The importance of temperature in the inactivation of seeds in biogas reactors

Abstract

Weed seeds can enter the biogas reactor by the harvest of biomass or by animal manure. All seeds that enter the biogas process chain and survive anaerobic digestion can be spread with the digestate. The inactivation of seeds in the biogas reactor is mainly due to temperature. In comparison of a laboratory-scale biogas reactor and a water bath experiment, we tested the contribution of temperature in the inactivation of seeds from one hardseeded and one non-hardseeded species. On average, as few as 20 % of the tomato seeds, which are used as an indicator species for the sanitation of fermentation plants, survived the maximum exposure time in the reactor and water bath. In the reactor the seeds lost their viability quicker than could solely be explained by temperature. Viability of the hardseeded species, Melilotus albus, declined to 70 % after the maximum exposure time of 12 days. The decline was similar in water baths and reactor. Inactivation of M. albus seeds was mainly due to temperature. For tomato seeds, factors other than temperature must have contributed to inactivation. Tomato appears to be no appropriate indicator for inactivation of (hardseeded) seeds in biogas reactors.

Keywords

• biogas reactor
• hardseededness
• temperature
• tomato
• water bath