Effect of particle size on biogas yield from sisal fibre waste

The degradation and biogas production potential of sisal fibre waste could be significantly increased by pre-treatment for reduction of particle size. Batch-wise anaerobic digestion of sisal fibre waste was carried out in 1-l digesters with fibre sizes ranging from 2 to 100mm, at an ambient temperature of 33°C. Sediment from a stabilisation pond at a sisal production plant was used as starter seed. Total fibre degradation increased from 31% to 70% for the 2mm fibres, compared to untreated sisal fibres. Furthermore, the results confirmed that methane yield was inversely proportional to particle size. Methane yield increased by 23% when the fibres were cut to 2mm size and was 0.22m3 CH4/kg volatile solids, compared to 0.18m3 CH4/kg volatile solids for untreated fibres. By anaerobic digestion and biogas production, the 148,000tonne of waste sisal fibres generated annually in Tanzania could yield 22millionm3 of methane, and an additional 5millionm3 of methane if pre-treatment by size reduction to 2mm was applied.