Guaranteeing the microbiological safety of drinking/tap water is of paramount importance all over the world and conventional drinking water treatment has always included the use of chlorine for final disinfection.
In the last few decades, there have been new challenges in water treatment because of the increased presence or emergence of waterborne pathogens like Giardia and Cryptosporidium to which Chlorine has been moderately effective and ineffective respectively. Also, the possible link between halogenated disinfection-by-products (DBPs) caused by chlorination and cancer have impelled many water systems to look for alternatives.
Some of these chemical alternatives are chloramines, ozone, and chlorine dioxide. These chemical alternatives all have their issues. All chloramines and chlorine dioxide still produce DBPs but chloramines produce DBPs at lower concentrations in comparison. In the US, some states saw an increase in lead concentration when the switch was made from chlorine to chloramines. This was found to result from lead leaching into the water from the lead pipes used for water distribution, which was not the case when chlorine was used. A major concern for ozone is the production of bromates, aldehydes, and ketones in areas where there are high concentrations of bromides and organic compounds in the source water and so depending on water source, pre-treatment to remove bromides and organic compounds may be required.
Non-chemical alternatives include Membrane and UV radiation technologies. Membrane processes can remove bacteria, viruses and protozoa as well as a range of chemical contaminants. They are generally only used on a small scale to ensure effective monitoring. UV radiation is capable of inactivating bacteria and viruses, and possibly protozoan parasites. In both cases, high amount of energy is required.
A few northern European countries, have abandoned final chemical disinfection in many areas, reliance being placed on multiple barriers, often including natural barriers and biological treatment stages, to prevent contamination and to remove or inactivate micro-organisms.
From research, it can be deduced that the development of a successful water system, free of chlorine will require an in-depth understanding of the area to ensure that the best location is selected where natural systems can be used optimally in combination with current technology. According to Fuller, J of Engineering360, the Netherlands may be the most successful to date because chlorine as a disinfectant was last used in the Netherlands in 2005.
Effectiveness of method on Different Pathogens: Microorganism Reduction Ability
|Chemical/Non- Chemical options||E. Coli||Giardia||Cryptosporidium||Viruses|
|Chlorine||Very effective||Moderately effective||Not effective||Very effective
|Ozone||Very effective||Very effective||Very effective||Very effective|
|Chloramines||Very effective||Moderately effective||Not effective||Moderately effective|
|Chlorine dioxide||Very effective||Moderately effective||Moderately effective||Very effective|
|Ultraviolet radiation||Very effective||Very effective||Very effective||Moderately effective|
|Membrane processes||Very Effective||Very effective||Very effective||Very effective|
Table 1: The data on ozone, chloramines, chlorine dioxide , ultraviolet radiation were obtained from Reference No. 4 below
- Alternatives to Chemical Disinfection of Drinking Water. Retrieved Oct 3, 2017 – http://www.fwr.org/waterq/dwi0808.htm
- Chlorine Substitutes In Water May Have Risks Retrieved Oct 3, 2017 –http://www.npr.org/2011/01/07/132743638/disinfectant-to-clean-water-has-problems-of-its-own
- A Water Treatment Alternative to Chlorine? Retrieved Oct 3, 2017 – http://insights.globalspec.com/article/3112/a-water-treatment-alternative-to-chlorine
- Chlorine and Alternative Disinfectants Guidance Manual Retrieved Oct 3, 2017 Prepared for Office of Drinking Water Prepared by Earth Tech (Canada) Inc. Mar, 2005 https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&cad=rja&uact=8&ved=0ahUKEwir5aaylNXWAhUJzIMKHfK8DWQQFghwMA8&url=https%3A%2F%2Fwww.gov.mb.ca%2Fwaterstewardship%2Fodw%2Freg-info%2Fapprovals%2Fodw_chlorine_and_alternative_disinfectants.pdf&usg=AOvVaw3Wn0gIEQh7nL-FlqtVX2j1