Importance of natural pyrite in treating carbon-constraint wastewater by constructed wetland-microbial fuel cells

Pyrite is regarded as a natural electron donor and can potentially enhance autotrophic nitrogen removal and electricity generation. However, few studies have been devoted to exploring the feasibility of pyrite in treating carbon-constraint wastewater by constructed wetland-microbial fuel cells (CW-MFCs). In this study, two CW-MFCs with pyrite as anodic filling materials were constructed to treat wastewater with low-carbon sources (e-PCW1) and without carbon sources (e-PCW2). In the e-PCW2, the removal efficiency of nitrogen and phosphorus was 11.44 %–15.79 % and 79.79 %–84.35 %, respectively. The e-PCW1 system removed up to 63.56 % nitrogen and 86.37 % phosphorus when the aeration rate and COD loading were 0.2 L/min and 180 mg/L, respectively. The best electricity generation was also obtained during this stage. The enhanced nitrogen removal in e-PCW1 was attributed to the higher abundance of Thauera, a denitrifying and sulfate-reducing bacterium, while phosphorus removal relied on chemical precipitation and the contributions of Candidatus_Competibacter and norank_o__Run-SP154. In conclusion, pyrite can play a significant role in enhancing pollutant removal efficiency and electricity generation of CW-MFCs, especially for treating carbon-constrained wastewater.