Establishment Of Phenol-Cr(Ⅵ) Coupled Microbial Electrolysis Cell And Mechanism Of Phenol Anodic Oxidation

In recent years,the rapid development of industry has led to the discharge of a large amount of wastewater,of which phenol and hexavalent chromium（Cr（Ⅵ））are two main contaminants.Anaerobic biological method has been widely used to treat industrial wastewater due to its advantages of environmental protection,economy and convenience.Thermodynamically,the oxidation of phenol and the reduction of Cr（Ⅵ）can constitute a complete reaction in anaerobic microbial method,without additional carbon sources and electron acceptors.But this relation would be blocked due to mutual toxic suppression to functional microbes.Bioelectrochemical system（BES）could combine anaerobic biological method and electrochemical method,and it has been extensively focused because of its ability of electricity generation and pollutant degradation.BES can separate two half reactions into different chambers,so it may be an effective method for the simultaneous removal of phenol and Cr（Ⅵ）.In addition,considering that most of electroactive bacteria are sensitive to phenol and cannot utilize it directly,it was assumed that fermentative bacteria and electroactive bacteria in mixed-culture BESs cooperated to degrade phenol,which might reveal the mechanism of phenol anodic oxidation.This paper firstly established a double bioelectrode H-type MEC to treat phenolic wastewater and Cr（Ⅵ）-containing wastewater simultaneously,and preliminarily investigated the mechanism of phenol anodic oxidation.The main results are as follows:（1）A Phenol-Cr（Ⅵ）coupled MEC combined the oxidation of phenol and the reduction of Cr（Ⅵ）was established in this study.At domestication stage,Phenol-Cr（Ⅵ）MEC treated phenol of 100 mg/L and Cr（Ⅵ）of 20 mg/L.And at stabilization stage,Phenol-Cr（Ⅵ）MEC could efficiently remove phenol of 500 mg/L to 1000 mg/L and Cr（Ⅵ）of 100 mg/L to 200 mg/L.From the domestication stage to stabilization stage,the removal efficiency of phenol and Cr（Ⅵ）gradually increased,the external current showed a significant increasing trend,and the anodic coulombic efficiency also increased relatively.XPS spectra and SEM image of the cathodic sludge confirmed the bio-reduction of Cr（Ⅵ）.The domestication of Phenol-Cr（Ⅵ）MEC accelerated the growth of related microorganisms.Functional bacteria have been significantly enriched,such as anodic electroactive bacteria Clostridium_sensu_stricto₁,or the cathodic chromium-reducing bacteria Aquamicrobium and Trichococcus.（2）The mechanism of phenol anodic oxidation was preliminarily investigated based on the Phenol-Cr（Ⅵ）MEC,and it was assumed that the syntrophic metabolism between phenoldegrading bacteria and electroactive bacteria might affect the phenol anodic oxidation.To clarify this assumption,mixed-culture MECs with phenol or acetate as sole carbon source were operated for comparison.Results showed that phenol served as anodic electron donor was more efficient than acetate for cathodic reduction of Cr（Ⅵ）,since the slow release of acetate from phenol degradation with fermentative bacteria might make full use of acetate as electron donor for anodic oxidation.The production of quorum sensing（QS）signal molecules were higher in phenolic anolyte,confirming the syntrophic metabolism among phenol-degrading bacteria and electroactive bacteria.Cyclic voltammetry（CV）test and Fourier transform infrared spectroscopy（FT-IR）indicated that phenolic anolyte and anodic sludge had higher electron transfer ability due to enhanced bio-electrochemisty processes in syntrophic metabolism.