Reutilization of Brewer’s Spent Grain as Spent Mushroom Substrate for the Generation of Biogas in a Semi-Continuous Digester

Abstract

In this work we explore the use of brewers’ spent grain 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 and (ii) brewers’ spent grain to feed the digester. We produced the mushroom using a mixture of sawdust and brewers’ spent grain and the resulting spent mushroom substrate was used to feed the digester. The mono-digestion of both substrates was carried out in 19 l semi-continuos biodigesters, in mesophilic conditions (35 °C), constant stirring of 200 rpm and a hydraulic retention time of 30 days. The start-up of biodigesters was carried out in stages. PH, volume and biogas composition were recorded daily. Accumulated biogas volumes of 59.97 l and 465.73 l were obtained for the spent mushroom substrate and brewers’ spent grain respectively. The yield and average methane composition produced were 35.95 l CH4/kgVS and 42% for spent mushroom substrate; while for brewers’ spent grain 265.495 l CH4/kgVS and 55% were obtained. The use of brewers’ spent grain, first as substrate for mushroom production, and then, using spent mushroom substrate 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 brewers’ spent grain is used directly. The results obtained from the use of brewers’ spent grain show that this substrate improves the yield of mushroom production and can be used for the production of biogas in semi-continuos biodigesters with a high performance.