When much of NSW faced drought conditions for more than five years, the inland city of Goulburn became a symbol of the hardships faced by the State as a whole.
The situation in Australia’s first inland city attracted national attention as drinking water dam levels plunged, ratepayers halved their water consumption, level five water restrictions were introduced, and the Goulburn Mulwaree Council prepared contingency plans to truck in drinking water if things didn’t get better.
Fortunately, things did get better over the last year, but the council has continued with water conservation and water quality initiatives that will stand it in good stead for the future - and perhaps serve as a model for other centres increasingly facing similar issues in the face of global warming.
One of Goulburn Mulwaree Council’s successful initiatives involves the selection of medium pressure ultraviolet (UV) disinfection for its effluent irrigation scheme, which has conserved potable water, achieved high water discharge quality and resulted in savings of several hundred thousand dollars in civil works associated with the scheme.
The project’s main contractors, Ted Wilson & Sons, submitted an innovative design for a pressured on-demand irrigation scheme, simplifying the infrastructure and providing the council with a more economical project – as well as reducing the long term operating cost.
CST Wastewater Solutions (formerly Contra Shear Technology) was awarded the UV disinfection equipment supply contract. The company chose Berson InLine medium pressure lamp technology that is now fully integrated into the council’s PLC/SCADA process control system.
Berson UV-techniek developed the cross flow in-line system now employed in the Goulburn Mulwaree effluent irrigation scheme.
Pieter Groenewegen, Business Manager of CST Wastewater Solutions, said that the germicidal properties of ultraviolet (UV) light are now understood and have become widely accepted as a method of wastewater disinfection. Medium pressure UV technology is relatively new in Australia but is rapidly gaining recognition for its advantages.
He also said that many wastewater treatment plants worldwide are now using UV technology, with an increasing emphasis on reuse applications.
According to Greg Finlayson, Manager Water Services, Goulburn Mulwaree Council: “We were already using effluent for irrigation but the UV treated effluent gave the council more opportunities for reuse – as well as improving the quality of water that eventually finds its way into the Wollondilly River, which is part of the Sydney Water catchment.”
“The UV disinfection system is achieving a good microbial kill rate and the overall performance of the completed scheme is excellent,” said Marina Hollands, water and waste engineer, Goulburn Mulwaree Council.
There are two main types of UV mercury lamps for disinfection. Low pressure monochromatic lamps that have a single wavelength spike of 254nm, while medium pressure UV is polychromatic with a variety of wavelength spikes.
Both disinfect, but the medium pressure technology prevents photo-reactivation.
The Goulburn Mulwaree construction contract, completed in 2007, was originally based on a NSW Department of Commerce design that called for pumping from the storage pond through an in-channel low pressure UV disinfection system to a secondary 200 cubic metre storage tank, followed by an on-demand pumped irrigation system.
The alternative Ted Wilson design took an innovative approach, selecting high efficiency submersible pumps, eliminating a new pump wet well, plus eliminating the secondary tank and pumping directly to the irrigation scheme from the storage pond through the Berson UV system as an on-demand irrigation system.
The advantages of this system were:
- Lower capital cost - the single pump station resulted in simpler infrastructure.
- Much simplified construction - the storage pond embankment would have required significant reconstruction to fit the new pump wet well and the concrete channel for the UV disinfection. The new design used a floating pontoon for the submersed pumps. The medium pressure UV system is in-pipe and has a compact foot print.
- Lower operating cost - a single pump station uses considerably less operating power and maintenance is simplified. The medium pressure UV system has fewer lamps and is easier to maintain. Everything is accessible above ground with no need for lifting gear.
A low-flow jacking pump system maintains the irrigation system pressure when there is no demand.