Insights into the effects of micro and nanoscale Fe0 on elimination of excessive acidification during anaerobic digestion of the organic fraction of municipal solid waste: Similarities and differences in reactor performance and syntrophic metabolism

Fe 0 above the micro size (zero valent iron; ZVI) can effectively eliminate or inhibit excessive acidification during anaerobic digestion of the organic fraction of municipal solid waste, particularly at high organic loading rates. However, the role of nanoscale ZVI (NZVI) in anaerobic digestion remains controversial. In this study, the effect of NZVI at different dosages (0.4, 0.5, 0.6, 0.7, 0.8 g/g volatile solids [VS]) on the anaerobic digestion stability of the organic fraction of municipal solid waste was investigated and compared with the performance of ZVI, as were its effects on microbial syntrophism. Similarly to ZVI, NZVI recovered methane production from excessive acidification conditions, but the optimal NZVI dosage (0.4 g/gVS) was far lower than that for ZVI (0.8 g/gVS), and eventually the methane yield reached 324 mL/gVS. Microbial structure changes coupled with substance transformation revealed that NZVI enhanced the metabolism of hydrogenotrophic methanogens for interspecies hydrogen transfer and acetotrophic methanogens.