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What is a UV-C dose and how is it calculated?
The UV Dose is a sum of the UV irradiance in W/m^2 multiplied the exposure time in seconds, i.e the Contact Time or 'CT'. Selecting the correct UV-C dose is dependent on water quality, UV-C light has to penetrate the water and therefore the clarity is taken into consideration, this is measured in UVT (Ultraviolet Transmittance) and is compared to distilled water at 100% clarity. Lesser water quality requires more power to make the UV-C light penetrate the water, as such (and assuming a UVT test is not available) we use an assumed table to match varying water qualities to the UV-C dose required.
Below are some examples of common water sources and the UV-C dose required.
Drinking Water: UVT typical 90 - 95% = Dose required 16mJ/cm^2
Rain Water Harvesting: UVT typical 80 - 85% = Dose required 30mJ/cm^2
Borehole water: UVT typical 95% = Dose required 16 - 40mJ/cm^2
River water: UVT typical 80% = Dose required 30mJ/cm^2
Please Contact Us should you have any queries regarding flow rates, water quality and dose rates required.
What is the difference between Pt-Co and UVT?
While the Pt-Co colour scale and Ultraviolet Transmittance (UVT) are related, they are not directly convertible, as they measure different properties of water samples.
The Pt-Co colour scale is a visual method for assessing the colour of water by comparing it to a series of platinum-cobalt standard solutions. It provides an indication of the presence of dissolved organic or inorganic materials in the water.
On the other hand, UVT is a measure of how much ultraviolet (UV) light can pass through a water sample at a specific wavelength (usually 254 nm). UVT is an important parameter for the efficiency of UV disinfection systems, as the transmittance affects the ability of UV light to penetrate and inactivate microorganisms in the water.
While both Pt-Co and UVT are related to the clarity and quality of the water, they provide different information about the water sample. A high Pt-Co value might indicate the presence of organic or inorganic compounds that can reduce UVT, but there is no direct formula to convert Pt-Co values into UVT values.
To accurately determine UVT, you should use a UV spectrophotometer, which measures the percentage of UV light transmitted through the water sample at the specified wavelength. This will provide a more reliable assessment of the water's suitability for UV disinfection than relying solely on Pt-Co colour values.
What is a 'log' reduction?
The percentage of micro-organisms inactivated by any disinfection process are commonly known as 'LOG' reductions. The below illustrates the comparison between the log and the percentage reduction.
1 Log = 90%
2 Log = 99%
3 Log = 99.9%
4 Log = 99.99%
5 Log = 99.999%
6 Log = 99.9999%
Is there a requirement for pre-treatment of water before the UV-C Disinfection system?
Depending on your water source pre-treatment may be required.
If you are considering using UV-C light to disinfect your mains water supply, this water should be clean and relatively free of particulate load. Most UV-C disinfection systems suggest a maximum particulate size of 10 microns, therefore an inline pre-filter is advisable.
If your water source is from a borehole where there may be iron and manganese present, it is advisable to install and iron and manganese filter as well as a particulate filter to prevent rust stains and discolouration in the water.
If you are recovering rain water for use in washing machines, dishwashers, toilets etc. a dedicated series of pre-filtration will be required before the UV-C disinfection unit to mechanically remove the particulate load and increase the UVT. Please contact us if you have any queries.
Will UV-C inactivate Legionella pneumophila?
Legionella pneumophila is a thin, aerobic, pleomorphic, flagellated, non-spore-forming, Gram-negative bacterium of the genus Legionella. L. pneumophila is the primary human pathogenic bacterium in this group and is the causative agent of Legionnaires' disease, also known as legionellosis. UV-C Photons at a dose of 9.4 mj/cm^2 have proven a 4 log reduction (99.99%) of Legionella pneumophila sero group 1. - Cervero-Aragó et al. 2014
Will UV-C inactivate Pseudomonas aeruginosa?
Pseudomonas aeruginosa causes urinary tract infections, respiratory system infections, dermatitis, soft tissue infections, bacteremia, bone and joint infections, gastrointestinal infections and a variety of systemic infections, particularly in people with low immune responses. UV-C Photons at a dose of 10 mj/cm^2 have proven a 3 log reduction (99.9%) of Pseudomonas aeruginosa. - Abshire & Dunton 1981
Will UV-C inactivate Cryptosporidium?
Cryptosporidium is a microscopic parasite that causes the diarrheal disease cryptosporidiosis. Both the parasite and the disease are commonly known as “Crypto.” There are many species of Cryptosporidium that infect animals, some of which also infect humans. A dose of UV-C at 6mj/cm^2 inactivates Cryptosporidium spp. at a 4 log reduction (99.99%). - Qian et al. 2004
Will UV-C Inactivate E.Coli?
Escherichia coli (E. coli) is a bacteria that normally lives in the intestines of both healthy people and animals. In most cases, this bacteria is harmless. It helps digest the food you eat. However, certain strains of E. coli can cause symptoms including diarrhoea, stomach pain and cramps and low-grade fever. Some E. coli infections can be dangerous. The most familiar strains of E. coli that make you sick do so by producing a toxin called Shiga. This toxin damages the lining of your small intestine and causes your diarrhoea. These strains of E. coli are also called Shiga toxin-producing E. coli (STEC). A UV-C dose of 10mj/cm^2 will give 99.99% inactivation of the 6 main E.coli strains whilst a 14mj/cm^2 dose will give 99.99% inactivation of 97% of E.coli strains. Chen et al. 2015, Sommer et al. 1998, Bowker et al. 2011, Sholtes et al. 2016
What is Biofilm?
A biofilm is a collection of organic and inorganic, living and dead material collected on a surface. It may be a complete slime/film or, more commonly in water systems, small patches on pipe surfaces. Biofilms in drinking water pipe networks can be responsible for a wide range of water quality and operational problems. Biofilms can be responsible for loss of distribution system disinfectant residuals, increased bacterial levels, reduction of dissolved oxygen, taste and odour changes, red or black water problems due to iron or sulphate-reducing bacteria, microbial-influenced corrosion and reduced materials life (Characklis and Marshal, 1990).
Viruses and parasites like Cryptosporidium can be trapped in biofilms and bacteria such as legionella pneumophila will propagate. When a biofilm matures and starts seeding (releasing further bacteria into the water system) a risk of either consumption, infection or further contamination is present. Pseudomonas aeruginosa, is a notorious producer of slime and can be effectively inactivated with UV-C.
What Are the Key Benefits of UVC Disinfection Over Traditional Chemical Dosing in Water Treatment?
Water treatment using Ultraviolet (UV) light, particularly UVC photons, has several advantages over chemical dosing methods such as chlorination, ozonation, or chloramination. Some of the key benefits include:
No harmful by-products: UVC treatment does not produce harmful disinfection by-products (DBPs) like trihalomethanes (THMs) and halo-acetic acids (HAAs), which can form when chlorine reacts with organic matter in water. Some DBPs are known carcinogens and have been linked to various health issues.
Environmentally friendly: UVC disinfection is an environmentally friendly method, as it does not introduce any chemicals into the water. This makes it a more sustainable option for water treatment, especially in sensitive environments like natural water bodies or aquatic ecosystems.
No change in taste, odour, or pH: UVC treatment does not alter the taste, odour, or pH of the water, unlike some chemical disinfectants that can leave an unpleasant taste or smell.
Broad-spectrum disinfection: UVC photons are effective against a wide range of microorganisms, including bacteria, viruses, protozoa, and algae. This can help reduce the risk of waterborne diseases and improve overall water quality.
Rapid disinfection: UVC light inactivates microorganisms quickly, often within seconds, making it a fast and efficient disinfection method.
No risk of overdosing or underdosing: With UVC disinfection, there's no risk of overdosing or underdosing, which can be a concern with chemical disinfection methods. This ensures consistent and effective treatment.
Low maintenance: UVC systems typically require minimal maintenance, with the main task being periodic replacement of the UV lamps.
Cost-effective: UVC disinfection can be a cost-effective solution in the long run, as it requires less maintenance and avoids the need to purchase, store, and handle hazardous chemicals.
However, it's important to note that UVC treatment does not remove dissolved chemicals, heavy metals, or other non-organic contaminants. In many cases, a multi-barrier approach combining UVC disinfection with other treatment methods, such as filtration or chemical disinfection, is necessary to achieve comprehensive water treatment.
What are Hydroxyl Radicals?
Hydroxyl radicals (·OH) are highly reactive chemical species that contain one oxygen atom and one hydrogen atom. They are often referred to as the "detergent" of the atmosphere, as they play a crucial role in the removal of pollutants from the air.
Hydroxyl radicals are also important in water treatment processes. They are highly reactive and can quickly react with and break down a wide range of organic and inorganic contaminants, including pesticides, pharmaceuticals, and endocrine-disrupting compounds.
Hydroxyl radicals are produced through a process known as advanced oxidation. This process involves the use of ultraviolet light and/or hydrogen peroxide to create highly reactive hydroxyl radicals that can attack and break down organic contaminants in water.
Due to their highly reactive nature, hydroxyl radicals have a very short lifespan and do not accumulate in the environment. This makes them highly effective for removing contaminants from water without leaving behind harmful by-products.
Overall, hydroxyl radicals are a powerful tool for removing contaminants from air and water. They are highly reactive and effective against a wide range of pollutants, making them an important part of many environmental and water treatment processes.
What is UV AOP
UV AOP (ultraviolet light advanced oxidation process) is a water treatment technology that combines ultraviolet light with advanced oxidation processes to remove contaminants from water. The process involves the use of UV light to create highly reactive hydroxyl radicals that can oxidize and break down organic and inorganic contaminants.
UV AOP has several advantages over traditional water treatment methods. It is highly effective against a wide range of contaminants, produces fewer by-products, and operates at lower temperatures and pressures, reducing energy requirements. UV AOP has been used in water treatment applications for many years and is an important tool in the fight for clean and safe water.
UV AOP treatment processes can sustainable and environmental friendly alternative compared to traditional methods for organics removal.