| Bioelectrochemical systems (BESs) are gaining increasing attentions in many areas for the past few years. The two main applications of BES are:wastewater treatment, biosensor, a research platform for electrochemically active bacteria study, greenhouse gas reduce and bio-energy production. The work present in this thesis focuses on innovations in BES based wastewater treatment.Firstly, we exploited the reducing power in the cathode chamber of a microbial fuel cell (MFC) to treat Cr6+containing electroplating wastewater. The operation parameters are optimized to improving both the treatment efficiency and output power density. A real electroplating containing 204 ppm Cr6+ was treated in this system with a graphic paper electrode at pH=2. In 25 h,99.5% Cr6+ and 66.2% total chromium were removed under the optimized condition. Electrical power could be recovered simultaneously with removing Cr6+. A maximum power density of 1600 W/m2 could be produced in this process. The mechanism of chromium ion removal was also studied in our work. By analyzing the deposition on the cathode surface with X-ray photoelectron spectroscopy (XPS), we found chromium ion was removed in the form of Cr2O3.To treat wastewater containing refractory pollutant by taking advantage of both anode and cathode in BES, we developed an anaerobic-aerobic (A/O) sequential reactor and MFC coupled system (A/O-MFC). An azo dye (Congo red) containing wastewater was treated in the A/O-MFC.1000 mg/1 glucose and a hydraulic retention time of 14.8 h were determined as the best operational condition. Under the optimized condition, the COD and color removal could achieve 92.7% and 94.1%, respectively. Simultaneously with azo dye removal, the maximum power density produced in this process was 552 mW/m2。The UV-vis and GC-MS results indicated that the azo bond could be cleaved in the anode chamber and the amine compound produced in the anode chamber was removed in the cathode chamber. Furthermore, to make BES more suitable for industrial application and overcome the disadvantage of conventional membrane-less MFCs, we developed an over-flow type wetted wall MFC (WWMFC). The new design could efficiently eliminate oxygen diffusion from cathode to anode and thus resulting in high columbic efficiency. Under the optimized operational condition, the maximum power density was 18.21 W/m3 and the highest columbic efficiency achieved in WWMFC was 39.5%.Besides WWMFC, we developed laminar flow microfluidic device based membrane-less MFC by taking the advantage of laminar flow in microfluidic channel to separate anode and cathode. The maximum power density can be produced in this reactor was 378.12 W/m3. The laminar flow microfluidic BES was also used to study the immediate effect of short term chemical shock on microbial electrochemical activity in wastewater treatment processes. Immediate responses of Geobacter sulfurreducens electrochemical activities to six different chemical stimuli were tested in this device. The results indicated that anthraquinone disulfide could shuttle electrons between G. sulfurreducens and the electrode and short term exposure to oxygen would not cause irreversible damage to G. sulfurreducens.To logically control BES based wastewater treatment processes and reacrors, we developed an electrochemically active bacteria based logic AND gate. The logic AND gate was built within a potentiostatically controlled three-electrode system. Pseudomonas. aeruginosa PA 14 lasl/rhll double mutant was chosen as the core part of the logic AND gate, two quorum sensing signal molecules were used as two input signals. These two biochemical molecules were processed through the quorum sensing cascade system and were eventually converted into a clear electric current signal by logically controlling the electron shutter production. In addition, the same logic AND gate was operated in MFC mode. This made the logic gate a self-powered biosensor. This work could be a valuable example for accurate, in-situ and real-time monitoring BES based wastewater treatment.
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