Enhancement of biogas production from cattle manure pretreated and/or co-digested at pilot-plant scale. Characterization by SEM

The aim of this study was to evaluate the enhancement of biogas production from cattle manure (CM) at pilot-plant scale using: a) ultrasound pretreatment (US) (520 kJ/kg Total Solids (TS); 409.59 kJ), b) co-digestion with crude glycerine (Gly) from the biodiesel industry (6% w/w), and c) US pretreatment (520 kJ/kg TS; 340.84 kJ), applied to the aforementioned mixture of both substrates prior to anaerobic co-digestion. The reactor used for this purpose was an Induced Bed Reactor (IBR), with a useful volume of 1250 L. Methane production from CM was enhanced by the application of low-energy ultrasound pretreatment (520 kJ/kg TS) (from 0.29 to 0.46 m3 CH4/kg Volatile Solids (VSadded)), and by co-digestion with Gly (from 0.29 to 0.44 m3 CH4/kg VSadded). The best results were obtained when the mixture of CM + Gly was pretreated by US (up to 0.59 m3 CH4/kg VSadded). Observation by Scanning Electron Microscopy (SEM) of the microstructural changes the CM underwent after pretreatment and/or co-digestion with crude glycerine enabled the discussion and justification of the results obtained in the present study.