From Big Medical Encyclopedia

DECHLORINATION OF WATER — removal of excess amount of chlorine from chlorinated water. It is necessary for of century when chlorination is made by the high doses several times exceeding the doses applied to disinfecting or to improvement of organoleptic properties of water.

Of century can be made physical. by methods with use of such sorbents, as active coal, wood charcoal, coke, etc., and chemical means by means of reaction of an inactivation of chlorine sodium hyposulphite, sodium sulfite, green vitriol, sulfur dioxide gas.

Active coal has well-marked ability to adsorption. For D. century use active coal in the form of powder, and also dust dry coal or its suspension. Into water coal or suspension are entered before the water flow processed on treatment facilities arrives on filters. The coal added to water occludes chlorine, further, getting on the filter, it is postponed by a loose coating there, in Krom process of sorption of excess chlorine continues.

The wood charcoal or coke applied to D. century load into special filters. Height of a layer of loading is defined by concentration of excess chlorine and the expected speed of filtering. Practically in stationary conditions height of a filter-bed of 1,5 — 2 m is accepted. Diameter of grains of coal fluctuates from 1,5 to 2 mm. Because sorption properties of coal gradually weaken, periodically (approximately once a month) regeneration of a filter medium by means of washing with its hot 1 — 2% with solution of soda ash, caustic soda, hypochlorite shall be made, etc.

the Chemical substances transferring chlorine to an inaktivny state usually concern to group of reducers. When it is required to process rather small amount of water (e.g., in field conditions), it is more reasonable to apply hyposulphite (thiosulphate) of sodium to the purposes D. of century. On 1 mg of the inactivated chlorine 2 — 3 mg of hyposulphite are required. For higher effect of dechlorination it is reasonable to define a dose of hyposulphite by practical consideration. For the prevention of possible secondary pollution of water the microbes which are contained in solution of hyposulphite it is necessary to bring hyposulphite in such quantity that after an inactivation of chlorine there was still its small surplus (0,3 — 0,5 mg/l). It is possible to use sodium sulfite (3,5 mg of sodium sulfite are spent for 1 mg of the inactivated chlorine) or green vitriol (on 1 mg of the inactivated chlorine there are 8 mg of green vitriol). Dechlorination of large volumes of water these reagents demands bulky devices therefore in stationary conditions it is recommended to use sulfur dioxide gas (sulfur dioxide). In this case 0,9 mg of sulfur dioxide are spent for 1 mg of the inactivated chlorine. Dosing of reagent is made by means of special devices. Reaction of an inactivation of chlorine proceeds within 1 — 2 min.

In field conditions in case of lack of the above described means for D. broths and infusions of leaves, needles, herbs can be used by century.

See also Water , Water treatment , Chlorination of drinking water .

Bibliography: Besan V. S. Ustroystvo for preparation of a coal pulp at an uglevaniye of water, Vodosnabzh. and dignity. equipment, No. 7, page 7, 1972; B at l y the p e in I. A. The plant dechlorinating substances, the Gigabyte. and dignity., No. 10, page 13, 1946; Zhytomyr-with to and y L. G. Dechlorination of water sulfur dioxide gas, Rostov N / D., 1940; To at l-sky L. A., etc. Processing of water on water supply systems dust active coal, Kiev, 1965; The Guide to hygiene of water supply, under the editorship of S. N. Cherkinsky, M., 1975; The P e r to and N-skiys. N and Trakhtmann. H. Disinfecting of drinking water, M., 1962, bibliogr.,

I. I. Belyaev.