Chemical treatment of Raw/reservoir water 

1. Collection of rain water into reservoir
2. Coagulation and Flocculation – adding of chemicals such as Aluminium sulphate, hydrated lime and polyelectrolytes. Aluminium sulphate binds and precipitates impurities. Hydrated lime and polyelectrolytes allow better pH for flocculation. Aluminium sulphate precipitates impurities.  
3. Sedimentation – large particles settle to the bottom of the tank
4. Filtration – using rapid sand filters to remove the finer particles
5. Disinfection

• Chlorine destroys bacteria and viruses
• Ammonium keep chlorine free to form stable chlorine residual
• Activated carbon removes bad taste and odor.

Text Reference:

Publics Utilities Board. 2016. Water treatment [Internet]. [Cited 12 March 2017]. Available from: https://www.pub.gov.sg/watersupply/watertreatment

 

NEWater Technology

Stage 1 – First Stage The first stage of the NEWater production process is known as Microfiltration (MF). In this process, the treated used water is passed through membranes to filter out and retained on the membrane surface suspended solids, colloidal particles, disease-causing bacteria, some viruses and protozoan cysts. The filtered water that goes through the membrane contains only dissolved salts and organic molecules.

Stage 2 – Reverse Osmosis The second stage of the NEWater production process is known as Reverse Osmosis (RO). In RO, a semi- permeable membrane is used. The semi-permeable membrane has very small pores which only allow very small molecules like water molecules to pass through. Consequently, undesirable contaminants such as bacteria, viruses, heavy metals, nitrate, chloride, sulphate, disinfection by-products, aromatic hydrocarbons, pesticides etc, cannot pass through the membrane. Hence, NEWater is RO water and is free from viruses, bacteria and contains negligible amount of salts and organic matters.

Stage 3 – UV Disinfection At this stage, the water is already of a high grade water quality. The third stage of the NEWater production process really acts as a further safety back-up to the RO. In this stage, ultraviolet or UV disinfection is used to ensure that all organisms are inactivated and the purity of the product water guaranteed. Before Storing NEWater in Water Tanks – Balance the pH in NEWater With the addition of some alkaline chemicals to restore the acid-alkali or pH balance, the NEWater is now ready to be piped off to its wide range of applications.

 

Text Reference:

Public Utilities Board. 2016. NEWater Technology [Internet]. [Cited 19 March 2017].

Available from: https://www.pub.gov.sg/Documents/NEWater%20Technology.pdf