Quick reference for common UV terms used across documents.
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UV is powerful technology with a range of applications across markets. It’s user-friendly, effective and compact.
Quick reference for common UV terms used across documents.
Scientific research has proven UV light’s ability to inactivate an extensive list of microorganisms.
Ultraviolet (UV) light is a form of light that is invisible to the human eye
UV is powerful technology with a range of applications across markets. It’s user-friendly, effective and compact.
When selecting a UV system, it is important to understand a few of the key design variables and certification requirements.
Industrial and domestic scale UV disinfection systems must attain an NSF or National Sanitation Foundation Certificate.
Due to the unstable municipal water supply and quality in South Africa, several households and industries have resorted to securing independent water supply…
UV is powerful technology with a range of applications across markets. It’s user-friendly, effective and compact.
UV reactor validation is a critical requirement for ensuring a given reactor performs to its listed specifications.
Any water source can become contaminated by biological or chemical contaminants naturally occurring in the environment or introduced through human activity.
UV System
All the UV lamps, modules, reactors and reactor trains under the control of one UV control system.
UV Dose
UV dose refers to the amount of ultraviolet (UV) energy applied to a surface or substance over a given period. It is measured in millijoules per square centimeter (mJ/cm²) and is crucial in applications like water disinfection and sterilization.
The UV dose is calculated using the formula:
UV Dose (mJ/cm2) = UV Intensity(mW/cm2)×Exposure Time(seconds)
Different microorganisms require different UV doses for effective inactivation, making it an essential factor in designing UV-based disinfection systems.
UV Absorbance
A measure of the amount of UV light that is absorbed by a substance (e.g., water, microbial DNA, lamp envelope, quartz sleeve) at a specific wavelength (e.g., 254 nm). This measurement accounts for absorption and scattering in the medium (e.g., water). Standard Method 5910B details this measurement method. However, for UV disinfection applications, the sample should not be filtered or adjusted for pH as described in Standard Methods.
UVT
UVT (Ultraviolet Transmittance) is a measurement of how much ultraviolet (UV) light at 254 nanometers (nm) can pass through a water sample. It is expressed as a percentage and helps determine water quality, particularly for UV disinfection systems. A higher UVT means clearer water, while a lower UVT indicates more particles that absorb or scatter UV light. This measurement is crucial for ensuring effective water treatment and optimizing UV system performance
UVI
Ultraviolet intensity is a measure of the UV systems efficiency. UV intensity is measured in millijoules per square centimetre (mJ/cm²) and determines the effectiveness of the system in inactivating microorganisms. Systems are typically sized to ensure a minimum level of UV intensity at the furthest point from the UV lamp. Factors like turbidity and UV absorbance influence how much UV light reaches pathogens and therefore the UVI will vary under each application.
UV Sensor
A photosensitive detector used to measure the UV intensity continuously at a point within the UV reactor that converts the signal to units of milliamps (mA).
A significant body of scientific research has proven UV light’s ability to inactivate an extensive list of microorganisms. UV offers a key advantage due to its ability to inactivate certain chlorine-resistant microorganisms – most notably Cryptosporidium and Giardia among others.
In municipal applications, the release of these microorganisms into receiving lakes and rivers by wastewater facilities utilizing chlorine increases the potential of contamination in communities that rely on these same bodies of water for their drinking water source and recreational use. Drinking water treatment plants can benefit by using UV since it can easily inactivate chlorine-resistant microorganisms, while reducing chlorine usage and by-product formation.
Key advantages:
Microbiological Inactivation via Ultraviolet Light
Ultraviolet (UV) light is a form of light that is invisible to the human eye. It occupies the portion of the electromagnetic spectrum between X-rays and visible light.
A unique characteristic of UV light is that a specific range of its wavelengths, those between 200 and 300 nanometers (billionths of a meter), they are capable of inactivating microorganisms such as Cryptosporidium and Giardia. This capability has allowed widespread adoption of UV light as a highly effective way to treat wastewater and drinking water.
How UV Light Treats Water
A UV lamp is quite different than your standard incandescent light bulb. Yes, electricity is still passed through a tungsten filament which heats up, but that energy “excites” a very small amount of mercury vapor contained in the lamp. It is the mercury vapor that glows and emits the UV light.
Electricity is passed through a tungsten filament which heats up, and that energy “excites” a very small amount of mercury vapor contained in the lamp.
In water treatment applications, UV light provides rapid, effective inactivation of microorganisms through a physical process. When microorganisms are exposed to wavelengths of UV light, they are instantaneously rendered incapable of reproducing.
Microorganisms are inactivated by UV light as a result of damage to nucleic acids. The high energy associated with short wavelength UV energy, primarily at 254 nm, is absorbed by cellular RNA and DNA. This absorption of UV energy forms new bonds between adjacent nucleotides, creating double bonds or dimers. Dimerization of adjacent molecules, particularly thymine, is the most common photochemical damage. Formation of numerous thymine dimers in the DNA of microorganisms prevents replication.
Rendering of UV energy damaging a microorganism’s DNA.
UV light has demonstrated efficacy against organisms, including those responsible for cholera, polio, typhoid, hepatitis and other diseases.
When selecting a UV system, it is important to understand a few of the key design variables and certification requirements (see link to definitions page). The first and most important requirement is to ensure the UV system is certified by recognized standards, such as NSF/ANSI Standard 55 Class B or A, indicating its efficacy in reducing microbial contaminants.
Most household applications receive either municipal or borehole water and will mainly be sized based on flow rate and dose/target contaminant requirements. In all applications, it is necessary to include filtration step upstream of the UV system to prevent shading of bacteria and reduce fouling on the quartz sleeve.
When selecting a UV system the flow rate and dose are inversely related. The higher the flow rate, the lower the UV applied dose. And the lower the flow rate the higher the UV dose.
Therefore, when selecting a UV system, flow rate and UV dose are the key sizing parameters as they determine the level of disinfection by directly influencing the applied UV dose to the water. It is strongly advised to select a flow rate that is slightly higher than your anticipated water consumption. This ensures that the UV dose requirements are always being met and exceeded during periods of low water use.
The amount of UV light needed depends on the target contaminant or microorganism as each microorganism requires a different UV dose to achieve disinfection. The industry standard is a 30mj/cm UV dose which achieves a 4-log reduction in most of the common water borne pathogens.
As can be seen from the image above, a UV dose of 30mj/cm2 covers the vast majority of pathogens with a NSF class A validated dose at 40mj/cm covering inactivation of all common pathogens.
Therefore when selecting your preferred UV system, the supplier will request the flow rate, dose requirements and water source, to ensure the right sized reactor is selected to apply the right UV dose and inactivate the desired microorganisms accordingy.
Introduction
Industrial and domestic scale UV disinfection systems must attain an NSF or National Sanitation Foundation Certificate. UV reactor validation is a critical requirement for ensuring a given reactor performs to its listed specifications. With the multiple, cheap entry level UV disinfection manufacturers in the market, there is no guarantee that a given reactor can perform to the specifications required to achieve adequate disinfection of contaminants.
A key certification which ensures that a given UV reactor will perform to a certain standard and is not simply a lamp in sleeve, is a NSF validation certificate.
An NSF Validated UV system is a UV water treatment system that has been certified by NSF International, an independent organization that sets public health and safety standards.
Key points about NSF validation:
Class A for pathogen inactivation and Class B for aesthetic water improvement.
NSF/ANSI 55 – Overview
Class | Purpose | Target Contaminants | Application |
Class A | Disinfect microbiologically unsafe water | Bacteria, viruses, protozoa (e.g., Cryptosporidium, Giardia) | Intended for water already deemed unsafe (e.g., from private wells, reuse) |
Class B | Reduce non-pathogenic microorganisms | Nuisance microbes (taste, odor, and color-causing) | Used where water is already microbiologically safe (e.g., municipal tap water) |
NSF Validation – Testing Process
1. Microbiological Performance Testing
Class A Validation
Class B Validation
2. Electrical & Safety Testing
3. Structural Integrity & Pressure Testing
4. Material Safety Testing
5. Monitoring & Control Systems
For Class A, the system must include:
Due to the unstable municipal water supply and quality in South Africa, several households and industries have resorted to securing independent water supply such as borehole water and rainwater harvesting. These water sources are however not free of contaminants and disinfection is key to ensuring this water is safe for consumption and use.
Contaminants can enter rain water sources in several ways:
Borehole water
The rise in borehole water usage in south Africa is extensive. Multiple households and industries have undertaken the switch from municipal to borehole water as a cost saving measure and to decrease dependence on an unreliable municipal supply. Borehole water contamination is inevitable and adequate disinfection is a requirement for safe drinking and process water.
There are multiple ways that borehole water contamination can happen. Heavy rainfall, spring runoff, and flood events can overwhelm even well-constructed, recently drilled wells, introducing surface contaminants into the aquifer below. If the borehole is older, the risk of surface contamination infiltrating the borehole is even greater.
Potential Borehole Water Contamination Issues:
Microbes in borehole Water
The most important thing to know about microbes in borehole water is that they cannot be seen, smelled, or tasted. Conducting a bacterial test with a certified laboratory is the only way to determine if the drinking water presents a risk.
According to the CDC, the common causes of disease outbreaks in boreholes are:
In any situation involving microbial contamination, the primary concern is to eliminate illness-causing microorganisms that may be present in the water.
Giardia
-Escherichia coli
The microorganism most often identified as a cause for concern in drinking water is E. coli, a type of coliform bacteria. Coliform bacteria are naturally present in the environment and also live in the intestinal tracts of animals. The presence of coliforms in water indicates a general water quality issue. However, if E. coli is found in the water, it indicates the presence of fecal contamination and signals an elevated risk of other pathogenic contaminants also being in the water. Some other waterborne bacteria of concern are salmonella, shigella, and campylobacter.
-Protozoa
Giardia and cryptosporidium are both organisms that live in the intestinal tracts of animals. As part of their lifecycle, these organisms are flushed out with feces and form an extremely difficult-to-penetrate cyst to protect them, even in harsh environments. These organisms can live in the environment, even in cold water, for months until they are ingested and start the cycle over again.
These cysts typically originate from surface water intrusion due to flooding events, poor well construction, or the deterioration of well components. Both giardia and cryptosporidium can cause illness, and in children, the elderly, or immune-compromised people, they can be serious illnesses. Because of their protective cyst coatings these organisms are resistant to chlorine.
Introduction
UV reactor validation is a critical requirement for ensuring a given reactor performs to its listed specifications. With the multiple UV disinfection manufacturers in the market, there is no guarantee that a given reactor can perform to the specifications required to achieve adequate disinfection of contaminants. For municipal drinking and waste water treatment plants this validation is critical to ensure public health and safety is maintained. For municipal applications, the certification of a reactors performance is conducted by a third and independent party and is referred to as a bioassay validation certificate.
Bioassy Validation
Bioassy validation is the process by which a UV reactor’s disinfection performance is determined relative to operating parameters that can be monitored. The reactors are validated to indicate that they achieve a certain delivered UV dose for a range of flow, UV intensity and water quality conditions. This validation procedure is essentially a biological performance test that uses live microorganisms to confirm that a UV reactor achieves the required level of disinfection (measured in log inactivation). It is not just based on UV lamp power or dose calculations, but rather on actual biological effect.
The U.S. EPA UV Disinfection Guidance Manual has defined third-party validation as “the process by which a UV reactor’s disinfection performance is determined relative to operating parameters that can be monitored. The reactors are validated to indicate that they achieve a certain delivered UV dose for a range of flow, UV intensity and water quality conditions”
The treatment objective of an ultraviolet disinfection system used in a wastewater application is to protect aquatic and ecological environments. To ensure this objective is adequately met it is important to validate or verify equipment performance for a specific application. The widely accepted method for completing this validation is by determining the UV dose delivery performance using biodosimetry. Whilst several protocols exist for completing biodosimetry tests, or bioassays, for different applications, only two methods are in wide scale use in the industry worldwide;
The bioassay validation protocol takes elements of existing protocols for drinking water and reuse water and applies them to the specific application of wastewater. However, unlike drinking water or reuse water, the wastewater regulatory community looks to effluent disinfection compliance as the sole target for UV disinfection performance and not system design or system testing processes.
Validation testing of UV reactors produces the following types of data for each experimental test, it is thus a tool that allows for direct comparisons of UV systems during the design of such systems and to help to properly size a UV systems
Bioassay validation of UV reactors is critical for ensuring that ultraviolet disinfection systems actually deliver the intended microbial inactivation and not soley based on a theoretical assumption.
Any water source can become contaminated by biological or chemical contaminants naturally occurring in the environment or introduced through human activity. Water that will be used for drinking or cooking must be free of contaminants that can damage our short or long-term health. Surface water is exposed to the environment, so it can be contaminated by human and animal activity. Cryptosporidium parvum and Giardia lamblia, two common protozoan cysts, are microorganisms introduced to a water source through faecal contamination. These cysts can cause illness, specifically severe gastroenteritis. Viruses, another microbial contaminant, are also prevalent in surface waters.
In surface water sources, contaminants can enter water through several pathways;
Surface water provides the bulk of the municipal water supply to South Africa. There have been several cases of municipal water supply containing contaminants and compliance with water regulations is not a guarantee. Industries and domestic water users are largely dependant on municipal water supply in South Africa and may benefit from an added layer of protection through UV treatment, particularly during times of drought.
Certain contaminants have become immune to standard chlorine disinfection applied in municipal drinking water treatment plants. Giardia and cryptosporidium are two common protozoan cysts found in contaminated surface and groundwater sources. UV disinfection is one of the most effective methods for inactivating Cryptosporidium and Giardia in drinking water because it targets their DNA/RNA, preventing them from reproducing. Both organisms live in the intestinal tracts of animals. As part of their lifecycle, these organisms are flushed out with feces and form an extremely difficult-to-penetrate cyst to protect them, even in harsh environments. These organisms can live in the environment, for months until they are ingested and start the cycle over again.
Both giardia and cryptosporidium can cause illness, and in children, the elderly, or immune-compromised people, they can be serious illnesses.