The existing consistency of different waters can be of a quality which does not meet the requirements for just this water.

Regardless whether these are legal regulations, given specifications or individual requirements of the user, those waters will be uniquely conditioned in different water treatment plants, writes Silke Haupthoff-Lau.

We begin with the most valuable: potable water (that may have to be reduced in its iron content), well water (where suspended matter may have to be removed), and even waste water (which has to be treated until it can be released back into circulation). In addition, process waters (that may be treated by demineralising) so that they can fulfill their respective tasks in their individual processes.

What kind of water treatment plants are available? The simplest are the mechanical devices, ie rake, strainer, filter or sediment basin. Then there are the physical treatments, like flotation, flocculation and coagulation, membrane technology, and absorption.

Beyond that, biological treatment systems may be applied (aeration systems, activated sludge systems, bioreactors).

How do all these processes work at their optimum? All the different systems of measuring and control technology that are available keep water treatment plants in automatic mode. Below are two examples that explain the operation of modern control systems.

A water sampling station with controller measures the current pH value of the waste water prior to its release to the final clarification basin. If the pH value deviates from the set point, the controller activates the dosing pump at the corresponding metering station with acid or caustic solution until the set point is reached again. In order to adapt to ever varying flows the controller accepts signals from a water meter.

Another kind of application is the dosage of chlorine gas depending on the content of free effective chlorine in the water. An open potentiostatic measuring cell measures the content of so-called hypochlorous acid. The controller activates a continuously acting valve and proportions the chlorine addition.

Dipl Ing Silke Haupthoff-Lau is with Lutz JESCO GmbH, Wedemark, Germany. www.jesco.de