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About UNEP
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United Nations Environment Programme
Division of Technology, Industry and Economics
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Newsletter and Technical Publications
Freshwater Management Series No. 10

Managing Urban Sewage
An Introductory Guide for Decision-makers


VII. Addressing Local Environmental Issues

A. Enhancing Green Space and Recreational Opportunities

In the case of sewage facilities near residential or commercial areas, ensuring harmony with the surrounding environment is important. In areas adjacent to wastewater treatment plants, the integration of green space within the local ecosystem is an important objective. In some cities, green space and recreational facilities have been established on the roofs of pumping stations and wastewater treatment plants.

B. Preventing Odours and Emissions

It is also necessary to take measures to prevent odours and smoke from affecting the comfort of residents in areas near sewage facilities. One measure of confining odour is to contain diffusion of vapours and gases produced during the sewage treatment process. Another technique is to deodorize foul-smelling substances by chemical washing, activated carbon absorption, use of microorganisms, or incineration. A catalytic oxidation process can be used to mitigate exhaust fumes, including nitrogen and sulfur oxides that arise from the sludge incineration process.

C. Improving the Performance of Combined Sewer Systems (CSOs)

In a combined sewer system, both rainwater and wastewater are conveyed in the same conduit during wet weather, and part of this is discharged into the receiving waters without treatment. This poses a serious problem in protecting water quality. For this reason, some cities have adopted an interceptor strategy to increase the volume of wastewater that is treated. In some cases, a CSO storage tank is installed to prevent polluted first flush from flowing into the receiving water in the early stage of rainfall. In addition, screens can be installed to prevent rubbish from flowing from the rainwater outlets into natural drainage areas.

D. Flood Control

In some cities, the sewage system is used for flood control. However, even in areas with sewers, floods can occur. The cause is often dense clusters of buildings and paved areas arising from urbanization. As a result, rainwater is unable to infiltrate the ground, and large amounts of rainwater exceeding sewer capacity accumulates and overflows. The resulting flooding is referred to as "urban flooding". In order to improve the capacity of sewage facilities to cope with these conditions, various countermeasures against flooding can be undertaken, including:

  • Augmenting the capacity of sewers and pumping stations and constructing rainwater storage tanks in areas where the rainwater runoff exceeds the capacity of existing sewers.
  • Promoting the installation of rainwater storage and infiltration facilities to control the inflow of rainwater into sewers.

 

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