Sand Removal: Past Industry Operation In Present Water Treatment Process

During the 1950’s pumice sand was dredged from a section of the Waikato River near Tuakau. This sand was used for commercial purposes, primarily to support the booming residential construction industry in Auckland.

In 2002, the Waikato Water Treatment Plant (WTP) was commissioned with intake infrastructure installed in the Waikato River. The location of the plant’s inlet screens was determined based on the depth of the river and distance from the underlying sand banks. However, bathometric data has shown that the sand banks in the river are constantly on the move, and the plant experiences periods of heavy sand loading in the water abstracted by the Waikato WTP. The presence of sand in the abstracted water reduced process efficiency/performance and ultimately the plant’s capacity. These periodic events caused damage to equipment and the sand itself was extremely expensive to remove from the installed process units, with the confined space entry required to do so.

To address the sand loading issue, multiple measures have been implemented, most prominent of which is a sand separation system.

This system consists of six LAKOS sand hydrocyclone systems, capable of operating together, at the maximum plant capacity (175,000 m3/day treated water production). The hydrocyclones produce a raw water supply with a significantly reduced quantity of entrained sand, and graded river sand.

The graded sand separated from the raw water is of excellent quality, and has been used as a construction material during recent upgrades to the WTP. Now, over half a century later, Watercare is currently investigating a number of future beneficial uses for this valuable resource.

This paper outlines the sand removal options considered for Waikato WTP, those implemented (in addition to the sand separation system, this also includes installation of a sand mobilisation pump in the raw water wet well), the lessons learnt and outcomes from this process.