Unraveling the hydraulic regulation mechanisms in iron-carbon materials enhanced anaerobic digestion of kitchen waste: Insights from carbon and nitrogen metabolismlllk

This study investigated the effects of different rotation speeds on the performance, microbial communities, and carbon and nitrogen metabolism functions of an iron-carbon material-enhanced semi-continuous anaerobic digestion system for kitchen waste. The reactors were operated at 36 ± 1 °C, an organic loading rate of 2.51 g VS/L/d, and a sludge retention time of 45 d, with four stirring conditions of 20, 60, 80, and 120 rpm. The results showed that the 60 rpm group achieved the highest average methane production rate of 492.0 mL/g VS, which was 5%–7% higher than that of the other groups. Moderate stirring helped maintain stable concentration levels of volatile fatty acids and ammonia nitrogen. Community analysis showed that Chloroflexi, Bacteroidetes, Proteobacteria, and Firmicutes were the dominant bacterial phyla, while Methanothrix was the dominant methanogen. Functional analysis indicated that stirring at 60 rpm enhanced the potential for glycolysis, pyruvate metabolism, and volatile fatty acid metabolism, while promoting ammonia assimilation. Excessive stirring may enhance denitrification and intensify competition for carbon sources between denitrifying bacteria and methanogens.