The Raetihi Wastewater Network provides for the collection and treatment of wastewater generated from approximately 629 properties within the Raetihi community.
The below schematic shows flow through the network:
The Raetihi wastewater collection network is partly made up of clay and asbestos pipes which were installed in the 1970s. An ongoing relining program has seen quite an extent of the town re-lined with PVC (plastic) pipe which achieves the following:
- Extends the life of the pipe by 30 years
- Reduces root intrusion and inflow of groundwater from unsealed joints.
Wastewater Treatment Plant
Wastewater is transported through the Raetihi Wastewater Network to the Raetihi Wastewater Treatment Plant, where it is treated prior to discharge.
The Raetihi Wastewater Treatment Plant provides treatment of wastewater through the following steps:
1. Primary Treatment
1.1 Primary Oxidation Lagoon: Wastewater is piped into a Primary Oxidation Lagoon where heavier solids separate from the wastewater through settling as sludge to the bottom of the lagoon. This sludge is colonised by anaerobic bugs (bacteria that don't need oxygen to survive) which help to break it down by using it as a food source. Bugs also live suspended in the wastewater and use up organic matter “food” throughout the lagoon.
2. Secondary Treatment
2.1 Secondary Oxidation Lagoon: Wastewater remaining at the top of the Primary Lagoon contains less solids and is piped through a curtain to the Secondary Oxidation Lagoon where further settling and removal of organic solids takes place. Bugs are present in this lagoon in lower numbers and need oxygen to survive. The below figure shows the Primary and Secondary Oxidation Lagoons sitting adjacent to one another.
3. Tertiary Treatment
Discharge of treated wastewater to the environment
The treated wastewater from the Raetihi Wastewater Treatment Plant is discharged into the Makotuku River.