Bulk Water Treatment South Africa – How is Our Tap Water Processed?
Water is made up of 2 hydrogen atoms and 1 oxygen atom (H2O). When a lot of these H2Os join together – they form water. When water falls on the earth’s surface from the clouds, a lot of substances dissolve in the water, such as silt, minerals, bacteria, etc. Water is the train that moves along the tracks and the passengers are these substances that get on and off the train. By the time water enters the dams it has many passengers, both good and bad to humans.
There is silt and minerals from the land. There are germs (bacteria) that may cause people to get sick if they enter the human body. It is for this reason that the dirty water needs to be cleaned before it is supplied to taps. This cleaning process is called water purification. Rand Water is the company that cleans (purifies) the dirty water for Gauteng.
The Vaal, Klip and Wilge Rivers naturally flow into the Vaal Dam, which has a catchment area of 38 000 km2. Rand Water draws raw water for purification (cleaning) from the Vaal Dam via an intake tower. This raw water is then transported via canals and pipelines to Rand Water’s two purification stations in Vereeniging.
How is Tap Water Treated Before it Gets to Us?
Bulk water treatment occurs in 4 steps:
When raw water first arrives at a purification station it passes through metal bars or screens. These screens trap large water plants, water animals, sticks, leaves & litter, but allows the rest of the water to pass through.
- Coagulation and Flocculation
Now the raw water enters a spiral flocculator where slaked lime is added. The raw water contains sand, silt and clay particles that have small negative electric charges that repel each other. The water moves around very quickly so that there is good contact between the slaked lime and the particles. The slaked lime neutralises these electric charges and causes the particles to attract to each other. This process is called coagulation. A further chemical, sodium silicate, is added to assist the process.
As the water moves around the spiral flocculator the sand, silt and clay particles, as well as some small water plants and animals, germs, and all the bad minerals, “stick together” to form floc. This is called flocculation. Water moves very quickly in the middle of the spiral flocculator whilst on the outside it moves slower making it much easier for the objects to stick together.
The water, together with the floc, now flows slowly into a large sedimentation tank where the floc settles to the bottom of the tank. This is called sedimentation.
The floc at the bottom of the tank is now called sludge and is sucked out by desludging bridges and sent to a sludge deposit site. The top of the water in the tank is now much cleaner. This clean water flows over the side of the sedimentation tank into the carbonation tank.
When water leaves the sedimentation tank it has a pH of about 10.5 because of the lime that was added in the spiral flocculator. This high pH (alkaline) makes the water feel and taste soapy. In order to make the water less alkaline (a lower pH), carbon dioxide is bubbled through the water. This is called carbonation. The pH of the water is now between 8.0 and 8.4. This makes the water taste and feel much better. The water is kept at this pH level because it causes Calcium Carbonate to deposit inside the pipes which forms a protective layer for the pipes.
While tap water is deemed safe to drink, it might be considered unsavoury and less-than-perfect by many users. For this reason, we strongly recommend at least one type of filtration method be employed before drinking any tap water. Boiling assists in removing bacteria, but to improve taste 0- further measures such a filtration or reverse osmosis may be beneficial.
To get your hands on premium, purified water with none of the harsh chemicals present in tap water, get in touch with us by filling out the form below and find out more today!
Source credit: http://www.randwater.co.za/CorporateResponsibility/WWE/Pages/tapwater.aspx
Cover Image Credit: Financial Tribune