Enhancing the Valorization of Spent Pleurotus Substrate Through Anaerobic Digestion by Extracted Enzymes

Spent mushroom substrate (SMS) could be used as a substrate in anaerobic digestion (AD), but some studies have reported modest production and yield of methane. Several solutions have been proposed to mitigate this issue, such as co-digestion with other substrates, various pretreatments, and the use of additives. In this study we report for the first time the possibility of enhancing the process of methane production from spent Pleurotus substrate (SPS) using a pretreatment with enzymes recovered by a simple aqueous extraction from SPS. This represents an alternative to harsher chemical and physical pretreatment methods. The pretreatment increased the methane production from SPS by 16% at saturation, and a 25% faster anaerobic digestion process was obtained. After 2 days of AD, the methane volume for SPS + enzyme was 287 ± 9 NmL, approaching the maximum of 295 ± 14 NmL obtained for this variant, and was 39% more than SPS without pretreatment (207 ± 16 NmL). Pleurotus cultivation, AD, and the enzymes increased the crystallinity of the substrate. The enzymes increased the chemical oxygen demand, total carbon, and the concentration of pentanoic acid and 2-methyl-butanoic acid and decreased the concentration of hexanoic acid in the liquid digestate. The pretreatment increased, in general, the P and K content in the liquid and solid digestates. All data were compared with the hay used for Pleurotus cultivation.