Quay Technologies, Ltd. was asked by Scottish Water in the U.K. to help resolve a problem at a coastal water treatment plant in Rockcliffe near Dumfries. The area has a population of about 300, which rises to 2,000 in the summer months.
The site had failed to meet consent for the Scottish Environment Agency (SEPA) bathing water regulations in 2002 and 2003. The existing plant had only secondary treatment consisting of a proprietary fine screen, activated sludge plant and a final settlement tank.
Tertiary treatment needed
Investigation by Scottish Water and the SEPA established that tertiary treatment was needed at the Rockcliffe wastewater treatment works. This required the installation of an ultraviolet (UV) disinfection system. A proposal was submitted by Quay Technologies to provide a suitably engineered system that could be installed onto what was a compact site in terms of size and location. It was agreed that Quay Technologies would supply its novel UV system with the option for the system to become a permanent installation if all the requirements were met.
System features & design
The system to be installed included Quay's patented high-intensity UV technology, which makes use of "electrode-less" lamps excited by a microwave power source. The Quay system has numerous advantages over conventional low-pressure and medium-pressure UV systems, and this has been demonstrated at Rockcliffe.
One of the major benefits is the longevity of an electrode-less lamp. Failures in conventional lamps are often due to the electrodes, which can cause complete failure and a diminishing output over time. A conventional low-pressure lamp normally has a life of approximately one year; medium-pressure lamps last about six months. A Quay lamp has a guaranteed life of three years and can be expected to last much longer without any reduction in UV output.
Other benefits include a low operating temperature, which prevents the problems normally associated with medium-pressure systems, where the quartz sleeves require chemical cleaning and the lamps require a permanent flow or cooling. The Quay system has a much smaller footprint than low-pressure systems due to the higher output of a Quay lamp. The Quay lamp also has flexible dose output-the lamps can be turned up or down to reflect the changes in flow rate, which reduces the power consumption.
Compared to a conventional low-pressure lamp, the Quay lamp has the same output spectrum and similar electrical efficiency, which means that most of the UVC produced is at 254 nm-the most efficient germicidal wavelength.
The UV system provided for Rockcliffe comprises a 316 stainless steel chamber, which is 1,000 mm long and 400 mm in diameter. There are four 1-kw high-intensity, low-pressure Quay lamps within the chamber; four microwave power supplies; and a wiper mechanism and internal baffles to ensure that all the effluent is treated. There is also a UV monitor to ensure that an optimum dose is provided.
Meeting stringent consents
Operation of the Quay UV system between March and December 2004 showed that the treatment was effective on flows ranging between 4 and 15 l/s with UV transmissivity as low as 45%. The SEPA took a total of 20 tests on the beach at Rockcliffe, and the bathing water met consent for the first time in three years. Further testing at the outlet of the UV plant confirmed that the bacteria kill met the most stringent consents.
During the 10 months of 24-hour operation, the Quay system had no failures, downtime or maintenance requirements. The only operating costs have been for the power consumed (up to 4 Kw per hr, depending on demand).
Scottish Water Solutions has now asked for the system to be permanently installed, and the controls are undergoing further enhancements to meet Scottish Water specification.
