Author(s)

Peter Tumutegyereize^1,2, Clever Ketlogetswe¹, Jerekias Gandure¹, Noble Banadda²

¹Department of Mechanical Engineering, University of Botswana, Gaborone, Botswana.
²Department of Agricultural and Biosystems Engineering, Makerere University, Kampala, Uganda.

This paper presents the results of batch anaerobic co-digestion of matooke, cassava, and sweet potato peels and vines. These agricultural wastes and others form the biggest portion of household wastes in developing countries. However, they have remained an unexploited resource amidst the ever increasing needs of clean energy and waste disposal challenges. Efforts to use them individually as biogas substrates have been associated with process acidification failure resulting from their fast hydrolysis. The aim of this work was to exploit agricultural wastes is co-digestion among themselves and assess their effect on methane yield and its kinetics, pH and hydraulic retention time (HRT). Sixteen ratios of Matooke peels (MP), cassava peels (CP) and sweet potato peels (SP) were assessed in duplicate. Methane yield and its kinetics, pH and HRT demonstrated dependence on the proportion of substrates in the mixture. Depending on the ratio mixture, HRT increased to 15 days compared to less than 5 days for single substrates, hydrolysis rate constant (k) reduced to a range of 0.1 - 0.3 d^-1 compared to single substrates whose k-values were above 0.5 d^-1, pH was maintained in the range of 6.38 - 6.43 and CH₄ yield increased by 15% - 200%. Ratios 2:1:0, 2:0:1, 0:1:2, 1:1:1 and 1:1:4 were consistent all through in terms of model fitting, having a positive synergetic effect on HRT, hydrolysis rate constant, lag phase and methane yield. However, more research is needed in maintaining the pH near the neutral for process stability assurance if household wastes are to be used as standalone substrates for biogas production without being co-substrates with livestock manure.

Co-Digestion, Household Wastes, Hydrolysis, Methane Yield, Kinetics

Tumutegyereize, P. , Ketlogetswe, C. , Gandure, J. and Banadda, N. (2016) Effect of Variation in Co-Digestion Ratios of Matooke, Cassava and Sweet Potato Peels on Hydraulic Retention Time, Methane Yield and Its Kinetics. Journal of Sustainable Bioenergy Systems, 6, 93-115. doi: 10.4236/jsbs.2016.64009.