Inherent Metals of a Phytoremediation Plant Influence Its Recyclability by Hydrothermal Liquefaction

GhRCD1 promotes cotton tolerance to cadmium by regulating the GhbHLH12-GhMYB44-GhHMA1 transcriptional cascade

Heavy metal pollution poses a significant risk to human health and wreaks havoc on agricultural productivity. Phytoremediation, a plant-based, environmentally benign, and cost-effective method, is employed to remove heavy metals from contaminated soil, particularly in agricultural or heavy metal-sensitive lands. However, the phytoremediation capacity of various plant species and germplasm resources display significant genetic diversity, and the mechanisms underlying these differences remain hitherto obscure. Given its potential benefits, genetic improvement of plants is essential for enhancing their uptake of heavy metals, tolerance to harmful levels, as well as overall growth and development in contaminated soil. In this study, we uncover a molecular cascade that regulates cadmium (Cd2+) tolerance in cotton, involving GhRCD1, GhbHLH12, GhMYB44, and GhHMA1. We identified a Cd2+-sensitive cotton T-DNA insertion mutant with disrupted GhRCD1 expression. Genetic knockout of GhRCD1 by CRISPR/Cas9 technology resulted in reduced Cd2+ tolerance in cotton seedlings, while GhRCD1 overexpression enhanced Cd2+ tolerance. Through molecular interaction studies, we demonstrated that, in response to Cd2+ presence, GhRCD1 directly interacts with GhbHLH12. This interaction activates GhMYB44, which subsequently activates a heavy metal transporter, GhHMA1, by directly binding to a G-box cis-element in its promoter. These findings provide critical insights into a novel GhRCD1-GhbHLH12-GhMYB44-GhHMA1 regulatory module responsible for Cd2+ tolerance in cotton. Furthermore, our study paves the way for the development of elite Cd2+-tolerant cultivars by elucidating the molecular mechanisms governing the genetic control of Cd2+ tolerance in cotton.

Speciation, leachability, and phytoaccessibility of heavy metals during thermochemical liquefaction of contaminated peanut straw

In this study, the speciation, leachability, phytoaccessibility, and environmental risks of heavy metals (Cd, Zn, and Cu) during liquefaction of contaminated peanut straw in ethanol at different temperatures (220, 260, 300, 340, and 380 °C) were comprehensively investigated. The results showed that elevated temperatures facilitated heavy metal accumulation in the biochar. The acid-soluble/exchangeable and reducible fraction percentages of heavy metals were substantially reduced in the biochar after liquefaction as the temperature increased, and the oxidizable fraction became the dominant heavy metal fraction, accounting for 44.14-78.67%. Furthermore, although an excessively high liquefaction temperature (380 °C) increased the residual fraction percentages of Zn and Cu, it was detrimental to Cd immobilization. The acid-soluble/exchangeable Cd in the contaminated peanut straw readily migrates to the bio-oil during liquefaction, with the highest concentration of 1.60 mg/kg at 260 °C liquefaction temperature, whereas Zn and Cu are predominantly bound to the unexchangeable fraction in the bio-oil. Liquefaction inhibited heavy metal leachability and phytoaccessibility in biochar, the lowest extraction rates of Cd, Zn, and Cu were 0.71%, 1.66% and 0.95% by diethylenetriamine pentaacetic acid, respectively. However, the leaching and extraction concentrations increased when the temperature was raised to 380 °C. Additionally, heavy metal risk was reduced from medium and high risk to no and low risk. In summary, liquefaction reduces heavy metal toxicity and the risks associated with contaminated peanut straw, and a temperature range of 300-340 °C for ethanol liquefaction can be considered optimal for stabilizing heavy metals.

Selective recovery of rare earth elements and value-added chemicals from the Dicranopteris linearis bio-ore produced by agromining using green fractionation

The increasing demand for Rare Earth Elements (REEs) and the depletion of mineral resources motivate sustainable strategies for REE recovery from alternative unconventional sources, such as REE hyperaccumulator. The greatest impediment to REE agromining is the difficulty in the separation of REEs and other elements from the harvested biomass (bio-ore). Here, we develop a sulfuric acid assisted ethanol fractionation method for processing D. linearis bio-ore to produce the pure REE compounds and value-added chemicals. The results show that 94.5% of REEs and 87.4% of Ca remained in the solid phase, and most of the impurities (Al, Fe, Mg, and Mn) transferred to the liquid phase. Density functional theory calculations show that the water-cation bonds of REEs and Ca cations were broken more easily than the bonds of the cations of key impurities, causing lower solubility of REEs and Ca compounds. Subsequent separation and purification led to a REE-oxide (REO) product with a purity of 97.1% and a final recovery of 88.9%. In addition, lignin and phenols were obtained during organosolv fractionation coupled with a fast pyrolysis process. This new approach opens up the possibility for simultaneous selective recovery of REEs and to produce value-added chemicals from REE bio-ore refining.

Mutation of NtNRAMP3 improves cadmium tolerance and its accumulation in tobacco leaves by regulating the subcellular distribution of cadmium

Cadmium (Cd) is a harmful element that affects plant growth and development. Genetic improvements could be applied for enhancing Cd tolerance and accumulation in plants. Here, a novel Cd stress-induced gene, NtNRAMP3, was identified in tobacco. We constructed two NtNRAMP3-knockout (KO) tobacco lines using the CRISPR/Cas9 system, which enhanced Cd tolerance and Cd accumulation in tobacco leaves compared with those in the wildtype (WT). Subcellular localization analysis suggested that NtNRAMP3 is a tonoplast protein and GUS (β-glucuronidase) histochemical analysis showed that NtNRAMP3 is highly expressed in the conductive tissue of leaves. NtNRAMP3-KO tobacco showed reduced Cd translation from vacuole to cytosol in leaves compared with the WT, and its vacuolar Cd concentration was significantly higher (20.78-22.81%) than that in the WT; in contrast, Cd concentration in the cytosol was reduced by 13.72-20.15%, preventing chlorophyll degradation and reducing reactive oxygen species accumulation in the leaves. Our findings demonstrate that NtNRAMP3 is involved in regulating Cd subcellular distribution (controlling Cd transport from vacuoles to the cytosol) and affects Cd tolerance and its accumulation in tobacco. This provides a key candidate gene to improve the phytoremediation efficiency of plants via genetic engineering.

Thermochemical conversion of heavy metal contaminated biomass: Fate of the metals and their impact on products

With the rapid depletion of fossil energy and increasingly severe environmental pollution, the development of biomass resources for biorefineries has become a new research focus. However, heavy metals may be released during the thermochemical treatment when the biomass materials used in biomass conversion are contaminated by heavy metals. This can cause secondary environmental pollution or transference to the target products, reducing product quality. Therefore, having a systematic understanding of the fate of heavy metals in biomass conversion is necessary for alleviating potential risks. This study presents the current status of contaminated biomass and conversion products involving thermochemical processes, the migration, transformation, and impact of heavy metals in biomass conversion was investigated, and the utilization of heavy metals in contaminated biomass was briefly outlined. This review aims to link biomass conversion to the fate of heavy metals, avoid existing risks as much as possible to produce cleaner products efficiently, and promote the sustainable development of heavy metal contaminated biomass resources.

Metabolic engineering of Oryza sativa for complete biodegradation of thiocyanate

Industrial thiocyanate (SCN^-) waste streams from gold mining and coal coking have caused serious environmental pollution worldwide. Phytoremediation is an efficient technology in treating hazardous wastes from the environment. However, the phytoremediation efficiency of thiocyanate is very low due to the fact that plants lack thiocyanate degradation enzymes. In this study, the thiocyanate hydrolase module was assembled correctly in rice seedlings and showed thiocyanate hydrolase activity. Rice seedlings engineered to express thiocyanate degrading activity were able to completely remove thiocyanate from coking wastewater. Our findings suggest that transforming the thiocyanate hydrolase module into plants is an efficient strategy for rapid phytoremediation of thiocyanate in the environment. Moreover, the rice seedlings expressing apoplastic or cytoplasmic targeted thiocyanate hydrolase module were constructed to compare the phytoremediation efficiency of secretory/intracellular recombinant thiocyanate hydrolase. The most obvious finding from this study is that the apoplastic expression system is more efficient than the cytoplasm expression system in the phytoremediation of thiocyanate. At last, this research also shows that the secreted thiocyanate hydrolase from engineered rice plants does not influence rhizosphere bacterial community composition.

Stabilization of heavy metals in biochar derived from plants in antimony mining area and its environmental implications

Heavy metals pollution in mining soils seriously threatens the ecological environment and human health worldwide. Phytoremediation is considered to be an ideal method to reduce the toxicity, mobility, and bioavailability of heavy metals in the soils. However, the disposal of plant-enriched heavy metals has become a thorny problem. To estimate the effect of pyrolysis on the stabilization of heavy metals in post-phytoremediation plant residues, different biochars were prepared from Conyza canadensis (CC), Gahnia tristis (GT), and Betula luminifera (BL) at different pyrolysis temperatures (300, 450, and 600 °C). Results indicated that pyrolysis was effective in the stabilization of heavy metals (Cr, Ni, As, Sb, Hg, and Pb) in plants and significantly (P < 0.05) decreased the bioavailability of most heavy metals. Among them, GT₆₀₀ prepared by pyrolysis of GT at 600 °C has the best stabilization effect on Sb, which increases the residual fraction by 7.32 times, up to 82.05%. The results of environmental risk assessment show that pyrolysis of biomass at high temperature (600 °C) can effectively mitigate the environmental impact of As, Sb, and Hg. Additionally, the reutilization potential of biochar produced by post-phytoremediation plant residues as adsorbents was investigated. The results of adsorption experiments revealed that all biochars have an excellent performance to adsorb Pb(II), and the maximum adsorption capacity is 139.16 mg g^-1 for CC₄₅₀. The adsorption mechanism could be attributed to complexation, electrostatic attraction, and cation exchange. This study demonstrates that pyrolysis is an effective and environment-friendly alternative method to stabilize heavy metals in plants, and their pyrolysis products can be reused for heavy metal adsorption.

Hydrothermal conversion of Cd/Zn hyperaccumulator (Sedum alfredii) for heavy metal separation and hydrochar production

The harmless treatment of heavy metal-enriched hyperaccumulator biomass is the main barrier to the industrialization of phytoremediation. Hydrothermal conversion of Sedum alfredii using different solvents (i.e ·H₂O and HCl) at 210-300 ℃ was performed to investigate the behaviors of Cd and Zn, and the characteristics and potential application of the derived hydrochars were determined. Low temperature and HCl addition favored the removal of Cd/Zn from the solid phase. The highest removal efficiencies of Cd (95.0%) and Zn (89.3%) were achieved at 210 ℃ with the presence of HCl. The yield, pH, ash content, element concentration, functional groups, and crystalline minerals of the derived hydrochar were influenced by the reaction temperature and addition of HCl. The leaching risk of Cd and Zn was significantly reduced by hydrothermal conversion. The addition of HCl facilitated the immobilization of Zn, while it enhanced the mobility of Cd. Moreover, the hydrochar derived at 210 ℃ showed increased sorption capacity towards Cu, and the addition of HCl greatly improved the energy density of hydrochar. These results suggest that HCl-mediated hydrothermal conversion could be a promising technique to achieve the separation of Cd and Zn from hyperaccumulator biomass as well as the production of value-added hydrochar.

Overexpression of FaHSP17.8-CII improves cadmium accumulation and tolerance in tall fescue shoots by promoting chloroplast stability and photosynthetic electron transfer of PSII

Genetic improvement could play a significant role in enhancing the Cd accumulation, translocation and tolerance in plants. In this study, for the first time, we constructed transgenic tall fescue overexpressing a class II (CII) sHSP gene FaHSP17.8-CII, which enhanced Cd tolerance and the root-to-shoot Cd translocation. After exposed to 400 μM CdCl₂, two FaHSP17.8-CII overexpressing lines (OE#3 and OE#7) exhibited 30% and 40% more shoot fresh weight, respectively, relative to the wild-type (WT). Both transgenic lines showed higher tolerance to Cd, as evidenced by lower levels of electrolyte leakage and malondialdehyde compared to the WT plants under Cd stress. FaHSP17.8-CII overexpression increased shoot Cd contents 49-59% over the WT plants. The Cd translocation factor of root-to-shoot in OE grasses was 69-85% greater than WT under Cd stress. Furthermore, overexpression of FaHSP17.8-CII reduced Cd-induced damages of chloroplast ultra-structure and chlorophyll synthesis, and then improved photosystem II (PSII) function under Cd stress, which resulted in less reactive oxygen species (ROS) accumulation in OE grasses than that in WT exposed to Cd stress. The study suggests a novel FaHSP17.8-CII-PSII-ROS module to understand the mechanisms of Cd detoxification and tolerance, which provides a new strategy to improve phytoremediation efficiency in Cd-stressed grasses.

Enhanced phytoremediation of TNT and cobalt co-contaminated soil by AfSSB transformed plant

2,4,6-trinitrotoluene (TNT) and cobalt (Co) contaminants have posed a severe environmental problem in many countries. Phytoremediation is an environmentally friendly technology for the remediation of these contaminants. However, the toxicity of TNT and cobalt limit the efficacy of phytoremediation application. The present research showed that expressing the Acidithiobacillus ferrooxidans single-strand DNA-binding protein gene (AfSSB) can improve the tolerance of Arabidopsis and tall fescue to TNT and cobalt. Compared to control plants, the AfSSB transformed Arabidopsis and tall fescue exhibited enhanced phytoremediation of TNT and cobalt separately contaminated soil and co-contaminated soil. The comet analysis revealed that the AfSSB transformed Arabidopsis suffer reduced DNA damage than control plants under TNT or cobalt exposure. In addition, the proteomic analysis revealed that AfSSB improves TNT and cobalt tolerance by strengthening the reactive superoxide (ROS) scavenging system and the detoxification system. Results presented here serve as strong theoretical support for the phytoremediation potential of organic and metal pollutants mediated by single-strand DNA-binding protein genes. SUMMARIZES: This is the first report that AfSSB enhances phytoremediation of 2,4,6-trinitrotoluene and cobalt separately contaminated and co-contaminated soil.

Migration and transformation of heavy metals in hyperaccumulators during the thermal treatment: a review

The pollution of heavy metals (HMs) in the soil has become one of the important factors affecting the national environment and human health. Phytoremediation, as a technology to deal with HM pollution in soil, has been extensively studied and applied due to its sustainability and environmental friendliness. However, hyperaccumulators polluted by HMs need to be properly treated to avoid secondary pollution to the environment. This paper reviews the migration and transformation of HMs during the incineration, pyrolysis, gasification, and hydrothermal treatment of hyperaccumulators; comprehensively evaluates the advantages and disadvantages of each technology in the treatment of HM-enriched hyperaccumulators; and analyzes the current development status and unsolved problems in detail for each technology. Generally speaking, thermal treatment technology can fix most of the HMs of exchangeable fraction in biochar, reducing its bioavailability and biotoxicity. In addition, the application direction and research focus of the target product are discussed, and it is clarified that in the future, it is necessary to further optimize the reaction conditions and explore the mechanism of HM immobilization to maximize the immobilization of HMs and improve the quality and output of the target product.

Tolerance and detoxification mechanisms to cadmium stress by hyperaccumulator Erigeron annuus include molecule synthesis in root exudate

Cadmium (Cd) is one of the most toxic environmental pollutants affecting the growth and reproduction of various plants. Analysis of the biological adaptation and tolerance mechanisms of the hyperaccumulator Erigeron annuus to Cd stress may help identify new plant species for phytoremediation and in optimizing the process. This study is to the first to analyze the molecular composition and diversity of dissolved organic matter (DOM) secreted by roots using FT-ICR MS, and multiple physiological and biochemical indexes of E. annuus seedlings grown in solutions containing 0-200 Cd μmol L-1. The results showed that E. annuus had strong photosynthetic adaptation and protection ability under Cd stress. Cd was immobilized or compartmentalized by cell walls and vacuoles in the plant, thus alleviating Cd stress. Activation of anti-oxidation defense mechanisms also played an important role in alleviating or eliminating Cd toxicity in E. annuus. High Cd stress promoted production of a higher proportion of new molecules in DOM secreted by E. annuus roots compared to low Cd stress. DOM secreted by roots contributed to plant resistance to Cd-induced stress via producing more carbohydrates, aromatic structures and tannins. Results indicate the mechanisms underpinning the potential use of E. annuus as a phytoremediator in environments with moderate Cd pollution.

Transformation behaviors and environmental risk assessment of heavy metals during resource recovery from Sedum plumbizincicola via hydrothermal liquefaction

Environmentally sound disposal of hyperaccumulator harvests is of critical importance to industrialization of phytoremediation. Herein, transformation behaviors and environmental risk of heavy metals were comprehensively examined during subcritical hydrothermal liquefaction of Sedum plumbizincicola. It is concluded that low temperature liquefaction favored resource recovery of heavy oil and hydrochars in terms of higher energy density, improved carbon sequestration and less energy consumption. Heavy metals were mainly distributed into hydrochars and water soluble phase with less than 10% in heavy oil. All metal elements except As could be accumulated in hydrochars by extending reaction time, whereas more than 96% of As was redistributed into water soluble phase. Prolonged liquefaction time facilitated immobilization of Cd, Cr and As in hydrochars, but fast liquefaction favored Pb stabilization. Liquefaction significantly reduced environmental risk level of Cd, Zn and As, but may mobilize Pb and Mn, especially for Mn to very high risk level at 240 ºC. High temperature with long reaction time tended to inhibit leaching rate of Mn, whereas low liquefaction temperature with short reaction time prevented the leaching of Zn and As from hydrochars. Overall, these findings are essential for downstream upgrading of heavy oil and metals recovery from hydrochars.

The migration, transformation, and risk assessment of heavy metals in residue and bio-oil obtained by the liquefaction of pig manure

The total contents and chemical speciation analysis of Zn, Cu, Pb, Cr, Mn, Ni, Cd, and As in pig manure (PM), liquefaction residues (LRs), and bio-oils (BOs) derived from PM by liquefaction with ethanol as a solvent at 180-300 °C were thoroughly investigated in this study. The environment risk assessment, leachability, and bioavailability of heavy metals in PM and LRs were studied. The results showed that more than 75% of heavy metals remained in LRs. The total contents of heavy metals in LRs were markedly elevated, but those in BOs gradually decreased with the increase in liquefaction temperature. Moreover, the acid soluble/exchangeable fraction and reducible fraction (F1 + F2) of heavy metals in LRs and BOs was significantly reduced, while oxidizable fraction and stable fraction (F3 + F4) desirably increased after liquefaction. Furthermore, the potential risk of heavy metals in LRs was decreased in comparison to that in PM, but the risk of Pb, Mn, and As had not been obviously reduced; therefore, the LRs from the liquefaction of PM should be pretreated before recycling. Temperatures from 220 to 260 °C were the optimum conditions for disposing of PM by liquefaction with ethanol.

Molecular characterization and environmental impacts of water-soluble organic compounds of bio-oil from the thermochemical treatment of domestic sewage sludge

Water-soluble organic compounds derived from bio-oil (WOCB) are regarded as potential risk sources of sludge thermochemical treatment. This study showed that 10.35 mg of water-soluble organic carbon and 1.32 mg of water-soluble organic nitrogen were released per gram of sludge when the final temperature of thermochemical treatment was 600 °C. WOCB was mainly formed at 300-500 °C. Furthermore, FT-ICR MS results indicated that high temperatures promoted deamination reactions, and low molecular weight (LMW) compounds with low oxygen number polymerized into aromatic compounds with increasing temperature. Noteworthily, WOCB released at 20-600 °C showed strong phytotoxicity to wheat. LMW compounds with lignin/carboxylic rich alicyclic molecules (CRAM)-like structures derived from low temperatures (200-400 °C) induced this inhibitory effect, but lipids containing nitrogen and sulfur from high temperatures (400-600 °C) can act as nutrients to promote wheat growth. This study provides theoretical support for the risk control and benefits assessments of sludge thermochemical treatment.

Organoarsenic conversion to As(III) in subcritical hydrothermal reaction of livestock manure

Liquid phase produced by the subcritical hydrothermal liquefaction (HTL) of livestock manure is extensively used in agronomic and environmental applications, but the potential risks caused by inherent pollutants (e.g., roxarsone, ROX) of the livestock manure have not been considered. This study shows that less toxic ROX is completely converted into highly toxic As(III) and As(V) in the HTL reaction with temperature more than 240 °C. Moreover, more than 81.5% of As is distributed in the liquid phase generated by the livestock manure HTL reaction. Notably, the hydrothermal products of livestock manure facilitate the conversion of As(V) to As(III). The resulting hydrochar and aldehydes act as electron donors for As(V) reduction, thus resulting in the formation of As(III). Furthermore, the dissociated As promotes the depolymerization and deoxygenation of the macromolecular compounds to produce more small oxygen-containing compounds such as aldehydes, further boosting the As(V) reduction to As(III). These results indicate that the liquid phase of the livestock manure has potential risks in applications as a fertilizer. Such findings have substantial implications in biomass utilization and redox reactions of envirotechnical and biogeochemical relevance.

Effect of biochar on Cd and pyrene removal and bacteria communities variations in soils with culturing ryegrass (Lolium perenne L.)

Organic contaminations and heavy metals in soils cause large harm to human and environment, which could be remedied by planting specific plants. The biochars produced by crop straws could provide substantial benefits as a soil amendment. In the present study, biochars based on wheat, corn, soybean, cotton and eggplant straws were produced. The eggplant straws based biochar (ESBC) represented higher Cd and pyrene adsorption capacity than others, which was probably owing to the higher specific surface area and total pore volume, more functional groups and excellent crystallization. And then, ESBC amendment hybrid Ryegrass (Lolium perenne L.) cultivation were investigated to remediate the Cd and pyrene co-contaminated soil. With the leaching amount of 100% (v/w, mL water/g soil) and Cd content of 16.8 mg/kg soil, dosing 3% ESBC (wt%, biochar/soil) could keep 96.2% of the Cd in the 10 cm depth soil layer where the ryegrass root could reach, and it positively help root adsorb contaminations. Compared with the single planting ryegrass, the Cd and pyrene removal efficiencies significantly increased to 22.8% and 76.9% by dosing 3% ESBC, which was mainly related with the increased plant germination of 80% and biomass of 1.29 g after 70 days culture. When the ESBC dosage increased to 5%, more free radicals were injected and the ryegrass germination and biomass decreased to 65% and 0.986 g. Furthermore, when the ESBC was added into the ryegrass culture soil, the proportion of Cd and pyrene degrading bacteria Pseudomonas and Enterobacter significantly increased to 4.46% and 3.85%, which promoted the co-contaminations removal. It is suggested that biochar amendment hybrid ryegrass cultivation would be an effective method to remediate the Cd and pyrene co-contaminated soil.

Phytohormones-induced senescence efficiently promotes the transport of cadmium from roots into shoots of plants: A novel strategy for strengthening of phytoremediation

Due to the long growth period of plants, phytoremediation is time costly. Improving the accumulation of cadmium (Cd) in shoots of plants will promote the efficiency of phytoremediation. In this study, two senescence-relative phytohormones, abscisic acid (ABA) and salicylic acid (SA), were applied to strengthening phytoremediation of Cd by tall fescue (Festuca arundinacea S.). Under hydroponic culture, phytohormones treatment increased the Cd content of shoots 11.4-fold over the control, reaching 316.3 mg/kg (dry weight). Phytohormones-induced senescence contributes to the transport of heavy metals, and HMA3 was found to play a key role in this process. Additionally, this strategy could strengthen the accumulation of Cu and Zn in tall fescue shoots. Moreover, in soil pot culture, the strategy increased shoot Cd contents 2.56-fold over the control in tall fescue, and 2.55-fold over the control in Indian mustard (Brassica juncea L.), indicating its comprehensive adaptability and potential use in the field. In summary, senescence-induced heavy metal transport is developed as a novel strategy to strengthen phytoremediation. The strategy could be applied at the end of phytoremediation with an additional short duration (7 days) with comprehensive adaptability, and markedly strengthen the phytoremediation in the field.

Characterization of biofuel production from hydrothermal treatment of hyperaccumulator waste (Pteris vittata L.) in sub- and supercritical water

In this study, hyperaccumulator waste, i.e., Pteris vittata L. was converted into bio-oil, biogas and biochar via sub- and supercritical hydrothermal liquefaction processes. These products were characterized in terms of EI/MS, FTIR, TGA and GC to understand their chemical composition, thermal decomposition, structural properties and high biofuel reactivity. Characterization results revealed that the dominant chemical components in the heavy bio-oil were esters (40.22%), phenols (20.02%), alcohols (10.16%), organic acids (9.07%), nitrogenous compounds (8.83%) and ketones/aldehydes (6.42%), while the light oil was rich with a higher fraction of phenols (54.13%) and nitrogenous compounds (27.04%). Particularly, bio-oils obtained from supercritical conditions contained increased phenolic compounds and reduced oxygenated chemicals such as alcohols, aliphatic acid, ketones and aldehydes, suggesting the improved quality of bio-oil due to the reduction in oxygen contents. Meanwhile, H₂-rich syngas production with the H₂ yield of 38.87% was obtained at 535 °C for 20 min, and higher reaction temperature presented a positive influence on H₂ production during Pteris vittata L. liquefaction. Moreover, the remaining biochar product was analyzed to determine whether it could be used as a direct solid fuel or auxiliary fuel. This study provided full exploitation of this feedstock waste in energy and valuable chemical complexes.

This study evaluated the utilization of HTL to handle hyperaccumulator waste, i.e., Pteris vittata L. in both sub and supercritical water for the production of biofuels as a partial substitute for fossil fuels and valuable chemicals.