Methods of clearing of flow waters

Prevention of pollution of water objects by sewages can be provided with organizational and technical arrangements.

Organizational arrangements are taken to prevention of sewage disposal to the reservoirs without their clearing. Technical arrangements foresee clearing of sewages by different methods: repeated use of sewages for technical necessities and watering, creation of the circulating and closed systems of water use, perfection of technological processes on enterprises in the direction of decreasing of pollution coming in the flows, transition to zero-emission technologies, decreasing of territory pollution by oil products which with sewages can get to the reservoirs.

Clearing of sewages on enterprises can be carried out by one of such schemes:

· clearing of sewages on factory cleansing buildings;

· clearing of sewages after their pollution on a factory, and then on city cleansing buildings with the subsequent lowering in reservoirs;

· continuous clearing of industrial waters and solutions on local cleansing buildings during certain time, whereupon they are passed on a regeneration, after a regeneration go back to a turn and only after clarification of impossibility of regeneration are averaged and passed on factory cleansing buildings and utilized.

The methods of clearing of muddy industrial waters can be combined in such groups: the mechanical, physical, physical-mechanical, chemical, physical-chemical, biological, complex (fig.3.1.)

Figure 3.1 – Classification of methods of waters flow clearing

Mechanical methods of clearing are used for purging of flows from hard and oily contaminations. The mechanical clearing is carried out by one of such methods:

· grinding down of large contaminations to smaller by mechanical devices;

· thickening of pollutions from flows by oil remover, sand catcher and other precipitation tank;

· division of water and pollutants by centrifuges and hydro cyclones;

· averaging of flows by clean water with the purpose of decline of concentration of harmful matters and admixtures to the level by which flows can be thrown down in reservoirs or in the sewage system;

· exception of mechanical admixtures to the level by which flows can be thrown down in reservoirs or in the sewage system;

· exception of mechanical admixtures by elevators, grates, scrapers and other devices;

· filtration of flows through nets, sieves, special filters, and more frequent by admission them through sand;

· illumination of water by admission it through sand or special devices, filled with compositions or minerals, able to take in hangings-up particles.

Choice of scheme of water clearing from hangings-up particles and oil products depends on a kind and amount of pollutios, necessary degree of cleaning.

The physical-mechanical methods of water and flows clearing are based on flotation, membranous methods of clearing, anisotropic filter.

Flotation is a process of molecular adhesion of particles of pollutions to the surface of division of two phases (water − air, water − hard matter). Clearing process of SPAR, oil products, fibred materials by flotation consists of formation of the system of "particle of pollution − bubbles of air", which emerge on a surface and utilized. On principle of the action of the flotation settings are classified by such method:

· flotation with mechanical dispersion of air;

· flotation with the giving air through poral materials;

· electroflotation;

· biological flotation.

Back osmosis (hyper filtration) is a process of filtration of sewages through semipermeable membranes under pressure. By the concentration of salts of 2...5 g/l there must be pressure to 1 MPa, and by the concentrations of salts 10...30 g/l − about 10 MPa.

Ultrafiltration is a membranous process of solutions division osmotic pressure of which is small. It is used for purging of sewages from high molecular matters, hangings-up particles and colloids.

An electro-dialysis is a process of separation of ions of salts in a membranous vehicle which is carried out under act of direct electric current. An electro-dialysis is used for demineralization of sewages. A basic equipment is electrodialysis apparatuses, that consist of cation and anion membranes.

Chemical clearing is utilized as an independent method or as previous method before the physical-chemical and biological clearing. It is utilized for the decline of corrosive activity of sewages, deleting from it heavy metals, clearing of galvanic areas flows, for oxidization of sulphuretted hydrogen and organic matters, for disinfection and discolouring of water.

Neutralization is used for flows ablution of galvanic, etching and other manufactures, where acids and alkali is used. Neutralization is carried out by mixing of sour sewages with alkalis, adding to sewages reagents (lime, carbonates of calcium and magnesium, ammonia and others like that) or filtration through neutralizing materials (lime, dolomite, magnesite, chalk, limestone and others like that).

An amount of reagent is for neutralization of sewages

where − a coefficient of supply of reagent

− mass of active constituent in sewage;

− volume of sewages;

− expense of reagent for neutralization of active matters;

− concentration of acid and alkali.

Oxidation is used for disinfecting of sewages from toxic admixtures (copper, zinc, sulphuretted hydrogen, sulfides), and also from organic compounds. Oxidants are a chlorine, ozone, oxygen, chloride of lime, to the hypochlorite of calcium and others like that.

Let’s consider physical-chemical methods.

Coagulation is a process of connection of small particles of pollutants in greater by coagulators. Coagulating ions for positively charged particles are anions, and for negatively charged are cations. Coagulators are lime milk, salts of aluminum, iron, magnesium, zinc, sulfur-sour calcium, carbon dioxide and others like that. Coagulating ability of salts of trivalent metals is in ten one times higher, than bivalent, and in thousand one times more than univalent.

Flocculation is a process of aggregation of small particles of pollutants in water due to formation of bridges between them and the molecules of fluctuons. Fluctuons are active silicic acid, ethers, starch, cellulose, synthetic organic polymers (polyacrylamide, polyoxyethylene, polyacrylate, polyethylenamine and others like that).

Coagulates and fluctuons are simultaneously used for illumination of water is, for example sulfur-sour aluminum and polyacrylamide PPA. Coagulation and flocculation are carried out in the special capacities and chambers.

Electro-coagulation − process of enlargement of particles of pollutants by the action of direct electric current is used at water clearing.

Sorption is a process of absorption of pollutions by hard and liquid sorbents (by an absorbent carbon, ash, small coke, peat, silica gel, active clay and others like that). Adsorption properties of sorbents depend on the structure and size of pore, division by sizes, nature of creation. Activity of sorbents is characterized by mass of pollutions which are taken in on unit of their volume or the mass (). Devices for an exception from sewages or solutions according to this method are maked as filters.

Three types of sorption processes of sewages clearing are distinguished: absorption, adsorption, chemical adsorption.

At absorption absorption of pollutions is carried out by all mass (volume) of the absorbed matter.

At adsorption absorption of pollutants takes a place only by the surface of adsorbent due to molecular forces of two bodies which co-operate.

At chemical adsorption absorption of pollutants by the sorbents takes a place with creation on the surface of division of new component or phase.

A choice of sorbent is determined by character and properties of pollutions. The process of flows clearing is carried out by the different kinds of sorbents in the special columns, filled with sorbents.

Extraction is an exception from sewages valuable matters by extragens, which must have such characteristics: high extragenic ability, selectivity, small solubility in water, to have closeness, separated from the closeness of water, small specific warmth of evaporation, small heat capacity, to be explosion-proof and untoxic, to have a small cost.

Extracting of matters from sewages is carried out one of methods: cross-flow, stepwise-antisudorific, uninterruptedly-antisudorific. Volume of extragen, essential for extraction,

,

where − specific gravity of extragen for one extraction;

− amount of extractions;

− volume of sewages, liable extraction.

This method is utilized for an exception from sewages phenol.

An ionic exchange is based on an exception from sewages valuable admixtures of chrome, zinc, copper, PAR due to an exchange ions between admixtures and ion exchangers (ion-exchange resins) on the surface of division of phases "solution − resin". By the sign of charge ion exchangers are divided into cationites and anionites, which nave sour and alkaline characteristics accordingly. Ion exchangers can be natural and synthetic. Natural ion exchangers by type of aluminum silicate, hydrates and salts of polyvalent metals, ion exchangers from coal and cellulose and various synthetic ion-exchange resins are practically used.

Basic property of ion exchangers is their taking-in ability − exchange capacity (an amount of gram-equivalents in flow water which is taken in by 1 of ion exchanger to the complete satiation).

After mechanical, chemical and physical-chemical methods of cleaning there can be various viruses and bacteria in sewages (dysenteric bacteria, choleric vibrio, exciters of typhoid, virus of poliomyelitis, virus of hepatitis, cytopathogenic virus, adenovirus, viruses which entai the disease of eyes). That is why with the purpose of prevention of diseases sewages before the repeated use for domestic necessities are liable to the biological cleaning.

Water sterilization is carried out by heating, chlorinating, ozonization, processing by ultraviolet rays, bioprocessing, electrolysis of silver, when an anode is a silver electrode, and a cathode is coal. The ions of silver have a bactericidal action. For sterilization of 20 it is needed to withdraw from the anode 1 g of silver.

The second method of electrolysis treatment of water consists of adding to water kitchen salt which at admission of current is laid out, exuding a free chlorine.

Biological clearing is carried out in biofilters, in aerotanks, in oxidizing channels, in biotsnks, in aerotanks with fillers.

Biological clearing can be carried out and in natural terms on sewage farms, fields of filtration, in biological reservoirs.

Depending on microorganisms which undertake participating in destruction of organic matters, aerobic (oxidative) and anaerobic (renewed) biological clearing of sewages is distinguished.

In production conditions complex methods of clearing which are based on mechanical, chemical, physical-chemical, biological methods and devices for the exception of pollutants has often to be utilized.

Дата добавления: 2015-10-31