| With the rapid development of automobile industry,automobile painting wastewater has become a difficult and focal point in industrial pollution treatment process.Painting wastewater is a kind of typical refractory industry wastewater,with the characteristics of large changes of discharge amount,high concentration of organic contaminants,complex compositions,low biodegradability etc.In order to meet more stringent discharge standards of industry wastewater,focused research and optimization on the automobile painting wastewater treatment processes is needed to realize maximum energy saving and emission reduction.This is not only conducive to promoting the long-term sustainable development of automotive industry,but also has very important significance on our water environment protection.In this study,a Multi-Stage Biological Contact Oxidation(MSBCO)system was first used to treat the simulated industry wastewater by a pilot scale test.The rule of carbon and nitrogen removal during the start-up and running process of MSBCO system was investigated and its mechanism was analyzed.After that,the MSBCO system was used to conduct the secondary biological treatment on actual automobile painting wastewater by a pilot scale test.During the start-up and running process of MSBCO reactor,the removal effect of COD,TN and NH4+-N was investigated and analyzed.The impact resistance property as well as the carbon and nitrogen removal stability of MSBCO system during the painting wastewater treatment was analyzed.During the influent flowrate increasing from 80 L/d to 240 L/d,very obvious concentration difference of organic matter was formed among each stage of the MSBCO tank.With the flow direction of wastewater,the organic matter concentration decreased gradually in the MSBCO tank.The average COD value of influent was 1214 mg/L.After the MSBCO treatment process,the COD value of final effluent could stably achieve the discharge standard of internal control all the time,namely,COD is less than 500 mg/L.The average COD removal rate in the first stage of MSBCO system was about 55%,of which contribution was the largest.Besides,the fluctuation of COD removal rate in the first stage was most affected by the change of influent flowrate,and the fluctuation in the last stage was the least and kept in a relatively stable state.When the hydraulic residence time was 24h,16h,12h and 8h,the average removal rate of COD in the MSBCO system was 81%,86%,84%and 83%,respectively;The average removal rate of TN was77%,76%,76%and 65%,respectively;The average removal rate of NH4+-N was 97%,96%,94%and 86%.The biodegradability of painting wastewater is low.The BOD and COD ratio was only about 0.15,which meant the painting wastewater was difficult to be biodegraded.After MSBCO process treatment,the BOD and B/C of wastewater increased first and then decreased.The MSBCO process could not only improve the biodegradability of wastewater,but also realize the stable and efficient removal efficiency of organic matter.The experiment results showed that MSBCO process could effectively reduce the excess sludge production,and the average excess sludge yield was about 0.03,which was only about one tenth of that of the conventional activated sludge method,and about one fifth of that of the traditional biofilm method.The MSBCO system could realize high removal rate of suspended solid.When the hydraulic residence time was 8h,the average removal rate of suspended solid in the MSBCO system was 82.8%.According to the principle of excess sludge reduction,this research analyzed the mechanism of excess sludge reduction in the MSBCO system from four aspects.In the pilot scale test of actual automobile painting wastewater treatment,the effect of three important process parameters(dissolved oxygen concentration,temperature,organic load)on the treatment efficiency of MSBCO system was studied and the optimum process conditions were determined.Under the optimum process conditions(the hydraulic residence time was 8h,water temperature was 25?30?,pH was 6.5?7.5,the dissolved oxygen concentration in the first stage,the middle stage and the last stage of MSBCO system were kept in the range of 0.5?1 mg/L,2?3 mg/L and 2?3 mg/L,respectively,and the COD was kept below 5000 mg/L),the total removal rate of COD was about 90%,the total removal rate of NH4+-N was in the range of 86.4%?92.5%,the total removal rate of TN was in the range of 70.1%?85.6%.A kinetic model of organic matter biodegradation in the MSBCO system was built.The relationship between the organic matter concentration of effluent and the influent flowrate,organic matter concentration of influent,carrier volume,carrier surface area as well as kinetic parameters was described in the kinetic model.The kinetic model could be applied to the design and calculation of MSBCO system,providing a theoretical reference and technical support for the engineering promotion and application of MSBCO system.Based on the pilot scale studies,the MSBCO system was further enlarged and implemented in the engineering application.The economic feasibility of MSBCO system was further studied through this engineering application.During the engineering application and implementation process,many aspects involved were discussed and analyzed in detail,including technological process,equipment installation,process commissioning,removal efficiency,improvement measures,project effectiveness and evaluation,etc.,which could provide technical support for the engineering demonstration and relevant upgrading research of MSBCO system.By means of the high-throughput sequencing technology,the differences and dynamic changes of microbial community structure in different running stages and different positions of MSBCO system were revealed through the analysis of species abundance and diversity,microbial community differences and similarities,microbial community structure compositions,etc.In terms of the removal efficiency of organic matters,biodegradability improvement and sludge reduction of MSBCO system,the facilitation mechanism of microbial community structure was investigated and discussed from a perspective of microbiology. |
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