Efficiency Of Wastewater Treatment And Electricity Generation In A Microbial Fuel Cell Coupled Constructed Wetland System

Both constructed wetlands(CWs) and microbial fuel cells(MFCs) rely on microorganisms to remove contaminants in wastewater. The anode area is anaerobic and the cathode area is aerobic, the redox conditions can be naturally developed in CWs. As a recently emerged technology, CWs combined with MFCs(CW-MFC) system has a double-effect of wastewater treatment and electricity generation. From the limited publication, the single-stage and 2-stage vertical flow CW-MFCs have been studied. In this study, a hybrid CW-MFC system of vertical and horizontal flow CWs embedded with MFC operated in series was set up to characterize its performance for swine wastewater treatment and electricity generation.In the system, a vertical upflow CWs served as 1st stage while a horizontal subsurface flow CWs served as 2nd stage. The influent was pumped into the 1st stage and the effluent flowed into the 2nd stage by gravity. The dewatered alum sludge cakes(derived from a local drinking water treatment plant) were used as the main wetland substrates. The electrodes were made of Stainless steel mesh. Both the cathode electrodes were semi-submerged acting as air-cathode to improve aerobic environment of the cathode area. The experiment was run continuously and separated into three periods with average swine wastewater influent COD concentration of 412±25.1mg/L and 603±6.8mg/L for swine wastewater and 633±7.3 mg/L for synthetic wastewater. The system was run for180 days at room temperature(20℃~25℃). Influent and effluent water quality and voltage etc. were monitored.The overall removal efficiency of COD, SS, TN, NH4+-N, NO3--N, TP and PO43--P was 69±24.0%, 76±12.4%, 47±19.7%, 59±28.3%, 69±25.6%, 85±9.5% and 88±8.7% respectively. Both the stages continuously generated electrical power during the operation with average voltages of 0.435±0.091 v and 0.338±0.092 v, power densities of 33.3±13.81 m W/m3 and 8.97±2.51 m W/m3, separately. The average NERs of 1st stage and 2nd stage are 0.912±0.164 Wh/kg·COD and 2.763±0.699 Wh/kg·COD.The results indicated that 2-stage CW-MFC system has higher removal efficiency than single stage system, but not superior than 2-stage VF-CWs since the lower vertical height and refractory organics in effluent of stage 1. More sets of electrodes could extract more energy from wastewater.