SEPARATE DIGESTION OF LIQUID AND SOLID FRACTIONS OF THERMALLY PRETREATED SECONDARY SLUDGE. ASSESSMENT AND GLOBAL EVALUATION

Abstract -The fractioning into separate liquid and solid fractions obtained by centrifugation of thickened fresh and thermally pretreated (170 ºC, 50 minutes) secondary sludge showed that 30% of the particulate organic matter was released during the pretreatment, correspondingly increasing the methane production of the particulate matter by 30% (from 259 to 329 mL CH 4 /g VS fed ). The responsible of this enhancement was the liquid fraction, as the biodegradability of the solid fraction remained constant after the pretreatment. Mass balances showed that 34% of the VS were released to the liquid fraction, generating nearly 50% of the total methane produced, with much faster kinetics compared to the solid fraction. These results support the hypothesis of a separate liquid-solid digestion of thermally pretreated sludge, which would result in decreasing the digestion volume to half while duplicating the methane productivity per kilogram of sludge fed to digestion

Is anaerobic digestion a feasible alternative to the combustion of olive mill solid waste in terms of energy production? A critical review

The use of olive mill solid waste (OMSW) for energy production has mainly been promoted through combustion processes. However, the EU is promoting the substitution of combustion in favor of greener alternatives. Several publications have stated that the energy obtained from anaerobic digestion (AD) is a feasible waste-to-energy technology for OMSW. However, these studies lack reliable energy balances that can assess this statement. The present research work aims to address this issue by evaluating the energy potential of the biomethanization of OMSW in comparison with the current combustion technology, based on a review of the available scientific literature. The present analysis demonstrates that the AD of OMSW can generate a net energy production in the same range as that obtained from the OMSW combustion, qualifying AD as an alternative to combustion but not clearly offering a surplus of energy production