Agricultural Runoff and UK River Degradation: How Chitosan Can Turn the Tide

UK rivers face an agricultural pollution crisis: only 14% achieve good ecological status. Natural chitosan treatment offers a practical pathway to protect waterways like the River Wye while helping farms meet compliance standards. (Image by Adobe Stock)

A staggering 69% of English dairy farms inspected between 2020 and 2021 violated environmental pollution regulations, contributing to a national water quality crisis where agriculture accounts for 40% of UK river damage (River Action, 2024). Recent government announcements in June 2025 to double enforcement funding and increase farm inspections to 6,000 annually highlight the urgency of this challenge. With agriculture contributing 50–60% of nitrate and 20–30% of phosphorus pollution to waterways, chitosan—a natural biopolymer derived from chitin—emerges as a scientifically validated, cost-effective solution capable of addressing multiple dimensions of agricultural runoff pollution (Ball, 2025).

The Scope of the Agricultural Pollution Crisis

An Environment Agency officer checks the readings of the affected watercourse, discoloured olive-green, a sign of slurry pollution.(The Environment Agency)

UK dairy farms face mounting pressure to comply with environmental regulations. Recent enforcement actions demonstrate the reality of this crisis: in October 2025, Manor Farm Dairy Ltd in Dorset was fined £6,000 and ordered to pay £10,158.50 in costs after cattle slurry polluted a local river for 4 kilometres (UK Government, 2025a). In January 2025, E & A Forshaw Partnership was fined £3,000 and ordered to pay £7,301.70 for breaching slurry storage regulations (UK Government, 2025b).

These violations reflect systemic infrastructure and management gaps. Only 14% of English rivers achieve good ecological status, with agricultural runoff identified as a primary contributor to this degradation (Green Alliance, 2024). The updated Farming Rules for Water guidance, enforced in June 2025, now requires farmers to demonstrate sound agronomic reasoning and evidence-based nutrient planning, placing greater responsibility on individual operations to prevent pollution (Williams, 2025).

The economic pressures on farms complicate compliance efforts. Intensive production demands and inadequate storage capacity create overflow risks during wet weather, while capital constraints limit investment in pollution control infrastructure. Yet the consequences are severe: beyond fines exceeding £16,000, pollution incidents trigger increased regulatory scrutiny, reputational damage, and potential loss of quality assurance certifications.

Why Current Approaches Fall Short

Traditional chemical treatment systems for agricultural wastewater present practical barriers for on-farm implementation. Conventional coagulants such as aluminium sulfate require precise dosing and pH control, necessitating technical expertise beyond typical farm capacity (Desbrières & Guibal, 2018). Furthermore, chemical coagulants raise environmental concerns, with residual metals potentially accumulating in soil and water systems (Eltaweil et al., 2021).

The updated regulatory environment compounds these challenges. The new enforcement guidance emphasises nutrient planning backed by agronomic analysis, positioning compliance as a technical management task requiring data collection, planning tool use, and record-keeping. Many farms lack access to the technical support, analytical tools, and practical technologies needed to translate these requirements into effective field-level implementation.

The Science of Chitosan for Agricultural Runoff Treatment

Chitosan is a cationic linear polysaccharide derived from chitin, characterised by amino (−NH₂) and hydroxyl (−OH) groups that confer exceptional water treatment properties (Riofrio et al., 2021). In acidic conditions, amino groups become protonated, enabling electrostatic interaction with negatively charged particles including suspended solids, phosphate ions, and pathogens (Eltaweil et al., 2021).

Eutrophication in action: excessive phosphorus from farm runoff triggers algal blooms that deplete oxygen and damage aquatic life. Chitosan treatment intercepts phosphate before it reaches waterways, protecting river ecosystems.

Phosphorus Removal: Chitosan demonstrates remarkable efficacy in removing phosphorus through charge neutralisation, complexation, and precipitation mechanisms. Research on chitosan-graphite composites achieved 70% phosphate removal at 25 mg/L concentration from agricultural runoff (Dongre, 2018). Modified chitosan materials achieved adsorption capacities up to 221.89 mg/g for phosphate from livestock wastewater (Muniz et al., 2022). The positively charged amino groups provide abundant adsorption sites for negatively charged phosphate ions, whilst chelating properties capture dissolved forms (Eltaweil et al., 2021).

Nitrogen Capture: Chitosan-based materials capture multiple nitrogen species through different mechanisms. Chitosan-graphite composites achieved up to 70% nitrate removal at 25 mg/L, whilst ammonium adsorption achieved capacities of 35.59 mg/g on chitosan-modified biochar (Mondal et al., 2023). Chitosan-NPK nanostructures achieved 30% reduction in synthetic fertiliser requirements whilst maintaining crop yields, demonstrating enhanced nitrogen use efficiency (Elshayb et al., 2024).

Suspended Solids and Organic Matter Reduction: Laboratory studies on dairy effluent treatment using chitosan gel at 0.2 g per 400 mL sample achieved extraordinary results: 99.5% turbidity removal, 99.1% total suspended solids (TSS) removal, 96.6% biological oxygen demand (BOD) removal, and 91.6% chemical oxygen demand (COD) removal (Muniz et al., 2022). The mechanism combines charge neutralisation, bridging flocculation, and adsorption, producing large, rapidly settling flocs that dramatically improve solid-liquid separation (Desbrières & Guibal, 2018).

Antimicrobial Properties: Chitosan's positively charged amino groups interact with negatively charged bacterial cell membranes, causing structural damage and cell death. Studies demonstrated complete inhibition of Staphylococcus aureus, Listeria monocytogenes, and Salmonella typhimurium in dairy products (Godoy et al., 2025). Chitosan nanoparticles combined with H₂O₂ enhanced bactericidal efficacy against E. coli O157:H7 and other pathogens common in dairy environments (Bandara et al., 2020). This broad-spectrum antimicrobial capacity addresses multiple categories of biological contamination simultaneously (Godoy et al., 2025).

Practical On-Farm Applications

Treatment Pond Systems: Retrofitting existing or modified treatment ponds with chitosan treatment represents a low-cost infrastructure pathway. Field testing at Mere Fish Farm in the UK demonstrated that chitosan's naturally positive charge binds with negatively charged suspended effluent, creating larger chains that settle rapidly (Mere Fish Farm, 2024). A typical system incorporates a reception chamber, chitosan dosing point, flocculation zone, settling zone, and clarified effluent discharge. Operational parameters include chitosan dosage (0.2–1.0 g/L), rapid mixing time (1–10 minutes), slow mixing time (20–30 minutes), and settling time (30–60 minutes).

Slurry Facility Settling Tanks: Incorporating chitosan treatment into dedicated slurry storage enhances solid-liquid separation at the point of highest pollutant concentration. The clarified liquid fraction exhibits dramatically reduced suspended solids, BOD, and pathogen levels (Muniz et al., 2022). For a typical 100,000-litre storage tank, approximately 50 kg of chitosan achieves effective treatment at estimated cost of £420, dramatically lower than potential fines exceeding £16,000 (Riofrio et al., 2021).

Economic Viability: Chitosan offers competitive cost-effectiveness compared to conventional coagulants like alum through its superior performance at lower dosages, elimination of pH adjustment requirements, and production of biodegradable rather than metal-laden sludge.

Sustainability and Compliance Benefits

Protecting our planet starts with clean water: Chitosan's complete biodegradability and environmental safety make it a cornerstone of sustainable agricultural practices, supporting farmers in achieving compliance whilst safeguarding aquatic ecosystems for future generations.

Chitosan offers complete biodegradability as its fundamental sustainability advantage. Unlike synthetic polymeric flocculants and chemical coagulants that persist in the environment or leave toxic residues, chitosan undergoes enzymatic degradation by chitinase enzymes produced by soil and aquatic microorganisms, yielding non-toxic glucosamine units (Bandara et al., 2020).

The environmental safety profile proves extensive. Ecotoxicology studies demonstrate no significant toxicity to non-target organisms at water treatment concentrations (Bandara et al., 2020). Unlike aluminium-based coagulants raising neurotoxicity concerns, chitosan presents no comparable risks. Sludge from chitosan treatment forms a biodegradable material suitable for composting, land application, or anaerobic digestion for biogas production.

Chitosan-based pollution control aligns with multiple dimensions of agricultural sustainability frameworks. Reducing nutrient pollution minimises nitrous oxide conversion in waterways (a potent greenhouse gas), whilst treated wastewater can be recycled for irrigation, reducing fresh water abstraction. Through all these pathways, chitosan treatment directly supports the UK's legally binding targets requiring 77% of water bodies to achieve good ecological status by 2027 and 40% reduction in agricultural nutrient pollution by 2038 (UK Government, 2025c).

Conclusion and Partnership Opportunities

The UK's agricultural pollution crisis demands urgent, practical solutions. With 69% of English dairy farms violating regulations and agriculture responsible for 40% of river damage, systemic change is imperative. Chitosan offers a scientifically proven pathway combining environmental effectiveness with economic viability and operational simplicity.

Entoplast supplies premium-grade chitosan specifically formulated for agricultural applications. We actively seek partnerships with dairy farms for pilot programmes, agricultural cooperatives, water authorities pursuing catchment improvement targets, and environmental technology developers.

Only 14% of English rivers achieve good ecological status. The technology to improve these outcomes exists today. Together, we can transform dairy farming's environmental impact and protect precious river ecosystems for generations to come.

For partnership inquiries and technical support, please contact Entoplast at hello@entoplast.com.