Continuous fermentative hydrogen production from sucrose and sugarbeet

To produce hydrogen by fermentation of biomass, a continuous process using a non-sterile substrate with a readily available mixed microflora is desirable. This work investigates a simple batch start-up procedure at pH 5.2 and 32°C, using anaerobically digested sewage sludge, and continuous hydrogen production from refined sucrose, pulped sugarbeet and a water extract of sugarbeet. Without heat treating the sludge, and with initial nitrogen sparging, a hydrogen producing culture was established within 5 days and remained stable during two experiments of 45 and 32 days duration. At 14–15 h retention time (16 kg total sugar m−3 d−1 organic loading rate) hydrogen yields for refined sucrose and pulped sugarbeet were, respectively, 1.0±0.1 and 0.9±0.2 mol/mol hexose converted. With nitrogen sparging hydrogen yields were 1.7±0.2–1.9±0.2 and 1.7±0.2 mol/mol hexose converted for refined sucrose and water extract of sugarbeet, respectively. Increasing ethanol concentration during operation on sugarbeet, and in some cases a higher redox potential (>−150 mV), correlated with lower hydrogen yield.