Correlations between bacterial populations and process parameters in four full-scale anaerobic digesters treating sewage sludge

• Protein and lipid removals were positively intercorrelated while carbohydrate wasn’t.
• Bacterial diversity and evenness were lower in digesters with better performance.
• “Richness” of major bacterial genera was higher in digesters with better performance.
• Poor-performance digesters almost lacked fatty acid and protein-utilizing syntrophs.
• Putatively WAS-borne bacteria were more abundant in digesters with poor performance.

Process parameters and bacterial populations were investigated in four full-scale anaerobic digesters treating sewage sludge. Although the four digesters were operated under similar conditions, digesters A and B had higher pH (7.2–7.4) and lipid removal efficiencies (>50%) than C and D (pH 6.1–6.4; average lipid removal <16%). Bacterial richness, diversity, and evenness were higher in digesters C and D. Among the top-populated genera, ten (group I) were more abundant in digesters A and/or B; they were putative syntrophic fatty acid or protein/amino acid-utilizers. In contrast, fifteen others (group II) were less abundant in A and/or B and included potentially dormant/dead cells originated from activated sludge. Despite the overall richness trend, the presence of the 25 genera in groups I/II was greater in digesters A and B (24) than in C and D (17); this observation suggests that group I bacteria might be essential in AD of sewage sludge.

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