Coupling effects of biochar and sediment microbial fuel cells on CH4 and CO2 emissions from straw-amended paddy soil

Abstract

Purpose: The independent incorporation of biochar and sediment microbial fuel cells (SMFCs) into paddy soil has been shown to reduce methane (CH4) emissions. However, the application of rice straw into paddy soil enhances the availability of labile carbon that stimulates methanogen growth, counteracting the mitigation effects of both methods. This study, therefore, aimed to investigate the effect of coupling biochar and SMFC on CH4 and CO2 emissions from straw-amended paddy soil. Materials and methods: Single chamber SMFC setups constructed using acrylic columns (height, 25 cm; inner diameter, 9 cm) with six treatments were established using soil amended with 0% (0BC), 1% (1BC), and 2% (2BC) biochar: with and without SMFC conditions. Stainless steel mesh (15 × 3 cm) and graphite felt (6 × 5 cm) were used as anode and cathode materials, respectively. Results: Cumulative emission of CH4 in the 0BC treatment with SMFC was 39% less than in that without SMFC. Biochar addition and SMFC operation together further reduced CH4 emission by 57% and 60% in 1BC and 2BC treatments, respectively, compared to that in the 0BC treatment without SMFC operation. The relative abundance of microbial communities indicated methane-oxidizing bacteria were enriched in the presence of biochar and hydrogenotrophic Methanoregula were suppressed by SMFC operation. This suggested that SMFC mainly inhibited CH4 production by outcompeting hydrogenotrophic archaea. Conclusion: The use of biochar made from leftover rice straw has an interactive effect on SMFC operation and both methods can be used to reduce CH4 emission from straw-amended paddy soil.