Remove RO water systems bacteria

The production of water for pharmaceutical purposes is made from drinking water. This is required by law in most countries, including Germany and the USA. The specifications for drinking water (stipulated in Germany by the Drinking Water Ordinance, in the USA by the National Primary Drinking Water Regulation) are, however, very broad compared to the pharmacopoeia requirements for water for pharmaceutical use. The quality of drinking water is also very different, as drinking water can come from a wide variety of sources, such as groundwater or surface water from lakes, for example. But groundwater also differs locally in its quality, depending on the depth from which it comes, but the seasons can also play a role. If, for example, agricultural areas are fertilized in a few months, this can have an impact on the quality of the drinking water. This is the reason why water treatment systems for the pharmaceutical industry are not prefabricated goods, but always an individual solution that must be developed in cooperation between the subsequent user and the system supplier. At the beginning of a project, the system supplier will always ask about the quality of the drinking water in order to be able to offer the appropriate treatment technologies. The operator is well advised if this data is available for one or more years, if possible.

In particular, the following parameters or impurities in the input water will play a role:

Particles: These can consist of undissolved organic or inorganic material. In addition to the number, the size of the particles is decisive. Particles larger than 40 µm can be seen with the naked eye. With particle filters, particles larger than 10 µm can be removed, so it makes sense to speak of particles larger than 10 µm.

I.onen: In contrast to particles, ions are dissolved in water. In water systems, chloride, magnesium, calcium, nitrate, hydrogen carbonate, sulfate and some heavy metal ions play a role. Depending on their solubility product, ions can also precipitate out of the aqueous phase. There are also basic or acidic salts that affect the pH. It should be noted here that their basic or acidic effect is based on equilibrium reactions and that some of the salts are not dissolved. This can play a role if, for example, you want to adjust the pH of the water to 8-9 to remove carbon dioxide. It is not so easy to calculate the acids or bases required for this, so that one has to resort to the titration of the water to determine the quantity.

Non-reactive dissolved gases: Oxygen and nitrogen should be mentioned here, i.e. gases that do not dissociate into ions in water and have hardly any influence on water treatment. The concentration of these gases in the water falls as the temperature rises. Oxygen can, however, have a negative effect on oxygen-sensitive products.

Reactive dissolved gases: The most important representatives here are carbon dioxide and ammonia. Both have an effect on the pH value when dissolved in water and both pass through the membranes of reverse osmosis systems in the non-dissociated state. This can lead to problems in the conductivity test point in the water distribution system. The influence of carbon dioxide on the development of rouging is also under discussion.

Microorganisms: Microorganisms can be represented in large numbers in drinking water. Limits are set by the Drinking Water Ordinance or internationally comparable specification documents, but drinking water pipes are often placed next to heating or steam pipes and can then subsequently become contaminated with low consumption or on weekends due to "warm storage" during longer periods of standstill. In addition to bacteria and viruses, algae should also be mentioned here. The determination of the germ load in drinking water is strongly influenced by the cultivation method. Only a small part of the germs that occur in the water can be found through the cultivation used on agar plates. This may be due to the type of nutrient medium used - not all germs grow on all nutrient media, as well as the occurrence of viable germs that cannot be induced to germinate on nutrient media. The amount of water germs can be safely reduced by means of an ultrafiltration step in water treatment.

Endotoxins: Gram-negative bacteria have an inner and an outer membrane. This outer membrane contains, among other things, very stable lipopolysaccharides. These are released when the bacterial cell or membrane is destroyed. These substances, known as endotoxins, can cause a fever if they enter the body parenterally and, in the worst case, lead to death. Gram-negative bacteria are found in drinking water, especially surface water and groundwater affected by surface water.

Organic material: In addition to pesticide or fertilizer residues, the naturally occurring humic acids should be mentioned as organic contamination. These are important because they have a negative impact on the service life of activated carbon filters and can cause fouling on the membranes of reverse osmosis systems and on ion exchange resins. For this reason, it can make sense to include a TOC measurement in the drinking water supply, i.e. an online measurement of the total carbon content in the raw water.

Colloids: Colloids move in an order of magnitude between ions and particles and are found in surface water than in groundwater. Colloids based on silicate, iron or aluminum, which are often complexed in organic material, are important for water treatment plants. Colloids can lead to the blocking of RO membranes and thus to short service lives. Therefore, if the colloid index is high, the RO is usually always preceded by a sand / gravel filter.

Colloids can also affect WFI quality. Colloids in the feed water of the WFI distillation can settle above the evaporation area and lead to the breakthrough of the feed water into the distillate. Regular maintenance and removal of these residues can help.

Compiled by: Dr Robert Eicher, CONCEPT HEIDELBERG