State-owned water utility Rand Water’s Vereeniging-based Zuikerbosch water purification plant, which has been named a National Key Point, provides purified water to more than ten-million people a day in nineteen municipalities across Mpumalanga, Gauteng, the North West and the Free State, rendering it the largest plant of its kind in the country.

The facility, which supplies water to some 17 000 km² of surrounding urban and rural sprawl, produces just over three-trillion litres of potable water a day following the purification of raw water sourced from the nearby Vaal river.

Water from the river reaches the plant through a large canal, after which it is filtered to remove large debris and sent to the lime plant.

Calcium oxide, which has been crushed to 20 mm in diameter and converted to a calcium hydroxide in slurry form, is then added to the raw water to act as a flocculent, which aids in the purification process.

The water is then passed through a flocculator, in which lime, polyelectrolytes and silica are added. Thereafter, the water is directed through a series of circular canals to decrease the speed of the water flow and to promote the settling of sediment.

Speaking at a media visit to the plant on Wednesday, process laboratory supervisor Ernst Marais explained that water from the flocculator was then sent to several canal systems, where impurities continued to settle on the canal floor.

“Submersible pumps, which operate much like a household pool cleaner, suck up the sludge deposited on the bottom of the canals. This is then sent to a central point at which additional lime is added, after which it is sent to the sludge plant for any excess water to be removed and returned to the purification process,” he commented.

The water in the canals is then decanted and fed to a carbonation bay, where carbon dioxide is added to stabilise the water and reduce its pH to around 8.3.

“At this point, about 95% of the dirt has been removed from the water,” said Marais.

The water is then sent to the filter house, where the remaining dirt particles are removed through a sand filtration process, before chlorine gas is added to remove any remaining micro organisms.

“The purified water is then held in reservoirs until it is piped to the various booster stations for distribution,” noted Marais, adding that the entire purification process took between six and eight hours.