Sodium Hypochlorite
NaOCl · 2–5 mg/L · 10–12% Cl2
High-strength disinfectant (10–12% active chlorine) for pre-disinfection and biofouling control on UF/MBR membrane trains. Low continuous dosing at the intake or UF feed inactivates bacteria before they build EPS cake layers — measurably slowing transmembrane pressure rise.
Specifications
| Chemical Formula | NaOCl |
|---|---|
| Primary Function | Pre-disinfection & biofouling control (UF / MBR membranes) |
| Physical Form | Yellow liquid (10–12% active chlorine) |
| Application Point | Raw water / UF feed tank |
| Typical Dosage | 2–5 mg/L |
| Packaging | 30 L / 50 L carboys |
Where it's used
- UF / MBR Biofouling Control
- Raw Water Pre-disinfection
- Intake Chlorination
- Treated Water Disinfection
- Membrane Cleaning
Related solutions
What it is and when to use it
Sodium hypochlorite (NaOCl) is a liquid chlorine disinfectant supplied at 10–12% active chlorine. Use it for raw water pre-disinfection, biofouling control on UF and MBR membrane trains, treated-water disinfection and membrane cleaning, wherever chlorine is needed without handling chlorine gas.
Low, continuous dosing at the intake or UF feed tank inactivates bacteria before they form biofilms and EPS cake layers on membranes, slowing the rise in transmembrane pressure. PVDF UF membranes tolerate oxidants well, and EuroTec highlights oxidiser tolerance as a feature of its membrane.
Polyamide RO membranes do not tolerate chlorine. NWPL RO manuals limit free chlorine to 0.1 mg/L, so any chlorine dosed upstream must be removed with SMBS or activated carbon before RO. Hypochlorite loses strength over time, faster in heat and sunlight, so store it cool and shaded and rotate stock. Never mix it with acids, as this releases chlorine gas. The typical dosage is 2–5 mg/L; set it according to chlorine demand and residual targets.
Use it for
- Biofouling control on UF and MBR membrane feed
- Raw water intake and pre-disinfection
- Final disinfection of treated water
- Chemically enhanced backwash and cleaning of chlorine-tolerant membranes
How to choose
- Measure chlorine demand, and set the dose to hold the target residual
- Confirm downstream membranes are chlorine tolerant, or plan dechlorination before RO
- Store in a cool, shaded area and use stock promptly to limit strength loss
- Use compatible dosing pumps and tubing, and keep acids separate
- Monitor residual chlorine continuously at critical points
Frequently asked questions
Can sodium hypochlorite be used before RO membranes?
Only if it is removed before reaching them. Polyamide RO membranes are damaged by chlorine, and the NWPL RO manuals limit free chlorine to 0.1 mg/L. Chlorine is often dosed upstream for biofouling control, then neutralised with sodium metabisulphite (SMBS) ahead of the RO cartridge filter.
Why does sodium hypochlorite lose strength in storage?
Hypochlorite solutions decompose naturally over time, and heat and sunlight speed up the process. A product delivered at 10–12% active chlorine will gradually weaken, so store it in closed containers in a cool, shaded area, order quantities you will use promptly, and check strength if stock has been stored for a long time.
How does hypochlorite help control membrane biofouling?
Bacteria in feed water attach to membrane surfaces and produce EPS, a sticky layer that raises transmembrane pressure and cleaning frequency. Low, continuous chlorination at the intake or UF feed tank inactivates bacteria before they settle, slowing biofilm growth. PVDF UF membranes tolerate this oxidant well.
Technically reviewed by Prashant Dwivedi, Co-Founder & Director ·