Caustic Soda
NaOH · 20–200 mg/L (pH dependent)
Industrial-grade alkalinity builder for neutralising acidic wastewater streams in equalisation and pH-correction tanks — ahead of biological treatment and metal precipitation. Also used in UF/membrane CIP regimes. Supplied as lye or flakes.
Specifications
| Chemical Formula | NaOH |
|---|---|
| Primary Function | Alkaline pH adjustment |
| Physical Form | Lye / flakes |
| Application Point | Equalisation tank / pH correction tank |
| Typical Dosage | 20–200 mg/L (pH dependent) |
| Packaging | 50 kg bags / IBC totes |
Where it's used
- pH Neutralisation
- Equalisation Tanks
- Acidic Effluent Streams
- Metal Precipitation Prep
- Membrane CIP
Related solutions
What it is and when to use it
Caustic soda (sodium hydroxide, NaOH) is a strong alkali used to raise pH. Use it to neutralise acidic wastewater in equalisation and pH-correction tanks, to prepare effluent for biological treatment or metal precipitation, and in alkaline cleaning (CIP) of UF and other membranes.
Biological treatment and most coagulants work in a defined pH window, so acidic effluent from plating, chemical, textile or pharmaceutical processes is usually neutralised first. Caustic soda reacts quickly and completely, making it easy to control with a pH meter and dosing pump. Raising pH also precipitates many dissolved metals as hydroxides, which can then be removed by coagulation and settling.
It is supplied as lye (liquid) or flakes in 50 kg bags or IBC totes. Dosing depends on the acidity and buffering of the stream, typically 20–200 mg/L, so it is best set by titration and controlled automatically by pH. Caustic is highly corrosive and dissolves with a lot of heat: add flakes slowly to water, never water to flakes.
Use it for
- Neutralising acidic effluent in equalisation and pH-correction tanks
- Raising pH before biological treatment
- Metal hydroxide precipitation
- Alkaline CIP of UF and membrane systems
How to choose
- Titrate a representative sample to estimate demand, then control dosing automatically by pH
- Choose lye for automated dosing and flakes for smaller sites or remote storage
- Use compatible tanks, pumps and piping, and protect lines from low-temperature crystallisation of strong lye
- Consider mixing and retention time so pH stabilises before the next stage
- Provide PPE, eyewash and safety showers for operators
Frequently asked questions
How much caustic soda do I need to neutralise my effluent?
It depends on the acidity and buffering capacity of the stream, which is why the typical range (20–200 mg/L) is so wide. Titrate a representative sample to your target pH to estimate demand, then use a pH controller linked to the dosing pump so the dose follows real-time changes in the effluent.
Can caustic soda be used to clean UF membranes?
Yes. Alkaline solutions are commonly used in UF cleaning to remove organic and biological fouling. For EuroTec PVDF modules such as the ETUF-9060R, the datasheet allows pH 1–12 during cleaning. Follow the membrane supplier's cleaning procedure for concentration, temperature and contact time.
What precautions are needed when handling caustic soda?
Caustic soda is highly corrosive to skin and eyes and releases a lot of heat when dissolved. Always add flakes slowly to water, never water to flakes. Wear goggles or a face shield, chemical gloves and an apron, and provide an eyewash station and safety shower nearby. Follow the safety data sheet.
Technically reviewed by Prashant Dwivedi, Co-Founder & Director ·