Effects of adding osmoprotectant on anaerobic digestion of kitchen waste with high level of salinity

Anaerobic digestion of kitchen waste can be inhibited by a high concentration of Na⁺ in the substrate. The aim of this study was to determine the extent to which the effect of salinity during KW anaerobic digestion could be reduced by adding osmoprotectant. The results show that when Na⁺ concentrations were increased from 0 to 20 g/L, the yield of cumulative methane production decreased from 623.97 to 0 mL/g volatile solids (VS). Adding 2.0 and 2.5 g/L glycine betaine (GB) to reactors during anaerobic digestion of KW with concentrations of 5 and 10 g Na⁺/L were determined to be the optimal dosages to alleviate Na⁺ inhibition; this resulted in 29.07% and 63.49% improvements in methane yield respectively. The maximum soluble chemical oxygen demand reductions that resulted from adding 2.0 and 2.5 g GB/L to kitchen waste anaerobic digestion with 5 and 10 g Na⁺/L were 90.00% and 82.92%, respectively. Adding GB was helpful to both the production and degradation of acetic and butyric acids, which enhanced the rate of conversion of raw material to methane. Archaeal community changes between the medium and high salt concentration groups were revealed by high-throughput sequencing and by adding GB. The most abundant archaeal phyla in all samples were Euryarchaeota and Crenarchaeota. The hydrogenotrophic methanogens showed more salt tolerance than acetoclastic methanogens. The hydrogenotrophic pathway was predominant for methanogenesis of high-level Na⁺ inhibition anaerobic digestion.