Simultaneous Anaerobic Biological Removal Of Sulfate And Chromate Under Solid Carbon Source

Electroplating wastewater,acidic mine wastewater,leather wastewater,and solid waste detoxification industries contain large amounts of SO₄^2-and Cr???.Reducing both using biological methods is the most cost-effective method.However,the low levels of organic compounds in such composite pollution wastewater result in insufficient electron donors and insufficient bioreduction power.In addition,the organic complex chromium formed by the bioreduction Cr???has a strong mobility,and when it migrates in the environment,it can be reoxidized by the bacteria to Cr???,resulting in secondary pollution of the water.In order to solve these two problems,a solid-phase carbon source technology is proposed,that is,the use of a solid substance?natural or synthetic material?as a carbon source for bioreduction can slowly release carbon and increase the volume load of the reaction system.At the same time,the solid material can be used as a biofilm carrier to enhance the adsorption and fixation of a certain amount of chromium.In this study,the biodegradable meal box?BMB?was selected as the solid carbon source and biofilm support material to effectively solve the problem of organic carbon source fluctuations and the migration of Cr???reduction products in the environment,achieving Cr???and SO₄^2-synchronous removal and effective fixation of Cr?III?.The surface structure analysis also confirmed the feasibility of BMB as a carbon source and biofilm carrier.Afterwards,the effects of different influencing factors on sulfate removal efficiency were examined by control variables,and it was determined that under the optimal conditions,the sulfate removal rate could reach 92.11%within 48 h.Further comparisons of SO₄^2-and Cr???treatment efficiencies under different influent loadings were conducted and the degradation pathways for Cr???and SO₄^2-were explored.In a total of 160 days of continuous experiments,the influent sulfate concentration was maintained at 600 mg-S/L,and the influent Cr???was gradually increased from 0.0 mg/L to140.0 mg/L.When the influent Cr???does not exceed 90.0 mg/L,the sulfate removal rate is greater than 70%,the total effluent Cr is less than 5.0 mg/L,and Cr?III?only accounts for1%-15%.When the influent Cr???concentration was 140.0 mg/L,the removal rate of SO₄^2-was reduced to 53.32%and the removal rate of Cr???was reduced to 79.42%.In the chromium distribution experiments,it was found that Cr distributed in the activated sludge system was 79.90%-82.01%,and 16.80%-19.36%of Cr was distributed in the biofilm system,more than 79%of Cr was distributed in cells in activated sludge.Internal,and its main form is Cr?III?.In addition,the presence of elemental sulfur was detected in the cells,indicating that the chemical reduction reaction of Cr???and sulfate reduced products occurred in the cells.The results showed that the bioreduction and chemical reduction coexist in the reaction system.The existence of chemical reaction can improve the system's impact load capacity,strengthen Cr???reduction,and the presence of biofilm system can strengthen the fixation of Cr?III?and reduce the total Cr in water outflow.In addition Cr???reduction takes place in the sludge system and is mainly dominated by intracellular reduction.In addition,microbial flora analysis confirmed that the majority of bacterial population diversity and abundance gradually decreased with increasing Cr???concentration.In addition Cr???reduction takes place in the sludge system and is mainly dominated by intracellular reduction.In addition,the microbial flora analysis confirmed that the majority of bacterial population diversity and abundance gradually decreased with the increase of Cr???concentration.Analysis of the community structure at the genera level showed that the ratio of Desulfovibrio increased to5.31%at the later stage of reactor operation.Desulfovibrio is a sulfate-reducing bacteria.Its surface contains a large number of sulfate channels and contains Cr???reductase.It was demonstrated that Cr???is reduced to trivalent chromium through the sulfate channel into the cell body,producing Cr?OH?₃,elemental S,and Cr?III?-protein-DNA crosslinks.