The single factor method has been employed to investigate the impact of varying the H₂O₂ concentration, pretreatment temperature, and pretreatment time during alkaline hydrogen peroxide (AHP) pretreatment of vinegar residues prior to their anaerobic digestion. The optimal H₂O₂ concentration, pretreatment temperature, and pretreatment time were found to be 4%, 40 ℃, and 12 h, respectively. Under these optimal conditions, the highest cumulative methane yield was 302.0 mL/g (VS basis) and the biodegradation reached 70.0%, which was 54.4% higher than that for the untreated vinegar residue.

The single-phase anaerobic digestion of food waste suffers from systematic instability at high loading. Traditional indicators of acidification only give a belated warning. In this work, warning of acidification based on changes in pH value, gas production rate, and changes in amounts of volatile fatty acid (VFA) and extracellular polymeric substances (EPS) have been compared during anaerobic digestion of simulated food wastes. It was found that pH values and gas production have serious hysteresis effects. The amount of VFA is of limited use in early warning due to its wide variations in different systems and fermentation types. However, the EPS composition is closely related to the state of the microorganisms, and thus can response sensitively to acidification. After 18-20 h of anaerobic digestion, the content of extracellular polysaccharide decreased significantly, and the content of extracellular protein increased significantly. The ratio of protein to polysaccharide (PN/PS) increased continuously before acidification. Thus, the PN/PS ratio can be used as an early warning indicator of acidification, since it shows a response five hours before traditional indicators.

Hydrogen production in dark fermentation has been investigated using corn stover pretreated under different conditions. Two different reagents (1% H₂SO₄ and 2% NaOH) and different temperatures (40, 80, 120, 160 ℃, and 200 ℃) were used in the pretreatment of the corn stover. Dark fermentation experiments were carried out at mesophilic ((37±1) ℃) temperature, and the inoculum was the liquid fraction of digestate from an anaerobic digester composed of a continuously stirred tank reactor with pig manure as the raw material. The results showed that the optimal pretreatment used 1% H₂SO₄ at 80 ℃ for 60 min. The maximum hydrogen production and the maximum hydrogen production rate reached 27 mL/g (total solid, TS) and 15 mL/h, values which are 56% and 84% higher than the corresponding values for untreated corn stover, respectively. The optimum pH range for hydrogen production was found to be from 5.0 to 5.5. The fermentation types were all butyric type. Since the pretreatment temperatures can affect acid production and product composition, it is an important factor affecting hydrogen production in dark fermentation.

The anaerobic co-digestion of pig manure and KOH-pretreated corn stover has been investigated. The method of sampling every three days was used to analyze the performance parameters during the process of anaerobic digestion. The results showed that after KOH pretreatment, the maximum biogas production peak advanced by 3-6 days and the biogas production rate increased by 9.6%-65.6% compared to co-digestion of the untreated corn stover and pig manure. In addition, the cumulative methane production was 14 013.3 mL, which was 13.8% higher than that of the untreated material. The volatile solid removal ratio was 71.1%. The methane production process in anaerobic digestion could be fitted by the modified Gompertz equation. The methane production rate in the co-digestion of pig manure and KOH-pretreated corn stover group was 8.8% higher than that of the untreated material. Therefore, the anaerobic co-digestion of pig manure and corn stover can be improved by KOH pretreatment of the corn stover.

Anaerobic co-digestion has been carried out using eggplant stalks pretreated with alkaline hydrogen peroxide (PES) and two types of manure (pig manure, PM and chicken manure, CM) in varying proportions in order to investigate the effect on methanation performance. The results showed that co-digestion shortened the lag phase and peak times of the daily methane yield and the cumulative methane yield (CMY) increased with higher proportions of PM and CM. At PES/PM mass ratios of 1:1, 1:2, and 1:4 (volatile solid, VS basis), the CMYs were 283.4 mL/g, 338.8 mL/g, and 359.2 mL/g (VS basis), respectively. Compared to the CMY of PES alone, the CMY of the co-digested PES and PM increased by 24.7%, 49.1%, and 58.0% at PES/PM ratios of 1:1, 1:2, and 1:4, respectively. Similarly, in comparison with eggplant stalk (ES) alone, the CMY of the co-digested PES and PM increased by 187.7%, 243.9%, and 264.6% at PES/PM ratios of 1:1, 1:2, and 1:4, respectively. Moreover, co-digestion of PES and CM resulted in increases in CMY of 3.1%-26.5% and 137.9%-192.0%, respectively, compared to PES and ES alone.