Freshwater aquaculture

Unit 6 - Sewage Fed Fish Culture

6.2. Sewage and its characteristics
The term sewage is used loosely to include the combined liquid waste discharges of domestic and Industrial sources within a given area. It is a cloudy liquid having minerals and organic matter in solution, colloidal form and solids floating as suspension.
It contains about 90-99% water. It also contains bacteria and protozoa. It is rich in phosphorus (1-14 mg/l) and nitrogen (18-120%). It contains traces of heavy metals such as zinc, copper, chromium, Manganese, nickel and lead. The BOD and COD of the sewage are very high. The direct use of raw sewage is detrimental to fish because of its high BOD, low DO, High CO2, high levels of ammonia, hydrogen sulphide and bacterial and organic load.

Problems related to sewage fed culture system

• Accumulation of silt and high organic matter at the pond bottom.
• Incidence of parasites and fish diseases.
• Possibilities of pathogens being transferred to humans.
• Accumulation of heavy metals in the system.

Solutions

• Regulation of treated sewage intake into ponds
• Dilution with freshwater and use of prophylactics.
• Depuration of fish in freshwater before marketing.