Removal of organic matters and nitrogenous pollutants simultaneously from two different wastewaters using biocathode microbial fuel cell

Role of electrode and proton exchange membrane configurations on microbial fuel cell performance toward bioelectricity generation integrated wastewater treatment

In the present study, the effects of electrode surface area, proton exchange membrane area, and volume of the anodic chamber were investigated on the performance of five different dual chamber microbial fuel cells (MFC) using synthetic wastewater toward wastewater treatment coupled electricity generation. In the batch mode, the five different MFC's were operated with the anodic chamber volumes of 93-890 mL, 17.33-56.77 cm² electrode surface area, obtained volumetric power densities of 137.72-58.13 mW/m³, and unit area power densities ranging from 27.04 to 11.94 mW/m². Fed-batch studies were done with the MFC having 740 mL anodic chamber volume at different wastewater COD concentrations. The power density per unit area increased from 22.93 mW/m² to 36.25 cm² when the distance between electrodes was reduced from 10 to 6 cm. A maximum volumetric power density of 135.21 mW/m³ has been attained with a 6 cm electrode distance with the accomplished COD reduction of 93.21%. The presence of biofilm on the anode has been visualized through the SEM images. The higher COD concentration of wastewater and the fed-batch operation resulted in increased power output and wastewater treatment efficiency.

Progress in Nitrogen Removal in Bioelectrochemical Systems

Nitrogenous compounds attract great attention because of their environmental impact and harmfulness to the health of human beings. Various biological technologies have been developed to reduce the environmental risks of nitrogenous pollutants. Bioelectrochemical systems (BESs) are considered to be a novel biological technology for removing nitrogenous contaminants by virtue of their advantages, such as low energy requirement and capacity for treating wastewaters with a low C/N ratio. Therefore, increasing attention has been given to carry out biological processes related to nitrogen removal with the aid of cathodic biofilms in BESs. Prior studies have evaluated the feasibility of conventional biological processes including nitrification, denitrification, and anaerobic ammonia oxidation (anammox), separately or combined together, to remove nitrogenous compounds with the help of BESs. The present review summarizes the progress of developments in BESs in terms of the biological process, cathodic biofilm, and affecting factors for efficient nitrogen removal.

Enhancing the Electricity Generation and Nitrate Removal of Microbial Fuel Cells With a Novel Denitrifying Exoelectrogenic Strain EB-1

Microbial fuel cells (MFCs) have been tentatively applied for wastewater treatment, but the presence of nitrogen, especially nitrate, induces performance instability by changing the composition of functional biofilms. A novel denitrifying exoelectrogenic strain EB-1, capable of simultaneous denitrification and electricity generation and affiliated with Mycobacterium sp., was isolated from the anodic biofilm of MFCs fed with nitrate containing medium. Polarization curves and cyclic voltammetry showed that strain EB-1 could generate electricity through a direct electron transfer mechanism with a maximum power density of 0.84 ± 0.05 W m⁻². Additionally, anodic denitrification, as a concurrent metabolism, was demonstrated with an efficient removal rate of 0.66 ± 0.01 kg N m⁻³ d⁻¹ at a COD/N ratio of 3.5 ± 0.3. Importantly, voltage output was not negatively influenced by nitrate, indicating that the concurrent process of nitrate removal and electricity generation was a limitation of the electron donor rather than an inhibition of the system. Furthermore, various organic materials were successfully utilized as anode donors for strain EB-1, and demonstrated the exciting performances in terms of simultaneous denitrification and electricity generation. Mycobacterium sp. EB-1 thus expands the diversity of exoelectrogens and contributes to the potential applications of MFC for simultaneous energy recovery and wastewater treatment.

Hexavalent chromium removal and bioelectricity generation by Ochrobactrum sp. YC211 under different oxygen conditions

Bioremediation is an environmentally friendly method of reducing heavy metal concentration and toxicity. A chromium-reducing bacterial strain, isolated from the vicinity of an electroplate factory, was identified as Ochrobactrum sp. YC211. The efficiency and capacity per time of Ochrobactrum sp. YC211 for hexavalent chromium (Cr(VI)) removal under anaerobic conditions were superior to those under aerobic conditions. An acceptable removal efficiency (96.5 ± 0.6%) corresponding to 30.2 ± 0.8 mg-Cr (g-dry cell weight-h)(-1) was achieved by Ochrobactrum sp. YC211 at 300 mg L(-1) Cr(VI). A temperature of 30°C and pH 7 were the optimal parameters for Cr(VI) removal. By examining reactivated cells, permeabilized cells, and cell-free extract, we determined that Cr(VI) removal by Ochrobactrum sp. YC211 under anaerobic conditions mainly occurred in the soluble fraction of the cell and can be regarded as an enzymatic reaction. The results also indicated that an Ochrobactrum sp. YC211 microbial fuel cell (MFC) with an anaerobic anode was considerably superior to that with an aerobic anode in bioelectricity generation and Cr(VI) removal. The maximum power density and Cr(VI) removal efficiency of the MFC were 445 ± 3.2 mW m(-2) and 97.2 ± 0.3%, respectively. Additionally, the effects of coexisting ions (Cu(2+), Zn(2+), Ni(2+), SO4(2-), and Cl(-)) in the anolyte on the MFC performance and Cr(VI) removal were nonsignificant (P > 0.05). To our knowledge, this is the first report to compare Cr(VI) removal by different cells and MFC types under aerobic and anaerobic conditions.