Pilot-scale test for biofilm rapid formation in biofilter ofrecirculating mariculture system

Biofilm formation is a time-consuming process with more than 30 days in recirculating aquaculture system. In order to improve its efficiency, a pilot scale test was performed in a seawater recirculating aquaculture farm. There were 4 shunt-wound biofilters with runway-like, two-stage structure in each one and total capacity of 800 m3. The biofilm carrier was needle-like polyethylene. Before the test beginning, high concentrated bacterial suspension and "clay + zeolite powder mixture (filtered by 200 mesh screen and mixed at w/w 4:1)" suspend solution were prepared. And then, about 200 m3 wastewater flowed into the biofilter with 100 m3 in each stage. After that, bacterial and "clay + zeolite powder mixture" suspension were poured into the biofilters with respective concentration of 103 cfu/mL and 5g/L. Stable biofilm can be observed on the surface of biofilm carrier after 8 days incubation with constant aeration but without water changing in the biofilters. The concentration of ammonia, nitrate, nitrite and COD (chemical oxygen demand) were measured once a day from the 11th day to the 15th day after the system running for 2 days since the 9th day. Their average removal rates reached to 52.04%, 17.24%, 26.82% and 62.94%, respectively. Comparing to traditional biofilm forming method, the method in this paper can advance the time of biofilm formation more than 20 days. Beyond this, the method is feasible to demonstrate and popularize in recirculating mariculture farm.