sold as compost (plate 2 shows Agus Guntaro in front of the sludge drying bed). The final tank is stocked with Ikan Lele, the local catfish. The fish are harvested and sold for human consumption (plate 3 shows Agus Guntaro, fishing for Ikan Lele in the final tank of the treatment system).

Plate 2: Agus Guntaro holding dried sludge, which is sold as compost.

Photo: Christine Harris

An operation and maintenance system has been devised in order to ensure the system continues to function as planned (which it has been doing since it was first operational in 1987). Each household connected to the system pays IRP750 (Aus$0.15) per month for operation and maintenance. 60% of this goes to paying a caretaker, who supplements his income by selling the dried sludge and fish.

The effluent from this treatment system contains 60mg/L BOD* and 23mg/L suspended solids (UNDP-World Bank 1999). The BOD level is above the 20mg/L required in most developed countries. However considering the effluent is being discharged to the Brantas River and the BOD level of water in the Brantas River is between 50-100mg/L BOD (ibid), there is little concern from BOD levels in the effluent. It should be noted that subsequent replications of this system are producing effluent of a lower standard. The main reason for this appears to be a lack of technical knowledge, with systems being under designed for the load they will be receiving (ibid). Thus this system is a step in a learning process of how sewage based aquaculture systems can be used effectively and safely.

Plate 3: Agus Guntaro fishing for Ikan Lele in the sewage based aquaculture system.

Photo: Christine Harris

*BOD - Biochemical Oxygen Demand, refers to the amount of oxygen utilised in breaking down organic matter in a period of 5 days. It is a standard measurement for water quality.

Community -Based Technologies for Domestic Wastewater Treatment and Reuse: Options for Urban Agriculture provides more information on sewage based aquaculture.

References

Bodlovich A. (1994) Lessons from China, the work of George Chan. Permaculture International Journal No. 51, June 1994.

Ruddle K. & Zhong G. (1988) Integrated agriculture-aquaculture in South China. The dike-pond system of the Zhujiang Delta. Cambridge University Press, Cambridge.

UNDP-World Bank (1999) Community based sewer systems in Indonesia: A case study in the city of Malang. UNDP-World Bank Water and Sanitation Program, Jakarta.