Cape Town - Robust mechanical filtration screens were recently installed at the Raapenberg, Lourens River, Retreat Main, and Muller Street sewer pump stations to prevent large items from entering the wastewater system.
This initiative by the City of Cape Town’s Water and Sanitation Directorate aims to reduce the risk of overflows and damage to pump stations.
To date, 10 of Cape Town’s sewer pump stations across various areas have been fitted with uniquely designed mechanical bar/basket screens at the cost of R8.1 million.
This includes installations at the Langa Main, Bokmakierie, Phoenix, Joe Slovo, Grey Road, and Koeberg Road pump stations over the last two years.
These screens act like sieves, filtering out large objects such as wet wipes, sanitary towels, disposable nappies, clothes, rags, and condoms, which should not be in the sewerage system.
This initiative is part of a dynamic, collaborative effort between the City’s Water and Sanitation Directorate’s Engineering and Asset Management (EAM) and Reticulation branches.
The Design and Contracts team at the EAM branch leads the design and specifications for each screen, considering the existing infrastructure of each pump station.
When sewage pump stations fail to operate optimally, it results in a surcharge within the sewer network, triggering overflows from manholes and leading to outflows into residential and environmentally sensitive areas.
This poses significant health risks.
About the screens:
- The easy-to-operate system includes a covered gantry/steel structure (ranging from 1 to 3 tons), an electrical hoist, and a removable screen that slides in and out of the pump station’s inlet chambers on guide rails. The screen size depends on the size of the inlet, the layout, and available space at each pump station. All screens have a 50mm aperture to catch most larger solids in the flow.
- The screens are designed to be lifted out of the inlet chamber easily, allowing the captured solids to be dumped into a skip bin. The e-hoist is controller-operated with various movement controls. The latest screens are also fitted with a drop-bottom for ease of cleaning.
- Some larger pump stations, such as those at Langa, Raapenberg, and Lourens River, require double screens, either stacked or positioned in separate chambers/channels. A grapple has been designed to service multiple screens using a single hoist/crawl beam. The grapple, attached to the hoist chain, features a release mechanism to latch onto and release each screen for cleaning.
Installations at pump stations are prioritised based on pump block/failure rates, existing infrastructure, and available land.
Screens are currently being installed at Mosselbank and Ascot Street pump stations.
Future installations are planned for the following pump stations: College Road, Wesbank, Tambo Street, Wallacedene, Sarel Cilliers, Fisantekraal 2, Fisantekraal 4, Keyser River, Sand River, Philippi West, Philippi East, Rietvlei, Macassar, Elsies River and Freezia.
Mayco member for water and sanitation Zahid Badroodien said: “This collaborative effort will go a long way to help protect the City’s 487 pump stations from damage and reduce the risk of sewer overflows, improving the lives of residents.
“One of the major challenges the Water and Sanitation Directorate faces with sewer pump stations is the debris and foreign materials that enter the sewer system due to vandalism and misuse.
“We ask residents to avoid flushing wet wipes, sanitary towels, disposable nappies, clothes, rags, and condoms down the toilet,” Badroodien said.
“These upgrades are essential and will reduce the frequency of pump breakdowns and repair costs.
“With the EAM branch leading the design, we can continuously enhance or improve the screens for easier operation.”