7.5 Properties of sewage for pumping
Properties of sewage for pumping
The properties of sewage for pumping is important to understand when selecting pumps for waste water from households, businesses, hotels, offices, restaurants. Waste water serves as a carrier for the contaminants from water closets and other sources of waste in the sewage system.
Sewage is a generic term for:
- Soil sewage: discharge from water-closets, urinals, slop sinks including waste water from domestic baths etc. and even industrial effluent.
- Cooling water: thermally ” contaminated” water.
- Surface water: rainfall and storm water
- Drain water: drainage from building sites, fields, leaks in broken pipes etc.
The size of the waste matter is limited in principle to the area of the intake connected to the pipeline. It is not easy to define the limits of length of a soft and pliable body. These, such as sheets of plastic, nylon stockings etc., pass unchecked down the water closet and into the public sewer. It is forbidden to discharge, into any drain or sewer, matter which is likely to cause damage or which could have a prejudicial affect upon the treatment of their contents (i.e. waste matter which should be dealt with by municipal refuse disposal).
The legal regulations applying to local sewage works are enforced by the Regional Water Authorities.
There is a steady increase in the quantity of unwanted or forbidden objects collected at rain water and sewage grills. Especially difficult, and containing a high content of textile matter among others, is the sewage from densely populated city centres. The heart of the city with its restaurants, offices and department stores presents a far greater sewage problem than do the surrounding dormitory suburbs.
The demand on pumps and other means of transporting the daily sewage should be assessed according to the contaminants (permitted or not) which are contained in the sewage. The larger contaminants can be classified as deformable thus requiring a non clogging (chokeless) design.
Different types of industry produces varying types of effluent which often contains substances which can cause damage to the sewage Cleaning works and the recipient water installation.
The law regarding the discharge of industrial waste into sewers is restricted by local public health authorities and should be checked for each individual pump selection or project.
Limiting values for the discharge of substances which are poisonous, toxic, corrosive, explosive and/or damaging to pump materials, driving gear, piping systems etc. are the subject of consent which must be obtained from the local authorities. Many of these fluids appear in the Liquid tables.
Cooling water, surface water and drain water display properties as in section 7.1 Water properties for pump applications
Solid precipitations from the circulating water can accumulate in cooling tower installations in the form of lime furring, sludge and concentrations of minerals giving rise to corrosion and blockage in pumps and piping.
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