Hydrodynamic Cavitation-Based Pretreatment of Primary Digestate: Feasibility and Role in Overall Enhancement of Valorization

Hydrodynamic cavitation (HC) is a promising biomass pretreatment technology for enhancing methane production from anaerobic digestion (AD). While HC has been widely studied for sludge and fresh biomass feedstock, its application to digestate remains largely unexplored. This study evaluates the impact of HC pretreatment on digestate from different sources to enhance biochemical methane potential (BMP) and biodegradability. The results demonstrate a significant increase in methane yield, with the BMP increase ranging from 100 to 200% after HC pretreatment. The biodegradability index improved almost 3 times, and sCOD increased >20% for all of the digestate samples, indicating enhanced substrate accessibility. Energy analysis revealed that the methane production energy yield (E_Yield) exceeded the HC-based pretreatment energy input (E_HC), with the highest E_Yield/E_HCratio of 9.18 at 40 passes, confirming HC as an energy-efficient strategy. The BMP data was interpreted by using appropriate kinetic models, which included the lag phase. The results demonstrated for the first time that HC pretreatment reduces lag phase and improves the rate as well as the BMP of primary digestate. This study provides valuable insights into the potential of HC pretreatment for digestate pretreatment to enhance biomethane recovery from the secondary digester and highlights its feasibility as an energy-efficient solution for improving the overall performance of AD plants employing secondary digesters.