Energy Production by Hydrothermal Treatment of Liquid and Solid Waste from Industrial Olive Oil Production

Abstract

This work studies the use of olive oil mill waste (OMW) treated as subcritical or supercritical water to produceboth, a biofuel by liquefaction and a gas fuel by gasification. The increasing amount of OMW, both liquid and solid, isbecoming a serious environmental problem. This wastewater is highly resistant to biodegradation and contains a widevariety of compounds such as polyphenols, polyoils, organic acids, etc, that require depuration treatments to remove theodour and pollutant load before being discharged.This work studies both, liquefaction and gasification of OMW streams in subcritical and supercritical water in differentbatch reactors at temperatures between 200 and 530 ºC and pressures between 150 and 250 bar. This study also teststhe effectiveness of various types of homogeneous (KOH 0.01 g/gsample dry) and heterogeneous catalysts (TiO2, V2O5 andAu-Pd 0.1-0.5 g/gsample dry) for supercritical water gasification (SCWG) and studied the way they affect biomassconversion yields. It also covers the effect that the use of different organic compound concentrations (23, 35, and 80 gO2/l of chemical oxygen demand concentration (COD)) and compositions (mixtures of solid and liquid OMW) has onenergy production results. A maximum of 82% oil yield was obtained from the hydrothermal liquefaction of OMW underoptimum conditions (330 ºC, 150 bar, 23 g O2/l as initial concentration and 30 minutes reaction time). Meanwhile, a yieldof 88.6 mol H2/kgOMW dry was obtained when Au-Pd was used as a catalyst for the gasification of OMW supercritical water.