Methanogenic potential of residues of fruits and vegetables depending on the type of inoculum

Abstract

The objective of this work was to evaluate the potential and quality of biogas production from anaerobic digestion, using fruit and vegetable waste (FVW) as substrate and two different sources of inoculum as a source of bacterial biomass. The residues were collected at a Food Supply Center and the inocula included secondary anaerobic sludge collected at a wastewater treatment plant (ES/inoculum) and anaerobic sludge collected in a biodigestor that treats swine manure (DS/inoculum). The determination of the biogas production potential was carried out following the guidelines proposed by the VDI 4630. The biogas volume was measured daily and the composition determined weekly by gas chromatography. The FVW had acid pH, absence of alkalinity, high humidity and high concentration of volatile organic material. The inocula presented pH close to neutrality, resulting from well-stabilized anaerobic processes and the main difference was observed for the alkalinity contents. The accumulated biogas production of the FVW was 362 mLN g SV-1 using the ES-inoculum and 348 mLN g SV-1 using DS/inoculum, indicating similarity regardless of the type of inoculum. However, there were differences in daily production and methane concentration. The use of ES-inoculum allowed the rapid conversion of organic matter into biogas, with approximately 90% of the total production generated in the first four days. Testing with the DS/inoculum showed 60% methane (totaling 210 mLN CH4 g SV-1) and with the ES/inoculum showed 51% (totaling 184 mLN CH4 g SV-1). Even with higher degradation capacity during the process, DS/inoculum allowed a cumulative production of methane 14% higher when compared to ES/inoculum.