The plant, which discharges treated wastewater into the region’s surface water system, wasn’t meeting legislated discharge standards due to its activated sludge system being overloaded – a result of surrounding residential area’s rapid expansion over recent years. As a cost-effective alternative to constructing a new treatment plant, ERWAT decided to upgrade the existing trickling filter system located at the site. This type of upgrade is the first of its kind in South Africa and marks the start of a trend towards cost-effective infrastructure upgrades across the country.
“The trickling filter treatment system was originally designed to treat 4.5 megalitres per day, but because of the efficiency of our trickling filter technology, we have been able to increase the daily capacity to 6.5 megalitres and still meet the stringent water quality standards,” says Ian Lemberger, General Manager at Veolia Water Technologies’ Engineered Systems division.
The upgrade has involved replacing the existing trickling filter system’s stone carrier elements with new generation plastic honeycomb media that offers a significantly larger surface area for improved biological performance and enhanced flow. “In a trickling filter system, improved flow and more biological growth means more organic matter can be processed by the existing infrastructure,” he says.
The plant’s two existing structures, each 30 metres in diameter and 3.9 metres in height, house these new carrier elements, which means minimal civil works or alterations were required to complete the upgrade. To maintain the plant’s set minimum treatment capacity during the upgrade, Veolia upgraded each tower separately. Veolia was also responsible for the trickling filter system’s mechanical and electrical components, including the installation of civil tanks.
“After having the organic matter broken down in the trickling filter system, the water will pass through clarifiers to remove residual biological solids, and then to chlorination, which disinfects the water before discharge,” says Lemberger.
ERWAT awarded Veolia Water Technologies South Africa the upgrade contract based on the success of similar trickling filter projects completed by its Namibian subsidiary, Aqua Services & Engineering (ASE). “It is relatively easy to refurbish and upgrade older trickling filter plants by utilising the existing infrastructure. Under the right circumstances, and in certain conditions, it is possible to complete such an upgrade in less than six months. It is a very cost-effective way to increase treatment capacity,” concludes Lemberger.