Characteristics Analysis Of Degradation Characteristics In Denitrification With Characteristics Organic Pollutants Of Coking Wastewater

Coking wastewater is a high concentration of industrial waste water containing high concentration of refractory organics and ammonia,with characteristics of water complex,large water and toxicity.Currently coking wastewater treatment widely uses biological nitrogen of A/O,A2/O removal process.In 2012,Ministry of Environmental Protection issued a new standard for coking wastewater treatment--" Coking Chemical Industry Emission Standards "(GB 16171-2012),the new standard for ammonia emission limit decreased from 15mg/L to 10mg/L,added total nitrogen emission limits(20mg/L),which put a higher nitrogen removal efficiency requirement.However,due to the complexity and toxic characteristics of coking wastewater,making the removal efficiency of biological nitrogen difficult,large enterprises adopt a "chemical method " based tail water depth treatment process,which increases the operating costs of enterprises.NO2--N as an important intermediate product of denitrification process,not only inhibite the denitrifying bacteria,but also increases the demands of subsequent aerobic oxygen and energy consumption.Therefore,the present study intends to anoxic degradation characteristics on denitrification stage of organic pollutants in coking wastewater,aiming to optimize the design and operation of coking wastewater anoxic denitrification process,and according to the change of pH and ORP in denitrification process,providing on-line monitoring and controlling of the entire denitrification process a theoretical basis.In this paper,taking the coking characteristics organic pollutants in wastewater,phenol,quinoline,indole and pyridine as carbon souces,with NaNO3 as denitrification nitrogen source,under different initial influent COD/NO3-N condition,by studing and analyzing the NO2--N accumulation characteristics of denitrification process,COD degradation characteristics,denitrification kinetic features,pH and ORP variation,provided the feasible stratages of on-line monitoring and control strategies denitrification process,achieving the following main results:1?At different COD/N O3--N ratio,the denitrification process appeared NO2-Naccumulation phenomenon.At the COD/NO3-N ratio were 2.5,6,9,13 and 17,the time of NO2--N accumulation reached the maximum amount reduced from 140min to 60min,the largest accumulation ofNO2--N reduced from 36.2mg/L down to 16.3mg/L,the maximum accumulation rate of NO2--N fell from 51.7 percent to 23.1 percent.2.Taking the characteristics organic pollutants of coking wastewater as denitrification carbon source,the reasons of NO2--N accumulation are two main aspects,one had relation with quinoline,pyridine and indole itself toxicity;another had relation with nitrate and competitive effects of nitrite reductase and nitrate reductase concerning the electron donor.3?Based on the complete denitrification and the highest COD removal rate of water conditions,influent COD/NO3--N ratio is 6,namely characteristics organic pollutants of coking wastewater as carbon source,the best COD/N03-N ratio for denitrification is 6.4?At NO2--Naccumulation phase,when the COD/NO3--N ratio increased from 2.5 to 17,NO3--N ratio reduction rate increases from 0.129 gN/(gVSS·d)to 0.262gN/(gVSS·d);NO2--Nratio reduction rate increases from 0.058 gN/(gVSS·d)to 0.188 gN/(gVSS·d).Under each group of different COD/NO3--N condition,COD/NO3--N ratio reduction rate is greater than COD/N O3-N ratio reduction rate,which is the direct cause of N03-N accumulation in denitrification process.At NO2--Nreduction stage,each NO2--N ratio reduction rate is less than NO2--N ratio reduction rate.5?At NO2--N accumulation phase,when the COD/NO3--N ratio is 2.5?17,the NO2--N accumulation rate respectively are 0.071,0.070,0.072,0.071 and 0.074 gN/(gVSS·d),the basic remaining unchanged.6?At NO2--N accumulation phase,when COD/NO3--N ratio are 2.5,6,9,13 and 17,pH values shows a downward trend;at NO2--N reduction phase,pH value shows a rising trend.In the COD/NO3--N ratio is 6 to 17,when the end of denitrification,pH,showed a slow downward trend.denitrification process,pH curve shows an upward trend after the first drop,which is mainly caused by the NO2--N accumulation in denitrification process.The pH value after the denitrification ended is higher than that of denitrification initial stages,the heterocyclic acid produced intermediates of quinoline in the denitrification process resulted in lower pH after denitrification.7?When the COD/NO3--N ratio are 2.5,6,9,13 and 17,NO2--N accumulation around the highest point,the ORP curve is rising slowly at first and then declines:After denitrification,ORP value of the uniform slowly reduces.8?dpH/dt and dORP/dt curve can be a good characterization of NO2--Naccumulated the highest point of denitrification process under different COD/NO3--N ratio and the end point of denitrification;d2pH/dt2 curve can not characterize the degree of denitrification;d2ORP/dt2 curve can characterize the denitrification end points under COD/NO3--N ratio of 6,9 and 13,but can not characterize the COD/NO3--N ratio of 2.5 in the denitrification process,can not accurately characterize the COD/NO3--N ratio of 17 denitrification end point.