Magneto-bio-production of extracellular polymeric substances from starch wastewater: mechanistic insights into green valorization

Abstract

Starch wastewater (SW) has high organic loading (OL), rapid biodegradability, and strong oxygen demand, which often cause unstable treatment performance and excessive energy consumption in conventional aerobic processes. Magnetic field (MF) application was investigated as an auxiliary strategy to promote the magneto-bio-production of extracellular polymeric substances (EPS) during SW treatment, wherein a static MF served as a non-chemical stimulus for biological EPS generation in an aerobic sequencing batch reactor (SBR). The MF maintained chemical oxygen demand (COD) and soluble COD (SCOD) removal in the aerobic SBR at above 96.8% under low-to-medium OL conditions under six operational scenarios with varying OL and dissolved oxygen (DO) levels. Such stabilization could be attributed to MF-reinforced sludge structure with increased diameter of 247.7 µm and fractal dimension up to 0.41, which substantially reduced system sludge volume index and achieved high-quality effluent. Moreover, interfloc viscosity and aggregation were improved, with bound-EPS secretion of up to 80.22 mg/g mixed liquor suspended solids (MLSS). EPS flocculation rates reached 88.3%, thereby demonstrating potential for high-value applications. Mechanistically, MF enriches EPS-producing and magnetotactic bacteria (MTB), like Flavobacterium and Cloacibacterium. It also reorients intracellular metabolism by reinforcing the tricarboxylic acid (TCA) cycle and suppressing gluconeogenesis to accelerate glycolysis. The metabolic alteration expands α-ketoglutarate and succinate pools, thereby increasing the availability of amino acid and sugar precursors. Consequently, Kyoto Encyclopedia of Genes and Genomes (KEGG)-based functional redistribution may support the coordinated synthesis of proteinaceous EPS enriched in glutamate, histidine, valine, and polysaccharide EPS dominated by rhamnose, xylose, and fucoidan, whereas MTB-mediated spatial organization may further promote EPS retention and matrix stabilization. Comparative evaluation suggested that low-to-medium OL with medium DO was optimal for maximizing EPS production and sludge structural stability. Importantly, MF can enhance the stability and robustness of SW treatment through EPS-mediated sludge aggregation, community structure changes, and metabolic shifts, thereby enabling value-added EPS production.

Graphical abstract

Keywords

Starch wastewater treatment / Extracellular polymeric substance / Green valorization / Magnetic field / Microbial community

Highlight

	● MF stabilized SW treatment, maintaining > 96% COD and SCOD removal.
	● MF enhanced sludge aggregation, with MD 247.7 µm and FD 0.41.
	● B-EPS reached 80.22 mg/g MLSS with 88.3% flocculation efficiency.
	● MF enriched EPS-producing bacteria and MTB to form floc matrices.
	● MF upregulated EPS and iron genes to remodel glycolysis and TCA cycle.

References

[1] An N , Zheng Y F , Wei Y , Ma B . (2023). How to form aggregates of free anammox bacteria to improve sedimentation performance. Water, 15(10): 1836

[2] APHA, AWWA, WPCF (1989). Standard Methods for the Examination of Water and Wastewater. 17th ed. Washington, DC: American Public Health Association.

[3] Asgari G , Seid-Mohammadi A , Shokoohi R , Samarghandi M R , Daigger G T , Malekolkalami B , Khoshniyat R . (2023). Exposure of the static magnetic fields on the microbial growth rate and the sludge properties in the complete-mix activated sludge process (a lab-scale study). Microbial Cell Factories, 22(1): 195

[4] Bala Subramanian S , Yan S , Tyagi R D , Surampalli R Y . (2010). Extracellular polymeric substances (EPS) producing bacterial strains of municipal wastewater sludge: isolation, molecular identification, EPS characterization and performance for sludge settling and dewatering. Water Research, 44(7): 2253–2266

[5] Ben Hamed H , Mainardis M , Moretti A , Toye D , Léonard A . (2025). Extracellular polymeric substances (EPS) in sewage sludge management: a call for methodological standardization. Journal of Environmental Management, 376: 124407

[6] Bylesjö M , Rantalainen M , Cloarec O , Nicholson J K , Holmes E , Trygg J . (2006). OPLS discriminant analysis: combining the strengths of PLS‐DA and SIMCA classification. Journal of Chemometrics, 20(8−10): 341–351

[7] Chaiwong C , Koottatep T , Polprasert C . (2020). Comparative study on attached-growth photobioreactors under blue and red lights for treatment of septic tank effluent. Journal of Environmental Management, 260: 110134

[8] Cheng D L , Ngo H H , Guo W S , Chang S W , Nguyen D D , Bui X T , Wei W , Ni B J , Varjani S , Hoang N B . (2022). Enhanced photo-fermentative biohydrogen production from biowastes: an overview. Bioresource Technology, 357: 127341

[9] Comte S , Guibaud G , Baudu M . (2006). Relations between extraction protocols for activated sludge extracellular polymeric substances (EPS) and eps complexation properties : part i. comparison of the efficiency of eight EPS extraction methods. Enzyme and Microbial Technology, 38(1−2): 237–245

[10] Coyte K Z , Schluter J , Foster K R . (2015). The ecology of the microbiome: networks, competition, and stability. Science, 350(6261): 663–666

[11] De Bruin S , Riisgaard-Jensen M , Hansen S H , Van Loosdrecht M C M , Nielsen P H , Lin Y M . (2026). Global insights into extracellular polymeric substances from activated sludge: yield, composition, and microbial communities. Water Research, 289: 124726

[12] Domingues V S , Monteiro A S , Ferreira G F , Santos V L . (2017). Solid flocculation and emulsifying activities of the lipopolysaccharide produced by Trichosporon mycotoxinivorans CLA2. Applied Biochemistry and Biotechnology, 182(1): 367–381

[13] Frankel R B . (2009). The discovery of magnetotactic/magnetosensitive bacteria. Chinese Journal of Oceanology and Limnology, 27(1): 1–2

[14] Geng S Y , Fu W Z , Chen W F , Zheng S L , Gao Q , Wang J , Ge X H . (2020). Effects of an external magnetic field on microbial functional genes and metabolism of activated sludge based on metagenomic sequencing. Scientific Reports, 10(1): 8818

[15] Guo X , Wang X , Liu J X . (2016). Composition analysis of fractions of extracellular polymeric substances from an activated sludge culture and identification of dominant forces affecting microbial aggregation. Scientific Reports, 6(1): 28391

[16] Hahn M W , Pitt A , Koll U , Schmidt J , Maresca J A , Neumann-Schaal M . (2021). Aurantimicrobium photophilum sp. nov., a non-photosynthetic bacterium adjusting its metabolism to the diurnal light cycle and reclassification of Cryobacterium mesophilum as Terrimesophilobacter mesophilus gen. nov., comb. nov. International Journal of Systematic and Evolutionary Microbiology, 71(8): 004975

[17] Han J L , Jia J N , Hu X J , Sun L , Ulbricht M , Lv L Y , Ren Z J . (2024). Effect of magnetic field coupled magnetic biochar on membrane bioreactor efficiency, membrane fouling mitigation and microbial communities. Science of the Total Environment, 931: 172549

[18] Hong C , Yang Y , Yao L . (2025). Enhancing activated sludge process efficiency using static magnetic fields: implications for microbial growth and sludge management. Journal of Environmental Management, 394: 127286

[19] Hou J C , Hong C , Ling W , Hu J S , Feng W B , Xing Y , Wang Y J , Zhao C W , Feng L H . (2024). Research progress in improving sludge dewaterability: sludge characteristics, chemical conditioning and influencing factors. Journal of Environmental Management, 351: 119863

[20] Hu B , Gu X , Wang Y L , Leng J T , Zhang K , Zhao J Q , Wu P , Li X L , Wan C J , Xu J T . (2022). Revealing the effects of static magnetic field on the anoxic/oxic sequencing batch reactor from the perspective of electron transport and microbial community shifts. Bioresource Technology, 345: 126535

[21] Hu X Y , Zhang S , Wang S , Wang J B , Wang M Y , Bi Y K , Wang J . (2025). Magnetic field enhanced the biological nitrogen removal in sequencing batch reactor: based on extracellular polymeric substances, microbial activity, and community functions. Journal of Environmental Chemical Engineering, 13(5): 117433

[22] Jogler C , Schüler D . (2009). Genomics, genetics, and cell biology of magnetosome formation. Annual Review of Microbiology, 63: 501–521

[23] Ju H Q , Lin J F , Tian T , Xie D , Xu R H . (2020). NADPH homeostasis in cancer: functions, mechanisms and therapeutic implications. Signal Transduction and Targeted Therapy, 5(1): 231

[24] Kuang L J , Damayanti N P , Jiang C H , Fei X , Liu W J , Narayanan N , Irudayaraj J , Campanella O , Deng M . (2019). Bioinspired glycosaminoglycan hydrogels via click chemistry for 3D dynamic cell encapsulation. Journal of Applied Polymer Science, 136(5): 47212

[25] Kweon Y , Rothe A , Conibear E , Stevens T H . (2003). Ykt6p is a multifunctional yeast R-SNARE that is required for multiple membrane transport pathways to the vacuole. Molecular Biology of the Cell, 14(5): 1868–1881

[26] Łebkowska M , Rutkowska-Narożniak A , Pajor E , Tabernacka A , Załęska-Radziwiłł M . (2018). Impact of a static magnetic field on biodegradation of wastewater compounds and bacteria recombination. Environmental Science and Pollution Research, 25(23): 22571–22583

[27] Li J R , Li D Y , Liang D B , Wu Y D , Zhu Y H , Du L Z , Yin M C , Geng Y X , Wu Y S , Li J . (2024). Static magnetic fields enhance microbial aggregation and adhesion to promote aerobic granulation. Chemical Engineering Journal, 489: 151392

[28] Li M , Zhu X Q , Yang H , Xie X C , Zhu Y T , Xu G Z , Hu X J , Jin Z Y , Hu Y , Hai Z B . et al. (2020). Treatment of potato starch wastewater by dual natural flocculants of chitosan and poly-glutamic acid. Journal of Cleaner Production, 264: 121641

[29] Li X Y , Yang S F . (2007). Influence of loosely bound extracellular polymeric substances (EPS) on the flocculation, sedimentation and dewaterability of activated sludge. Water Research, 41(5): 1022–1030

[30] Li Y B , Qin L L , Li X R , Tang X L , Zhao X , Jia X N , Kong X Q . (2025). Response of aerobic granular sludge to organic loading rate under micro-electric stimulation environment. Frontiers of Environmental Science & Engineering, 19(5): 64

[31] Lin H M , Zheng Y C , Yang Y K , Liu F Y , Yang K , Zhang B , Wen X H . (2023). The role of the core microorganisms in the microbial interactions in activated sludge. Environmental Research, 235: 116660

[32] Liu D , Huang Y J , Hu J W , Wang B , Lu Y . (2022). Multiscale catalysis under magnetic fields: methodologies, advances, and trends. ChemCatChem, 14(24): e202200889

[33] Liu Z F , Ye J X , Zou Z N . (2023). Closeness centrality on uncertain graphs. ACM Transactions on the Web, 17(4): 1–29

[34] Lorenc-Plucińska G , Walentynowicz M , Lewandowski A . (2017). Poplar growth and wood production on a grassland irrigated for decades with potato starch wastewater. Agroforestry Systems, 91(2): 307–324

[35] Luo J Y , Huang L X , Cheng X S , Liu X Y , Zhao C X , Cheng S . (2025). Field-based strategies for enhanced chemical/biological wastewater treatment: key mechanisms, critical influencing factors, and bottlenecks. Frontiers of Environmental Science & Engineering, 19(11): 153

[36] Lv Y F , Pan J J , Huo T R , Zhao Y P , Liu S T . (2019). Enhanced microbial metabolism in one stage partial nitritation-anammox system treating low strength wastewater by novel composite carrier. Water Research, 163: 114872

[37] Lyu W L , Song Q , Shi J , Wang H Y , Wang B , Hu X L . (2021). Weak magnetic field affected microbial communities and function in the A/O/A sequencing batch reactors for enhanced aerobic granulation. Separation and Purification Technology, 266: 118537

[38] Ma B R , Wang S , Li Z W , Gao M C , Li S S , Guo L , She Z L , Zhao Y G , Zheng D , Jin C J . et al. (2017). Magnetic Fe₃O₄ nano-particles induced effects on performance and microbial community of activated sludge from a sequencing batch reactor under long-term exposure. Bioresource Technology, 225: 377–385

[39] Manikandan N A , Pakshirajan K , Pugazhenthi G . (2020). A closed-loop biorefinery approach for polyhydroxybutyrate (PHB) production using sugars from carob pods as the sole raw material and downstream processing using the co-product lignin. Bioresource Technology, 307: 123247

[40] McLaughlin A, Bader D A (2014). Scalable and high performance betweenness centrality on the GPU. In: SC ’14: Proceedings of the International Conference for High Performance Computing, Networking, Storage and Analysis. New Orleans: IEEE, 572–583

[41] More T T , Yadav J S S , Yan S , Tyagi R D , Surampalli R Y . (2014). Extracellular polymeric substances of bacteria and their potential environmental applications. Journal of Environmental Management, 144: 1–25

[42] Mu T H , Liu Y , Zhang M , Sun H N . (2014). Protein recovery from sweet potato starch wastewater by foam separation. Separation Science and Technology, 49(14): 2255–2260

[43] Nakajima H , Amano W , Fujita A , Fukuhara A , Azuma Y T , Hata F , Inui T , Takeuchi T . (2007). The active site cysteine of the proapoptotic protein glyceraldehyde-3-phosphate dehydrogenase is essential in oxidative stress-induced aggregation and cell death. Journal of Biological Chemistry, 282(36): 26562–26574

[44] Obaideen K , Shehata N , Sayed E T , Abdelkareem M A , Mahmoud M S , Olabi A G . (2022). The role of wastewater treatment in achieving sustainable development goals (SDGs) and sustainability guideline. Energy Nexus, 7: 100112

[45] Pan Z , Chen Y H , Zhou M , McAllister T A , Guan L L . (2021). Microbial interaction-driven community differences as revealed by network analysis. Computational and Structural Biotechnology Journal, 19: 6000–6008

[46] Roux P , Siano R , Collin K , Bilien G , Sinquin C , Marchand L , Zykwinska A , Delbarre-Ladrat C , Schapira M . (2021). Bacteria enhance the production of extracellular polymeric substances by the green dinoflagellate Lepidodinium chlorophorum. Scientific Reports, 11(1): 4795

[47] Santos L O , Deamici K M , Menestrino B C , Garda-Buffon J , Costa J A V . (2017). Magnetic treatment of microalgae for enhanced product formation. World Journal of Microbiology and Biotechnology, 33(9): 169

[48] Schmid J , Sieber V , Rehm B . (2015). Bacterial exopolysaccharides: biosynthesis pathways and engineering strategies. Frontiers in Microbiology, 6: 496

[49] Shen Y , Huang D M , Chen Y P , Yan P , Gao X . (2020). New insight into filamentous sludge bulking during wastewater treatment: surface characteristics and thermodynamics. Science of the Total Environment, 712: 135795

[50] Shen Y X , Xiao K , Liang P , Ma Y W , Huang X . (2013). Improvement on the modified lowry method against interference of divalent cations in soluble protein measurement. Applied Microbiology and Biotechnology, 97(9): 4167–4178

[51] Sheng G P , Yu H Q , Li X Y . (2010). Extracellular polymeric substances (EPS) of microbial aggregates in biological wastewater treatment systems: a review. Biotechnology Advances, 28(6): 882–894

[52] Shu D T , He Y L , Yue H , Wang Q Y . (2015). Microbial structures and community functions of anaerobic sludge in six full-scale wastewater treatment plants as revealed by 454 high-throughput pyrosequencing. Bioresource Technology, 186: 163–172

[53] Sincak M , Luptakova A , Matusikova I , Jandacka P , Sedlakova-Kadukova J . (2023). Application of a magnetic field to enhance the environmental sustainability and efficiency of microbial and plant biotechnological processes. Sustainability, 15(19): 14459

[54] Stoian I A M , Vlad A , Gilca M , Dragos D . (2025). Modulation of glutathione-s-transferase by phytochemicals: to activate or inhibit—that is the question. International Journal of Molecular Sciences, 26(15): 7202

[55] Tian Y J , Li J Z , Meng J , Li J L . (2023). High-yield production of single-cell protein from starch processing wastewater using co-cultivation of yeasts. Bioresource Technology, 370: 128527

[56] Vadasarukkai Y S , Gagnon G A . (2017). Influence of the mixing energy consumption affecting coagulation and floc aggregation. Environmental Science & Technology, 51(6): 3480–3489

[57] Wang H T , Guo L , Ren X M , Gao M C , Jin C J , Zhao Y G , Ji J Y , She Z L . (2022). Enhanced aerobic granular sludge by static magnetic field to treat saline wastewater via simultaneous partial nitrification and denitrification (SPND) process. Bioresource Technology, 350: 126891

[58] Wu J , Jiang B , Feng B , Li L , Moideen S N F , Chen H , Mribet C , Li Y Y . (2020). Pre-acidification greatly improved granules physico-chemical properties and operational stability of upflow anaerobic sludge blanket (UASB) reactor treating low-strength starch wastewater. Bioresource Technology, 302: 122810

[59] Wu J , Jiang B , Kong Z , Yang C Y , Li L , Feng B , Luo Z B , Xu K Q , Kobayashi T , Li Y Y . (2021). Improved stability of up-flow anaerobic sludge blanket reactor treating starch wastewater by pre-acidification: impact on microbial community and metabolic dynamics. Bioresource Technology, 326: 124781

[60] Xu R H , Fu Y , Xu Y B , Zheng X , Huang Y X , Meng F G . (2022). Comparing biotransformation of extracellular polymeric substances (EPS) under aerobic and anoxic conditions: reactivities, components, and bacterial responses. Chemosphere, 296: 133996

[61] Yang S N , Liu H H , Liao X J , Kong X K , Xu Z Z . (2022). Extraction and profiling of proteins in yellow powder from sweet potato starch wastewater using response surface methodology and proteomic approach. Journal of Food Science, 87(1): 339–352

[62] Yu G H , He P J , Shao L M , Zhu Y S . (2008). Extracellular proteins, polysaccharides and enzymes impact on sludge aerobic digestion after ultrasonic pretreatment. Water Research, 42(8−9): 1925–1934

[63] Zaidi N S , Muda K , Sillanpää M . (2019). Effects of extra-cellular polymeric substances towards physical properties of biomass under magnetic field exposure. International Journal of Environmental Science and Technology, 16(7): 3801–3808

[64] Zhang D J , Li W , Hou C , Shen J Y , Jiang X B , Sun X Y , Li J S , Han W Q , Wang L J , Liu X D . (2017). Aerobic granulation accelerated by biochar for the treatment of refractory wastewater. Chemical Engineering Journal, 314: 88–97

[65] Zhang Y , Zhao Y , Chen Y N , Lu Q , Li M X , Wang X Q , Wei Y Q , Xie X Y , Wei Z M . (2016). A regulating method for reducing nitrogen loss based on enriched ammonia-oxidizing bacteria during composting. Bioresource Technology, 221: 276–283

[66] Zhang Y Q , Zha M , Gao M M , Wang X H . (2022). How weak static magnetic field contributes to rapid granulation and better performance of microalgal-bacterial granular sludge?. Chemical Engineering Journal, 450: 138162

[67] Zhou H H , Liu B F , Wang Q S , Sun J M , Xie G J , Ren N Q , Ren Z J , Xing D F . (2017). Pulse electromagnetic fields enhance extracellular electron transfer in magnetic bioelectrochemical systems. Biotechnology for Biofuels, 10(1): 238

[68] Zhu L , Lv M L , Dai X , Yu Y W , Qi H Y , Xu X Y . (2012). Role and significance of extracellular polymeric substances on the property of aerobic granule. Bioresource Technology, 107: 46–54

[69] Zhuang Z , Xia X , Yang G Q , Zhuang L . (2022). The role of exopolysaccharides in direct interspecies electron transfer. Frontiers in Microbiology, 13: 927246

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