| More and more recalcitrant organic wastewater was generated with the rapid development of chemical industry recently. Due to the low B/C, poor biodegradability and high toxicity, traditional bioremediation cannot effectively treat this kind of wastewater. A bioelectrochemical system (BES) equipped with biocathode was employed for recalcitrant organic wastewater treatment in this work.Reactive blue13(RB13) and pentachlorophenol (PCP) were treated as typical recalcitrant organic pollutants in this paper. Firstly, a novel method for screening and acclimating electrochemically active bacteria (EAB) for the degradation of recalcitrant organic pollutions was provided. EAB for RB13degradation and EAB for PCP degradation were obtained, which can significantly reduce the time of biocathode set-up. Biocathodes used for RB13and PCP treatment were also built, and the performance of biocathodes for RB13degradation and PCP degradation were significantly improved. In the optimized conditions, the decolorination rate of RB13in BES reached80.2±5.5%during8hours operation, and the PCP removal rate in BES reached89.7±3.7%after100hours treatment.For understanding the degradation pathways of recalcitrant organic pollutants on biocathode, the electron transfer mechanisms of EAB on biocathode were studied. The electron transfer pathway from electrode to EAB was determined. We proved that direct electron transfer mechanism from the electrode to EAB could be involved in biocathode. A pair of oxidation-reduction peaks around+0.2V existed in the cyclic voltammograms, which could be caused by cytochrome C protein.454pyrosequencing tests showed that Proteobacteria, Bacteroidetes and Firmicutes were three predominant phyla in BES, which were three dechlorinating microorganisms.Given the importance of EAB biofilm in biocathode, EAB formation mechanisms were studied. A novel method for in situ determination of the EAB biofilm thickness was developed. By employing a platinum ultramicroelectrode (Pt UME) as the detector, thickness of Shewanella oneidensis MR-1biofilm was measured, and the results were also confirmed by confocal laser scanning microscope tests. According to our results, lower electrode potential, higher concentrations of sodium lactate and riboflavin could accelerate the formation of S. oneidensis MR-1biofilm on the electrode. The maximum biofilm thickness was100μm to110μm when S. oneidensis MR-1grown in the anaerobic medium. Capdeville equation was found describing the formation of EAB biofilm well. When the concentration of sodium lactate was20mM and the electrode potential was+100mV, the specific growth rate of S. oneidensis MR-1biofilm thickness was0.27h-1.A bipolar microbial fuel cell stack equipped with biocathode was constructed. It provided a guideline for the designation of the large scale reactor for recalcitrant organic wastewater treatment. When the external resistance was1000Ω and the initial RB13concentration was50mg/L, the RB13removal rate and the total organic carbon (TOC) removal rate in this reactor were85.4±2.4%and33.4±3.4%respectively during8hours operation.This work focused on the development of a novel technology for recalcitrant organic wastewater treatment. By employing biocathode in a BES, recalcitrant organic pollutants were degraded effectively. Furthermore, the electron transfer mechanisms during the progress of pollutants degradation and the formation mechanisms of EAB biofilm were determined. This work extended the application of BES in wastewater treatment. |
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