Effects of water flow on performance of soil microbial fuel cells: Electricity generation, benzo[a]pyrene removal, microbial community and molecular ecological networks.

Soil microbial fuel cells with water flow (W-SMFCs) as a driven force of substrate transport were constructed. Electricity generation, benzo[a]pyrene (BaP) removal, microbial communities and microbial molecular ecological networks were compared between W-SMFCs and their control reactors (without water flow, C-SMFCs) in 240 days of operation. The W-SMFCs started up faster than C-SMFCs (37 days vs. 50 days) and output higher startup voltage (148.45 mV vs. 111.90 mV). The water flow caused higher removal efficiency of BaP at sites >1 cm from the anode (S > 1 cm) than at sites <1 cm from the anode (S < 1 cm) in W-SMFCs, whereas in C-SMFCs, the removal efficiency of BaP at S< 1 cm was higher than that at S> 1 cm. The removal efficiency of BaP at S> 1 cm in W-SMFCs was up to 1.7 times higher than that at S> 1 cm in C-SMFCs on the 91st day. After 240 days of operation, the biodegradation efficiency of absolute BaP amount was 45.95% in W-SMFCs, being 20% higher than that in C-SMFCs (38.17%). Moreover, the water flow caused highly tight interaction among the microbial species, which could be beneficial to BaP biodegradation. Conclusively, the water flow in soil was very beneficial for startup and biodegradation of BaP in SMFCs.