Hydrothermal carbonization of olive oil mill waste water -

Abstract

Hydrothermal carbonization (HTC) is an emerging technique for wastewater treatment. It uses water at moderate temperatures (180-250℃) and autogenous pressures (35-55 bar) to break down organic waste. In this work, HTC was used to treat olive oil mill wastewater. The reaction time and the water-sludge (W-S) ratio were varied, over a broad set of values, to study their effect on the hydrochar products. As the reaction time and dilution factor increased, the hydrochar conversion was low and decreased from 36 percent to 7 percent while the liquid product mass was always high and increased from 93.5 g to 176.5 g. HTC upgraded both carbon and energy content to very high values, 72 percent and 36 MJ-Kg respectively. Hence, the produced hydrochar is a good candidate for energy production. Besides, the produced hydrochars were amorphous and had a hydrophobic structure due to their phenolic and acidic content. Their filament structure became apparent and more evident as the dilution factor increased. Hydrochar yield was the highest at the lowest dilution factor (i.e. 1.5) and reaction time (2 hours), while carbon percentage and calorific values were significantly high and not affected by the change in the operating conditions. The Sulfur level was always negligible while chlorine level reached approximately zero at higher operating condition. Liquid extracts were taken under various operating conditions, and different analytical techniques were used to analyze the acids-phenols quality and concentrations along with the non-polar hydrocarbons in the liquid phase. Different extraction methods were developed and tested in this work along with GC-MS and UV analyses. Many simple biophenols such as Tyrosol, hydroxyl-Tyrosol, phenol, homo-vanillyl alcohol, along with various ketones, flavones, flavonols, alcohol, aldehydes, cyclic-aromatics, alkanes, alkenes and even alkynes were detected in the liquid phase product. In contrast, negligible amounts of polyaromatic hydrocarbons (PAH) were found. The hydrocarbons concentration decreased as