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 (CH4) potential (BMP) of dairy cattle slurry was studied. The BMP of the untreated slurry (control) was 210 ± 10 N m3 CH4/ton volatile solids (VS) added; after ultrasound pre-treatment it was 250 ± 10 N m3 CH4/ton VSadded and after hygienization 280 ± 20 N m3 CH4/ton VSadded. The specific methanogenic activity (SMA) of the inoculum increased from 22 (untreated) to 26 (ultrasound treated) and up to 28 N ml CH4/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 (Nsol) content in digestates (20 ± 5%) and biodegradability of the slurry (8 ± 3%) as estimated via elevated VS removal.

► Ultrasound pre-treatment and hygienization significantly increased the hydrolysis of dairy cattle slurry.
► Ultrasound pre-treatment and hygienization significantly increased the specific methanogenic activity of inoculum.
► Ultrasound pre-treatment and hygienization increased the biological methane potential of dairy cattle slurry.
► Hygienization produced a positive net energy yield via increased CH4 production.
► Ultrasound pre-treatment and hygienization increased the fertilizer potential of digestate.