Hydrothermal carbonization of sewage sludge: The effect of feed-water pH on fate and risk of heavy metals in hydrochars

Catalysed Hydrothermal Carbonization of Woody Biomass and Recycling of Process Liquid

“…Mixed results have been reported regarding ash content and accumulation within recycled processes [5], [7], [45]. 1 Sulfur was less than 0.01% for all hydrochar samples 2 Energy densification ratio 3 Energy yield…”

“…reducing the volume of process liquid to be treated to remove organic substances. Additionally, the process liquid has shown catalytic properties that increase dehydration reactions [5], and lower pH of the process liquid has been found to improve properties of the hydrochar, including higher energy density [2], [3], [73], [77], [85].…”

“…Several operating conditions of the HTC process, such as temperature, time, and liquid:biomass ratio, have been found to affect the production yields and characteristics of the hydrochar, gases, and other organic compounds in the liquid [1]. The addition of acidic and basic compounds to the process liquid (pH adjustment) has been shown to improve the quality of the hydrochar, e.g., higher heating value (HHV) and increased carbon content [1]- [3].…”

“…3 shows IR spectra of the feedstock biomass, the hydrochar processed using only the catalyst solution (Fresh), and the hydrochar after 15 partial recycles (R15), and HTC hydrochar produced in this study (HTC). Chemical bonds found in woody biomass include -OH, C-H, and C-O, which are absorbed at 3400, 2900, and 1100 cm -1 , respectively[56].The intensity of the hydroxyl group peak, at 3400 cm -1 , decreased after CHTC of the woody biomass, which suggests a decrease in the number of OH bonds consistent with the enhanced dehydration inferred from the lower O/C and H/C ratios shown inFigure 3-2.…”

“…3 shows the effects of changing L:B ratio of CHTC on the concentration and production yields of the VACs. The production yield for all the known VACs, except for the LA, was found to be the highest at 10:1 L:B ratio.…”