Study On A New Reactor For Improving Carbon And Nitrogen Removal From Coking Wastewater And Its Microbial Mechanism

The coking wastewater(CWW)produced in the coking process is a main industrial wastewater in C hina,which has a huge amount of discharge.CWW is characterized with the high concentration of organic matter,high toxicity,poor biodegradability,and complex composition.The inhibition of toxic substances on nitrification and the scant carbon source available for denitrification will seriously affect the nitrogen removal of traditional biological treatment.The pre-anaerobic process treatment is used to preferentially provide carbon sources for denitrification,but microorganisms are often inhibited by the toxicity of wastewater.And the pre-aerobic process treatment is used to remove most of the organic toxic substances,but the carbon source is first depleted and cannot continue to support denitrification.Therefore,it is necessary to explore a new denitrogen model that can avoid the suppression of high concentrations of toxic substances and provide sufficient organic carbon source for denitrification.Nitrification and denitrification have different time and space requirements for oxygen and carbon sources,which makes carbon and nitrogen pollutant difficult to be coordinately utilized and simultaneously removed.In order to solve this problem,this study used a slef-built fixed-carrier fluidized-bed reactor to achieve the purpose of organic carbon source being removed and utilized by microorganisms,and to promote nitrogen removal.Compared with the traditional aerobic fluidized-bed reactor,the COD removal rate of the new reactor reached 91%,9% higher than the former;the ammonium degradation rate reached 97%,12% higher than the former;the total nitrogen removal rate reached 87%,twice that of the former;the degradation effect of toxic substances was 3 times that of the former;the removal effect of refractory substances was twice that of the former.A series of experimental results proved that a dissolved oxygen concentration gradient was formed inside the carrier of the new reactor,so that the aerobic space and the anaerobic space coexisted in a single reactor.In the aerobic area,the nitrification reaction were carried out,the toxic substances were degraded to reduce the toxicity inhibition.In the anaerobic area,the macro-molecules were disintegrated to improve the biodegradability of the wastewater and promote the denitrification.Through the microbial analysis for experimental sludge,the dominant bacteria in the microbial community related to the degradation of carbon and nitrogen pollutants were distinguished.At the same time,the new reactor was found to enable aerobic and anaerobic bacteria to coexist and function synergistically.By analyzing the distribution of functional denitrgen genes in the microbial community,key nitrifying bacteria and denitrifying bacteria were identified and found to occupy the generally low.Quantitative analysis of the abundance and expression of denitrogen genes proved that the better the denitrification effect,the higher the gene abundance and the lower the gene expression abundance.The new reactor showed excellent performance in simultaneously removing carbon and nitrogen pollutants of wastewater,reducing the toxicity of wastewater on microorganisms and removing refractory organic matter.This study provided a new alternative model for the simultaneous removal of carbon and nitrogen pollutants from CWW.