ASW Engineering, a supplier of water treatment systems in southern Africa, was awarded the contract by Umgeni Water to refurbish 12 twin-cell rapid gravity sand filters.
The company’s initial assessment of the problem was that the sealing between the filter nozzle sleeves and the concrete panels, and the sealant used in between the precast slabs of the filter floor, had deteriorated due to the acidity of the raw water leaching the calcium out of the concrete.
This is a common fault with conventional floor construction and results in uneven air scour, leading to a loss of media during backwash and also media migration between the slabs into the plenum chamber.
The solution proposed by ASW was to lay Cadar’s corrugated GRC panels fitted with nozzle sleeves, onto which concrete would be poured, creating a jointless monolithic floor.
The construction of the nozzle sleeves supplied by Cadar provided a superior bond with the concrete, and the GRC panels acted as an additional primary seal against the acidity of the raw water.
ASW issued a 15 year guarantee that media loss would not exceed two percent per annum on completion of the contract.