Development of a municipal sludge-based water-retaining material for soil improvement and plant growth

Abstract

Crop production is threatened by both water scarcity and poor soil water retention in arid or semi-arid regions. At the same time, the industrial-scale accumulation of municipal sludge creates substantial environmental and resource pressures. The goal of this work was to recycle municipal sludge into a low-cost, environmentally friendly, and multifunctional sludge-based water-retaining material (SBWRM) for enhancing soil water retention capacity and nutritional status. Sludge was used as the primary raw material, and extracellular polymeric substances were extracted using a combined alkaline ultrasonic method. These extracts were then mixed with polyvinyl alcohol to prepare the sludge-based material. The water retention capacity of the material, as well as its effects on seed germination and plant growth in a planting substrate, were systematically evaluated. The results suggested that the SBWRM achieved a maximum water retention capacity of 18.7 times its own weight. The addition of 40% SBWRM effectively promoted ryegrass seed germination and plant height, increased soil moisture and pH value, and enhanced the nutrient contents of nitrogen, phosphorus, and potassium. The findings indicate that SBWRM can effectively enhance water conservation, soil quality, and nutrient supply, thereby providing a practical approach for utilizing sludge resources and supporting ecological restoration in agricultural systems.

Keywords

Sludge-based water-retaining material / Extracellular polymeric substances / Soil improvement / Plant growth / Water retention

Funding

This work was supported by the National Natural Science Foundation of China (22306078), the Natural Science Foundation of Jiangsu Province (BK20230714), and the Natural Science Research of Jiangsu Higher Education Institutions of China (23KJB610006).

Conflict of interest

The authors declare that they have no competing interests. Six authors are employees of POWERCHINA Chengdu Engineering Corporation Limited, and one author is affiliated with academic institutions. No commercial or financial relationships influenced the conduct of this research.

References

[1] Li, Y, Sun, J, Liu, J, et al. Straw returning to the field alleviates drought stress in maize by enhancing radiation use efficiency to promote agronomic character and dry matter accumulation. J Agric Food Res. 2025; 23:102243. doi: 10.1016/j.jafr.2025.102243

[2] Drei, P, Mancuso, G, Lavrnić S, et al. A novel methodology to develop EU water reuse risk management plan in agricultural water distribution networks and crop irrigation systems. Water Research X. 2025; 28:100395. doi: 10.1016/j.wroa.2025.100395

[3] Mitra, NA, Usama, IS, Nasrin, A. Role of impoundment and irrigation in intensive agriculture watersheds. J Hydrol. 2025; 662:134075. doi: 10.1016/j.jhydrol.2025.134075

[4] Liu, F, Yue, C, Ma, J, Guo, S, Li, L. Water resources evaluation and driving factor analysis in nine provinces of Western China based on water footprint theory. Ecol Indic. 2025; 174:113457. doi: 10.1016/j.ecolind.2025.113457

[5] Yang, M, Ji, C, Chao, K, et al. Enhanced wheat yield and flag leaf physiology in saline-alkali soils using modified straw water-retaining agent. Agric Water Manag. 2025; 307:109264. doi: 10.1016/j.agwat.2024.109264

[6] Zheng, H, Mei, P, Wang, W, et al. Effects of super absorbent polymer on crop yield, water productivity and soil properties: A global meta-analysis. Agric Water Manag. 2023; 282:108290. doi: 10.1016/j.agwat.2023.108290

[7] Ma, X, Qu, K, Zhao, X, et al. Oxidized sodium alginate/ polyacrylamide hydrogels adhesive for promoting wheat growth. Int J Biol Macromol. 2023; 253:127450. doi: 10.1016/j.ijbiomac.2023.127450

[8] Sreenivasulu, D, Swamy, GM, Balaji, M. Glutathione S-transferase is a good biomarker in acrylamide induced neurotoxicity and genotoxicity. Interdiscip Toxicol. 2018; 11(2):115-121. doi: 10.2478/intox-2018-0007

[9] Zhang, J, Yu, Y, Li, W, et al. A novel sludge dewatering conditioner of chitin derivatives from waste black soldier fly puparia: Efficacy, key factors, and mechanisms. Process Saf Environ Prot. 2025; 202:107789. doi: 10.1016/j.psep.2025.107789

[10] Feng, J, Yu, Y, Huang, S, Zhu, N, Mojiri, A, Ge, D. Tannic acid as a green chemical for the removal of various heavy metals: A critical review of recent developments. J Environ Manag. 2025; 375:124390. doi: 10.1016/j.jenvman.2025.124390

[11] Wang, Z, Wang, R, Yuan, H, Zhu, N. A novel strategy for high efficiency of anaerobic digestion of waste activated sludge by using a Fe-Cu microelectrolysis method: Performance, electron transfer, key enzymes and microbial community. Water Res. 2025; 287:124322. doi: 10.1016/j.watres.2025.124322

[12] Zhang, J, Yu, Y, Li, W, Zhu, N, Mojiri, A, Ge, D. Recent development of tannic acid-based flocculants in sewage and sludge treatments: A crucial review. Water Air Soil Pollut. 2025; 237(1):237. doi: 10.1007/s11270-025-08727-z

[13] Kominko, H, Gorazda, K, Wzorek, Z. The possibility of organo-mineral fertilizer production from sewage sludge. Waste Biomass Valori. 2017; 8(5):1781-1791. doi: 10.1007/s12649-016-9805-9

[14] Micaela, T, Elena, T, Anna, G, et al. Characterization of chitin and chitosan derived from Hermetia illucens, a further step in a circular economy process. Sci Rep. 2022; 12(1):6613. doi: 10.1038/s41598-022-10423-5

[15] Zhu, Y, Xiao, K, Zhou, Y, et al. Profiling of amino acids and their interactions with proteinaceous compounds for sewage sludge dewatering by Fenton oxidation treatment. Water Res. 2020; 175:115645. doi: 10.1016/j.watres.2020.115645

[16] Lloret, E, Pascual, JA, Brodie, EL, et al. Sewage sludge addition modifies soil microbial communities and plant performance depending on the sludge stabilization process. Appl Soil Ecol. 2016; 101:37-46. doi: 10.1016/j.apsoil.2016.01.002

[17] El Sayed, MM. Production of polymer hydrogel composites and their applications. J Polym Environ. 2023; 31(7):2855-2879. doi: 10.1007/s10924-023-02796-z

[18] Shen, L, Cheng, J, Wang, J, et al. Comparison of extraction methods for extracellular polymeric substances (EPS) and dynamic characterization of EPS from sessile microorganisms during pyrite bioleaching. J Environ Chem Eng. 2022; 10(3):107922. doi: 10.1016/j.jece.2022.107922

[19] Tanan, W, Panichpakdee, J, Saengsuwan, S. Novel biodegradable hydrogel based on natural polymers: Synthesis, characterization, swelling/reswelling and biodegradability. Eur Polym J. 2019; 112:678-687. doi: 10.1016/j.eurpolymj.2018.10.033

[20] Zhang, Y, Jiang, Z, Zhao, Q, et al. Treatment of soil eluate containing nitro aromatic compounds by adsorption on activated coke (AC). Water Sci Technol. 2015; 73(6):1313-1319. doi: 10.2166/wst.2015.581

[21] Grintzalis, K, Georgiou, CD, Schneider, YJ. An accurate and sensitive coomassie brilliant blue G-250-based assay for protein determination. Anal Biochem. 2015; 480:28-30. doi: 10.1016/j.ab.2015.03.024

[22] Chen, YF, Roan, HY, Lii, CK, Huang, YC, Wang, TS. Relationship between antioxidant and antiglycation ability of saponins, polyphenols, and polysaccharides in Chinese herbal medicines used to treat diabetes. J Med Plants Res. 2011; 5(11):2322-2331.

[23] Zhang, G, Yang, J, Liu, H, Zhang, J. Sludge ozonation: Disintegration, supernatant changes and mechanisms. Bioresour Technol. 2009; 100(3):1505-1509. doi: 10.1016/j.biortech.2008.08.041

[24] Chen, G, Zhou, T, Song, Y, et al. Alkaline hydrothermal treatment of gentamycin mycelial residues: Characteristics of disintegration, solid-state fermentation, and antibiotic resistance genes reduction. Biomass Conv Bioref. 2024; 15(4):5493-5507. doi: 10.1007/s13399-024-05568-4

[25] Zhang, L, Yang, J, Wu, B, et al. Enhanced VFAs production from microalgal hydrolytic acidification with ultrasonic-alkali pretreatment. Algal Res. 2023; 71:103056. doi: 10.1016/j.algal.2023.103056

[26] Xu, X, Cao, D, Wang, Z, et al. Study on ultrasonic treatment for municipal sludge. Ultrason Sonochem. 2019; 57:29-37. doi: 10.1016/j.ultsonch.2019.05.008

[27] Yang, Y, Zhong, M, Bian, X, You, Y, Li, F. Preparation of carbon-based material with high water absorption capacity and its effect on the water retention characteristics of sandy soil. Biochar. 2023; 5(1):61. doi: 10.1007/s42773-023-00260-8

[28] Ge, D, Zhang, W, Yuan, H, Zhu, N. Enhanced waste activated sludge dewaterability by tannic acid conditioning: Efficacy, process parameters, role and mechanism studies. J Cleaner Prod. 2019; 241:118287. doi: 10.1016/j.jclepro.2019.118287

[29] Huang, W, Lai, H, Du, J, Zhou, C, Liu, Z, Ni, Q. Effect of polymer water retaining agent on physical properties of silty clay. Chem Biol Technol Agric. 2022; 9(1):47. doi: 10.1186/s40538-022-00309-z

[30] Kim, HN, Park, JH. Monitoring of soil EC for the prediction of soil nutrient regime under different soil water and organic matter contents. Appl Biol Chem. 2024; 67(1):1. doi: 10.1186/s13765-023-00849-4

[31] Paradelo, R, Basanta, R, Barral, MT. Water-holding capacity and plant growth in compost-based substrates modified with polyacrylamide, guar gum or bentonite. Sci Horticul. 2019; 243:344-349. doi: 10.1016/j.scienta.2018.08.046

[32] Di Carlo, E, Chen, CR, Haynes, RJ, Phillips, IR, Courtney, R. Soil quality and vegetation performance indicators for sustainable rehabilitation of bauxite residue disposal areas: A review. Soil Res. 2019; 57(5):419. doi: 10.1071/sr18348

[33] Yang, M, Shi, Y, Casimiro, T. Categories and application fields and manufacturing process and action mechanism of water retaining agent. Adv Polym Technol. 2022; 2022:2211441. doi: 10.1155/2022/2211441

[34] Yang, Y, Zhang, L, Feng, J, et al. Amendment of dredged sediment from a contaminated lake and assessment of suitability as a planting medium for Urban greening. Environ Eng Sci. 2024; 41(5):180-189. doi: 10.1089/ees.2023.0309