Upgrading the Midmar WTP

Aerial view of the Midmar WTP during the early stages of the contract

The Midmar Water Treatment Plant (WTP), located in Howick, needed to be upgraded from a design operating capacity of 250 Mℓ/day to 395 Mℓ/day on a raw water intake basis.

The project required upgrades to the chemical dosing system, an additional new super pulsator clarifier, and six new rapid gravity sand filters at the main water treatment works. Additional upgrades included a new backwash water recovery tank, two new clariflocculators and a gravity thickener at the sludge treatment works, with associated mechanical, electrical, control, and instrumentation upgrades and integration.

The professional services contract was awarded to Hatch in 2013 and construction commenced in May 2015. The scope of work conducted by Hatch was extensive and covered full multidisciplinary design.

The newly upgraded plant produces 375 Mℓ/day of potable water utilising chemical dosing, super pulsators and rapid gravity sand filters, with disinfection using chlorine gas.

With growing water supply demands, Umgeni Water required significant upgrades to its Midmar Water Treatment Plant to provide reliable and safe water to the surrounding communities.

Design considerations

The upgrading of the WTP required the addition of several key modules to an active water treatment plant. On the surface, it may appear that adding modules of an existing, proven design should be straightforward, but there were various multidisciplinary elements that had to be integrated into the existing plant. This work had to be carried out with minimal disruption to the production of water and brought online without affecting the environmental compliance of the plant’s discharge to the Mgeni River. The design elements were also influenced by the requirements and preferences of the client’s project office, quality assurance, operations, asset and maintenance management teams. The raising of Midmar Dam, which was Requirements from the engineering disciplines completed several years earlier, affected included hydraulics to integrate the new the system hydraulics. In order to supply the elements, a second rising main pipeline from required new quantity of raw water to the plant, the upgraded Midmar raw water pump station the existing system hydraulics were reviewed, and geotechnical engineering for piled and it was determined that the rising main foundations. Structural engineering included would need to be duplicated, reinforced concrete, steel, masonry and GRP, New clariflocculators in operation at the sludge plant three of the existing pumps process, chemical, mechanical, electrical, control had to be replaced, and a and instrumentation. fourth pump and motor with associated pipework had to be installed to provide the necessary redundancy to ensure uninterrupted raw water intake into the WTP, while mitigating the risks of the Umgeni System’s failure.

PROFESSIONAL TEAM

Client: Umgeni Water Consulting engineer: Hatch Main contractor: Icon Construction