Part 5 | Cavitation – When Physics Meets Microorganisms

Controlled cavitation uses physical forces to specifically influence microorganisms in water.

Cavitation has a rather poor reputation in engineering. It can damage ship propellers, accelerate wear in pumps and cause significant damage to turbines. For decades, engineers have therefore tried to avoid this physical phenomenon wherever possible.

However, the forces generated in the process can do more than cause damage. When produced under controlled conditions, they can also be used specifically for technical processes.

Controlled cavitation is becoming increasingly important in water technology. It offers the possibility of influencing microorganisms through physical forces without adding chemical substances to the water.

What is cavitation?

Cavitation occurs when the pressure of a liquid briefly falls below its vapour pressure. This causes tiny vapour bubbles or cavities to form in the water.

When the pressure rises again immediately afterwards, these bubbles collapse within fractions of a millisecond. During this process, known as implosion, a large amount of energy is released within an extremely small area.

This can generate locally high pressures, intense shear forces and brief temperature peaks. However, these effects remain limited to microscopic areas and do not cause the water as a whole to heat up accordingly.

It is precisely these concentrated physical forces that make cavitation interesting for a wide range of technical and industrial applications.

A phenomenon known for decades

Cavitation is not a new discovery. The phenomenon has been studied for many decades and is already used technically in a variety of fields.

In addition to water technology, cavitation is used, for example, in ultrasonic cleaning, medical technology, industrial cleaning processes and various process engineering applications.

The fundamental physical mechanisms are therefore well researched. What is relatively new is the question of how these effects can be used specifically and under controlled conditions for hygiene-related applications in drinking water installations.

What happens to microorganisms?

Microorganisms have sensitive cellular structures. When exposed to the strong pressure changes and shear forces generated by controlled cavitation, their cell membranes can be mechanically affected or damaged.

Unlike chemical processes, this effect is not based on a chemical reaction with the water. The effect is generated solely by physical processes.

No additional active substances need to be added to the water for this purpose. Instead, the pressure and flow conditions generated within the water are deliberately used to produce the desired physical effects.

Physical processes as a complementary approach

For many decades, drinking water hygiene has primarily been shaped by thermal and chemical processes. Physical processes are now also receiving increasing attention.

The aim is not necessarily to replace established measures entirely. Rather, depending on the specific application, physical technologies can offer a complementary or alternative approach.

One advantage is that no disinfectant chemicals need to be added to the water. As a result, no disinfection by-products are formed that are directly attributable to the use of such chemicals. Their storage and dosing are also no longer required.

However, it is not possible to give a general answer as to which technology is suitable for a specific installation. The technical conditions, operating mode and respective hygiene requirements must always be taken into account.

Controlled generation is crucial

In order to make targeted use of the physical forces generated by cavitation, pressure conditions, flow velocity and system geometry must be carefully coordinated.

Even small changes can influence where cavitation occurs, how intense it is and what effect it produces within the system. Technical solutions for controlled cavitation can therefore differ significantly in their design and operating principles.

Not every visible formation of bubbles is automatically cavitation. Likewise, not every form of cavitation generates the same physical forces or produces a comparable effect.

For targeted applications, it is therefore essential to generate the process under defined and reproducible conditions.

A growing field of research

As interest in sustainable and resource-efficient processes continues to grow, research into physical water treatment is also expanding.

Cavitation is one of the technologies whose potential is currently being investigated for a range of applications. Research is focusing, among other things, on microbiological effectiveness, energy efficiency and technical integration into existing systems.

The question of how controlled cavitation can be reliably transferred to real operating conditions also plays an important role.

Current developments indicate that physical processes could play a greater role in future concepts for modern water treatment and water hygiene.

Conclusion

Cavitation is not a new physical phenomenon. What is new is primarily the targeted use of the forces it generates for hygiene-related applications in water technology.

Through the controlled formation and subsequent collapse of microscopic vapour bubbles, intense local pressure changes and shear forces are generated. These can affect microorganisms and their cellular structures without requiring chemical active substances to be added to the water.

Controlled cavitation therefore represents an interesting approach for modern water hygiene concepts. It demonstrates how a phenomenon that is undesirable in many technical applications can be deliberately harnessed under controlled conditions.