Choline chloride-modified hydrochar from organic waste for the removal of PFOA from aqueous matrices: feasibility, isotherm, and kinetic studies

Abstract

This study investigated the feasibility of valorizing potato peel, a widely generated organic waste, through hydrothermal carbonization to produce hydrochar for the removal of perfluorooctanoic acid (PFOA), an emerging contaminant from aqueous matrices. Hydrochar was synthesized under four operating conditions, combining two temperatures (180 and 200 °C) with two reaction times (2 and 4 h). The hydrochar produced at 180 °C for 4 h exhibited the maximum specific surface area (28.055 m²/g) and was selected for modification with 0.1 M choline chloride (ChCl) to enhance its adsorption performance. After modification, the specific surface area increased to 62.188 m²/g, indicating an improved surface area. Batch adsorption experiments using 0.1 M ChCl-modified hydrochar (ChCl-HC) in the presence of 20 mM calcium chloride (CaCl₂) showed increased PFOA removal efficiency (95.4%) at 400 mg/L optimal adsorbent dose, attributed to Ca²⁺ induced bridging effect and electrostatic interactions. The adsorption isotherm model showed that the Langmuir model best fit the experimental data [the coefficient of determination (R²) = 0.9976], followed by the Dubinin-Radushkevich (D-R), Temkin, and Freundlich models. The maximum monolayer adsorption capacity was calculated to be 72.621 mg/g, and the separation factor (0.030) indicated favorable adsorption. The calculated mean adsorption energy (1.35 kJ/mol) from the D-R model suggested physical adsorption. Kinetic analysis further showed that the data fit well with the pseudo-second order. Overall, three mechanisms were identified as responsible for PFOA adsorption on the 0.1 M ChCl-HC: electrostatic interaction, hydrogen bonding, and hydrophobic interaction. These findings highlight that ChCl-HC, combined with CaCl₂ serving as a bridging agent, offers a sustainable and efficient solution for PFOA removal. Overall, this approach offers a promising solution for the valorization of organic waste into hydrochar, with potential application in the removal of PFOA, an emerging contaminant, from aqueous matrices.

Keywords

Organic waste / hydrothermal carbonization / hydrochar / perfluorooctanoic acid / choline chloride / calcium chloride

References

[1] Singh SV,Kumar N.Sustainable food waste utilization in the context of the Indian hospitality industry. In Promoting sustainable gastronomy tourism and community development. IGI Global; 2024. pp. 229-41.

[2] Swati A.Greenhouse gas emission during composting and vermicomposting of organic wastes - a review.CLEAN Soil Air Water2018;46:1700042

[3] UN Environment Programme. Solid waste management. https://www.unep.org/explore-topics/resource-efficiency/what-we-do/cities/solid-waste-management. (accessed 2025-10-29)

[4] Khanal S,Majumdar S.Sustainable utilization and valorization of potato waste: state of the art, challenges, and perspectives.Biomass Conv Bioref2024;14:23335-60

[5] Vescovo D,Ruggieri R.The valorization of potato peels as a functional ingredient in the food industry: a comprehensive review.Foods2025;14:1333 PMCID:PMC12026436

[6] Amenyeku G,Asare W.Hydrothermal carbonization of organic waste using faecal sludge as a water source: response surface methodology-Box Behnken design.Environ Challenges2024;15:100900

[7] Mahata S,Akkupalli NK,Matli C.A review on co-hydrothermal carbonization of sludge: effect of process parameters, reaction pathway, and pollutant transport.J Energy Inst2023;110:101340

[8] Basso D,Castello D.Agro-industrial waste to solid biofuel through hydrothermal carbonization.Waste Manag2016;47:114-21

[9] Li L,Flora JR.Hydrothermal carbonization of food waste and associated packaging materials for energy source generation.Waste Manag2013;33:2478-92

[10] Niinipuu M,Boily JF,Jansson S.The impact of hydrothermal carbonization on the surface functionalities of wet waste materials for water treatment applications.Environ Sci Pollut Res Int2020;27:24369-79 PMCID:PMC7326807

[11] Fang J,Chen J.Hydrochars derived from plant biomass under various conditions: characterization and potential applications and impacts.Chem Eng J2015;267:253-9

[12] Czerwińska K,Wilk M.Hydrothermal carbonization process: fundamentals, main parameter characteristics and possible applications including an effective method of SARS-CoV-2 mitigation in sewage sludge. A review.Renew Sustain Energy Rev2022;154:111873

[13] Kozyatnyk I,Weidemann E,Jansson S.Influence of hydrothermal carbonization conditions on the porosity, functionality, and sorption properties of microalgae hydrochars.Sci Rep2023;13:8562 PMCID:PMC10219968

[14] Goyi AA,Omer KM.Nitrogen-rich, potato peel-derived hydrochar as an effective dye adsorbent.Biofuels2024;15:1131-44

[15] Xiao K,Li Y.Correlations between hydrochar properties and chemical constitution of orange peel waste during hydrothermal carbonization.Bioresour Technol2018;265:432-6

[16] Monlau F,Antoniou N,Solhy A.Pyrochars from bioenergy residue as novel bio-adsorbents for lignocellulosic hydrolysate detoxification.Bioresour Technol2015;187:379-86

[17] Sun T,Xie Y.Biochar remediation of PFOA contaminated soil decreased the microbial network complexity.J Environ Chem Eng2023;11:109239

[18] Xu M,Zhao L,Zong W.Characterizing the binding interactions of PFOA and PFOS with catalase at the molecular level.Chemosphere2018;203:360-7

[19] Zhang DQ,Liang YN.Adsorption of perfluoroalkyl and polyfluoroalkyl substances (PFASs) from aqueous solution - a review.Sci Total Environ2019;694:133606

[20] Guo R,Liu J.Occurrence, partition and environmental risk assessment of per- and polyfluoroalkyl substances in water and sediment from the Baiyangdian Lake, China.Sci Rep2020;10:4691 PMCID:PMC7069980

[21] Miserli K,Konstantinou I.Analysis of perfluorinated compounds in sewage sludge and hydrochar by UHPLC LTQ/Orbitrap MS and removal assessment during hydrothermal carbonization treatment.Sci Total Environ2024;929:172650

[22] Araújo RG,González-González RB.Detection and tertiary treatment technologies of poly-and perfluoroalkyl substances in wastewater treatment plants.Front Environ Sci2022;10:864894

[23] Miserli K,Boti V,Konstantinou I.Determination of PFAS in wastewaters and natural waters by solid phase extraction and UHPLC LTQ/Orbitrap MS for assessing occurrence and removals.Case Stud Chem Environm Eng2023;8:100505

[24] Afrooz M,Soltan J.A novel biochar adsorbent for treatment of perfluorooctanoic acid (PFOA) contaminated water: exploring batch and dynamic adsorption behavior.J Water Process Eng2025;69:106586

[25] United States Environmental Protection Agency. Per- and polyfluoroalkyl substances (PFAS). Final PFAS National Primary Drinking Water Regulation. 2025. https://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas. (accessed 2025-10-29)

[26] Liu F,Sun R,Xiao F.A comprehensive review of novel adsorbents for per- and polyfluoroalkyl substances in water.ACS EST Water2024;4:1191-205

[27] Chen F,Liu X.Removal of per- and polyfluoroalkyl substances by activated hydrochar derived from food waste: sorption performance and desorption hysteresis.Environ Pollut2023;:122820

[28] Buarque FS,Ribeiro BD.Choline chloride-based deep eutectic solvent as an inhibitor of metalloproteases (collagenase and elastase) in cosmetic formulation.3 Biotech2023;13:219 PMCID:PMC10229499

[29] Huang J,Liu Z,Xi C.High-efficiency removal of methcathinone from water using a novel DES modified magnetic biochar nanocomposite.J Environ Chem Eng2022;10:108456

[30] Xu J,Zhao D,Fu X.Enhanced adsorption of perfluorooctanoic acid (PFOA) from water by granular activated carbon supported magnetite nanoparticles.Sci Total Environ2020;723:137757

[31] Hassan M,Liu Y.Magnetic biochar for removal of perfluorooctane sulphonate (PFOS): interfacial interaction and adsorption mechanism.Environ Technol Innov2022;28:102593

[32] García-Suárez EJ,García AB.Chemical stability of choline-based ionic liquids supported on carbon materials.J Mol Liq2012;169:37-42

[33] Kalam S,Kamal MS.Surfactant adsorption isotherms: a review.ACS Omega2021;6:32342-8 PMCID:PMC8655760

[34] Boparai HK,O’Carroll DM.Kinetics and thermodynamics of cadmium ion removal by adsorption onto nano zerovalent iron particles.J Hazard Mater2011;186:458-65

[35] Niaz W,Ahmad Z.Efficient removal of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) from aqueous solution using modified biochar: preparation, performance, and mechanistic insights.J Environ Chem Eng2024;12:114894

[36] Angı A,Erkey C.Catalytic activity of copper (II) oxide prepared via ultrasound assisted Fenton-like reaction.Ultrason Sonochem2014;21:854-9

[37] Robertson M,Griffin A,Ma B.Critical role of pore size on perfluorooctanoic acid adsorption behaviors in carbonaceous sorbents.Mater Horiz2025;12:2935-44

[38] Barmina I,Zake M,Solodovnik V.Experimental study of thermal decomposition and combustion of lignocellulosic biomass pellets.Latv J Phys Tech Sci2013;50:35-48

[39] Li P,Hou Q.Preparation of cellulose nanofibrils from okara by high pressure homogenization method using deep eutectic solvents.Cellulose2020;27:2511-20

[40] Khan Z,Ahmad MM.Thermogravimetric analysis of palm oil wastes decomposition. In 2011 IEEE Conference on Clean Energy and Technology (CET), Kuala Lumpur, Malaysia. June 27-29, 2011. IEEE; 2011. pp. 205-8.

[41] Adebisi GA,Abd Hamid SB.Hydrothermally treated banana empty fruit bunch fiber activated carbon for Pb(II) and Zn(II) removal.BioResources2016;11:9686-709

[42] Goyi AA,Omer KM.Preparation and characterization of potato peel derived hydrochar and its application for removal of Congo red: a comparative study with potato peel powder.Int J Environ Sci Technol2024;21:631-42

[43] Sevilla M.The production of carbon materials by hydrothermal carbonization of cellulose.Carbon2009;47:2281-9

[44] Mukti NIF,Sediawan WB.Efficacy of modified carbon molecular sieve with iron oxides or choline chloride-based deep eutectic solvent for the separation of CO₂/CH₄.RSC Adv2023;13:23158-68 PMCID:PMC10392867

[45] Gao P,Meng F.Preparation and characterization of hydrochar from waste eucalyptus bark by hydrothermal carbonization.Energy2016;97:238-45

[46] Liang M,Lei P,Shu C.Fuel properties and combustion kinetics of hydrochar derived from co-hydrothermal carbonization of tobacco residues and graphene oxide.Biomass Conv Bioref2020;10:189-201

[47] Prasannamedha G,Kyzas G.Hydrothermal carbonization of waste sugarcane bagasse for the effective removal of emerging contaminants from aqueous solution.Adsorpt Sci Technol2022;2022:8684737

[48] Liu P,Liang S,Wang J.Choline chloride and itaconic acid-based deep eutectic solvent as an efficient and reusable medium for the preparation of 13-aryl-5H-dibenzo[b,i]xanthene-5,7,12,14(13H)-tetraones.Monatsh Chem2016;147:801-8

[49] Potchamyou Ngatcha AD,Zhang S.Determination of active sites on the synthesis of novel Lewis acidic deep eutectic solvent catalysts and kinetic studies in microalgal biodiesel production.RSC Adv2023;13:10110-22 PMCID:PMC10054363

[50] Pervez MN,Mahato JK.Surface modification of graphene oxide for fast removal of per- and polyfluoroalkyl substances (PFAS) mixtures from river water.ACS ES T Water2024;4:2968-80 PMCID:PMC11249979

[51] Lei X,Lian Q.Enhanced adsorption of perfluorooctanoate (PFOA) onto low oxygen content ordered mesoporous carbon (OMC): adsorption behaviors and mechanisms.J Hazard Mater2022;421:126810

[52] Yu Q,Deng S,Yu G.Sorption of perfluorooctane sulfonate and perfluorooctanoate on activated carbons and resin: kinetic and isotherm study.Water Res2009;43:1150-8

[53] Yan Z,Yan J,Zhang J.Rapid adsorption of per- and polyfluoroalkyl substances (PFAS) on N-doped porous carbons (NPCs) derived from ZIF-8 over a wide pH range: adsorption behaviors and mechanisms.Sep Purif Technol2025;365:132575

[54] Kasalica K,Radulovic J.Adsorption analysis of PFOA on activated carbon and ion-exchange resin: a comparative study using four isotherm models.J Serb Chem Soc2024;89:1619-28

[55] Tian D,Tyler Mehler W.Removal of perfluorooctanoic acid (PFOA) from aqueous solution by amino-functionalized graphene oxide (AGO) aerogels: influencing factors, kinetics, isotherms, and thermodynamic studies.Sci Total Environ2021;783:147041

[56] Sahu S,Gupta AK.Modeling defluoridation of real-life groundwater by a green adsorbent aluminum/olivine composite: isotherm, kinetics, thermodynamics and novel framework based on artificial neural network and support vector machine.J Environ Manage2022;302:113965

[57] Ghaedi M,Hossainian H.Comparison of activated carbon and multiwalled carbon nanotubes for efficient removal of eriochrome cyanine R (ECR): kinetic, isotherm, and thermodynamic study of the removal process.J Chem Eng Data2011;56:3227-35

[58] Wang F,Shih K.Adsorption behavior of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) on boehmite.Chemosphere2012;89:1009-14

[59] Hakimabadi SG,Pham AL.Factors affecting the adsorption of per- and polyfluoroalkyl substances (PFAS) by colloidal activated carbon.Water Res2023;242:120212

[60] Yang H,Park S,Lee C.Enhanced removal of perfluorooctanoic acid (PFOA) from water using ZnO-Ag-ZnAl₂O₄ composites: performance and mechanistic insights.J Water Process Eng2024;61:105288

[61] Lei X,Zhang X.Removal of perfluorooctanoic acid via polyethyleneimine modified graphene oxide: effects of water matrices and understanding mechanisms.Chemosphere2022;308:136379

[62] Imran A,Shoemaker DJ.Adsorption of PFCAs using polyethyleneimine modified Biochar: role of chain length and effects of water matrices.Chemosphere2025;386:144650

[63] Niinipuu M,Boily JF,Jansson S.Influence of water matrix and hydrochar properties on removal of organic and inorganic contaminants.Environ Sci Pollut Res Int2020;27:30333-41 PMCID:PMC7378115

[64] Fagbayigbo BO,Fatoki OS,Olatunji OS.Removal of PFOA and PFOS from aqueous solutions using activated carbon produced from Vitis vinifera leaf litter.Environ Sci Pollut Res Int2017;24:13107-20

[65] Wu Y,Chen G.A mechanical investigation of perfluorooctane acid adsorption by engineered biochar.J Clean Prod2022;340:130742

[66] Saba A,Reza M.Techno-economic assessment of co-hydrothermal carbonization of a coal-miscanthus blend.Energies2019;12:630

[67] Du Z,Bei Y.Adsorption behavior and mechanism of perfluorinated compounds on various adsorbents - a review.J Hazard Mater2014;274:443-54

[68] Mahanty B.Synthesis of magnetic biochar using agricultural waste for the separation of Cr(VI) from aqueous solution.Arab J Sci Eng2021;46:10803-18