Chemical water treatment

The term ‘chemical treatment of water’ refers to the treatment of water through dosing with auxiliary chemicals and preparations for the purpose of achieving the required parameters. The set of processes used to treat water for industrial purposes, regardless of whether this concerns the production of energy or various chemicals, foods and pharmaceuticals, is also considered to be chemical treatment of water. The quality of such treated water fulfils the stringent requirements of these plants for the purity and quality of the output water.

USE OF CHEMICAL WATER TREATMENT

Ensuring the hygienic safety of water. For removal of microbial contamination or viruses, reduction of the presence of algae and other recovery, the water is treated by dosing with a suitable disinfectant. The most common chemicals dosed in the drinking water for the purpose of hygienic safety include sodium hypochlorite and other chlorine-based oxidisers or disinfectants. Subsequent microbiological stability in the distribution network is also secured through them.

Regulation of pH. A decree of the Ministry of Health of the Czech Republic stipulates the permissible pH range in drinking water. This range is chosen for health and technological reasons. The pH of drinking water resources is usually in this range, and it should thus not be necessary to adjust them. The most common reason for changing pH is to set suitable reaction conditions for some water treatment technologies, like coagulation. The effectiveness of the coagulation process can be increased by correctly choosing the pH value according to the properties of the raw water and the dominant pollutant removed. For instance, manganese is effectively transformed into an insoluble clot at pH>8, whereas aluminium is most effectively removed at pH~6.3. Furthermore, the pH value is usually adjusted, due to a reduction in the aggressive properties of water, for instance.

Oxidation of the contaminant admixture. For the purpose of transforming some pollutant admixtures into easily removable forms, oxidation reagents such as potassium permanganate or chlorine compounds (sodium hypochlorite, chlorine dioxide) are added to the water. For example, the ions of metals in dissolved and hence non-removable form are oxidised more or less to multivalent insoluble forms, which can be removed from the water by standard separating methods (sedimentation, filtration). Ammoniacal nitrogen is oxidized to nitrates, which can be easily removed, for example, on ion exchange materials, etc.

Removal of residual chlorine. It is sometimes necessary to remove already-present free chlorine from the water – to protect subsequent technological elements that are susceptible to the action of chlorine (typical for membrane technology), and for other reasons. This is possible either by adsorption of the chlorine on active carbon, or by addition of certain chemicals to the treated water, such as sodium metabisulphite or sodium bisulphite.

The dosage of antiscalant in reverse osmosis technology. In reverse osmosis technology, dissolved substances collect on the inlet side of the membrane, resulting in overrun of the solubility product with an ensuing risk of coagulation of the undissolved substances on the membrane, leading to clogging. The dosage of the so-called antiscalant helps keep the concentrated salts in dissolved form, extending the life of the membranes and lowering the RO technology operating and maintenance costs.

DOSING

Dosing is most frequently done by means of automatically controlled dosing pumps, which dispense the appropriate volume of the required solution into the treated water flow. The pump is controlled according to the local measurement of the flow rate so that the dosage is as effective as possible, and the required final concentration is as precise as possible. For implementation, we use time-proven and reliable products from Grundfos, the leading global manufacturer of pumps and dosing equipment.