Research On Processing Performance And Microorganism Properties Of Biological Aerated Filter For Municipal Wastewater Treatment

Water pollution is one of the most serious environmental problems in China, andmunicipal wastewater is a major pollution source to water bodies in our country.Biological treatment process is the most efficiently used method to treat municipalwastewater. Biological aerated filter （BAF） as one of the representative process ofthird-generation biofilm process has a great application potential in the secondarytreatment of municipal wastewater. In the biological treatment systems,microorganisms are key organisms in pollutant removal. Therefore, a better study ofthe bacterial community structure and function in the treatment system can help toelucidate the pollutant removal mechanism of BAF and enhance the treatmentperformance stability. Traditional technologies for environmental microbiologyresearches mainly based on culture and separation could not satisfy nowadaysenvironmental microbiology research. In this paper, the BAF used in Qingdao Maidaosewage treatment plant is studied, microorganism characteristic in full-scale BAF isinvestigated using molecular techniques, including nucleic acids extraction, clonelibrary construction,16S rDNA sequence homology analysis, polymerase chainreaction （PCR）, denaturing gradient gel electrophoresis （DGGE）, and quantitativereal-time PCR techniques. The factors affecting the microbial community structureare identified. The relationship between microbial community dynamics and systemfunction is analyzed.Qingdao Maidao wastewater treatment plant uses Biostyr BAF for municipalwastewater treatment, major pollutants COD, NH3-N, TP and SS removal efficiencyof the annual average are89.1%,75.3%,83.4%and93.0%, respectively. Processingperformance and stability, the effluent indexes are better than the Ⅰ-B criteriaspecified in discharge standard of pollution for municipal wastewater treatment plant（GB18198-2002）, shows that the process has a good capacity of sewage treatment.The results of the affecting factors of BAF show that when COD and NH3-N ininfluent are between60-260mg/L and22-65mg/L, respectively. The optimumhydraulic loading is between2.5-3.3m³/m².h. The optimum COD loading is below 3.3kg/m³.d. The optimum ammonia nitrogen loading is below0.6kg/m³.d；Theoptimum gas to liquid ratio is5:1. The optimum temperature is between15-28℃. Theoptimum backwash time is21-24h. The organic removal kinetic model of BAF isC/C₀=e^{0.0118H/q-0.9423}The difference of microbial composition and activity can cause diverse ability ofdifferent pollutants removed. Results of microbial population distribution show thatthe dominant microbes are heterotrophic bacteria and denitrifying bacteria along theheight, respectively. For BAF, the best height of COD degradation is0-150cm,nitrifying NH3-N best height is100-350cm, and0-100cm segment of media take thelargest contribution to the removal rate of SS.BAF biofilm bacterial diversity results show that the bacterial diversity in theBAF is very rich, dominant microorganisms is β-proteobacterium groups, γ-proteobacterium groups, Bacteroidetes group,-proteobacterium groups,-proteobacterium groups, Nitrospirae and Firmicutes in the order. In the Biostyr BAF,Pseudomonas, Sphaerotilus, Xanthomonas and Flavobacterium are dominantmicroorganisms to remove organic pollutants, Nitrosomonas is advantage nitrosationbacteria, Nitrospira is advantage nitrification bacteria, Hyphomicrobium andComamonas are advantage denitrifying bacteria.The influence of gas water ratio, temperature and backwash on BAF communitystructure are analyses, the results show that BAF has good ecological stability. Whenthe gas water ratio is5:1, the filter flow of BAF is in stability, biological membranestructure is reasonable and the effluent is the best. Low temperature （T＜15℃） willaffect the bacterial diversity of BAF, make advantage bacterium group within thefilter becomes single, but this kind of single advantage bacterium group can maintainthe stable operation of the BAF. Low temperature will affect the bacterial diversity ofBAF, make advantage bacterium group within the filter becomes single, but this kindof single advantage bacterium group can maintain the stable operation of the BAF.Clustering analysis indicates that the backwash as influence factor greatly affects thecommunity structure of BAF. Therefore, a good control for the intensity andfrequency of backwash is a key link in efficient operation of BAF.The DCCA analysis results show that, the gas/water ratio, backwashing and temperature are the main effect factors of BAF community structure. The effects ofCOD, ammonia nitrogen and total phosphorus removal rate, and the concentration ofnitrate nitrogen on BAF species is significantly （P<0.001）, in which the correlationbetween COD removal rate and community structure is the largest, the value is-0.7947（P<0.001）. However, the nitrite nitrogen concentration did not reachstatistical correlation with the axis, so there is no obvious relationship betweenmicrobial community structure succession in BAF and the nitrite nitrogenconcentration.