A pressure sewer provides a method of discharging sewage from properties into a conventional
gravity sewer
A gravity sewer is a conduit utilizing the energy resulting from a difference in elevation to remove unwanted water. The term ''sewer'' implies removal of sewage or surface runoff rather than water intended for use;''Design and Construction of Sa ...
or directly to a
sewage treatment
Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water p ...
plant.
Pressure sewers are typically used where properties are located below the level of the nearest gravity sewer or are located on difficult terrain.
Operation
In a typical set-up, a receiving well is provided close to the properties being served so that all sewage can gravitate to the well. An electric
macerator pump (also called a ''grinder pump'') pumps the finely macerated sewage through a narrow diameter continuous plastic pipe which discharges into the nearest gravity sewer or treatment plant. The operation of the pump is controlled by a float switch in the pumping well. The pumping well is sized to allow for periods of power outage or pump maintenance.
The discharge pipe may be as small as 50mm diameter carrying sewage at very high flow rates.
Pressure sewers are also used to collect the discharge from septic tanks and discharge this into the local gravity sewer to protect local ground water from contamination.
Advantages
Pressure sewers enable properties constructed below the nearest gravity main to connect to the local
sewerage
Sewerage (or sewage system) is the infrastructure that conveys sewage or surface runoff ( stormwater, meltwater, rainwater) using sewers. It encompasses components such as receiving drains, manholes, pumping stations, storm overflows, and scr ...
system avoiding the need for a
septic tank
A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the treatment ...
or
cesspit
Cesspit, cesspool and soak pit in some contexts are terms with various meanings: they are used to describe either an underground holding tank (sealed at the bottom) or a Dry well, soak pit (not sealed at the bottom). A cesspit can be used for ...
.
In areas where washouts or earthquakes are common, conventional earthenware or cast iron sewerage system may be prone to breakage and leakage. The plastic discharge pipe of a pressure sewer is much more robust and can accommodate substantial movements in the ground without failing.
Costs can be lower than conventional sewers since the pipework is much cheaper and there is no requirement for manholes or other intermediate infrastructure. Installation costs can also be very low as the pipes can be laid very close to the surface and may be installed using no-dig methods such as moleing.
Disadvantages
The pumping well and pump controls require expert maintenance and repair should they fail.
Electricity is required to power the pump and this cost would typically fall on the local house-holder.
Although the pump well is usually designed to accommodate several days storage, failure of the pump or of the local electricity supply for an extended period would result in a local overflow.
References
Hydraulic engineering
Sewerage infrastructure
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