Application of modified ADM1 to long-term experiments for methane/hydrogen production from model organic waste

The modified ADM1 including lactate and ethanol was verified using experimental data for methane/hydrogen production processes from model organic waste. Monosaccharides were presumably degraded into acetate, lactate, butyrate, and ethanol; lactate is further degraded into propionate and acetate; ethanol is degraded into acetate. The methane production experiment was carried out using an 8-L reactor operated at 55°C, pH 6.8, and sludge retention time (SRT) of 7–20 days for 370 days. Concentrations of carbohydrates, monosaccharides, butyrate, propionate, valerate, acetate, and the methane production rate were simulated well by the modified ADM1. The ratio of degradation pathways from monosaccharides to acetate, lactate, butyrate, and ethanol were inferred, respectively, to be 0.4, 0.6, 0.0, and 0.0. The hydrogen production experiment was carried out using a 2-L (1.5L) reactor operated at 35°C, pH 6.0-6.5, and SRT of 0.5–2.0 days for 370 days. The simulation results suggested that all bacterial populations except the sugar-degrading bacteria were washed out from the reactor because of the short SRT. The respective ratios of degradation pathways from monosaccharides to acetate, lactate, propionate, and ethanol were inferred to be 0.55, 0.0, 0.4, and 0.05 at pH 6.5 and 0.7, 0.2, 0.05 and 0.05 at pH 6.0.