Forest and Wood Products

Forest and Wood Products

Treatment of kraft pulp mill wastewater by electrocoagulation: influence of initial pH and electrolysis time

Articles in Press

Document Type : Research Paper

Authors
Armin Afraz 1
Ahmad Jahan Latibari 1
Yahya Hamzeh 2
Ajang Tajdini 1
1 Department of Wood and Paper Sciences and Technology, College of Agriculture and Natural Resources, Karaj Branch, Islamic Azad University, Karaj, Iran.
2 Department of Wood and Paper Science and Technology, Facukty of Natural Resources, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.
10.22059/jfwp.2026.417204.1397
Abstract
Introduction: The pulp and paper industry is one of the most water-intensive industries and generates large volumes of highly polluted wastewater. Kraft pulp mill effluents contain considerable amounts of persistent organic compounds, lignin derivatives, dissolved solids, and suspended particles, resulting in high chemical oxygen demand (COD), turbidity, and a black color. Discharge of such wastewater without proper treatment poses serious environmental concerns. Various treatment methods, including biological processes, chemical coagulation, membrane technologies, and advanced oxidation processes, have been employed to reduce pollutant loads. However, their widespread application is limited by high operational costs, excessive chemical consumption, and large sludge production. In recent years, electrocoagulation has attracted considerable attention as an efficient and environmentally friendly wastewater treatment technology, because of its operational simplicity, low chemical requirement, and high capability for removing organic contaminants. Therefore, the objective of the present study was to investigate the effects of electrolysis time and initial pH on the efficiency of electrocoagulation for the treatment of kraft pulp mill wastewater.
Methods: Wastewater samples were collected from a hardwood kraft pulp mill located in northern Iran. The initial characteristics of the wastewater were COD of 860 mg/l, total dissolved solids (TDS) of 507 mg/l, and turbidity of 309 NTU. Electrocoagulation experiments were conducted in a batch reactor at room temperature under a constant voltage of 15 V. Iron and aluminum electrodes were used as the anode and cathode, respectively, without the addition of any supporting electrolyte. The initial pH of the wastewater was adjusted to four levels (3, 5, 7, and 10), while electrolysis time was varied at 10, 20, and 40 minutes. COD, TDS, and turbidity were measured before and after treatment according to APHA standard methods. All experiments were carried out in triplicate. Data were statistically analyzed using a factorial experiment based on a randomized complete block design, and mean comparisons were performed using Duncan's multiple range test at the 5% significance level.
Results: The results indicated that increasing electrolysis time significantly improved the efficiency of the electrocoagulation process. The individual effects of electrolysis time and initial pH on COD, TDS, and turbidity were significant at the 99% confidence level, whereas their interaction effect was not significant. Increasing the electrolysis time from 10 to 40 minutes enhanced pollutant removal due to greater dissolution of the iron anode, increased formation of metal hydroxides, and improved adsorption and separation of contaminants. Initial pH also had a noticeable effect on treatment efficiency, with the highest removal efficiency observed under near-neutral conditions (pH= 5-7). Lower efficiencies obtained under strongly acidic and alkaline conditions were attributed to changes in iron hydroxide species and reduced floc stability. Under the optimum conditions (pH 7 and 40 minuntes of electrolysis time), COD, TDS, and turbidity decreased from their initial values of 860 mg/L, 507 mg/L, and 309 NTU to 298.5 mg/L, 264.5 mg/L, and 26.5 NTU, corresponding to reductions of 65%, 47%, and 91%, respectively.
Conclusion: The results demonstrated that electrocoagulation using iron and aluminum electrodes is an effective, simple, and environmentally friendly method for the treatment of kraft pulp mill wastewater. Electrolysis time and initial pH were identified as the most influential operational parameters, and near-neutral conditions provided the highest pollutant removal efficiency. Overall, the process exhibited a high capability for reducing COD, TDS, and turbidity, and can be considered a promising option for pretreatment or supplementary treatment of pulp and paper mill effluents.
Keywords
Industrial wastewater
Black liquor
Kraft process
Electrocoagulation
Treatment efficiency
Subjects
[1] Kamali, M., & Khodaparast, Z. (2015). Review on recent developments on pulp and paper mill wastewater treatment. Ecotoxicology and Environmental Safety, 114, 326-342.
[2] Naeijian, F., Arefinia, A., Zaki, M.T., Orner, K.D., Tafazzoli, M., & Rowles, L. S. (2026). AI-driven deployable water quality management: Benchmarking effluent BOD prediction at a European pulp and paper mill. ACS Engineering Au, 6(1), 170–184.
[3] Bai, Y., Liu, S., Liu, X., & Zhao, X. (2026). Recent advances in electrocatalytic treatment and valorization of pulping and papermaking wastewater. Molecules, 31(10), 1604.
[4] Ram, C., Rani, P., Gebru, K.A., & Abrha, M.G.M. (2020). Pulp and paper industry wastewater treatment: Use of microbes and their enzymes. Physical Sciences Reviews, 5(10), 20190050.
[5] Amacosta, J., Poznyak, T., Siles, S., & Chairez, I. (2024). Sequential treatment by ozonation and biodegradation of pulp and paper industry wastewater to eliminate organic contaminants. Toxics, 12(2), 138.
[6] Izadi, A., Hosseini, M., Darzi, G.N., Bidhendi, G.N., Shariati, F.P., & Mosaddeghi, M. R. (2018). Perspectives on membrane bioreactor potential for treatment of pulp and paper industry wastewater: A critical review. Journal of Applied Biotechnology Reports, 5(4), 139-150.
[7] Shankar, S.U., Suresh, P., Jain, R.K., & Tripathi, Y.C. (2020). Assessment of physicochemical characteristics of effluents from paper mill in the state of Uttar Pradesh, India. International Journal of Engineering Research & Technology, 9(7), 318-318.
[8] Ramos, M.D.N., Rangel, A.S., Azevedo, K.S., Melo, M.G.B., Oliveira, M.C., Watanabe, C.M.U., Pereira, F.F., Silva, C.M., & Aguiar, A. (2022). Characteristics and treatment of Brazilian pulp and paper mill effluents: A review. Environmental Monitoring and Assessment, 194(9), 651.
[9] Carnevale Miino, M., Collivignarelli, M.C., Bellazzi, S., Abbà, A., Baldi, M., Baltrocchi, A.P.D., Rada, E.C., & Torretta, V. (2025). Removal of adsorbable organic halides from wastewater: A review of advanced chemical and electrochemical processes. Environmental Progress & Sustainable Energy, 44(5), e70053.
[10] Gurung, A., Gautam, B., & Acharya, B. (2026). Increasing treatment efficiency of black liquor from wheat straw pulping process through electrocoagulation followed by anaerobic digestion. Waste and Biomass Valorization, 17(2), 867-894.
[11] Rastegarfar, N., Behrooz, R., & Bahramifar, N. (2015). Electrocoagulation treatment of black liquor from soda-AQ pulping of wheat straw. Environmental Monitoring and Assessment, 187(2), 45.
[12] Kamali, M., Khalaj, M., Costa, M.E.V., Capela, I., & Aminabhavi, T.M. (2020). Optimization of kraft black liquor treatment using ultrasonically synthesized mesoporous tenorite nanomaterials assisted by Taguchi design. Chemical Engineering Journal, 401, 126040.
[13] Shariatmadari, H. (2023). Wastewater treatment at kraft pulp mills: Effect of temporary effluents and mitigation measures. https://ltu.diva-portal.org/smash/get/diva2:1771863/FULLTEXT02.pdf
[14] Leontieff, D. A., Ikehata, K., Inanaga, Y., & Furukawa, S. (2025). Ozone for industrial wastewater treatment: Recent advances and sector applications. Processes, 13(8), 2331.
[15] Vadgama, D., Srivastava, R., & Shinde, S. (2026). A study of theoretical mechanism on wastewater components of paper industry with process generated radicals in gaseous and aqueous phase. Materials Today: Proceedings, 124, 37-42.
[16] Flores-López, Z.D., Solís-Díaz, A.B., Cervantes-Aviles, P.A., Thangarasu, P., Kumar, D., Kaur, H., Singh, J., Lokande, P., Huerta-Aguilar, C.A., & Mubarak, N.M. (2024). Insight mechanism of magnetic activated catalyst derived from recycled steel residue for black liquor degradation. Scientific Reports, 14(1), 19057.
[17] Jagaba, A.H., Kutty, S.R.M., Naushad, M., Lawal, I.M., Noor, A., Affam, A.C., Birniwa, A.H., Abubakar, S., Soja, U.B., Abioye, K.J., & Bathula, C. (2022). Removal of nutrients from pulp and paper biorefinery effluent: Operation, kinetic modelling and optimization by response surface methodology. Environmental Research, 214, 114091.
[18] Esmaeeli, A., Sarrafzadeh, M.H., Zeighami, S., Kalantar, M., Bariki, S.G., Fallahi, A., Asgharnejad, H., & Ghaffari, S.B. (2023). A comprehensive review on pulp and paper industries wastewater treatment advances. Industrial & Engineering Chemistry Research, 62(21), 8119-8145.
[19] Dagar, S., Singh, S.K., & Gupta, M.K. (2022). Economics of advanced technologies for wastewater treatment: Evidence from pulp and paper industry. Frontiers in Environmental Science, 10, 960639.
[20] Soloman, P.A., Basha, C.A., Velan, M., & Balasubramanian, N. (2009). Electrochemical degradation of pulp and paper industry wastewater. Journal of Chemical Technology & Biotechnology, 84(9), 1303–1313.
[21] AlMuhanna, K.J., Asiri, F., Abu-Arabi, M., & AlMansour, H. (2025). Treatment of paper and pulp wastewater using coagulation-flocculation with alum: Optimization and performance evaluation. Water, Air, & Soil Pollution, 236(1), 52.
[22] Toczyłowska-Mamińska, R. (2017). Limits and perspectives of pulp and paper industry wastewater treatment—A review. Renewable and Sustainable Energy Reviews, 78, 764-772.
[23] Yamazaki, E. R., Yuan, Y., He, X., Verma, A., Jang, G. G., Giammar, D., Chellam, S., Jassby, D., Tsouris, C., & Hatzell, M.C. (2026). Electrocoagulation in water treatment: Targeted contaminant removal and laboratory best practices. ACS ES&T Water, 6(6), 3255-3282.
[24] Bhagawati, P.B., & Shivayogimath, C.B. (2021). Electrochemical technique for paper mill effluent degradation using concentric aluminum tube electrodes (CATE). Journal of Environmental Health Science and Engineering, 19(1), 553-564.
[25] Sadaf, S., Roy, H., Fariha, A., Rahman, T.U., Tasnim, N., Jahan, N., Sokan-Adeaga, A.A., Safwat, S.M., & Islam, M.S. (2024). Electrocoagulation-based wastewater treatment process and significance of anode materials for the overall improvement of the process: A critical review. Journal of Water Process Engineering, 62, 105409.
[26] Sharan, S., Khare, P., Shankar, R., Dhariya, S., Kunwar, A., Yadav, S., Patel, R.K., Gole, V.L., Yadav, V.K., Varma, A.K., & Mondal, P. (2023). Treatment of lignin enriched paper industry wastewater by electrocoagulation: Modelling approach and economic evaluation. Chemical Engineering Research and Design, 197, 708-720.
[27] Bassyouni, D., Ali, S., Abdel-Aziz, M.H., & Elashtoukhy, E. (2023). Electrocoagulation technique and statistical analysis for treatment of real effluent from the pulp and paper industry. International Journal of Electrochemical Science, 18(12), 100389.
[28] Zaied, M., & Bellakhal, N. (2009). Electrocoagulation treatment of black liquor from paper industry. Journal of Hazardous Materials, 163(2-3), 995-1000.
[29] Ghosh, A.S., & Sarkar, A. (2026). Electrocoagulation as a sustainable treatment strategy for wastewater from the pulpwood industry. Separation Science and Technology, 1–13.
[30] Wagle, D., Lin, C.J., Nawaz, T., & Shipley, H.J. (2020). Evaluation and optimization of electrocoagulation for treating kraft paper mill wastewater. Journal of Environmental Chemical Engineering, 8(1), 103595.
[31] Dogan, A.D., Kara, N., Caglak, A., & Sari Erkan, H. (2025). Improving paper mill effluent treatment: A hybrid approach using electrocoagulation and electrooxidation with oxone. International Journal of Environmental Science and Technology, 22(4), 2461-2478.
[32] Greenberg, A.E., & American Public Health Association. (1999). Standard methods for the examination of water and wastewater. 20th ed. American Public Health Association (APHA), USA.
[33] Moussa, D.T., El-Naas, M.H., Nasser, M., & Al-Marri, M.J. (2017). A comprehensive review of electrocoagulation for water treatment: Potentials and challenges. Journal of Environmental Management, 186, 24-41.
[34] İrdemez, Ş., Demircioğlu, N., & Yildiz, Y.Ş. (2006). The effects of pH on phosphate removal from wastewater by electrocoagulation with iron plate electrodes. Journal of Hazardous Materials, 137(2), 1231-1235.
[35] Hematabadi, H., & Behrooz, R. (2013). Investigation of electrocoagulation process on TSS and COD removal from effluent of the paper recycling mill using Al electrodes. Iranian Journal of Wood and Paper Industries, 3(2), 53-64.
[36] Rahmani, A.R., Samarghandi, M.R., Nematollahi, D., & Zamani, F. (2019). A comprehensive study of electrochemical disinfection of water using direct and indirect oxidation processes. Journal of Environmental Chemical Engineering, 7(1), 102785.
[37] Vlyssides, A.G., Karlis, P.K., Rori, N., & Zorpas, A.A. (2002). Electrochemical treatment in relation to pH of domestic wastewater using Ti/Pt electrodes. Journal of Hazardous Materials, 95(1-2), 215–226.
[38] Mahesh, S., Garg, K.K., Srivastava, V.C., Mishra, I.M., Prasad, B., & Mall, I. D. (2016). Continuous electrocoagulation treatment of pulp and paper mill wastewater: Operating cost and sludge study. RSC Advances, 6(20), 16223-16233.
[39] Rahmani, A.R., Shabanloo, A., Mehralipour, J., Fazlzadeh, M., & Poureshgh, Y. (2015). Degradation of phenol in aqueous solutions using electro-Fenton process. Research Journal of Environmental Sciences, 9(7), 332-342.
[40] Soloman, P.A., Basha, C.A., Velan, M., Balasubramanian, N., & Marimuthu, P. (2009). Augmentation of biodegradability of pulp and paper industry wastewater by electrochemical pre-treatment and optimization by RSM. Separation and Purification Technology, 69(1), 109–117.
[41] Khansorthong, S., & Hunsom, M. (2009). Remediation of wastewater from pulp and paper mill industry by the electrochemical technique. Chemical Engineering Journal, 151(1-3), 228-234.
[42] Mahesh, S., Prasad, B., Mall, I.D., & Mishra, I.M. (2006). Electrochemical degradation of pulp and paper mill wastewater. Part 1. COD and color removal. Industrial & Engineering Chemistry Research, 45(8), 2830-2839.
[43] Azarian, G., Rahmani, A.R., Atashzaban, Z., & Nematollahi, D. (2018). New batch electro-coagulation process for treatment and recovery of high organic load and low volume egg processing industry wastewater. Process Safety and Environmental Protection, 119, 96-103.
[44] Azadi Aghdam, M., Kariminia, H.R., & Safari, S. (2016). Removal of lignin, COD, and color from pulp and paper wastewater using electrocoagulation. Desalination and Water Treatment, 57(21), 9698-9704.
[45] Costa, C.R., Botta, C.M., Espindola, E.L., & Olivi, P. (2008). Electrochemical treatment of tannery wastewater using DSA® electrodes. Journal of Hazardous Materials, 153(1-2), 616-627.
[46] Irfan, M., Butt, T., Imtiaz, N., Abbas, N., Khan, R.A., & Shafique, A. (2017). The removal of COD, TSS and colour of black liquor by coagulation–flocculation process at optimized pH, settling and dosing rate. Arabian Journal of Chemistry, 10, S2307-S2318.
Forest and Wood Products

Articles in Press, Accepted Manuscript
Available Online from 28 July 2026