FACT SHEET 3 PALMERSTON NORTH CITY COUNCIL BEST PRACTICABLE OPTIONS REVIEW
PALMERSTON NORTH’S EXISTING WASTEWATER SCHEME
THE EXISTING WASTEWATER SCHEME Palmerston North City Council provides a wastewater system that collects and treats the majority of the city’s wastewater and trade wastes. The collection and treatment methods must meet strict public health and discharge standards. Every year, up to 12.9 billion litres of wastewater is collected from 25,300 connections around the city. Thirty four pumping stations help move the wastewater along a network of pipes that, if laid on end, would stretch for 404 kilometres. Council operates three treatment plants: Tōtara Road, being by far the largest, with supporting plants in the communities of Ashhurst and Aokautere. The following diagram shows the various inputs into the existing wastewater scheme, and how wet weather flows also enter the scheme.
Ashhurst, Bunnythorpe & Longburn Oxidation ponds at Ashhurst and Longburn Communities Tōtara Road WWTP
Residential Discharge to PNCC Urban Area Manawatū River Domestic Wastewater (Sewage)
Business/ Commercial/ Industrial Basically Domestic Wastewater (Sewage)
Wet Industries
Trade Waste Discharges
Raw Wastewater (Sewage) Dry Weather Flow 24,000m3 per day Peak Wet Weather Flow 120,000m3 per day 99% Water Ratio around 5 times
Wastewater (Sewerage) Scheme 8% Daily Volume Connections 25,300 23 LARGE WET INUSTRIES DISCHARGES Pipelines 404km 35% organic strength WITH INDIVIDUAL TRADEWASTE CONSENTS Pump Stations 34 8% total phosphorus Oxidation Ponds 2 Treatment Plants 3 Manawatū River Discharge
Wet Weather Flows Downpipes, Gully Traps etc Surface Water + Stormwater Low Area Service Access In ltration + Surface Water & In ow + Ground Water Sewer Connectors (l&l) Ground Water Seepage Seepage
Public Sewer
ABOUT THE TŌTARA ROAD WASTEWATER TREATMENT PLANT The Tōtara Road Wastewater Treatment Plant (WWTP) has the capacity to serve a population of 100,000. It is made up of one plant that has two aerated lagoons which undertake the secondary or biological treatment phase of the overall process. Around 24 million litres of wastewater arrive at the plant every day during dry weather, and this can increase to 120 million litres per day during heavy wet weather.
Revision: 6 August 2018
HE TIROHANGA HOU KI TE WAI PARA | A FRESH LOOK AT HOW WE MANAGE WASTEWATER HOW WASTEWATER IS TREATED AT THE TOTARA ROAD WASTEWATER TREATMENT PLANT The WWTP provides preliminary, secondary and tertiary phosphorous removal and UV disinfection treatment to the wastewater before it is discharged to the Manawatū River. The WWTP removes the majority of contaminants from the wastewater before it is passed through a wetland pond for further treatment in response to Māori cultural concerns. It is then discharged to the Manawatū River, through a rock structure located on the river bank. During wet weather, lagoons are also used to store excess treated wastewater, to ensure that consented discharge limits are not exceeded. The diagram below depicts the arrangement of treatment processes at the WWTP.
Emergency Out ow to Mangaone Stream
Incoming untreated wasterwater Screening 2 Pre-aeration & 3 Primary 4 Secondary Sedimentation Screenings to composting Grit Removal Sedimentation Tanks in erated Lagoon
Grit to land ll Sludge to sludge Wastegas Flare digestion
Bio Gas Generator Sludge Digesters
Dewatering Composting
5 Phosphorus (DRP) Removed at Low River Flows
8 Rock Land Passage Dose coagulant chemical Discharge
9 Final Treated 6 UV (Ultra Violet 7 Wetland Pond Sludge Wastwater Discharge Clari er Composting Dewatering Light) Disinfection to Manawatū River
The marked up aerial photo shows the location and interrelationship of the main treatment processes.
TYPICAL PLANT FLOW
1 2 Screens
3 Primary Treatment 3 Sludge Digsestors
4a Aerated Lagoon
5 Clari er for Dissolved Reactive Phosphorus
4b Aerated Lagoon
8 River discharge through rock structure 6 UV Disinfection
7 Wetland Pond