Study On Zeolite Media Biological Aerated Filter For Treating Aquaculture Wastewater

In this paper, a new zeolite biological aerated filter(ZBAF) was developed and employed for the treatment of aquaculture wastewater that was not controlled efficiently and economically. And more attention has been paid to the adsorption of zeolite, process characteristics, removal dynamics, etc.The adsorption capacity for ammonia was significantly improved by 26.77% after modifying natural zeolite under the optimal temperature of 200℃for 3 hours. The adsorbing process was fitted well by Freundlich with correlation parameter over 0.99, and also consonant with pseudo-second-order kinetic equation.It took more time of 10 days for autotrophic bacteria than heterotrophic bacteria to form stable biofilm in ZBAF. During biofilm maturity, ammonia removal is the result of both zeolite adsorption and autotrophic microorganism nitrification. Through continuous stable operation, the optimal operation conditions were obtained as follows: pH 7.5-9.0, hydraulic load 0.25m³Â·m^-2·h^-1,gas water ratio 30:1;and the removals of COD and NH₄⁺-N were 85%-95% and 65%-70%, respectively. Furthermore, most COD was removed at the bottom of thereactor(0^#-1^# segment) with removal efficiency above 75%, whereas NH₄⁺-N removal was obtained at the top of the reactor(3^#-4^# segment) with efficiency above 50% in the total. It means that autotrphic and heterotrophic bacteria proliferated in different mode of space and time in the biofilter. And segment with lower DO concentration could be regarded as the boundary for separating these two different groups of chemotrophic bacteria. Moreover, in order to illustrate well the block process during ZBAF operation, drag coefficient was firstly established and used as the basis for backwashing determination. And 4-5d was therefore found as the acceptable cycle period.Removal dynamics was investigated as well using experimental data, and the results showed that COD removal was in accordance with first order reaction, with exponential decay model asρ_A=ρ_A0 exp(-0.0082t).According to the plus-flow state in the reactor, degradation of organicscould be simulated as S=S₀·e^?.