Methane generation from chemically pretreated cellulose by anaerobic fluidized-bed reactors

Abstract

Alkali cooking of cellulose at 10% (w/v) consistency, performed at 250°C, gives a liquor containing organic acids as main components (lactic, acetic and succinic acids). A synthetic substrate, representative of this liquor, was used as feed for two anaerobic fluidized-bed reactors operating at 35°C. The effects of hydraulic retention time and influent substrate concentration on substrate consumption and methane generation were studied. Organic removals of up to 95% and methane generation rates of 1·09 litres CH 4 litre R −1 day −1 were achieved at a retention time ( θ R ) of 8·3h and at an influent substrate concentration of 1400 mg COD litre −1. At θ R = 3·5 h, conversion decreased to 60%. When feeding the cooked liquor, conversions were slightly lower, around 50% at θ R = 4 h and 1300 mg COD litre −1 of influent substrate concentration. However, the methane volumetric production rate was as high as 2·5 litres CH 4 litre R −1 day −1 under the same conditions. The results suggest that alkaline cooking with subsequent methane fermentation offers a viable process for the treament of cellulosic materials, such as municipal solid waste.