Quality and Characteristics of Effluents from Hybrid Catfish Ponds

Abstract

Hybrid catfish pond effluents were found to contain high concentrations of total suspended solids, phosphorus and nitrogen. The effluents contained 568.3-925.5 mg/l total suspended solids, 25.1-61.7 mg/l BODS, 0.652-6.140 mg/l total phosphorus, 0-0.170 mg/l hydrogen sulfide, 0-1.666 mg/l nitrite nitrogen, 5.654-69.389 mg/l ammonia nitrogen, 0.014-0.292 mg/l nitrate nitrogen and 12.354-114.901 mg/l total kjeldahl nitrogen. Average concentrations of the pollutants in the effluents were 699.2, 43.0, 2.710, 51.293, 31.790, 0.205, 0.148 and 0.033 mg/l for total suspended solids, BOD₅, total phosphorus, total kjeldahl nitrogen, total ammonia nitrogen, nitrite nitrogen, nitrate nitrogen and hydrogen sulfide, respectively. pH of the effluents varied between 6.8-8.2 and dissolved oxygen concentrations varied between 0.3-4.2 mg/l. Most of the suspended solids in the effluents from hybrid catfish ponds were settleable suspended solids with very high settling velocity. Almost half of the total suspended solids settled down within 3 hrs while 74.4-80.9 % settled down within 12-24 hrs. Organic matter and phosphorus in the effluent were mostly in particulate form of settleable suspended solids and were quickly removed from the effluent by sedimentation. Removal rates were 43.5, 46.9,  52.8, 71.1, 78.0, 78.6 and 78.9 % for BOD5 and 53.8, 55.7, 65.6, 71.3, 73.4, 73.9 and 79.1 % for total phosphorus at 3, 6, 12, 24, 48, 72 and 96 hrs of sedimentation, respectively.