Lecture 5
2. Sewerage
2.1 Systems and schemes of sewerage
2.1.1. Types of sewer water
Water that was used for different needs at home or in production and got during this additional admixtures (contamination), that changed its chemical content or physical properties, are named sewer water. To the sewer water the atmospheric water is also referred, which is drained from the territory of settlements and industrial enterprises.
Contamination of sewer water can be mineral and organic. To the mineral contamination are referred sand, clay, slag, solutions of mineral salts, acids and alkalis. Organic contamination can be of vegetable and animal origin. Contamination of vegetable origin contains remains of plants, fruits, cereals, vegetables and paper. From the chemical point of view in this contamination basically the carbon in form of cellulose is included. Organic contaminations of animal origin contain physiological waste of people and animals, fatty substances, organic acids, etc. The basic chemical element of this contamination is nitrogen in form of protein substances. Sewer water, besides carbon and nitrogen, contain phosphorus, potassium, sulphur, sodium and other chemical connections.
So named bacterial and biological contamination is marked, which in sewer water is introduced by different bacterium, yeast and mildew mushrooms, small water-plants.
Contamination that is contained in sewer water, by the physical state can be in form of solution, colloid, suspension and insoluble admixtures. Depending on sizes of particles, their specific weight and motion speed of sewer water, substances can swim downstream to the surface, to be in hanged-up state in water or settle to the bottom. Degree of contamination of sewer water is evaluated by concentration, i.e. by weight of admixtures in the unit of volume in mg/l or g/m3.
By origin and character of contamination the sewer water is subdivided into domestic (economic-fecal), production and atmospheric. To the domestic one is referred the water from kitchens, toilets, showers, bath-houses, laundries, dining rooms, hospitals, and also domestic water that is created from the cleaning of
apartments. It comes either from the dwelling and public buildings or from domestic apartments of industrial enterprises. By nature of contamination the sewer water can be fecal, which comes from the toilets and mainly contaminated by physiology bio-wastes of man, and economic, which contaminated by different types of domestic wastes.
Content of domestic sewer water relatively permanent and is characterized mainly by organic contamination (nearly 60%) in insoluble, colloidal and soluble states, and also by different bacterium and microorganisms, also including pathogenic.
Industrial sewer water is created in technological processes of industry.
Content and concentration of industrial sewer water contamination are very different and depend on type and technology of production, feedstock and different components, which are present in technological process. Industrial sewer water can have organic, mineral, radioactive admixtures, and also poisonous and harmful substances. Contaminated and conditionally clean industrial sewer water is distinguished. An example of conditionally clean sewer water can be water that was used for cooling in warm-exchanging apparatus.
Atmospheric sewer water is created from falling of rain or snow melting and they contain mineral, and in less amount – organic contamination. Atmospheric sewer water that are created on the territory of industrial enterprises, contain wastes and garbage of responsible enterprises.
Abduction and rendering harmless of atmospheric sewer water also are included in tasks of sewerage. During this it is necessary to mark large unevenness of receipt of this water. In dry weather they are absent, and during thundershower their amount can be considerable.
Content of sewer water is studied with the aim of the most rational determination of such conditions and circumstances:
choice of way of sewer water cleaning;
possibility of utilization of valuable substances, which are contained in sewer water and sediment (fats, fertilizers and others);
possibility of usage of cleaned sewer water as a source of technological water-supply;
determination of the materials of pipes and canals, by which the sewer liquid is removed and foreseen the measures prevention of influence on them of sewer water.