Effect of high pH and heat to eliminate Ascaris suum eggs in biogas sediment

• Quick lime (CaO) can be used to increase the pH and temperature in biogas sediment. • Under alkaline conditions, eggs of Ascaris suum can be heat-inactivated. • 15 min of treatment at 65 °C is sufficient for a 3-log reduction in viability. • Proposed protocol can be used to avoid the costly destruction of biogas sediment. According to European Union legislation, a hygienisation step is often required before using digestate or other materials from biogas reactors. The standard hygienisation protocol involves treatment at 70°C for at least one hour. However, alternative protocols are permitted if they can achieve the reduction targets for specific microorganisms. For thermochemical treatments, the required reduction target is a three-log reduction of the roundworm Ascaris sp . This thermochemical treatment can be applied to the bottom sediment of the reception pit or the reactor in biogas production. The objective of this study was to identify conditions for reducing Ascaris suum to acceptable levels as per legislation, enabling the treated sediment to be spread on arable land and avoiding the costly incineration process. The experiment utilized lime (CaO) and predefined temperatures to increase both the pH and temperature of the sediment. The results indicated that using 5% CaO maintained a stable pH above 12.5, and a 15-minute treatment at 65°C was sufficient for a three-log reduction of A. suum . These conditions, upon approval, can be adopted as national standard protocols for hygienisation of biogas sediment within the European Union and associated states, and potentially worldwide, depending on local legislation.