Effect of water-sludge ratio and reaction time on the hydrothermal carbonization of olive oil mill wastewater treatment: Hydrochar characterization

Hydrothermal carbonization (HTC) was used to treat olive oil mill wastewater (OOMW) by using water in the absence of any additional reagent. 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 reaction time and water-sludge ratio increased, the hydrochar yield decreased from 36% to 7%. In addition, HTC upgraded both carbon and energy contents to very high values, 76% and 36 MJ/kg respectively. Hence, the hydrochars products are good candidates for energy generation. Moreover, the hydrochars products were amorphous and had a hydrophobic oleophilic structure. Their quality and energy yield increased with the decrease in water-sludge ratio while reaction time slightly affected the hydrochar properties. Operating the process at the lowest water-sludge ratio and short reaction time leads to hydrochars with the finest characteristics but at the expense of higher cost due to evaporation rate.