Water purification generally means freeing water from any kind of impurity it contains, such as contaminants or micro organisms. Water purification is not a very one-sided process; the purification process contains many steps. The steps that need to be progressed depend on the kind of impurities that are found in the water. This can differ very much for different types of water. In which ways is polluted water treated?
Before the purification process begins some contaminants, such as oil, can be settled in a settling tank. They can then be removed easily, after they have reached the bottom of the tank.
Removal of dangerous microorganisms
Often polluted water has to be freed from microorganisms. The water is than disinfected, usually by means of chlorination.
Removal of dissolved solids
Microrganisms are not only a threat to water; they can also be an advantage when it comes to water purification processes. They can convert harmful contaminants to harmless substances. This biological purification process usually takes a long time and it is only used for water that is polluted with contaminants that the microrganisms, usually bacteria, can convert.
Physical/ chemical techniques
When treatment by microrganisms is not an option we often use different treatment techniques, called physical/ chemical treatment techniques. Chemical treatment often deals with the addition of certain chemicals, in order to make sure that the contaminants change structure and can then be removed more easily. Fertilizers such as nitrates are removed this way. Removal of contaminants can also be done through more difficult specific chemical processes. It takes a lot of education to fully understand these purification steps. Physical treatment usually deals with purification steps such as filtration. More information on water treatment chemicals
Water pollution treatment process
More detailed descriptions of water purification steps are available here How can bacteria be removed from water?
Bacteria and other microorganisms are removed from water through disinfection. This means that certain substances are added to kill the bacteria, these are called biocides. Sometimes disinfection can also be done with UV-light.
10 STEPS IN THE PURIFICATION OF WATER
Step 1: Ion Exchange
The complex process of purification begins with the removal of various metal ions through a process known as ion exchange. Sometimes referred to as water "softening", ion exchange utilizes large tanks which are filled with a special resin which carries a slight negative charge. The resin serves as a reservoir for a large number of positively charged potassium ions. As the water passes through the ion exchange system, metallic ions, which carry a relatively strong positive electric charge, displace the weaker charged potassium ions. The metallic ions are trapped via electromagnetic attraction to the resin beads. The ion exchange beds are automatically regenerated at prescribed intervals (every 6000 gallons). Ion exchange provides effective removal of the metals responsible for "hard water" pipe scaling and deposits. Additionally, the process removes various heavy metals, such as lead, iron, mercury and cadmium, many of which have been associated with a number of well-publicized health concerns. Step 2: Granular Activated Carbon
Once the water passes through the ion exchange system it moves into an oversized granular activated carbon bed. Carbon filtration, which utilizes a process known as adsorption, is a particularly effective technique for chlorine removal. Pesticides, herbicides and other organic contaminants (especially volatile organic) are also removed at this stage. Carbon also does an excellent job of removing trihalomethanes (THM's) from the water which are the result of chlorination of the public water supply. THM's are known carcinogens. Granular activated carbon filtration is the...