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• The food waste/cow manure (FW/CM) and substrate/inoculum (S/I) were optimized. • The optimum FW/CM and S/I ratios were changed after long-term acclimatization. • Key AD enzymes and lignocellulose activities were improved after acclimatization. • Variation in the microbial community in the codigestion sludge was analyzed. The effects of long-term acclimatization on the optimum food waste to cow manure ratio (FW/CM) and substrate to inoculum ratio (S/I) in anaerobic codigestion with FW and CM were investigated by batch trials. For the unacclimated sludge, the highest CH 4 yields of 646.6 and 653.4 mL/g VS were achieved under the optimum FW/CM (2.5 VS/VS) and S/I (0.07 VS/VS) ratios, respectively. After more than 550 days of acclimatization, the optimum FW/CM and S/I of the acclimated sludge were improved to 3.4 and 0.68 VS/VS with more anaerobic digestion enzymes and lignocellulose, respectively. Based on high-throughput sequencing analysis, the microbial community structures of bacteria, fungi, and archaea were changed, which was the main reason for the change in the optimum FW/CM and S/I. Therefore, the FW/CM and S/I should be periodically optimized during the long-term operation of codigestion to improve the codigestion efficiency for biogas production. [ABSTRACT FROM AUTHOR]

• Long-term acclimatization of anaerobic sludge was conducted with cow manure (CM). • Acclimated sludge showed stable microbial community and enzyme activity. • High-rate FW digestion and CH 4 production was achieved without continued CM addition. • Maximum CH 4 production was as high as 5.86 L/L/d with OLR = 16.8 g COD/L/d. • Continued enrichment of functional bacteria contributed to high-rate FW digestion. Long-term acclimatization of anaerobic sludge was conducted by operating a mesophilic continuously stirred anaerobic reactor (CSTR) with continuous feeding of food wastes (FW) and cow manure (CM). During the long-term acclimatization, continued increase of enzyme activity was revealed, while the microbial structure tended stable as shown by the Shannon index and microbial community. By biomethane potential analysis, the acclimated sludge had a methane yield about 13 times higher than the initial anaerobic sludge. The acclimated sludge was subsequently used for FW digestion with stepwise organic loading rate increase without CM addition. The functional phyla of Bacteroidetes and Proteobacteria, which originated from CM but not very abundant, were significantly enriched not only during sludge acclimatization with CM addition but also in the process of FW digestion without CM addition. A microbe coexistence network was proposed to support an explanation of the metabolic pathways of FW digestion using the acclimated sludge. [ABSTRACT FROM AUTHOR]

Cow manure (CM) was added to a dynamic membrane bioreactor (DMBR) operated under anaerobic condition for enhancing food waste (FW) digestion for over 300 days with stepwise increase of organic loading rates (OLRs) from 1.07 to 11.9 g COD/L/day. At a FW/CM ratio of 3.5:1 (based on volatile solids), the mixed liquor pH was always above 8.0 and no apparent volatile fatty acids (VFAs) accumulation occurred even at the highest OLR of 11.9 g COD/L/day (hydraulic retention time as 10 days and solid retention time as 15.5 days, correspondingly), indicating a very stable operation condition which resulted in an average CH 4 yield as high as 250 mL/g COD and CH 4 production as high as 2.71 L CH 4 /L/day. The hardly biodegradable organic components, such as cellulose, hemicellulose, and lignin, were effectively degraded by 78.3%, 58.8%, and 47.5%, respectively. Significantly high anaerobic digestion reaction ratios, especially the hydrolysis ratio which is usually the limiting factor, were calculated based on experimental results. Furthermore, the high lignocellulase contents and coenzyme F 420 levels, along with the decrease of cellulose crystallinity from 72.6% to 16.4% in the feedstock, provided strong evidence of an enhanced biological activity by CM addition. By high-throughput sequencing analysis, more abundant and diverse bacterial, archaeal, and fungal genera were identified from the DMBR sludge. With CM addition, the biodegradation of lignocellulose might have produced sufficient H 2 and CO 2 for the hydrogenotrophic methanogens such as Methanoculleus , Methanomassiliicoccus , and Methanobacterium , which were highly tolerant to ammonium inhibition, and then the elevated ammonium level would have provided high buffering capacity in the DMBR thus ensuring a stable condition for high rate FW digestion and CH 4 production. Image 1 • Long-term operation of a DMBR was conducted for FW digestion with CM as additive. • Steady pH and low VFA level were maintained with increasing OLR to 11.9 g COD/L/day. • CH 4 production continuously increased with increasing OLR up to 2.71 L/L/day. • More abundant and diverse bacteria, archaea and fungi were detected with CM addition. [ABSTRACT FROM AUTHOR]