Effects of biofilter on water quality in closed recirculating system for black tiger shrimp

Abstract

To investigated the efficiency of using biofilter for ammonia removal in the outdoor shrimp ponds. The experiment was divided in to two parts. The first part was the evaluation of ammonia removal by biofilter under both laboratory and field conditions. The second part was the study of using biofilter in the outdoor shrimp ponds. The results from the first part showed that, under laboratory condition, active biofilter (incubated in shrimp pond for one month) had higher ammonia removal efficiency than control (unused biofilter). The average ammonia removal rate was 447.59 +- 205 mg ammonia nitrogen/sq.m. surface area/day. The results from field study using 77.7L chamber placed in shrimp pond also showed that significantly higher ammonia removal was found in the chamber containing biofilter. Increased in nitrite and nitrate in all chambers together with the decreased of ammonia indicated that nitrification process appear in the chamber and the attempt ofusing biofilter in shrimp pond is possible. In the second part, postlarva 17 of black tiger shrimp (Penaeus monodon) were cultured in four 29x29 sq.m. shrimp ponds (0.5 Rai) with 1.2 m depth at the density 60 postlarva/sq.m. Shrimp were grown in 6 psu salinity without water exchanged for 113 and 114 days for the first and second trials, respectively. The results from the first trial showed that ammonia concentration in both treatment ponds (containing 5 sets of biofilter with the aerators) and control ponds (containing only the aerators) was not different (less than 0.5 mg. ammonia nitrogen/L. However, the average shrimp production in treatment ponds was higher than control ponds (120.8 and 57.6 kg/pond, respectively). After the first trial, water in all ponds was drained out and soon refilled with the water from reservoir without pond bottom cleaning. With the second trial, all four ponds were installed with biofilter and aerators. The results showed that ammonia concentration in all ponds was less than 0.5 mg. ammonia nitrogen/L although dense blooming of phytoplankton was found throughout the culture period. However, shrimp production in all ponds was lower than the previous trial