Production of biogas and biomanure from the textile-processing residue, willow-dust, by dry anaerobic fermentation

Willow-dust is one of the solid cellulosic textile mill wastes available in large quantities. A batch fermentation method to process this material for the production of biogas and biomanure has been previously standardised. This process involves an initial aerobic fermentation of willow-dust treated with sodium hydroxide (1% w/w) and inoculated with slurry from anaerobically digested willow-dust followed by anaerobic fermentation with a substrate to liquid ratio of 1:6. With a 100 kg capacity biogas plant 17 m³ of biogas could be generated in 30 days. The spent slurry served as a good manure. The present work showed that it was possible to produce biogas as effectively as before with a substrate to liquid ratio of 1:1·5. The process was further improved by replacing most of the sodium hydroxide with lime to obtain an agriculturally suitable biomanure without affecting the biogas yield.