Anaerobic Digestion of Lime Waste in Batch Assay Digestion for Potential Biogas Recovery

The accumulation of lime wastes on dumpsites causes economic and environmental problems. Nonetheless, there is a potential to recover biogas from lime wastes due to their high concentration in soluble sugars. DLimonene, a chemical compound present in lime peels, is, however, known to negatively affect the anaerobic digestion and conversion of lime waste to biogas. This study is aimed at reducing the effect of D-Limonene on biogas production from lime wastes. The study assessed the impact of lime waste pretreatment and co-digestion with poultry litter on improving biogas recovery. In co-digestion, an equal mass of lime waste was mixed with that of poultry litter. The pre-treatment of lime waste was done using a solid-liquid extraction process to filter out essential oil, containing D-Limonene, from lime wastes. Different samples from untreated, pre-treated, and mixed wastes were digested in laboratory batches for 28 days under mesophilic conditions. The total biogas production results from the samples are 66.9 mL/g VS, 66.8 mL/g VS, 93.2 mL/g VS and 138.1 mL/g VS for untreated lime waste, untreated lime waste mixed with poultry litter, pre-treated lime waste and pre-treated lime waste mixed with poultry litter, respectively. These results indicate that the pretreatment process alone increased biogas yield by about 40% while the codigestion of untreated lime waste with poultry litter did not affect improving biogas yield. Economic estimation of the biogas production process from lime waste on a large scale revealed that gas could be produced at a cost rate of N574.28 ($1.25usd) per cubic meter, which is less than the current market price of N620.69 ($1.35usd) with cost savings of 92% for cooking gas in Nigeria. The findings of this research show that there is a viable recovery option of biogas from lime waste, and an economically viable biogas plant process that efficiently utilizes lime wastes developed which would boost the drive of government towards an alternative source of energy and also fulfill two of the sustainable development goals as presented by the United Nations.