RECLAMATION OF WASTE-WATER FOR POLYCULTURE OF FRESH-WATER FISH - WASTE-WATER TREATMENT IN PONDS

The main objective of the present study is to investigate the possibil ity of wastewater treatment in ponds for fish culture. A series of eig ht ponds (Au Tau pond system) were constructed at Au Tau Fisheries Off ice, Hong Kong Agriculture and Fisheries Department. Polluted river wa ter was pretreated in the first four ponds by providing sedimentation (S1, S2) and aeration (Al, A2), the effluent from A2 was introduced in to the remaining four ponds (C1-C4) for fish culture. Fries of six spe cies of freshwater fish including silver carp, big head, grass carp, t ilapia, common carp and black bass were stocked in the ponds (C1-C4) d uring 11/93-2/94, and 1/4 of normal fish feed (peanut cake) were used in the fish ponds. The pond water physico-chemical and microbiological qualities were monitored during the pond operation period (7/93-9/95) . The results showed that the average removal efficiencies of BOD, NH3 -N and PO4-P in the ponds (S2-C4) were 73.5%, 93.4% and 82.7%, respect ively, while more than 99% of pathogen indicators (total coliform, fec al coliform and E, coli were removed. Up to 97% total coliform, 95% fe cal coliform and 95% E. coli were removed in S2 (the 2nd sedimentation pond), The water treatment ponds (S2-A2) played an important role in removing pollutants (organic matter, nutrients and pathogenic bacteria ) and algal promotion, while the fish culture ponds (C1-C4) also demon strated the high ability in PO4-P and NO2--N removal. The average feca l coliform concentrations in fish ponds C1-C4 (6.35 x 10(3) no. 100 ml (-1)) were within the range of WHO guideline (10(3)-10(4) no. 100 ml(- 1)), but a maximum of 2.3 x 10(4) no. 100 ml(-1) was detected in pond C4 in May, 1995. (C) 1998 Elsevier Science Ltd. All rights reserved.