The Effect of Feeding Frequency and Organic Loading Rate on the Anaerobic Digestion of Chinese Rice Straw

Abstract

Abstract China produces over 200 tonnes of rice straw (RS) a year. This is an underutilized energy source that is often burned in the fields causing pollution and health problems for populations near and far. Anaerobic digestion (AD) can produce methane (CH 4 ) rich biogas (45-55%) from waste RS as an alternative to burning whilst being affordable. Five 2L reactors were used to test the effect of feeding frequency (FF) and organic loading rates (OLR) on the anaerobic digestion of rice straw with input rates of between 5 feeds per week and one feed every 3 weeks. Two OLRs were used: 1gVS/L/d (OLR1) for 56 days and 2gVS/L/d (OLR2) for 83 days. At the lower OLR1, the best average biogas yield was 300 ml/L of reactor/d at 50% CH 4 and at OLR2 the best reactor achieved a mean biogas yield of 447 ml/L/d at 52%CH 4 . The best performing FF at OLR1 was 1/21 day whilst at OLR2 the 5/7 day FF produced the highest volume and quality of biogas. Results confirm that biogas from rice straw anaerobic digestion could be used with combined heat and power (CHP) technology to potentially produce 0.5-0.8MWh of electricity per day per tonne of rice straw.