Microbiocide Chemical Guide for Sohar Industrial Cooling Towers

Slime on the fill, algae on the distribution deck and a rising approach temperature on your heat exchangers all call for the same fix: a microbiocide chemical dosed to a plan. For cooling towers at Sohar steel, aluminium, refinery and petrochemical plants, that plan usually pairs an oxidising biocide with a non-oxidising one, adds a biodispersant and checks results every week. We supply two cooling water microbiocides from our Barka warehouse. This page explains how to choose between them, how much to dose and how to tell that the treatment is working.

What a microbiocide chemical does in a cooling tower

An open recirculating cooling tower is warm, wet, aerated and often in full sun, so bacteria, algae and fungi grow easily in it. Microbes settle on surfaces and build biofilm, a slimy layer that insulates heat transfer surfaces, blocks fill and nozzles, and shelters sulphate-reducing bacteria (SRB) that cause corrosion under deposits. A microbiocide kills or controls these organisms in the bulk water and on wetted surfaces.

Biocide is one part of a full cooling water programme. A complete programme combines a corrosion and scale inhibitor, at least one biocide (preferably two used in rotation) and a biodispersant to help remove biofilm. Dirt and sludge shield bacteria from the biocide, so no biocide programme works well in a dirty system. Dead legs get no biocide at all, so flush or remove them.

Why Sohar cooling towers foul fast

Plants in Sohar Industrial Zone and around Sohar port share conditions that speed up microbial growth. Basin water runs warm for most of the year, strong sun on open decks drives algae, and wind carries dust and sand from the industrial area into the basin. The dust settles as sludge and feeds biofilm. Plants that run high cycles of concentration, or use high-TDS make-up, also concentrate nutrients and suspended solids in the circulating water.

Your make-up water sets how much oxidiser is used up before any residual shows. Halogen demand is typically 2 to 5 ppm for surface water make-up and below 1 ppm for treated municipal water. Measure the demand of your own make-up before you set chlorine or bromine feed rates, and measure it again if the source changes.

Oxidising and non-oxidising biocides: building a dual programme

Cooling water microbiocides fall into two classes. Oxidising biocides such as chlorine, bromine and chlorine dioxide kill bacteria, fungi and algae in seconds by oxidising the cell wall. They penetrate biofilm poorly and leave no lasting protection. Non-oxidising biocides such as glutaraldehyde, isothiazolinone and DBNPA poison the cell instead and need a longer retention time.

Grouped by active ingredient, the main options are:

• Halogen oxidisers: hypochlorite, bromine from BCDMH or from sodium bromide plus an oxidiser, and chlorine dioxide.
• Non-halogen oxidisers: hydrogen peroxide, peracetic acid and ozone.
• Fast-acting non-oxidisers: DBNPA and glutaraldehyde.
• Long-residual non-oxidisers: isothiazolinone (CMIT/MIT), quaternary ammonium compounds and THPS.

Bromine holds up better than chlorine at higher pH, which suits towers run on the alkaline side for scale control. It is often generated by reacting liquid sodium bromide with chlorine or sodium hypochlorite in a sidestream of the make-up water.

Most plants run a dual biocide programme, one oxidising and one non-oxidising, to get the strengths of each. A typical rotation holds free halogen at 0.2 to 0.5 ppm at the basin for at least 4 hours a day, adds an isothiazolinone shock of about 50 to 100 ppm product every 3 to 7 days with a 4 to 8 hour hold before blowdown, and rotates in DBNPA or glutaraldehyde every 2 to 4 weeks. These figures are typical for the product class. The label and TDS of the product you buy govern its dose.

Our cooling water microbiocides and how to dose them

We stock two products for Sohar plants. MICRO BIOCIDE Cooling Water (RXSOL-40-4009-025) is a microbiocide based on an organo-sulphur compound for open recirculating systems. It is a non-oxidising biocide with broad spectrum activity and is compatible with other treatments. It is designed for use alongside both oxidising and non-oxidising programmes and breaks down rapidly in water and soil through processes including hydrolysis.

BIOCIDE MICRO for Water Treatment (RXSOL-40-4009-020) is a strong algae depressant, fully compatible with the alkalising and flocculating agents normally used in cooling and boiler water. Our product record lists it as oxidising in nature, a biocidal adjunct used for generating hypobromous acid, effective at high pH and at low concentrations. Routine weekly additions build a buffer action against very rapid algae growth, which is useful on sunlit decks.

Both products control microbial biofilms, bacteria, algae and fungi in industrial recirculating cooling towers, closed loop cooling systems, brewery pasteurisers and can warmers. Both are compatible with commonly used antifoulants and corrosion inhibitors. Ask us about the rest of our range of cooling water chemicals.

For RXSOL-40-4009-025, the routine dosage is 50 to 100 ppm based on the total water capacity of the system, once or twice per week depending on the severity of the problem. For badly fouled systems, give an initial higher dosage of 100 to 150 ppm for the first week or two. Clean badly fouled systems before treatment. Add the calculated quantity directly at any convenient point where it mixes evenly.

Start with the system volume: basin, pipework, heat exchangers and headers. For a tower holding 400 m3 (400,000 litres), 50 to 100 ppm by volume works out at 20 to 40 litres of product per dose, and a 100 to 150 ppm start-up works out at 40 to 60 litres. Confirm the ppm basis on the TDS before you order.

Feed a non-oxidiser by system volume so that it reaches a toxic dose, ideally within 60 minutes. Close or reduce blowdown during the hold. The hold should last at least twice the system half-life, and non-oxidisers are not meant for continuous dosing. Feed oxidisers over 1 to 4 hours and test the free halogen residual about 1 hour after the feed.

Monitoring, materials and safe handling

Check the microbiology and the biocide level every week. Dip slides, plate counts and ATP tests track microbiology. Free chlorine (DPD) and ORP track the oxidiser. Typical targets are:

• Total bacteria below 10⁴ CFU/mL as a baseline, with action at 10⁵.
• ORP of 600 to 700 mV during oxidiser dosing; below about 450 mV signals that the oxidiser is exhausted.
• Free halogen of 0.2 to 0.5 ppm by DPD while the oxidiser is on.
• Any positive SRB test is a signal to act.

Legionella lives inside amoebae and biofilm, so oxidisers alone may need high, corrosive levels to reach it. A non-oxidiser that keeps biofilm down, used with a low oxidant residual, works better for Legionella control.

Watch your metals and membranes. Halogens become corrosive to copper alloys above about 0.5 ppm free residual, which matters for copper-tubed exchangers and condensers. Some membranes are sensitive to chlorine, and some oxidisers can affect certain polymers. Liquid isothiazolinone biocides are typically compatible with PVC, PE, HDPE and PTFE for tanks and lines. Test other metals before you use them.

Biocide concentrates can be corrosive and skin-sensitising. Wear gloves, goggles and protective clothing during mixing and loading, and use dosing pumps rather than hand pouring where you can. In Omani summer heat, keep packs in their original containers, in shade and out of direct sunlight. A typical shelf life for liquid isothiazolinone biocides is 12 to 24 months. Check the label for your batch.

Where to buy microbiocide chemical in Sohar

Sohar Chemical is part of the RXSOL group in Oman. We deliver from our Barka warehouse to plants in Sohar and across Al Batinah. Call +968 99489269 or message us on WhatsApp with your tower volume, make-up source and current programme, and we will propose a dose and pack size.

Before you order from any supplier, ask for the SDS and TDS, the active content on the label, the pack size and the delivery time to your site. The same BIOCIDE MICRO for Water Treatment is also listed on our Muscat site.

Request a quote for your cooling water microbiocide on WhatsApp at +968 99489269 or through our quote request page.

Frequently asked questions

What is the difference between oxidising and non-oxidising biocides?

Oxidising biocides such as chlorine, bromine and chlorine dioxide kill bacteria, fungi and algae in seconds by oxidising the cell wall, but they penetrate biofilm poorly and leave no lasting protection. Non-oxidising biocides such as isothiazolinone, glutaraldehyde and DBNPA poison the cell, need a longer retention time and are fed as shock doses. Most cooling towers use one of each in a dual programme.

How much non-oxidising biocide should I dose in a cooling tower?

For our MICRO BIOCIDE Cooling Water RXSOL-40-4009-025, the routine dosage is 50 to 100 ppm based on the total water capacity of the system, once or twice per week depending on the severity of the problem. Badly fouled systems take an initial 100 to 150 ppm for the first week or two, after cleaning. For other products, follow the label and TDS.

Does a biocide control Legionella in cooling towers?

Legionella lives inside amoebae and biofilm, so oxidisers alone may need high, corrosive levels to reach it. Keeping biofilm down with a non-oxidising biocide, used with a low oxidant residual and a biodispersant, works better. Clean the system, remove dead legs and monitor regularly as part of the same programme.

How do I know if my cooling tower biocide is working?

Test weekly with dip slides, plate counts or ATP for microbiology, and DPD free halogen or ORP for the oxidiser. Typical targets are total bacteria below 10^4 CFU/mL with action at 10^5, ORP of 600 to 700 mV during oxidiser dosing, and free halogen of 0.2 to 0.5 ppm. A positive SRB test or ORP below about 450 mV means you need to act.

Where can I buy cooling tower biocide in Sohar?

Sohar Chemical supplies MICRO BIOCIDE Cooling Water RXSOL-40-4009-025 and BIOCIDE MICRO for Water Treatment RXSOL-40-4009-020 from our Barka warehouse, with deliveries to Sohar and Al Batinah. Call or WhatsApp +968 99489269 for a quote, the SDS and the TDS.