Severn Trent Services can now monitor Trihalomethanes (THMs) on line in processed water, using the AquaSen THM100 On-line Total Trihalomethanes Monitor. THMs are the most prevalent disinfection by-products. They are formed when chlorine used in water treatment and bromine react with naturally occurring organic compounds in raw source water. THM regulation is enforced by UK drinking water regulations and is part of the requirement for the Operational Performance Assessment. UK Regulations prescribe that drinking water can’t exceed 100ug/l with similar levels being maintained throughout the EU.
There is also a general obligation to reduce the levels of THM as far as possible.
The Aquasen THM100 system enables real-time monitoring of disinfectant by-products (trichloromethane, dichlorobromomethane, chlorodibromethane and tribromethane) enabling process control of disinfection. The monitor allows for periodic (hourly), near real-time results, providing many advantages, not least that process conditions can be adjusted so that levels of THMs remain within the regulated limit at all times. Action can then be taken immediately in the event of any changes.
In particular, warnings of upward trends will aid in avoiding incidents and therefore potential fines for Water Companies. It also means that the use of chlorine in disinfection and the coagulants used in reducing THMs can be monitored consistently and adjustments can be made on a much smaller time frame. This increases potential savings in the raw materials used for disinfection and coagulation.
Currently, THMs are measured by routinely taking samples during water production, transporting samples to a lab and analysing them using Gas Chromatographic techniques, which generally produce results within 3-10 days. This can lead to a delay in taking action when incidents occur. The intermittent nature of sampling is unable to reflect the changes in THMs due to rainfall, agricultural activities, ambient temperature etc.