Co-hydrothermally carbonized sewage sludge and lignocellulosic biomass: An efficiently renewable solid fuel

• Published in: Arabian journal of chemistry 2023-12, Vol.16 (12), p.105315, Article 105315
• Main Authors: Piboonudomkarn, Siridet, Khemthong, Pongtanawat, Youngjan, Saran, Wantala, Kitirote, Tanboonchuy, Visanu, Lubphoo, Yingyote, Khunphonoi, Rattabal
• Format: Article
• Language: English
• Subjects: Co-hydrothermal carbonization; Hydrochar; Lignocellulosic biomass; Sewage sludge; Solid fuel
• ISSN: 1878-5352; 1878-5379
• DOI: 10.1016/j.arabjc.2023.105315

•Rational design is established for producing renewable biocoal-like solid fuel.•Co-HTC is a key process to convert agricultural wastes and brewery sludge into solid fuel.•The combustion behavior of solid fuel is enhanced by biomass addition.•Co-HTC of agricultural wastes and brewery sludge can reduce environmental impact. The objectives of this investigation were to elucidate the potential use of metal oxide-rich sewage sludge obtained from the treated brewery wastewater into a value-added solid fuel via co-hydrothermal carbonization process (co-HTC). Two residue biomass including spent coffee grounds and bagasse were supplied as co-combustion. The effects of sewage sludge and biomass addition on fuel properties were evaluated to optimize the best condition for biocoal-liked production. The chemical composition and mineral phase of solid product were further analyzed. Combustion kinetics analysis including activation energy (E) and pre-exponential factor (A) were derived from thermogravimetric analysis. It was found that the addition of coffee grounds and bagasse enhanced the fuel properties of the solid products, remarkably increasing high heating value (HHV) along with a low ash content, providing an increased fuel ratio of 0.34 – 1.01 and higher HHV as 14.29 – 22.19 MJ/kg. The highest rate of energy recovery was achieved when combining 75 wt% sewage sludge with 25 wt% spent coffee grounds. A substantial decrease of H/C and O/C atomic ratios was distinguished after bagasse addition compared to commercial lignite coal. It was also noticed that the relationship between the sewage sludge and biomass feedstocks during co-HTC is synergistic by increasing the amount of oxidative carbon during the char combustion stage and enhancing the degree of thermal stability. Moreover, it was also emphasized that during co-HTC some carbon and inorganic contents of sludge and lignocellulosic biomass were partially transferred into a liquid phase confirmed by TOC and ICP-OES analyses. A heavy metal leaching toxicity in a liquid product was also determined according to the USA-EPA standard. The combustion reactivity was improved, especially combustion reactivity of the biomass-sewage sludge-derived hydrochar. Interestingly, the hydrochar product was anticipated to possess enhanced safety and stability. Moreover, the co-combustion of hydrochar and coal improved the devolatilization properties and ignition of coal. This strategy revealed that co-hydrothermal process with biom