Sludge composition and characteristics shaped microbial community and further determined process performance: A study on full-scale thermal hydrolysis-anaerobic digestion processes.

• Adjusting OLR alone is not sufficient in designing and operating TH-AD process, NH 4 +-N and VFAs should be equally considered. • NH 4 +-N, VFAs and tCOD in feed sludge were the most influential factors for AD microbial community structure. • Higher diversity of microorganisms and methanogens that adapted to more diverse substrate transformation pathways could lead to superior performance. • Microbial community information could help the precise design and operation of full-scale TH-AD process. Anaerobic digestion (AD) with thermal hydrolysis (TH) pretreatment is a promising process for excess sludge treatment, while there lacks of the knowledge from full-scale process about the impact of sludge composition and characteristics on microbial community and performance. The sludge physiochemical indices, microbial community and performance data of four full-scale TH-AD plants were characterized, and their relationships was elucidated. The four plants were operated under almost similar total organic loading rate (OLR) but their methanogenesis performance differentiate into two groups, namely superior group (SupG) and the inferior group (InfG). In both groups, TH effectively solubilized particulate organic compounds, meanwhile raised the ammonia nitrogen (NH 4 +-N) and volatile fatty acid (VFA) concentration. Compared with the SupG, thermal hydrolyzed sludge of InfG had higher level of VFAs, NH 4 +-N and total chemical oxygen demand (tCOD), which showed higher inhibition effect on microbes, leading to a community with lower diversity, lower abundance of carbohydrate degrading functional guild, higher protein degrading one, and methanogens that adapted to limited substrates, and further declined the methane production rate. Thus, it was recommended that OLR alone was not sufficient for controlling the system in design and operation, the concentration of VFAs, NH 4 +-N and tCOD should be equally considered. Their higher concentration, together with the higher abundance of Defluviitoga and Proteiniphilum were recommended as indicators for inferior running condition. Our results proposed that microbial communities played a role of bridge between environmental factors and performance, provided implications for engineering ecology and operational regulation for full-scale sludge TH-AD process. [Display omitted] [ABSTRACT FROM AUTHOR]