Hopes Reservoir is located in the scenic Lammermuir Hills, East Lothian, Scotland, and is operated by Scottish Water for the supply of drinking water to approximately 2,500 residents.
The typical daily demand from the site is 2.5 million liters, with additional capacity to supply 4 million liters at times of peak demand.
As part of an ongoing water quality redevelopment strategy to ensure continuous improvements, Scottish Water chose to include ultraviolet water treatment as a worthwhile addition to the existing infrastructure, to further increase the quality of the water supply for the local area.
The existing system flows raw water under gravity to the works from Hopes Reservoir. Before entering the works building the raw water is dosed with aluminum sulfate, a coagulant to form flocs and remove colloidal particles and micro-organisms from the water. After coagulation, the water flow is divided between twelve pressure filters. This type of filter is fully enclosed and flows downwards through sand media. These pressure filters remove the flocs caused by coagulation from the water, together with any other suspended matter, impurities, and bacteria. Water flows into the top of each filter before passing through the sand media.
As the water passes through the sand, impurities are trapped within the voids between the grains. This causes the media to become progressively choked, as measured by the increasing pressure drop across the filter (i.e. loss of head). Clear filtered water emerges from the bottom of the filter. The sand media requires periodic backwashing to restore the filter to its original condition.
Clean filtered water leaves the building via a 12-inch pipe, which passes through the same chamber as the raw water inlet pipe. A manual isolation valve is located within the chamber. Further downstream, the filtered water is disinfected using sodium hypochlorite.
In collaboration with Daro UV, two 3rd party ÖNORM M 5873-1 validated MR4-220 SSV systems were installed at the facility.
While the production and delivery of the two UV systems were organized, the initial pipework and structure were prepared. The final UV system delivery consisted of a completely prefabricated framework, as a plug-and-play on-site solution. As the project included compact installation space, this was a huge advantage to make the best use of the limited available space. Additionally, it allowed the whole system to be assembled efficiently while minimizing the amount of work required at the installation site.
To reach the stringent levels of the water quality redevelopment strategy that Scottish Water aimed to achieve, a UV disinfection treatment stage was added to the existing infrastructure at this final stage to further improve the water supply before the treated water flows to the local supply. UV technology was selected due to its many advantages such as no additional dosing of chemicals to the water, coupled with its capabilities for inactivating waterborne pathogens that are resistant to chlorine and other disinfectants, such as Cryptosporidium and Giardia. UV also possesses other desirable traits, such as not affecting the taste, color, or clarity of the water, while achieving a 4-log reduction in microorganisms and harmful microbes.
The units are operated in a duty/duty configuration, which means zero run-to-waste during occasions where the isolation of one unit is required, such as during servicing or maintenance. The ULTRAWIPER™ system ensures that quartz sleeves are cleaned at regular intervals with wiping scheduled twice daily, to ensure that the UV-C output levels from each of the four UV lamps in the reactor are kept at operational levels while preventing any deposits from building up on the quartz sleeve.
Since the installation, over a year has passed with no breakdowns or failures of the equipment or lamps, highlighting the reliability and quality of the validated UV system. All involved stakeholders continue to be satisfied with the overall speed, quality, and delivery of the project.
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