The Analysis And Determination Of The Influent Wastewater Qulity Of The Municipal Wastewater Treatment Plant

The analysis and determination of the influent wastewater qulity has significant meaning to the Wastewater Treatment Plants in design, operation and management. This paper investigated and analysised the influent quality of Xi'an Beishiqiao sewage purification center, Xi'an Dengjiacun wastewater treatment plant, Yan'an wastewater treatment plant, the wastewater treatment plant in A city and in B city of Shandong province, the results indicate that there is a great difference between the practical operation influent quality and the designed influent quality, and the influent quality is changes with time and belongs to normal distribution and lognormal distribution, so the method of probabilistic statistical analysis can be used to determine the designed influent wastewater quality of wastewater treatment plants reasonable. But compared with the influent quality of wastewater treatment plants, the conformance to normal distribution and lognormal distribution of the effluent quality is poor. Combined with the effluent standard-reaching rates of these wastewater treatment plants, this paper gets the designed influent quality assurance rates which should be taken 82%, 73%, 86%, 70% and 87%.Through the investigation and analysis of these wastewater treatment plants and the results of the step-feeding A/O pilot-scale bioreactor, this paper suggests that when a wastewater treatment plant is designed, it should base on the curve of statistical accumulative frequency of influent quality and take the concentration value of water quality indexes which are no less than 85% assurance rate as the designed influent quality. The result of the step-feeding A/O pilot-scale bioreactor shows that the process works well in nitrogen removal, although the influent quality is far beyond the designed influent quality and water inflow is unchanging. In addition, batch experiments are also conducted to determine the oxygen uptake rate, the ammonium uptake rate, and the denitrification rate. The result shows that the activated sludge bears high activity in the mixed liquid. There are three obvious different denitrification rates stages in the denitrification process, and with the reaction time prolonging, the denitrification rate declined gradually. According to the experimental results, the reference value of the denitrification rate and hydraulic retention time is suggested which is used in designing and calculating the anoxic selecting tank and the bio-reactor anoxic zone of the municipal wastewater treatment plant.