Enhancing BMP and digestibility of DAF sludge via hydrodynamic cavitation

This study addresses fats, oils, and grease bioconversion challenges in dissolved air floatation (DAF) sludge from dairy processing waste streams. A hydrodynamic cavitation (HC) based pre-treatment method was developed for enhanced anaerobic digestion of DAF sludge. Bench-scale pre-treatment experiments were carried out using a vortex-based HC device at 20 L/min and 250 kPa pressure drop. Influence of severity of the pre-treatment (number of passes through HC device) and substrate concentration on biomethane potential (BMP) was quantified. The study revealed that soluble chemical oxygen demand (sCOD) increases with number of passes (34 % after 80 passes). Higher sludge concentration was found to increase the lag time observed in the BMP data. It was possible to tolerate 3 % VS sludge. The pre-treatment showed a notable increase in BMP, exceeding 82 % of theoretical BMP, with VS removal surpassing 73 %. The highest methane yield achieved was 756 mL/gVS of sludge. The net energy gain (after subtracting energy required for pre-treatment) was found to be more than 100 kWh/ton of sludge. The developed pre-treatment process and presented results provide a basis for the effective valorisation of DAF sludge, promoting a circular economy approach.