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Freshwater Management Series No. 10

Managing Urban Sewage
An Introductory Guide for Decision-makers

V. Operation and Maintenance

Sewage facilities must operate under severe conditions created by the constant flow of highly corrosive wastewater and have to continuously pump and treat wastewater on a 24-hour basis. To ensure the provision of safe and reliable services, it is necessary to operate and maintain these facilities in an efficient manner.

A. Sewers

Since most sewer mains and pipelines are located under roads, they are affected by external factors such as loads and vibrations caused by traffic as well as the settling or sinking of ground, often resulting in breakage or cracking of pipes. For this reason, regular inspections, cleaning and repair work are essential for maintenance. In addition to constant surveillance, systematic inspections are carried out to ensure that damage is detected at an early stage and that repairs are made. To maintain the flow and capacity of the system, cleaning is performed on a regular basis. Care must also be taken to ensure that damage identified during monitoring or cleaning does not lead to a future accident or system failure.

To ensure that sewer mains and pipelines are properly operated and that their status is clearly understood, data relating to sewer mains, pipes and soil chambers should be collected and recorded using a sewage ledger system. This can help facilitate improved preventative operation and maintenance, allowing damage to be identified sufficiently in advance to prevent the occurrence of accidents. Furthermore, by adopting new techniques, such as nondestructive inspection, operational costs can be reduced.

B. Pumping Stations

When heavy rain occurs, pumping stations must quickly drain away rainwater runoff that rushes into the sewers and discharge it into the sea, adjacent rivers, or underground. Pumping stations are often unmanned and remotely controlled or monitored by master pumping stations, however they must be operated continuously and maintained, since swift operation is essential.

C. Wastewater Treatment Plants

The operation and maintenance of a wastewater treatment plant is complex and requires trained operators and sufficient financial resources to ensure that these facilities continue to operate in an acceptable manner. The volume of wastewater requiring treatment in a large city can be substantial. For example, in Tokyo, the amount of wastewater treated in 1999 was on average 4,740,000 cubic meters a day, and the amount of sludge treated was on average 154,330 cubic meters a day.


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