Analysis of the anaerobic co-digestion of pine wood sawdust and pig manure for biogas production: Co-digestion of pine wood sawdust and pig manure

Globally, the conventional sources of energy, including fossil fuels, oil and natural gas are faced with challenges such as cost, depleted over time, scarcity, greenhouse gas emissions and public health menaces. Thus necessitates the search of renewable energy resources that will produce energy on a sustainable basis and protect the environment. Biogas technology utilizing biomass as substrates has been viewed as a promising strategy to address the adverse effects delineated above. We investigated the anaerobic co-digestion of mechanically pre-treated pine wood sawdust waste combined with pig manure in the ratio 1:3 in a 100L single stage steel bio-digester which was batch operated under atmospheric pressure and ambient temperature for a retention period of seven months. The total anaerobic and aerobic bacteria count and physicochemical parameters were evaluated via viable plate count and standard methods, respectively. Ideally, the temperature was measured by logging via a temperature sensor embedded into the slurry and connected to a Hobo data logger configured to log every one (1) minute interval. Data revealed that the pH ranged from 5.45-6.62 and the temperature was between 13.16 and 26°C. The total anaerobic and aerobic counts were 2.9 x 10⁶ cfu/g and 5.0 x 10⁶ cfu/g, respectively, at the point of charging, however, gradually reduced over the digestion period to 6.0 x10³ cfu/g and 1.27 x 10³ cfu/g, respectively. These showed that further treatment time would increase the chances of further reduction of microbial load. A linear regression model was established that predicted the influence of pH, the average temperature on log total bacterial count. The percentage total solids in saw dust, pig wastes and combined matrix were 74.34 and 28.19 and 5.2 %, respectively, whilst the percentage total volatile solids were 99.56, 92.86 and 96.7%, respectively. Results indicated that these undigested wastes contained biodegradable portion and relevant anaerobic microbes that anaerobically degraded the combined substrate to generate biogas. Biogas (2500cm³) was produced after 65days of digestion. Conclusively, co-digestion of sawdust with pig slurry expedited the breakdown of saw dust whose mono digestion is fraught with setbacks owing to its composition of cellulose, hemicellulose and lignin.