Hydrothermal carbonization (HTC) offers a promising pathway for valorizing food waste into hydrochar for soil amendment applications; however, the release of toxic compounds during post-application leaching remains a key concern. This study evaluated how feedstock composition and HTC conditions influence the ecotoxicity of hydrochar wash waters generated under laboratory-simulated washing conditions designed to represent potential rainfall or irrigation-driven leaching. Wash water composition and toxicity (via Escherichia coli and Aliivibrio fischeri assays) were measured. Food wastes (e.g., fruit, vegetable, grain, meat and dairy/confectionery products) were carbonized at 200-250 °C across multiple residence times. All hydrochars were sequentially washed to simulate rainfall or irrigation events. Across all conditions, cumulative washing was the strongest factor associated with toxicity, with the first wash producing the most toxic leachates and toxicity declining rapidly with subsequent washes, indicating that inhibitory compounds are largely water soluble. Feedstock composition appeared to significantly influence toxicity magnitude, with fruit-derived hydrochars consistently producing the least toxic wash waters, while vegetable- and grain-derived materials exhibited higher and more variable toxicity. A generalized linear model indicated that hydrogen richness was among the most influential feedstock properties associated with toxicity, with lower H:C values associated with reduced E. coli toxicity and higher A. fischeri EC50 values across the evaluated conditions and O:C ratio exerting a comparatively minor influence. Overall, these results provide a screening-level assessment of potential ecotoxicity risks associated with hydrochar-derived leachates.

Hydrothermal carbonization (HTC) has emerged as a pivotal technology in the battle against climate change and fosters circular economies. Operating within a unique reaction environment characterized by water as a solvent and moderate temperatures at self-generated pressures, HTC efficiently converts biomass residues into valuable bio-based products. Despite HTC’s potential—from the management of challenging biomass wastes to the synthesis of advanced carbons and the implementation of biorefineries—it encounters hurdles transitioning from academic exploration to industrial implementation. Gaps persist, from a general comprehension of reaction intricacies to the difficulty of large-scale integration with wastewater treatments, to the management of process water, to the absence of standardized assessment techniques for HTC products. Addressing these challenges demands collaboration to bridge the many scientific sectors touched by HTC. Thus, this article reviews the current state of some hot topics considered crucial for HTC development: It emphasizes the role of HTC as a cornerstone for waste management and biorefineries, highlighting potentialities and challenges for its development. In particular, it surveys fundamental research aspects, delving into reaction pathways, predictive models, analytical techniques, and HTC modifications while exploring HTC’s crucial technological applications and challenges, with a peculiar focus on combined HTC, wastewater integration, and plant energy efficiency.

Recycling underutilized resources from food waste (FW) to agriculture through hydrothermal carbonization (HTC) has been proposed to promote a circular economy in food, energy and water nexus. However, most HTC studies on FW have been conducted at laboratory scale, and little is known on efficacy of field application of HTC products from FW, i.e. aqueous product (AP) and solid hydrocharr(HC), to support agriculture production. To address these gaps, an integrated pilot-scale HTC system in this study is established to evaluate the reaction conditions and procedures for the HTC processing of FW. A peak temperature of 180 ℃ at a residence time of 60 minutes with 3 times recirculation of AP are recommended as the condition to achieve effective recovery of nutrients and water resources, and desirable AP and HC properties. Dilution of the raw AP and composting of the fresh HC eliminate potential phytotoxicity. Applying properly diluted AP and the composted HC can significantly improve plant growth and soil nutrient availability with comparable level to commercial fertilizer and soil amendment, respectively, in both greenhouse and field. The HTC treatment yields the most net negative carbon emission among common processing methods of FW and the direct potential profit. The current integrated pilot-scale study demonstrates that the HTC of FW and the agricultural application of its products have promising environmental advantages and economic feasibility.

Hydrothermal carbonization (HTC) has the potential to be a sustainable and environmentally beneficial approach for organic waste treatment. It is likely that HTC product use will dictate the viability of large-scale HTC facilities; therefore, understanding the viability and environmental implications associated with HTC product valorization pathways is critical. The overall goal of this review is to gain an understanding of how HTC product valorization is currently being modeled in life cycle assessment studies, and to use such information to assess current research and/or data needs associated with product valorization. To accomplish this, a review of existing HTC literature was conducted and used to assess the current state of knowledge surrounding the environmental implications of HTC product use. From this review of the literature, it is clear that potential exists for HTC product valorization. To realize this potential in a full-scale application, research gaps and data needs were identified that included a system-level integration to evaluate location-specific information as well as more extensive characterization of the impact of HTC product properties on valorization impacts.

Three Rivers Solid Waste Authority (TRSWA) operates a MSW landfill outside Jackson, South Carolina at which leachate is stored in a collection pond then trucked to a local wastewater treatment plant (WWTP) for treatment. This landfill operates a droplet spraying/misting system (referred to as the Lilypad system) to enhance leachate evaporation and ultimately reduce the quantity of leachate in the pond that requires subsequent treatment. Little work investigating the efficacy in using such a system to enhance leachate evaporation has been reported. The overall goal associated with this study was to quantify the amount of evaporation enhanced by the droplet spraying system and evaluate how the economics of the enhanced leachate evaporation compare to hauling leachate to a WWTP. This was accomplished by performing a water balance on the pond, developing a simple model to link leachate evaporation to the droplet spraying system, and performing an economic evaluation of the system. Overall, results from this work indicate the use of a droplet spraying/misting system to enhance leachate evaporation at on-site storage/collection ponds is effective, resulting in between 2.1 to 2.6 times more evaporation than what would occur naturally. In addition, the economic evaluation of this system indicates that operating the Lilypad system at maximum speed/flow for the greatest number of hours results in saving up to 7% of the total cost when compared to no operation of the Lilypad system.

This work studies the fate of nutrients (N, P, and K) during the hydrothermal treatment of anaerobically digested sewage sludge to raise their concentrations in the liquid phase and facilitate their recovery as solid minerals by chemical precipitation. The hydrothermal process has been optimized by evaluating the temperature (170-230 degrees C) and reaction time (5-60 min) in an acid-free medium or with the addition of HCl (0.1-0.5 M). In the acid-free hydrothermal reactions, nutrients were mainly concentrated in the hydrochar, which were extracted with 0.5 M HCl (10% w/v). Following this route, 6.9 g N/kg, 13.8 g P/kg, and 8.8 g K/kg contained in the feedstock were extracted from the hydrochar produced at 230 degrees C, which, considering direct nutrient solubilization to process water by acid-free hydrothermal treatments, accounts for 82, 83, and 78% N, P, and K release, respectively. In the HCl-assisted hydrothermal treatment, the release of nutrients directly into the process water was improved and depended mainly on the acid concentration used and to a lesser extent on the reaction temperature. Operating at 230 degrees C and 0.5 M HCl, the release of 98% N (more than 45% as NH4-N), 87% P (as PO4-P), and 70% K contained in the feedstock was achieved in the process water. Chemical precipitation of phosphorus and nitrogen from the process water allowed the recovery of a solid identified as crystalline struvite, with high contents in P, Mg, and NH4-N and negligible heavy-metal content. The estimated cost of digested sewage sludge treatment could reach 13.7 euros per tonne, considering the energy inputs required in the hydrothermal treatment.

The Three Rivers Solid Waste Authority (TRSWA) operates a MSW landfill outside Jackson, South Carolina (USA) at which leachate ammonia concentrations are of concern. The landfill operates a droplet spraying/misting system (known as the Lilypad system) in their pond to enhance both leachate evaporation and, possibly, ammonia volatilization. The overall goals of this study were to determine the fate of nitrogen in the pond and to ultimately quantify the role the Lilypad system plays in enhancing ammonia removal. To accomplish the study goals, an empirical model based on collected leachate and mist samples, climatological data, and pond hy-draulic data was developed to quantify the extent of ammonia volatilization, nitrifica- tion, and denitrification that occurred in the pond over the study period. Results from this work indicate that volatilization, nitrification, and denitrification were occurring in the pond, with volatilization of ammonia-nitrogen accounting for the majority of nitrogen removed from the pond. Results also indicate that the Lilypad system has the capability to significantly enhance the volatilization process.

The work studies the fate of nutrients (N, P and K) during the hydrothermal treatment of anaerobically digested sewage sludge. The hydrothermal process has been optimized by evaluating temperature (170 – 230 °C) and reaction time (5 – 60 min) in a non-acidic medium or with the addition of HCl (0.1 – 0.5 M). In the acid-free hydrothermal reactions, nutrients were mainly concentrated in the hydrochar, favoring N and K leaching at temperatures ≤ 200 °C, while P solubilization was slightly higher at the highest working temperature (230 °C). In this case, hydrochar was washed with 5 M HCl (10% w/v), solubilizing more than 80% of the nutrients contained in the feedstock, and obtaining a solid biofuel for industrial use that complies with ISO/TS 17225-8. In the HCl-mediated hydrothermal treatment, the release of nutrients into the process water depended mainly on the acid concentration used and to a lesser extent on the reaction temperature. Operating at 230 °C and 0.5 M HCl, a release of 98% N (more than 45% as NH4-N), 87% P (as PO4-P) and 70% K contained in the feedstock was achieved in the process water.

To produce hydrochar with less volatile matter (VM) and more fixed carbon (FC) to increase its stability, this study compared the hydrothermal carbonization (HTC) of hen (HM) and swine (SM) manures at typical HTC sub-critical temperature of 210 °C and slightly super-critical temperature of 400 °C. Physico-chemical properties such as proximate analysis; ultimate analysis; Brunauer–Emmett–Teller (BET) surface area; higher heating value (HHV); chemical oxygen demand (COD); and inorganic nutrients of hydrochar, gaseous, and liquid products were determined. As expected, both VM and yield decreased with temperature. The heats of HTC reactions were estimated to be exothermic, ranging from −5.7 to −8.6 MJ/kg. The FC approximately doubled, while VM significantly decreased with a yield of 42.7%, suggesting the high potential of producing more stable hydrochar via near-critical HTC (NCHTC) treatment of SM. Additional work is needed before recommendations on carbonization temperatures can be made. Specifically, there is a need to experimentally investigate how the chars produced from each carbonization condition influence plant growth and soil emissions.

Introduced in the literature in 1913 by Bergius, who at the time was studying biomass coalification, hydrothermal carbonisation, as many other technologies based on renewables, was forgotten during the “industrial revolution”.

Hydrothermal carbonization (HTC) is a wet, low temperature thermal conversion process that continues to gain significant attention for the sustainable generation of value-added solid, liquid, and gas products from organic waste streams. Although it is well documented that both waste properties (e.g., elemental composition) and carbonization process conditions influence hydrochar properties, their specific influence on the total energy that can be recovered using HTC remains unclear. Non-linear random forest models were developed based on data collected from HTC-related literature to describe hydrochar yield and energy content, both of which are required to determine the total energy recovered in the hydrochar. Results indicate that total recoverable energy from organic wastes using HTC is correlated with feedstock carbon content; overall, the total energy content for feedstocks with carbon contents ranging from approximately 40 - 48% are similar. In addition, the total energy that can be recovered from the feedstock remains fairly constant when the initial solids concentrations are greater than 20%. Reaction time appears to have little influence on total recoverable energy from each feedstock at reaction times greater than approximately 150min, while increases in reaction temperature result in a slight decline in total recoverable energy because of decreases in hydrochar yields at higher temperatures. (c) 2019 Elsevier Ltd. All rights reserved.

Atmospheric pressure dielectric barrier discharge (DBD) plasma operating in octamethylcyclotetrasiloxane (D4)-helium gas mixture was studied as a prospective method for the reformation of the organosilicon compounds in the carrier stream. It was found that with the application of DBD, a significant amount of D4 precipitates out of the carrier stream in the form of a white residue on the reactor walls. Structural characterization of this residue with x-ray photoelectron and nuclear magnetic resonance spectroscopy revealed that the deposits are primarily composed of a linear chained polymerized form of D4 referred to as polydimethylsiloxane. The dependency of the carrier gas flow rate on the removal rate of D4 from the helium carrier gas was investigated for five different flow conditions. Solvent absorption with gas chromatography and mass spectrometry were used to deduce the concentration of D4 in the effluent from the reactor and hence the siloxane reformation ratio. A maximum of similar to 80% conversion of D4 in the helium stream was achieved.

Adequate landfill operation and monitoring of a landfill are essential to control and reduce short- and long-term emissions during operation and aftercare. In addition, health and safety procedures have to be met. Equipment is necessary for waste and soil movement, compaction as well as for onsite maintenance, dust and snow control, etc. In addition, littering, noise, and nuisance control are necessary. Monitoring is imperative to detect any environmental pollution in the soil, water (surface and ground water), and air.

The sustainability of energy production can be increased by combusting waste-derived solid fuels, alone or as blends with coal. This paper investigated whether two thermochemical processes (hydrothermal carbonization and pyrolysis) can be used in sustainable manure management systems to convert surplus manure waste streams into renewable fuels. Hydrochars and pyrochars derived from swine manure and poultry litter at various process conditions were characterized. Their combustion behavior was studied by thermogravimetric analysis, individually and simulated as a blend with fossil coal. The hydrochars underwent two combustion stages, active and char combustion, while the pyrochars and four fossil coals showed only one stage. The substantial differences in characteristic combustion temperatures, kinetic parameters, and ash content between animal-manure-derived chars and coal suggest that fossil coals should not be replaced entirely with char, but used preferably as a blend. Simulation of blends with coal showed combustion characteristics similar to coal alone with amounts up to 10% (hydrochar) and 80% (pyrochar). Although more scale-up and ash characterization study is needed before implementation, the results suggest high potential of cocombusting small percentages of animal-manure based hydrochar and pyrochar with coal in existing coal power generation facilities.

•Literature associated with ENM-containing waste was reviewed and summarized.•Knowledge gaps about ENM release during waste treatment exist.•Key processes and mechanisms of ENM fate and transport were reviewed.•Specific research questions have been identified.

Hydrothermal carbonization (HTC) is a wet, low temperature thermal conversion process that continues to gain attention for the generation of hydrochar. The importance of specific process conditions and feedstock properties on hydrochar characteristics is not well understood. To evaluate this, linear and non-linear models were developed to describe hydrochar characteristics based on data collected from HTC-related literature. A Sobol analysis was subsequently conducted to identify parameters that most influence hydrochar characteristics. Results from this analysis indicate that for each investigated hydrochar property, the model fit and predictive capability associated with the random forest models is superior to both the linear and regression tree models. Based on results from the Sobol analysis, the feedstock properties and process conditions most influential on hydrochar yield, carbon content, and energy content were identified. In addition, a variational process parameter sensitivity analysis was conducted to determine how feedstock property importance changes with process conditions.

Active research on biomass hydrothermal carbonization (HTC) continues to demonstrate its advantages over other thermochemical processes, in particular the interesting benefits that are associated with carbonaceous solid products, called hydrochar (HC). The areas of applications of HC range from biofuel to doped porous material for adsorption, energy storage, and catalysis. At the same time, intensive research has been aimed at better elucidating the process mechanisms and kinetics, and how the experimental variables (temperature, time, biomass load, feedstock composition, as well as their interactions) affect the distribution between phases and their composition. This review provides an analysis of the state of the art on HTC, mainly with regard to the effect of variables on the process, the associated kinetics, and the characteristics of the solid phase (HC), as well as some of the more studied applications so far. The focus is on research made over the last five years on these topics.