12 ก.พ. 2556

EnvironmentAsia

7

81-88

สมาคมสถาบันอุดมศึกษาสิ่งแวดล้อมไทย

This research aims to describe the nitrogen and phosphorus removal in Recirculating Aquaculture System (RAS) by crop plants biomass production. The 3 experiment systems consisted of 1 treatment (fish tank + baked clay beads + Chinese cabbage) and 2 controls as control-1 (fish tank only) and control-2 (fish tank + baked clay beads), were performed. With all experimental RAS, Nile tilapia (Oreochromis niloticus) was cultured at 2 kg/m 3 density. The baked clay beads (8-16 mm in diameter) were filled as a layer of 10 cm in the water treatment tank of control-2. While in the treatment tank, Chinese cabbage (Brassica pekinensis) was planted at 334 plants/m 2 in baked clay beads layer. During 35 days of experiment, the average fish wet-weight in control-1, control-2 and treatment systems increased from 16.31±1.49, 15.18±1.28 and 11.31±1.49 g to 29.43±7.06, 28.65±3.12 and 27.20±6.56 g, respectively. It was found that the growth rate of 0.45±0.15 g-wet weight/ day in a treatment tank was higher than in those 2 controls, which were rather similar at 0.37±0.16 and 0.38±0.05 g-wet weight/day, respectively. The fish survival rate of all experimental units was 100%. The average Chinese cabbage wet-weight in treatment system increased from 0.15±0.02 g to 1.00±0.38 g. For water quality, all parameters were within the acceptable range for aquaculture. The assimilation inorganic nitrogen in a treatment tank showed a slower rate and lower nitrite accumulation relative to those in control tanks. The nitrogen and phosphorus balance analysis illustrated that most of the nitrogen and phosphorus input in all systems was from feed (82-87% and 21-87%) while at the final day of experiments, nitrogen and phosphorus in tilapia culture revealed at 15-19% and 4-13%. The accumulation of nitrogen and phosphorus in the water, up to 56% and 70%, was found in control-1 while water in the tank with baked clay beads had substantial lower nitrogen and phosphorus concentration. The most important part was unaccounted nitrogen and phosphorus as high as 60% and 17% in treatment and 53% and 10% in control-2 systems. Nitrogen and phosphorus incorporated in plant (treatment) was only 1.31% and 0.11%, respectively. It can be implied from the results that the assimilation in plant was a minor process for nutrient removal in this RAS. On the other hand, the nitrification and denitrification occurred in the sediment layer of baked clay beads tank were the major treatment processes to maintain water quality in the recirculating system. Without baked clay bead, nitrogen waste was accumulated as nitrate in the water while in treatment tank with backed clay beads, nitrogen was significantly removed by denitrification process.

http://www.tshe.org/ea/pdf/EA7(1)_11.pdf