| This study focused on the VFA concentration and distribution of domestic sewage through the nine points pH value of titration method and ion-exclusion chromatography, selected the best experimental conditions and summed up a set of methods about low concentration of volatile fatty acids in sewage composition test method for urban sewage VFA determination. In order to get the component and concentration of VFA in influent, the appropriate testing methods were selected to monitor the VFA in Chongqing Qiezixi sewage treatment plant; according to the comparation and the specific technological features of sewage treatment plant, the influences of the VFA concentration in influent on the COD, TP removal rate were studied, and some measures were proposed to improve the performance of biological phosphorus removal system. The conclusions were as follows:(1) The veracity and the accuracy of measurement results of nine points pH value of titration method have been studied at the case of pure acetic acid and acetic acid with ammonia buffer system coexisting, acetic acid with carbonate buffer system coexisting, acetic acid with phosphate buffer system coexisting etc. Titration results show that nine points pH value of method possesses high accuracy and repeatability, is easy to operate and has little influence by a buffer of common waste water system. At the same nine points pH value of titration was verified with the real wastewater experiment, the results show that the coefficient of variation was below 2% when three parallel water samples were measured and each for five times and the experimental results were stable.(2) The best chromatographic condition was determined by single factor analysis and optimization of orthogonal experiment: 0.4mmol/L perfluorobutyric acid solution and acetonitrile(97:3,v/v)as the eluent, 5mmol/L tetrabutylammonium hydroxide solution as the regeneration fluid(TBAOH), a flow rate of 1.0ml/min.(3) The experiments of laboratory synthesis of wastewater and real wastewater showed that the chromatographic method could be used to determine the concentration of VFA in wastewater with low concentration of each component. It also indicates the advantages of ion chromatography: simple operation, high accuracy and precision. This method can not only measure the total amount of the VFA in wastewater, but also determine the VFA concentration of each component.(4) Through monitoring continuously the influent of Qiezixi wastewater treatment plant for 20 times, distribution characteristics of acetate in VFA, account for more than 80% of the total acid, was obtained. Low propionate acid content was accorded with previous relevant reports at home and abroad.(5) Statistics data in May and June of Qiezixi wastewater treatment plant showed that the maximum COD removal rate was up to 90%, and the minimum was 53%. The maximum removal rate of phosphorus was 93%, the minimum was 37%, with an average removal rate of 75.65%. VFA concentration in influent was positively related with COD removal rate and TP removal rate.(6) The reasons for the low rate of phosphorus removal were analyzed and some measures were proposed to improve the performance of biological phosphorus removal: regular system maintenance of facilities to ensure the normal operation of the whole system; an appropriate extension of hydraulic retention time in the biological selection pool. At the same time, by adjusting the CAST system operation cycle in different seasons, results not only the wastewater treatment efficiency was improved, but also the energy consumption was reduced due to the shorter running period of the sewage plant.(7) Here we analyzed the reason of TN over standard in influent of Qiezixi sewage plant, and put forward the corresponding measures. The following was properly increasing sludge concentration, prolonged the time of precipitation stage in order to improve low removal efficiency of TN situation, timely connected between environment protection department to reform some over standard discharge firm, and at the same time, we analyzed the unknown nitrogen element in influent to find out the method of degradation of the unknown nitrogen element. |
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