Effects of pH buffering agents on the anaerobic hydrolysis acidification stage of kitchen waste

This study investigated effects of initial pH buffering agents on the lab-scale anaerobic hydrolysis acidification stage of kitchen waste (KW). Different cheap, available and suitable buffering agents (NaOH(s), NaOH(l), CaO(s)-NaOH, KOH(l)-NaOH, K2HPO4(s)-KOH, Na2CO3(s)-NaOH) were added under optimal adjusting mode (first two days: per 16 h, after: one time per day) which was obtained in previous work. The effects of buffering agents were evaluated according to indexes of pH, VFAs, NH4+-N, TS, VS, VS/TS, TS and VS removal rate. The results showed treatment 5 with adding K2HPO4-KOH buffering agents had the most stable pH (6.7-7.0). Also treatment 5, 2, 4 and 6 provided stable pH ranging in 5-8. Among the treatments, treatment 6 with adding Na2CO3 as initial buffering agents and 10 mol/L NaOH as regulator was chosen as the optimal mode for highest VFAs content (44.05 g/L) with high acetic acid and butyrate acid proportion (42.64%), TS and VS removal rate (44.84% and 58.67%, respectively), low VS/TS ratio (58.55), fewer adding dosage and low adjusting frequency. The VFAs content of treatment 6 at the end of hydrolysis acidification stage could be used for methanogenic phase of anaerobic two-phase digestion. Thus, treatment 6 (adding Na2CO3 as initial buffering agents and 10 mol/L NaOH as regulator) with highest VFAs content and TS and VS removal rate could be considered using in anaerobic hydrolysis acidification stage pH adjustment.