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

Evolution of the Olive Oil Industry along the Entire Production Chain and Related Waste Management

“…The remainder can be used for electricity production, heating, as a carbonaceous material with adsorbent properties, for soil improvement, and other applications [162,163]. As already mentioned, a different hydrothermal technology for the treatment and valorization of wet and very wet biomass, such as SOMW, is the liquefaction of the organic fraction under supercritical water conditions [135,164]. The very severe operating conditions of pressure and temperature make these technologies less attractive than HTC for full-scale applications.…”