All About Cooling Towers with Low Minerality make-up

Better Makeup Water Does Not Mean Easier to Treat

Using high-quality makeup water in an evaporative cooling system appears, at first sight, to simplify water treatment. When the makeup water is naturally low in minerals, extensively softened, or produced by reverse osmosis, calcium carbonate scaling is significantly reduced. This can allow higher cycles of concentration, lower blowdown volumes, and better water-use efficiency.

However, removing hardness does not remove every operational risk. Low-hardness and low-mineral-content waters may have:

• limited buffering capacity,
• low calcium and magnesium concentrations,
• unstable pH,
• high corrosivity toward carbon steel and other metals,
• limited ability to form naturally protective mineral layers.

The treatment strategy must therefore change.

The objective is no longer primarily to prevent calcium carbonate scale. It is to maintain stable, protected, and clean surfaces under highly concentrated operating conditions. However, conventional treatment programs based primarily on scale inhibition, biocides, or dispersants may show limited effectiveness under these conditions, particularly when corrosion mechanisms and fouling are driven by the combined effects of low buffering capacity, airborne contamination, and high concentration cycles.

Better Control of Corrosion and Biofouling

In low-mineral systems, corrosion becomes a primary design constraint rather than a secondary effect.

In this situation, filming amines (FFAs) represent one of the most effective corrosion-control technologies available on the market. By adsorbing directly onto metal surfaces, they form a thin, hydrophobic molecular barrier that isolates the metal from the water phase. This mechanism provides continuous protection even in aggressive, low-buffered waters where conventional mineral-based protection cannot form.

Their corrosion-control performance includes:

• protecting carbon-steel surfaces through direct surface passivation,
• limiting general corrosion in low-alkalinity environments,
• reducing the release of iron corrosion products,
• helping control under-deposit corrosion,
• maintaining protection during operational fluctuations.

At the same time, cooling towers and evaporative condensers continuously act as air scrubbers. Every airborne impurity is introduced into the circulating water: dust, organic matter, aerosols, microorganisms, and process residues. As cycles of concentration increase, these contaminants accumulate and become increasingly significant.

This air-washing effect is a major driver of biofouling. Deposits formed from airborne solids create ideal conditions for microbial attachment and biofilm development. Once established, these biofilms reduce heat transfer efficiency, clog components, increase under-deposit corrosion risk, and raise overall chemical demand.

At high concentration factors, even small airborne loads become operationally critical.

In this context, FFAs-based formulations also play a key role beyond corrosion protection. When combined with dispersant and cleaning functionalities, they help:

• reduce adhesion of airborne contaminants,
• disperse organic matter and corrosion products,
• limit the formation and consolidation of deposits,
• maintain cleaner heat-transfer surfaces,
• improve biocide accessibility to microbial populations.

Finally, biocides alone are not sufficient. They remain essential for controlling planktonic microorganisms, but are significantly less effective once biofilms or deposits are established. Effective control therefore requires a coordinated strategy combining surface protection, deposit control, blowdown management, and microbiological control.

The key operational question is no longer the biocide strength alone, but whether the surfaces remain sufficiently clean and protected to prevent permanent fouling.

Case Study – Evaporative Condensers in a Dairy Facility

The following case concerns a major dairy company in North America. The installation includes evaporative condensers connected to an ammonia refrigeration system serving cold-storage rooms. Reverse osmosis was used to optimize water consumption.

Before implementation of the new program, the site faced two interconnected challenges that were not satisfactorily addressed by the existing treatment program, which relied on conventional solid chemical products, phosphonate-based scale inhibitors, and sodium hypochlorite:

• maintaining corrosion protection despite the very low mineral content of the makeup water,
• controlling deposits and water discoloration caused by concentrated contaminants and corrosion products.

Due to previous leaks from the pretreatment system, which persisted during the program, we opted for the use of a phosphonate-based scale inhibitor.The implemented protocol combines:

• an all-in-one phosphonates / FFAs-based formulation,
• an oxidizing biocide,
• automatic conductivity-controlled blowdown for CC = 15

During the initial stabilization period, iron concentrations were variable and occasionally elevated. This was consistent with the progressive removal of existing corrosion products and the conditioning of metal surfaces.

Over time, iron concentrations continued to decrease and stabilize at consistently low levels.

This trend provided an important operational indicator:

• less release of corrosion products,
• improved surface stability,
• cleaner circulating water,
• reduced contribution of iron deposits to fouling.

Conclusion

Low-hardness and low-mineral-content makeup water can support higher water efficiency and significantly reduce scaling risk. But it also removes part of the natural mineral protection on which conventional cooling-water programs may rely.

At the same time, cooling towers and evaporative condensers continuously capture contaminants from the surrounding air. High cycles of concentration then amplify even minor contamination.

FFAs provide a dual response:

• a protective molecular film for corrosion control,
• an integrated cleaning and dispersing action that helps keep surfaces free from persistent deposits.

The result is not simply cleaner water.

It is a more stable interface between water, metal, air, and microbiology.