Study On The Performance And The Mechanism Of Two BAF Processes With Different Media Combination

In order to improve the nitrogen removal efficiency and the shock loadresistance of biological aerated filter process (BAF) for nitrogen removal, and toeffectively save the capital and operation cost, the ceramic and nature zeolite wereemployed to construct two pre-denitrification BAF processes with different mediacombination. These were ceramic-zeolite BAF (C-Z BAF) and zeolite-ceramic BAF(Z-C BAF) systems. The performance of the two combinations on different stagessuch as start-up, optimizing operational parameter condition and different C/N ratioscondition were compared, as well as the elementary exploration of nitrogen removalmechanism within the two systems.The results of start-up revealed that at the beginning of start-up, the ammoniaremoval efficiency of C-Z BAF system was higher than that of Z-C BAF systemobviously. The nitrogen distribution of system’s effluent confirmed that the twocombinations were mainly through the absorption of ammonia by zeolite to maintaina highly ammonia removal efficiency at the initial stage, while the ammonia wasremovaled by nitrification of nitrifying microbe at the middle or later stage. Inaddition, the growth of nitrifying microbe in the Z-C BAF was faster than that of C-ZBAF.The optimized HRT, air-liquid ratio and reflux ratio of C-Z BAF and Z-C BAFwas1.5h,5:1,1:1and1.5h,5:1,2:1respectively. Under the optimal condition, themean removal efficiency of COD, NH3-N, and TN were94.7%,99.0%, and62.2%,respectively for the C-Z BAF; and93.2%,99.5%, and70.1%, respectively for theZ-C BAF. The profile of pollutants along the flow path in the two BAF systemsindicated that:(1) the nitrification mainly happened in the media of0~0.6m in oxicfilter;(2) both of the two combinations’s oxic filter had remarkable simultaneousnitrification and de-nitrification phenomenon. The analysis of total bacterialcommunity structure along the flow path in the two BAF systems showed that: thedissolved oxygen and the filling height were two primary drivers of the variations of the bacterial community structure. These two factors captured by the first and secondinteraction principal components, while different media combination had lowerimpact on the bacterial community.Under different C/N ratio conditions, the average removal efficiency of TN ofZ-C BAF was significantly higher than C-Z BAF, and the advantage was morenotable under low C/N ratio. Comparing the microbial community structure of thetwo combinations under different C/N ratio conditions, it was found that the richnessand diversity of denitrification bacterial community dereased significantly with thedecrase of C/N ratio. At low C/N ratio, within the whole oxic filter of Z-C BAF, nosZgenetic T-RFs were detected with more than20%relative abundance, but none nosZgenetic were detected effectively by PCR applification at the upper oxic filter of C-ZBAF. The result proved that the simultaneous nitrification and denitrification functionof Z-C BAF was better than C-Z BAF.Under normal C/N ratio, the nitrogen removal efficiency of the two systems wasnearly equal to each other，while the nitrogen removal efficiency of Z-C BAF systemwas higher than that of C-Z BAF system obviously under the low C/N ratio. Thus,compared to C-Z BAF system, Z-C BAF system had greater potential on thetreatment of low strength and low C/N ratio wastewater.