Testing Processing Methods to Enhance Anaerobic Co-Digestion of Orange Peels

Anaerobic co-digestion is a process where microorganisms break down municipal wastewater in combination with other organic materials, such as food waste, under oxygen-free conditions. Not only diverting wastes from going to landfills, this process results in the production of biogas for energy. Over 51 million tons of oranges were produced globally from 2017 to 2018 with an anticipated 4.2 million ton expansion the following year. Orange peel wastes account for about 44% of the total mass of an orange. Orange waste has been shown to inhibit anaerobic digestion due to it containing high concentrations of D-limonene, an antimicrobial compound. Different methods for acclimating anaerobic digesters to orange peel waste were tested. The effectiveness of biological pretreatment of homogenized orange peels was assessed using a biomethane potential test (BMP). Adaptation of an anaerobic digester microbe culture in a continuously stirred tank reactor (CSTR) to increasing levels of Dlimonene was also assessed and CSTRs with and without d-limonene were monitored for gas production and chemical composition over 100 days. BMP results show a significantly higher biomethane potential for the biologically pretreated orange peel. The CSTR results demonstrate the ability to add up to 1000ppm D-limonene in the reactor utilizing an acclimation process. Overall, these results support different processing methods that can enable efficient utilization of homogenized orange peels for anaerobic co-digestion.