Hydraulic,wastewater Quality And Microbial Characteristics And Key Inter-Relationships For Municipal Sewer In An Urban Area Of Chongqing

The changing characteristics of the water quality along the sewer pipe affect the efficiency of the urban drainage system and the wastewater quality of the sewer treatment plant.At present,While the drainage facilities are further improved,the water volume and water quality treatment capacity of sewer plants are limited,the improvement of urban drainage system efficiency has entered a bottleneck period,reasonable prediction and control of the wastewater quality change process in sewer pipes has become the key to improve the efficiency.This study explored the important hydraulic and microbiological factors that affect the changes in wastewater quality characteristics of urban sewer through various methods such as the characterization of actual sewer wastewater quality changes,spectroscopy analysis,and microbial community sequencing,and the following conclusions were obtained:（1）To a certain extent,the water quality characteristics of sewer changes during the flow of sewer pipes.Among the conventional wastewater quality indicators,the concentration of COD,TN,and NH₃-N along the sewer pipe shows an increasing trend,the concentration of NO₃-N shows a decreasing trend,and the concentration of TP first decreases and then increases.In terms of water quality characteristics indicators,C/N and C/P along the sewer pipe both increase first and then decrease.The concentration of dissolved organic matter along the sewer pipe is generally increasing,while the concentration of particulate organic matter is generally decreasing.During the flow of sewer,the particulate organic matter tends to be deposited,and the conversion path of dissolved organic matter is more complicated,which mean microbial metabolites may affect the composition characteristics of wastewater.Dissolved organic matter in sewer is mainly protein,microbial metabolites and humic acids,which are mainly affected by external and internal input.aromatic protein substance II is the highest content of soluble microbial metabolites,the lowest content of soluble microbial metabolites is microbial metabolites,and the content and the proportion of total dissolved organic matter of microbial metabolites have the most significant increase.As the residence time and transport distance of the sewer increase,the microbial metabolites released into the main water is accumulating,and the impact on the sewer wastewater quality characteristics becomes more significant.（2）The dominant Phylum in the main wastewater microbial community of sewer pipe are Proteobacteria（77.65%）,Firmicutes（16.88%）,Bacteroidetes（3.25%）and Actinobacteria（1.08%）.The dominant bacteria are Pseudomonas（40.29%）and Acinetobacter（27.74%）.The dominant Genus in the biofilm microbial community are Proteobacteria（44.99%）,Bacteroides（15.39%）,Firmicutes（12.06%）,Actinobacteria（6.42%）,Epsilonbacteraeota（9.64%）and Synergistetes（5.51%）,the dominant Genus are Mycobacterium（6.06%）,Arcobacter（5.75%）,Metallibacterium（5.61%）and Acidithiobacillus（4.94%）.Microbial biochemical reactions in sewer pipes are dominated by hydrolytic fermentation process.Proteobacteria,Bacteroides and Firmicutes constitute the dominant hydrolytic fermentation flora,and Actinobacteria are also important sewer treatment microorganisms.To a certain extent,the reduction of high molecular weight organic matter in sewer can inhibit the growth of hydrolytic fermentation bacteria,and changes in environmental factors and available substrates affect the growth of functional microorganisms in the main water and biofilms,which forms a competitive mechanism.The KEGG metabolic pathway shows that there is significant metabolic activity in the main body water of the sewer pipe and the biofilm microbial community.（3）Spearman correlation analysis showed that the relative abundance of Proteobacteria and Bacteroides in the main wastewater was significantly positively correlated with C/P,and was significantly negatively correlated with the concentration of TP;Firmicutes and Actinobacteria were related to them.On the contrary,the concentration of C/P and TP in sewage are important environmental factors that affect the structural characteristics of the dominant microbial community in the main wastewater.The relative abundance of Actinobacteria in biofilms has a very significant negative correlation with the concentration of TN,NH₃-N and DO,a very significant positive correlation with the concentration of NO₃-N,a significant negative correlation with the concentration of COD and p H;The relative abundance ofε-Proteobacteria has a very significant positive correlation with TP and a significant negative correlation with C/P.Actinobacteria andε-Proteobacteria are important microorganism affecting the change process of wastewater characteristics along the sewer pipeline.The increase in the relative abundance of the Proteobacteria and Bacteroides in the main wastewater promotes the reduction of COD concentration and C/P.The increase in the relative abundance of Actinobacteria and Firmicutes in main wastewater is beneficial to increase the carbon source of sewer,and the increase in the relative abundance of Actinobacteria in biofilm may promote the reduction of COD and TN concentration,and the increase in the relative abundance ofε-Proteobacteria is beneficial to increase the C/P of sewage and increase the carbon source of sewage.（4）Spearman correlation analysis shows that hydraulic factors affect the migration process of sewage particles and the process of oxygen mass transfer.The sedimentation effect is significant when the pipeline fullness is small,and the PCOD tends to decrease.When the sewage flow rate is faster,the shear force of the water flow has a significant erosion effect,and the PCOD tends to increase.In the gas-liquid and liquid-biological phase oxygen mass transfer process,the less fullness of the pipeline is beneficial to the gas-liquid oxygen mass transfer process,inhibiting the liquid-biological phase oxygen mass transfer process,and the sewage flow rate increases Conducive to the liquid-biological phase oxygen mass transfer process.Longer wastewater retention time is conducive to the progress of microbial biochemical reactions,and C/N and C/P tend to decrease,but the bio-refractory organic compound increases,which is not conducive to the biodegradation of wastewater.It can provide theoretical basis for further research on and practice of sewerage network.