Effects of different particle size of zero-valent iron (ZVI) during anaerobic digestion: Performance and mechanism from genetic level

Abstract

Although zero valent iron (ZVI) has been widely studied as an additive in anaerobic digestion, the effect of ZVI particle size on anaerobic methane production and the mechanism by which this occurs have not been reported. This study investigated the effects of ZVI particles with different diameters (0.1 μm to 250 μm) on the glucose-substrate anaerobic digestion process. It was found that different particle sizes of ZVI had different optimal dosages, as 2 g/L of 48 μm ZVI increased methane production by 84.12% when compared with the blank group, whereas ZVI of 0.1 μm reached its optimal dosage at 0.5 g/L, increasing methane production by only 37.32%. Further study of the mechanism showed that 4 μm ZVI could increase the abundance of bacteria Bacteroidota and Proteobacteria (from 1.46% and 0.07% to 15.56% and 2.27%, respectively) and Archaea Methanosaeta (from 3.59% to 51.64%). Gene’s prediction showed that ZVI particles with a size range of 4–48 μm could facilitate cell replication and increase enzyme activity involved in methane production. Additionally, it could mediate direct interspecies electron transfer between fermentative bacteria and methanogens while avoiding cell lysis caused by the nano effect.