The effect of organic loading rates (OLRs) on the performances of food wastes and maize husks anaerobic co-digestion in continuous mode

A continuous anaerobic digestion experiment was carried out to investigate the co-digestion of 75% food waste and 25% maize husk at different organic loading rates (OLRs) of 1-4.5 gVS/L/d. Results obtained showed that pH fluctuated between 7.3 and 7.5 and total alkalinity (TA) between 0.4 and 6.7 g CaCO3/L, indicating that the system was not inhibited by acidification. The range of the ratio of volatile fatty acid (VFA) to TA of 0.06-0.25 was also well below 0.4 and showed that the anaerobic co-digestion was stable and feasible. Though there was no significant difference (p < 0.05) between biogas yields at OLRs of 3.5 and 4.5 gVS/L/d, the methane content at OLR of 4.5 gVS/L/d was higher than that of 3.5 gVS/L/d and suggests that carbon dioxide producing microorganisms were more active in OLR of 3.5 gVS/L/d. The OLR of 4.5 gVS/L/d was therefore found to be the most satisfactory for large scale operation of anaerobic digesters for co-digestion of food waste and maize husk. From a separate batch test, the average biogas yield of 0.50 ± 0.04, 0.24 ± 0.02 and 1.31 ± 0.07 L/gVS were obtained from digesters A, B and C, respectively, indicating that the addition of maize husk to digester C significantly improved the production of biogas from food waste when compared to the biogas yield of digester A that contained food waste alone. Digester B with 100% maize husk was by far the least performed digester.