Study On The Treatment Of Acid Mine Drainage With SRB Using Agricultural And Forestry Wastes As Carbon Source

As the demand for mineral resources grows,the treatment of acid mine wastewater is becoming an increasingly serious issue.sulfate reducing bacteria(SRB)is one of the most popular methods for acid mine drainage(AMD)treatment.In this study,based on the design of SRB bioreactors,we used agroforestry solid waste and agroforestry waste fermentation broth as SRB carbon sources respectively to investigate the effect and mechanism of action of remediating acid mine wastewater.The effect of different agroforestry waste as substrate/carbon source on the treatment of AMD in the SRB bioreactor was investigated by using solid waste such as wine lees and leaf compost as substrate fillers;using agroforestry waste(cow dung and straw)fermentation broth as carbon source and different materials(quartz sand,steel residue,biochar and peanut shells)as fillers to explore the effect of different fillers on the treatment of AMD in the SRB bioreactor when using agroforestry waste fermentation broth as carbon source.The effect of different fillers on the effectiveness of the SRB bioreactor in treating AMD was investigated.The following conclusions were drawn from this study:When using wine lees as bioreactor filler,the high dissolved organic carbon(DOC)content of wine lees could achieve rapid removal of sulphate and facilitate rapid bioreactor start-up,with sulphate removal rates as high as 67% in the early stage of the reactor(14 days).Compared to wine lees,leaf compost has a lower DOC and a lower sulphate removal rate of 48%in the early stages of the bioreactor.However,over the entire experimental period,both bioreactor groups were found to be effective sources of SRB carbon for remediation of acid mine wastewater.Effective removal of Fe,Cd,Cr,Al and Zn could be achieved with the use of wine lees and leaf compost as the carbon source for the bioreactor,with removal rates greater than 95%.Due to the high solubility of Mn S,the SRB bioreactor was less effective in removing Mn with 46%and 40%,respectively.The sulphate balance revealed that sulphate entering the bioreactor was mainly converted to sulphide combined with metal ions to form acid-soluble sulphide as well as monomeric sulphur deposited in the bioreactor.Secondly,it flows out with the effluent in the form of sulphide.The microorganisms in the bioreactors show a clear stratification,with the microbial communities in the different bioreactors having a similar composition in the same location.At the inlet of the bioreactor,the dominant groups are iron-reducing bacteria,acid-sulphur bacteria and other acid and salt-tolerant bacteria,while in the middle of the bioreactor,anaerobic fermenting bacteria,SRB and sulfate-oxidising bacteria dominate,and at the outlet of the bioreactor,the dominant microorganisms are mainly SRB and sulfate-oxidising bacteria.All four groups of bioreactors had good treatment effects on AMD when the fermentation broth was used as the carbon source and four different materials,namely quartz sand,steel slag,biochar and peanut shells,were used as fillers for the bioreactors.Overall,the steel slag group was the most effective,followed by the biochar and quartz sand groups,and the peanut shells group was the least effective.In the bioreactors with four different substrates,the steel slag group had the best removal rate of 61% due to its high SRB activity,which converted sulphate into sulphide,while the calcium ions released from the slag combined with sulphate to form calcium sulphate precipitate,resulting in the best removal of sulphate among the four substrates.This resulted in the highest amount of acid-soluble sulphide being formed.The biochar group removed 49% of the sulphate and produced the most sulphide of the four bioreactors.The peanut shell group had the lowest sulphate removal rate despite having the most abundant carbon supply,mainly due to the fermentation of cellulose in the peanut shells to produce high concentrations of acetic acid which inhibited the activity of the SRB.A four-group treatment system using fermentation broth as the carbon source could achieve effective removal of Fe,Cd,Cr,Al and Zn,which were all above 92%,while the removal of Mn was lower.The results indicated that different filling substrates affected the sulfur transport transformation and the remediation effect of acid mine wastewater.The bioreactor has a rich microbial community,with sulphate-reducing bacteria mainly located in the inlet and middle of the bioreactor,and also near the outlet.Sulfate-oxidising bacteria were mainly found in the middle of the bioreactor and at the outlet,while a certain amount of anaerobic fermenters were also present in the bioreactor.More anaerobic fermenting bacteria were found in the PS group than in the remaining three groups,which resulted in higher acetic acid production in the PS group and suppressed the activity of SRB in the PS group.