Biogas potential determination and production optimisation through optimal substrate ratio feeding in co-digestion of water hyacinth, municipal solid waste and cow dung

Abstract

Modelling and optimisation of biogas production from different substrate mixtures is lagging behind in research and development. Current biogas production processes are not fully exploiting co-digestion of multifaceted biomaterials with manures and other biowastes. A model is presented for the determination of biogas production potential from water hyacinth (WH), municipal solid waste (MSW) and cow dung (CD) as well as the subsequent optimisation of the co-digestion mix ratios of these substrates. In this study biogas is assumed to comprise of methane, carbon dioxide, ammonia and hydrogen sulphide. Baseline biogas potential yields of 747.4 ml/gVS, 790.83 ml/gVS and 884.24 ml/gVS were obtained from WH, MSW and CD, respectively. A linear programming mathematical optimisation was done. The objective is to find substrate blend ratios in the co-digestion mixture that maximises biogas production. Optimal co-digestion results in percentage substrate blending ratios of 53.27:24.64:22.09 for WH, MSW and CD, respectively in a case study. One kilogram of substrate mixture yields 124.56m3 of biogas which translates to 124,560 ml/gVS. Co-digestion and optimisation of substrate blend mix proportions increased the biogas output by 157.11%. The biogas fratenity benefits in having an informed optimal co-digestion model that foretells substrate blending ratios.