Microbial Dynamics and Biogas Production during Single and Co-digestion of Cow Dung and Rice Husk

Abstract

Anaerobic digestion is achieved by the combined effort of hydrolytic, acetogenic and methanogenic bacteria. Microbial dynamics and biogas production during anaerobic digestion of cow dung and rice husk were studied in this research. The experiment lasted for 30 days using a 10 L scale bio-digester. All proximate parameters reduced significantly after digestion for CD (cow dung), RH (rice husk), and CD:RH (cow dung and rice husk) except moisture content, which increased for all substrates. Ash content (1.08-1.67 mg) and crude fibre (1.27-1.96 mg) increased in CD only. The pH ranges for the substrates were CD (7.0-7.5), RH (6.1-7.6), and CD:RH (6.1-7.8). Temperature ranges were CD (27.4 ^oC-33.5 ^oC), RH (27.2 ^oC-33.3 ^oC) and CD:RH (27.3 ^oC-33.4 ^oC). The total biogas production of the substrates and components of each gas produced were, CD (4327.65 cm³ : 62.4 % CH₄, 37.4 % CO₂, 0.2 % H₂S), RH (150 cm³ : 100 % CO₂), and CD:RH (4730.55 cm³ : 73.8  % CH₄, 25.8 % CO₂, 0.4 % H₂S). Percentage distribution of the digester’s microflora include aerobes (40.75 %), anaerobes (31.25 %), fungi (25 %) and methanogenic bacteria (3 %). Hydrolytic bacteria and fungi isolated were Bacillus spp, Enterobacter spp, Pseudomonas spp, Proteus spp, Micrococcus spp, Aspergillus spp, Penicillium spp and Streptococcus spp. Acetogens isolated were Clostridium spp, Streptococcus spp and Pseudomonas spp. Methanococcus spp and Methanobacterium spp were the only isolated methanogens. Rice husk produced the least amount of biogas.