Enhanced biomethane production via hydrodynamic cavitation pretreatment and co-digestion of brown and DAF sludge

This study introduces a co-digestion and vortex-based hydrodynamic cavitation (HC) pretreatment of brown and dissolved air flotation (DAF) sludge derived from dairy processing waste streams to enhance biomethane potential (BMP). Co-digestion experiments were carried out for varying ratios of brown-to-DAF sludge (1:1, 2%; 3:1, 4%). The BMP tests, conducted at 39 °C using a 15-reactor system with a 400 mL reaction volume and overhead stirrers, demonstrated that HC treatment elevated soluble chemical oxygen demand (sCOD) of brown and DAF sludges by over 34% after 80 passes through HC device. Combining DAF with brown sludge improved methane yields and reduced the time to reach peak BMP. Loading 2% volatile solids (VS) with a 1:1 ratio resulted in methane production exceeding 90% of theoretical BMP, surpassing individual brown and DAF sludge BMPs (73 and 84%, respectively). Maximum VS removal surpassed 85%, achieving a peak methane yield of over 717 mL/g-VS. These findings offer insights into addressing effluent treatment challenges and highlight the potential of co-digestion for enhanced waste valorisation.