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Abstract
The study aimed to determine the wastewater treating area of water lettuce (Pistia stratiotes) in a recirculating aquaculture system (RAS) based on total amount of waste released by bighead catfish (Clarias macrocephalus) at different stages. Data calculation based on results of the two experiments including the nutrients mass balance in RAS for grow-out bighead catfish and the efficiency of wastewater treatment by aquatic plant in the intensive culture system of bighead catfish. Water lettuce performed well functional in treating wastewater discharged from the culture system. In the first 10 days of experiment, concentrations of COD, TAN, N-NO3-, P-PO43-, TN and TP of outlet water from water lettuce tanks reduced at 34.28, 40.70, 46.70, 24.56, 39.92 and 9.16%, respectively, in comparision with those of inlet waste from biofilter tank. Based on nutrient mass balances, daily waste releases from 4 m3 culture tanks of bighead catfish stocking at 1,000 fish/m3 contained 17.51mg/L COD, 1.22 mg/L TAN, 16.40 mg/L N-NO3, 2.92 mg/L P-PO43-, 28.55 mg/L TN and 17.32 mg/L TP. In order to control waste dischage according to the regulations of the Ministry of Natural Resources and Environment, the area of water lettuce needed for treating waste produce from 4 m3 culture volume in RAS culture bighead catfish was in 1.30 - 2.30 m2.