Membrane Bioreactor-Desalination Microbial Fuel Cell Hybrid System

Abstract

The microbial desalination fuel cell (MDFC) is an emerging desalination technology offering great promise of high salinity removal with zero energy input. Moreover, the membrane bioreactor (MBR) is of great reliability in treating domestic and industrial wastewater. The objective of this work is to introduce a hybrid system of a membrane bioreactor and a microbial desalination fuel cell for simultaneous wastewater treatment, seawater desalination and production of electricity. This hybrid system allows low cost resources, energy conservation and low sludge and carbon footprints. Synthetic wastewater, exoelectrogenic microorganisms (yeast) and substrate (glucose) were employed as the anode feed in the MDFC. Two system configurations with an immersed MBR and side-stream MBR have been proposed and compared. In addition, the hybrid system was studied under open circuit (no external load) and closed circuit modes (three different resistive loads). This research presents the success of the hybridization in comparison with a MDFC employing only yeast solution as the anolyte. In addition, it investigates the effect of some modifications namely, the cell size, solutions volume ratio and type of ion exchange membrane. Experimental tests revealed that a bench scale system of 350-ml chamber capacity can achieve higher salinity removal (+6%) and voltage production (+0.035 V) than its alternative 4500-ml chamber. Also, reducing the volume of seawater to anolyte and catholyte volumes by 29% accomplished higher desalination by 6% for the hybrid system removing almost 20% of the salts in 8 days. A total desalination rate (TDR) of 6.25 mg/hr, and a power density of 4.34×10-3 W/m3 are obtained using a 300-KΩ external resistance. On the other hand, a power density of 0.222 W/m3 and 4.69 mg/hr TDR are achieved using a 4-KΩ external load. Thus, the choice of external resistance involves a trade-off between desalination efficiency and power generation. With regards to wastewater treatment by the MBR, the system was evaluated in terms of total dissolved solids (TDS), total suspended solids (TSS), Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD) and turbidity for the permeate water. The effluent quality enhanced by more than 50% except for the COD and BOD analyses. MDFCs are good alternatives to the energy intensive desalination methods.