Optimization of biogas production from cattle manure by pre-treatment with ultrasound and co-digestion with crude glycerin

Abstract

Biogas production by co-digestion of cattle manure with crude glycerin obtained from biodiesel production was studied after pre-treatment of the cattle manure or mixtures of cattle manure with different amounts of added glycerin with ultrasound. Batch experiments with 1750mL of medium containing 1760g of screened cattle manure or mixtures of cattle manure (screened or ground) and 70–140mL or crude glycerin were incubated under mesophilic and thermophilic condition in stirred tank reactors. Under mesophilic conditions, the addition of 4% glycerin to screened manure increased biogas production by up to 400%. Application of sonication (20kHz, 0.1kW, and 4min) to a mixture of manure+4% glycerin increased production of biogas by up to 800% compared to untreated manure. The best results were obtained under thermophilic conditions using sonicated mixtures of ground cattle manure with 6% added glycerin (348L methane/kg COD removed were obtained).