UV Light NSF
We’re all familiar with the saying “The lights are on but nobody’s home which implies that someone may look like they are awake and functional,but in reality are not. What I would like to try and explain in this blog post is that just because the is on, doesn’t mean that it is effectively disinfecting your drinking water as promised.
There are 3 primary factors at play to ensure successful water disinfection when using UV light. In the simplest of terms, the first is the brightness of the light multiplied by how long it shines through the water. This is commonly referred to as UV Dosage. The second is Operational or Environmental factors affecting the performance of the UV light. The third is the Quality of the Waterbeing treated which can obviously restrict the light from fully penetrating the water stream.
If we use an analogy of car headlights, there are a lot of factors that can affect how well the driver sees on a dark night. This includes the lamps themselves (are they burnt out?), any dust, dirt or snow on the outside of the headlight cover (is the light produced by the lamp being blocked?) and lastly, the air in front of the vehicle (is there a contaminant like fog or rain that blocks or absorbs the light being produced by the headlights?). If the headlights on your car aren’t working properly, or there is something in the air reducing their effectiveness, it presents a significant safety hazard when driving at night doesn’t it? The same thought process can be applied to water disinfection by UV light. A life threatening hazard exists when treating water contaminated with waterborne disease if:
- The UV Lamp is not working or not adequate in power to shine through the entire water stream,
- The quartz sleeve surrounding the UV Lamp is dirty thus preventing the UV light from reaching the water stream and
- The water itself is not clear enough to allow the UV light to fully penetrate it.
Let’s look at the technical background of each factor affecting the performance of UV disinfection and then how certification by NSF International (www.nsf.com) ensures the safe and successful operation of UV systems in the field. Founded in 1944, NSF International is committed to protecting and improving human health on a global scale. NSF International is an independent, not-for-profit organization that provides standards development, product certification, auditing, education and risk management for public health and the environment. Manufacturers, regulators and consumers alike look to NSF International for the development of public health standards and certification that help protect the world’s food, water, health and consumer products.[i] The USEPA also provides a certification for UV disinfection systems but it is for larger systems of 30 gpm or greater, a category of equipment that we will examine in future blog posts.
Dosage is defined as UV intensity multiplied by time. This is represented as milliJoules per square centimeter (mJ/cm2), which is equal to milliWatt-seconds per square centimeter (mW-sec/cm2) or 1000 microWatt seconds per square centimeter (¼W-sec/cm2). Within the UV industry, there is a wide variety of lamp types and UV intensity. Some are designed to treat drinking water; some are designed to treat waste water commonly referred to as grey or black water; and some are even designed to treat air. Without jumping into a rabbit hole of technologies, lamp types and complicated technical jargon, most small to medium size UV light systems for the treatment of drinking water fall into 2 classifications: those offering 16 mJ/cm2 and those offering 40 mJ/cm2 or higher (16,000 uw-sec/cm2 and 40,000 uw-sec/cm2 respectively).
NSF describes 2 different types of water sources for human consumption, detailing the amount of UV intensity required to effectively treat the water sources involved.
- Class A systems (40,000 uw-sec/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.
Within the realm of disaster preparedness, disaster aid, remote industry, etc., it is rare to find a water source that falls within the Class B description. Therefore, it is critical to ensure that any portable water purification system to be used for such applications has a UV system capable of delivering the Class A dose of 40 mJ/cm2. However, a correctly sized UV lamp with sufficient intensity doesn’t automatically mean that the light can fully penetrate all water sources nor does it mean that it can’t be impacted by environmental factors affecting the lamp or lamp sleeve. Let’s look at the environmental factors that can affect the performance of a UV system, regardless of classification or certification.
Operational & Environmental Factors
At the most basic levels, before the UV light even reaches the water source, there are environmental factors which can affect the ability of the UV light to work properly or make it past the protective quartz sleeve that separates the lamps from the water source.
- Iron, manganese and hardness can cause staining of the UV lamp or quartz sleeves (depending on system design), preventing the UV light being produced from even reaching the water. Individual UV light manufacturers provide a listing of the maximum levels that need to be met for successful validation of their claims. Some manufacturers are now providing automated quartz sleeve cleaning systems which can help while others may require frequent removal and cleaning of the sleeve when iron, manganese and hardness is present. This is a situation that may be hard to detect without certain sensors and safeguards.
- Water temperature and ambient air temperature are environmental factors which can affect the performance of UV disinfection systems. UV lights are designed to work within certain ambient temperature ranges and with water streams that are also within a certain temperature range. Individual UV light manufacturers provide a listing of the maximum temperatures that need to be met for successful validation of their claims.
Once the UV light makes it into the water stream, there are a wide range of contaminants and conditions which can restrict its ability to fully penetrate the water stream and make it safe for human consumption. The main parameters I would like to stress are as follows:
- Even low levels of turbidity and total suspended solids (TSS) can block UV light and shield microorganisms from being inactivated. Total suspended solids is a water quality measurement usually abbreviated TSS.[ii] Turbidity is the cloudiness or haziness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality.[iii] Turbidity is measured by nephelometric turbidity units or NTU. Individual UV light manufacturers provide a listing of the maximum levels that need to be met for successful validation of their claims.
- Total dissolved solids (TDS) will reduce the ability of the UV light to fully penetrate the water stream. Total Dissolved Solids (often abbreviated TDS) is a measure of the combined content of all inorganic and organic substances contained in a liquid in: molecular, ionized or micro-granular (colloidal sol) suspended form. Generally the operational definition is that the solids must be small enough to survive filtration through a sieve the size of two micrometer.[iv] Individual UV light manufacturers provide a listing of the maximum levels that need to me met for successful validation of their claims.
- In my discussions with customers and end users, I find that the most overlooked yet most critical factor affecting UV performance is the raw waters UV transmittance, commonly referred to as UVT. UVT is essentially a measurement of the clarity of the water and the ability of a UV light source @ 254 nm to penetrate the water. The more UV light that is absorbed by the water stream, the less there is to inactivate the microorganisms present in the water. UVT is so critical to the successful operation of UV disinfection that I am going to expand on the subject and jump outside of this bullet.
More about UVT
Poor UVT within the water stream can be caused by particulate (reflected by higher turbidity readings) or dissolved substances such as TDS or tannins. At high levels, tannins often present as tea coloured or stained water. Individual UV light manufacturers provide a listing of the minimum levels of UVT that need to be met for successful validation of their claims. These levels can vary widely, ranging anywhere from 70% to 95%. (NOTE – A conventional system which claims effectiveness at 95% UVT levels could be ineffective in real-life situations.). While some systems include built in monitoring systems and alarms, some do not.
In the systems that do not monitor UV dosage or UVT; it is up to the end user to ensure that the water being treated meets the minimum UVT levels as specified by the manufacturer. This is where it can get tricky as:
- UVT cannot always be judged by the naked eye,
- UVT can change without notice (seasonal, heavy rains and runoff, etc.) and
- UVT can only be measured by expensive portable testing equipment or by sending samples to an appropriate water testing lab
What may look like clean and clear water to you could have a UVT level lower than the minimum required by your UV system. If so, the light may indeed be on, but not sufficient to fully penetrate the water stream thus providing the end user with a false sense of security. The best UV systems include onboard technology capable of monitoring UVT and/or dosage at the far side of the water stream and then reacting to low UVT or low UV dosages, creating audible and visual alarms as well as triggering an automatic shut off of the water being distributed.
UVT is so important to the efficacy of a UV disinfection system that it is specifically addressed by NSF / ANSI within their regulation ANSI / NSF 55, Class A Ultraviolet Microbiological Water Treatment Systems.
NSF certifies a UV systems effectiveness by requiring a minimum dosage of UV light in a water source with a minimum level of UVT (or clarity). To pass NSF/ANSI 55 Class A standards, a UV system must deliver a UV dosage of 40 mj/cm2 at the maximum flow rate of water (specified by the manufacturer) that has a UVT level of 70% or more.
So why should you make sure that the UV system in your water purification or treatment system is NSF 55, Class A certified?
- In general, third party organizations like NSF ensure that products do what they are supposed to do. They provide a way for end users to not simply rely on the manufacturers own claims.
- Specific to water disinfection by UV light, NSF 55, Class A provides independent, third party specification detailing the UV dosage and UVT required for the creation of safe drinking water when using different types of water sources (Class A and B).
- NSF 55, Class A certified systems mandate the inclusion of critical safety features such as audible alarms, visual alarms and automatic shut of valves in the event of a low UV dosage or low UVT event.
- Using an NSF 55, Class A certified system ensures compliance with regulations and/or guidelines posted by health authorities (provincial, state and/or federal).
- Using an NSF 55, Class A certified system also demonstrates that the maximum level of due diligence has been taken when interacting with applicable insurance companies and health and safety committees. This can be doubly important in the event of an audit or complaint of sickness unrelated to drinking water (food poisoning, fraudulent complaints by disgruntled staff, etc.)
- Most importantly, using an NSF 55, Class A certified system demonstrates to end users who are actually consuming the treated water that maximum care has been taken to ensure their safety and that of their families.
For the reasons outlined above, ensuring that your fixed or portable water purification system includes an NSF 55, Class A certified UV light is critical to the production of safe drinking water, especially when treating surface water sources such as lakes, ponds and rivers. UV Light NSF.
I hope that this blog post has been valuable in explaining the complexities of UV disinfection; the complications that can interfere with the successful operation of a UV system; and the benefits of choosing a UV system certified to NSF 55, Class A standards when choosing a portable or fixed water purification system. Questions and comments are always welcome. Please send us an email or drop us a line by web form or snail mail.