Incorporating hydrothermal liquefaction into wastewater treatment – Part II: Characterization, environmental impacts, and potential applications of hydrochar. (10th January 2023)

• Record Type: Journal Article
• Authors: Liu, Huan; Lyczko, Nathalie; Nzihou, Ange; Eskicioglu, Cigdem
• Is Part Of: Journal of cleaner production. Volume 383(2023)
• Publication Date: 2023-01-10
• Subjects: Sludge treatment -- Hydrochar composition -- Environmental concerns -- Phosphorus recovery -- Graphitization -- Waste valorization; AAEMs alkali and alkaline earth metals -- AI alkali index -- ANOVA analysis of variance -- AP apatite phosphorus -- BET Brunauer–Emmett–Teller -- CCD central composite design -- COPCs constituents of potential concern -- db dry basis -- DTG derivative thermogravimetry -- FTIR Fourier transform infrared spectroscopy -- HHV higher heating value -- HTC hydrothermal carbonization -- HTL hydrothermal liquefaction -- IP inorganic phosphorus -- LSP liquid-solid partitioning -- MS mixed sludge -- NAIP non-apatite inorganic phosphorus -- OP organic phosphorus -- SEM scanning electron microscopy -- TCLP toxicity characteristic leaching procedure -- TEM-EDX transmission electron microscopy with energy dispersive X-ray spectroscopy -- TGA thermogravimetric analysis -- TP total phosphorus -- WWTP wastewater treatment plant -- XRD X-ray diffraction; Factory and trade waste -- Management -- Periodicals; Manufactures -- Environmental aspects -- Periodicals; Déchets industriels -- Gestion -- Périodiques; Usines -- Aspect de l'environnement -- Périodiques; 628.5
• DOI: 10.1016/j.jclepro.2022.135398
• Languages: English
• ISSNs: 0959-6526

Abstract

Abstract: Hydrothermal liquefaction (HTL) is a promising technique for renewable biofuel (biocrude) production from municipal sludge. However, its solid byproduct, hydrochar, requires sustainable management for further resource recovery and pollution control. This study comprehensively assessed the properties, environmental influences, and possible utilizations of hydrochar generated from mixed sludge (MS). With the increase of HTL reaction temperatures (290–360 °C) and residence time (0–30 min), the dry-weight contents of ash and fuel ratio increased from 10.5% and 0.1 in MS to 48.7–68.5% and 0.4–0.7 in hydrochar, respectively. However, the dry-basis contents of volatile matter, carbon, and higher heating value sharply decreased to 18.7–35.9%, 22.9–37.3%, and 8.6–16.0 MJ/kg, respectively. The leaching risks of inorganic contaminants from hydrochar were limited and controllable in various scenarios. Hydrochar performed more stable combustion than sludge, but its high ash contents and alkali index (0.28–0.72 kg/GJ) implied high risks of slagging and fouling. Hydrochar has a good potential for carbon sequestration due to low O/C ratios (<0.2) and improved recalcitrance index (0.43–0.48). Benefiting from intrinsic metals (e.g., Ca and Fe), catalytic hydrochar graphitization was feasible at a moderate temperature (1200 °C). Although hydrochar was restricted from land application for heavy metals accumulation, it is promising for metals and nutrient recovery. It has a total phosphorus (P) of 7.2–8.5% by weight, and thus P recovery is critical and necessary for mitigating environmental challenges and global P scarcity. Overall, this study contributed to the state-of-the-art in waste-to-resource development and cleaner production. Graphical abstract: Image 1 Highlights: Hydrothermal temperature and time had significant effects on hydrochar composition. Most heavy metals in hydrochar had limited leachability (<1 mg/L) at pH 2–13. Direct combustion of hydrochar is not proper for its high risk of slagging/fouling. Hydrochar showed improved stability and recalcitrance for carbon sequestration. Hydrochar had great potential for P recovery and in-situ catalytic graphitization.