Hydrochar Pelletization towards Solid Biofuel from Biowaste Hydrothermal Carbonization

Hydrothermal carbonization is highly applicable to high moisture biomass upgrading due to the fact that moist-ure involved can be directly used as reaction media under the subcritical-water region.With this,value-added utilization of hydrochar as solid fuel with high carbon and energy density is one of the important pathways for biomass conversion.In this review,the dewatering properties of hydrochar after the hydrothermal carbonization of biowaste,coalification degree with elemental composition and evolution,pelletization of hydrochar to enhance the mechanical properties and density,coupled with the combustion properties of hydrochar biofuel were discussed with various biomass and carbonization parameters.Potential applications for the co-combustion with coal,cleaner properties and energy balance for biowaste hydrothermal carbonization were presented as well as the challenges.

Effects of Biowaste-Derived Hydrochar on Anaerobic Digestion:Insights into Hydrochar Characteristics

Hydrochar prepared with four typical biowastes,pine wood,food waste,digested sewage sludge,and Chlorella were applied for the promotion of anaerobic digestion.The gas production and substrate composition were analyzed associated with the hydrochar characteristics.The results suggested that Chlorella hydrochar(C-C)showed the highest cumulative yield of methane(approximately 345 mL)with high total organic carbon(TOC)removal efficiency and low volatile fatty acids(VAFs)concentration.Especially,food waste hydrochar(F-C)showed a poor effect on anaerobic digestion and aroused 1.4–1.6 g/L accumulation of VAFs,in which the toxic components may account for the low efficiency.The C-C and sludge hydrochar(S-C)may develop direct interspecific electron transport(DIET)to facilitate the generation of methane by both surface groups and conductivity of the body structure,unlike pinewood hydrochar(P-C),which mainly depended on the aromatic matrix structure of hydrochar body.This work suggested that C-C can be the best candidate for the facilitation of anaerobic digestion,and N-containing biowaste like algae and lignocellulose like pine wood may establish different DIET pathways based on the physicochemical characteristics of hydrochar.

The Hydrochar Characters of Municipal Sewage Sludge Under Different Hydrothermal Temperatures and Durations

Innovative measure is a urgent requirement for managing the huge volume of municipal sewage sludge. The hydrothermal carbonation （HTC） shows some potential advantages for using hydrochar as a soil conditioner. The aim of this work was to investigate the properties of hydrochars, by means of the HTC of municipal sewage sludge under different temperatures （190 and 260~C） and reaction hours （1, 6, 12, 18 and 24 h）. The HTC led to the decreases of N, O and H contents by more than 54.6, 37.9 and 10.0%, respectively, and slight changes of C content. The Py-GC-MS analysis showed that a large proportion of fatty acids, in particular hexadecanoic acid, transferred into alkenes, olefins and aromatic compounds. The 13C-NMR and fourier transform infrared spectra （FTIR） confirmed the transformation and changes in chemical structure in which hydrochar contained lower oxygen-containing organic C of O-alkyl, carboxylic and carbonyl C and aliphaticity, but higher aromatic C and aromaticity. The rich hydrophobic functions induced in high positive charges in the charred sludge. The HTC facilitated the pore structure development, proved by higher specific surface area and specific pore volume, with a maximum of 17.30 and 0.83 cm^3 g^-1, respectively. The availabilities of N, P and K markedly reduced during HTC treatment. The activities of most heavy metals were depressed though they accumulated in the hydrochar. Further work is required to investigate the values and risk of the charred sludge amended to soil.

Bio/hydrochar Sorbents for Environmental Remediation

A rising global population and aspirational higher living standards has driven a step change in resource utilization and concomitant anthropogenic pollution across the biosphere.Low-cost and scalable technologies for environmental remediation are therefore urgently sought,with an emphasis on trash-to-treasure strategies that exploit abundant but underutilized waste by-products of existing sectors.Biochars are carbon-rich,porous solids produced by biomass pyrolysis under anaerobic or oxygen-scarce conditions at high temperature(350–700°C),while hydrochars are produced by hydrothermal biomass carbonization at lower temperature(130–250°C)and high autogenous pressures(0.3–4.0 MPa).Bio/hydrochars possess unique physicochemical properties,notably high surface areas(100–1500 m2 g-1)and porosity(0.25–2.5 cm^(3)g^(-1))and rich surface chemistry featuring carboxylic,phenolic,hydroxyl,and carbonyl functions,amenable to chemical,physical,or biochemical modification,rendering them ideal sorbents for pollutants such as heavy metals(e.g.As and Cr),and toxic organic(e.g.,dyes and xenobiotics)and inorganic(e.g.,SO_(2))molecules.Bio/hydrochars are attractive for environmental remediation of pollutant mixtures by surface complexation,redox chemistry,electrostatic interactions/ion exchange,or coprecipitation.This review discusses recent opportunities and challenges in creating bio/hydrochar sorbents and their nanocomposites through grafting,doping,and chemical/physical activation,for the depollution of aquatic and atmospheric environments.

Synergistic effects of phosphoric acid modified hydrochar and coal gangue-based zeolite on bioavailability and accumulation of cadmium and lead in contaminated soil

In this paper,a novel compound was developed by mixing H_(3)PO_(4)-modified cauliflower leaves hydrochar(CLH)and coal gangue-based Na-X zeolite(ZL).An alkaline soil contaminated with cadmium(Cd)and lead(Pb)was amended through the individual and synergistic application of CLH and ZL(1%CLH,2%CLH,1%ZL,2%ZL and 1%CLH+1%ZL),and Chinese cabbage was grown on it.Individual application of CLH was superior to ZL on decreasing the pH of alkaline soil and increasing soil available phosphorus(Olsen-P)and soil organic matter(SOM).In contrast,their combined application significantly improved the soil cation exchange capacity(CEC).Besides,the 1%CLH+1%ZL was the most efficient treatment in decreasing diethylenetriamine pentaacetate(DTPA)-extractable Cd/Pb and concentrations of these two metals in cabbage root and shoot.Their synergistic application could better increase Cd and Pb immobilization and cabbage yield than their alone application.Furthermore,the immobilization of Pb for all treatments was higher than that of Cd.The synergistic immobilization mechanism of CLH and ZL reflected that the CLH precipitated and complexed with these two metals,which may block the pores of hydrochar or wrap on the surface of hydrochar.So the continuous adsorption and complexation were prevented.Nevertheless,ZL could probably alleviate this obstacle.This finding provides helpful information about using CLH combined with ZL as a soil stabilizer to immobilize heavy metals in contaminated alkaline soil.

Experimental,Thermodynamic and Kinetic Studies for the Adsorption of Phenolic Compounds Derived from Oilfield Wastewater by the Corncob Hydrochar

The corncob hydrochar is prepared by using a stainless autoclave at 230?C for 8 h.The products are characterized by elemental analyzer,Fourier Transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD)and scanning electron microscope(SEM).The effects of hydrochar dosage,pH,adsorption time and phenol concentration on the adsorption performance of hydrochar are investigated by means of single-factor experimental analysis.Based on the experiments the adsorption thermodynamic and kinetics are tentatively discussed.The results show that abundant oxygen-containing functional groups are scattered on the surface of the corncob hydrochar.The adsorption kinetics of phenol on the hydrochar corresponds well with pseudo-second-order kinetic model.Thermodynamic studies indicate that Freundlich adsorption isotherm model is much better than Langmuir model in describing the adsorption of phenol on the corncob hydrochar at 25?C-45?C.This study provides scientific basis for the development of cheap and efficient adsorbents for the removal of phenols derived from oilfield wastewater.

Selective hydrodeoxygenation of guaiacol to cyclohexanol using activated hydrochar-supported Ru catalysts

Lignin,an abundant aromatic polymer in nature,has received significant attention for its potential in the production of bio-oils and chemicals owing to increased resource availability and environmental issues.The hydrodeoxygenation of guaiacol,a lignin-derived monomer,can produce cyclohexanol,a nylon precursor,in a carbon-negative and environmentally friendly manner.This study explored the porous properties and the effects of activation methods on the Ru-based catalyst supported by environmentally friendly and cost-effective hydrochar.Highly selective cleavage of C_(ary)-O bonds was achieved under mild conditions(160°C,0.2 MPa H2,and 4 h),and alkali activation further improved the catalytic activity.Various characterization methods revealedthat hydrothermal treatment and alkali activation relatively contributed to the excellent performance of the catalysts and influenced their porous structure and Ru dispersion.X-ray photoelectron spectroscopy results revealed an increased formation of metallic ruthenium,indicating the effective regulation of interaction between active sites and supports.This synergistic approach used in this study,involving the valorization of cellulose-derived hydrochar and the selective production of nylon precursors from lignin-derived guaiacol,indicated the comprehensive and sustainable utilization of biomass resources.

Two-step hydrothermal conversion of biomass waste to humic acid using hydrochar as intermediate

Converting biomass materials to humic acid is a sustainable method for humic acid production and achieve biomass valorization. A two-step hydrothermal treatment method was adopted in this study to produce humic acid from corn stalks. In the first step of the process, hydrochar was prepared at different hydrothermal temperatures and pH values. Their chemical properties were then analyzed, and the hydrochar-derived humic acids were produced under alkaline hydrothermal conditions (denoted as HHAalk). The hydrochar, prepared under high temperature (200 °C) and strong acidic (pH 0) conditions, achieved high HHAalk yields (i.e., 67.9 wt% and 68.8 wt% calculated based on weight of hydrochar). The sources of HHAalk formation were as follows: 1) production in the hydrochar preparation stage, and 2) increment under the alkaline hydrothermal treatment of hydrochar. The degree of hydrochar unsaturation was suggested as an indicator for evaluating the hydrochar humification potential under alkaline hydrothermal conditions. This study provides an important reference for the preparation of suitable hydrochar with high hydrothermal humification potential.

ASSESSMENT OF HEAVY METALS IN HYDROCHAR PRODUCED BY HYDROTHERMAL CARBONIZATION OF DAIRY MANURE

Hydrochar produced from dairy manure is a regulated biosolid if being promoted for agricultural applications thus must have the properties that comply with all environmental standards and government regulations,including the levels of heavy metals(HMs).In this study,systematic research was conducted on HM levels in hydrochar from dairy manure and on the effects of processing conditions,including processing temperature(180–255℃),holding time(30–120 min)and solid content of manure slurry(2%–15%),through a central composite design and statistical analyses.It was found that HMs can be retained in hydrochar,ranging from 40%to 100%.The processing temperature and solid content in the feed were the most influential process parameters that affected HMs retention in hydrochar.Statistical analysis showed that there was no single optimal point to minimize HMs retained in hydrochar,but there were minimization points at given processing time and solid content.Most HMs concentrations were higher in hydrochar than those initially in dairy manure but were greatly below the thresholds as set by the US government regulations.Thus,hydrochar is feasible for use as a phosphorus-enriched organic fertilizer and/or soil amendment for agricultural applications without serious concerns about HMs it might contain.

Co-digestion of food waste and hydrothermal liquid digestate:Promotion effect of self-generated hydrochars

Hydrothermal treatment(HTT)can efficiently valorize the digestate after anaerobic digestion.However,the disposal of the HTT liquid is challenging.This paper proposes a method to recover energy through the anaerobic co-digestion of food waste and HTT liquid fraction.The effect of HTT liquid recirculation on anaerobic co-digestion performance was investigated.This study focused on the self-generated hydrochars that remained in the HTT supernatant after centrifugation.The effect of the self-generated hydrochars on the methane(CH_(4))yield and microbial communities were discussed.After adding HTT liquids treated at 140 and 180
C,the maximum CH4 production increased to 309.36 and 331.61 mL per g COD,respectively.The HTT liquid exhibited a pH buffering effect and kept a favorable pH for the anaerobic co-digestion.In addition,the self-generated hydrochars with higher carbon content and large oxygen-containing functional groups remained in HTT liquid.They increased the electron transferring rate of the anaerobic co-digestion.The increased relative abundance of Methanosarcina,Syntrophomonadaceae,and Synergistota was observed with adding HTT liquid.The results of the principal component analysis indicate that the electron transferring rate constant had positive correlationships with the relative abundance of Methanosarcina,Syntrophomonadaceae,and Synergistota.This study can provide a good reference for the disposal of the HTT liquid and a novel insight regarding the mechanism for the anaerobic co-digestion.

Rice Husk at a Glance:From Agro-Industrial to Modern Applications

Excessive waste production has led to the concept of a circular bioeconomy to deliver valuable by-products and improve environmental sustainability.The annual worldwide rice production accounts for more than 750 million tons of grain and 150 million tons of husk.Rice husk(RH)contains valuable biomaterials with extensive applications in various fields.The proportions of each component depend primarily on rice genotype,soil chemistry,and climatic conditions.RH and its derivatives,including ash,biochar,hydrochar,and activated carbon have been placed foreground of applications in agriculture and other industries.While the investigation on RH’s compositions,microstructures,and by-products has been done copiously,owing to its unique features,it is still an open-ended area with enormous scope for innovation,research,and technology.Here,we reviewed the latest applications of RH and its derivatives,including fuel and other energy resources,construction materials,pharmacy,medicine,and nanobiotechnology to keep this versatile biomaterial in the spotlight.

玉米秸秆水热生物炭施用对土壤重金属Cd生物有效性和微生物群落的影响

为了探究玉米秸秆水热生物炭(简称水热炭)施用对镉(Cd)污染土壤的修复效果及作用机制,通过盆栽试验,分析了不同水热炭在不同添加率下(1%和3%)对土壤Cd生物有效性和作物吸收的影响,并探究了不同条件下的微生物群落结构。结果表明:与对照相比,水热炭施用显著提高了土壤有机质和溶解性有机碳含量,土壤中二乙烯三胺五乙酸提取的Cd(DTPA-Cd)和油菜叶片Cd含量分别降低了5.01%~20.98%和10.82%~34.16%。提高水热温度和水热炭添加率有助于降低土壤DTPA-Cd含量。此外,施用水热炭显著增强了根际土壤细菌的多样性和丰度,且明显改变了微生物群落结构。与对照组相比,施用水热炭显著降低了根际土壤中Actinobacteriota的相对丰度,提高了Proteobacteria和Bacteroidota的相对丰度。冗余分析表明土壤溶解性有机碳含量是影响根际土壤细菌群落结构的关键因素。因此,水热炭对重金属污染土壤有很大的修复潜力,但其对土壤重金属的长期效应有待进一步研究。

两种铁改性水热炭对土壤中铬固化效能及其形态影响

本实验采用机械球磨法分别制备零价铁(ZVI)、黄铁矿负载水热炭,通过土壤提取实验和土柱淋溶实验,对比添加不同材料后土壤中铬(Cr)含量的变化,分析淋溶液中Cr累积释放规律及Cr在土柱中的纵向迁移行为.实验结果表明,与其他材料相比,施加ZVI改性水热炭(ZBC)和黄铁矿改性水热炭(HBC)对土壤中Cr均有优秀的固化效果.在低投加量(5 g·kg^(-1))下ZBC、HBC使土壤浸出液中总铬浓度分别降低35.8%、39.6%,而土壤中有效铁含量涨幅均小于0.1%,解决了使用ZVI和黄铁矿引起的土壤铁含量过度增加的问题.在土柱淋溶实验中,施加ZBC、HBC后淋溶液总铬含量较CK(未加改性水热炭的对照组)分别下降27.3%、39.3%;土柱下部未污染土壤总铬含量分别降低31.4%、56.3%,Cr(Ⅵ)浓度分别降低51.7%、44.4%.结合表征可得,土壤中的Cr可被ZBC、HBC吸附,水热炭负载的Fe可将Cr(Ⅵ)还原成Cr(Ⅲ)并附着在土壤中,HBC中的FeS_(2)有效参与了对Cr(Ⅵ)的还原.总的来看,HBC对土壤中Cr的固化效果更好,可为水热炭修复重金属污染土壤的应用提供思路与探索.

壳聚糖改性污泥水热炭活化过硫酸盐降解活性黑5染料废水

印染废水可生化性低,生物处理难度大.通过在剩余污泥中掺杂壳聚糖,经水热处理制备出壳聚糖改性生物炭(CBC),并用于活化过二硫酸盐(PDS),实现对活性黑5(RB5)染料废水的高效降解.在水热温度为200℃,水热时间为6 h时制备的CBC对RB5的去除效果最优,反应60 min去除率可达到100%.此外,PDS投量为2 mmol·L^(−1),CBC投量为5 g·L^(−1),初始pH=5时反应效果最佳.反应系统中的Cl^(-)和NO_(3)^(-)对RB5去除几乎无影响,而PO_(4)^(3-)、HCO_(3)^(-)有明显抑制作用.机理研究证实了单线态氧(^(1)O_(2))对RB5的降解起主要贡献,而不是PDS氧化体系常见的硫酸根自由基.

废弃生物质水热炭化衍生碳基光催化材料的研究进展

水热炭化是一种经济且环境友好的废弃生物质热化学转化技术.废弃生物质通过水热炭化制备碳基光催化材料,不仅可实现废弃物的高值利用,而且可通过光催化材料的的应用缓解环境污染和能源危机.本综述将水热炭化制备的废弃生物质碳基光催化材料分成水热炭、碳点和碳基复合材料三类,并系统总结其制备、光催化机理和应用方面的研究进展.首先,归纳了3种光催化剂的制备,包括形成机理和物化结构;然后分别阐述了各类催化剂的光催化过程和光催化性能提高途径,以及从有机污染物降解、重金属去除、消毒、产氢和CO_(2)还原等领域介绍了光催化应用;最后,对该领域未来的研究重点和发展方向进行了展望.

吸附法处理含吡啶废水的试验研究

利用水热碳化技术制备了一种莲房基水热炭。通过产物表征､正交实验､吸附等温线､吸附动力学､再生实验等探讨了水热炭在含吡啶废水处理中的应用。结果表明,莲房水热炭具有不同尺寸的孔隙结构,其表面分布着较为丰富的含氧官能团;水热炭吸附吡啶过程中各因素影响顺序为:吡啶初始浓度>水热炭投加量>溶液pH>吸附时间;莲房水热炭对吡啶的吸附动力学符合准二级模型,在35℃与45℃时Freundlich模型可较好地描述吸附等温线规律;25℃时莲房水热炭对吡啶的最大吸附量为31.28 mg/g;磷酸溶液对莲房水热炭的再生效果优于NaOH溶液;莲房水热炭经6次再生后,对吡啶仍具较好的吸附能力。

沼渣水热炭与沼渣热解炭强化餐厨垃圾厌氧消化对比研究

餐厨垃圾厌氧消化产生大量沼渣,亟需得到妥善处理。采用水热与热解将沼渣分别制备为水热炭与热解炭,并对比研究了其对餐厨垃圾厌氧消化的影响。结果表明:与对照组(23.8 mL/g)相比,水热炭组(投加量1、5、10 g/L)甲烷产量分别为24.0、38.9、34.9 mL/g,分别提高了0.8%、63.4%、46.6%;热解炭组(投加量1、5、10 g/L)甲烷产量分别为29.7、35.7、31.1 mL/g,分别提高了24.8%、50.0%、30.7%。投加水热炭和热解炭促进了有机物溶出,且水解产酸菌包括Fastidiosipila、 W5053、 Propioniciclava、 Actinomyces (放线菌属)、Norank_f__ST-12K33的总相对丰度由73.0%分别提升至84.6%和82.0%。投加水热炭和热解炭后,Methanosaeta(鬃毛甲烷菌属)相对丰度分别高达60.3%和50.6%,Methanobacterium (甲烷杆菌属)相对丰度仅为26.5%和36.9%。沼渣生物炭可以强化餐厨垃圾厌氧消化,随着投加量的增加,甲烷产量先上升后下降,最优投加量为5 g/L,且水热炭效果优于热解炭。

以粪污水热资源化为核心的高效种养结合系统分析与展望

种养结合系统是实现养殖业和种植业可持续发展的重要途径。水热技术可以将畜禽粪污快速直接转化生产生物原油、水热炭、水相产物和气体产物,生成物分别具有燃料、土壤改良、农用杀菌剂和气体肥料应用潜力,以粪污水热资源化为核心构建的高效种养结合系统有助于提升畜禽粪污的无害化资源化水平和消纳能力、构建生态可持续的绿色循环农业,实现畜禽粪污资源化利用、种植业和养殖的协同高效发展。该研究基于国内外近十余年的研究,系统综述了粪污水热资源化产物在种养结合生态循环农业模式中的作用和应用潜力,论述了畜禽粪污水热转化生物原油在农业内燃机中作为燃料的研究现状,阐述了水相产物作为潜在的农用杀菌剂在作物病害防控中的作用,梳理了畜禽粪污源水热炭在转化机理、理化特性和还田应用中的研究进展,分析了气相产物中的组分和用于温室种植的潜力。在此基础上总结了以粪污水热资源化为核心的高效种养结合系统面临的主要挑战,并对水热资源化产物农业循环应用的研究方向进行展望。研究为畜禽粪污水热资源化和高效种养结合系统研究提供理论参考。

小球藻水热催化联产功能化碳材料过程反应特性研究

微藻水热碳化技术具有无需干燥高含水率微藻、反应溶剂绿色无污染、反应条件相对温和等优势,可用于制备碳点和水热炭等功能化碳材料,受到广泛研究关注。然而,目前微藻水热碳化制备的碳材料存在质量产率较低、性能较差的问题,需通过添加适宜的催化剂以提高碳材料的产率与品质。因此,研究了H_(2)SO_(4)、CH_(3)COOH、NaOH、Na_(2)CO_(3)等催化剂对蛋白核小球藻水热碳化制备碳点与水热炭的影响规律,并采用集总参数法建立了水热碳化过程中多相产物的生成反应动力学模型。研究结果表明,4种催化剂均能提高微藻碳点质量产率,其中NaOH可使碳点产率提高约73.3%。添加酸性催化剂使碳点尺寸变小,碳点平均粒径最小仅为1 nm;而在碱性条件下获得的碳点尺寸变化不明显,粒径主要集中在3.0~4.0 nm之间。在230℃和100 min条件下,CH_(3)COOH作为水热催化剂制备的微藻碳点的荧光量子产率最高可达7.88%,并在340 nm的吸收波长激发下发射出波长为420 nm的最强发射荧光。元素分析表明,4种催化剂均降低碳点中的N元素含量,且均能提高水热炭的高位热值。催化剂对水热炭高位热值的提高效果由强到弱为H_(2)SO_(4)>CH_(3)COOH>NaOH>Na_(2)CO_(3)。热重分析发现,在水热碳化过程中,微藻碳水化合物的水解转化比蛋白质更快;添加CH_(3)COOH可以促进蛋白质水解转化,而碱性催化剂不利于碳水化合物的水解转化,这4种催化剂对微藻脂质降解过程的影响均不明显。动力学分析发现,水热碳化过程中主要反应包括碳点聚合生成水热炭、微藻生物油的析出以及微藻降解生成其他相产物。碳点主要是通过其他相产物中的小分子聚合和微藻大分子裂解直接生成;在230℃、CH_(3)COOH催化条件下,微藻碳点较难发生水解,且微藻生物油水解后难以发生逆向反应。

The stability of carbon from a maize-derived hydrochar as a function of fractionation and hydrothermal carbonization temperature in a Podzol

Hydrochar(HC)produced by the hydrothermal carbonization(HTC)of typically wet biomass is generally considered to be less effective for carbon(C)sequestration in soils compared to biochar(BC)by pyrolysis,due to a higher content of more easily decomposable C.Although the recalcitrance of HC is suggested to improve with increasing HTC production temperature,the way it interacts and becomes associated with soil organic matter(SOM)fractions of different stabilities against decomposition,may also influence its effectiveness for C sequestration in soils.In that respect,this study aimed to verify the potential of HCs from maize silage produced at different HTC temperatures(190,210 and 230℃)for C sequestration in a HC-amended sandy loam Podzol.To do this,we conducted a pot trial experiment and traced the fate of HC-derived C(HC-C)within different SOM fractions,namely the free-and occluded particulate organic matter(POMF and POMO,respectively)fractions and that comprising organic matter(OM)bound to clays(OMCl).Approx.1 year after applying 5%of the different HTC temperature HCs to the soil,the SOM fractions were isolated by density fractionation for each HC treatment(HC190,HC210 and HC230)and the control(absent of HC).All fractions and the HCs were analyzed for organic C(OC)content and isotopic signatures(δ^(13)C).From the δ^(13)C signatures,the amount of HC-C and native soil organic carbon(SOC)within each fraction was calculated.Increased C contents and decreased H/C and O/C ratios were observed with increasing HTC production temperatures,which sug-gests a lower stability for the low temperature HC.After ca.1 year,a loss of~20-23%of the bulk soil TOC was found in the HC-amended soils.The POMF fraction of the HC-amended soils showed losses of 68-81%HC-C and 52-72%native SOC,which may be due to a positive priming effect caused by HC addition.The POM_(O) and OM_(Cl) fractions of the HC-amended soils contained more OC than the control,indicating the integration of HC-C together with SOM within these more stable fractions,while the effect of HTC production temperature on the level of decomposition of the resultant HCs was negligible.In all HC treatments,the OM_(Cl) fraction comprised the least amount of HC-C,thus showing the weakest response to C amendment.In conclusion,long(er)-term research on the C net balance that accounts for the observed priming-induced TOC losses and the HC-C enrichment in more stable fractions is required to verify the potential of the different HCs for the purpose of C sequestration in soils.