pH measurement is one of the most important chemical values, its determination and control is a standard activity in many industrial applications, including water treatment and purification. The desired pH level in the neutralization process can be adjusted by adding solutions of acidic and alkaline substances (bases).
In the process of water purification, the finest particles dissolved in the water do not settle while the water is at rest, as they are negatively electrically charged and repel each other. In order to achieve a better effect of their removal, chemical treatment is used. In this method, positively charged substances are introduced into the water, which enter into a chemical reaction with those dissolved in water and form aggregated neutrally charged compounds. The agglomerations thus obtained in the form of large flocs are rapidly deposited, and in the presence of stirring of the liquid the effect is higher. This process is called coagulation-flocculation, and the substances used are called coagulants. The choice of the optimal coagulant for a particular water to be treated is determined on the basis of laboratory tests.
The process of flocculation is applicable to water purification, compaction and dewatering of sludge, in which the result is aggregation of particles formed during the coagulation step and the formation of the so-called flocs. Such treatment can be applied only after coagulation, since the reduction of repulsive forces between the particles favors their formation in aggregates, and flocculation, in turn, promotes growth and accelerates the separation of these phases from particles. The process takes place under the influence of a polymer - a substance composed of high molecular weight molecules formed from a large number of identical molecules called monomers linked by covalent bonds. The electric charge (+ or -) of the flocculant is chosen depending on the nature of the particles dissolved in the water, usually an anionic flocculant (-) is applied to mineral particles and a cationic flocculant (+) to organic particles.
Water purification processes have led to a reduction in water-borne diseases due to the fact that most of the pathogenic microorganisms (bacteria, viruses and parasites) are eliminated in the stages of coagulation, flocculation, sedimentation or filtration. To have safe drinking water necessary the process of disinfection is also a condition. The most commonly used disinfectants are: chlorine, peroxide, bromine, silver, ozone and ultraviolet rays, each of which has advantages or disadvantages and can be used to disinfect water under certain conditions.
