Research On Efficiency And Microbial Communities Of Coking Wastewater Treatment By Step-feed Multistage A/O Process

Based on the wastewater treatment plant of a coking enterprise in Hebei,we fully acquainted with the existing problems of this wastewater treatment plant through a number of early research and tracking investigation in the background of the further improvement of the wastewater discharge standard in the coking industry.The pollution efficiency and economic benefits of the A/O/O system and the multistage A/O system before and after the transformation are also carried out.In addition,the microbial community structure in two sets of biochemical treatment system cells was analyzed and compared by using high throughput sequencing analysis technology.The following conclusions are drawn:(1)The COD,ammonia nitrogen,total nitrogen in the influent and effluent of the original A/O/O process were 2500?4000mg/L,50?200mg/L,200?350mg/L and 250?450mg/L,0?10mg/L,100?150mg/L,Respectively.The effluent clearly failed to reach the requirements of the new standard of pollutants for coking chemical industry(GB16171-2012).(2)It was verified that the carbon source of raw water can be utilized by denitrifying bacteria through laboratory experiments.(3)The Step-feed A/O Process runs stably after 162 days of startup,load increase and full load operation.The experimental results show that,when the residence time,the reaction temperature,pH and the SV value of the sludge was 80h,25?35?,7-8 and 25%-30%of the system,the ammonia nitrogen and total nitrogen in the influent and effluent was 50?200mg/L,200-350mg/L and 0?10mg/L,0?50mg/L,the effluent from the advanced treatment meets the indirect emission standard of Emission standard of pollutants for coking chemical industry(gb 16171-2012).(4)After a month of stable operation monitoring,the average COD,ammonia nitrogen,and total nitrogen of the effluent in the secondary sedimentation unit of AO AO biochemical system were 388.3 mg/L,4.81 mg/L,and 33.3 mg/L,respectively,and the average removal rate was 88.4%,91.8%and 88.8%.After the system transformation,the biological treatment of operating costs significantly reduced by enhancing denitrification,saving aeration,step feed and other measures to save electricity by 36%,saving the amount of alkali 40%.Operating costs from the original 5.059 yuan/ton fell to 3.434 yuan/ton,tons of water running cost savings 1.625 yuan.(5)After the system is commissioned,two of the operating AO AO system and AOO system are investigated.High-throughput sequencing technology is used to analyze andcompare the diversity,abundance,and different levels of the community structure of the collected microbial samples.The analysis of the system from the perspective of the microbial communities showed:little difference of the two systems in the levels of the phylum,order,family,and genus.Thiobacillus was the dominant genus.In the AOO system,the microbial community structure of the first aerobic unit is quite different from that in the second aerobic unit.