Analysis on purification effect of closed circulating aquaculture water by planting and aquaculture combined with BAF process

Abstract: For achieving the requirement of fish production and water sustained regeneration in controlled ecological life support system, a pilot-scale modified biological aerated filter (BAF) coupled with vegetable cultivation system was constructed as a purification plant for the closed recirculating aquaculture system (RAS). The performance of the modified purification process on RAS was investigated, and its principle was also discussed in this research. At initial stage, 300 L municipal water as well as 60 tilapia mossambica were inset in the freshwater pond of RAS. In the followed experimental 200 days, the variation of water quality and fish growth was tracked and investigated, and then the navigability of purification process for RAS was analyzed and discussed. The experimental results showed that in the first research period (1-60 days), the single BAF process showed poor performance on the pollutant removal, and there were a mount of TOC, N and P accumulation after 60 days raising period. For resolving this problem, a modified BAF process coupled with vegetable cultivation system was constructed and carried out in the following 140 days. The followed experimental results exhibited that the modified BAF process coupled with vegetable cultivation showed significant good performance on the pollutant control, where the concentration of TOC and NH4+-N decreased form 60.3 and 2.9 mg/L to 11.2 and 1.2 mg/L, respectively, and the concentration of NO3--N and PO43--P obviously decreased form 114.2 and 43.1 mg/L to around 54.7 and 15.6 mg/L, respectively. Besides, the concentration of NO2--N remained below 0.1 mg/L. Modified purification process could provide health-safety environment for the tilapia mossambica growth and vegetable cultivation in closed RAS, more than 95% water was regenerated, and the maximum aquiculture density was 41.3 kg/m3 and without fish death. At the same time, four batches of vegetables were harvested. The total weight of vegetables was 23 420 g, and the individual weight was 195.17 g, respectively. The results showed that the modified BAF process coupled with vegetable cultivation could ensure the sustainable and stable operation of RAS and provide technical reference for fish culture in the controlled ecological life security system.