The Kouga local municipality, in the Eastern Cape, has upgraded its St Francis Bay wastewater treatment works (WWTW) from a capacity of 750 m3/d to 2 000 m3/d.

The upgrades, which started in February 2018 and were completed in February this year, included the refurbishment of the existing works – covering civils, mechanical and electrical – as well as the upgrade of the sludge-handling capacity to accommodate the increase in sludge volumes.

The newly upgraded plant, which serves the growing communities of St Francis Bay, Cape St Francis and Sea Vista and will cater for future development in the area, ensures that effluent being discharged from the WWTW complies with the relevant standards.

The plant has been operating since 1995 and has undergone two previous upgrades.

“Prentec constructed the original plant back in 1995, with two subsequent upgrades in capacity in 2000 and 2007,” says Prentec MD Stewart Buchanan, noting that the company was appointed as the main contractor on the latest project and was responsible for the design and construction of the plant.

The upgraded plant was designed by Prentec process director Martin Pryor and senior process engineer Kathy Visentin.

Appointed consulting engineers for the project, SRK Consulting designed and implemented the upgrading of the WWTW, including the additional infrastructure to meet the increased volumetric and organic loading of the works.

The two-year project was split into three portions, with the scope of work including the installation of two sequential batch reactors (SBRs), with floating aerator, inlet, decant, desludge pipework and sludge drying beds, says Prentec project manager Duncan Klinkert.

Further tasks included the upgrading of the existing mechanical and electrical equipment, the construction of new inlet works and a new concrete balancing tank and the upgrading of the balancing tank pumps, as well as the replacement of the switchgear and the construction of an artificial wetland.

The first portion of the project comprised the refurbishment of the existing works, including all civil, mechanical and electrical works, the construction and commissioning of the new inlet works and the new balancing tank.

The second portion included the construction and commissioning of the new plant equipment, the commissioning of the two new SBR units and the associated civil, mechanical and electrical and electronic works, in addition to the construction of new buildings such as an office, ablution facilities, a generator room and a chlorine dosing building.

This portion also encompassed the refurbishment and repurposing of existing buildings; the demolition of existing buildings; the construction of the sludge drying beds, the dried sludge handling facility and a gravel access road; making redundant infrastructure safe; and the installation of security fencing.

The third portion comprised the construction of the wetland area for the plant discharge, including fencing and landscaping of the area, Klinkert continues.

SRK Consulting principal engineering technologist Tiaan Claassen says that various technologies were investigated for the upgrade, concluding that cost-effective technology, such as the SBRs, which may be classified as extended aeration activated sludge technology, would be the best for the municipality to use.

“This technology was also considered favourable, as the plant operators were already accustomed to the existing plant’s operational processes and procedure.

“The upgrade employs the same principles and technology which enables ease of operation by the client,” he says.

Prentec’s SBR plants are batch process treatment plants that produce high-quality effluent requiring minimal supervision and maintenance.