What influence does water temperature have in industrial treatment systems?

Water temperature in industrial treatment systems is often underestimated, but in reality it is one of the most critical parameters for the stable and efficient operation of any system. It directly affects the physical properties of water, the rate of chemical reactions, biological activity, and the service life of equipment.

Below, we examine the impact of temperature on four main stages in an industrial treatment system from a purely technical perspective.

Impact on Sand Filters

Viscosity Decreases and Filtration Rate Increases

As temperature rises, the physical properties of water change. Viscosity decreases significantly in the range of 5–30°C, which allows water to move more easily through the filter bed.

Approximate values of dynamic viscosity:

at 10°C — around 1.31 cP;

at 20°C — around 1.00 cP;

at 30°C — around 0.80 cP.

This has the following consequences for sand filter operation:

flow through the bed becomes easier, as lower viscosity reduces hydraulic resistance;

differential pressure ΔP increases more slowly compared to cold water, which may create a misleading impression that the filter is cleaner;

the increased passage velocity reduces the contact time between the water and the media, which may lead to higher turbidity in the outlet water, especially at linear velocities above 20–25 m/h.

It is important to emphasize that, in practice, flow rate should not be automatically increased with temperature. The design linear velocity should be maintained by adjusting the flow rate, rather than following the natural reduction in viscosity.

Behavior of Suspended Particles

At higher temperatures, the viscosity of water decreases, which makes it easier for larger suspended particles to settle. Although Brownian motion increases with temperature, the effect of lower hydraulic resistance dominates, and particles are more easily retained in the upper layers of the filter.

This can lead to two opposite effects:

a visible improvement in filtration, as particles are retained more quickly;

an increased risk of breakthrough at high flow rates, when particles fail to attach stably and pass through the bed.

The combination of elevated temperature and high velocity significantly increases the risk of sand filter breakthrough.

Filter Media Stability and Structural Effects

Quartz sand and standard mineral media have high thermal stability and do not thermally degrade at temperatures up to 80–100°C. The limitation in industrial systems is not the material itself, but the operating mode.

During prolonged operation at elevated temperature:

mechanical wear accelerates;

grains break more easily due to higher velocities and more frequent backwashing;

fine fractions of 0.1–0.5 mm are formed;

the filter bed becomes compacted and ΔP begins to rise more rapidly.

Backwashing

With warm water, the filter media behaves as lighter and more mobile. This leads to:

excessive bed expansion at standard backwash flow rates;

increased media losses;

risk of sand carryover into the upper distribution system.

Therefore, at temperatures above 25–30°C, the backwash flow rate should be reduced by around 10–20% compared to the design value at 20°C.

Conclusion for Sand Filters

Temperature fundamentally changes the hydraulic and mechanical behavior of sand filters. All parameters such as ΔP, flow rate, and filtration quality should be evaluated with temperature compensation.

Impact on Carbon Filters

Adsorption Capacity Decreases as Temperature Increases

Activated carbon works through adsorption, based on physical bonds between contaminants and the surface of the carbon. It has a highly developed microporous structure with a specific surface area of 800–1200+ m²/g.

As temperature increases:

the kinetic energy of molecules increases;

the tendency toward desorption rises;

adsorption isotherms become flatter;

the saturation point is reached faster.

Practical observations show:

25°C — reference level;

35°C — around 8–10% capacity loss;

45°C — around 15–20% capacity loss.

The loss of capacity is partially reversible and depends on the type of activated carbon — coconut shell, bituminous, or lignite-based.

Chlorine Removal

Chlorine removal by activated carbon is a redox process. At higher temperatures, the reaction rate increases, and every 10°C increase can accelerate the reaction by approximately 1.5–2 times.

This means:

faster chlorine reduction;

faster depletion of the carbon’s reducing zones;

shorter filter service life.

Biological Fouling

Activated carbon creates an excellent environment for biological activity. At temperatures above 30°C:

the rate of bacterial growth increases sharply;

biofilm formation accelerates;

ΔP increases due to pore blockage;

the risk of biological contamination of downstream RO membranes increases significantly.

Under these conditions, activated carbon practically becomes a biological reactor if disinfection measures are not planned.

Conclusion for Activated Carbon

Warm water:

reduces adsorption capacity;

accelerates chlorine reduction;

intensifies biological fouling;

shortens the life of the carbon filter;

increases the risk to RO membranes.

Temperature control here is critically important.

Impact of Temperature on Water Softening Systems

Softening resins are synthetic polymer materials with sulfonic groups loaded with Na⁺. The optimal operating range is 10–30°C.

As temperature increases:

regeneration becomes weaker;

the resin matrix swells;

microcracks form;

the capacity to retain Ca²⁺ and Mg²⁺ decreases;

wear accelerates.

At temperatures above 45°C, resin degradation is irreversible and the resin must be replaced.

The solubility of NaCl increases with temperature, but this does not compensate for the loss of ion exchange capacity and does not improve system performance.

Conclusion for Softeners

The feed water should be within the range of 5–35°C, with 40°C considered the absolute limit. In processes involving heat exchange, pre-cooling is mandatory.

Impact of Temperature on Reverse Osmosis Systems

RO membranes are the most sensitive element in the system. As temperature rises, permeate flow increases by around 2% for every 1°C.

This leads to:

disruption of design flows;

increased membrane load;

shorter service life.

For this reason, RO systems are designed at a reference temperature of 20–25°C with temperature correction of the flow rate.

Temperature and Scaling

At elevated temperature:

the solubility of CaSO₄, BaSO₄, and SrSO₄ increases;

the solubility of CaCO₃, Mg(OH)₂, and SiO₂ decreases.

CaCO₃ and silica remain the most critical, especially at high pH and high system recovery.

Conclusion

Water temperature is a key parameter that directly affects the reliability, efficiency, and service life of all industrial treatment systems. Underestimating it leads to hidden problems, higher costs, and premature failures.