In the middle of June 2021, Matamata Piako District Council (MPDC), Filtec and Lutra began physical work on the renewal of all 12 gravity filters in the district. The project comprises of renewal of the existing media, replacing the nozzles and increasing the height of the backwash launders.
The Matamata Piako district has three WTP's running gravity filters:
- Tills Rd WTP (Matamata) has three direct filtration filters with anthracite as the media. These filters are all original Patterson Candy designs constructed in the 1960's.
- Te Aroha WTP has 4 gravity filters, two were original Patterson Candy design (1960's), and two more were constructed in 2006. The existing media in these filters is sand.
- Morrinsville WTP has five gravity filters all original 1960's Patterson Candy design. As Te Aroha the existing media is sand.
As part of the project scope, it was decided to opt for anthracite media, with two support layers of gravel at all 3 WTP's. To accommodate this, modifications had to be made to the backwash launders in the Te Aroha and Morrinsville filters as a larger volume of media was required.
The anthracite media and nozzles were shipped from Australia in 10 x 20-foot shipping containers in early 2020. Work began on the 17June at Tills Rd WTP. The decision was made to start at Tills Rd primarily due to access issues making the loading of the new media very labour intensive. At Morrinsville and Te Aroha WTP we can use 1T sacks and a crane to unload the media into the filters.
At Till Rd WTP, 22kg bags had to be manually transferred and loaded into the filters. Below is a breakdown of how many bags were needed per filter:
-
120 x 22kg bags of 6-12mm gravel.
- 72 x 22kg bags of 3-6mm gravel.
- 432 x 22kg bags of Anthracite media.