Effect of particle size, temperature, loading rate and stirring on biogas production from castor cake (oil expelled)

Abstract

The effect of particle size, temperature, loading rate and stirring on biogas production from oil-expelled castor cake was studied in 5-liter capacity single-stage fermentors protected from light at 30 and 37° C. Four particle sizes in the range less than 0·5 to 2·0 mm were used. The volumetric loading rates ranged from 4 to 12 g Total Solids per liter per day. Stirring of the cultures was continuous with a magnetic stirrer or intermittent with a platform shaker. The hydraulic retention time (HRT) was 15 days in all cases. The fermentors were fed once a day. The rate of production (liters of biogas per liter of fermentor per day) and the yield (liters of biogas per gram of Total Solids) were the criteria employed. Both rate and yield were higher with particles 2·0 to 1·4 mm and 0·5 mm, and less with particles of intermediate size; 1·4 to 1·0 mm and 1·0 to 0·5 mm. Both rate and yield were higher at 37° C than at 30° C. The optimal loading rate without stirring was 4 g of Total Solids per liter per day, and with stirring 8 g of Total Solids per liter per day at 37° C. Conversion of the feed calculated on the basis of Total Solids was 30% to 35%.