Building Cleaner Projects: Using Chitosan to Cut the Impact of Construction Wastewater

Skyline of modern high-rise construction projects, highlighting the growing need for cleaner, more sustainable management of construction wastewater on complex urban sites.

Introduction

Construction and demolition sites generate substantial volumes of dirty water—from concrete washout operations, drilling and piling slurries, and sediment-laden site runoff. Concrete washout water alone can be highly alkaline (pH > 11–12), laden with cement fines and suspended solids, and potentially contaminated with admixture residues and trace metals (de Paula et al., 2014). Historically, many contractors have relied on simple settlement tanks or direct discharge, but this approach is increasingly untenable.

Regulatory scrutiny has intensified. The UK Environment Agency's Regulatory Position Statement (RPS) 287 establishes clear limits on discharge: suspended solids must be minimised, pH must be controlled (6–8.5), and metals must not exceed safe thresholds. Beyond regulation, main contractors and clients now demand proof of ESG compliance and environmental accountability. "Pump it to the ditch" is no longer acceptable.

Fortunately, a natural, biodegradable solution exists: chitosan, a cationic biopolymer derived from chitin. This article explores how chitosan functions as a coagulant and flocculant for construction-related waters, how it compares to conventional chemical treatments, and why BSF-derived chitosan offers a sustainable alternative.

The Construction Wastewater Challenge

Concrete washout water exhibits high alkalinity (pH 11–13), high suspended solids (cement fines, sand, unreacted cement), and admixture residues. When discharged untreated, the high pH can kill aquatic organisms within minutes and alter soil chemistry.

Drilling, piling, and tunnelling slurries produce high-turbidity streams with clay, bentonite, spoil particles, and geogenic metals (iron, manganese, copper, zinc), often exceeding 5,000 mg/L suspended solids initially (Yamada et al., 2017).

Site runoff carries sediment, silt, hydrocarbons, and metals that clog watercourses and smother riverbeds. High-pH and high-solids discharges damage aquatic ecosystems through organism stress, siltation, oxygen depletion, and long-term metal bioaccumulation. Discharge consents typically impose limits: suspended solids ≤ 100 mg/L, pH 6–8.5, total aluminium ≤ 1 mg/L, turbidity < 5 NTU (UK Environment Agency, 2024).

Conventional Treatment: Limits of Alum and Synthetic Polymers

Large circular settling tank handling cloudy site water, showing how conventional construction wastewater treatment relies on gravity separation before advanced aids like chitosan are introduced.

Most construction sites rely on settlement tanks, lagoons, and chemical coagulation (alum, iron salts) or synthetic polymers (polyacrylamide, polyaluminium chloride).

Alum's limitations:

• Produces large volumes of metal-rich sludge (residual aluminium ≥ 10 mg/L)

• Highly pH-dependent (narrow optimal range 6–8); requires pre-acidification in high-pH scenarios

• Treated water often exceeds discharge limits (≤ 1 mg/L total aluminium)

• Sludge disposal incurs significant tankering and landfill costs

Synthetic polymers' concerns:

• Residual acrylamide monomer (toxic at ppb levels) and microplastic fragments in treated water (Miserli et al., 2025)

• Regulatory pressure: UK Environment Agency now evaluates polyelectrolytes against aquatic toxicity thresholds; cationic polymers limited to 0.1 × 24h LC50 for fish

• Construction clients increasingly oppose persistent synthetic polymers, viewing them as contrary to circular-economy goals

• High-turbidity waters require elevated dosing, driving up costs without guaranteeing sludge compaction

Traditional approaches work but carry hidden costs: residual metal risks, microplastic concerns, regulatory compliance complexity, and poor ESG optics. ESG targets and reputational risk make this stance untenable.

How Chitosan Works in High-Solids, High-pH Waters

Chitosan's fundamental mechanisms:

Chitosan is a deacetylated derivative of chitin, found in crustacean shells and insect exoskeletons. Its amino groups (-NH₂) become protonated at pH < ~6.5, conferring a positive charge that drives coagulation (Badawi et al., 2023).

Suspended solids and colloids carry negative surface charges. When chitosan is added, its cationic amino groups neutralise these charges, destabilising the colloidal suspension and promoting particle aggregation. Chitosan's long polymer chains physically bridge multiple particles, creating larger, denser flocs that settle faster and more completely than individual colloids, improving clarification and sludge compaction (Yamada et al., 2017). Its amino and hydroxyl groups also chelate dissolved metal ions (Fe²⁺, Cu²⁺, Zn²⁺) and bind phosphates, improving overall water quality (Badawi et al., 2025).

pH considerations:

A critical advantage is pH independence. Research on tunnel construction slurries found chitosan's turbidity removal efficiency remained relatively constant across pH 6–10, unlike alum which shows a narrow optimal range (Yamada et al., 2017). In very high-pH concrete washout scenarios (pH > 12), practical approaches include pre-acidification using CO₂ sparging or mild acid (de Paula et al., 2014), modified chitosan formulations (chitosan chloride solutions), or combination approaches pairing chitosan with limestone. Best practice: Each site should conduct jar testing to establish optimal dosage and pre-treatment conditions.

Performance and Benefits for Construction Wastewater

Concrete washout generates highly alkaline, sediment-laden wastewater that must be captured and treated responsibly on construction sites.

Evidence for chitosan efficacy:

• 98% turbidity removal in tunnel construction slurry, residual turbidity < 5 NTU (well below discharge limits) Yamada et al. (2017)

• 99% suspended solids removal from high-solids wastewater at 10 g/L chitosan dosage Rockson-Itiveh (2025)

• Chitosan removes 87–90% of copper, iron, zinc, and chromium from industrial wastewaters (Gidas, 1999)

• Chitosan achieves 65–97% COD removal, rivalling or exceeding alum and PAC performance (Rockson-Itiveh, 2025)

Key benefits:

• Flocs are larger, denser, settle faster than those from alum or PAM

• Sludge shows improved dewatering, reducing disposal volumes and costs

• Settled sludge is non-toxic, biodegradable, suitable for land use or composting

• 100% biodegradable; no residual metal or synthetic polymer concerns

• Regulatory alignment: increasingly favoured by UK Environment Agency

• Competitive cost: ~£3–8/m³ for typical dosing (alum ~£2–5/m³, but hidden disposal costs favour chitosan on lifecycle basis)

On-Site Deployment Models

Concrete washout treatment:

• Collect washout water in sump tank

• Monitor pH and turbidity

• Dose chitosan (5–20 mg/L depending on solids load) and mix gently for 5–10 minutes

• Allow settling for 20–40 minutes (faster than alum)

• Decant clarified supernatant for reuse in concrete batching or safe discharge

• Dispose of settled sludge off-site or allow drying and composting

Drilling and piling slurries:

• Modular treatment skid (20–50 m³ capacity) at borehole or rig

• Chitosan dosed in-line or in batch tank (5–10 mg/L, optimised for slurry type)

• Gentle mixing and settling (15–30 minutes)

• Clarified water reused in drilling circuit; compact sludge dewatered

Stormwater and site runoff:

• Chitosan solution dosed into flow path upstream of settlement tank (5–15 mg/L)

• Simple venturi or static mixer for contact

• Settlement in baffled tank (30–60 minutes)

• Discharge to surface water or infiltration system

Critical success factors: Jar testing (site-specific optimisation), real-time turbidity/pH monitoring, staff training, sludge disposal planning, weather-resilient equipment sizing.

Why BSF-Derived Chitosan Strengthens the Value Proposition

Historically, chitosan has been sourced almost exclusively from crustacean shells—a byproduct of the seafood industry. This creates challenges: supply volatility (dependent on fishery seasons), marine ecosystem linkage perception, ESG ambiguity, and geographic concentration.

Black soldier fly, a circular-economy source of chitin and chitosan that underpins Entoplast’s natural coagulant solutions for cleaner construction wastewater treatment.

Entoplast's Black Soldier Fly (BSF)-derived chitosan offers a compelling alternative:

• Land-based farming: BSF reared on controlled farms using organic by-products (food waste, agricultural residues), creating a truly circular model

• Decoupled from fisheries: No ocean ecosystem dependence; supply scales independently

• Controlled quality: Consistent exoskeleton composition and purity

• Carbon efficiency: Lower carbon footprint than crustacean-dependent processing

• Supply resilience: Reduces geopolitical and seasonal disruptions

Performance equivalence: At the molecular level, BSF-derived chitosan performs identically to crustacean-derived chitosan. Both are cationic polysaccharides with comparable degree of deacetylation (75–95%), molecular weight, and charge density.

ESG and reputational benefit: For contractors targeting net-zero or carbon-neutral status, BSF-chitosan demonstrates circular-economy commitment, decouples from marine-resource concerns, and offers a genuinely nature-positive narrative. A concrete plant using Entoplast's BSF-chitosan can credibly claim a "nature-based," "zero-fishery-impact" water treatment process, strengthening sustainability credentials in tenders and audits.

Conclusion

Construction wastewater is a persistent, large-volume challenge. Current approaches—alum, synthetic polymers, or simple settlement—manage the problem but carry hidden costs: residual metal contamination, persistent microplastics, regulatory compliance risk, and poor ESG optics.

Chitosan delivers:

• Effective treatment: ≥95% turbidity and suspended solids removal, compatible with high-pH concrete washout and high-solids slurries

• Operational simplicity: Jar-test optimisation followed by straightforward dosing and settling

• Environmental responsibility: Fully biodegradable, non-toxic, no residual metal or polymer concerns; compostable sludge

• Regulatory alignment: Increasingly favoured by UK Environment Agency as a natural coagulant

• Cost competitiveness: On a lifecycle basis, competitive with or cheaper than alum + PAM combinations

Entoplast's BSF-derived chitosan enhances this value proposition by delivering guaranteed performance through controlled production, supply resilience, and genuinely nature-positive impact. By adopting chitosan-based treatment systems—on-site for concrete washout, drilling slurries, and stormwater—contractors can meet regulatory targets, reduce costs, support sludge reuse, and build a reputation as environmental leaders.

Contact us today to discuss your specific use case and discover how chitosan can help build cleaner, greener construction projects.