Lecture 4

1.10 Improving of water quality

1.10.1 Main technological processes and schemes of improving of water quality

Main technological processes of water quality improving consist in deleting from water of one or other admixtures that are located in the amount that exceeds the norms. As a rule, clearing up, discoloring and disinfection are used.

Clearing up of water consists in removing from the water of hanging up particles, i.e. its turbidity decreasing. It can be done by settling and filtration. However, traditional settling passes very quickly and if water expanses are large than it needs considerable areas and bulky structures. To make settling quiсker, the chemical substances – coagulants are moved in the water, and they create flakes together with hanging up and colloid particles and this flakes separate from water very quickly (speed of settling-out is nearly in 100 times more, than of micronized clay particles).

Water disinfection is a decreasing of microorganisms, bacteria, viruses (mainly pathogenic), that can cause gastro enteric diseases: cholera, dysentery, paratyphoid, etc. Considerable part of bacteria and viruses are detained during water clearing up by settling and filtration, and those that remained, are destroyed through water treatment by chlorine, ozone, silver or through irradiation by bactericidal ultraviolet rays.

Water discoloring - is a removing of substances, which cause water coloring. As a rule, water discoloring takes place during clearing up and disinfection. Substances that cause water coloring are moved out by coagulation and oxidization.

Fig. 1.47. Water-purifying stations’ schemes:

a – during clearing with reagents: b – during clearing without reagents: 1–service of uncleared water; 2-reagent economy; 3-mixer; 4-flakes’ creation chamber; 5-settling and clearing up structures with hanging up sediment; 6-quikly filter; 7-water disinfection; 8-reservoir of clean water; 9-pipelines for sediment’s and washed water removing; 10-horizontal settling structure; 11-slow filter.

Water is cleaned up with help of chemical agents (coagulants, chlorine, ozone, etc.) and also without them. In the last case water is cleared up by natural settling and slow filtration through fine-grained filters. So, reagent and without reagent methods are distinguished.

Scheme of water-purifying station with reagent water clearing is shown at fig.1.47a. Water that isn’t cleared is served into mixer to which certain amount of coagulant solutions is served at the same time. Then water gets into the chamber, where the reaction of flakes’ creation takes place, and than into settling structure. Settled water for the final clearing up is served on filters, after what, it is disinfected and sent to reservoirs of clean water.

During water-purifying without reagents, the technology is simplified (fig.1.47b), because there is no reagent economy in it (i.e., structures and devices for storing, preparing, transportation and dosage of reagents; mixers and chambers of flakes’ creation). Main structures in such systems are settling structures, fine-grain slow filters and devices for water disinfection.

Technological schemes of underground water treatment for economic-drinkable needs are considerably simpler than for superficial water, as schemes contain only structures for water disinfection. With presence of iron, fluorine, manganese and other elements in underground water, the schemes of their treatment contain structures for iron removing and removing of corresponding admixtures.