Wet Organic Waste Research Articles

Evaluation of sorption properties of biochar produced by hydrothermal liquefaction of Phragmites australis

Relevance. The need to use an innovative method of thermochemical conversion of wet biomass and organic waste – hydrothermal liquefaction. This paper focuses on the further application of the by-product of the process – solid coal residue (biochar). The obtained solid residue is proposed to be used as sorbent. Aim. To evaluate the sorption capacity of carbon residues from hydrothermal liquefaction of common reed, as well as to select methods for their activation. Object. Hydrochar produced by hydrothermal liquefaction from plant biomass – common reed (Phragmites australis). Methods. Hydrothermal liquefaction, chemical activation of hydrochar sorbents by hydrogen peroxide and vapor-gas activation, sorption capacity by methylene blue, elemental analysis, specific surface area measurement by the Brunaer, Emmett and Teller method, nitrogen sorption–desorption at 77 K. Results. Sorbent yield during activation was 45 and 30% with chemical activation and 91% with steam-gas activation. The maximum sorption capacity for methylene blue of 18.4 mg/g was achieved due to chemisorption for the sample after carbon activation with peroxide in the presence of sulphuric acid. The maximum BET surface area (18.47 m2/g) and total pore volume (0.186 cm3/g) were achieved for the sample after gas-vapor activation. Based on the results of porous structure evaluation, the mesoporous structure of the obtained coals was discovered. The obtained coals showed sorption properties as good as those of similar cheap waste sorbents. The authors have proved the possibility of using the obtained sorbents for solving environmental problems, including wastewater treatment.

Co-hydrothermal carbonization of lignocellulosic biomass and swine manure: Optimal parameters for enhanced nutrient reclamation, carbon sequestration, and heavy metals passivation

Hydrochar, the primary product of hydrothermal carbonization (HTC) of wet organic waste, is recognized as a versatile, carbon-abundant material with diverse applications. However, optimizing its performance for specific uses remains challenging. Therefore, this study introduced a co-HTC process involving carbon-rich lignocellulosic materials and ash-rich livestock manure [i.e., Zanthoxylum bungeanum branch residue (ZB) and swine manure (SM), respectively]. The impacts of HTC temperature (i.e., 180 °C, 220 °C, and 240 °C) and mass ratios (i.e., 1:0, 7:3, 5:5, 3:7, and 0:1) on hydrochar properties (e.g., pH, EC, nutrient contents, heavy metal content and availability, chemical stability, etc) and the characteristics of process water were evaluated. Results reveal that co-HTC dramatically improved the quality of hydrochars compared with that derived from a single feedstock. Notably, the ZB:SM ratio had a more substantial impact on total nutrient content, carbon stability, and heavy metal accumulation and mobility. Additionally, the synergistic effects of ZB and SM were greatly dependent on the HTC temperature. By adjusting the feedstock mass ratio and HTC temperature, a highly-functionalized hydrochar can be produced. For example, hydrochars produced at 240 °C with a 7:3 ZB to SM ratio (HC240-7) is optimal for degraded soil amendment, enhancing carbon sequestration and nutrient supplementation. Results from this study could provide valuable insights for improving waste management through HTC and expanding the environmental and agricultural application of hydrochar.

Detection of volatile hydroperfluoroalkanes during hydrothermal liquefaction of perfluoroalkyl carboxylic acids at circumneutral pH

Hydrothermal liquefaction (HTL) is a promising technology for converting wet organic waste such as sewage sludge into biocrude oil while simultaneously destroying per- and polyfluoroalkyl substances (PFAS). This study tracked the fate and degradation of six representative PFAS in water to address the effect of perfluoroalkyl chain length on degradation rates and the formation of volatile transformation products at 300–350 °C. While perfluorosulfonic acids were recalcitrant, perfluoroalkyl carboxylic acids (PFCAs) were rapidly and completely decarboxylated to hydroperfluoroalkanes (1 H-perfluoroheptane in the case of perfluorooctanoic acid). The volatile hydroperfluoroalkane was subsequently defluorinated without detectable fluorocarbon intermediates yielding 30–60 % defluorination for ammonium perfluoro(2-methyl-3-oxahexanoate), perfluorobutanoic acid and perfluorooctanoic acid after 2 h at 350 °C. Increasing temperature (especially at 350 °C) and longer perfluoroalkyl chains substantially enhanced the defluorination. This is the first study to report volatile hydroperfluoroalkanes from PFCAs in HTL, raising concern about the potential emission of long-lived greenhouse gasses into the atmosphere, but also opening new avenues for PFAS destruction through HTL.

The Efficiency of Black Soldier Fly Larvae with Vegetable, Fruit and Food Waste as Biological Tool for Sustainable Management of Organic Waste

This study investigated the sustainable management of wet organic waste using Black Soldier Fly Larvae (BSFL) for an innovative biological approach to waste management. The organic wet wastes such as fruit, vegetable, and food wastes were processed and fed to BSFL larvae from day 5 and the bioconversion process was carried out at Black Soldier Fly Unit, Tamil Nadu Agricultural University for 21 days. Among the three wastes, the highest bioconversion efficiency was recorded in fruit waste with 67% Substrate Reduction, 10.8% Efficiency of Conversion of Digested feed, 5.7% Bio Conversion Rate, and 4.18 Waste Reduction Index after 21 days. Whereas vegetable and food waste achieved similar bioconversion efficiency. The results suggest that BSFL-based bioconversion can be an effective and eco-friendly waste management and resource recovery technique to significantly lower the volumes of organic wet waste while converting it into high-value biomass and leading to a circular economy model.

Characterizing the Opportunity Space for Sustainable Hydrothermal Valorization of Wet Organic Wastes.

Resource recovery from wet organic wastes can support circular economies by creating financial incentives to produce renewable energy and return nutrients to agriculture. In this study, we characterize the potential for hydrothermal liquefaction (HTL)-based resource recovery systems to advance the economic and environmental sustainability of wastewater sludge, FOG (fats, oils, and grease), food waste, green waste, and animal manure management through the production of liquid biofuels (naphtha, diesel), fertilizers (struvite, ammonium sulfate), and power (heat, electricity). From the waste management perspective, median costs range from -193 $·tonne-1 (FOG) to 251 $·tonne-1 (green waste), and median carbon intensities range from 367 kg CO2 eq·tonne-1 (wastewater sludge) to 769 kg CO2 eq·tonne-1 (green waste). From the fuel production perspective, the minimum selling price of renewable diesel blendstocks are within the commercial diesel price range (2.37 to 5.81 $·gal-1) and have a lower carbon intensity than petroleum diesel (101 kg CO2 eq·MMBTU-1). Finally, through uncertainty analysis and Monte Carlo filtering, we set specific targets (i.e., achieve wastewater sludge-to-biocrude yield >0.440) for the future development of hydrothermal waste management system components. Overall, our work demonstrates the potential of HTL-based resource recovery systems to reduce the costs and carbon intensity of resource-rich organic wastes.

Biocrude extraction from human-excreta-derived hydrochar for sustainable energy and agricultural applications

Hydrothermal carbonization may be a sustainable sanitary treatment for wet organic waste including human excreta. Human-excreta-derived hydrochar properties differ from those of typical wet biomass due to the formation of a biocrude-like phase at low reaction temperatures. This study characterized the importance of this phase in terms of hydrochar combustion properties and potential agricultural use. Hydrothermal carbonization of raw human excreta was undertaken at 180, 210, and 240 °C, after which the biocrude phase was extracted with dichloromethane. Physicochemical properties, surface-area parameters, combustion profiles, and gas emissions of non-extracted hydrochar, biocrude, and extracted hydrochar were compared. The potential agricultural use of extracted hydrochar was assessed in germination experiments. Biocrude comprised up to 49.5% of hydrochar mass with a calorific value of >60% that of extracted hydrochar. Biocrude combustion properties were better than those of hydrochar, before and after extraction as demonstrated by higher combustion index value (Si). The extracted hydrochar surface area (34.7 m2 g−1) was greater than that of non-extracted hydrochar (<2 m2 g−1), and seeds germinated more readily due to the lower phytotoxin content. Most macro and micronutrients required for plant growth were retained in the extracted hydrochar. The extraction of biocrude from human-excreta-derived hydrochar not only provided a higher-quality fuel with enhanced combustion properties but also improved hydrochar characteristics, suggesting its potential as a soil additive for enhanced plant growth.

Coupling electrokinetic technique with hydrothermal carbonization for phosphorus-enriched hydrochar production and heavy metal separation from sewage sludge

Hydrothermal carbonization is a promising treatment technology for wet organic solid wastes, due to its energy-efficient production of functionalized carbonaceous materials. However, the usage of sewage sludge (SS) derived hydrochar as phosphorus (P) fertilizer for agricultural soil is inhibited by the presence of heavy metals (HMs). Appropriate HM removal technology is required prior to its land application. In this study, an innovative FeCl3-assisted electrokinetic technique coupling with hydrothermal carbonization (FEK–HTC) is proposed to produce SS hydrochars with reduced HM content and increased P-retention. FEK–HTC treatment showed synergistic effects in terms of P retention and HM content reduction (56–64 % for Ni, Cu, and Zn). Furthermore, the toxicity of the remaining HMs was dramatically reduced, e.g., by 39.35 % in the case of Zn. Additionally, FEK–HTC transformed P species in hydrochars into highly bio-available form. Electrokinetic treatment resulted in decreased pH values of SS feedstock and promoted the solubilization and erosion of Ca-associated P, resulting in higher non-apatite inorganic phosphorus contents (12.47 to 23.19 mg·g−1) compared to hydrochars from untreated sludge. The P migration patterns during the FEK-HTC treatment were assessed based on the combined result of chemical extraction, 31P NMR, X-ray absorption near edge structure (XANES), and diffusive gradients in thin film (DGT). DGT analysis showed that the addition of treated hydrochars greatly increased the available P content in the soil. The results provide new insights into applying FEK-HTC technique for SS management.

Potential Renewable Energy Source from Nutmeg-Coconut Shell Waste in North Maluku, Indonesia

In 2019, North Maluku exported 54,470,489 kg of copra and 2,712,999 kg of nutmeg. The large export value of these two commodities shows that not a small amount of organic waste is produced per year. The high market demand for these two superior commodities will have an impact on the high production of waste generated. Nutmeg shells and coconut shells are dry organic waste. Although organic waste can decompose naturally, both wastes will take a long time to decompose compared to wet organic waste. Waste that is not handled properly will have a worse impact in the future. On the other hand, these wastes have excellent potential if utilized as a renewable energy source. In this study, briquettes were made from nutmeg shell charcoal (NSC) and coconut shell charcoal (CSC) as basic materials, while the adhesive used a 4 % starch solution. This study aims to obtain the optimum ratio of nutmeg shell and coconut shell mixture as raw material for briquettes. The ratio of AP:AK in the briquettes is as follows: Formula B1 (3:1); Formula B2 (1:1); and Formula B3 (1:3). The briquettes were evaluated with reference to SNI 01-6235-2000. The results of the briquette evaluation are as follows: Formula B1 (water content 7.21 %; volatile matter 36.28 %; ash content 7.50 %; calories 6219.07 cal/g); Formula B2 (water content 7.18 %; volatile matter 32.39 %; ash content 6.52 %; calories 6485.14 cal/g); and Formula B3 (water content 6.93 %; volatile matter 29.41 %; ash content 7.06 %; calories 6813.80 cal/g). Based on the briquette evaluation results, Formula B3 is the best quality briquette.

Environmental Sustainable in Household Waste Management For Urban Resilience: Insight From Makassar City, Indonesia

This study only focuses on a small aspect of environmental protection, namely proper household waste management for urban resilience in Makassar City, Indonesia. This study discusses how household waste in Makassar City can be converted into useful products and economic value that will reduce waste generation and maintain the preservation of densely populated urban environments in Makassar City, Indonesia. This study methodology is qualitative with a case study approach in looking at environmental degradation caused by an increase in household waste generation in Makassar City which has an impact on the environment and socio-economic activities of Makassar City community. The results of this study indicate that the development of environmental problems in household waste management in Makassar City is still experiencing problems. So in good governance, it is driven by the helix innovation system which involves various stakeholders to turn household waste into useful products with economic value. The helix innovation system as a solution to the problem of increasing household waste in Makassar City utilizes Incineration Technology and the Waste Bank and Composting Innovation Program for organic waste as environmental preservation for densely populated cities in Makassar City, Indonesia which involves community groups. Wet household organic waste is made into compost which can be used in plantations and livestock. Waste management in Makassar City is regulated in Makassar Mayor Regulation No. 4 of 2011 concerning Waste Management and Makassar Mayor Regulation No. 35 of 2018 concerning Policies and Strategies for Household Waste Management and Household Waste.

Role of Accumulated Alkali and Alkaline-Earth Chloride Salts in Hydrochar Formation Produced from Lignocellulosic Biomass

Hydrothermal carbonization (HTC) is an effective method for recovering useful carbon-rich solids from biomass and wet organic waste. This study investigated the effects of the type and amount of alkali and alkaline-earth chloride salts (AAECS) in HTC media on the properties of cornstalk hydrochar by analyzing the yield, elemental composition, surface functionality, and morphology, as well as fuel characteristics. The results suggest that the abundance of AAECS in HTC media may increase the aromaticity and energy recovery of hydrochar by facilitating the dehydration and decarboxylation of biomass. Both anions and cations in AAECS are responsible for these variations, especially for Ca2+, which can selectively affect the dehydration reaction of biomass by promoting the formation of anhydride and inhibiting the reaction between carboxyl and hydroxy to form a lactone. In addition, the high concentration of AAECS in HTC media is beneficial for improving the electron-donating capacity of hydrochar. This work could provide important insights into AAECS’ effects on hydrochar preparation, which arose from the recirculation of HTC aqueous solution.

Energy and exergy assessments of supercritical water oxidation of wet organic wastes under hydrothermal flames with a Y-shape reactor for power generation

A novel Y-shape reactor combined the concepts of transpiring wall reactor (TWR) and hydrothermal flame was proposed for supercritical water oxidation (SCWO) of wet organic wastes. Hydrothermal flames can enhance feed degradation, and the Y-shaped structure enables the efficient gas–solid separation and allows extracting a part of uncooled supercritical fluids for power generation. The proposed reactor and corresponding system were simulated using Aspen Plus 8.2, and simulation results agree well with experimental flame temperatures and reaction products. Exergy analysis results indicate the reactor, heat exchanger 7, heat exchanger 1, and turbine contribute to the main destruction of the system, with exergy distribution coefficients of 18.65%, 17.75%, 11.95%, and 7.64%, respectively. The exergy destruction coefficient for the reactor has been greatly reduced compared with previous TWR-SCWO systems, indicating great improvement in exergy efficiency with the Y-shape reactor. The exergy efficiency can be increased from 24.83% to 40.50% when hot water output is replaced with steam production because of the great reduction in exergy destruction. Lower ratios of fuel flow to feed flow contribute to higher exergy efficiencies on the premise of the safety and economy of the system. The increases of separation efficiency and split coefficient are helpful for increasing system efficiency for more supercritical fluids can be converted into high-grade energy. The increase of feed concentration is beneficial for the increase of system economy even though at a relative low exergy efficiency.

The future role of MFCs in biomass energy

Microbial fuel cells (MFC) are an emerging green technology which offers several comparative advantages over other technologies for utilizing biomass. It is a technology that treats (cleans) wet organic waste, converting chemical energy to electricity that is used for connected peripherals and target applications. The main advantage is the technology’s ability to utilise wet biomass in suspension or in solution (i.e., too wet to burn) and change the biomass directly into bioenergy in the form of electricity. All other technologies either combust the biomass directly (e.g., wood fuel) or change the biomass into refined fuels which are then combusted or fed to chemical fuel cells to generate heat or electricity. Excluding methane production from biomass, and fermentation leading to hydrogen production, all other biomass/biofuel technologies utilize dry plant matter, which mainly consists of cellulose or lignocellulose and they cannot directly utilize sludge or slurries of organic detritus material. The substrates used for MFCs are not traditionally made into organic fuels, as with other biomass technologies, but are used directly as fuel, recasting the “waste” suspensions and solutions, and promoting them into fuels themselves. To a stack of MFCs, a polluted river, landfill leachate or farmland run-off, can all be reassigned as fuel. This wet fuel is widespread around the planet, the amounts found and the energy contained within are significant, and the cost as a fuel is close to zero. This review gives a general overview of biomass energy along with extraction techniques and compares advantages and disadvantages of MFCs with other biomass technologies for producing electrical energy.

Co-Processing Agricultural Residues and Wet Organic Waste Can Produce Lower-Cost Carbon-Negative Fuels and Bioplastics.

Scalable, low-cost biofuel and biochemical production can accelerate progress on the path to a more circular carbon economy and reduced dependence on crude oil. Rather than producing a single fuel product, lignocellulosic biorefineries have the potential to serve as hubs for the production of fuels, production of petrochemical replacements, and treatment of high-moisture organic waste. A detailed techno-economic analysis and life-cycle greenhouse gas assessment are developed to explore the cost and emission impacts of integrated corn stover-to-ethanol biorefineries that incorporate both codigestion of organic wastes and different strategies for utilizing biogas, including onsite energy generation, upgrading to bio-compressed natural gas (bioCNG), conversion to poly(3-hydroxybutyrate) (PHB) bioplastic, and conversion to single-cell protein (SCP). We find that codigesting manure or a combination of manure and food waste alongside process wastewater can reduce the biorefinery's total costs per metric ton of CO2 equivalent mitigated by half or more. Upgrading biogas to bioCNG is the most cost-effective climate mitigation strategy, while upgrading biogas to PHB or SCP is competitive with combusting biogas onsite.

Evolving tolerance of Yarrowia lipolytica to hydrothermal liquefaction aqueous phase waste.

Hydrothermal liquefaction (HTL) is an emerging method for thermochemical conversion of wet organic waste and biomass into renewable biocrude. HTL also produces an aqueous phase (HTL-AP) side stream containing 2-4% light organic compounds that require treatment. Although anaerobic digestion (AD) of HTL-AP has shown promise, lengthy time periods were required for AD microbial communities to adapt to metabolic inhibitors in HTL-AP. An alternative for HTL-AP valorization was recently demonstrated using two engineered strains of Yarrowia lipolytica, E26 and Diploid TAL, for the overproduction of lipids and the polyketide triacetic acid lactone (TAL) respectively. These strains tolerated up to 10% HTL-AP (v/v) in defined media and up to 25% (v/v) HTL-AP in rich media. In this work, adaptive laboratory evolution (ALE) of these strains increased the bulk population tolerance for HTL-AP to up to 30% (v/v) in defined media and up to 35% (v/v) for individual isolates in rich media. The predominate organic acids within HTL-AP (acetic, butyric, and propionic) were rapidly consumed by the evolved Y. lipolytica strains. A TAL-producing isolate (strain 144-3) achieved a nearly 3-fold increase in TAL titer over the parent strain while simultaneously reducing the chemical oxygen demand (COD) of HTL-AP containing media. Fermentation with HTL-AP as the sole nutrient source demonstrated direct conversion of waste into TAL at 10% theoretical yield. Potential genetic mutations of evolved TAL production strains that could be imparting tolerance were explored. This work advances the potential of Y. lipolytica to biologically treat and simultaneously extract value from HTL wastewater. KEY POINTS: • Adaptive evolution of two Y. lipolytica strains enhanced their tolerance to waste. • Y. lipolytica reduces chemical oxygen demand in media containing waste. • Y. lipolytica can produce triacetic acid lactone directly from wastewater.

Chemical modification of straw hydrochar as additive to improve the anaerobic digestion performance of sludge hydrothermal carbonization wastewater

Hydrothermal carbonization (HTC) is a promising technology for treating highly wet organic solid waste such as sewage sludge (SS), but it generates a large amount of organic wastewater accompanied with solid fuel. In this study, hydrothermal carbonization wastewater (HTCWW) of SS was treated through anaerobic digestion (AD), and methanogenic performance was improved by adding straw hydrochar and its chemically modified products, which could reduce the adverse effects of refractory and toxic substances in HTCWW on microorganisms. After the hydrochar was modified through KOH, H2O2, and HCl immersion at room temperature, the abundance of oxygen-containing functional groups and the average pore size of the hydrochar increased, especially KOH, which had the most remarkable effect. By adding KOH-modified hydrochar at the optimal dosage of 20 g/L, the cumulative methane yield was 152 mL CH4/g-COD, which was 148.4 % higher than that of the control group (61.2 mL CH4/g-COD) without any hydrochar. At the beginning of AD, as some toxic substances, such as nitrogen compounds in HTCWW, was adsorbed by the added hydrochar, microorganisms could quickly adapt to the substrate environment. In addition, the hydrochar acted as a buffer to avoid the adverse effects of organic acid accumulation, thus reducing the lag period of AD by 0.2–1.3 days. In the middle and later stages of AD, hydrochar could provide colonization sites for the microorganisms, thereby enriching Metalosarcina and Metalosaeta, enhancing direct interspecific electron transfers, and further promoting the degradation of organic substances and generation of methane. The finding of this study showed that using modified hydrochar as the promoter of AD is a feasible method to improve the energy recovery of HTCWW, which will provide a novel paradigm for the clean and efficient utilization of wastes.

Solvothermal Liquefaction of Blackcurrant Pomace in the Water-Monohydroxy Alcohol Solvent System

Wet organic wastes are especially troublesome in valorization. Therefore, innovative solutions are still in demand to make valorization feasible. In this study, we tested a new transformation route of a blackcurrant pomace as a high-moisture industrial waste through a series of high-temperature and pressure solvothermal liquefaction experiments. The feedstock was directly converted under near-critical conditions of the binary solvent system (water/2-propanol). The goal was to examine the effect of conversion parameters (temperature, biomass-to-solvent ratio) on the change in the yield of resultant bioproducts, as well as the quality thereof. The experiments were conducted in a batch autoclave at a temperature between 250 and 300 °C. The main product of the transformation was liquid biocrude, which was obtained with the highest yield (ca. 52 wt.%) at 275 °C. The quality of biocrude was examined by ATR-FTIR, GC-MS, and elemental analysis. The ultimate biocrude was a viscous heterogeneous mixture containing various groups of components and exhibiting evident energy densification (ca. 145–153%) compared to the value of the feedstock. The proposed processing method is suitable for further development toward efficient valorization technology. More specifically, the co-solvent additive for liquefaction is beneficial not only for the enhancement of the yield of the desired product, i.e., biocrude, but also in terms of technological aspects (reduction of operational pressure and temperature).

Current Status and Prospects of Valorizing Organic Waste via Arrested Anaerobic Digestion: Production and Separation of Volatile Fatty Acids

Volatile fatty acids (VFA) are intermediary degradation products during anaerobic digestion (AD) that are subsequently converted to methanogenic substrates, such as hydrogen (H2), carbon dioxide (CO2), and acetic acid (CH3COOH). The final step of AD is the conversion of these methanogenic substrates into biogas, a mixture of methane (CH4) and CO2. In arrested AD (AAD), the methanogenic step is suppressed to inhibit VFA conversion to biogas, making VFA the main product of AAD, with CO2 and H2. VFA recovered from the AAD fermentation can be further converted to sustainable biofuels and bioproducts. Although this concept is known, commercialization of the AAD concept has been hindered by low VFA titers and productivity and lack of cost-effective separation methods for recovering VFA. This article reviews the different techniques used to rewire AD to AAD and the current state of the art of VFA production with AAD, emphasizing recent developments made for increasing the production and separation of VFA from complex organic materials. Finally, this paper discusses VFA production by AAD could play a pivotal role in producing sustainable jet fuels from agricultural biomass and wet organic waste materials.

Applications of Hydrochar and Charcoal in the Iron and Steelmaking Industry—Part 1: Characterization of Carbonaceous Materials

The iron and steelmaking industry faces the dilemma of the need to decrease their greenhouse gas emissions to align with decarbonization goals, while at the same time fulfill the increasing steel demand from the growing population. Replacing fossil coal and coke with biomass-based carbon materials reduces the net carbon dioxide emissions. However, there is currently a shortage of charcoal to fully cover the demand from the iron and steelmaking industry to achieve the emission-reduction goals. Moreover, the transportation and energy sectors can compete for biofuel usage in the next few decades. Simultaneously, our society faces challenges of accumulation of wastes, especially wet organic wastes that are currently not reused and recycled to their full potentials. Here, hydrothermal carbonization is a technology which can convert organic feedstocks with high moisture contents to solid fuels (hydrochar, one type of biochar) as an alternative renewable carbon material. This work studied the differences between a hydrochar, produced from lemon peels (Lemon Hydrochar), and two types of charcoals (with and without densification) and an Anthracite coal. Characterizations such as chemical and ash compositions, thermogravimetric analyses in nitrogen and carbon dioxide atmospheres, scanning electron microscope analyses of carbon surface morphologies, and pyrolysis up to 1200 °C were performed. The main conclusions from this study are the following: (1) hydrochar has a lower thermal stability and a higher reactivity compared to charcoal and Anthracite; (2) densification resulted in a reduction of the moisture pickup and CO2 reactivity of charcoal; (3) pyrolysis of Lemon Hydrochar resulted in the formation of a large amount of tar (17 wt%) and gas (39 wt%), leading to its low fixed carbon content (27 wt%); (4) a pyrolyzed hydrochar (up to 1200 °C) has a comparable higher heating value to those of charcoal and Anthracite, but its phosphorous, ash, and alkalis contents increased significantly; (5) based on the preliminary assessment, hydrochar should be blended with charcoal or Anthracite, or be upgraded through slow pyrolysis to fulfill the basic functions of carbon in the high-temperature metallurgical processes.

Hydrothermal carbonization processes applied to wet organic waste streams

Various organic waste streams are generated daily by human activities such as municipal, agricultural and industrial. The sustainable disposal of these organic wastes is a serious societal challenge. When the disposal process is not efficient, this type of wastes creates important pollution risks for air, soil, underground water and sea. Especially, wastes that have high moisture content cannot be eliminated cost effectively via thermo-chemical conversion by conventional processes such as pyrolysis, gasification and combustion. These processes necessitate the pre-drying of wet wastes which require additional energy input and increase the operational costs. One promising approach for the management and valorization of highly wet waste streams is the use of hydrothermal technologies. Hydrothermal carbonization is a very appropriate approach for valorizing wet organic wastes using water as a medium at high temperature and pressure under subcritical conditions. The generated “hydrochar” is a solid lignite like material that can be used for energy generation (by gasification or combustion) but also for environmental practices such as soil remediation and carbon fixation. This review focuses on the feedstock potential of wet organic wastes of sewage sludge, food wastes, various animal manure and macroalgae, and their valorization by hydrothermal carbonization. Structural, physical and energy conversion characteristics of hydrochars produced from various wet organic wastes are compared and discussed. Usage areas of hydrochars are also assessed.

Efficient Disposal of the Aqueous Products of Wet Organic Waste Hydrothermal Carbonization by Paddy Constructed Wetlands

Efficient Disposal of the Aqueous Products of Wet Organic Waste Hydrothermal Carbonization by Paddy Constructed Wetlands