Water Purification
Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids and gases from contaminated water. The aim is to produce water which is fit for a specific purpose.

Water can be purified to produce drinking water for human consumption, but water purification is required for a number of other uses, including meeting the requirements of medical, pharmacological, chemical and industrial applications.

Many industries require water quality to be better that what is available from the mains water supply. Alternatively some industries abstract their own water from rivers or boreholes. There are several processes for the treatment of water to reduce the amount of dissolved solids that are present. This is often covered under the broad headings of de-salination, de-mineralisation or de-ionisation.

The purification process of water can reduce the concentration of particulate matter including suspended particles, parasites, bacteria, algae, viruses and fungi.

The standards for drinking water quality are typically set by governments or by international standards. These standards will typically set minimum and maximum concentrations of contaminants for the water.

It is not possible to tell whether water is of an appropriate quality by visual examination. Simple procedures such as boiling or the use of a household activated carbon filter are not sufficient for treating all the possible contaminants that may be present in water from an unknown source. Even natural spring water – considered safe for all practical purposes in the 19th century – must now be tested before determining what kind of treatment, if any, is needed. Chemical and microbiological analysis, while expensive, are the only way to obtain the information necessary for deciding on the appropriate method of purification.

Conductivity is a very simple method of providing a measurement of the total dissolved solids in the sample, this can then be used to provide control of the treatment plant, or as an alarm if the treatment process is not functioning correctly.

In large de-ionisers, additional conductivity measurement systems are frequently used to monitor the concentration of acid and caustic solutions used for regeneration of the beds.

An efficient properly maintained operating de-ioniser will remove between 98-99.9% of all ionic impurities.

In a mixed-bed de-ioniser, the anion and cation resins are mixed. This produces the same effect as that of a number of two-bed de-ionisers in series and produces very pure water.

In this system a conductivity sensor on the outlet is used and when it detects a rise in conductivity this indicates the depletion of either of the resins.  Again, additional conductivity measurement systems are frequently used to monitor the concentration of acid and caustic solutions used for regeneration of the beds.

The final product water will be ultra-pure water having a conductivity of 0.055 μS/cm (@ 25°C). This may also be displayed in resistivity as 18.2 MΩ/cm (@25°C) The temperature coefficient of a solution is normally between 1-3% per °C but it should be noted that the conductivity of pure water – below 0.1µS/cm there is a large and non-linear temperature dependence.

In order to ensure the conductivity measurement is accurate it is essential that the conductivity instrument used has the correct temperature compensation algorithms for pure water measurement.

LTH Electronics offer a range of on-line instruments and sensors for conductivity measurement in de-ionisation applications and the AquaCal 2000 pure water measurement kit for the measurement and validation of pure water systems.

Call us on +44 (0)1582 593693 or email sales@lth.co.uk to find out how we can help you.