Effect of Feedstock Concentration on Biogas Production by Inoculating Rumen Microorganisms in Biomass Solid Waste

A methane production system with continuous stirred-tank reactor, rumen liquid as inoculate microorganisms, and paper mill excess sludge (PES) as feedstock was studied. The work mainly focused on revealing the effect of feedstock concentration on the biogas production, which was seldom reported previously for the current system. The optimal fermentation conditions were found as follows: pH = 7, T = 39 ± 1 °C, sludge retention time is 20 days, sludge with total solids (TS) are 1, 2, 3.5, 5, 10, and 13% in weight. Daily gas yields were measured, and biogas compositions were analyzed by gas chromatograph. Under such conditions, the optimum input TS was 10 wt%, and the biogas yield and volume gas productivity were 280.2 mL/g·TS and 1188.4 mL L^-1·d^-1, respectively. The proportions of CH₄ and CO₂ in the biogas were 65.1 and 34.2%. The CH₄ yield reached 182.7 mL/g VS (volatile suspended solid), which was higher than previously reported values. The findings of this work have a significant effect on promoting the application of digesting PES by rumen microorganisms and further identified the technical parameter.