Comparison of Disinfection Methods in Drinking Water Treatment

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I’m currently learning about drinking water treatment and I’d like to know concisely of summarized comparison between various disinfection method e.g. Chlorine, Chlorine Dioxide, Ozonation, UV-Radiation.

Can someone give me explanation regarding to the comparison of those methods?

Thank you.

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11 Answers

  2. In water treatment,  the choice of different methods depends on sources,  quantity and end use.

    You can find good comparison of different water treatment methods at www.eawag.org

     

  3. You ask for advantages and disadvantages of each.

    If we start with UV.  Its advantage is that it doesn't use chemical and it reduces bacterial numbers and viruses as well as killing Cryptosporidium and Giardia.  The main disadvantage with UV is that it has no residual effect so there is nothing to stop growth of bacteria further down.  If the water has suspended solids then it is not effective.  But a system using UV then chlorine can be highly effective.

    Ozone is wonderful in that it kills all known organisms and viruses while remaining highly corrosive to metal.  It is very effective at killing at a point but will decline with time and further away from dosing so it can't be described as having residual treatment.  It will oxidise any metal and cause corrosion.

    Chlorine dioxide is a gas dissolved in water and anything such as turbulence will cause it to de-gas.  Because it is a gas dissolved in water, as the temperature increases it is less soluble and again comes out of solution.  In theory it is supposed to penetrate biofilms, but having coming across situations where chlorine dioxide has been dosed and biofilm is present, this is not always the case.  There is a limit on chlorite/chlorate which must not be exceeded in drinking waters.  Despite claims, it does not kill Cryptosporidium under practical conditions.  It has to be made in a reaction chamber where two chemicals are dosed into to react so the chemical dosing must be well engineered and have alarms to make sure that acid or unreacted chlorite are not injected into the water.  After saying this, it is a very good agent at killing bacteria but is more expensive than chlorine.

    Chlorine is in reality the ion OCl-.  It can be produced by the use of chlorine gas, which is the cheapest method but the most dangerous.  It can be produced by the use of liquid sodium hypochlorite which is injected into water.  If this is the method, then the use of an impulse pump with a de-gassing head or a peristaltic pump should be used otherwise oxygen and salt can form preventing the pump from operating.  Sodium hypochlorite bulk does deteriorate over time, so when newly made it has a strength of approximately 14% but will deteriorate over a period of weeks to months  so the strength will be less.  Chlorine can be generated by in place salt generators.  Chlorine is good at killing bacteria and some viruses but is ineffective at killing protozoa such as Cryptosporidium.  It is easily inactivated by organic matter so can realistically be used on clean water.  High levels of chlorine are corrosive and because it is inactivated by organic matter it is no good at controlling bio-film in systems.  It is less expensive than chlorine dioxide and is has been used in many systems safely for many years.

  4. Hello Muhammad, so there are a large number of articles on this in the literature.  Just my own thoughts to add to those below:

    • chlorine is the most used in drinking and wastewater treatment for post disinfection and sometimes also for pre-oxidation.  There may be unwanted by-products such as THMs, but these have to be weighed up against the alternatives.  For large reticulation systems, ammonia is usually dosed to convert free chlorine to chloramines which have a much longer residual stability.
    • chlorine dioxide has specific applications where it is more beneficial than chlorine, such as mine service water treatment where there are high levels of ammonia (from explosives) in the water, taste and odour control, biofilms, etc.  It is significantly more costly than chlorine, but under particular circumstances is cost effective.
    • Ozonation is a stronger oxidant than chlorine or chlorine dioxide, but does not leave a residual.  This may be an advantage for wastewaters to be discharged to a stream where you do not want any residual oxidant.  It is also useful as a pre-oxidant of a treatment system to breakdown difficult organics so that they may be removed in the treatment process.
    • UV radiation like ozone does not leave a residual.  It is useful for final treatment of an effluent being discharged to a natural water course.  It does require a water with a low turbidity (or high transmissivity) to be effective.
    • A combination of disinfectants is sometimes used in what is termed "advanced oxidation processes" whereby a combination of e.g. ozone and UV produces the hydroxyl radical, a short lived extremely potent oxidant.

  5. Hi Muhamad

    You need to know the final use of the treated water. Sometimes you need a residual concentration of disinfectant to ensure microbial inactivation. For example, if you need to supply  drinking water to a big city or you have a long time of storage for water, chlorine is an economic option for disinfection, because the residual concentration belongs in the time, the disvantage of chlorine is toxical subproducts and bad taste of water. Ozonation is a good option for disinfection and chemical oxidation treatment, the disvantage of ozone is the expensive cost and the short time of residual concentration, due to the ozone is an unestable molecule, the ozone needs to be produced in situ

  7. Dear Water Network community,

    the topic of biocide treatments  will be reviewed in the next White Paper which will be released by ALVIM Biofilm Technologies in the next few weeks.  You will be able to find it, together with other informative documents, in the 'about biofilm' section of our website at:

    http://www.alvimcleantech.com/cms/en/about-biofilm

    In case you are interested, please feel free to follow  my personal LinkedIn profile:

    https://www.linkedin.com/in/manuel-anselmo-b21a60b1

    where I periodically post recent insights concerning biofilm and related topics.

  8. Hi Muhhamad,

    The EPA "Design Manual, Municipal Wastewater disinfection" is a good source that covers the areas you have indicated.

    Best

    Ali Amiri (a.amiri@cogeco.ca)

     

  9. Very interesting to look at one place these comparisons (yrsrao.nihr@gov.in). Thanks

     

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  10. Kindly share your mail id to share the files. 

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