| 4-Chlorophenol (4-CP), one of the most important organic intermediate, is widely usedfor the synthesis of insecticides, fungicides, herbicides, wood preservatives and so on, whichis used in industries and agriculture at large. However, due to the aromatic ring structure of4-CP and the strong C-Cl bond, chlorophenols are resistant to biodegradation and thenpersistent in the environment, and cause serious pollution of nutural water. Therefore, manycountries have listed4-CP as priority pollutants. Besides, almost all of the governments hadestablished the strict discharge standard for the4-CP wastewater. At the same time, thetreatment technology for the4-CP wastewater has received more and more attention.General speaking, the aerobic bio-treatment process can remove most organic matter inthe wastewater effectively. But for the4-CP, the removal rate was much lower, especiallywhen the concentration of4-CP was higher, most microbes can be killed due to the toxicity of4-CP. The common treatment technologies were micro-electrolysis, electrochemical reductionand anaerobic bio-transform, but which of them have the same problem that the conflict ofcost and treatment efficiency was hard to be harmonic. Bioelectrochemical systems (BESs)are some electrochemical systems in which electrochemically active microorganisms catalysethe anode and/or the cathode reaction and mainly include microbial fuel cells (MFCs) andmicrobial electrolysis cells (MECs). These systems integrate three important wastewatertreatment options, namely, biological treatment, electrolytic dissociation and electrochemicaloxidation/reduction, and are regarded as a new sustainable and effective strategy for treatmentof wasteswater.In this study, we demonstrated that4-CP can be degraded effectively in BESs with verylow energy consumption. Besides, this technology has no secondary pollution. Firstly, anair-cathode single chamber BES was built successfully. The maximum power density and theremoval efficiency of4-CP decreased with the increase of4-CP concentration in theair-cathode single chamber MFC, and the efficiency of4-CP could reach to68.3%with0.023kWh/mol energy output in24h when the initial concentration of4-CP was100mg/L as a solefuel. Besides, the removal efficiency of4-CP improved10-20%compared with the conditionof open circuit. However, the efficiency of4-CP reached to99.8%at an energy consumptionof0.052kWh/mol which was much lower than electrochemical oxidation/reduction and the efficiency enhanced nearly30%. At the same time, the retention time reduced twice.Secondly, we explored the use of a double BES to abioticlly cathodic dechlorination ofaromatic chlorides such as4-chlorophenol, where the process was driven by microbialoxidation of glucose at the anode. It was confirmed that the4-CP reduction process wasfeasible in BES, and the dechlorination efficiency of4-CP could achieve50.3%at the cathodewhile the maximum power density was0.1838W/m~3when the cathodic pH was3.0and theinitial concentration of4-CP was100mg/L. The4-CP dechlorination efficiency wassignificantly enhanced when the BES was supplied with voltages, reaching up to92.5%at anenergy consumption of0.549kWh/mol4-CP (at applied voltage of0.7V). Besides, phenolwas identified as the major product of4-CP dechlorination at the cathode of BES in this study,which was the same as electrochemical reduction.Furthermore, a ferricyanide-cathode MFC was used to degrade4-CP in the anode.Compared to controls with only sodium acetate, the present of4-CP in the anode of MFCcaused the decrease of the current in the circuit, the maximum power density, the open circuitvoltages and the efficiency of4-CP. At the same time,4-CP could be as a single anodic fuel ofMFC, and the removal efficiency of4-CP was60.2%with the power density of0.32W/m~3,but compared with the conventional biological method, the efficiency of4-CP improved morethan10%.The obtained results indicated that the bioelectrochemical technology should be apotential method for4-CP degradation with energy output or less energy consumption. |
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