UV Disinfection

UV disinfection inactivates pathogens physically without chemicals, producing no disinfection byproducts and leaving no residual disinfectant in the water. Chlorination is more effective at providing a residual disinfectant for distribution system protection but can form regulated byproducts such as trihalomethanes and haloacetic acids when reacting with natural organic matter. UV is significantly more effective than chlorine against Cryptosporidium and Giardia cysts. In municipal drinking water treatment, UV and chlorine are frequently used together, with UV providing primary pathogen inactivation and chlorine providing distribution system residual.

UV dose, expressed in millijoules per square centimetre (mJ/cm²), is the product of the UV intensity delivered to the water and the exposure time within the reactor. It is the key parameter determining disinfection efficacy for a given pathogen and log reduction target. UV dose is validated through biodosimetry testing using challenge microorganisms under defined flow and water quality conditions. Ongoing dose delivery is verified continuously by calibrated UV intensity sensors within the reactor, with real-time monitoring and alarms integrated into the PLC control system.

Regulatory requirements for UV dose vary by jurisdiction and target pathogen. A dose of 40 mJ/cm² is widely accepted as the minimum for 4-log inactivation of bacteria and viruses in drinking water. For Cryptosporidium and Giardia, a dose of 10 mJ/cm² achieves 3-log inactivation and 40 mJ/cm² achieves greater than 4-log inactivation. USEPA and WHO guidance documents and European standards such as DVGW W294 and ONORM M5873 specify validated dose requirements for specific log reduction credits. IWTE designs each system to the dose specified by the applicable standard and regulatory framework.

UV transmittance (UVT) is the percentage of UV light at 254 nanometres that passes through a 1-centimetre path length of the water sample, and is a direct measure of how much UV energy reaches the target microorganisms in the reactor. Lower UVT, caused by dissolved organics, colour, iron or turbidity in the water, reduces the effective UV dose delivered for a given lamp intensity. IWTE designs UV reactors using site-specific UVT data to ensure the system delivers the validated dose across the full range of expected water quality conditions, including seasonal variation.

Yes. UV disinfection is one of the few treatment technologies proven effective against Cryptosporidium parvum oocysts, which are highly resistant to chlorine disinfection at normal drinking water doses. A UV dose of 10 mJ/cm² achieves 3-log inactivation and 40 mJ/cm² achieves greater than 4-log inactivation of Cryptosporidium. This makes UV a critical treatment barrier in surface water and groundwater under the direct influence of surface water where Cryptosporidium is a regulatory concern.

Low-pressure and low-pressure high-output UV lamp assemblies typically achieve service lives of 12,000 to 16,000 operating hours before lamp output degrades below the level required to maintain the validated dose. Medium-pressure lamps have shorter lives of 8,000 to 12,000 hours but produce higher intensity output from fewer lamps. IWTE programmes lamp life monitoring and replacement alerts into the PLC control system, and supplies genuine replacement lamp assemblies and sleeve seals through its spare parts programme.

Yes. IWTE designs and supplies UV disinfection systems as standalone units and as integrated disinfection stages within complete water treatment plants, reuse systems and high-purity water trains. The UV system is engineered to match the plant flow rate, water quality and disinfection objectives, with unified PLC and SCADA control across the full treatment train. IWTE also provides commissioning, dose validation support, operator training and ongoing service and lamp replacement contracts.