The upgrade of Zandvliet Waste Water Treatment Works

Compiled by Megan O’Connor, with technical input from Richard Craig, Greenfields Plumbing

Recently, the City of Cape Town completed a R2-billion upgrade of the Zandvliet Waste Water Treatment Works (WWTW). Greenfields Plumbing was the appointed plumbing contractor for the project that has been in-the-works since 2014.

“Proper, functioning sanitation is the difference between a life of struggle and a life of dignity” – Gordon Hill-Lewis, mayor of Cape Town. All images supplied by Greenfields Plumbing

The Zandvliet upgrade in Khayelitsha, Western Cape is one of the city’s largest infrastructure projects to date, providing improved sanitation for the many regions whose effluent it treats. Prior to the upgrade, the existing WWTW was overloaded, and was suffering from failing plant infrastructure – equipment and pipelines.

Urgent rehabilitation was needed to meet the ever-rising demands of the region, and the additional 18 million litres-per-day processing capacity provided by the upgrade was the solution. Further, the upgrade would ensure that high-quality treated effluent meets all licence requirements outlined by the National Department of Water and Sanitation.

Urgent rehabilitation was needed to meet the ever-rising demands of the region, and the additional 18 million litres-per-day processing capacity provided by the upgrade was the solution

The goal of the upgrade

Greenfields Plumbing managing director Richard Craig outlined what the City of Cape Town’s aim of the project was: “Due to water scarcity at the time, the City of Cape Town invested heavily to improve available water quality and supply.” Considering the vast number of areas Zandvliet WWTW serves, the importance of the project is highlighted – Zandvliet treats the effluent of the southern parts of Kuils River, Delft, Blackheath, Blackheath Industria, Blue Downs, Eerste River, De Wijnlanden, Thembokwezi, Mxolisi Phetani and Khayelitsha.

The upgrade increased treatment capacity from 72Mℓ/day to 90Mℓ/ day – ultimately aiding in supporting the growing population and economy. The plant’s effluent quality was also improved significantly thanks to cutting-edge membrane treatment technology that treats water to near-potable levels.

The upgrading process from start to finish

The project started as early as 2014, when the City of Cape Town appointed Zutari to design and construct the new WWTW to include state-of-the-art water purification technology. Zutari used virtual reality (VR) to compensate for the highly technical nature of the project and large number of involved stakeholders. Through VR ad 3D-model software, the design phase was streamlined and the client, stakeholders and plant operators were able to give input on the design to optimise it for their needs, as well as learn how the plant would function once built.

Stefanutti Stocks Coastal’s Cape Town-based civils team first constructed new enlarged inlet works, two new screw-pump stations, four new primary settling tanks, a primary sludge pump station, a sludge dewatering building, a service water pump station, a Waste Activated Sludge (WAS) pump station, sundry holding tanks (two primary sludge and two WAS), pipelines, access roads, as well as some minor services (such as water connection and site drainage). Following the completion of the live diversion to the new works, a portion of the old inlet works structure was demolished.

An HDPE waste reticulation, a MLP and copper water
reticulation, along with a black mild steel fire reticulation design
and installation was provided.

To increase the processing capacity of the plant by 18Mℓ/d, a new activated sludge reactor – utilising membrane biological reactor technology – was first constructed. Following this, additional structures to the existing works’ conventional active sludge reactors was constructed. Craig emphasised that “this vital upgrade ensured that the employer was able to continue with the essential treatment of wastewater for the ever-growing population”.

For Greenfields Plumbing, the project lasted 12 months from start to finish. Its work included providing an HDPE waste reticulation, a MLP (multilayer pipe) and copper water reticulation, along with a black mild steel fire reticulation design and installation. Due to the new buildings, no old plumbing or piping stood in the way of the upgrade.

Challenges faced during the project

• During the length of the project, occasional community protests to access work opportunities were faced by those involved in the project
• Co-ordinating site support proved to be the most difficult part of the works
• During the construction commencement, technical constraints arising from implementing an upgrade for a poorly functioning plant, as well as social and environmental challenges arising from discharging sewage into the lower Kuils River arose
• The project featured an extremely complicated inlet works – situated 10m below ground level and approximately seven metres below the water table – which required staged dewatering as well as construction of a raft foundation, comprising 700m3 of continuous concrete, to anchor the table pump station located below the water table
• The installation of new pipelines required precision, care, risk identification and management thereof
• The plant is gravity-fed with no retention capacity, thus connecting the new works was a live tie-in operation, which required meticulous planning and execution

The Zandvliet Waste Water Treatment Works.

The results

Gordon Hill-Lewis, mayor of Cape Town, commented on the WWTW noting: “Proper, functioning sanitation is the difference between a life of struggle and a life of dignity. Today we’re not just celebrating an impressive piece of infrastructure – we’re celebrating a big step up in the dignity of the residents of these communities.”

Craig agreed, adding that these upgrades and improvements ultimately impact “lives – and the dignity – of the families who live in the areas serviced by this plant”.

Urgent rehabilitation was needed to meet the ever-rising demands of the region, and the additional 18 million litres-per-day processing
capacity provided by the upgrade was the solution.

References

1. Cape Town ETC
2. Zutari
3. Stefanutti Stocks
4. Richard Craig, Greenfields Plumbing