Study On Cr(Ⅵ)and Cr(Ⅲ)-contained Wastewater Treatment With Microbial Fuel Cells Technology

From last century in1960th, Microbial fuel cell （MFC） technology has beenwidely attracted as a wastewater treatment technique, which can degrade pollutionand generate energy at the same time. In this study, traditional dual-chamberedmicrobial fuel cells （MFCs） with carbon brush as the anode and carbon cloth as thecathode were utilized. The first stage, studying on the basic properties of MFC andobtaining the best experiment conditions; The second stage, comparing with twokinds of cells, Cell A and Cell B, to treat with artificial Cr-contained wastewater in astudy performed on Cr（Ⅵ） removal efficiency and power generation characteristics,achieving the goal of decontamination and energy production simultaneously. In thethird stage, double cells system was employed to try to reduce Cr（Ⅵ） and Cr（Ⅲ） atthe same time. Cell1used Cr（Ⅵ） as the cathode electron acceptor, and it can directlysupply Cell2with the generated power, then Cr（Ⅲ） in the catholyte of Cell2couldreduce to lower valence state or Cr metal, in this way wastes recycling could berealized. With the experiments, conclusions were got:（1） The salinity of solution is an important factor in improving the powergeneration. when300mM KCl and25mM KCl were added to the catholyte and theanolyte, respectively, there was a51.5%improvement in power density achievedfrom the addition of200mM KCl to the catholyte and no KCl addition to the anolyte.（2） A catholyte kept in a low pH （2.0） benefited Cr（Ⅵ） reduction. KH₂PO₄wasadded to the catholyte, which served as a buffer solution that stabilized the pH andincreased the Cr（Ⅵ） removal efficiency from70.0%to99.9%.（3） Comparing the catholyte air-bubbling with N2-bubbling, the intermediateH₂O₂, generated by aeration, which can turn to be as an reduzate when coexisted withCr（Ⅵ） in acid system. H₂O₂not only accelerated the removal of Cr（Ⅵ）, but alsomade the cells function well.（4） Comparing with different cells, the size of the cell and gas flow rate botheffected the reduction of Cr（Ⅵ） and the power generation of cells. More air addedresulted in a higher power density in a certain extent. Comparing to the big cell A, small cell B was not suitable for treating with high Cr（Ⅵ） when air bubbled. Andwithout O₂evolved, good performance could be found in Cell A, while Cell B didn’tget a good result, it can be supposed that small cell was not suitable for this research.（5） In this double MFCs system, Cr（Ⅵ） and Cr（Ⅲ） could be removed at thesame time in a certain degree. Air-bubbling in No.1cell and buffer condition of thecatholyte in No.2cell both affected Cr（Ⅵ） and Cr（Ⅲ） removal efficiency. Theremoval of Cr（Ⅲ） could obtain higher efficiency than that of Cr（Ⅵ）, and Cr（Ⅲ）removal was increased with an increase of the initial concentration, and all of themgot a quickly removal within10hours. Keeping a concentration ratio of Cr（Ⅵ） andCr（Ⅲ） to2:1guaranteed an effective removal efficiency for Cr（Ⅲ） recovery. It’sdeduced that a higher concentration ratio of Cr（Ⅵ） and Cr（Ⅲ） was supposed to allowfor a complete and effective removal and/or recovery efficiency of Cr（Ⅲ）.（6） Using SEM-EDS method to analyze the surface of cathode. From the surfacecharacteristics of carbon cloth, it could be infered that with the Cr（Ⅵ） reduction,Cr₂O₃was existed in No.1cell, while a small quantity of Cr metal was detected in No.2cell. This experiment provided the foundation of the feasibility of this double cellssystem.