Study On Technology Of Mobile Biological Aerated Filter(MBAF) Process In Aquaculture Wastewater Treatment And The Dynamic Principle During The Process

In recent years, the nitrogen compounds pollution in aquaculture water was becoming more and more serious for the boom of intensification of aquaculture industry. Nitrides (e.g. ammonia nitrogen and nitrite nitrogen) have toxic effects on fish and shrimp, and are harmful for the healthy development of aquaculture industry.In this paper, processes of mobile biological aerated filter(MBAF) in aquaculture wastewater treatment and the dynamic principle during processes were studied, a laborato-ry-scale BAF was set up to evaluate the degradation efficiency of NH4+-N and NO2--N in treating simulated wastewater. Basing on the BAF, pilot experiment was conducted to discuss the startup, characteristics and the dynamic principle of the process.The main results were obtained as follows:(1) A up-flow Biological Aerated Filter (BAF) which the cylindrical ceramics carriers used to immobilize microorganisms was designed and evaluated. The system was started by natural inoculation of microorganisms. After inoculating for14days, the mean degradation rate of NH4+-N reached to80%. In simulated wastewater treatment, the degradation efficiency of NH4+-N reached to99.2%after running the BAF for14days with a hydraulic load of0.96m3/(m2-h)and gas-water ratio of5:1, and the terminal concentration of NH4+-N decreased to0.29mg/L, and NO2-N generated as intermediate product. The continuous degradation test of NO2--N suggested that the NO2--N degradating capacity of BAF was stable at98.9%, with the degrading period of3days. In Penaeus vannamei Boone aquaculture wastewater treatment,0.516mg/LN02--N was degraded to0.055mg/L after running for6h;. InClarias fuscus aq-uaculture wastewater treatment,9.549mg/L NH4+-N was degraded to0.129mg/L after run-ning for23h. According to the high efficiency of BAF in treating aquaculture wastewater, the technological conditions of pilot experiment were partially confirmed.(2) The MBAF was started up according to the conclusions that obtained in Chapter2.After inoculating for21days,the degradation rate of NH4+-N and NO2--N was relatively sta-ble and more than99%, which suggested the MBAF was started successfully. In the first stage of bio film domestication by aquaculture wastewater, NO2--N was accumulated for the formation rate (NH4+-N transformation rate) was greater than that the degradation rate,. Owe to the gradual mature of bio film during the domestication, NH4+-N and NO2--N removal rate tended to be stable, and DO was stable at4-5mg/L. However, pH decreased at first and then increased to be stable. (3) The study of disposal ability of MBAF in aquaculture wastewater treatment showed that it can be affected by hydraulic loading and gas-water ratio. When hydraulic loading var-ied from4.0to5.0m3/(m2·h), the MBAF kept at a high degradation rate of NH4+-N and NO2--N; With the hydraulic loading of4.5m3/(m2·h) in14-20h, the degradation rate of NH4+-N and NO2--N achieved at99%and89.55%, respectively. However, a continuous in-crease of hydraulic loading did not result in the increase of degradation rate, on the contrary, it decreased to54%when the hydraulic loading increased at6.0m3/(m2·h). Thus the opti-mums hydraulic loading was confirmed as4.0-5.0(m3/m2·h). When gas-water ratio was2.2:1, the removal rate of NH4+-N and NO2--N were91%and87.33%, respectively. As gas-water ratio continually increased, the removal rate of NH4+-N had a decrease tendency, and the re-moval rate of NO2--N maintained at87%. When gas-water ratio was more than2.8:1, the re-moval rate of NO2--N decreased, and accompanied by a small amount of sludge flocculent body fall off. The optimums gas-water ratio was determined as2.2:1-2.8:1.(4)The dynamic model study of MBAF in removing NH4+-N and NO2--N showed that the removal kinetics parameter of NH4+-N and NO2--N was k1=0.0499h-1and k2=0.0275h-1, respectively and the corresponding dynamic model was fitting asST=S0×e-0.0499T ST=S0×e-0.0275T, respectively. The removal patterns of NH4+-N and NO2--N were reflect-ed and the certain conditions of outlet water quality could be predicted by the models. The appropriate operation time could be determined by the dynamic model according to target quality of outlet water, thus it can offer a certain guiding significance for the engineering in aquaculture wastewater treatment.(5) The application of dynamic model of NH4+-N and NO2--N was evaluated in treating667m3of aquaculture wastewater of penaeus vannameiboone, two schemes was obtained and the optimum one was determined by investment and operating cost estimation. The corre-sponding parameters were:A=2.508m2, Q=11.286m3/h, T=59.09h, and the cost was about8557yuan with the NO2--N(0.5mg/L) and NH4+-N(0.6mg/L) degraded to the discharge re-quirement for aquaculture waste water.