Part 4 - UltraViolet (UV) Method of Water Disinfection

To remove or nullify the harmful bacteria in water, two types of techniques can be applied.  First, is chemical, wherein a chemical such as Chlorine is added to the water, and the chemical reacts with the bacteria and neutralises its potent.  The second technique is physical, such as boiling, filtration or Ultraviolet disinfection.

Historically, Chlorine was the disinfectant of choice to combat water borne diseases such as Typhoid or Dysentery.  In 1887, Downes and  Blunt discovered the germicidal properties of sunlight.  The development of mercury lamps as artificial UV source, and the use of Quartz as a transmitting medium accelerated the develoment of UV based disinfection techniques.   Although European countries began using UV based disinfection by the 1960s, by the late 1980s the US EPA began considering UV disinfection as a primary disinfectant for municipal drinking water.

The layman is confused with disinfection, sanitization and sterlization  -

Sanitization : 2 log reduction : 50 - 99% reduction
Disinfection: 4 log reduction : 99.99% reduction
Sterilization: 6 log reduction : 99.9999% reduction

Standards: In the US, NSF International, a non-government non-profit company has set benchmark standards for water purification. For ultraviolet technique of disinfection, NSF Standard 55 discusses the standards required for ultraviolet disinfection.  Class A systems (40,000 uwsec/cm2) are designed to disinfect and/or remove microorganisms from contaminated water, including bacteria and viruses, to a safe level. Class B systems (16,000 uw-sec/cm2) are designed for supplemental bactericidal treatment of public drinking water or other drinking water, which has been deemed acceptable by a local health agency.

For most of us in Urban India, assuming that the water is already treated prior to supply to the home, the minimum requirement would be Class B, 16,000 uJ/cm2 or 16 mJ/cm2.  So what does this number mean?

In Ultraviolet technique of disinfection, central to the technique is a lamp that emits Ultra violet light, or light with wavelength less than 400nm, that is not visible to the human eye.  The following precautions should be taken -

• If the UV lamp is glowing, it does not mean it is emitting UV light.  UV light is invisible. What you see is not UV light, but some indicative lamp. You got to ensure it is emitting UV light at the stated power.
• UV light, once emitted, passes through the surroundings and water to reach the target microorganisms. 
• UV dosage is the intensity of the UV lamp multiplied by the residence time in seconds.
• Once the microorganisms are exposed to UV light for the critical time, they are rendered inactive, and cannot multiply anymore.
• UV light can damage the skin and the eyes, so keep away from the UV lamp.
• Regularly service the UV lamp and check for emittance.  UV lamp has a certain life, and although the light glows, it may not emit uV anymore.
• Dosage = UV Intensity at target x dose time.  The key is UV intensity not emitted, but what reaches or hits the target micro-organisms.  UV has to transmit through the Quartz sleeve surrounding the UV lamp, and through the turbid water before reaching its target. Also, as most home based UV Filter systems are not batch UV reactors, but continuous, not the same intensity hits all the micro-organisms. 

 
In industrial water treatment systems, a batch reactor is used with a fixed residence time so UV rays are impinged upon the micro-organisms for a certain duration of time until they are rendered ineffective. There are sensors in place to measure the real time intensity.  Daily and periodic tests are conducted to measure the effectiveness of the treatment.

In comparison, home based systems are a lot smaller in scope.  Most are based on continuous flow of water.  Depending on the flow rate of water, the dosage intensity varies.  There are no online sensors that display the intensity of the UV.  It is difficult to actually test the effectiveness of the system. 

Manufacturers hide much of the factual data when they sell such systems.  Users think that from the moment they start using a UV based filter, they have access to pure, disease free water, which may not be true. 

To be fool proof, we continue to advise people to use a fool proof method such as boiling the water to kill all harmful germs and micro-organsisms.

Part 3 - Review of TATA Swach

TATA entered the lucrative Water purifier market in 2010 with its revolutionary Tata Swach Model, developed by Scientists at TATA Chemicals.  Its salient features are -

• Does not use Electricity or Battery
• Portable
• Cost Effective
• Does not require Running water

Let us analyze the constitution of this Water purifier.  For any one with no access to pure filtered water, any purifier is certainly better than no purifier at all, so from that standpoint, TATA Swach provides access to clean, filtered water to millions of rural Indians.

TATA Swach does not use any of the following methods (that most of its competitors use) for its purification -

• Ultraviolet disinfection
• Activated Carbon Filter
• Reverse Osmosis
• Chemical disinfection

Instead TATA uses a in-house developed filter that is composed of natural ingredients such as Rice Husk ash impregnated with nano silver particles according to a company press release dated 9 Dec 2009.

Let us understand the role of silver in water purification. Silver by itself can be harmful if consumed with water. The US Environmental Protection Agency (EPA) registers all filters with added silver as bacteriostatic, and it does not endorse these methods for reducing bacterial levels in the filter, or in water.  So a bacteriostatic filter is not safe to treat microbially unsafe water.  Silver is typically used to prevent growth of micro-organisms on any medium, but by itself, Silver does not kill any micro-organisms. Our worry is there are no laws in place in India that restrict filter manufacturers from ensuring that no silver gets released into the water.

US EPA's Office of Water also classifies Silver as a Group D Carcinogen in 1988.  So, please dont get carried away by terms such as nano silver particles.

Whichever filters use Silver impregnated particles as part of the filtration mechanism should also inform customers not to use hot water as they are likely to erode the silver particles from the filter.

While we have not broken apart and analyzed the filter cartridge, we assume that their filter does a good job of filtering out solid particles and certain bacteria.  Our opinion is such a filter can only filter out certain solids, but cannot kill or incapacitate smaller bacteria and other viruses. Silver coated nano particles can at best prevent growth of any additional micro-organisms in the filter, but certainly cannot kill or stop existing bacteria or viruses to pass through.

So in summary, TATA Swach offers portability, and good value as an effective water filter where none existed before.  It offers freedom to use in places where there is no access to power. We also believe that it cannot filter out certain bacteria and viruses based on its filtration mechanism. As of the publication date of this blog, the reported price of TATA Swach is Rs 1000, and a replacement filter costs Rs 299 which is good for 3000 litres (Rs 0.10/litre estimated operating cost)

After we conduct a full test on the water, we would report additional findings.

Reverse Osmosis Water Purifiers for Household uses

Reverse osmosis is a proven technology that has been used successfully on a commercial basis. One of the better known uses of RO is the removal of salt from seawater. Household RO units typically deliver small amounts (8 to 40 liters per day) of treated water and waste 8 to 15 times the amount of water treated. Reverse osmosis units remove many inorganic contaminants from household drinking water supplies. The removal effectiveness depends on the contaminant and its concentration, the membrane selected, the water pressure and proper installation.

RO units require regular maintenance and monitoring to perform satisfactorily over an extended period of time. Before purchasing an RO unit or any other water treatment equipment, purchasers should test their water to be certain that treatment is needed and that the equipment being selected is appropriate to the problem requiring treatment. All costs need to be considered when comparing competitive systems and when making purchase decisions.

How effective RO is depends on the initial level of contamination, and water pressure.  It is principally used to reduce the levels of Total Dissolved Solids (TDS) and suspended matter. 

RO systems are used in two applications - industrial and household water treatment.  The process involves pushing contaminated water at pressure through a semi-permeable membrane. The membrane has microscopic openings that allow water molecules, but not larger compounds to pass through. 

Some of the companies that make Household water purifiers for the Indian market using RO are Kent, EurekaForbes.  Kent makes models such as Grand, Pearl, Elite, Excell+ and Pride.  EurekaForbes makes models such as AquaSure RO.

Advantages of a RO System:

1. Very convenient for commercial usage, as a much higher percent of water is recovered.

2. Useful for places where there is a serious shortage of fresh water.

Disadvantages of a RO System: 

1. Wastage:  RO Systems waste a lot of water, as they recover anywhere from 5 to 20% of the total water.  The balance is discharged as waste water.  For commercial or industrial systems, much more is recovered. But for small, household systems it is not cost effective to recover more water.

2. Cost:  For example, for Kent Grand RO Purifier, the company charges Rs 1800 annual maintenance contract which does not include cost of filters and membranes.  Filters plus membrane costs about Rs 2000, which should be changed anywhere from a year to two years, of course depending on usage, type of water being treated etc. 

3.  The membrane is very sensitive, and should it be clogged or torn, it would not be purifying any water, but for most system users, it would be difficult to find out.  Some of the newer systems have built in alarms for such accidents.

Other Related Posts

Part I - Summary of Water Filters in India

Part 3 - Review of TATA Swach
Part 4 - UltraViolet (UV) Method of Water Disinfection

Part I - Summary of Water Filters In India

We cannot live without water, and the water we use has a significant influence on our health and well-being.  Other than cities and towns, most people in India depend on ground water or rivers for their water needs.  Use of water filters is increasing, but they are not understood well.  Marketing ploys by the Filter manufacturers tend to be biased, and there are no BIS standards to adhere to.

With all these complexities, there are very few unbiased, independent analyses of water purifiers and filters in India.  This blog is an attempt to demystify the techniques and buzzwords that Filter producers use, and portray in black and white what is really needed.

Depending on the source of our water (municipal supply, river, borewell, tanker etc), it may contain micro-organisms (bacteria, viruses etc), solid contaminants (calcium, magnesium...) and potentially heavy metals (lead, arsenic etc) among others.

Most Water Purifiers use a combination of the following techniques for purification:

• Filter (Activated carbon, granular carbon, carbon block are popular) for removing oils, solids and most bacteria
• Reverse Osmosis - using a semi-permeable membrane to filter out solids, metals, salts and bacteria
• Ultraviolet disinfection - using a UV lamp (8-20W) which basically re-arranges the DNA of bacteria so that it cannot replicate itself
• Cation Exchange Softener - to eliminate Calcium and Magnesium
• Chemical Purification (using Chlorine, Iodine etc ) to disinfect

Let us look at our choices in the market - major brands are AquaGuard (owned by Shapoorji Pallonji), PureIt (UniLever), Kent and Tata Swach.  All except Kent are owned by large companies with deep pockets. Other companies that manufacture water purifiers include Philips, Godrej, Usha, Jaipan, Kenstar and Whirlpool.

AquaGuard has the most extensive range - most of their models use combinations of activated carbon filter and UV.  More recent models of Aquaguard have been incorporating RO in response to Kent.  UniLever entered the market in the last decade using Chlorine and activated carbon filter as their core technique. Kent entered the market with models that use Reverse osmosis, and emphasized taste as their USP. TATA is the latest entrant, targeting the bottom of the pyramid.

Let us look at positives and negatives of each technique.

None of them can kill viruses, as a National Institute of Virology study indicated recently. Another recent article in The Hindu states that even water purified by water purifiers may not be safe, hence the need to test the water regularly. 

Most filters are effective against bacteria, but not viruses and spores.  So you remain vulnerable to viral diseases, should the water be home to such viruses.  

Chlorine has been demonstrated to be a very effective disinfectant, but it leaves a bad taste and smell behind. For a long time most city municipal water agencies used Chlorine to disinfect the water reservoirs, and gradually gave way to UV based disinfection.  UniLever's PureIt filters use a technique which releases Chlorine slowly into the stream, and the later models use an additional step to remove Chlorine.  Most PureIt Filters use no electricity just because activated carbon filters and Chlorine tablets do not require power.

For Ultraviolet disinfection to be effective, a certain minimum exposure, dosage and residence time are needed to re-arrange the DNA of bacteria, and neutralize them.  In most cases,consumers just open the tap full speed thus exposing the water to minimal time for UV to take effect.  Additionally, some of the commercial UV lamps are low in intensity (8-10W) so I doubt if such treatment affects the micro-organisms.

Activated Carbon and other granular carbons have been proven to be very effective in adsorbing contaminants and bacteria.  But at times, during transportation or handling, the carbon blocks may break, and if that happens - water may just pass through unfiltered. Also, if the activated carbon is not replaced regularly, it may re-release the contaminants back into the water.

So, back to the fundamental question, which is the Best filter out there in the Indian Market?

If you see the ads of most of these companies, most of them use the words "As safe as Boiled Water" in their ads. Boiled Water is their benchmark to which they compare their own effectiveness.

Water raised to 72 deg C kills almost all known bacteria AND VIRUSES.  At boiling temperatures (100C), one can be rest assured that no micro-organisms are left in the water. This has been demonstrated by several laboratories.

But boiled water cannot remove solid contaminants, heavy metals etc which remain.

Our recommendation is to use a simple activated carbon filter (any company is fine) and then boil the water so as to ensure that all micro-organisms are rendered ineffective.  If you think this is tedious, pretty much most of the commercial filters do a mediocre job.  There are no standards  yet, so these products are not really regulated, nor are there Bureau of Indian Standards (BIS)  yet.  This is one market where spending big bucks does not correlate to getting the best. Our opinion is also that Reverse Osmosis filters are overkill, waste too much water, consume a lot of electricity, and tend to be expensive.

Other Related Posts:

Part 2 - Reverse Osmosis Water Filters

Part 3 - Review of TATA Swach

Part 4 - UltraViolet (UV) Method of Water Disinfection

Upcoming Posts:

Maintenance and Service of Water Filters

Comparison of Various Brands