Simulation And Influent Based Operation Parameter Optimization Of Dadukou WWTP At Chongqing, China

The regularity of influent of Dadukou wastewater treatment plant was investigated through statistical analysis, and an influent model was developed to include the effect of season, weather, and day type. The characteristic of influent water quality was researched with respirometry and routine test method. The CAST process model for Dadukou WWTP was established with GPS-X simulation soft based on ASM2d considering frame parameters,hydraulics parameters and operate parameters of Dadukou WWTP, and the model was calibrated and validated with influent and effluent data. The operation and control strategy was obtained through simulation of process model according to research results of influent at last, and it is benefit to improving operation efficiency and stabilization of Dadukou WWTP. The main conclusions were obtained as follows:(1) The influent amount and quality patterns of Dadukou WWTP at Chongqing of China were accorded with the normal distribution. The results predicted by accumulation normal distribution function showed that the concentrations of TN and TP in the influent are easy to over the design standard.(2) Although the influent of WWTP is influenced by many factors, the characteristic and regularity of influent amount and quality are stable from the long-term point of view. An influent model including the effect of season (temperature), weather (raining or not), and day type (holiday or not) was developed based on the First-order Fourier series. The relativity coefficient between measured and simulated data is over 80%. The hourly influent data during any day can be efficiently formed from the model, based on which the operational strategy of WWTP could be optimized through the scenario simulation.(3) Both of the average influent COD and BOD5 of 2008 and 2009 are lower than the design value according to the influent capability target. The average BOD5/COD of two years is 0.415, which is lower than the design value 0.50. The characterizing COD components results measured by COD components characterization benchmark method is: readily biodegradable COD (RBCOD), slowly biodegradable COD (SBCOD), soluble inert component (SI) and particulate inert component (XI) occupied about 9.3%,26.3%,16.2%,48.2% of the total COD of wastewater respectively. The biodegradable COD (BCOD, RBCOD+SBCOD) occupied about 35% of the total COD, which is lower than BOD5, and it indicates that biodegradable COD is much less in practical process. Therefore, the carbonaceous components concentration of influent is low in Dadukou WWTP, and biodegradable COD component is much less, thus the demand of carbon of biology treatment system is hard to satisfy.(4) The design C/N of Dadukou WWTP is 10.28, and measured values are 3.61～9.78, whose average is 6.87, lower than design value, so it indicates the lack of carbon. The results of experiments of nitrogen balance show that, the concentration of else nitrogen component (the nitrogen component exclude kjeldahl nitrogen and nitrate nitrogen) is 7.08mg/L, occupying about 13.59% of the total nitrogen in influent, and the concentration of else nitrogen component is 5.28mg/L, occupying about 13.59% of the total nitrogen in effluent. The else nitrogen component is hardly biodegradable in biology treatment system, and it is a source of danger to effluent TN. The concentration of effluent nitrate nitrogen is high, reaching to 10.28mg/L, much higher than that of influent. So the denitrification is not sufficient, and nitrate nitrogen has much contribution to TN of effluent.(5) With some hypothesis and simplification, the process model includes 1 CAST wastewater treatment system 4 SBR reaction cells. Three modeling schemes were put forward considering the particularity of anaerobic basin for pick, and the model was built with the scheme of putting anaerobic basin into SBR according to results of operation investigation. The CAST process model for Dadukou WWTP was established with GPS-X simulation soft based on ASM2d at last.(6) The simulation result is well after setting model parameters based on ASM2 and calibrating some important parameters with measured data. The operation simulation results of 2008 and 2009 show that, simulated data fluctuate around measured data, and absolute error of effluent COD are all less than 10mg/L, absolute error of TN less than 5mg/L, and absolute error of NH4+-N less than 3.5mg/L. The veracity of process model is well, and it can be applied to simulation of Dadukou WWTP.(7) There are three regulation ways for operation of Dadukou WWTP: influent pattern, aeration control, and concentration of sludge control. The influent pattern is changed from traditional method to step-feed method, and it can supply carbon in order to enhance efficiency of denitrification behind. The impact of aerobic, sludge return and excess sludge discharge to treatment system efficiency were researched by single factor analysis method. With the optimal step-feed scheme, all of the factor levels were analyzed by orthogonal test, and seasonal regulation strategies for each season were obtained according to variation trend of each effluent component changing along with each factor in different season..(8) The applicability of seasonal regulation strategies were validated by measured data of 2008 and 2009. With the seasonal regulation strategies, treatment system efficiency can be improved by controlling aeration in allusion to influent water peak and low valley. The seasonal regulation strategies and daily regulation strategy of Dadukou WWTP were established that can be applied and used for reference in practical.