One unit was installed at the Bradan WTWs, another at the Tullich WTWs and one was transported throughout the region as needed at other Scottish Water facilities.
Prior to the purchase of the online THM monitors Scottish Water relied on standard laboratory analysis. Analytical results could take up to a week to be returned, making it very difficult for operations staff to fully optimise the treatment processes at any given facility since they were working off THM results that were a week old.
The THM-100 monitor enabled Scottish Water to have visibility of process improvement changes and their impact on DBP formation by providing the operational staff with immediate and accurate daily reports on THM levels. The THM-100 proved especially valuable at the Tullich WTWs when the facility tested and implemented an aeration system to further minimise THM formation.
Online THM Monitor Validates TRS Process
The Tullich Water Treatment Works in Oban, Scotland services the needs of approximately 13,000 inhabitants through a 11,000 m3/day plant consisting of pre-filtration using microstrainers, pre-ozonation, granular activated carbon and post-ozonation.
Chlorine gas is used as the primary disinfectant. THMs are formed when natural organic matter present in the water reacts with the chlorine disinfectant during the water treatment process. A profile of the THM levels at the Tullich WTWs from February 2014 to December 2015 is detailed in Figure 1, data was provided by the online THM-100 monitor.
When Tullich was built in 1970s it was a state-of-the-art WTW designed to meet the challenges for that period. New water quality regulations introduced to protect and improve public health require Scottish Water to invest in a new WTW that will be commissioned by the end of 2017. Until then a concerted effort by staff is required to optimise treatment processes and keep the current facility in compliance with all quality standards.
Having already optimised its existing process scheme, Scottish Water introduced aeration at the Tullich WTWs in 2015 to aid THM removal. As volatile organic compounds, THMs can be removed from water through volatilization given sufficient gas transfer opportunities. When water is exposed to and mixed with air inside a reservoir, the THMs are transferred into the air and can escape.
There are four primary species of THMs; chloroform (CHCl3), bromodichloromethane (CHCl2Br), dibromochloromethane (CHClBr2) and bromoform (CHBr3). Chloroform is the most volatile of the primary THMs and is the most dominant THM speciation found in treated water at the Tullich WTWs, averaging approximately 70%.