Factors Affecting Biological Sulfur Reduction Process And Its Role In Treatment Of Heavy-Metals-Loaded Acidic Sludge Bioleach Solution

Smelting and processing,plating and mining generate a large number of acidic heavy metals-laden wastewater.Acidic heavy metals-laden wastewater is one of the most serious water in the world,because of its high acidity and concentration of heavy metals.Sulfur reducing bacteria(S0RB)could reduce S to H2S under anaerobic conditions.The produced S2-in this process can be precipitated with heavy metals,and the produced HCO3-and HS-by the decomposition of organic carbon can neutralize the H+in waste water.In recent years,because of the advantages of high efficiency and low energy consumption,the biological treatment method is widely believed as an effective way to deal with acidic heavy metals-laden wastewater.Sulfate is often used as sulfur source for biosulfidogenesis to remove and recover metals from wastewater from the mining and metallurgical industry,as it is naturally present in many metal-richwaters,such as metal recovery.However,elemental sulfur reduction is economically much more attractive than sulfate reduction.Therefore,this paper studied the performance of bacterial sulfur reducing system under acidic conditions,and established a combined process to treat the acidic heavy metals-laden wastewater.Sulfur reduction is performed under different pH values,CCOD/S,electron donor(acetate,glycerol,glucose,ethanol),and concentration of heavy metals ion(Cu2+、Zn2+、Ni2+、Pb2+)through batch experiments.Based on these results,the performance of the system is tested using the acid sedment leachate.(1)The results show that biological treatment is effective at various CCOD/S(0.3-0.75)and pH(3-5)values.The activity of sulfur reducing bacteria(S0RB)and the rate of sulfur reduction increase gradually with the increase of influent pH and CCOD/S.Furthermore,the concentration of S2-and TOC increase from 97.69 and 52.2 mg/L to 120.4 and 75.2 mg/L with the increase of influent pH(2.5-5).This results may be related with the change of relative abundances of the dominant phylogenetic groups in the bacterial sulfur reducing system.The ratio of Desulfurella and Proteobacteria increase from 2%and 14%to 73%and 73.6%with the increase of influent pH(2.5-5).(2)The concentration of S2-increase gradually with the increase of CCOD/S.However,as the inhibiting effect of the acetic acid,pH and concentration of S2-at various CCOD/S=1 increase slowly.In addition,sulfate reduction process can be performed under acidic conditions simultaneously with sulfur reduction process.(3)In the range of heavy metals concentration in this experiment,the sulfur reduction can be effectively carried out.In the caseof respectively adding 50 mg/L Cu2+、400 mg/L Zn2+、200 mg/L Ni2+、200 mg/L Pb2+,the removal rates of heavy metals are above 99%at the end of reaction.These 4 kinds of heavy metals have a certain inhibitory effect for sulfur biological reduction,and with the increase of the concentration of heavy metals,the inhibitory effect gradually increases.The inhibitory sequence is Cu2+>Pb2+>Ni2+>Zn2+.(4)For the acid sediment leachate treatment,it is demonstrated effective that the effluent pH is stable at around 4.3,and more than 99%of the initial concentrations of Cu2+,Zn2+,Pb2+,Ni2+were removed,respectively.