Performance assessment of constructed wetland-microbial fuel cell for treatment of mariculture wastewater containing heavy metals

Abstract

Mariculture wastewater poses potential risks to the sustainability of the coastal environment. In this study, different types of constructed wetland-microbial fuel cells (CW-MFC), including up-flow CW-MFC (UCW-MFC), down-flow CW-MFC (DCW-MFC), and hybrid up-flow/down-flow CW-MFCs (HCW-MFC) were constructed to evaluate their efficiency to treat mariculture wastewater containing heavy metals (Cu and Zn). The results showed that both the UCW-MFC and DCW-MFC operated with aeration demonstrated better removal performance for conventional pollutants. The presence of heavy metals in wastewater reduced the removal of NH4+-N and total inorganic nitrogen, but had no significant effect on the removal of chemical oxygen demand (COD) and total phosphorus (TP). The HCW-MFC had better removal performance than the UCW-MFC and DCW-MFC, especially when treating heavy metal containing wastewater. All systems had excellent removal performance for (Cu2+ and Zn2+), resulting in concentrations below the first discharge standard. All the systems produced S2-, which could react with Cu2+/Zn2+ to form CuS/ZnS, leading to the removal of heavy metals from the systems. The average output voltage of the three systems was 561.64 ± 16.64 mV for UCW-MFC, 634.73 ± 9.33 mV for DCW-MFC, and 1074.88 ± 49.90 mV for HCW-MFC, respectively. In addition, the maximum power density (PAmax) increased by 160.81 % and 44.16 % in HCW-MFC compared to those of UCW-MFC and DCW-MFC systems, respectively. Further, connecting the three systems successfully derived a light-emitting diode to emit light, which indicated that CW-MFC systems have promising application prospects for both pollutant removal as well as energy recycling.