Process Assessment Associated To Microbial Community Response Of Quinoline Digestibility And Its Methane Recovery In Wastewater Enhanced By Zero-valent Iron

Quinoline is a kind of common refractory nitrogen-containing heterocyclic compound that can cause malformations,carcinomas and mutations.With the rapid development of industrial processes,quinoline is widely found in coking wastewater and dyeing wastewater,which has become the main pollutants in soil and water environment,having a huge harm to human health and the growth of plants and animals.There are three traditional methods for the treatment of quinoline-containing wastewater: physical,chemical and biological;however,they each have some fatal flaws: physical method could only transfrom quinoline on the phase level that could not convert it into non-toxic and harmless substances;although chemical method has a high degradation rate,its operation is too complex and costly to be extensively applied in engineering;biological degradation of quinoline is facing a bottlenecks due to the limited hydrolysis rate which further lead to lower efficiency of biological treatment.Zero-valent iron(ZVI)is a reductant which is low cost and does not cause secondary pollution,it can not only adjust the pH value of the environment to maintain stability,but also provide electrons for the growth of micro-organisms.These traits provide the theoretical feasibility for promotingthe degradation of quinoline by anaerobic microorganisms.Therefore,this study proposed a method of treating quinoline-containing wastewater with zero-valent iron coupled anaerobic microorganisms.In our research,the optimal values ??of the process parameters(initial pH value and ZVI dosage)in the zero-valent iron-anaerobic microbial coupling system(ZVI-AD)were investigated.Also,we demonstrate the trend of some key parameters in the process of quinoline degradation and methane production treated by different types of iron under optimum conditions.Finally,the microbial community structure was analyzed by high-throughput sequencing technology,in order to explore the potential mechanism of different types of iron in promoting the degradation of quinoline by anaerobic microorganisms.Mainly draw the following conclusions:(1)When the initial pH values ??of the ZVI-AD coupling system were6.5,7.0,7.5,8.0 and 8.5,respectively,the quinoline degradation rates were63.3%,71.3%,76.7%,70% and 64.6% after 96 h.Therefore,the optimal initial pH of the ZVI-AD coupling system was 7.5.(2)The degradation rate of quinoline was 50.6%,71.6%,78.9%,88.6%,76.2% in the ZVI-AD coupling system after 96 h when the dosage of ZVI was1 g / L,2g / L,3g / L,4g / L and 5g / L,respectively.The optimal dosage of ZVI was 3 g / L.(3)The degradation rates of quinoline were 74.1%,82.9% and 90.1%,respectively,and the yield of methane was 8 mL,17.5 mL,26.9 mL in different coupling systems which are composed of anaerobic microorganisms and different types of iron(iron powder,iron filings,rusty iron filings)respectively.This may safely draw the conclusion that rusty iron filings have the best effect on promoting the degradation of quinoline and methane production by anaerobic microbial,followed by iron filings,and then iron powder.(4)The microbial community structure of the blank group and the experimental group(separate AD system,three different types of iron)were analyzed by high-throughput sequencing technology.The results showed that there was a big difference between the microbial community structure of separate AD and coupling system.The content of specific microbial bacteria speices which is related to quinoline degradation was significantly increased in the coupling system,which also essentially explained that the addition of ZVI to promote anaerobic microbial degradation of quinoline is feasible and reasonable.In addition,the comparative analysis of different experimental groups(iron powder,iron chip and rusty iron chips)found that the three experimental groups had different effect on the bacterial community at the level of phylum,class and genus.