Effects of Substrate to Inoculum Ration on Biogas Production from Anaerobic Co-digestion of Office Paper and Cow Manure

Abstract

Anaerobic digestion can utilize renewable resources to produce energy in the form of biogas. Cow manure inoculum contains the microorganisms needed for this application and unrecycled paper waste can be used as a substrate. The use of these feedstocks together is not well studied. Finding ideal operating parameters and modelling biogas production is vital for future integration of anaerobic digestion. The use of various models when examining anaerobic digestion is important to ensure the best models are used for future research and industrial applications. Office paper and cow manure were combined at the different substrate to inoculum ratios with a total solids content of 6% at 38.4°C for 15 days. Four models (Time-Lag, No-Lag, Modified Gompertz, and Modified Logistic) were fitted to the experimental data to find which model best represented each biogas production process. Models varied in the accuracy of their fit to the data and no single model had the lowest RMSE values for each treatment. The digester containing a paper to manure ratio of 2:1 produced the most biogas (82 mL biogas/g VS), but the 5:1 reactor had the greatest biogas production potential over a longer period based on the model parameters (maximum cumulative biogas yield and biogas production potential). More biogas was produced in this study compared to other works reported in the literature, showing that this combination of co-digestion substrates could be expanded upon in the future. New models need to be examined or developed for these systems to better represent this co-digestion process for future research and commercial applications.