- Sewage collection and disposal
Urban areas require some methods for collection and disposal of
A sewage system may convey the
wastewaterby gravityto a sewage treatmentplant. Where pipeline excavation is difficult because of rock or there is limited topographic relief (i.e., due to flat terrain), gravity collection systems may not be practical and the sewage must be pumped through a pipeline to the treatment plant. In low-lying communities, wastewater may be conveyed by vacuum. Pipelines range in size from pipes of six inches (150 mm) in diameter to concrete-lined tunnels of up to thirty feet (10 m) in diameter.
Sewage can also be collected by low pressure
pumps and vacuum systems. A low pressure system uses a small grinder pumplocated at each point of connection, typically a house or business. Vacuum sewersystems use differential atmospheric pressureto move the liquid to a central vacuum station. Typically a vacuum sewer station can service approximately 1,200 homes before it becomes more cost-effective to build another station.
Design and Analysis of Collection Systems
Design and sizing of
sewagecollection systems considers population served, commercial and industrial flows, flow peaking characteristics and wet weather flows. Combined sewersystems are designed to transport both stormwaterrunoff and sewage in the same pipe. Besides the projected sewage flow, the size and characteristics of the watershed are the overriding design considerations for combined sewers. Often, combined sewers can not handle the volume of runoff, resulting in combined sewer overflows and causing water pollutionproblems in nearby water bodies.
sanitary sewersystems are designed to transport sewage alone. In communities served by separate sanitary sewers, another pipe system is constructed to convey stormwater runoff directly to surface waters. Most municipal sewer systems constructed today are separate sewer systems.
Although separate sewer systems are intended to transport only sewage, all sewer systems have some degree of inflow and infiltration of surface water and
groundwater, which can lead to sanitary sewer overflows. Inflow and infiltration is highly affected by antecedent moistureconditions, which also represents an important design consideration in these systems.
Historical sewage conveyance and disposal
As recently as 100 years ago in major cities of developed countries, and up to the present day in many parts of the world, the primary concern with sewage was the matter of conveying it away from inhabited areas. Aside from its unpleasant
odor, even early humans were aware that health problems arose when human waste was allowed to contaminate drinking watersuppliesFact|date=February 2007.
Therefore, the historical focus of sewage treatment was on conveyance of raw sewage to a natural body of water, such as a
riveror ocean, where it would be satisfactorily diluted and dissipated. Early humanhabitations were often built next to water sources. Rivers could double as a crude form of natural sewage disposal.
Higher population densities required more complex sewer collection and conveyance systems in order to maintain (somewhat) sanitary conditions in crowded cities. The ancient cities of
Harappaand Mohenjo-daroof the Indus Valley civilizationconstructed complex networks of brick-lined sewage drains from around 2600 BC and also had outdoor flush toilets connected to this network.
The urban areas of the Indus Valley civilization provided public and private baths, sewage was disposed through underground drains built with precisely laid bricks, and a sophisticated water management system with numerous reservoirs was established. In the drainage systems, drains from houses were connected to wider public drains. [Rodda, J. C. and Ubertini, Lucio (2004). "The Basis of Civilization - Water Science?" pg 161. International Association of Hydrological Sciences (International Association of Hydrological Sciences Press 2004).]
Minoan civilizationhad stone sewers that were periodically flushed with clean water.
Roman towns and garrisons in the
United Kingdombetween 46 BC and 400 CE had complex sewer networks sometimes constructed out of hollowed out Elmlogs which were shaped so that they butted together with the down-stream pipe providing a socket for the upstream pipe.
A significant development was the construction of a network of sewers to collect waste water, which began from the
Indus Valley civilization. In some cities, including Romeand Istanbul( Constantinople), networked ancient sewer systems continue to function today as collection systems for those cities' modernized sewer systems. Instead of flowing to a river or the sea, the pipes have been re-routed to modern sewer treatment facilities.
However, many cities had no
sewers and relied on nearby rivers or occasional rainto wash away sewage. In some cities, waste watersimply ran down the streets, which had stepping stones to keep pedestrians out of the muck, and eventually drained as runoff into the local watershed. This was enough in early cities with few occupants but the growth of cities quickly overpolluted streets and became a constant source of disease. Even as recently as the late 19th century sewerage systems in parts of the highly industrialised United Kingdom were so inadequate that water-borne diseases such as choleraand typhoidwere still common. In Merthyr Tydfil, a large town in South Wales, most houses discharged their sewage to individual cess-pits which persistently overflowed causing the pavements to be awash with foul sewage.
A sewer bed is a piece of land typically used by a municipality for the dumping of raw sewage. Usually raw sewage was brought by truck or drawn by horses to be dumped, but the practice stopped back in the 1940s.
Select Society of Sanitary Sludge Shovelers
William Lindley– pioneering 19th century engineer
* [http://www.straightdope.com/mailbag/msolidwaste.html What happens to all the stuff that goes down the toilet?] (from
The Straight Dope)
* [http://www.yucatanliving.com/yucatan-survivor/mexican-fosa-septica.htm Why you do not put toilet paper in the toilet in Mexico]
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