Search Results (168)

This study investigates the potential of converting waste biosolids from industrial sources, focusing on economic viability and heavy metal removal efficiency. Traditional management methods like landfilling and incineration are increasingly impractical due to land constraints and environmental concerns, prompting a shift towards thermal and biological conversion technologies including anaerobic digestion, pyrolysis, gasification, and hydrothermal liquefaction. Incorporating a pretreatment for heavy metal removal is essential, as industrial wastes are highly subjected to metal contamination. The study screens a range of metal removal processes, including precipitation, adsorption, ion exchange, and microwave induction. Although a techno-economic analysis can help give a perspective on the economic viability and environmental impact of each technology, it does not account for technical limitations and variations in the treated waste stream. A mixed integer linear programming (MILP) optimization model is developed to fill in this gap and assist in waste stream allocation to the most appropriate technology, taking into account both technology capacities and feed characteristics. This study looked into the optimal treatment route at different feed moisture contents and varying flow rates. The results demonstrate that the model distributes the feed across the different technologies on the basis of maximizing the capacity of the optimal technology while ensuring the moisture and heavy metal content limits are satisfied. Thus, it maximizes profitability and ensures heavy metal removal efficiency. By optimizing industrial biosolids treatment pathways, this study promotes sustainable resource recovery aligning with circular economy principles in waste management. The developed model facilitates informed decision-making in biosolids management and industrial waste treatment practices. Full article

In the energy transition process, aiming for zero disposal and clean production in the elimination of waste is crucial; consequently, agricultural residues have significant potential for reduction in the use of fossil fuels. This study investigates the hydrothermal liquefaction (HTL) of sugarcane bagasse (BSC) and straw (SSC), examining the products’ distribution and bio-oil composition relative to the reaction conditions. The experiments used a 2³ factorial design, evaluating the temperature (300–350 °C), constant heating time (0–30 min), and the use of the K₂CO₃ concentration as the catalyst (0–0.5 mol/L⁻¹). The main factor affecting the biocrude yield from BSC and SSC was the use of K₂CO₃. Statistically significant interaction effects were also observed. Milder conditions resulted in the highest bio-oil yields, 36% for BSC and 31% for SSC. The catalyst had no impact on the biocrude production. The bio-oils were analyzed by GC/MS and FTIR; a principal component analysis (PCA) was performed to evaluate the samples’ variability. The FTIR highlighted bands associated with common oxygenated compounds in lignocellulosic biomass-derived bio-oils. The GC-MS results indicated a predominance of oxygenated compounds, and these were highest in the presence of the catalyst for both the BSC (90.6%) and SSC (91.7%) bio-oils. The SSC bio-oils presented higher oxygenated compound contents than the BSC bio-oils. Statistical analysis provided valuable insights for optimizing biomass conversion processes, such as determining the optimal conditions for maximizing product yields. Full article

Hydrothermal liquefaction (HTL) is an effective biomass thermochemical conversion technology that can convert organic waste into energy products. However, the HTL process is influenced by various complex factors such as operating conditions, feedstock properties, and reaction pathways. Machine learning (ML) methods can utilize existing HTL data to develop accurate models for predicting product yields and properties, which can be used to optimize HTL operation conditions. This paper presents a bibliometric review on ML applications in HTL from 2020 to 2024. CiteSpace, VOSviewer, and Bibexcel were used to analyze seven key bibliometric attributes: annual publication output, author co-authorship networks, country co-authorship networks, co-citation of references, co-citation of journals, collaborating institutions, and keyword co-occurrence networks, as well as time zone maps and timelines, to identify the development of ML in HTL research. Through the detailed analysis of co-occurring keywords, this study aims to identify frontiers, research gaps, and development trends in the field of ML-aided HTL. Full article

Hydrothermal liquefaction technology (HTL) is a promising thermochemical method to convert biomass into novel liquid fuels. The introduction of oxides and inorganic acids/bases during the hydrothermal process significantly impacts the yield and composition of bio-oil. However, systematic research on their effects, especially at lower temperatures, remains limited. In this paper, we examine the effects of acidity and alkalinity on cotton stalk hydrothermal bio-oil by introducing homogeneous acids and bases. Given the operational challenges associated with product separation using homogeneous acids and bases, this paper further delves into the influence of heterogeneous oxide catalysts (possessing varying degrees of acidity and alkalinity, as well as distinct microstructures and pore architectures) on the production of cotton stalk hydrothermal bio-oil. The effects of nanoscale oxides (CeO₂, TiO₂, ZnO, Al₂O₃, MgO and SiO₂) and homogeneous acid–base catalysts (NaOH, K₂CO₃, Na₂CO₃, KOH, HCl, H₂SO₄, HNO₃) on the quality of cotton stalk bio-oil under moderate hydrothermal conditions (220 °C, 4 h) were investigated. Characterization techniques including infrared spectroscopy, thermogravimetric analysis, elemental analysis, and GC-MS were employed. The results revealed that CeO₂ and NaOH achieved the highest bio-oil yield due to Ce³⁺/Ce⁴⁺ redox reactions, OH-LCC disruption, and ionic swelling effects. Nano-oxides enhanced the formation of compounds like N-ethyl formamide and aliphatic aldehydes while suppressing nitrogen-containing aromatics. The total pore volume and average pore width of oxides negatively correlated with their catalytic efficiency. CeO₂ with low pore volume and width exhibited the highest energy recovery. The energy recovery of cotton stalk bio-oil was influenced by both acid and base sites on the oxide surface, with a higher weak base content favoring higher yields and a higher weak acid content inhibiting them. The findings of this research are expected to provide valuable insights into the energy utilization of agricultural solid waste, such as cotton stalks, as well as to inform the design and development of highly efficient catalysts. Full article

In response to the increasing global demand for sustainable energy alternatives, this research explores the efficient conversion of sugarcane bagasse to bio-oil through hydrothermal liquefaction (HTL) processes with modified Zeolite Socony Mobil-5 catalysts (ZSM-5). The study systematically investigates the impact of feedstock quantity, reaction temperature, duration, and catalyst loading on bio-oil yield and quality. Optimisation experiments revealed that a feedstock amount of 10 grammes, an HTL temperature of 340 °C for 60 min and a ZSM-5 catalyst loading of 3 grammes resulted in the highest bio-oil yield. Furthermore, the introduction of Ni and Fe metals to ZSM-5 exhibited enhanced catalytic activity without compromising the structure of the zeolites. Comprehensive characterisation of modified catalysts using SEM-EDS, XRD, TGA, TEM, and FTIR provided insight into their structural and chemical properties. The successful incorporation of Ni and Fe into ZSM-5 was confirmed, highlighting promising applications in hydrothermal liquefaction. Gas chromatography–mass spectrometry (GC-MS) analysis of bio-oils demonstrated the effectiveness of the 2% Fe/ZSM-5 catalyst, highlighting a significant increase in hydrocarbon content. FTIR analysis of the produced bio-oils indicated a reduction in functional groups and intensified aromatic peaks, suggesting a shift in chemical composition favouring aromatic hydrocarbons. This study provides valuable information on HTL optimisation, catalyst modification, and bio-oil characterisation, advancing the understanding of sustainable biofuel production. The findings underscore the catalytic prowess of modified ZSM-5, particularly with iron incorporation, in promoting the formation of valuable hydrocarbons during hydrothermal liquefaction. Full article

Algae is a promising sustainable feedstock for the generation of bio-crude oil, which is a sustainable alternative to fossil fuels, through the thermochemical process of hydrothermal liquefaction (HTL). However, this process also generates carbon particles (algae-derived carbon, ADC) as a significant byproduct. Herein, we report a brand-new and value-added use of ADC particles as a reinforcing agent for epoxy matrix composites (EMCs). ADC particles were synthesized through HTL processing of Chlorella vulgaris (a green microalgae) and characterized for morphology, average size, specific surface area, porosity, and functional groups. The ADC particles were subsequently integrated into a representative epoxy resin (EPON 862) as a reinforcing filler at loading levels of 0.25%, 0.5%, 1%, and 2% by weight. The tensile, flexural, and Izod impact properties, as well as the thermal stability, of the resulting EMCs were evaluated. It is revealed that the ADC particles are a sustainable and effective reinforcing agent for EMCs at ultra-low loading. Specifically, the ADC-reinforced EMC with 1 wt.% ADC showed improvements of ~24%, ~30%, ~31%, and ~57% in tensile strength, Young’s modulus, elongation at break, and work of fracture (WOF), respectively, and improvements of ~10%, ~37%, ~24%, and ~39% in flexural strength, flexural modulus, flexural elongation at break, and flexural WOF, respectively, as well as an improvement of ~54% in Izod impact strength, compared to those corresponding properties of neat epoxy. In the meantime, the thermal decomposition temperatures at 60% and 80% weight loss of the abovementioned ADC-reinforced EMC increased from 410 °C to 415 °C and from 448 °C to 515 °C in comparison with those of neat epoxy. This study highlighted the potential of sustainable ADC particles as a reinforcing agent in the field of polymer matrix composite materials, which represented a novel and sustainable approach that would mitigate greenhouse gas remission and reduce reliance on nonrenewable reinforcing fillers in the polymer composite industry. Full article

We report a transformative epoxy system with a microalgae-derived bio-binder from hydrothermal liquefaction processing (HTL). The obtained bio-binder not only served as a curing agent for conventional epoxy resin (e.g., EPON 862), but also acted as a modifying agent to enhance the thermal and mechanical properties of the conventional epoxy resin. This game-changing epoxy/bio-binder system outperformed the conventional epoxy/hardener system in thermal stability and mechanical properties. Compared to the commercial EPON 862/EPIKURE W epoxy product, our epoxy/bio-binder system (35 wt.% bio-binder addition with respect to the epoxy) increased the temperature of 60% weight loss from 394 °C to 428 °C and the temperature of maximum decomposition rate from 382 °C to 413 °C, while the tensile, flexural, and impact performance of the cured epoxy improved in all cases by up to 64%. Our research could significantly impact the USD 38.2 billion global market of the epoxy-related industry by not only providing better thermal and mechanical performance of epoxy-based composite materials, but also simultaneously reducing the carbon footprint from the epoxy industry and relieving waste epoxy pollution. Full article

Hydrothermal co-liquefaction (co-HTL) is a process involving two sources of biomasses aiming at bio-crude production. Since there is a lack of studies performed with sugarcane bagasse and residual soybean oil, this study investigated different conditions for the co-HTL of these biomasses, with and without the presence of ethanol as a co-solvent to maximize the bio-crude yield. All co-HTL reactions were carried out in a 300 mL Parr^® reactor at temperatures ranging from 200 to 300 °C. After the reaction, a vacuum filtration was performed to separate the bio-char, later washed with ethanol to extract heavy bio-crude, while the liquid-phase was mixed with dichloromethane to recover light bio-crude. Bio-crude yields of around 95 wt.% were obtained at 300 °C using ethanol and water as solvents. The highest bio-char yield (16.6 wt.%) was achieved when using only sugarcane bagasse as the substrate, without the presence of soybean oil. Bio-crude samples obtained at higher temperatures (280 °C and 300 °C) using ethanol as a hydrogen donor presented higher contents of both free fatty acids and fatty acid ethyl esters. This work presents a promising process to produce high-quality bio-crude using an abundant feedstock (sugarcane bagasse) in the presence of a lipid source which could cause environmental problems if poorly handled. Full article

The stability of biocrude oil is a significant challenge for its storage, transportation, and refining. In this investigation, the thermal and oxidative stability of Spirulina-biocrude oil derived from a plug-flow continuous hydrothermal reactor was systematically studied. The biocrude oil was stored at three temperatures to simulate the winter (4 °C), spring and autumn (15 °C), and summer (35 °C) seasons, and in two atmospheres (air and N₂) to simulate the conditions of a storage tank being sealed or kept open. Results demonstrated that the physicochemical properties of biocrude oil were highly influenced by the storage environment. The viscosity of biocrude oil increased with increasing storage temperature and time. The maximum viscosity (17,577 mPa·s) was observed when biocrude oil was stored at 35 °C and in an air condition over 84 days, 145% higher than fresh biocrude oil (7164.2 mPa·s). The viscosity increased by 10.9% when biocrude oil was sorted at 4 °C in an N₂ atmosphere after being stored for 28 days. After long-term storage, biocrude oil still exhibited comparable characteristics to petroleum, with a slight decrease in HHV (31.36–33.97 MJ·kg⁻¹) and the nitrogen-to-carbon ratio (0.087–0.092). This study indicated that the viscosity and HHV of the biocrude oil derived from a continuous reactor stored at 4 °C in an N₂ atmosphere condition remained relatively unchanged, which enables the scheduling of oil refining production. Full article

With the worldwide awareness of sustainability, biomass-derived carbon electrode materials for supercapacitors have attracted growing attention. In this research, for the first time, we explored the feasibility of making use of the carbon byproduct from hydrothermal liquefaction (HTL) of microalgae, termed herein as algae-derived carbon (ADC), to prepare sustainable carbon electrode materials for high-performance supercapacitor development. Specifically, we investigated carbon activation with a variety of activating reagents as well as N- and Fe-doping of the obtained ADC with the intention to enhance its electrochemical performance. We characterized the structure of the activated and doped ADCs using scanning electron microscope (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and BET surface area and pore analysis, and correlated the ADCs’ structure with their electrochemical performance as evaluated using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), impedance, and cycle stability through an assembled symmetric two-electrode cell with 1 M H₂SO₄ as electrolyte. It was found that the ADC that is activated using KOH (KOH-ADC) showed the best electrochemical performance, and its specific capacitance was 14.1-fold larger with respect to that of the raw ADC and reached 234.5 F/g in the GCD test at a current density of 0.5 A/g. The KOH-ADC also demonstrated excellent capacitance retention (97% after 10,000 cycles at a high current density of 10 A/g) for stable long-term operations. This research pointed out a promising direction to develop sustainable electrode materials for supercapacitors from the carbon byproduct produced after HTL processing of algae. Full article

This article presents multiphase numerical computational fluid dynamics (CFD) for simulating hydrothermal liquefaction of sewage sludge in a continuous plug-flow reactor. The discrete particle method (DPM) was used to analyze the solid particles’ interaction in liquid–solid high shear flows to investigate coupling computational fluid dynamics (CFD). Increasing solid particles’ interactions were observed with the increasing liquid velocity. The study examined the influence of parameters such as flow rate, temperature, and residence time on the efficiency of bio-oil production. An increase in temperature from 500 to 800 K caused an increase in the amount of biocrude oil produced from 12.4 to 32.9% within 60 min. In turn, an increase in the flow rate of the suspension from 10 to 60 mL/min caused a decrease in the amount of biocrude oil produced from 38.9 to 12.9%. This study offers insights into optimizing the flow channel of tubular reactors to enhance the HTL conversion efficiency of sewage sludge into biocrude oil. A parametric study was performed to investigate the effect of the slurry flow rate, temperature, and the external heat transfer coefficient on the biocrude oil production performance. The simulation data will be used in the future to design and scale up a large-scale HTL reactor. Full article

As a byproduct of municipal wastewater treatment systems, sewage sludge has traditionally been treated in low-value applications such as landfilling, posing significant environmental risks due to its pollutant content. However, there is a growing interest in utilizing the energy potential of sewage sludge through thermochemical conversion methods. Among these methods, hydrothermal liquefaction (HTL) has come to the fore as a promising green approach, offering an environmentally friendly means of extracting bio-oils and biochemicals from sewage sludge. In this study, the HTL method, regarded as an innovative approach among sewage sludge treatment methods apart from incineration, pyrolysis, and landfilling, is comparatively investigated in terms of greenhouse gas (GHG) emissions alongside other methods. In particular, this study analyzes the projected amount and various characteristics of sewage sludge that could potentially be generated by 2030 for the city of Adana, which currently produces approximately 185 tons of sewage sludge per day. The findings indicate that without intervention, sludge production is projected to reach 68,897 tons per year by 2030. Moreover, this research demonstrates that the utilization of HTL for sludge treatment results in a reduction of emissions by approximately 7-fold compared with incineration of sewage sludge. Full article

In this study, hydrothermal co-liquefaction of restaurant waste for biocrude production was conducted. The feedstock was resembled using the organic fraction of restaurant waste and low-density polyethylene, polypropylene, polystyrene, and polyethylene terephthalate, four plastic types commonly present in municipal solid waste. Using design of experiment and a face-centered central composite design, three factors (feedstock plastic fraction, temperature, time) were varied at three levels each: feedstock plastic fraction (0, 0.25, 0.5), temperature (290 °C, 330 °C, 370 °C), and reaction time (0 min, 30 min, 60 min). The literature reports positive synergistic interactions in hydrothermal co-liquefaction of biomass and plastics; however, in this work, only negative synergistic interactions could be observed. A reason could be the high thermal stability of produced fatty acids that give little room for interactions with plastics. At the same time, mass might transfer to other product phases. Full article

Microalgae-based renewable energy, industrial chemicals, and food have received great attention during the last decade. This review article highlights the versatility of algal biomass as a feedstock for producing various commodities and high-value products, including aromatic hydrocarbons and lipids within biorefinery systems. Lipid content and the composition of algal biomass cultivated in various media, specifically in wastewater streams generated at agricultural and industrial production facilities, are reviewed. Technical and chemical aspects of algal biomass conversion via thermochemical techniques including pyrolysis, hydrothermal liquefaction, and hydrothermal carbonization are discussed. The properties of the final products are reviewed based on the conversion process employed. Studies published within the last 5 years are reviewed. The importance of further research on inexpensive and more effective catalysts and the development of downstream processes to upgrade crude products obtained from thermal conversion processes is emphasized. This review concludes with an in-depth discussion of the opportunities and challenges involved in algal biomass-based bioproduct manufacturing and commercialization. Full article

There is an opportunity for agriculture to utilize the many different waste streams in our world and capitalize on what would otherwise be viewed as waste products. Hydrothermal liquefaction (HTL) is an emerging technology for converting wet biomass to bio-crude oil, while aquaponics is a practice tracing back to indigenous communities around the world; both technologies have the potential to sustainably provide the necessary nutrients for crop growth. Food systems worldwide are actively transitioning to address the many challenges of climate change in a sustainable and efficient manner. Urban agriculture (UA) has the potential to generate localized crops in densely populated areas year-round, but has its challenges, involving high capital requirements, especially for vertical farming and controlled-environment agriculture, and being energy intensive due to artificial lighting and fossil fuel-based synthetic fertilizers. This study investigated the potential for aquaponic and HTL effluents to be used in hydroponic systems through a seed germination screening experiment. Buttercrunch lettuce (Lactuca sativa L.) seeds were placed in Ziploc plastic bags on paper towels saturated with the wastewater treatments for 10 days while their total length of growth was routinely measured from the tip of the root to the tip of the cotyledons. The Chicago High School for Agricultural Sciences (CHSAS) aquaponic effluent with a 5.8× times higher nitrate concentration and 4.25× higher ammonia concentration outperformed the Bevier aquaponic effluent and improved any other source water it was combined with. Results also showed that seed germination was not inhibited in the presence of 2–8% solutions of hydrothermal liquefaction aqueous phase (HTL-AP), which performed on par with standard hydroponic fertilizer; solutions of a higher percentage, though, may lead to inhibitory effects in plants, and those of a lower percentage may not provide enough nutrients in the proper forms to sustain plant growth. However, the nutrient analyses revealed that there is still much to investigate regarding the combination of wastewaters to provide a complete, well-rounded, and sustainable source for hydroponic crop production. Full article