Effective removal of nitrate nitrogen from water and soil using biochar-loaded nano zero-valent iron: performance and mechanisms

Abstract

Nitrogen leaching from agricultural soils serves as a main contributor to water pollution and nitrogen losses, posing significant challenges to sustainable agricultural practices. However, existing mitigation strategies often exhibit limited efficiency in reducing nitrate nitrogen (NO₃⁻–N) losses and enhancing ammonium nitrogen (NH₄⁺–N) retention under varying environmental conditions. To address this, our research investigated the effectiveness of biochar-supported nanoscale zero-valent iron (nZVI@BC) composites. The combination of nZVI with biochar is driven by the need to enhance biochar's adsorption capacity and provide an additional mechanism for nitrate reduction via the strong reductive properties of nZVI. Our findings indicated that nZVI@BC significantly enhanced nitrate reduction and ammonium retention compared to biochar alone, with the nZVI@BC0.6 achieving the best overall performance. The NO₃⁻–N concentration in leachate was reduced by up to 71.31%, while NH₄⁺–N retention increased by 53.12%, with notable improvements in nitrogen retention even in deeper soil layers. The adsorption kinetics revealed that nZVI@BC composites exhibited both rapid initial adsorption and sustained chemical reduction of NO₃⁻–N, with the pseudo-second-order model verifying the dominance of chemical adsorption for nZVI-enriched treatments. The nitrate nitrogen reduction potential of nZVI@BC at various pH levels revealed optimum performance at low pH. Structural analyses (XRD, FTIR, and XPS) showed that nZVI incorporation altered the chemical environment of biochar, enhancing its surface reactivity and functional group availability, which improved nitrogen immobilization efficiency. This study highlights the potential of nZVI@BC composites, particularly nZVI@BC0.6, as an effective and sustainable strategy for mitigating nitrogen leaching, improving nitrogen use efficiency, and addressing agricultural non-point source pollution.

Keywords

Nitrate nitrogen / Biochar-loaded nZVI / Nitrate reduction / Leaching mitigation / Water and soil remediation

References

[1] Afzal MTK, Firouzi AF, Zahedkolaei MT. Enhanced transport of zerovalent iron nanoparticles and nitrate removal in saturated porous media. Water Air Soil Pollut, 2024, 235: 548-567

[2] Alami NE, Bourguid M, Kouighat M. Advances in nitrogen use efficiency of ¹⁵N-enriched fertilizers: a thirty-year review of research and innovations for sustainable agriculture. J Soil Sci Plant Nutr, 2025, 1: 1-23

[3] Amin FR, Huang Y, He Y, Zhang R, Liu G, Chen C. Biochar applications and modern techniques for characterization. Clean Technol Environ Policy, 2016, 18: 1457-1473

[4] Awang NA, Wan Salleh WN, Aziz F, Yusof N, Ismail AF. A review on preparation, surface enhancement and adsorption mechanism of biochar-supported nano zero-valent iron adsorbent for hazardous heavy metals. J Chem Technol Biotechnol, 2023, 98(1): 22-44

[5] Bae W, Kim S, Lee J, Chung J. Effect of leachate circulation with ex situ nitrification on waste decomposition and nitrogen removal for early stabilization of fresh refuse landfill. J Hazard Mater, 2019, 371: 721-727

[6] Cai R, Wang X, Ji X, Peng B, Tan C, Huang X. Phosphate reclaim from simulated and real eutrophic water by magnetic biochar derived from water hyacinth. J Environ Manage, 2017, 187: 212-219

[7] Cao H, Ning L, Xun M, Feng F, Li P, Yue S, Song J, Zhang W, Yang H. Biochar can increase nitrogen use efficiency of Malus hupehensis by modulating nitrate reduction of soil and root. Appl Soil Ecol, 2019, 135: 25-32

[8] Chandra S, Medha I, Bhattacharya J. Potassium-iron rice straw biochar composite for sorption of nitrate, phosphate, and ammonium ions in soil for timely and controlled release. Sci Total Environ, 2020, 712 136337

[9] Chen D, Suter HC, Islam A, Edis R. Influence of nitrification inhibitors on nitrification and nitrous oxide (N₂O) emission from a clay loam soil fertilized with urea. Soil Biol Biochem, 2010, 42(4): 660-664

[10] Chen C, Yang F, Ma Y, Dai L, Zhang Z, Guo H, Ding Y. Ball milling boosted magnetic cotton husk-derived biochar adsorptive removal of oxytetracycline and ciprofloxacin from water. Carbon Res, 2024, 3: 63-76

[11] Cybulak M, Sokołowska Z, Boguta P. The influence of biochar on the content of carbon and the chemical transformations of fallow and grassland humic acids. Sci Rep, 2021, 11: 5698-5712

[12] Dewage NB, Liyanage AS, Pittman CUJr, Mohan D, Mlsna T. Fast nitrate and fluoride adsorption and magnetic separation from water on α-Fe₂O₃ and Fe₃O₄ dispersed on Douglas fir biochar. Bioresour Technol, 2018, 263: 258-265

[13] Dissanayaka Mudiyanselage T, Franks A, Xu J, Bolan N, Wang H, Tang C. Chemical and biological immobilization mechanisms of potentially toxic elements in biochar-amended soils. Crit Rev Environ Sci Technol, 2020, 50(9): 903-978

[14] Dong Y, Li Y, Kong F, Zhang J, Xi M. Source, structural characteristics and ecological indication of dissolved organic matter extracted from sediments in the primary tributaries of the Dagu River. Ecol Indic, 2020, 109 105776

[15] Fan Y, Sun S, Gu X, Yan P, Zhang Y, Peng Y, He S. Tracing the electron transfer behavior driven by hydrophyte-derived carbon materials empowered autotrophic denitrification in iron-based constructed wetlands: efficacy and enhancement mechanism. Water Res, 2025, 275 123169

[16] Gao C, Lu Y, Wang Y, Wang C, Hübner R, Li Y, Zhan J, Zhao M, Cai B. Tuning iron-oxygen covalency in perovskite oxides for efficient electrochemical sensing. J Phys Chem C, 2022, 126(41): 17618-17626

[17] Gillingham MD, Gomes RL, Ferrari R, West HM. Sorption, separation and recycling of ammonium in agricultural soils: a viable application for magnetic biochar?. Sci Total Environ, 2022, 812 151440

[18] Guo JH, Liu XJ, Zhang Y, Shen J, Han W, Zhang W, Christie P, Goulding K, Vitousek P, Zhang F. Significant acidification in major Chinese croplands. Science, 2010, 327: 1008-1010

[19] Guo X, Yang Z, Liu H, Lv X, Tu Q, Ren Q, Xia X, Jing C. Common oxidants activate the reactivity of zero-valent iron (ZVI) and hence remarkably enhance nitrate reduction from water. Sep Purif Technol, 2015, 146: 227-234

[20] Guo Z, Wang D, Yan Z, Qian L, Yang L, Yan J, Chen M. Efficient remediation of p-chloroaniline contaminated soil by activated persulfate using ball milling nanosized zero valent iron/biochar composite: performance and mechanisms. Nanomater, 2023, 13(9): 1517-1533

[21] He Y, Lin H, Dong Y, Li B, Wang L, Chu S, Luo M, Liu J. Zeolite supported Fe/Ni bimetallic nanoparticles for simultaneous removal of nitrate and phosphate: synergistic effect and mechanism. Chem Eng J, 2018, 347: 669-681

[22] Hei S, Xu H, Liu B, Zhu X, Zhang S, Zhang X, Li R, Huang X. Enhanced pre-treatment of sepiolite on coal gasification wastewater: performance and adsorption mechanism. J Hazard Mater, 2022, 440 129842

[23] Heydari H, Raissi H, Ghahari A. Engineered crystalline polymers for effective contaminant removal from water. Sci Rep, 2024, 14: 31869

[24] Hossain MZ, Bahar MM, Sarkar B, Donne SW, Ok YS, Palansooriya KN, Kirkham MB, Chowdhury S, Bolan N. Biochar and its importance on nutrient dynamics in soil and plant. Biochar, 2020, 2: 379-420

[25] Hu X, Xu J, Wu M, Xing J, Bi W, Wang K, Ma J, Liu XE. Effects of biomass pre-pyrolysis and pyrolysis temperature on magnetic biochar properties. J Anal Appl Pyrolysis, 2017, 127: 196-202

[26] Huang J, Jones A, Waite TD, Chen Y, Huang X, Rosso KM, Kappler A, Mansor M, Tratnyek PG, Zhang H. Fe (II) redox chemistry in the environment. Chem Rev, 2021, 121(13): 8161-8233

[27] Jin Z, Chen X, Chen C, Tao P, Han Z, Zhang X. Biochar impact on nitrate leaching in upland red soil, China. Environ Earth Sci, 2016, 75: 1109-1119

[28] Kim K, Baltus RE, Chellam S. Rejection and fouling of track-etched microfiltration membranes by Acholeplasma laidlawii: Clues to mycoplasma behavior during “sterile” dead-end filtration. J Membr Sci, 2023, 685 121925

[29] Kong Q, Shi X, Ma W, Zhang F, Yu T, Zhao F, Zhao D, Wei C. Strategies to improve the adsorption properties of graphene-based adsorbent towards heavy metal ions and their compound pollutants: a review. J Hazard Mater, 2021, 415 125690

[30] Li H, Yao R, Gao Q, Liu Y, Yang J, Wang X, Xie W, Zhang X. Nanoattapulgite reduces the stimulation effect of nitrogen fertilizer on ammonia-oxidizing microorganisms in salinized fluvo-aquic soil. Land Degrad Dev, 2023, 34(12): 3475-3486

[31] Li C, Hu Y, Yan C, Zhang Y, Fan Y, Ji D, Wang B, Zhu L. Biochar supported modified nZVI for effective remediation of hexavalent chromium: enhanced performance and remediation mechanism. J Environ Chem Eng, 2024, 12(6 114410

[32] Liu Y, Wang J. Reduction of nitrate by zero valent iron (ZVI)-based materials: a review. Sci Total Environ, 2019, 671: 388-403

[33] Liu B, Liu Z, Wu H, Pan S, Cheng X, Sun Y, Xu Y. Effective and simultaneous removal of organic/inorganic arsenic using polymer-based hydrated iron oxide adsorbent: capacity evaluation and mechanism. Sci Total Environ, 2020, 742 140508

[34] Liu J, Jiang J, Meng Y, Aihemaiti A, Xu Y, Xiang H, Gao Y, Chen X. Preparation, environmental application and prospect of biochar-supported metal nanoparticles: a review. J Hazard Mater, 2020, 388 122026

[35] Liu B, Li H, Li H, Zhang A, Rengel Z. Long-term biochar application promotes rice productivity by regulating root dynamic development and reducing nitrogen leaching. GCB Bioenergy, 2021, 13(1): 257-268

[36] Liu A, Ma X, Zhang Z, Liu J, Luo D, Yang L, Lv N, Zhang Y, Yang G, Dong H. Single dose fertilization at reduced nitrogen rate improves nitrogen utilization without yield reduction in late-planted cotton under a wheat–cotton cropping system. Ind Crops Prod, 2022, 176 114346

[37] Liu G, Dai Z, Liu X, Dahlgren RA, Xu J. Modification of agricultural wastes to improve sorption capacities for pollutant removal from water—a review. Carbon Res, 2022, 1: 24-48

[38] Liu M, Chen G, Xu L, He Z, Ye Y. Environmental remediation approaches by nanoscale zero valent iron (nZVI) based on its reductivity: a review. RSC Adv, 2024, 14: 21118-21138

[39] Liu M, Xu X, Wanek W, Sun J, Bardgett RD, Tian Y, Cui X, Jiang L, Ma Z, Kuzyakov Y, Ouyang H, Wang Y. Nitrogen availability in soil controls uptake of different nitrogen forms by plants. New Phytol, 2025, 245(4): 1450-1467

[40] Ma F, Zhao B, Diao J, Jiang Y, Zhang J. Mechanism of phosphate removal from aqueous solutions by biochar supported nanoscale zero-valent iron. RSC Adv, 2020, 10: 39217-39225

[41] Ma D, Yang Y, Liu B, Xie G, Chen C, Ren N, Xing D. Zero-valent iron and biochar composite with high specific surface area via K₂FeO₄ fabrication enhances sulfadiazine removal by persulfate activation. Chem Eng J, 2021, 408 127992

[42] Meng Z, Huang S, Xu T, Lin Z, Wu J. Competitive adsorption, immobilization, and desorption risks of Cd, Ni, and Cu in saturated-unsaturated soils by biochar under combined aging. J Hazard Mater, 2022, 434 128903

[43] Mokete R, Eljamal O, Sugihara Y. Exploration of the reactivity of nanoscale zero-valent iron (NZVI) associated nanoparticles in diverse experimental conditions. Chem Eng Process, 2020, 150 107879

[44] Noda I, Ozaki Y. Two-dimensional correlation spectroscopy: applications in vibrational and optical spectroscopy, 2004, London, Wiley

[45] Pei Y, Cheng W, Liu R, Di H, Jiang Y, Zheng C, Jiang Z. Synergistic effect and mechanism of nZVI/LDH composites adsorption coupled reduction of nitrate in micro-polluted water. J Hazard Mater, 2024, 464 133023

[46] Perveen S, Nadeem R, Iqbal M, Bibi S, Gill R, Saeed R, Noreen S, Akhtar K, Ansari TM, Alfryyan N. Graphene oxide and Fe₃O₄ composite synthesis, characterization and adsorption efficiency evaluation for NO₃^– and PO₄^3- ions in aqueous medium. J Mol Liq, 2021, 339 116746

[47] Qiao C, Liu L, Hu S, Compton JE, Greaver TL, Li Q. How inhibiting nitrification affects nitrogen cycle and reduces environmental impacts of anthropogenic nitrogen input. Glob Change Biol, 2015, 21(3): 1249-1257

[48] Qiu B, Shao Q, Shi J, Yang C, Chu H. Application of biochar for the adsorption of organic pollutants from wastewater: modification strategies, mechanisms and challenges. Sep Purif Technol, 2022, 300 121925

[49] Rushimisha IE, Li X, Han T, Chen X, Abdoul Magid ASI, Sun Y, Li Y. Application of biochar on soil bioelectrochemical remediation: behind roles, progress, and potential. Crit Rev Biotechnol, 2024, 44(1): 120-138

[50] Sonal S, Mishra BK. A comprehensive review on the synthesis and performance of different zirconium-based adsorbents for the removal of various water contaminants. Chem Eng J, 2021, 424 130509

[51] Su JZ, Wang CC, Zhang MY, Zong XB, Huang XF, Deng ZH, Xiang P. Advances and prospectives of iron/biochar composites: application, influencing factors and characterization methods. Ind Crops Prod, 2023, 205 117496

[52] Sun Y, Gao B, Yao Y, Fang J, Zhang M, Zhou Y, Chen H, Yang L. Effects of feedstock type, production method, and pyrolysis temperature on biochar and hydrochar properties. Chem Eng J, 2014, 240: 574-578

[53] Tan XF, Zhu SS, Wang RP, Chen YD, Show PL, Zhang FF, Ho SH. Role of biochar surface characteristics in the adsorption of aromatic compounds: pore structure and functional groups. Chin Chem Lett, 2021, 32(10): 2939-2946

[54] Tang TT, Xing QJ, Zhang SH, Mu Y, Jiang XH, Zhou ZG, Xiao X, Zou JP. High selective reduction of nitrate into nitrogen by novel Fe-Cu/D407 composite with excellent stability and activity. Environ Pollut, 2019, 252: 888-896

[55] Tang H, Wang J, Zhang S, Pang H, Wang X, Chen Z, Li M, Song G, Qiu M, Yu S. Recent advances in nanoscale zero-valent iron-based materials: characteristics, environmental remediation and challenges. J Clean Prod, 2021, 319 128641

[56] Tran HN, Lima EC, Juang RS, Bollinger JC, Chao HP. Thermodynamic parameters of liquid–phase adsorption process calculated from different equilibrium constants related to adsorption isotherms: a comparison study. J Environ Chem Eng, 2021, 9(6 106674

[57] Tu W, Liu Y, Xie Z, Chen M, Ma L, Du G, Zhu M. A novel activation-hydrochar via hydrothermal carbonization and KOH activation of sewage sludge and coconut shell for biomass wastes: preparation, characterization and adsorption properties. J Colloid Interface Sci, 2021, 593: 390-407

[58] Wan X, Li C, Parikh SJ. Simultaneous removal of arsenic, cadmium, and lead from soil by iron-modified magnetic biochar. Environ Pollut, 2020, 261 114157

[59] Wang H, Gao JE, Li XH, Zhang SL, Wang HJ. Nitrate accumulation and leaching in surface and ground water based on simulated rainfall experiments. PLoS ONE, 2015, 10(8 e0136274

[60] Wang S, Zhao M, Zhou M, Li YC, Wang J, Gao B, Sato S, Feng K, Yin W, Igalavithana AD. Biochar-supported nZVI (nZVI/BC) for contaminant removal from soil and water: a critical review. J Hazard Mater, 2019, 373: 820-834

[61] Wang Y, Wang Z, Pang WK, Lie W, Yuwono JA, Liang G, Liu S, Angelo AMD, Deng J, Fan Y. Solvent control of water O−H bonds for highly reversible zinc ion batteries. Nat Commun, 2023, 14: 2720-2731

[62] Wei A, Ma J, Chen J, Zhang Y, Song J, Yu X. Enhanced nitrate removal and high selectivity towards dinitrogen for groundwater remediation using biochar-supported nano zero-valent iron. Chem Eng J, 2018, 353: 595-605

[63] Wu P, Fu Y, Vancov T, Wang H, Wang Y, Chen W. Analyzing the trends and hotspots of biochar’s applications in agriculture, environment, and energy: a bibliometrics study for 2022 and 2023. Biochar, 2024, 6: 78-96

[64] Xu W, Huang D, Wang G, Li S, Du L, Zhou W, Huang H. Enhanced sulfamethazine degradation via peroxydisulfate activation by biochar-supported nano zero-valent iron-copper: the key role of Fe (IV) and electron transfer induced by doped Cu. J Clean Prod, 2024, 434 140133

[65] Xu Y, Zanli BLGL, Chen J. New consideration on the application of nano-zero-valent iron (nZVI) in groundwater remediation: refractions to existing technologies. J Nanopart Res, 2024, 26: 11-35

[66] Yan P, Li T, Ren T, Zang Y, Sun S, Fan Y, Zhang Y, Gu X, He S. Heterotrophic denitrification enhancement via effective organic matter degradation driven by suitable iron dosage in sediment. J Environ Manage, 2025, 375 124275

[67] Yi Y, Tu G, Zhao D, Tsang PE, Fang Z. Biomass waste components significantly influence the removal of Cr (VI) using magnetic biochar derived from four types of feedstocks and steel pickling waste liquor. Chem Eng J, 2019, 360: 212-220

[68] Yuan Y, Wei X, Yin H, Zhu M, Luo H, Dang Z. Synergistic removal of Cr (VI) by S-nZVI and organic acids: the enhanced electron selectivity and pH-dependent promotion mechanisms. J Hazard Mater, 2022, 423 127240

[69] Yuan T, Tai AP, Mao J, Tam OH, Li RK, Wu J, Li S. Effects of different irrigation methods on regional climate in North China Plain: a modeling study. Agric for Meteorol, 2023, 342 109728

[70] Zhang M, Song G, Gelardi DL, Huang L, Khan E, Mašek O, Parikh SJ, Ok YS. Evaluating biochar and its modifications for the removal of ammonium, nitrate, and phosphate in water. Water Res, 2020, 186 116303

[71] Zhang Z, Huang G, Zhang P, Shen J, Wang S, Li Y. Development of iron-based biochar for enhancing nitrate adsorption: effects of specific surface area, electrostatic force, and functional groups. Sci Total Environ, 2023, 856 159037

[72] Zhang Y, Bi Z, Tian W, Ge Z, Xu Y, Xu R, Zhang H, Tang S. Synergistic effect triggered by Fe₂O₃ and oxygen-induced hydroxyl radical enhances formation of amino-phenolic humic-like substance. J Environ Manage, 2023, 348 119312

[73] Zhang M, Wang L, Zhao Q, Wang J, Sun Y. Hydrogeochemical and anthropogenic controls on quality and quantitative source-specific risks of groundwater in a resource-based area with intensive industrial and agricultural activities. J Cleaner Prod, 2024, 440 140911

[74] Zhao X, Yu G, Li J, Feng Y, Zhang L, Peng Y, Tang Y, Wang L. Eco-friendly Pickering emulsion stabilized by silica nanoparticles dispersed with high-molecular-weight amphiphilic alginate derivatives. ACS Sustain Chem Eng, 2018, 6(3): 4105-4114

[75] Zhao F, Xin J, Yuan M, Wang L, Wang X. A critical review of existing mechanisms and strategies to enhance N₂ selectivity in groundwater nitrate reduction. Water Res, 2022, 209 117889

[76] Zhao X, Wang Q, Sun Y, Li H, Lei Z, Zheng B, Xia H, Su Y, Ali KMY, Wang H. Beryllium adsorption from beryllium mining wastewater with novel porous lotus leaf biochar modified with PO₄³⁻/NH₄⁺ multifunctional groups (MLLB). Biochar, 2024, 6: 89-103

[77] Zhu X, Zhou P, Miao P, Wang H, Bai X, Chen Z, Zhou J. Nitrogen use and management in orchards and vegetable fields in china: challenges and solutions. Front Agr Sci Eng, 2022, 9(3): 386-395

Funding

National Key R&D Program of China(2023YFD1701800)

RIGHTS & PERMISSIONS

The Author(s)