Effect of fruit flavor compounds on biogas production

Abstract: The purpose of the experiment was to investigate the effect of fruit flavor compounds on biogas production from fruit wastes. The flavor compounds from different fruits were selected and synthetic medium was used throughout the experiment. The experiment was carried out both in batch and continuous process using thermophilic inoculums obtained from Söbacken waste management plant. The inhibitors were added at three different concentrations 0.05g/L, 0.5g/L and 5g/L respectively and were carried out in triplicates for batch cultivation.The result from batch cultivation showed that hexanal, (E)-2-hexanal, myrcene and octanol showed inhibitory activity. Hexanal, (E)-2-hexanal, myrcene, and octanol decreased biogas production by factor of 316.8%, 434.22%, 329.68% and 433.61% at concentration of 5g/L. Continuous experiment was carried out on Automatic Methane Potential Test System AMPTS II. Eight reactors, each with inhibitor compounds were used with a retention time of 30 days and an organic loading rate of 3g VS/day. The inhibitor concentration was increased from 0.5g/L to 5g/L and for some compounds up to 10g/L. During cultivation, several factors were measured periodically such as pH, total biogas production, biogas composition, FOS/TAC and VFA.The inhibitory effect was clearly shown at concentration higher than 0.5g/L. Addition of 5g/L hexanal, nonanal, (E)-2-hexanal, α-pinene , car-3-ene, myrcene and octanol resulted in reduction of biogas production by 81.2%, 4.67%, 50.74%, 7.06%, 24.01%, 31.84% and 52.85% respectively. When compared to batch process, continuous process required higher concentration of flavor compounds to reduce biogas production. This might be due to adaptation of cells towards toxic compounds during continuous process.