Valorization of chestnut shell waste as a biocoagulant for turbidity removal: Optimization via Box-Behnken Design

Abstract

In this study, the influence of solid–liquid extraction conditions on the coagulation performance of a chestnut shell (Castanea sativa)-derived biocoagulant was systematically investigated. Extraction pH, chestnut shell mass, and extraction time were evaluated using response surface methodology based on a Box–Behnken design. The extracted tannins were subsequently chemically modified via the Mannich reaction to introduce positively charged groups and evaluated for turbidity removal from synthetic water through coagulation–flocculation jar test experiments using kaolin suspension as model turbid water. Statistical analysis indicated that the proposed model was not statistically significant (ANOVA, P = 0.531), and none of the evaluated extraction variables showed significant individual effects (P > 0.05). However, the quadratic effect of extraction time approached significance ( P = 0.068), suggesting a possible nonlinear influence on turbidity removal. However, extraction time showed evidence of a potential nonlinear influence on turbidity removal, suggesting the existence of an optimal extraction range. Despite the limited predictive capability of the model, the synthesized coagulant demonstrated high efficiency, achieving turbidity removal rates of up to 96% under optimal experimental conditions. Moreover, its performance was directly comparable to that of aluminum sulfate (Al₂(SO₄)₃), a conventional metal-based coagulant, when tested under identical operational conditions. Collectively, these results demonstrate the potential of chestnut shell-derived coagulants as effective and sustainable alternatives to metal-based coagulants for wastewater treatment applications, contributing to agricultural residue valorization and circular economy principles.

Keywords

bio-based materials / coagulation / response surface methodology / tannins / wastewater treatment

References

[1] Alshoubaki AY (2025) Harnessing vapor compression refrigeration systems to capture atmospheric water as a sustainable water source in response to climate change and water scarcity. J Environ Chem Eng 13: 118056. https://doi.org/10.1016/j.jece.2025.118056

[2] Tong S, Chen J, Xia R, et al. (2025) Quantifying ecosystem-human water trade-offs: A clean water scarcity perspective. J Hydrol-Reg Stud 60: 102526. https://doi.org/10.1016/j.ejrh.2025.102526

[3] United Nations (2015) Transforming Our World: The 2030 Agenda for Sustainable Development, New York: United Nations. Available from: https://sdgs.un.org/2030agenda.

[4] Rajendrakumar S, Mavhaire D, Shimly S, et al. (2025) Drivers and barriers towards achieving SDG 6 on clean water and sanitation for all-an Indian perspective. World Develop Sustain 7: 100228. https://doi.org/10.1016/j.wds.2025.100228

[5] Baird R, Rice EW, Eaton AD (2017) Standard methods for the examination of water and wastewater, American Water Works Association.

[6] Soros A, Amburgey JE, Stauber CE, et al. (2019) Turbidity reduction in drinking water by coagulation-flocculation with chitosan polymers. J Water Health 17: 204-218. https://doi.org/10.2166/wh.2019.114

[7] Song X, Li P, Shen Q, et al. (2025) Study on the influence of different factors on the direct treatment of high turbidity water by microfiltration processes. RSC Adv 15: 22699-22715. https://doi.org/10.1039/d5ra01817j

[8] Zourif A, Benbiyi A, Kouniba S, et al. (2023) Valorization of walnut husks as a natural coagulant for optimized water decolorization. Arab J Chem 17: 105399. https://doi.org/10.1016/j.arabjc.2023.105399

[9] Yang R, Li H, Huang M, et al. (2016). A review on chitosan-based flocculants and their applications in water treatment. Water Res 95: 59-89. https://doi.org/10.1016/j.watres.2016.02.068

[10] Al-Hanaktah A, Al-Rafayia RA, Al-Ghbabsheh AH, et al. (2025) A comparative analysis of defatted pumpkin seed extract and conventional coagulants for sustainable turbidity reduction in water and wastewater treatment. Cleaner Water 4: 100114. https://doi.org/10.1016/j.clwat.2025.100114

[11] Karnena MK, Dwarapureddi BK, Saritha V (2022) Alum, Chitin and Sago as coagulants for the optimization of process parameters focusing on coagulant dose and mixing speed. Watershed Ecol Environ 4: 112-124. https://doi.org/10.1016/j.wsee.2022.10.001

[12] Das AK, Islam MN, Faruk MO, et al. (2020) Review on tannins: Extraction processes, applications and possibilities. S Afr J Bot 135: 58-70. https://doi.org/10.1016/j.sajb.2020.08.008

[13] Aguilar CN, Rodríguez R, Gutiérrez-Sánchez G, et al. (2007) Microbial tannases: Advances and perspectives. Appl Microbiol Biot 76: 47-59. https://doi.org/10.1007/s00253-007-1000-2

[14] Tomasi IT, Boaventura RA, Botelho CM (2025) Environmental impact assessment of tannin-based coagulants production from chestnut shells. J Environ Manage 382: 125346. https://doi.org/10.1016/j.jenvman.2025.125346

[15] Tomasi IT, Ferreira RM, Boaventura RA, et al. (2025) Natural coagulants from chestnut shells: A sustainable approach for textile wastewater treatment. Chemosphere 376: 144286. https://doi.org/10.1016/j.chemosphere.2025.144286

[16] Arismendi WA, Ortiz-Ardila AE, Delgado CV, et al. (2018) Modified tannins and their application in wastewater treatment. Water Sci Technol 78: 1115-1128. https://doi.org/10.2166/wst.2018.336

[17] Tomasi IT, Boaventura RA, Botelho CM (2025) Comparative study of natural and chemical coagulants for continuous-flow treatment of textile wastewater. Chem Eng Sci 320: 122476. https://doi.org/10.1016/j.ces.2025.122476

[18] Rodrigues MBB, Lunkes N, Nascimento ASD, et al. (2026) Influence of the extraction medium of tannins from Eucalyptus Bark on the properties of Rigid Tannin-Furfuryl alcohol foams. ACS Omega 11: 11898-11910. https://doi.org/10.1021/acsomega.5c10855

[19] Tomasi IT, Santos SC, Ribeiro A, et al. (2024) Coagulants from chestnut shell tannins-Synthesis, characterization and performance on water treatment. J Water Process Eng 69: 106818. https://doi.org/10.1016/j.jwpe.2024.106818

[20] Carlqvist K, Arshadi M, Mossing T, et al. (2020) Life-cycle assessment of the production of cationized tannins from Norway spruce bark as flocculants in wastewater treatment. Biofuel Bioprod Bior 14: 1270-1285. https://doi.org/10.1002/bbb.2139

[21] Arbenz A, Avérous L (2015) Chemical modification of tannins to elaborate aromatic biobased macromolecular architectures. Green Chem 17: 2626-2646. https://doi.org/10.1039/c5gc00282f

[22] Bello A, Leiviskä T (2021) Sustainable tannin-based coagulants synthesized through Mannich reaction using melamine as an amine source for water treatment applications. Ind Crop Prod 176: 114336. https://doi.org/10.1016/j.indcrop.2021.114336

[23] Tomasi IT, Santos SC, Boaventura RA, et al. (2023) Optimization of microwave-assisted extraction of phenolic compounds from chestnut processing waste using response surface methodology. J Clean Prod 395: 136452. https://doi.org/10.1016/j.jclepro.2023.136452

[24] Hoyos-Martínez PL, Merle J, Labidi J, et al. (2018) Tannins extraction: A key point for their valorization and cleaner production. J Clean Prod 206: 1138-1155. https://doi.org/10.1016/j.jclepro.2018.09.243

[25] Benalia A, Derbal K, Amrouci Z, et al. (2024) Application of plant-based coagulants and their mechanisms in water treatment: A review. J Renew Mater 12: 667-698. https://doi.org/10.32604/jrm.2024.048306

[26] Sánchez-Martín J, Beltrán-Heredia J, Coco-Rivero B (2013) New lab-made coagulant based on Schinopsis balansae tannin extract: Synthesis optimization and preliminary tests on refractory water pollutants. Appl Water Sci 4: 261-271. https://doi.org/10.1007/s13201-013-0141-y

[27] Zedan T, Mossad M, Fouad M, et al. (2022) Potential application of natural coagulant extraction from walnut seeds for water turbidity removal. Water Pract Technol 17: 684-698.

[28] World Health Organization (2022) Guidelines for drinking-water quality: Fourth edition incorporating the first and second addenda. Available from: https://apps.who.int/iris.

[29] Ibrahim A, Yaser AZ, Lamaming J (2020) Synthesising tannin-based coagulants for water and wastewater application: A review. J Environ Chem Eng 9: 105007. https://doi.org/10.1016/j.jece.2020.105007

[30] Jesus JON, Medeiros DL, Esquerre KPO, et al. (2024) Water treatment with aluminum sulfate and tanin-Based biocoagulant in an oil refinery: The technical, environmental, and economic performance. Sustainability 16: 1191. https://doi.org/10.3390/su16031191

[31] Tomasi IT, Moreira IS, Boaventura RA, et al. (2026) Glyoxal-modified chestnut tannins as sustainable coagulants for textile wastewater treatment. J Water Process Eng 82: 109523. https://doi.org/10.1016/j.jwpe.2026.109523

[32] Sarika PR, Nancarrow P, Khansaheb A, et al. (2020) Bio-based alternatives to phenol and formaldehyde for the production of resins. Polymers 12: 2237. https://doi.org/10.3390/polym12102237