Unique treatment process

Ruapehu Bulletin, 11 August 1992, Page 9

Unique treatment process

The recent commissioning of Ohakune's 150 m3/hour water treatment plant has finally provided residents and visitors with the clean, safe drinking water for which they have waited so long. The plant design originally proposed was modified several times during the past six years, due to changes in councils and increasing concerns about Giardia. The present governing body, the Ruapehu District Council (RDC) decided that construction of the plant had been delayed too long and went forward with what is believed to be a unique procedure for selecting the treatment process and plant design. After preliminary submissions were examined, four companies were asked to carry out trials and present a proposal. Each tenderer received $10,000 from the RDC, to cover the costs incurred in the

preparation and submission of their proposal. The council employed a specialist, Stu Clark of Works Consultancy, to assist in the evaluation of the tenders. Each company was required to present its proposal in the presence of a group comprised of RDC staff, the consultant and the other tenderers. Each submission was evaluated during its presentation, with the proposals being rated in categories of process and price. At the end of the meeting, the companies were informed that a decision would be made within two days and further discussion would not be considered. True to its word, the council made an announcement on the following day when it formally awarded the contract to Water Systems Treatment Specialists Limited (WS). It was learned that the WS proposal had been ranked first on process and sec-

ond on price. The company was praised for being the only one of the four tenderers to have carried out meaningful trials. Ohakune's water is sourced from a stream comprised primarily of ice-melt mountain runoff water. The mineral content is low, but there is turbidity and Giardia has been detected on occasions. Chlorination of the supply was not desired. The treatment system installed by WS incorporates some of the world's leading technology while, at the same time, remaining user friendly and generating only low operating costs. The process involves the injection of shortchain polymers in the water, prior to the supply passing through Culligan high-rate, multi-media filters which are capable of filtering down to 10 microns. To ensure the removal of Giardia, these are followed by

Culligan diatomaceousearth pressure filters, and then Katadyn ultraviolet disinfection to ensure the water is micro-biologically safe. Two significant features of this process are the use of diatomaceousearth filtration in potable water treatment plant and the installation of the country's largest UV unit is such a system. The Katadyn unit is manufactured in Switzerland and can treat up to 214 m3/h, with only six lamps and 470 W power input. WS's managing director, Clive Mulgrew, commented that the company was given possession of an empty paddock in March, but finished final commissioning in July. "The project went smoothly throughout the construction period and today, the people of Ohakune are now enjoying water of excellent quality," he said. "The tendering process employed by the council Tum to page 10

Unique

From page 9 worked very well and it highlights the fact that good results can be achieved when local bodies work directly with contractors."

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Ohakune's innovative Water Treatment Plant is officially opened, 1 August 1992.