Sodium Metabisulfite for Water Treatment in Africa

Water treatment is one of the biggest uses of sodium metabisulfite (Na₂S₂O₅, CAS 7681-57-4), and Africa is one of the regions where the demand is growing fastest. Municipal utilities, desalination and reverse-osmosis plants, mines and food processors all use it to remove chlorine and control oxidation. This article explains where metabisulfite is used in water treatment, how much is typically dosed, and how to buy it for African projects.

1. Why dechlorination matters

Chlorine is added to water to disinfect it, but the residual chlorine that remains afterwards is reactive. It gives water a chlorinous taste and odour, attacks reverse-osmosis membranes and ion-exchange resins, and interferes with many industrial processes. Sodium metabisulfite reduces free chlorine and chloramine to harmless chloride, quickly and at low cost, which is why it is the standard dechlorination reagent.

2. Municipal drinking water

Where water is chlorinated for disinfection, metabisulfite is dosed after the contact tank to remove the excess chlorine before the water is delivered. The aim is to keep enough chlorine for safety through the network while avoiding a strong taste and odour at the customer’s tap. Dosing is set on the measured residual chlorine and the target at the point of use.

3. Reverse osmosis: desalination and brackish water

Africa’s growing reliance on seawater desalination and brackish-water RO makes this the fastest-growing use. Thin-film composite RO membranes are damaged by oxidants, so metabisulfite is dosed ahead of the membranes to reduce the chlorine in the feed. It is also used to protect membranes during shutdown and storage. Dosing is controlled tightly, because too little leaves the membrane exposed and too much wastes reagent and can promote biological growth downstream.

4. Mining and industrial water

Process water. Removes residual chlorine and lowers redox potential before it reaches reagents, membranes or circuits.
Tailings and return water. Supports cyanide destruction and oxidation control in gold plants.
Cooling and process systems. Controls oxidising species that cause corrosion and scaling.

5. Boiler water: oxygen scavenging

In boiler systems, sodium metabisulfite is used as an oxygen scavenger to remove dissolved oxygen from feedwater, protecting the boiler from pitting corrosion. It reacts quickly and is often used with a catalyst; the dose is set on the measured dissolved oxygen.

6. Chromium and metal reduction in wastewater

Because it is a reducing reagent, metabisulfite is used to reduce hexavalent chromium (Cr(VI)) to the far less harmful trivalent form (Cr(III)) in industrial wastewater, so the chromium can be precipitated and removed. This is common in metal-finishing and plating effluents.

7. Dosing guide

Application	Typical dose (starting point)	Control parameter
Dechlorination of water and wastewater	Approx. 1.5 – 3 mg/L metabisulfite per mg/L chlorine	Residual chlorine
RO feed protection	Set to keep feed oxidant below the membrane limit	Residual oxidant before the membrane
Boiler water (oxygen scavenging)	Set on dissolved oxygen, with small excess	Dissolved oxygen
Cr(VI) reduction	Stoichiometric plus a small excess	Cr(VI) / pH (about 2 – 3)

These are starting points only. Final doses depend on water chemistry, temperature and the target limit; confirm them with your water-treatment engineer.

8. Supplying metabisulfite to Africa

We supply sodium metabisulfite to African water and mining projects from China, in the packaging and documentation buyers in the region normally require:

Item	Detail
Packaging	25 kg PP/PE bags (palletised) or 1000 kg jumbo bags; full container loads available
Ports	Durban, Mombasa, Dar es Salaam, Tema/Takoradi, Lagos/Apapa, Beira, Walvis Bay and others
Terms	Quoted FOB or CIF; annual or quarterly volumes possible
Documents	COA and SDS per batch; third-party inspection (SGS/BV) on request

Because the same grade serves municipal, RO, mining and boiler applications, a utility or mine can standardise on one product and one supplier. Tell us the application, tonnage and discharge port for a quotation.

Frequently Asked Questions

How much metabisulfite is needed to remove chlorine?

As a starting point, about 1.5-3 mg/L of metabisulfite per mg/L of chlorine, but the real dose is set on the measured residual chlorine. Confirm it for your water.

Can sodium metabisulfite protect RO membranes?

Yes – it is dosed ahead of the membranes to reduce feed chlorine, which would otherwise damage thin-film composite membranes. Control on the residual oxidant before the membrane.

Is metabisulfite used for Cr(VI) reduction?

Yes – as a reducing reagent it converts hexavalent chromium to trivalent chromium in wastewater treatment so the metal can be precipitated.

Do you supply to African ports?

Yes. We quote FOB or CIF to Durban, Mombasa, Dar es Salaam, Tema/Takoradi, Lagos/Apapa, Beira, Walvis Bay and other ports, in 25 kg bags or 1000 kg jumbo bags.