Anaerobic co-digestion strategies are needed to enhance biogas production, especially when treating certain
residues such as cattle/pig manure. This paper presents a study of co-digestion of cattle manure with
food waste and sewage sludge. With the aim of maximising biogas yields, a series of experiments were
carried out under mesophilic and thermophilic conditions using continuously stirred-tank reactors, operating
at different hydraulic residence times. Pretreatment with ultrasound was also applied to compare
the results with those obtained with non-pretreated waste. Specific methane production decreases when
increasing the OLR and decreasing HRT. The maximum value obtained was 603 LCH4/kg VSfeed for the
co-digestion of a mixture of 70% manure, 20% food waste and 10% sewage sludge (total solid concentration
around 4%) at 36 C, for an OLR of 1.2 g VS/L day. Increasing the OLR to 1.5 g VS/L day led to a
decrease of around 20–28% in SMP. Lower methane yields were obtained when operating at 55 C. The
increase in methane production when applying ultrasound to the feed mixtures does not compensate
for the energy spent in this pretreatment.