Production of biogas from sugarcane residues

Abstract

Due to high production costs facing South African sugar manufacturing industries, production of sugar alone may not be profitable. For sugar manufacturing industries to be economically viable, a novel approach research on other value-added potential products is of paramount importance. The aim of this work was to conduct a feasibility study on biogas production from anaerobic digestion (AD) of sugarcane bagasse, molasses and leaves using cow dung as co- substrate.

Three sets of 12 independent batch laboratory experiments for each residue were carried out at temperature of 35oC and hydraulic retention time (HRT) of 14 days using 500 ml bottles as digesters. Design-Expert software was used for design of experiment, process optimisation and process modelling. One variable at a time (OVAT) and 2-Dimensional (2-D) graphical analysis methods were used to analyse the effects of cow dung to sugarcane residues (C:SR) feed ratio, media solution pH and digester’s moisture content on biogas volume, methane yield and kinetic constants.

The results indicated that the effect of C:SR feed ratio, media solution pH and digester’s moisture content on biogas volume, methane yield, biogas production potential, maximum biogas production rate and lag phase is mutually reliant between all variables, i.e., depended on conditions of other process variables. The optimum biogas volume generated by bagasse, sugarcane leaves, and molasses experiments were found to be 305.87 ml, 522.69 ml and 719.24 ml and respectively. The results showed that the optimum methane yield achieved by bagasse, sugarcane leaves, and molasses experiments were 28.75 ml/gVS, 87.18 ml/gVS, and 85.32 ml/gVS respectively. The overall results showed that sugarcane bagasse, molasses and leaves can be potentially converted into biogas through AD process.