Creating Value Addition for MSW Biogas Plants: Increasing Mushroom Yields with Biogas Plant Digester Liquid

Abstract

Municipal solid waste (MSW) is a good feedstock for biomethanation in biogas plants. As most of the solids in MSW digest away in a biogas plant (BGP), a large liquid effluent or biogas digester liquid (BDL) is left behind. This needs disposal. It is rich in N, P, K, and micronutrients. In this study, we examined its influence on mushroom growth and yields and its potential to supplement some nutrients on an otherwise nutrient-deficient mushroom feedstock such as Paddy Straw. Spraying BDL on mushroom (Pleurotus djamor) bags after spawn-run stage reduced the time required to reach various growth stages namely, pinhead and fruiting body formation as well as reduced time for mushroom harvest. The biological efficiency of the BDL sprayed mushroom bags was 558.33% and that of water (Control) sprayed bags was 288.30%. This is the highest BE achieved so far. Spraying of BDL could narrow the C:N ratio with “locked” nitrogen in the form of bacterial carcass which in turn leads to faster growth and higher yields of the mushroom. The substrate (paddy straw) was also analyzed for dry matter loss and degradation of organic fractions. Lignin degradation of 76.64% was achieved in controls against 66.90% loss in the BDL sprayed mushroom bags, at the end of three flushes. There was higher cellulose degradation in the BDL sprayed bags (88.03%) as compared to the control (77.84%). This softened biomass could be further composted or be directed towards bioethanol production.