Application And Mechanism Research Of Microbial Iron Removal And Acid Reduction Technology (RIAUM) For Acid Mine Drainag

Acid Mine Drainage（AMD）pollution is a global environmental problem.AMD is a kind of polluted water body with low pH value,high concentration（like）metals（such as Fe,Mn,Cu,Zn,Cd,Pb,Cr,As,etc.）and sulphates,which is formed by the violent oxidation of metal sulfide minerals such as pyrite mixed in coal seams under the action of water,oxygen and microorganisms during coal mining and accumulation.AMD is commonly present in coal mines in the Yunnan Guizhou region,southwestern Shandong region,and Shanxi region of China.The pH value is generally below 6,between 2-4,and contains a large amount of Fe,Mn,and other toxic metal elements.When these high concentration metal elements enter the groundwater or surface water system with AMD,they will seriously pollute the surrounding water environment and soil environment,endanger the growth of aquatic organisms and crops,and even affect human health.Guizhou is rich in coal resources,known as the"Jiangnan Coal Sea".Its coal reserves account for 61%of southwest China,more than the total coal reserves of 12provinces（districts and cities）in the south.Most of the coal in this area is high sulfur coal,with sulfur content close to or higher than 3%,mainly existing in pyrite.Under good rain and heat conditions,pyrite is easy to oxidize to form AMD.Due to the optimization and adjustment of energy policies by the country and Guizhou Province,as well as the influence of coal mine resource conditions in Guizhou Province,many small coal mines in Guizhou Province have been closed or abandoned since the 12th Five-Year Plan.However,after the closure of coal mines,a large amount of AMD will still be generated,posing a threat to ecological security.The AMD generated by these types of coal mines has the characteristics of multiple emission points,dispersion,and wide pollution range,and has become a prominent water environment pollution problem in Guizhou Province.For AMD in Guizhou,based on the previous microbial remediation technology,a new method for AMD treatment was developed,that is,reduction of iron and acidity using microbiology（RIAUM）,and a field pilot scale RIAUM system was constructed in Sunjiazhai,Kaili City,Guizhou Province to treat Fe rich AMD,The system consists of an oxidation precipitation reaction unit,a microbial reaction unit,a regulation unit,and an alkali neutralization reaction unit.This article conducts a two-year continuous monitoring of the operational effectiveness of the RIAUM system,evaluating its iron removal and acid reduction effects,as well as its long-term stability.The hydrogeochemical change characteristics of Fe in the RIAUM system and the diversity structure characteristics of microbial communities have been studied,and the mechanism of Fe and acid removal of the RIAUM system has been discussed,and the following understanding has been obtained:（1）After treatment by a microbial Fe removal and acid reduction system,the Fe content of the effluent AMD is lower than the 7 7 mg·L^-1 specified in the Emission Standard for Pollutants from the Coal Industry（GB 20426-2006）,with an average total Fe removal rate of over 94%,an average acidity removal rate of 79.77%,an average total manganese removal rate of 31.01%,and an average SO₄^2-average removal rate of22.76%.The system has a certain removal effect on trace element pollutants such as Zn,Pb,Cr,and Cd.（2）RIAUM system has two modes:Model 1 and Model 2.Under Model 2,when the oxidation sedimentation unit does not feed water,the system still has a high removal capacity for Fe,and the concentration of Fe in the effluent still meets relevant national standards.Therefore,in the future promotion and application of the system,it may be considered not to set up an oxidation sedimentation unit.（3）The coupling relationship between water quality parameters and Fe in RIAUM system was studied.The mechanism of rapid oxidation of Fe（Ⅱ）may be the participation of microorganisms in the system.Fe（Ⅲ）forms secondary minerals such as Schneider minerals and goethite through hydrolysis and precipitation.The filler in the reaction tank is a key factor affecting the oxidation of Fe（Ⅱ）and the removal of Fe and other polluting elements in the system.The oxidation rate of Fe（Ⅱ）in the microbial reaction unit with organic substrate addition is higher than that in the reaction unit without substrate addition,while the addition of carbonate rock promotes the rapid improvement of pH and the removal of Mn and SO₄^2-.The formation and transformation of secondary minerals affect the removal of polluting elements from water.Some minerals can utilize surface microstructure to adsorb and co precipitate metal ions,which can lead to the release of SO₄^2-during the mineral phase transformation process.（4）Based on 16S rRNA testing of microorganisms,genera such as Acidiphilium,Ferrovum,Thiomonas,Acidithiobacillus,Acidithrix,Gallionella,and Metallibacterium are Fe and S functional microorganisms,and have a significant impact on the oxidation of Fe（Ⅱ）and the removal of acidity in the system.Environmental factors such as Total Fe,Fe（Ⅱ）,Fe（Ⅲ）,SO₄^2-,EC,pH,Eh,DO,etc.jointly promote the composition and changes of microbial community structure in different reaction units of the RIAUM system.The RIAUM system has shown good iron removal and acid reduction effects,and has the advantages of simple daily maintenance,low operating costs,and sustainability.The application of this technology has strong theoretical and practical significance for the treatment of acidic mine wastewater in China and even around the world.