RESUMO
The aim of this work was to assess effect of saturated constructed wetland-Microbial fuel cell system on dissolved oxygen gradient, electricity generation and ammonium removal. Two laboratory-scale systems, one planted with Schoenoplectus californicus (SCW1-MFC) and other without plant (SCW2-MFC), were fed discontinuously with synthetic wastewater over 90 days. Both systems were operated at different organic loading rate (12 and 28â g COD/m2d) and ammonium loading rate (1.6 and 3.0â g NH4+- N/m2 d) under open circuit and close circuit mode. The results indicate that between lower and upper zones of wetlands the average values were in the range of 1.22 ± 0.32 to 1.39 ± 0.27â mg O2/L in SCW1-MFC and 1.28 ± 0.24 to 1.56 ± 0.31â mg O2/L in SCW2-MFC. The effect of operating mode (closed and open circuit) and vegetation on DO was not significant (p > 0.05). Chemical oxygen demand (COD) removal efficiencies, fluctuated between 90 and 95% in the SCW1-MFC and 82 and 94% in the SCW2-MFC system. Regarding NH4+- N, removal efficiencies were above 85% in both systems reaching values maximus 98%. The maximum power density generated was 4 and 10â mW/m2 in SCW1-MFC, while SCW2-MFC recorded the highest values (12 and 22â mW/m2).
RESUMO
Microbial fuel cells integrated into constructed wetlands have been previously studied. Nevertheless, their application as a suitable treatment for wastewater is still in the developmental stage. In this context, the aim of this study was to evaluate organic matter removal and nitrogen transformation by a microbial fuel cell integrated into a constructed wetland (CWMFC). To accomplish this, three experimental systems were operated under batch-mode conditions over 170â¯days: i) one was planted with Schoenoplectus californicus (P-CWMFC); ii) another was unplanted (NP-CWMFC); and iii) the third system did not have any electrodes (CW) and was used as a control. Chemical oxygen demand (COD) removal efficiency ranged between 74-87%, 69-81% and 62-72% for the P-CWMFC, NP-CWMFC and CW systems, respectively, with organic loading rates (OLR) ranging from 4.8 to 7.9â¯g COD/m2 d. NH4+-N removal efficiency exceeded 98%, 90% and 83% for P-CWMFC, NP-CWMFC and CW, respectively. Wastewater treatment performance was improved due to anaerobic oxidation that occurred on the anodes. Organic matter removal was 18% higher in closed-circuit mode than in open-circuit mode in both integrated systems (P-CWMFC and NP-CWMFC), and these differences were significant (pâ¯<â¯0.05). With respect to the performance of microbial fuel cells, the maximum power density (8.6â¯mW/m2) was achieved at an organic loading rate of 7.9â¯g COD/m2 d with an internal resistance and coulombic efficiency of 251â¯Ω and 2.4%, respectively. The results obtained in this work can provide positive impacts on CW development by enhancing anaerobic degradation without forced aeration.