DRINKING WATER – RURAL WATER AUTHORITY – AUSTRALIA
- pH Corrected
- Improved Disinfection
- Colour Improved
- Multiple Sites Treated With One Neutra-Mill
- Turbidity Lowered
- Requires Minimalexisting Infrastructure At Site
North-central Victoria, Australia. 150 kilometres north of Melbourne (Latitude: 36° 30′ S, Longitude: 145° 00′ E).
SETTING AND CLIMATE
The Goulburn Valley is recognised as one of the “food bowl” areas of Australia. Despite an annual rainfall of only 500mm, the region hosts a multi-billion dollar food industry based on dairy and horticultural produce. Much of this activity is dependent on irrigation derived from the Goulburn River through an extensive network of irrigation channels.
Goulburn Valley Water (GVW).
For most towns in the region, raw water for drinking purposes is sourced from clay-lined open irrigation channels, and is often of poor quality. Treatment facilities are not always present, especially in the smaller towns where it is generally uneconomic.
Raw water from the irrigation channels requires treatment to lower turbidity, improve colour, pH correction and disinfection to satisfy drinking water guidelines (5 NTU, 15 HU, pH 6.5-8.5). While most small towns have in-line chlorine gas disinfection systems, only a limited number have any additional beneficiation equipment, and very few could justify the expense of a conventional treatment plant. As a consequence residents tended to rely on rain water as their primary source of drinking water.
Following successful trials, a purpose-built mobile Neutra-Mill system, the Turbidity Mill, was developed and is now used as the primary method of coagulation/flocculation for five separate towns for the authority. The unit is transported to a site requiring treatment, treatment is conducted and then the unit is transported to the next site – often on the same day.
Once onsite the unit is deployed to the waterbody, charged with reagent (aluminium sulphate – alum, and/or hydrated lime) and then slowly propelled across the surface of the water body whilst it dispenses reagent. Further reagent is added continuously as required until the entire waterbody is treated.
Chemical dispensing can take as little as 2-3 hours, and clarification occurs in 2-7 days. The water storage capacity at many small towns means that treatment need only be conducted periodically (eg. 1-4 times per annum) rather than continuously.
Since routine water treatment started with the Neutra-Mill all water quality analyses for these five towns have stated “This water complies with the recommended guidelines [WHO] for drinking water quality”. Typical water quality analyses are presented in the table below showing conformance with WHO Water Quality Guidelines.
Significant cost benefits have been achieved by using one Turbidity Mill unit to treat the drinking water at the five towns:
- Capital costs – one Turbidity Mill unit cost $45,000 compared with planned conventional plant costs of $250,000-$400,000
- Operating costs – between 3-6 cents per thousand litres of WHO quality drinking water.
Raw water treatment with the Turbidity Mill had the additional benefits of lowering chlorine dosing requirements, raising residual chlorine levels in reticulation systems, and reducing consumer complaints.
|Typical water quality data; October 1999.|