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

Abstract

a b s t r a c tA 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.

Optimization of biogas production through selection of appropriate Inoculum-to-Substrate ((I/S) ratio

“…Batch anaerobic digestion was carried out to evaluate the effects of I/S ratio on biogas yield at pre-determined best combination of FW and MH (75% FW and 25% MH) as established by Owamah and Izinyon, 2015c). Following the recommendation in El-Mashad and Zhang, 2010, the inoculum added to the mixed substrate was the effluent from a mesophilic anaerobic reactor digesting the same type of substrate in order to enable enough initial micro-organisms for commencement of anaerobic digestion.…”

“…The FW: MH mixture percentage and values of other determined physiochemical parameters are shown in Table 1. Similar procedure was used by Owamah and Izinyon (2015c). The digestion was allowed to run for 44 days until biogas yield became negligible.…”

“…The present fast economic development and technological advancement occurring in many nations of the world implies that meeting energy demands without further deterioration of the environment may not be possible without a deliberate development and utilization of renewable energy (Zieminski et al, 2012;Roopnarain and Adeleke, 2017). Amongst the renewable energy resources, anaerobic digestion (AD) of waste organic substances (biomass) to biogas appears to be the most popular because AD has been noted to be among the few biotechnological processes that can generate bio-fuel, reduce environmental pollution and improve agricultural productivity through the use of its digestate as compost for organic farming (Owamah and Izinyon., 2015b;Zhang et al, 2016).…”

“…However, ensuring the viability and sustainability of industrial anaerobic digestion plants requires the optimal combination of process factors and substrates in the most costeffective manner. Co-digestion, which is the anaerobic digestion of two or more biodegradable substrates in a digester, has been used by several authors, for the optimization of biogas production potential of substrates (Haider et al, 2015;Owamah et al, 2015b). Co-digestion of different materials has been reported to enhance anaerobic digestion process due to better carbon to nitrogen (C/N) balance and good synergism for supporting microbial growth and biogas production (Haider et al, 2015;Mara-Alvarez et al, 2000;Mshandete et al, 2004;Parawira et al, 2004).…”

Laboratory Simulation of an Agricultural Biogas Plant Start‐up

“…As a result of the research, stable biogas and methane production was obtained at the OLR of the reactor of 4.5 kg VS m -3 d -1 . This result corresponds to the load generated in one-step technology in fermentation reactors [41][42][43][44].…”