Bound by a strict regulatory framework, the management of pharmaceutical-grade water is subject to close attention from industry professionals. However, ensuring microbiological cleanliness of a purified water system is a real challenge. The main issue lies in micro-organisms that adhere to the inner surfaces of the network, which escape standard measurement methods and jeopardise system compliance. Here’s an explanation of the issue and the solutions available.
Free bacteria vs biofilm
To keep a purified water production and distribution system in a satisfactory bacteriological state, it would ideally be necessary to evaluate its true level of bacterial contamination. In practice, however, this is difficult.
Microbiological sampling only provides information on free microorganisms — those circulating in the system and transported by the flow. The bacterial colonies temporarily attached to the internal surfaces — which are far more numerous — remain undetected during this analysis.
This biofilm represents a real ticking time bomb, as it regularly releases free cells. These travel further through the circuit before attaching again and forming new colonies.
It is therefore essential to limit the formation of this microbial surface ecosystem. Several effective prevention and decontamination methods can be implemented to achieve this.
Prioritise quality surfaces and fittings in your installation
Choosing a high-quality installation is essential. Minimal investment solutions may seem economical initially, but they often become more expensive over time due to the difficulty of maintaining satisfactory bacteriological conditions.
To limit biofilm development, stainless steel is preferred over plastic materials, and surface finish is critical.
Surface roughness — particularly at welds and junctions — creates ideal zones for bacterial colonisation and growth.
Prevent the entry and proliferation of free cells
To avoid biofilm formation, it is essential to limit the introduction of free microorganisms into the network and eliminate any contamination before cells have the opportunity to attach to surfaces.
In addition to an existing sterilising filtration system, several biodecontamination solutions can be used:
Exposure to UV radiation
Temperature elevation: 60 to 65 °C is sufficient to destroy most pioneer microorganisms
Use of ozone
| RELATIVE OXIDATION POWER | Formula | Index |
|---|---|---|
| Gaseous chlorine | Cl2 | 1.00 |
| Ozone | O3 | 1.52 |
| Peracetic acid | CH3COOOH | 1.33 |
| Minncare Cold Sterilant | CH3COOOH + H2O2 | >1.30 |
| Hydrogen peroxide | H2O2 | 1.30 |
| Hypochlorous acid | HOCl | 1.10 |
| Chlorine dioxide (gas) | ClO2 | 0.70 |
| Sodium hypochlorite | NaOCl | 0.69 |
Removing an established biofilm
When biofilm formation is suspected within the network, a treatment must be implemented to eliminate it, using an oxidising chemical agent. Such a shock treatment will eradicate all microbiological life, whether isolated or biofilm-based.
The use of oxidising agents must be carefully assessed in advance. In addition to the oxidising power of the chosen chemical species, the required concentration to eliminate the biofilm must also be considered. Selecting a product that remains effective at low dosage helps to reduce rinsing time, limit water consumption and minimise installation downtime.
As purified water has low buffering capacity, attention must also be paid to potential pH fluctuations in the circulating solution, which may reduce the effectiveness of chemical species used for decontamination — particularly chlorine-based formulations.
Among the available chemical agents are ozone, hydrogen peroxide and peracetic acid.
Conclusion: combining biocontamination control and filtration
A biodecontamination process, capable of eliminating both pioneer cells and established biofilm, is therefore an essential maintenance step to ensure the microbiological quality of purified water systems.
When used in addition to sterilising membranes, it helps extend their service life, thereby reducing operating costs.
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