Enhanced methane production from ultrasound pre-treated and hygienized dairy cattle slurry

The effect of hygienization (70 °C, 60 min) and ultrasound (6000 ± 500 kJ/kg total solids (TS)) pre-treatments on hydrolysis and biological methane (CH(4)) potential (BMP) of dairy cattle slurry was studied. The BMP of the untreated slurry (control) was 210 ± 10 Nm(3) CH(4)/ton volatile solids (VS) added; after ultrasound pre-treatment it was 250 ± 10 Nm(3) CH(4)/ton VS(added) and after hygienization 280 ± 20 Nm(3) CH(4)/ton VS(added). The specific methanogenic activity (SMA) of the inoculum increased from 22 (untreated) to 26 (ultrasound treated) and up to 28 N ml CH(4)/g VS d, after hygienization. However, only hygienization achieved a positive net energy balance. Both pre-treatments increased the VS-based hydrolysis of slurry (10-96%), soluble nitrogen (N(sol)) content in digestates (20 ± 5%) and biodegradability of the slurry (8 ± 3%) as estimated via elevated VS removal.