Development of microbial fuel cell for degradation of organic and inorganic containing wastewater and renewable energy recovery

Nitrate and dye wastewater pollution has been a serious environmental threat. The development of green technologies is in great need to overcome the environmental crisis. Microbial fuel cell (MFC) is emerging as a sustainable technology in the field of wastewater treatment to treat environmental pollutants with concomitant energy recovery. The main objective of this study was to develop MFC system for effective nitrate and azo dye wastewater treatment and bioelectricity production simultaneously. The results indicated that MFC was effective in removing nitrate while utilizing it as terminal electron acceptor to generate electricity. Besides, closed circuit MFC system demonstrated higher efficiencies in COD and nitrate removal than in open circuit system. The long term performance of MFC was evaluated and the maximum COD and nitrate reduction achieved were 82±4% and 88±4%, respectively, with power output of 669 mW/m3. Azo dyes were also utilized as terminal electron acceptors at the abiotic cathode in order to investigate the influence of dye’s structure on the decolourisation and power performance. The findings indicated that decolourisation rates of monoazo dyes were ∼50% higher than diazo dyes. This indicated azo dye with electron withdrawing group at para substituent to azo bond is more susceptible for dye reduction. A double chamber MFC reactor with continuous flow from anodic chamber to cathodic chamber was also developed to study the fate of electrons in MFC for azo dye decolourisation and bioelectricity generation. The study revealed that the increment in organic loading enhanced the decolourisation efficiency but deteriorated the power output ascribed to the competition between azo dye molecules and anode for electrons. This finding also corroborates that azo dye, New coccine (NC), was a preferable electron acceptor than anode. In addition, baffled MFCs (BMFCs) were designed and developed without membrane to further investigate the performance of the system. The results demonstrated that BMFC able to achieve up to 94% of decolourisation efficiencies for 300 mg/L of NC. The findings also discovered that 50 mg/L of NC loading improved ~53% of power density to 12.4 mW/m2 as compared to the dye-free condition. This suggested that the accumulation of dye decolourised intermediates could function as the redox mediator, subsequently the electron-shuttling mechanism of NC decolourised intermediate was proposed. The degradation pathway of NC was proposed based on the identified intermediates products via the UV-visible spectra, high-performance liquid chromatography and gas chromatography-mass spectrum analyses. The results indicated that the degradation of NC in MFC initiated with azo bond cleavage in the anaerobic anodic chamber, which led to the formation of aromatic amines. Then, further degradation of carcinogenic intermediates to less harmful lower molecular products occurred in the aerobic cathodic chamber of the MFC system.