Reutilization of brewer's spent grain as spent mushroom substrate for the generation of biogas in a semi-continuous digester

Abstract

Abstract In this work we explore the use of brewers' spent grain (BSG) to produce biogas after it was used to produce the edible mushroom Pleurotus pulmonarius within the concept of circular economy. We compare the production of biomethane obtained using: i) spent mushroom substrate (SMS) and ii) BSG to feed the digester. We produced the mushroom using a mixture of sawdust and BSG and the resulting SMS was used to feed the digester. The mono-digestion of both substrates was carried out in 19l semi-continuos biodigesters (SB), in mesophilic conditions (35°C), constant stirring of 200 rpm and a hydraulic retention time of 30 days. The start-up of SB was carried out in stages. PH, volume and biogas composition were recorded daily. Accumulated biogas volumes of 59.971 l and 465.73 l were obtained for the SMS and BSG respectively. The average methane composition was 42% for SMS and 55% for BSG. The methane yield obtained was 35.95 and 265.495 l CH4/KgVS for SMS and BSG, respectively. The use of BSG, first as substrate for mushroom production, and then, using SMS to produce biogas would not be a recommended practice if the main objective were the production of biogas. Since it is much more efficient to produce biomethane when BSG is used directly. The results obtained from the use of BSG show that this substrate improves the yield of mushroom production and can be used for the production of biogas in SB with a high performance.