Evaluation of reuse of shrimp farm effluent after chemical and biological treatments

Abstract

Possibility of reusing shrimp farm effluent water was evaluated after treatment of the water using chemical agents like calcium oxide (quick lime), ferric chloride, ferric aluminium sulphate (ferric alum) and fly ash. Among the chemicals used, treatments with fly ash (52.80%), quick lime (61.01%) and fly ash (72.5%) were found effective for the removal of ammonia, phosphate and for reduction in chemical oxygen demand (COD) respectively. In biological process, microalga Chlorella salina and the seaweed Ulva reticulata were tried. At the end of culture, highest net photosynthesis and assimilation number obtained from fly ash was 12.98 ± 0.096 g m-3 h-1 and 25.01 respectively. Level of ammonia and phosphate was drastically reduced from 152.01 to 1.18 µg at-N l-1 and 262 to 0.0719 µg at-P l-1 respectively in the waste water treated with fly ash cum microalgal culture. COD level was reduced from 102 to 5.31mg l-1 after treating the waste water with ferric chloride cum microalgal culture. The raw waste water yielded higher production of Ulva (7.74 g wet weight) followed by fly ash (7.26 g wet weight) and at the end of the culture period nitrogen concentration was 1.52 µg at-N l-1. No production of Ulva was registered from the waste water treated with lime, alum and ferric chloride. In culture experiment with post-larvae of the shrimp Fenneropenaeus indicus, fly ash treated (8.25%) and fly ash cum algal cultured waste water (8.56%) showed higher net growth efficiency. The larvae did not survive in other chemically treated waters.