Experimental Research On The Treatment Of Anaerobic Process Effluent Of Coal Gasification Wastewater By A/O-MBR Process

Coal gasification wastewater is a typical refractory industrial wastewater for which the conventional biological treatment is the combination of anaerobic and aerobic processes.However,the anaerobic effluent still contains various toxic and harmful substances such as phenols,PAHs,nitrogen-heterocyclic compounds,cyanide and so on,which pose high requirements for the stability of the subsequent aerobic biological treatment process.For the aims of finding an efficient and stable aerobic treatment process,two anoxia/aerobic(A/O)integrated membrane bioreactors(MBR)were used in this paper to treat the coal gasification wastewater after anaerobic process and to investigate the effects of carriers on A/O-MBR process.This research can be divided into three stages.Firstly,the bioreactors were started and removal efficiency of COD,total phenols and ammonia in the A/O-MBR and hybrid A/O-MBR was compared.Then the influence of operating parameters on the efficiency of bioreactors was investigated and thus the subsequent operating conditions were determined.During the stable period,the decrease and transformation characteristics of organic pollutants and the change of biological toxicity were studied by analyzing water samples along the process and the correlations between basic indicators,spectral properties and toxicity were analyzed.Finally,high-throughput sequencing was used to analyzing the changes in microbial community and help to understand the performance of bioreactors from the micro perspective.The experimental results during the start-up phase showed that the hybrid A/O-MBR performed better than traditional A/O-MBR when treating coal gasification wastewater.The removal rate of COD and total phenols in the hybrid A/O-MBR reached 92.3% and 97.5% when treating anaerobic effluent at the end of start-up phase,meanwhile the corresponding removal rate in traditional A/O-MBR was 92% and 96.9%,respectively.However,both bioreactors showed poor performance on ammonia removal with the efficiency of only 47% and 44.4%,respectively.Referring to the experimental results,HRT=36 h,R=300%,and DO=4.5 mg/L were determined as the operating parameters for the subsequent experiments.It was found that the A/O-MBR process perform well on organic pollutant removal and toxicity reduction,especially the hybrid A/O-MBR.The COD and total phenols in the effluent of traditional A/O-MBR were 77.36 mg/L and 11.10 mg/L,respectively,while were only 64.15 mg/L and 8.03 mg/L in that of hybrid A/O-MBR.Anoxic pools play a major role in the reduction of COD,total phenols,fluorescent substances,and biotoxicity.The composition of dissolved organic matter changes obviously,and the main components are changed from phenols in the influent to aromatic esters and long-chain alkanes in the effluent.The results of correlation analysis showed that aromatic compounds and nitrogen-containing compounds are associated with acute toxicity of luminescent bacteria.The microbial community is significantly affected by coal gasification wastewater and the microbial diversity of the suspended sludge in operation period was obviously lower than that of the inoculated sludge.The microorganisms in carriers are more diverse and the dominant genera are different from suspended sludge.Long-term treatment of coal gasification wastewater makes Sphingomonas,Flavobacterium,Comamonas,Thauera and other genera which are able to resist or degrade aromatic compounds become important members of the microbial community,giving a reasonable explanation for the efficient organic removal and toxicity reduction in A/O-MBR process.