Co-hydrothermal Carbonization of Water Hyacinth and Sewage Sludge: Effects of Aqueous Phase Recirculation on the Characteristics of Hydrochar

Abstract

Co-hydrothermal carbonization (Co-HTC) of sewage sludge (SS) and lignocellulosic biomass has been reported as a promising technology for SS pretreatment, in terms of sterilization, deodorization, and enhancing fuel properties. However, in current research, the aqueous phase from Co-HTC was generally dumped directly as a waste liquid, which was not conducive to the effective utilization of energy and environmental protection. Therefore, for the purpose of further improving the above process, Co-HTC of sewage sludge and water hyacinth (WH, a lignocellulosic biowaste) was employed in our study, coupling with aqueous phase recirculation during the Co-HTC process, aiming at harvesting value-added solid fuels and identifying the upgradation effects of aqueous phase recirculation on hydrochar fuel characteristics. The results demonstrated that excellent synergistic effects occurred during Co-HTC. Moreover, synergistic effects would be further enhanced during the aqueous phase recirculation process due to strengthened Maillard and Mannich reactions, contributing to superior experimental hydrochar yield, a higher heating value (HHV), energy yield, and a power consumption index compared with that of calculated values. The hydrochar from Co-HTC and the recirculation process showed lower ignition and burnout temperatures, facilitating the rapid release of heat during the combustion of hydrochar. Meanwhile, synergistic effects during Co-HTC and recirculation facilitated transforming the speciation of Cd and Pb from F1 and F2 fractions to F3 and F4 fractions, thereby reducing their direct ecotoxicity to the environment. The reaction mechanism during Co-HTC and the recirculation process was inferred by further characterizing components in the aqueous phase. In summary, these findings could provide referential information for the resource utilization of the aqueous phase during the Co-HTC process as well as scaling up the thermal utilization paths of SS and WH.

Hydrothermal Carbonization of Digestate Produced in the Biogas Production Process

“…Thus, they are characterized by high degradability [82]. Hydrochar is brittle and might easily be crushed, which significantly facilitates its transportation and storage and reduces economic and operating costs [83]. The effect of temperature is essential when it concerns nitrogen transfer during HTC.…”

Co-hydrothermal carbonization of sewage sludge and coal slime for clean solid fuel production: a comprehensive assessment of hydrochar fuel characteristics and combustion behavior

“…Saba and their workers believe that the surface of CS may act as a reaction center, thereby promoting the polymerization of organic matter generated by the decomposition of SS during the co-HTC process [ 39 ]. Furthermore, the decomposition of SS during the HTC process produced organic acids, which could further reduce the inorganic components of the hydrochar [ 40 ]. These interactions resulted in the increased experimental value of mass yield, HHV, carbon retention rate, ERE, fuel ratio, and energy balance rather than simple physical superpositions.…”

Investigation of Hydrothermal Carbonization of Exhausted Chestnut from Tannin Extraction: Impact of Process Water Recirculation for Sustainable Fuel Production

“…Prior investigations conducted by [15][16][17][18] have yielded promising results, showcasing the potential benefits of process water recycling in terms of enhancing hydrochar yield, improving energy recovery, optimizing combustion performance, and mitigating environmental impacts. Upon review of the existing literature, it became evident that there is a lack of studies investigating process water recycling specifically within the HTC process applied to spent chestnut wood biomass.…”