ChloroKlean BPR Compliant Chlorine Dioxide Disinfectant - UK Supplier

    Chlorine Dioxide vs Sodium Hypochlorite for Legionella Control

    Chlorine dioxide (ClO₂) and sodium hypochlorite (NaOCl, common bleach) are both chlorine-based oxidising biocides used for Legionella control and general water disinfection. Sodium hypochlorite is cheap and familiar but has well-documented limitations: its biocidal form (hypochlorous acid, HOCl) only dominates below pH 7.5, it reacts with ammonia to form chloramines and with organics to form trihalomethanes (THMs) and haloacetic acids (HAAs), and it cannot penetrate established biofilm. Effective dose rates are therefore high (2-4 ppm free chlorine residual). Chlorine dioxide is effective across pH 4-10 with no loss of biocidal action, does not form THMs or chloramines, penetrates biofilm in pipework, and achieves >4-log Legionella reduction at residuals as low as 0.1-0.5 ppm. For UK water systems regulated under ACoP L8 and HSG274, ClO₂ provides a more reliable, lower-dose route to compliance. ChloroKlean Plus L20 is BPR-compliant for PT5 (potable water) and PT11 (cooling systems).

    Author
    Key Advantage of ClO₂
    Works across pH 4-10, penetrates biofilm, achieves Legionella control at 0.1-0.5 ppm where hypochlorite needs 2-4 ppm.
    By-products
    ClO₂ produces no THMs, HAAs, or chloramines at typical doses. Sodium hypochlorite forms chloramines, THMs, HAAs, and chlorates - several are regulated by the DWI and WHO.
    pH Range
    ClO₂ effective at pH 4-10 with no loss of biocidal activity. Hypochlorite loses >50% efficacy above pH 7.5 as HOCl shifts to OCl⁻.
    Regulatory Sources
    HSE ACoP L8, HSE HSG274 Parts 1-3, DWI Regulation 31, WHO Guidelines for Drinking-water Quality, EU BPR 528/2012 PT5/PT11
    UK Compliance
    Both are widely used under UK GB BPR. ChloroKlean Plus L20 holds PT5/PT11 compliance. Hypochlorite is also PT5/PT11 listed but requires higher residual to meet ACoP L8 Legionella targets.
    Comparison Guide

    Chlorine Dioxide vs Sodium Hypochlorite

    Sodium hypochlorite (bleach) is the cheapest chlorine source - but it loses efficacy above pH 7.5, reacts with ammonia and organics, forms regulated by-products, and cannot penetrate biofilm. ClO₂ solves all four problems at sub-ppm doses.

    ClO₂

    Chlorine Dioxide

    • Effective pH 4-10 - works in real-world water systems
    • Penetrates biofilm where Legionella harbours
    • No THMs, HAAs, or chloramines at dosing rates
    • 0.1-0.5 ppm residual sufficient for ACoP L8 compliance
    • Does not react with ammonia or organics in mains water
    NaOCl

    Sodium Hypochlorite

    • Low chemical cost per litre
    • Familiar to operators, widely available
    • Loses biocidal efficacy above pH 7.5
    • Forms THMs, HAAs, chloramines from organics
    • Cannot penetrate established biofilm

    Detailed Comparison

    Detailed comparison of chlorine dioxide versus sodium hypochlorite
    FeatureChlorine DioxideSodium Hypochlorite
    Effective Dose for Legionella

    0.1-0.5 ppm

    Sub-ppm residual achieves >4-log reduction

    2-4 ppm

    Higher residual needed; often loses to demand

    pH Range Effectiveness

    pH 4-10

    Biocidal activity independent of pH

    Optimal pH <7.5

    >50% efficacy lost as HOCl shifts to OCl⁻

    Biofilm Penetration

    Excellent

    Diffuses into and oxidises EPS matrix

    Poor

    Reacts at biofilm surface only

    THM / HAA Formation

    None at dose

    Does not chlorinate organics

    Yes

    Regulated DBPs under DWI and US EPA rules

    Chloramine Formation

    None

    Does not react with ammonia

    Yes

    Reacts with ammonia; loses free chlorine

    Reaction with Organic Demand

    Low

    Selective oxidiser; survives demand

    High

    Demand consumes free chlorine rapidly

    Dosing Accuracy

    Precise

    Sub-ppm dosing via metering pump

    Variable

    Residual fluctuates with demand and pH

    Material Compatibility

    Good

    Compatible with stainless and most plastics

    Corrosive

    Attacks rubber, EPDM, mild steel

    UK BPR Status

    PT5/PT11 Compliant

    Full GB BPR compliance

    PT5/PT11 Listed

    Also BPR-listed active substance

    When to Choose Each

    Choose Chlorine Dioxide When:

    • Legionella control under ACoP L8 / HSG274 is required
    • Existing biofilm is documented or suspected
    • Water pH runs above 7.5 (most UK potable supplies)
    • Source water has measurable ammonia or organic demand
    • THM / HAA compliance is marginal at the tap
    • Lower chemical use is required for sustainability or cost

    Consider Sodium Hypochlorite When:

    • One-off shock treatment of a new or drained system
    • Lowest-cost basic disinfection of clear, low-demand water
    • Existing dosing infrastructure cannot be changed short-term
    • Used as a backup or emergency biocide alongside ClO₂
    • Local site policy mandates a free chlorine residual
    "In ACoP L8 audits we see the same pattern again and again - a hypochlorite-dosed system with the right total chlorine residual on paper, but biofilm fouling at every dead leg and Legionella counts that refuse to come down. Hypochlorite is reacting at the biofilm surface and being consumed before it can penetrate. Switching to chlorine dioxide at 0.3 ppm typically clears that biofilm within weeks. The maths is simple: less chemical, more biocide where it matters."
    GO

    Gavin Owen, Managing Director, ChloroKlean

    BPR-compliant disinfection specialist

    Why Choose ChloroKlean Plus L20

    If you're considering switching to chlorine dioxide, ChloroKlean Plus L20 is purpose-built for industrial and commercial applications.

    BPR PT5 / PT11 Compliant

    ChloroKlean Plus L20 holds GB BPR compliance for drinking water (PT5) and cooling system preservation (PT11). Direct replacement for hypochlorite in potable and process water.

    Stabilised Liquid Formulation

    Regenerative chemistry means no on-site generator and no chlorite/chlorate handling. Dose with a standard metering pump - simpler infrastructure than two-part ClO₂ generators.

    ACoP L8 Field Results

    Case studies in hospitals, cooling towers, and leisure facilities show sustained Legionella control where hypochlorite failed. >4-log reduction documented under BS EN 13623:2020.

    Regulatory and Scientific References

    This comparison is informed by the following authoritative sources. Always refer to the latest published guidance.

    HSE ACoP L8
    Health and Safety Executive (HSE)

    Legionnaires' disease: The control of legionella bacteria in water systems

    ACoP L8 is the Approved Code of Practice for Legionella control in UK water systems. It requires effective biocide residual and biofilm management - areas where ClO₂ outperforms hypochlorite.

    View source
    HSE HSG274
    Health and Safety Executive (HSE)

    Legionella: Technical guidance Parts 1, 2 and 3

    HSG274 sets technical detail for cooling towers (Part 1), hot and cold water (Part 2), and other risk systems (Part 3). All parts emphasise biofilm control as a Legionella management priority.

    View source
    DWI Regulation 31
    Drinking Water Inspectorate (DWI)

    Approval of products and substances for use in public water supply

    DWI Regulation 31 controls which chemicals can be used in UK public water supply. Both hypochlorite and approved chlorine dioxide products are listed; THM compliance under the Water Supply (Water Quality) Regulations remains the operator's responsibility.

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    WHO Guidelines
    World Health Organization (WHO)

    Guidelines for Drinking-water Quality (Chlorine and Chlorine Dioxide)

    WHO compares chlorine and chlorine dioxide as drinking water disinfectants, noting ClO₂'s pH independence, lower THM formation, and its chlorite/chlorate by-products.

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    US EPA D/DBPR
    US Environmental Protection Agency

    Disinfectants and Disinfection Byproducts Rules

    EPA sets enforceable limits on THMs (80 µg/L), HAA5 (60 µg/L), and chlorite (1.0 mg/L). Switching to ClO₂ commonly reduces THM and HAA formation in distribution.

    View source

    Frequently Asked Questions

    It depends on what 'stronger' means. Hypochlorite (as HOCl) has a higher standard oxidation potential, but it is consumed rapidly by ammonia, organics, and biofilm and loses biocidal efficacy above pH 7.5. Chlorine dioxide is a more selective oxidiser, works across pH 4-10, and penetrates biofilm. In real water systems, ClO₂ achieves Legionella control at 0.1-0.5 ppm where hypochlorite needs 2-4 ppm.

    Hypochlorite's biocidal form is hypochlorous acid (HOCl). Above pH 7.5, HOCl progressively dissociates into hypochlorite ion (OCl⁻), which is roughly 80 times less biocidal. UK potable water is commonly delivered at pH 7.5-8.5 for plumbosolvency control, so hypochlorite is operating outside its optimum almost everywhere. WHO Drinking-water Guidelines confirm chlorine dioxide is not affected by this dissociation.

    No, not at typical dosing rates. Chlorine dioxide is a selective oxidiser that does not chlorinate organic matter the way free chlorine does. ClO₂'s reduction by-products are chlorite and chlorate, regulated separately and typically well within limits at residuals below 1 ppm. Switching from hypochlorite to ClO₂ is a common way UK operators reduce THM and HAA formation.

    Yes, in almost all Legionella control and water treatment applications. The transition typically involves draining and cleaning the system, then commissioning a ClO₂ dosing rig sized for 0.1-0.5 ppm residual at the furthest sample point. Existing metering pump infrastructure can often be re-used. ChloroKlean's technical team provides commissioning support and ACoP L8 documentation.

    For ACoP L8 / HSG274 compliance, a continuous residual of 0.1-0.5 ppm ClO₂ at the furthest tap or sample point achieves >4-log Legionella pneumophila reduction. Higher residuals (2-5 ppm) are used for shock dosing in heavily fouled systems. See our hospital Legionella case study.

    Less so. Hypochlorite at high residuals attacks rubber gaskets, EPDM, mild steel, and copper, especially where it concentrates due to evaporation in cooling towers. Chlorine dioxide is compatible with stainless steel, PVC, PEX, PP, and most modern plumbing materials at typical residuals. Contact us for ChloroKlean's material compatibility data sheet.

    Move from Hypochlorite to Compliant ClO₂ Dosing

    ChloroKlean Plus L20 delivers ACoP L8 / HSG274 Legionella control at 0.1-0.5 ppm - with no THMs, no chloramines, and proven biofilm penetration.