Biological Analysis Of The Effect Of Water Temperature Change On The Removal Of Nitrogen And Phosphorus In The Reversed AAO System

There are many rivers and lakes in our country,and there are different degrees of eutrophication problems in water bodies.The function of nitrogen and phosphorus removal in sewage treatment plants is particularly important.The winter temperature in northern my country is relatively low,and the function of nitrogen and phosphorus removal in sewage treatment plants is easily affected.The core process of sewage treatment plants is mostly activated sludge biological treatment,but in winter,as the temperature decreases,the level of microbial metabolism is low,which in turn leads to problems such as reduced water treatment efficiency of the sewage treatment plant and increased nitrogen and phosphorus concentration in the effluent,so how to choose under low temperature conditions Appropriate methods to improve the removal rate of nitrogen and phosphorus by microorganisms,so that the discharge of nitrogen,phosphorus and organic matter in wastewater treatment plant effluents can be stably discharged,which has become a hot issue in current research.The experiment of this thesis adopts the inverted AAO（Anaerobic-Anoxic-Oxic）process to compare and study the effect of sewage biochemical treatment under normal temperature and low temperature conditions and carry out related biological analysis.It mainly studies the most suitable process parameters of microbial efficiency under normal temperature and low temperature conditions（The removal effect of activated sludge microorganisms on COD,NH₃-N,TN and TP under normal temperature and low temperature conditions when the sludge age,hydraulic retention time,dissolved oxygen and reflux ratio）and the most suitable process parameters are operated;and compared and analyzed The difference in microbial activity,diversity and microbial species composition of activated sludge under normal temperature and low temperature conditions has screened out low-temperature-resistant dominant strains of nitrogen and phosphorus removal in order to provide data support for the enhancement of biological nitrogen and phosphorus removal under low temperature conditions.The main conclusions are as follows:（1）Through the single factor variable test,the most suitable process conditions for microbial efficiency in the inverted AAO process at room temperature are SRT=15 d,HRT=10 h,DO=3～5 mg/L,and the reflux ratio is 200%.At this time,the microbial activity is the highest,and the nitrogen and phosphorus removal effect is the most suitable;the most suitable process conditions for microbial efficiency in the inverted AAO process under low temperature conditions are SRT=15 d,HRT=12 h,DO=3～5 mg/L,The reflux ratio is 200%,when the microbial activity is the highest,and the nitrogen and phosphorus removal effect is the most suitable.When operating with the most suitable process parameters,the average effluent concentrations of COD,NH₃-N,TN,and TP under normal temperature conditions are 35.3 mg/L,2.1 mg/L,4.8 mg/L,0.3 mg/L,and the average removal rates are respectively 93%,94.1%,89.3%,93.6%;the average effluent concentrations of COD,NH₃-N,TN,and TP under low temperature conditions are 50.6 mg/L,11.4 mg/L,15.8 mg/L,0.4 mg/L,respectively,The average removal rate is 89.9%,68.3%,64.9%,92.1%.Therefore,for the enhancement of the nitrogen and phosphorus removal effect of the inverted AAO process at low temperatures in winter,attention should be paid to and the removal of NH₃-N and TN-related microorganisms.（2）The TTC method is used to determine the activity of microbial dehydrogenase（DHA）,and the INT method is used to determine the activity of the microbial electron transport system（ETS）.The TTC-DHA activity of anoxic tank,anaerobic tank,and aerobic tank under low temperature conditions were reduced by 38.6μg/（mg?h）,31.8μg/（mg?h）and 33.8μg/（mg?h）,INT-ETS activity decreased by 22.2μg/（mg?h）,18.7μg/（mg?h）and 30.1μg/（mg?h）,respectively.（3）Through the 16S-rDNA high-throughput sequencing method,six samples from three reaction pools under normal temperature and low temperature were analyzed for microbial activity characteristics and species composition changes.The Good’s coverage index shows the reliability of the data of the six samples.All meet the standard:Under normal temperature and low temperature conditions,the species diversity and richness of anoxic tanks are the lowest;compared with normal temperature conditions,the species diversity and richness of the three reaction tanks under low temperature conditions are greatly reduced,of which the good The microbial species richness of the oxygen pond has the largest decrease.Under normal temperature and low temperature conditions,the number and types of microbial dominant bacteria in the three reaction tanks are clearly contrasted.Under low temperature conditions,the number of dominant bacteria is small but their proportion is high,showing a trend of simplification;while simple normal and low temperature conditions,especially low temperature conditions The number and type of dominant microorganisms in the next three reaction tanks are not significantly different.（4）Through the analysis of the composition of the microbial communities in the nor mal and low temperature systems,at the phylum level,the rich taxa under normal tempe rature conditions（average relative abundance≥1%）include Proteobacteria,Bacteroidetes,Chloroflexi,Acidobacteria and Gemmatimonadetes.The only rich taxa is Proteobacteria.At the genus level,the dominant bacteria under normal temperature conditions are Thioth-rix,Thaurea,Dechloromonas,Azoarcus,Acinetobacter,Hydrogenophaga,and Zoogloea;u nder low temperature conditions,the dominant bacteria that are resistant to low temperatu re are mainly Azoarcus,Thaurea and Acinetobacter.Among them,Azoarcus,Thaurea and Acinetobacter have been studied and reported to have denitrification and phosphorus re moval functions.Separating,cultivating and applying the low-temperature-resistant superior nitrogen and phosphorus removal bacteria in the later stage has important scientific and practical significance for solving the problems of poor nitrogen and phosphorus removal under low temperature conditions in winter and improving and preventing water eutrophi cation.