What once went down the storm drain is now used to decrease the demand on the municipality’s water supply – 12 million litres per year. Vodacom has developed a water storage system with the capacity to hold one million litres from a run off area of 40 000 square metres. The system is expected to meet 40% of the company’s cooling system needs.
It is unusual to harvest groundwater due to its turbid quality. The water may carry suspended and dissolved solids and be biologically polluted. Water treatment is crucial in this regard. The harvested water is filtered to 20 µm through a proprietary self-cleaning filtration unit. Physical matter is limited by a floating intake that is designed to pull the cleanest water into the reservoir by floating between the surface and the floor. Debris then floats to the top while sediment sinks to the bottom. The water then passes through a stilling basin where silt is trapped. Only at this stage does the water enter the underground storage tank.
The site of the storage tank was a stormwater retention pond/flood attenuation pond and the exsiting stormwater piping is used to pimp water to the cooling towers. Any overflow will be diverted to the existing stormwater drainage outlets. This situation isn’t expected as the combined capacity of the storage dam, stilling basin and flood attenuation area is on par with the natural run off.
The storage dam has a live bio-filter and water-wise garden. The former decomposes pollutants by using living material such as rocks inhabited by living organisms to capture and biologically degrade pollutants.
This model is the first of its kind and will be used to evaluate future designs and economic benefits as well as gauge the impact on water security.
*The full article appears in the Aug-Sept 2013 issue of earthworks magazine. Images: Elske Kritzinger (www.elskegallery.co.za).