Effect of limonene on batch anaerobic digestion of citrus peel waste

The objective of this study was to analyze the anaerobic digestion process inhibition by limonene, the main component of citrus essential oils (CEO) present in citrus peel. The biochemical methane potential (BMP) values of the citrus waste tested (orange peel, mandarin peel, mandarin pulp and rotten fruit) were 354-398 L-CH4 kg(VS)(-1). Grinding the orange peel (2.5 g(limonene) L-1) did not influence the BMP values, but slowed the kinetics, due to the increased availability of CEO caused by the grinding. The effect of (R)-limonene (0-3000 mg L-1) on the batch anaerobic digestion of microcrystalline cellulose was also assessed. The half maximal inhibitory concentration, IC50, was 423 mg kg(-1) in an initial run and 669 mg kg(-1) in a second run of batch experiments. The methane course and IC50 values indicate that there are reversible inhibition and biomass activity recovery during the anaerobic digestion process, despite the non-reversible antimicrobial mechanism described in the literature for limonene to date. (C) 2015 Elsevier B.V. All rights reserved.