Fig. 2.1. Systems of sewerage:

a)general-flow; b) totally separated; в)semi-separated; г)water throwing chamber: 1-collectors of domestic-industrial network; 2-thunderstorm flush; 3-rain network; 4-water-throwing chamber; 5-pump station; 6-clearing structure.

In all cases choosing of sewerage system at settlement should be described by technical-economical calculations with taking into account of sanitary-hygienic requirements and perspectives of settlement development.

While choosing the sewerage systems at industrial enterprises the next indexes are taken into account: amount and content on industrial sewer water, ability of usage of industrial sewer water in circulating and consequent water-supply, ability of valuable substances utilization and pertinence of integration with sewerage system of settlement, requirements to the content of industrial sewer water of the reservoir. As a rule, the sewerage at industrial enterprises is designed due to totally separated system.

Industrial sewer water can be drained to the city sewerage, but in this case it shouldn’t:

• influence the work of sewerage networks and structures;

• contain substances that can contaminate pipes of sewerage network or sink on pipe sides;

• show destructive influence on the materials of pipes and elements of sewerage structures;

• contain combustible admixtures and soluble substances, which can create explosive and toxic gases in sewerage networks and structures;

• contain harmful substances with concentrations that break the work of clearing structures or interrupt the usage of water in systems of technological water-supply or throwing into water reservoirs (with taking into account the effectiveness of clearing).

Requirements to the sewer water, that are thrown into the city sewerage network, are normalized and introduced in “Technical conditions to the quality and mode of sewer water of industrial enterprises throwing into the communal sewerage system of settlements”, adopted by Minschytlokomungosp of Ukraine (order № since 21.05.90).

Limit values of some polluting substances, mg/l:

• petroleum and petroleum products – 25;

• surface-active substances – 20-50;

• copper, nickel – 0.5;

• chromium (III-valence) – 2.5;

• zinc – 1.0;

• quicksilver – 0.005;

• lead – 0.1;

• synthetic dye staffs – 25;

• hanged up substances – 500;

• БПК – 750;

• animal fat – 50-100;

• pH of sewer water – 6.5-9.5.

Industrial sewer water that are not correspond to these requirements, have to be previously cleared.

Schemes of sewerage networks of settlements are decided on the base of master plan with taking into account the relief of locality, soil conditions, reservoirs location, and also the phased sewerage development. Because of considerable variety of local conditions, it is difficult to propose typical schemes of settlement sewerages. However, schemes that are the most frequently met at practice are marked:

1. Perpendicular scheme (fig.2.2a), at which sewerage pool collectors traces perpendicularly to the direction of river flow. Such scheme is basically used for removing of atmospheric water, which doesn’t need the clearing.

2. Intercept scheme (fig. 2.2б), at which sewerage pool collectors are intercepted by main collector, that is laid parallel to the river. This scheme is used at lowering of locality relief down to the reservoir and if it’s needed to clean the sewer water.

3. Parallel scheme (fig. 2.2в) – sewerage pool collectors are traced parallel or under small angles to the direction of water current and are intercepted by the main collector, that is located perpendicularly to the direction of river flow. This scheme is used at various inclination of the locality to the river; as during this it’s prevented the considerable deepening of main collector and the increasing of speed of sewer water movement in pipes isn’t appear.

4. Radial scheme (fig.2.2г) – clearing of sewer water is conducted at two or more clearing structures. Sewer water is removed from the territory in decentralized way at this scheme. Such scheme is used at complicated relief of locality and construction of sewerages at big cities.

5. Zonal scheme (fig.2.2 д) – territory that equipped with sewerage is divided into two zones: from the top one the sewer water is removed to the clearing structures by gravity, from the lower one – is pumped by pump station. The usage of such scheme of sewerage allows to decrease exploitation expends.

Choosing of sewerage network scheme is conducted by the same rules as the systems of sewerage.

Fig.2.2. Schemes of sewerage networks: а)perpendicular; б)intercept; в)parallel; г)radial; д)zonal: 1-sewerage pools collectors; 2-borders of sewerage pools; 3-clearing structures.