Anaerobic sludge exposure to stainless steel (SS316)

tainless steel (SS316) was incorporated into anaerobic sludge supplemented with glucose and CO2 as the sole carbon sources to explore its potential in enhancing direct interspecies electron transfer (DIET) and direct CO2 reduction via electron transfer from zero-valent iron (ZVI). Despite SS316's high conductivity and its inability to generate hydrogen, the methane (CH4) levels observed with its inclusion were similar to controls without SS316, around 47% with glucose and about 10% with CO2.Microbial community dynamics assessed through 16S ribosomal RNA (rRNA) sequencing revealed that the addition of SS316 did not significantly alter the composition of bacterial and archaeal communities. The dominant archaeal genera, Methanothrix and Methanolinea, remained consistent across various experimental conditions, indicating the microbial community's stability in the presence of SS316. Methanobacterium, although present, was detected in significantly lower amounts compared to the dominant genera.This stability extends to experiments involving both dewatered anaerobic sludge (DWAS) and anaerobic granular sludge that were independently enriched with acetic acid for about nine months. In these setups, despite different treatments, the microbial profiles were similar when exposed to CO2, with or without SS316. This included the similar methane production levels and the presence of Methanothrix as the predominant genus, followed by lesser quantities of Methanosarcina and Methanomassiliicoccus in the DWAS setup.These consistent microbial profiles across different experimental setups suggest that SS316 does not influence the microbial electron transfer processes substantially. The findings indicate that while SS316 does not disrupt existing microbial structures or enhance methane production, its role in facilitating DIET within these specific anaerobic environments appears limited.Future investigations may benefit from conducting targeted batch tests using SS316 to better elucidate its potential effects on DIET and direct electron transfer mechanisms in anaerobic microbial communities. This approach would be crucial in determining the practical applications of conductive materials like SS316 in biotechnological applications involving microbial consortia.