Potable Water Disinfection

As we all know, potable water – i.e. drinking water, comes from natural sources. For example, most of our drinking water comes from rainwater collected in dams, canals, rivers, lakes, aquifers, or rainwater tanks. Rainwater runoffs from many sources pick up contamination of all sorts along the way. Waterborne bacteria, viruses, cysts, spores and similar microorganisms are indeed responsible for many contagious diseases including Cryptosporidium outbreaks, Giardia infections, or cases like recent Nigeria Fowlerii infections.

As a result, we must adequately treat water to make it safe to drink.

Potable water treatment includes multiple steps to remove impurities. Disinfection is a key step to make water safe to drink.

Disinfection is the process of inactivating microorganisms like bacteria, viruses, protozoa, spores, cysts and the like to make water safe for potable uses.

Disinfection Processes

We can divide drinking water disinfection processes can into

Chemical disinfection (e.g. Chlorine, Ozone) and
Non-Chemical disinfection viz: Ultraviolet disinfection of drinking water

Chemical Disinfection of Potable water

Chlorine and Ozone are strongly oxidizing chemicals. These chemicals oxidize the cells of microorganisms and kill them. In fact, Chlorine is quite popular for water disinfection for almost a century. It looks cheap, oxidizes bacteria, has a residual effect and has been around for a long time, after all.

Is chlorine disinfection perfect? Nope!

Limitations of Chlorination of Drinking Water

Chlorine has many limitations:

First and foremost: Chlorine Resistant Microorganisms

Unfortunately, some microorganisms simply can’t be inactivated by Chlorine. It took a few cases of Cryptosporidium outbreaks and Giardia infections to highlight the fact that there are some Chlorine-resistant microorganisms. Yes, that’s right: some microorganisms like Crypto, Guardia and many viruses remain can’t be controlled by chlorination.

This is a major and serious limitation of chlorination. After all, what use is a disinfectant if it can’t protect us from waterborne diseases?

Even increasing chlorine dose requirements: The forces of natural evolution are available to all living things. This included microorganisms. So, microorganisms mutate into new strains that require even increasing chlorine dose levels for inactivation.

Secondly: Disinfection By Products

Chlorine is an oxidant. It doesn’t discriminate! As a result, it tries to chemically react with whatever substances it comes in contact with. This can includes microorganisms as well as many types of organic and inorganic impurities in water.

When Chlorine reacts with the many types of impurities in water, it forms a Disinfection By Products, also known as DBPs. This is a broad group of chemicals that may include complex chemicals. Some examples of DBPs are: TriHaloMethanes (THMs), Chlorite, halonitromethanes, haloacetonitriles, haloamides, iodo-acids, Chloramines, etc.

Many scientific studies have linked disinfection byproducts to a wide range of adverse health effects.

Of course, there are many factors that affect the type and amount of Disinfection By Products. For example, disinfection byproducts depend on the type of disinfectant chemical used, its dose, time, temperature, pH, types of contaminants in water, water chemistry, etc.

Limitations of Ozonation of Drinking Water

Though Ozone is a much stronger oxidant than chlorine, ozone disinfection of drinking water suffers the same limitations of disinfection byproducts. Ozone is known to form ozone disinfection byproducts like ketones, carboxylic acids, aldehydes & bromate. Many of the disinfection byproducts are potent carcinogens.

Ultraviolet Disinfection of Drinking Water

Germicidal ultraviolet (UV) radiation in UV-C band is proven to damage the DNA of microorganisms like bacteria, viruses, spores, cysts, oocysts, yeasts, fungi, algae, etc. UV disinfection of potable water is rapidly becoming the preferred disinfection method because of several key advantages.

Advantages of UV disinfection include

No microorganism is known to be immune to sufficient & properly delivered UV dose. Properly implemented ultraviolet disinfection of potable water is proven to be effective against bacteria, viruses, spores, cysts, oocysts, yeasts, fungi, algae, etc.
No disinfection byproducts
Non chemical hence inherently safe
Easy to measure and control online
Online disinfection without requiring mixing tanks or holding periods
Availability of UV Dose – response curves for most commonly occurring pathogens
No risk of overdosing – generally the higher the UV Dose the better
No need to deliver or manage hazardous chemicals
Very economical
No corrosion
Does not depend on water chemistry, water pH, etc.

Limitations of UV disinfection

UV disinfection depends on “optical clarity” of the water to UVC wavelength, measured by UVT (UV transmittance) at 254nm. The higher the UVT of water, the more effective the UV disinfection
No residual effect

UV Disinfection of Potable Water: Process Flow

While there are variations, the most common process for ultraviolet disinfection of potable water is

Micron filtration -> UV disinfection
UV Dose for drinking water disinfection

UV Dose for drinking water disinfection

UV dose delivered is the most important factor affecting efficacy of UV disinfection.

Depending on the main pathogen of concern in the water source, some applications may use UV dose of 300J/m2 (30mJ/cm2).

USEPA and majority of EU authorities recommend minimum UV Dose>400J/m2 (i.e. 40mJ/cm2) at the end of recommended UV lamp life.

Some microorganisms (e.g. viruses) require much higher UV dose to be effective.

Typically UV dose if selected based on the main pathogen/s of concern in the water source.

Whole house Potable water disinfection
Mine site Potable water disinfection
Applications by market …
Advance ADV-C Series is the popular choice for drinking water disinfection at peak flow rates up to …
Advance ADV-F Series is the choice of rainwater harvesting professionals for potable water treatment plants ….

Potable Water Disinfection