Effects of particle size on anaerobic digestion of tomato solid wastes

Abstract

Laboratory digesters with operating volumes of 4 litres were used to assess the effect of particle size on methane gas production. Substrates consisted of tomato solid waste chopped to particle sizes of 1·3, 2·4, 3·2, 12·7 and 20 mm. These were fed at 3 g Volatile Solids per litre of digester per day to mesophilic digesters with retention times of 18 days. Greatest gas production and volatile Solids reduction occurred with the most finely chopped substrate, 1·3 mm. This substrate produced 0·81 volume of methane per volume of digester per day (vol/vol/day) with a Volatile Solids reduction of 60·3%. In contrast, the 20 mm substrate produced only 0·25 vol/vol/day of methane and Volatile Solids reduction was 21·1%. The rate of methane gas production appears to be inversely linear to the product of the substrate's average particle diameter and its geometric description, sphericity.