| Wastewater treatment is a process susceptible to various factors,especially in the Tibetan region in the context of the plateau,with its special geographical environment,and the plateau wastewater treatment also has problems such as the removal rate of pollutants does not meet the standard.Therefore,the parallel AA-MBBR process is put forward to carry out experiments and optimize the influencing factors.The water quality indicators COD,BOD5,NH3-N,TN and TP were tested for inlet and outlet concentrations and removal rates,and the activated sludge was sequence using 16S r RNA high-throughput sequence technology for each working condition.The changes in water quality indicators and microbial community structure as well as the mechanism of nitrogen and phosphorus removal were discussed and analysed.The main results were obtained as follows:（1）Activated sludge culture,domestication and biofilm filler hanging and inlet water ratio aspects.The activated sludge reached full maturity after 45days,when the SV30,MLSS,MLVSS and SVI indicators were stable at 28%,3300mg/L,2800mg/L and 82ml/g respectively.The biofilm filler reached successful film attachment on day 12.The removal rates of BOD5 reached80.00%～81.80%,COD 60.45%～81.18%,NH3-N 58.96%～70.87%,TN37.29%～60.44%and TP 29.37%～49.65%during the hanging period.The optimal anaerobic tank to anoxic tank influent ratio is 4:6.The optimisation of the influent ratio increases the removal rates of TN and TP by 11.38%～28.05%and 19.86%～32.73%respectively,and the increase in the relative abundance of the relevant functional bacteria genera improves the system’s ability to remove nitrogen and phosphorus.（2）Influencing factors:biofilm filling rate and temperature.The biofilm filling rate should not be too high,the optimum working condition is 40%.The average removal rates for BOD5,COD,NH3-N,TN and TP at this time were93.65%,90.01%,81.24%,80.04%and 74.03%respectively.Variations in temperature have a significant effect on pollutant removal,with different temperature conditions having different advantages and disadvantages in terms of pollutant removal.The temperatures corresponding to the best removal rates for BOD5,COD,NH3-N,TN and TP are 21°C,21°C,17°C,13°C and 9°C respectively.At this point,the concentrations of BOD5,COD,NH3-N,TN and TP in the effluent meet the primary B standard,primary A standard,primary B standard,primary A standard and secondary standard of the Discharge Standards for Pollutants from Urban Wastewater Treatment Plants（GB 18918-2002）respectively.（3）Microbial community composition.The high biofilm filling rate（>20%）facilitated the increase of microbial abundance,and the microbial diversity was positively correlated with the biofilm filling rate.The main dominant phyla are Proteobacteria,Bacteroidetes,and Actinobacteria,and are also the dominant phyla in temperature conditions.The main dominant genera in biofilm filling rate conditions are Rhodobacter,Rhodanobacter,norank＿f＿＿AKYH767,norank＿f＿＿Comamonadaceae.The relative abundance of denitrifying bacteria spp.increased with increasing biofilm filling rate,outside of the removal of50%;the highest and lowest relative abundance of PAOs were the same for the working condition and the highest and lowest average removal rate of TP for the working condition;there was significant variability between the filling rate of10%and the other four groups.The increase in temperature had an inhibitory effect on both overall microbial abundance and diversity.The dominant genera in temperature conditions are norank＿f＿＿Saprospiraceae,norank＿f＿＿AKYH767,unclassified＿f＿＿Comamonadaceae,and microorganisms are more sensitive to temperature changes.The relative abundance of denitrifying bacteria was inhibited by the increase in temperature after 13°C;the relative abundance of PAOs was highest at 9°C;the relative abundance of related genera showed significant variability among temperature conditions.（4）Biological nitrogen and phosphorus removal mechanism.The increase in biofilm filling rate promoted the relative abundance of most COG functional proteins compared to the filling rate of 10%,while the increase in temperature decreased the relative abundance in the temperature condition compared to 9°C.The relative abundance of each level of metabolic pathway was little affected by the biofilm filling rate work and temperature work.The relative abundance of functional genes involved in the TCA cycle and glycolysis in carbon metabolism was most influenced by the biofilm filling rate work and temperature work.The relative abundance of denitrification genes in nitrogen metabolism tended to increase and then decrease with increasing biofilm filling rate,while the overall trend decreased with increasing temperature;the relative abundance of functional genes related to assimilatory nitrate reduction was negatively correlated with temperature.The main pathway involved in phosphorus metabolism is oxidative phosphorylation,and the temperature condition has a greater effect on the relative abundance of phosphorus metabolism genes than the biofilm filling rate condition.In this thesis,the parallel AA-MBBR process and the influencing factors are investigated to provide a relevant reference for highland wastewater treatment. |
