Study On Bioremediation System Amd Treatment Mechanism Of Acid Mine Drainage Optimized By Crab Shell

Acid Mine Drainage(AMD)has the characteristics of low pH,high sulfate and high dissolved metal content.Its direct discharge will lead to acidification of receiving water and decline of biodiversity,threatening the health of aquatic organisms and downstream residents.In this study,straw compost(SCP)and crab shell(CS)were used as carbon and nitrogen source substrates.Nine groups of continuous flow column reactor bioremediation systems with different mass ratios were constructed.The treatment performance was investigated by analyzing the changes of effluent indicators such as metal ions,sulfate,acidity and alkalinity,organic carbon,and material balance.In addition,The microbial diversity and community structure were studied with high-throughput sequencing data.The purification effect,treatment capacity and economic cost of different substrate combinations for AMD were explored,and the optimal substrate combinations were screened.The main conclusions are as follows:(1)The alkalinity of effluent,as well as pH and dissolved organic carbon(DOC),in eight groups of continuous flow column reactors with organic fillers reached the highest value in the whole operation period on the first day after domestication.The higher the content of crab shell in organic filler,the higher the alkalinity,pH,total DOC and NH4+-N contentration of thewater release,and the longer the sustained release time.This indicates that crab shell is a better neutralizer and organic carbon and nitrogen source slow-release agent than organic straw compost.(2)As a key microbial reaction to the AMD wastewater bioremediation system,sulfate reduction plays an important role in increasing/maintaining alkalinity and promoting metal sulfide precipitation.The sulfate concentration of the seven groups of crab shell reactors was generally lower than the influent concentration,and the higher the crab shell content,the higher the sulfate removal rate,which the removal rate reached 60%.The maintenance time of the sulfate reduction ability of the reactor was prolonged as the content of crab shells increases.(3)The metal removal efficiency of AMD treatment system depends largely on the type of metal,the operation stage of the reactor and the proportion of crab shells in the organic packing layer.The removal rates of Cd and Cu by seven groups of reactors containing crab shells were maintained above 90%,while traditional organic compost reactor were lower than 50%on the 6th and 30th days,respectively,and gradually decreased.For Fe,Mn,Al,Zn,Ni and Co,the higher the crab shell content in the reactor packing layer,the higher the removal rate at the same sampling time point,and the longer it takes to maintain(>50%).Among them,the average removal rate of Ni and Co in 90%CS reactor wass the highest,and the total removal rate was above 50%(the highest removal rate was 99%).(4)There are obvious differences in the utilization of organic carbon by microorganisms in different substrate reactors.The results of mass balance showed that microorganisms such as sulfate reducing bacteria(SRB)in traditional organic substrate straw compost reactor had poor utilization of organic carbon,which was one of the reasons for their inadequate AMD treatment capacity.The organic carbon source of the reactor containing crab shells was mainly volatile fatty acids produced in the process of substrate biodegradation,which was conducive to the efficient utilization of microorganisms.The metal mass balance calculation results showed that the retention effect of each organic filler reactor on different metals was different.Seven groups of reactors containing crab shells had better interception effect on cadmium and copper,and the metal interception rate was above 90%.The copper retention rate of the traditional compost reactor was 37%,and Cd was not effectively retained in the reactor.For Al,Zn,Ni and Co,the higher the content of crab shell in reactor filler,the higher the metal rejection rate.Reactors containing 50%or more of crab shells can intercept more than 50%of the four metals(the highest interception rate was 90%).Among them,the reactor containing 90%of crab shells had the highest metal interception rates for Al,Ni and Co in all reactors.(5)AMD bioremediation is based on the ability of microorganisms such as SRB to produce alkalinity,sulfides and fix metals.Through high-throughput sequencing of DNA samples and principal component analysis(PCA),as well non-metric multidimensional scale analysis(NMDS)and cluster analysis of sequencing results as,it was found that the community structure of microbial samples in reactor with 70%,80%,90%and 100%crab shell was similar,and the relative abundance of microorganisms in different samples was different at the generic classification level,which the main species were Acetobacteroides,Desulfovibrio and Desulfurispora.SRB-related bacteria were detected in the samples with organic fillers higher than 60%CS,including Desulfovibrio(1.2%-9.8%),Desulfo,microbium(0.1%-2.6%),Desulfoterium(0.6%-2.3%),Desulfurispora(0.20%-2.2%),Desulfatifera(0.2-0.70%)and Desulfatifier(0.2%-0.7%).Desulfotomaculum(0.1%-0.6%).