Study On Remediation Of Chromium-Containing Wastewater By Plant Cathode-Sediment Microbial Fuel Cell

In order to explore an efficient and clean method for treating chromium-containing wastewater,a novel installation of plant cathode-sediment microbial fuel cell(Plant Cathode-SMFC)was constructed to treat simulated chromium-containing wastewater,and the effects of various factors(current collector material of the cathode,plant,external resistance,initial Cr6+concentration,and initial COD concentration)on the electricity production performance and the treatment effect of the Plant Cathode-SMFC were also explored.The main results are as follows:(1)The best power generation performance could be obtained when the installation was set with stainless steel mesh,calamus,external resistance of 2000 Q,initial Cr6+and COD concentration of 229.99 mg/L and 2024 mg/L respectively in overlying water,the optimal power generation performance could be obtained.The maximum power density in each experimental group was 40.16 mW/m2,and the maximum removal rates of Cr6+and COD in overlying water were 99.94%and 99.61%,respectively,and the maximum removal rate of organic matter in sediments was 20.38%.After experimental operation,the Cr6+content in sediments of each group was decreased,while the total chromium content was increased.And the water-soluble and exchange forms of chromium in sediments of each group tended to convert to other stable forms of chromium(the organic bound state,iron-manganese bound state and residual state of chromium).(2)The closed-loop installation of the cell promoted the attachment of a large number of microorganisms,and reduced the species diversity in the anode and cathode as well as in the Sediments.Nitrospirae,Deltaproteobacteria,Chloroflexi and Acidobacteria in the sediments played an important role in the degradation of organic matter to generate electrons,and Anaerolineae played an important role in the reduction of Cr6+.In the anode of the installation,it was obvious that the two types of electrogenic bacteria,Proteobacteria and Geobacteraceae,played an important role in promoting the electricity-generating performance of the cell.And it was found in the anode of the device that Bacillus,which has the ability to efficiently transform Cr6+,accounted for 7.11%of the anode.In the cathode of the installation,the dominant species were Geobacter,Limnobacter,and Dechloromonas.There were abundant microbial species on the cathode of the device,most of which belong to Firmicutes,Bacteroidetes and Verrucomicrobia.They play an important role in the degradation of COD in the overlying water.Bacilli,which has the ability to efficiently transform Cr6+,played an important role in reducing the concentration of Cr6+at the cathode of the cell.(3)The kinetic analysis of Cr6+in each stage showed that the assumption that the redox reaction of Cr6+was a first-order reaction was true.As the external resistance increased,the initial Cr6+and COD concentrations of the overlying water decreased,which means the k value of the reaction rate increased.Visual MINTEQ simulation found that CrO42-,HCrO4-,Cr(OH)2+,Cr(OH)3 and Cr(OH)4-were the main elements of chromium in the cathode precipitation of the plant cathode-SMFC,and Cr(OH)3 was the main component,accounting for up to 97.85%.