1.10.4 Water disinfection

The disinfection is used for final elimination of alive organisms, including pathogenic, in the filtrated water. Water desinfection is made by chemical and physical methods. In the first case strong oxidants are used: chlorine, hypochlorite of sodium, chloride of lime, ozone, iodine, manganese, peroxide, etc. During physical methods the water is processed at bactericidal, electrolysis, thermo- and other devises.

Chlorination is the most speeded method for water disinfection and it is performed by solution of chlorine or chloride of lime, that create prechloric and muriatic acids: Cl₂ + H₂O ↔HOCl + HCl. Prechloric acid isn’t stable and disintegrates with emission of atomic oxygen and hypochlorite ion OCl^-, that show strong oxidation action.

For water disinfection the amount of entered in water chloride takes from 0.7-1mg/l (for underground water) till 3-5mg/l for uncleared water. Dose of active chlorine is determined investigation method and it’s sufficient to give chlorine in surplus, ensuring the concentration 0.3-0.5mg/l (so named remaining chlorine) at points of water partition, which testifies to sufficientness of entered dose for total water disinfection.

Chloric water is prepared from gaseous chlorine in chloric chambers. Chlorine is taken to the stations in liquid state in bulbs. Vacuum or pressure hypochlorinators are used for water mixing with chlorine and for dosage. Vacuum

hypochlorinators in point of view of accident prevention are more reliable, because the chlorine in them is located under the vacuum and there is less probability of pouring of poisonous gas into the apartment (fig. 1.55).

Fig. 1.55. Principal scheme of hypochlorinators лонп – 100:

1-evaporated bulb; 2-intermediate bulb; 3-filter; 4-regulation valve of pressure decreasing; 5-manometer; 6-rotametr; 7-mixer; 8-tank with water; 9-water from water-plumbing; 10-ejector; 11-chloric water.

At big water-pouring stations the chloride of lime (hydrochlorite of calcium) or hypochlorite are used, which are prepared as 0.5-1% solutions at devices, like those, at which coagulant solutions are prepared. However, this reagent is in the deficit, and their usage requires enough big economy. In these cases, it’s more economical and safer to use hypochlorite of natruim, which is obtained by electrolyze of kitchen salt. 8-15 kg of kitchen salt is used for preparation of 1 kg of active chlorine. Duration of chlorine and hypochlorite contact with water should be not less than 60 minutes.

In all cases, it’s desirably to locate chloric economy in buildings that located separately. It is separated by blank wall if it’s located in block with other buildings or structures. Chloric chambers should have two quits (one through vestibule, another – directly outside). The artificial ventilation with 12-times air exchange is organized in them. There wardrobe for overall, gas-masks, devices for switching on or off of illumination and ventilation are foreseen in vestibule.

Disinfection by ultraviolet radiation with help of bactericidal lamps is conducted mostly for underground sources water that have cole-index not more than 1000, iron content not more than 0.3 mg/l, water up to 20⁰, transparency not less than 30 cm. For ultraviolet radiation the electric lamps are used - quartz-mercury with high pressure or argon-mercury with low pressure. A device consists of radiation chambers, in which water is passed through thin layer under ultraviolet rays. Effectiveness of disinfection depends on duration and intensity of radiation.

Unlike the chloration, water after the treatment at bactericidal devices obtains unpleasant taste and smell, and the process of disinfection and exploitation quite simple and doesn’t require reagents, but sphere of usage of this method is limited, and the remaining action of disinfection is absent.

Ozination of water considers usage of ozone, which simply disintegrates with creation of atomic oxygen, which destroys bacteria, spores, viruses and destroys organic admixtures. This allows to use ozone not only for disinfection but for discoloring and deodorization of water. Its surplus (unlike chlorine) doesn’t worsen water quality.

For water disinfection of underground sources it’s needed 0.75-1mg/l of ozone, and filtrated water of superficial sources – 1-3mg/l. Ozone is obtained in electric ozonizers directly at plumbing stations during passing through dried and cleared air of electric digit. Mixing of ozone-air mixture that was got in ozonizers, is conducted in special ejectors or by barbituration in columns or reservoirs. Time of water contact with ozone is 5-7 minutes.