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Waikato River water treatment

The Waikato Water Treatment Plant is the one of the most sophisticated water treatment plants in Australasia. Located in Tuakau, some 40 km from the mouth of the Waikato River, the Waikato Treatment Plant was opened in 2002. Currently, it can treat a peak capacity of 150,000 m3 of water per day; an upgrade is currently under way to improve resilience and provide a sustainable production of 150,000 m3 per day and a peak production of 175,000 m3 per day.

The treatment plant removes microbiological, chemical and radiological contaminants via a four-stage, ultra-filtration treatment process, detailed below. The world leading membrane filter technology used here has already proved effective in other countries including France, America, Canada and Great Britain, where it is frequently used to treat raw water with considerably higher levels of pollutants, bacteria and viruses than are present in the Waikato River.

 

How the Waikato River water is treated

Step 1: Coagulation and clarification

After first passing through a screening filter to remove large debris such as leaves and branches, coagulant (aluminium sulphate or ‘alum’), lime, and carbon dioxide are mixed into the water. This causes the tiny dirt particles to stick together, making for easier removal. The water is then piped into settling tanks, where the mixture of alum and dirt (known as ‘floc’) sinks to the bottom of the tank.

Step 2: Membrane filtration

The clarified water is then treated by advanced, ultra-filtration membrane technology to remove pathogenic organisms. The pores of the membrane filters are so small (about 15 times smaller than the filter system in household water filters) that they prevent the spores of parasites, giardia, and cryptosporidium from passing through.

Step 3: Granular activated carbon filtration

During this stage, any organic compounds are adsorbed onto carbon particles. Carbon also removes any unpleasant tastes or odours from the water.

Step 4: Chlorine treatment

In the final stage, chlorine is added to the water to kill any remaining viruses and prevent bacterial growth during storage and transportation. The sophistication of the treatment process means the Waikato Water Treatment Plant uses around one-third less chlorine than Watercare’s other treatment plants.