Wastewater treatment plants play a crucial role in the removal of contaminants from wastewater and sewage in order for its conversion into an effluent that can be returned to the water cycle in an environment-friendly way or to be reclaimed for other purposes.

It is a critical process in the supply of safe water to local communities.

Concrete pipes manufacturer Rocla’s high density polyethylene (HDPE) vertical cast pipes were specified for two phases of the Polokwane Waste Water Treatment Project owing to the quality of the pipes and the technical support Rocla provides. The project commenced in 2018 and was completed at the end of December 2020.

The project, which was subdivided into three phases, is based in the Seshego area in Polokwane. It was initiated to upgrade existing sewage system, to meet the increased requirements of the Seshego local communities. Each phase of the project had a separate starting point with a common joining at a single point.

“The project was commissioned by the Polokwane Municipality to upgrade a now outdated sewage system which no longer met the local community’s requirements in the Seshego area of Polokwane. We worked closely with site contractor Safcrete Construction so that the quality of the pipes would be to the standard required and delivery scheduling would be as seamless as possible,” says Rocla regional sales manager Andrew Kruger.

He notes that the pipes were 2.5m silica rolling joint pipe, comprising a 3 mm sacrificial layer. Five sizes of pipe were required, namely 900 mm, 1 000 mm, 1 200 mm, 1 400 mm and 1 500 mm, which if placed end-to-end, the HDPE piping would be over 19 km in length.

The placement of each pipe required the insertion of a rubber ring and the welding of a ‘capping strip’ on the inside of each individual joint to ensure proper sealant.

Rocla’s HDPE lining offers water and sewer projects advantages such as a surface smoother than concrete, enabling smaller internal diameter piping to be used. The long-term pullout strength of the lining anchors is able to cope with a ground water pressure in excess of 10 m.

Contractor Safcrete Construction contracts manager Heelendren Thaver comments that he had worked with Rocla on many projects over the years and had always been impressed with the quality of the end product supplied.

“The Rocla HDPE pipes were specified for this project because they offer the best solution to waste and stormwater plant and projects of this nature. Their attention to customer requirements, in this case, an exceptionally challenging delivery schedule, is also a feather in their cap,” says Thaver.

Kruger adds that, in order for Rocla’s Polokwane factory to manufacture the various sizes of pipes and the required quantities, Rocla Polokwane underwent an overhaul in terms of the manufacturing sections needed to accommodate the upgraded equipment.

“We also made use of special vertical cast (VC) moulds which were required for use with the insertion of the sacrificial layer within the pipes. It was these changes that enabled us to meet the quantities of HDPE pipes required for the Polokwane Wastewater Treatment Plant projects as they enabled us to increase our production schedules and deliver to site timeously.”

Concrete pipe with a cast in HDPE lining has all the advantages of a strong rigid pipe that keeps its shape as well as those of a plastic pipe that is inert to acid attack .It is the best pipe for large diameter gravity pipelines in almost any condition. Standard HDPE lining is light green and 3 mm thick. Different colours and thicknesses can be supplied.