Plans to increase plant capacity by 50 Mℓ/day

Excellent progress is being made with the construction of the first of two 25 Mℓ/day modules which form part of the expansion of the Driefontein Waste Water Treatment Works in Johannesburg.

The project, located about 10 km from Lanseria International Airport, began in May last year and is scheduled for completion in May 2013.

Concor Civils, an operating division of Murray & Roberts Construction, was awarded the contract by Johannesburg Water and has sub-contracted the earthworks, piping and roadworks to Power Construction.

The scope of work includes site preparation and fencing, primary sedimentation tanks, balancing tank, BNR (biological nutrient removal) reactors, final clarifiers, a disinfection facility, raw sludge, RAS (return activated sludge), WAS (waste activated sludge), thickened sludge and wash water pump stations, a screening channel, gravity thickeners, control and minor buildings, VFA (volatile fatty acids) fermenter buildings, retaining walls, boxes and minor structures, interconnecting pipework and manholes, as well as roads, stormwater infrastructure and paving.

Stuart Graham, Concor Civils contract manager responsible for the project, explains that the existing wastewater treatment works (WWTW) at Driefontein originally had a nominal capacity of 25 Mℓ/day, which was increased to 30 Mℓ/day by upgrading and replacing existing infrastructure. However, a rapid increase in human developments within the catchment serviced by the WWTW rendered the existing plant capacity of 30 Mℓ/day inadequate and the plant struggled to achieve the required discharge standards, especially during peak flow conditions.

Studies commissioned by Johannesburg Water indicated that an ultimate capacity of 80 Mℓ/day — an additional 50 Mℓ/day — was required to accommodate future urban developments. The water authority decided to phase the expansion by building two 25 Mℓ/day modules, the first of which is currently being constructed. The second will be constructed at a later stage.

Expansion is imperative

The Driefontein WWTW is located in the upper part of the Crocodile River Catchment that drains to the Hartbeespoort Dam, a prominent water resource surrounded by high-level residential and recreational developments in North West Province.

“Pollution in the Crocodile River Catchment and Hartbeespoort Dam is well documented and catchment is now categorised as sensitive,” says Graham. “It therefore became imperative to expand the Driefontein WWTW to cater for these new developments and to avoid any uncontrolled waste spillages arising from a lack of capacity.

“The expansion project aims to deploy robust and reliable treatment technologies, which have a proven record with Johannesburg Water. At the same time, new energy efficient technologies will be installed with the capacity to serve the works facilities for the foreseeable future.”

Owing to bad founding conditions, Johannesburg Water has specified dynamic compaction under the primary sedimentation tanks and the new balancing tank, requiring of 12245m² of earth to be dynamically compacted. During the course of the project 21410 m³ of concrete will be poured and 68995m² of formwork will be erected, with 2572t of reinforcing being fixed and 260000m³ of earth moved.

“As a gesture of goodwill to the local residents, Johannesburg Water has also decided to upgrade the access road that leads to the works,” comments Graham.

As part of the upgrade, Johannesburg Water allocated funds for certified and accredited training of members of the local community and Concor Civils has already trained a number of local residents as shutter hands and bricklayers, allowing them to be employed on the project.

Sustainability

Sustainability is a primary focus that ensures that the Concor Civils team leaves each project knowing its teams have trained and skilled other people. Safety forms an important part of the company’s operating philosophy, guided by the Murray & Roberts ‘STOP.THINK’ philosophy that aims to achieve zero harm.