Immobilization methods for continuous hydrogen gas production biofilm formation versus granulation

Hydrogen gas was continuously produced by treating glucose-containing synthetic wastewater with sewage digester sludge. The activity of methanogenic bacteria in the sludge was repressed by pH-control at 5.0 under anaerobic conditions. For efficient continuous hydrogen production, two immobilization methods were employed, biofilm formation on poly vinyl alcohol (PVA) and granulation of the sludge with cationic and anionic polymers. Acetic acid was the dominant fatty acid in the early operation stage in both cases. In the case of the biofilm, biogas production at 20 h hydraulic retention time was severely repressed to around 50 ml/L-reactor/h when propionic acid was sharply increased after 20 days of operation. In the case of granular sludge, propionic acid was produced only during the early operation stage and the biogas production rate was maintained at around 300 ml/L-reactor/h at 20 h of hydraulic retention time. The hydrogen gas content in the biogas was in the range of 40-60% and no methane was detected either case. Since granular sludge harboured more microorganisms and its density was higher than the biofilm on PVA medium, granulation was considered to be a better method for continuous hydrogen gas production.