| Acid sulfate wastewater is currently one of the most serious water and soil pollution sources in the world,because of its high acidity,hard to control,and management difficulties,etc.Sulfate reducing bacteria(SRB)could reduce SO42-to H2S under anaerobic conditions.The produced S2-in this process can be precipitated with heavy metals,and also the produced CO32-by the decomposition of organic carbon can neutralize the H+ in waste water.At present,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 such acidic sulfate containing waste water.However,the hydrogen sulfide,produced in sulfate reduction processes produce,is a toxic and corrosive compound.Before the discharge of effluent and gas produced by anaerobic treatment process,the addition of sulfide removal steps is very critical.The oxidation of sulfide to elemental sulfur is of great importance as elemental sulfur can be separated by sedimentation from the effluent.And can be re-used as fertilizer or as the raw material for sulfuric acid production.Biological sulfide oxidation is also considered a clean alternative compared to physico-chemical alternatives.In views of the above,this paper studied the performance of bacterial sulfate reducing system under acidic conditions,bacterial sulfide oxidation system in heterotrophic environment,and established a combined process to treat the acidic sulfate wastewater.The main observations and conclusions are as follows:Compartmentalized ABR could resist the low pH conditions of acidic sulfate wastewater.Although the influent pH was decreased from 4.5 to 2.5,high sulfate reduction efficiency(88.8%-96.1),COD removal efficiency(60.6%-77.5%)and increased pH(6.7-7.3)could be maintained by ABR system.Microbial diversity decreases gradually with the decrease of influent pH.The Chao 1 index in each compartment is positively correlated with the influent pH.Desulfovibrio sp.is the most dominant microorganisms in the reactor,which accounts for a proportion in each phase is more than 10%,and it may be the most critical functional microorganisms in this experiment.What’s more,the Desulfobacter is enriched mainly in the compartment 4 of the stage 3,and it is capable to reduce SO42-and produce alkalinity by taking acetic acid as carbon source.The synergistic reaction of these two kinds of SRB is the key for the system maintaining high efficiency under the low pH condition.In the range of heavy metals concentration in this experiment,the sulfate reduction can be effectively carried out.In the case of respectively adding 10-200 mg/L of Cu2+,Zn2+,Fe2+,Ni2+,the SO42-concentration is respectively reduced to 823-2257 mg/L,696-2018 mg/L,902-2043 mg/L and 621-1755 mg/L,and the effluent pH was increased to 5.27-4.52,5.35-4.86,5.26-4.73 and 5.31-4.86,and 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 sulfate biological reduction,and with the increase of the concentration of heavy metals,the inhibitory effect gradually increases.The EC50 of sulfate biological reduction by Cu2+,Zn2+,Fe2+,Ni2+is respectively 92.4 mg/L,125 mg/L,108 mg/L and 190 mg/L.And its inhibitory sequence is Cu2+>Fe2+>Zn2+>Ni2+.By controlling the aeration intensity in the range of 16.90～5.20 mL/min cm2-,the biological sulfide oxidation system constructed by air lift reactor(ALR)has a good treatment capacity for sulfide waste water containing organic compounds.The removal rate of S2-maintains with 100%,the removal rate of COD decreases with the decreasing of aeration intensity,and it is reduced to 31.1%when the aeration intensity is 5.20 mL/min cm2-from 63.4%when the aeration intensity is 16.90 mL/min cm2-.While,the S0 conversion rate increases with the decrease of aeration intensity,and it increases from 7.63%to 89.1%when the aeration intensity is respectively from 16.90 mL/min cm2-to 5.20 mL/min cm2-.In the whole reaction period,Pseudomonas bacteria exist in large quantity,which respectively accounts for 34.4%,7.29%,and 10.4%of the three stages.This shows that Pseudomonas is probably the most important functional bacteria for sulfide oxidation in this experiment.Within the 0-3000 mg/L range of acetic acid content,the S2-can be oxidized by microorganisms to S0 and SO42-.Compared with the treatment without organic matter,acetic acid with low concentration can promote the biological sulfide oxidation efficiency,and after a period with 22 hours,S2-is oxidized completely.While the high concentration organic matter has a significant inhibitory effect.Through SEM-EDS and XRD analysis,we find that the main content of suspended solids was elemental sulfur.The results of the experiment for the comparison of the hydrophilicity of biological sulfur and chemical sulfur show that the hydrophilicity of biological sulfur is strong,its contact angle is 37.9°,and the hydrophilicity of chemical sulfur is poor,its contact angle is 139.5°.The sulfur formed by biological S0 is mainly polymeric sulfur(>50%),and a certain amount of organic components also exists(9.2%-11.1%).The combined process of anaerobic SO42-reduction-aerobic S2-oxidation is efficiency on the treatment of acid zinc and Nickel containing waste water.In the whole process,the pH of waste water can be increased from 3.0 to 8.24,while the removal rate of SO42-is 84.9%,both the removal rates of Zn2+and Ni2+are 100%,and the conversion rate of S0 is 70.9%.The recovery rate of total S of the process is 79.5%.It was concluded that,the biological sulfatereduction system constructed by ABR has a good treatment capacity for acid sulfate wastewater.The acidity,SO42-and metal ions could be removed simultaneously.After the effluent of ABR is connected with ALR for aerobic biological oxidation,a majority of sulfide could be oxidized to elemental sulfur.The whole combined process could remove the acidity,SO42-and metal ions simultaneously.and change waste into resourse. |
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