The water intake system normally requires pumping stations to remove water from the source to transport the water to the treatment facility. Some utilities may have the advantage of a water source that allows the use of gravity fed transport systems. Not only secure sufficient water quantities are needed, but there is a need to protect its quality. After source water protection, the next barriers to contamination of the drinking water system are those of water treatment processes, including disinfection and physical removal of contaminants. Although conventional treatment will provide safe drinking water in most cases, removal of certain harmful organisms such as Cryptosporiduim cannot be guaranteed. There are many technologies available, with each technology effective for a specific water contamination concern (i.e. there is no single treatment technology that works for all constituents of concern). When selecting and implementing a water treatment system, great care should be taken to ensure that it is the correct technology for the situation. In addition to the above, the section below provides an overview of common treatment technologies and their typical uses.
Coagulation/Flocculation
- Addition of chemicals to form floc that settles
- Used to remove colour, suspended matter, etc in water
- Majority of the contaminants are removed from settling of floc
Filtration
- Can utilise sand, disks or membranes as filter media
- Remove bacteria, sediment and particles
- Use specially rated filters to remove very small particles
- Various filter types are rated for different water types
- Need regular maintenance and replacement for proper operation
Chlorination
- Kills bacteria and viruses
- Can be used to remove some forms of iron, as long as water is filtered
- Needs filtration to remove microbes shielded or embedded in dirt particles
- Needs careful handling of chlorine, testing of chlorine levels, and maintenance of dosing pump
Stabilisation
- Addition of lime, soda ash, limestone, etc to soft waters to increase pH (and Alkalinity, Total Hardness)
- Important for the prevention of corrosion (metals) or aggression (cement concrete)
- Necessary for protection of infrastructure (reservoirs, pipe network, etc)
Reverse Osmosis
- Removes nitrates, sulphate, hardness, suspended matter and small amounts of some pesticides
- Can result in plugged membranes due to hard water
- Is costly because of the need to replace membranes
- Needs pre-filtration and softening of hard water
Activated Carbon
- Used for removing tastes and odours, and reducing trace levels of organic chemicals (e.g. pesticides)
- Not suitable for removing minerals, or larger amounts of chemicals
- Must be replaced regularly but difficult to determine when contactors are exhausted
- Can become a dangerous source of bacteria, taste and odour problems
Ozone
- Kills most microbes, but not cryptosporidium
- Removes organic compounds, including pesticides
- Can be used in combination with activated carbon filters
- Needs filtration to remove microbes embedded in dirt particles
- Varies in effectiveness depending on application and manufacturer
Ultraviolet Light
- Kills bacteria and viruses
- Needs filtration to remove microbes embedded in dirt particles
- Needs very fine (5 micron pre-filter), slow water flow and UV lamp must be clean
Greensand Treatment
- Removes moderate amounts of iron and manganese
- Unsuitable for removing microbes
- Not easy to operate or maintain
- Needs regular backwash and periodic reactivation with permanganate solution and/or bleach
Softeners
- Reduce hardness that produces lime deposits on dish-washed items and gives a starched effect on laundry
- Not suitable for removing microbes or most chemicals
- Increase sodium concentration in treated water
- Need periodic replacement of softener salt and disposal of concentrated salty water
Dissolved Air Flotation
- Used for removal of algae
- Can also be applied for clarification or sludge thickening
- When compared to other conventional settling systems, DAF has lower capital cost but higher operating costs (energy required to dissolve air)
Fluoridation
- Addition of fluoride compound to increase the fluoride concentration to reduce the incidence of tooth decay
Ion Exchange
- Used for water softening (removal of calcium and magnesium)
- Also used for removal of nitrates/nitrates
- Involves exchange of ions from solution for ions retained on a reactive material
- Ion exchange beds need re-generation from time to time