Membrane fouling severely limits the efficiency, lifetime, and sustainability of water treatment systems because the accumulation of organic matter and microorganisms blocks pores, lowers flux, and forces frequent chemical cleaning and membrane replacement, with associated economic and environmental costs. To address this, there is a critical need for antifouling strategies that actively suppress organic fouling and biofilm formation without leaching toxic biocides into aquatic environments, so that high permeability is maintained while avoiding harmful effects on ecosystems and reducing the risk of resistance development.[1,2]

Here, we show that nanocellulose coatings engineered from distinct architectures and surface chemistries—TEMPO‑oxidized cellulose nanofibrils (T‑CNF), sulfate‑functionalized cellulose nanocrystals (CNC), and lignin‑containing CNC (L‑CNC)—can be deployed as nano‑textured, highly hydrophilic, and strongly charged surface layers on polyethersulfone membranes and cellulose nonwovens to tackle fouling in an inherently renewable and water‑processable way. The coatings decrease surface roughness, increase negative surface charge, and form bound hydration layers that jointly mitigate non‑specific adsorption of proteins and other organic foulants, achieving up to about 75% lower BSA adhesion on T‑CNF‑based layers compared with unmodified polymeric substrates while preserving high water flux due to their nanometric thickness and porous nanocellulose network. [1–4]

At the same time, T‑CNF and L‑CNC introduce contact‑active, non‑leaching cytostatic effects: they stiffen E. coli cell walls, increase cell‑surface roughness, and slow proliferation and surface coverage by orders of magnitude, without causing acute cytotoxicity or releasing biocides, thus limiting biofilm formation while minimizing ecological risks. [2] Overall, these results establish charged nanocellulose coatings as scalable, largely or fully bio‑based active antifouling layers that reconcile high permeability with durable control of organic fouling and bacterial colonization, offering a promising route toward low‑impact, high‑flux filtration of complex waters without compromising water quality or environmental safety