Evoqua United States - Canada - EN

Shining a New Light on De-Chlorination

The water industry is changing its approach to de-chlorination

The drinking water industry has long relied on chlorine as its disinfection for the de-chlorination of drinking water. However, as regulations begin to tighten regarding the discharge of chlorinated water, and the penalties for failing to adequately control discharges become more severe, operators of municipal drinking water installations throughout the UK and Europe are finding a new use for an established, chemical-free technology – Ultraviolet Treatment Systems.

Chlorinated water, which is classified to the environment, wildlife and fish, has featured in the news numerous times in recent years due to chlorinated water being discharged into natural bodies of water, affecting the local environment and aquatic life.

During standard operations, when starting a drinking water plant or cycling treatment streams, it takes time for the required chlorine residual to reach the necessary levels to provide disinfection and meet the strict requirements of regulators such as the DWI. Therefore, set volumes of water are ‘run-to-waste’ and discharged to the environment until operators can confirm that the water is fit for human consumption.

Traditionally, a chemical such as sodium bio sulphide, have been used to de-chlorinate the water before discharge to protect the environment. However, due to the complex balance of chlorine vs sodium bio sulphide and difficulties in real-time water analysis, there is a high risk of under treated or over treated water slipping through and being discharged.

In addition, contact tanks and service reservoirs are regularly cleaned with a shock dose or wash down with high levels of Chlorine. Again, Sodium Bio sulphide tablets are used to reduce Chlorine levels before water is released into the environment. However, lack of standard practices surrounding this operation, and weaknesses in measurement and monitoring have again seen harmful levels of chlorinated water released into the environment.


In collaboration with a UK Utility company, Evoqua constructed an independently reviewed de-chlorination test rig and trial at its Lancashire headquarters in January of this year. A full 27 m3 tanker of chlorinated reservoir water was delivered to the atg UV site, where chlorine levels were increased in order to replicate a worst case scenario for the operator.

Results were conclusive, and following multiple trials, it was proven that when sized correctly, treatment with UV will effectively de-chlorinate water, and as a chemical free, physical technique using specially selected UV doses, de-chlorination with UV removes the complexities of dose, contact time and even chemical distribution.

Shining-a-new-light-on-de-chlorination De-chlorination by UV avoids all the pitfalls associated with both GAC and neutralising chemicals.



Whilst UV has been an established technology in the treatment of municipal drinking water and wastewater for over 50 years, chemical-free UV light is now a proven solution for the dechlorination of run-to-waste applications.

In response to operational requirements and to reduce capital expenditure and installation complexity, Evoqua have designed and developed a range of mobile, de-chlorination UV treatment packages that can be deployed by operators to site during run-to-waste startup scenarios that treat flows of 0.5 MLD to 8 MLD, with larger packages developed upon request.

These self-contained, mobile and fully equipped packages are available for both purchase and hire. The packages can be temporarily installed for the ‘run-to waste’ process, or contact tank cleaning process. Results are instantaneous and guaranteed.