The traditional pig manure wastewater treatment in Taiwan has been low in methane production efficiency due to unstable influent concentration, wastewater volume, and quality. Two-stage anaerobic systems, in contrast, have the advantage of buffering the organic loading rate in the first stage (hydrolysis-acidogenesis phase), allowing a more constant feeding rate to the second stage (methanogenesis phase). Response surface methodology was applied to optimize the operational period (0.5–2.0 d) and initial operational pH (4–10) for hydrolysis and acidogenesis of the swine manure (total solid 5.3%) at 35 °C in batch operation mode. A methanogenesis verification experiment with the optimal condition of operational period 1.5 d and pH 6.5 using batch operation resulted in peak volatile acid production 7 g COD/L, methane production rate (MPR) 0.3 L-CH₄/L-d, and methane yield (MY) 92 mL-CH₄/g-CODre (chemical oxygen demand removed). Moreover, a two-stage system including a hydrolysis-acidogenesis reactor with the optimal operating condition and a methanogenesis reactor provided an average MPR 163 mL/L-d and MY 38 mL/g volatile solids, which values are 60% higher than those of a single-stage system; both systems have similar dominant methane-producing species of Firmicutes and Bacteroidetes with each having around 30%–40%. The advantages of a two-stage anaerobic fermentation system in treating swine manure for biogas production are obvious.

Anaerobic digestion is an effective technology to convert cellulosic wastes to methane and hydrogen. Heat-treatment is a well known method to inhibit hydrogen-consuming bacteria in using anaerobic mixed cultures for seeding. This study aims to investigate the effects of heat-treatment temperature and time on activated sludge for fermentative hydrogen production from α-cellulose by response surface methodology. Hydrogen and methane production was evaluated based on the production rate and yield (the ability of converting cellulose into hydrogen and methane) with heat-treated sludge as the seed at various temperatures (60–97°C) and times (20–60 min). Batch experiments were conducted at 55°C and initial pH of 8.0. The results indicate that hydrogen and methane production yields peaked at 4.3 mmol H₂/g cellulose and 11.6 mmol CH₄/g cellulose using the seed activated sludge that was thermally treated at 60°C for 40 min. These parameter values are higher than those of no-treatment seed (HY 3.6 mmol H₂/g cellulose and MY 10.4 mmol CH₄/g cellulose). The maximum hydrogen production rate of 26.0 mmol H₂/L/d and methane production rate of 23.2 mmol CH₄/L/d were obtained for the seed activated sludge that was thermally treated at 70°C for 50 min and 60°C for 40 min, respectively.