The construction and commissioning of Stage 1of the upgrading and expansion of Tshwane’s Zeekoegat Wastewater Treatment Works (WWTW) is on schedule for completion in November this year.

This is according to Pierre van Vuuren, Concor Civils’ contracts manager responsible for this contract, which is being carried outin joint venture with Power Construction.Concor Civils forms part of Murray and Roberts Construction.“Completion will be two years from project start-up in October 2010, which is six months ahead of the scheduled contract period,” Van Vuuren says.

Work on the stressed 30Mℓ/day plant has been split into four stages for budgetary reasons. Stage 1comprises the construction of a new40 Mℓ/daybiological nutrient removal activated sludge module.

The elements of the first stage comprise additional screens and degritting chambers at the existing inlet works; three primary settling tanks; 10 000 m³ balancing tank; 30 000 m³ biological nutrient removal reactor with associated air blowers, diffusers and pipe work; four secondary settling tanks; chlorine contact tank; various small pump stations and sumps; all interconnecting pipework and valves; and the upgrading of the bulk electrical and reticulation systems.

“The project started on 21 October 2010 and from November to March 2011 we recorded 476mm of rain, causing a delay as a result of the works being flooded.”

A challenge of a more technical nature comprised setting up the formwork to allow for the varying angles of walls to accommodate the design shape of the bioreactor. One side of the wall is vertical, while the other side is at an angle. In addition, the angles are different where walls cross. A total of 46 572 m² of formwork is required for Stage 1.

The Concor Civils/Power Construction JV has set up a batch plant on site to produce the 14 239 m³ of concrete required for stage one of the project. Concrete mix designs were finalised with the assistance of Cyril Atwell, concrete and researchmanager at Murray and Roberts Group. AfriSam’s high-strength cement from the company’s Roodepoort blending plant is used for the concrete mix and aggregates are supplied from its Olifantsfontein quarry.

Van Vuuren points out that the concrete mix design is stipulated at 35 MPa. An average strength of between 45 and 48 MPa is being achieved after 28 days.

The Concor Civils/Power Construction JV has overall responsibility for all aspects of the first stage of the project, including electrical and electronic (subcontracted to EDSE) and mechanical (subcontracted to Lektratek Water). The plant will be fully automated with a SCADA system controlling operational parameters.

The consulting engineers, BAKV3 – a joint venture comprising Bigen Africa, KV3 (the latter now part of the international Worley Parsons Group) and DJJ Conradie as specialist electrical consultant – were briefed to plan the project to ensure there was an overlap of work on each of the stages.

David Turner, divisionaldirector responsible for waterandwastewater treatment at Worley Parsons, says the overall objectives of the four-part project are to increase plant capacity from 30 to 85 Mℓ/day, improve the quality of effluent entering the Roodeplaat Dam to meet more stringent phosphate limits of 0.035 mg/ℓ in order to better manage the treatment of raw water into potable water and to upgrade sludge handling capabilities at Zeekoegat to comply with the latest legislation.The contract also specifies the creation of job opportunities.

“The BAKV3 JV was appointed to undertake the detailed design and supervision of the entire upgrading and extension of the Zeekoegat plant. The completion of the overall project is set for 2015/16,” he explains.