Impact of cavitation destruction of cattle manure experiments on increasing methane yield in biogas and improving digestate quality in bioreactors under control system operating parameters

Abstract

This study aims to evaluate the effectiveness of a pilot-scale Raw Material Processing Unit (RMPU) that integrates hydrodynamic cavitation (HC), grinding, and heating to enhance anaerobic digestion (AD) of cattle manure and improve digestate nutrient recovery. Cavitation dynamics were modeled using the Rayleigh–Plesset equation, Bernoulli’s principle, and mass/energy balances to identify optimal parameters (σ ≈ 0.42 at 0.4–0.5 bar). A PLC-based control system was developed for real-time regulation of pressure, flow, and temperature. Semi-industrial experiments at the “Akzhar” farm (Kazakhstan) evaluated biogas yield, methane content, and digestate nitrogen, phosphorus, and potassium (NPK) concentrations before and after pretreatment. The RMPU increased biogas yield by 27.5 % (417 vs. 327 mL/g COD), methane content by 5.5 % (64.7 % vs. 59.2 %), and digestate NPK availability by 38–43 %. The time to peak methanogenesis was reduced by 37.5 % (5 vs. 8 days). The process remained stable with consistent pH and volatile fatty acid levels.Model-guided HC pretreatment, combined with automated control, reliably enhances AD efficiency and digestate agronomic value under farm-scale conditions.The compact RMPU can be integrated into existing agricultural biogas plants without major redesign, improving energy efficiency, reducing digestion time, and producing nutrient-enriched digestate suitable for sustainable and organic farming systems.