More Than a Coagulant: Chitosan as a Multifunctional Platform for Next-Generation Water Treatment

Advanced wastewater treatment plant handling complex flows of industrial and municipal effluent, where next‑generation chitosan-based materials can be integrated as modular polishing and retrofit solutions.

Water and wastewater treatment utilities face an unprecedented challenge: contaminant profiles have fundamentally shifted. Today's operators must address heavy metals, persistent pharmaceuticals, dyes, nutrient overloads, and emerging micropollutants within tightening regulatory limits. Chitosan has undergone a remarkable transformation, evolving from a simple "natural coagulant" into a versatile, tunable materials platform underpinning adsorbents, hydrogels, membranes, and nanocomposites.

By embedding chitosan as a functional scaffold within engineered structures—rather than using it solely for charge neutralisation—innovation teams and utilities can design tailored solutions for specific contaminant classes, integrate them modularly into existing plants, and achieve sustainability goals that purely synthetic approaches cannot. This article maps that evolution, connects emerging technologies to real contaminant challenges, and positions BSF-derived chitosan as a strategic feedstock for next-generation water treatment.

From Natural Coagulant to Materials Platform

The First-Generation Role and Its Limitations

For two decades, chitosan's primary role in water treatment has been as a natural coagulant. Its protonated amino groups (−NH₃⁺), which form readily in acidic to neutral pH, interact electrostatically with negatively charged suspended particles to promote aggregation into settleable flocs. Chitosan achieves turbidity removal of 74–98% across various initial turbidities without generating problematic residual aluminium or iron (Soros et al., 2019; Mehdinejad et al., 2009).

However, this narrative is limiting. Coagulation is inherently non-selective: chitosan neutralises any negatively charged colloid but provides no specificity for emerging contaminants—pharmaceuticals, endocrine disruptors, persistent dyes—that require active chemical interactions beyond electrostatic attraction. Treating complex wastewaters with multiple contaminant classes using coagulation alone often necessitates higher doses, longer settling times, and substantial sludge volumes. Modern discharge standards and circular-economy objectives demand more (Desbrières & Guibal, 2018; Eltaweil et al., 2021).

Why Advanced Materials Are Essential

Water quality standards have tightened dramatically: total phosphorus limits in sensitive watersheds now range from 0.5–1 mg/L; drinking water lead limits are 15 µg/L; many nations are developing PFAS limits below 100 ng/L. No single coagulant can selectively remove such diverse persistent contaminants whilst achieving regulatory compliance and waste minimisation.

Chitosan is not merely an ionic polymer; it is a tunable polymeric scaffold with abundant amino and hydroxyl functional groups that can be chemically modified, cross-linked, composited, and engineered into three-dimensional structures. By thinking of chitosan as a platform material rather than a single chemical, utilities can design systems combining selectivity, high capacity, regenerability, and compatibility with existing infrastructure.

Chitosan-Based Adsorbents: Targeting Complex Contaminants

Simulated dye plume in water, illustrating how chitosan-based adsorbents can selectively capture dissolved colour and organic pollutants from complex industrial effluents.

Heavy Metals: Chelation and Ion Exchange

Chitosan's amino and hydroxyl groups provide multiple binding sites for heavy metal cations through chelation, ion exchange, and electrostatic adsorption (Eltaweil et al., 2021; Wang et al., 2023). Lead, cadmium, chromium, arsenic, copper, and nickel are consistently removed at capacities ranging from 30–250 mg/g, depending on chitosan molecular weight, deacetylation degree, and pH (Muniz et al., 2022; Wang et al., 2023). Modified systems achieve even higher performance: a chitosan–alginate composite achieved 0.81 mmol Cd/g and 0.41 mmol Pb/g removal at pH 5.8, with 99% efficiency in industrial samples 653 and 203 times above drinking water standards (Malakootian et al., 2021). Equilibrium typically occurs within 30–120 minutes, making these materials practical for column and batch applications.

Dyes and Organic Pollutants: Multiphase Interactions

Dye removal operates through rich mechanistic pathways: anionic dyes interact via electrostatic attraction; cationic dyes via hydrogen bonding, π–π interactions, and hydrophobic effects—especially when chitosan is composited with carbon-based materials (Eltaweil et al., 2021). Chitosan hydrogels and composites achieve adsorption capacities of 263–1493 mg/g with removal efficiencies above 95% under optimised conditions (CWejournal, 2024)—far exceeding conventional activated carbon. For real textile and tannery wastewater, chitosan systems simultaneously reduce colour, BOD, and COD.

Nutrients and Emerging Contaminants

Secondary treatment removes only 20–40% of phosphorus and nitrogen; tertiary polishing is required for discharge limits (< 0.5 mg/L total phosphorus). Chitosan-based materials excel here. Phosphate adsorbs onto chitosan at capacities up to 6.65 mg/g, with optimal pH around 4–5 (Filipkowska et al., 2015). Chitosan modified with ion-exchange groups or composited with zeolites achieves 60–90% NH₄⁺ removal. Integration into tertiary filters after conventional treatment represents a low-cost pathway to meet nutrient standards without chemical precipitation's associated sludge. For pharmaceuticals (tetracycline, ciprofloxacin, acetaminophen), removal capacities range from 40–300 mg/g depending on modification and initial concentration (Sharifi et al., 2023; Patel et al., 2025).

Hydrogels, Aerogels, and Multifunctional Structures

Hydrogels: Three-Dimensional Networks

High‑water‑content chitosan hydrogel, illustrating the soft, hydrated matrices that enable simultaneous adsorption, contaminant capture, and controlled release functions in advanced water treatment.

Chitosan hydrogels are three-dimensional, cross-linked networks with high water-retention capacity, large internal surface area, and tunable pore sizes. Cross-linking (via glutaraldehyde, citric acid, or ionic methods) creates insoluble gels engineered for specific applications. A systematic review of 31 studies reported chitosan hydrogel dye capacities of 263–1493 mg/g and metal capacities of 61–459 mg/g—substantially outperforming activated carbon (CWejournal, 2024). Critically, these hydrogels enable simultaneous removal of multiple contaminant classes: a single engineered hydrogel removes both dyes and metals from the same wastewater stream.

Beyond adsorption, chitosan hydrogels can encapsulate catalysts or oxidants. Hydrogels embedded with TiO₂ nanoparticles or manganese oxides achieve simultaneous adsorption and photodegradation or oxidative degradation of persistent organics, combining polishing efficiency with reactive treatment in one unit (Liu et al., 2024; Zhang et al., 2025).

Aerogels and Regenerability

Aerogels—produced via freeze-drying—represent the limit of porosity engineering. With densities as low as 11 mg/cm³, porosities exceeding 99%, and specific surface areas of 150–500 m²/g, chitosan aerogels achieve exceptional adsorption kinetics and large treatment volumes per unit mass (Franco et al., 2021; Liu et al., 2024). The ultralight, microporous structure dramatically reduces mass transfer resistance, allowing equilibrium within minutes rather than hours.

A critical advantage lies in regenerability and reusability. After adsorption, the porous network can be flushed with mild acid (1–2 M HCl or acetic acid) or base to desorb contaminants. Multiple studies report 80–90% recovery of capacity after five regeneration cycles, making total cost-per-removal substantially lower than single-use activated carbon (Franco et al., 2021; CWejournal, 2024).

Mechanical Stability

Composite hydrogels address fragility concerns: reinforcement with graphene oxide, cellulose, or advanced cross-linkers (e.g., polyhedral oligomeric silsesquioxane, POSS) dramatically improves compressive strength and acid stability. POSS-cross-linked chitosan aerogels recovered 50% of compressed volume within 1 second and maintained 84% water absorption after ten compression–decompression cycles, addressing operator concerns about mechanical integrity in fixed-bed columns (Liu et al., 2024).

Chitosan@Magnetite and Nanocomposites

Magnetic Separation: The Game Changer

Integration of superparamagnetic iron oxide (Fe₃O₄) nanoparticles with chitosan creates Chitosan@magnetite (CMNC) systems combining exceptional adsorption capacity with rapid magnetic separation (Sharifi et al., 2023; Wang et al., 2023). After batch or column treatment, exposed magnets instantly separate the loaded sorbent from treated water, eliminating settling or filtration steps. This capability is transformative for decentralised systems and operations where sludge handling is a bottleneck.

Chitosan@magnetite achieves nickel removal at 30 mg/g, cobalt at 53 mg/g, and heavy metal mixtures at 2909 mg/g (Sharifi et al., 2023; Wang et al., 2023). The magnetic saturation is sufficient for practical separation whilst retaining full adsorption functionality. Cost analyses show synthesis via co-precipitation is scalable and economically competitive with conventional magnetic sorbents (Sharifi et al., 2023).

Other Nanocomposites

Chitosan–Graphene Oxide (CS-GO) combines chelating properties with graphene oxide's large surface area and π-electrons. CS-GO composites achieve Pb²⁺, Cd²⁺, and Cu²⁺ removal exceeding 100 mg/g with excellent mechanical properties (Lseee, 2025). Chitosan–Biochar composites provide low-cost support with inherent microporosity; methylene blue adsorption reaches 62 mg/g—7-fold improvement over pristine biochar—with stability across pH 5–11 (Xiong et al., 2024). Chitosan–TiO₂ nanofibers enable photocatalytic degradation of organic pollutants under UV, achieving water fluxes of 170 L·m⁻²·h⁻¹ and dye retention >94% (Liu et al., 2024).

Integration into Real Plants

Practical Deployment Pathways

Tertiary/Polishing Stage: The most straightforward integration is as a post-secondary treatment. A packed-bed column of chitosan beads, hydrogel, or nanocomposite operates at low pressure drop and high service flow rates (>10 L/min per m²), achieving polishing to sub-regulatory levels. This requires minimal retrofitting; most plants have space for a third filtration stage.

Side-Stream Treatment: For specific waste streams (concentrated leachate, dye-house effluent), chitosan materials can treat a dedicated loop whilst the main stream bypasses, minimising media use and allowing selective regeneration scheduling.

Decentralised and Point-of-Use: Small communities and industrial producers increasingly require on-site treatment. Chitosan hydrogels and aerogels are ideal: low media weight eases logistics; modular cartridge designs enable simple installation; regeneration can be scheduled during low-flow periods.

Operational Advantages

Pressure Drop: Hydrogels and aerogels exhibit lower pressure drop than activated carbon and ion-exchange resins, resulting in reduced energy consumption and equipment downsizing (0.1–0.5 bar vs. 0.5–2 bar for activated carbon).

Regeneration: Chitosan adsorbents are regenerable: mild acid or alkali strips contaminants, restoring 80–90% capacity. For polishing service, weekly or biweekly regeneration extends media life to 1–3 years versus months for single-use activated carbon—a major economic advantage.

Sludge: Unlike metal coagulation generating voluminous hydroxide sludge, chitosan's lower dosage (5–20 mg/L) and biodegradability result in minimal sludge volume. When regenerated in place, no net sludge generation occurs; end-of-life material is compostable.

Why BSF-Derived Chitosan Is Strategically Important

Limitations of Crustacean-Based Chitosan

Crustacean shells remain the dominant chitosan source today—but they are seasonal, geographically concentrated, and tied to vulnerable fisheries, underscoring the need for complementary insect‑derived supply.

Global chitosan traditionally relies on crustacean shell waste—primarily shrimp and crab processing—concentrated in Asia (80% of production). This creates vulnerabilities: geographic clustering, seasonal supply intermittency, quality variability across batches, potential allergenicity, and ESG concerns around aquaculture's environmental footprint.

BSF-Derived Chitosan: A Sustainable Alternative

Black Soldier Fly (Hermetia illucens) larvae offer a compelling alternative. BSF produces chitin-rich exoskeletons and exuviae as natural by-products; chitin comprises 7–10% of dry larval mass, reaching 35.7% in optimised systems (Etemadi et al., 2024). BSF production operates in land-based, controlled facilities—unaffected by seasons, geography, or wild-capture constraints. European insect production is projected to reach 1 million metric tonnes by 2030, yielding 21,000–30,000 metric tonnes of chitin from BSF alone (Etemadi et al., 2024).

Key BSF advantages:

• Year-round supply: 3–4 week larval cycles enable steady-state supply contracts and long-term R&D partnerships

• Full traceability: Documentation satisfies corporate ESG and sustainability audits

• Lower allergenicity: Insect proteins differ from crustacean proteins, opening pharmaceutical and biomedical pathways

• Reduced environmental footprint: Water and energy requirements are 2–10 times lower than shrimp farming; GHG emissions per tonne are substantially lower (Etemadi et al., 2024)

• Waste-to-value: BSF larvae are reared on organic waste; remaining compost returns to soil, aligning with circular-economy targets

Scientific validation: A 2024 study examined indigo carmine dye removal using BSF chitosan, achieving 211.7 mg/g maximum adsorption capacity at pH 4—directly comparable to or exceeding crustacean-derived values. Cost analysis showed Chit-BSF at US$2.97 per gram of contaminant removed, competitive with conventional adsorbents (Soetardji et al., 2024).

Conclusion

Chitosan has evolved from a simple natural coagulant into a multifunctional materials platform spanning adsorbents, hydrogels, aerogels, membranes, and nanocomposites. This addresses the critical gap in modern water treatment: the traditional single-barrier approach no longer manages complex, persistent contaminants now routine in wastewater. Chitosan-based materials offer utilities and technology developers a practical, sustainable pathway to achieve selectivity and high capacity, modular integration without costly retrofitting, regenerability reducing long-term media costs by 60–80%, and sustainability with full traceability.

For utilities and technology innovators, the imperative is clear: partner early with suppliers who understand both the science and operational realities of advanced chitosan materials. For Entoplast, BSF-derived chitosan represents a cornerstone feedstock enabling this transition—combining cutting-edge materials science with proven sustainability and circularity. The science is mature; regulatory and market drivers are aligning. The time to scale is now. Contact Entoplast to explore chitosan material options, joint development programmes, and demonstration projects.