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 Parameter / Calcite 

Basics

The calcite solubility is the amount of calcite a water sample of a defined volume can dissolve at 25°C. Calcite is the dominant modification of calcium carbonate under the temperature and pressure conditions usually found in water treatment plants. Responsible for the calcite solubility is excess carbonic acid, which can even cause corrosion of metal pipes or cement-based materials. An important measure to prevent corrosion is the deacidification, i. e. the physical or chemical removal of excess carbonic acid, which leads to a rise in pH. The upper limit for the pH is defined by the carbonate balance: If the pH is raised above the balance value, scaling will occur, causing problems both in the water conduits and in the treatment processes. The former German drinking water ordinance – TrinkwV – listed the delta-pH value with a set point of 0 to ensure that the treated water is in a balance state. The current drinking water ordinance lists the calcite solubility instead. The water is sufficiently deacidified if the calcite solubility at the outlet of the treatment plant is not higher than 5mg/l. According to TVO this condition is fulfilled if the pH-value is higher than 7.7.

 

 

Application - physical deacidification

Excess carbonic acid can be removed physically by means of a stripping process using aeration. With high-performance aeration systems, the aeration efficiency can be changed by adjusting the volumetric flow rate of the air. The flow rate is adjusted to react to changing carbonic acid concentrations caused, for example, by changing water sources, mixtures, or volumes. A variety of parameters can be used as command variable for an automatic adjustment. Besides the water volume flow and the pH value, the delta-pH value is a very useful parameter for precise deacidification control. It is an expression for the deviation between the current pH value of the water and the pH value of the same water at calcite saturation.  The delta-pH value allows a both technically and economically optimized operation of the aeration process. Since the energy consumption of the aeration system is proportional to the square of the air volume, a precise control provides a very noticeable saving of energy and therefore cost.

 

 

Dr. A. Kuntze measurement

Kuntze BalanceCon

Set the stage for such precise control of your aeration process and its costs with BalanceCon, our measuring and control system developed precisely for the deacidification of drinking water.The measuring system divides the water in two streams, one of which passes through a calcite saturation filter prior to measurement. The sojourn time is long enough to ensure that the water is in a state of carbonate balance when it comes out.  The centerpiece of the measuring system is a highly precise pH difference measurement between the untreated water and the water that has passed through the filter. The necessary precision is achieved by way of an automatic zero-calibration of the difference measurement. The sojourn time in the filter is maintained with stepmotor-operated peristaltic pumps. The water inflow can be as low as 15l/h, and the water volume used for the measurement is minimized to ensure slow consumption of the calcite filter and long exchange cycles.   

 

 


Plug & Play...
Mit dem Mess- und Regelsystem BalanceCon wird die Calcitsättigung in Trinkwasser bestimmt. Durch Messung des Delta-pH-Werts wird die Abweichung des aktuellen pH-Werts vom pH-Wert der Calcitsättigung ermittelt. Das Mess-System kommt zum Einsatz bei der Steuerung von physikalischen Entsäuerungsanlagen, der gemessene Delta-pH-Wert wird als Führungsgröße für die Anpassung der Luftfördermenge eingesetzt.

Ablauf...

Für das Mess-System muss bauseits Messwasser mit Vordruck geliefert werden.Der Zulauf ist mit einem schlauchanschluss DN 4/6 ausgestattet. Der Ablauf ist als Verschraubung DN10 ausgeführt. Ein freier Auslauf ist erforderlich. Der Messwasserstrom wird aufgeteilt und ein Teilstrom durchströmt das Messgefäß 1 mit integriertem pH-Sensor, während der andere Teilstrom über die Kalksteinschüttung (Marmorkies) geleitet wird.