Wastewater Treatment Plant

Wastewater Treatment Plant

The Wastewater Treatment Plant on Kioreroa Road is the largest processor of wastewater in the Whangārei district.

It processes an average of 21,000 cubic metres of wastewater from homes and businesses per day and has a replacement value of $65 million.

It treats wastewater for Whangārei’s main urban area, from Kamo in the north, Maunu in the west, Raumanga in the south to Onerahi and Whangārei Heads in the east.

Cleaning up the city’s wastewater involves a lot of steps – it is strained, mixed, filtered, feasted on by live bacteria, dried and disinfected. The resulting solid waste is taken to landfill and the treated water is discharged via constructed wetlands into the Limeburners Creek.

 

The wastewater process

The wastewater process consists of the following 6 steps: 

Step 1.Screening

Wastewater is screened to remove paper and other debris.

Step 2.Separating solids from liquids

Large settling tanks separate the wastewater – the solids (sludge) sink to the bottom and the fats and oils float to the top. The sludge, fats and oils are pumped to sludge digestors while the liquid flows to the basalt rock filters.

Step 3.Magical microbes

In our basalt rock trickling filters live millions of microbes that eat and digest the organic compounds in the wastewater. This is a 100% natural way to treat wastewater and these bugs are our heroes, doing all the hard work for us without the need for nasty chemicals.

These bugs are very susceptible to chemicals which is why it is important not to flush things like paint down our drains.

Step 4.Superbug soup

The aerators are like two giant eggbeaters – adding oxygen into the wastewater to create a nutrient-rich soup for superbugs that consume microscopic particles in the water.

Step 5.UV treatment

Before being discharged to the wetlands, the effluent is disinfected by ultraviolet (UV) tubes that kill any remaining bugs.

Step 6.A final filter

The treated water receives a final filter through thousands of native plants in the Limeburner Creek Wetlands.

In 2014, the wetlands had a major makeover and instead of the plants being planted in the ground they are now planted on floating mats, their roots extending down into the water. You can explore the wetlands, which provide a great habitat for birds, via a timber boardwalk.

  • The sludge digestors

Solid waste collected during the process is heated in two large digestors. Digestion reduces the total mass of solids, destroys pathogens, and makes it easier to dewater or dry the sludge.

The sludge is then fed into a conical sieve and spun around at speed to ‘squeeze’ out excess water, after which it is taken away to landfill. Two biogas generators harness the poo power created by methane gas during the sludge treatment process and turn it into electricity.

Does untreated water go into the harbour?

No, untreated water does not go into the harbour from the wastewater treatment plant.

When it rains, extra water enters the wastewater system and the plant struggles to cope with the higher flow. On a normal day, discharged water goes through the full treatment process but during storms this process is shortened. During storms, wastewater undergoes screening, settlement, disinfection by ultraviolet light and wetland treatment.

What is Council doing to improve harbour water quality?

Over the past ten years Council has spent $60 million improving water quality in the harbour through a number of successful projects.

In the past, heavy rainfall would trigger sewerage spills into the harbour due to stormwater and groundwater entering and overflowing the wastewater system.

The multi-million dollar projects completed to date include:

  • New storage and treatment facilities at Whareora Road and Tarewa Park which contain and treat extra water that enters the system during storms
  • Major upgrades to the Wastewater Treatment Plant which means all wastewater receives ultraviolet light and other treatments before being discharged into the wetlands
  • Upgrades to the Okara Park pump station and pipeline
  • Wastewater pipe renewals across the network

These improvements have dramatically reduced the number of sewerage spills into the harbour.

Council has also increased spending on stormwater as part of the 2018 - 2028 Long Term Plan to further improve harbour water quality.