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Email Link   Banora Point Wastewater Treatment Plant

The Banora Point Wastewater Treatment Plant underwent a major $35 million upgrade to service population and industrial growth in the region, while protecting the environment of the lower Tweed estuary.

The Banora Point Wastewater Treatment Plant services an area which, due to new housing developments and increased housing density, continues to experience considerable population growth. Further population growth is anticipated and the plant’s capacity needed to be increased to meet this heightened demand.

In addition, planning and environmental review studies identified that improved effluent quality from the plant would have beneficial effects on the quality of water in the lower Tweed estuary. The upgrade design included processes to significantly reduce nutrient levels in the final effluent discharged from the plant.

At a Glance

Location:Enterprise Avenue, Tweed Heads South
Services: Tweed Heads, Banora Point, Terranora and Bilambil Heights
Capacity: Up to 18 mega litres per day or approximately 75,000 people
Treatment: Tertiary level
Uses a biological nutrient removal process for the treatment of raw sewage.
Discharge Point:Terranora Inlet near the Dry Dock
Upgrades:In 1995, the Banora Point wastewater treatment plant was upgraded at a cost of $18 million.

To expand the capacity to 75 000 people another upgrade commenced in 2010 and being completed in December 2012. The total cost of the upgrade was $35 million. The project was funded by Council, with the assistance of a $16.8 million interest-free loan under the NSW State Government Local Infrastructure Fund.


Environmental Licensing and Monitoring

For details regarding the Environmental Protection Licence and Environmental Protection Authority (EPA) Pollution Monitoring, see Environmental Monitoring.

Primary Treatment

Banora Point WWTP Step ScreenStep Screen at Inlet of WWTP

Raw sewage enters the inlet works via four rising mains. Here the incoming (influent) flow is measured and it receives its Primary Treatment with the removal of debris and grit.

A Step Screen with 3mm apertures removes large foreign objects, rags and materials. Approximately one cubic metre is removed a day or about 365 m3 a year. This is placed in a skip bin and taken away to be disposed of.

Grit is removed by slowing the influent flow down to less than 0.3 metres/sec. Sand and most inorganic suspended material settle out and are removed. Similar quantities of grit are removed and taken away with the screenings.

The flow is calculated by measuring the depth of water before a narrowing section of channel (flume). An electronic ultrasound device measures the depth of water, these readings are sent to a microprocessor which calculates and records the flow. The average dry weather flow into the treatment plant is approximately 11.5 - 12.5 mega litres per day.

Biological Reactors

The Biological Reactors are divided into four separate zones. The influent is mixed with the active sludge (micro-organisms) returning from the clarifier.

Denitrification Zone (Secondary Anoxic Zone)

This zone removes nitrates in the return activated sludge (RAS) before it mixes with the influent in the selector chamber. This zone is deficient in dissolved oxygen so the micro-organisms utilise the nitrates (NO3 2- ), consuming the chemically combined oxygen and releasing nitrogen gas to the atmosphere.

Anaerobic Zone

Banora Point WWTP BioreactorBioreactor From the selector chamber, raw sewage combined with returning activated sludge flows into the anaerobic zone. As neither have dissolved oxygen or chemically combined oxygen available for micro-organism respiration, this environment promotes the release of phosphorus from the bacterial cells. In this zone fine particles in the raw sewage stream begin to clump or floc.

Anoxic Zone

This zone receives recycled flows from the Aeration Zone which are rich in oxidised nitrogen compounds (nitrites and nitrates) and flows from the Anaerobic Zone. This zone is also deficient in dissolved oxygen, promoting the denitrification of the oxidised nitrogen compounds, reducing the total nitrogen level in the effluent.

Aeration Zone

Air delivered through fine bubble diffusers raises the dissolved oxygen level to 1mg / L. This facilitates the growth of organisms that consume or breakdown the complex organic compounds in the wastewater to simple inorganic compounds such as carbon dioxide (CO2), water (H2O) and promote the nitrification of nitrogen compounds, such as ammonia, to nitrites and nitrates (NO2- and NO3- ).

In this zone, an oxygen rich environment, the bacteria previously depleted of phosphorus, uptake more phosphorus than was previously released in the Anaerobic Zone, providing a net reduction of the phosphorus in the wastewater.

Clarifiers

Banora Point WWTP ClarifierClarifier The clarifiers are used to separate the effluent from the activated sludge by settlement. The flow from the Biological Reactors enters at the centre of the clarifier and slowly moves outward towards the overflow weirs. The time taken for this is called the detention time and is calculated by dividing the volume of the clarifier by the total flow into the clarifier. At Banora Point, the detention time is currently about ten hours, this allows the suspended activated sludge to settle to the bottom of the clarifier. The sludge is then removed by collector scrapers connected to updraft tubes and returned to the Biological Reactor by the RAS pump station. The treated wastewater, or effluent, flows over the outer weirs and flows to the Ultra Violet disinfection system.

Disinfection System

This system is designed to reduce the potential risk of harmful micro organisms to acceptable levels before being discharged from the plant. The effluent flows past the Ultra Violet tubes. The UV radiation reduces the faecal coliforms (indicator bacteria) from 1 000 000 to less than 1 000 FC’s / 100mL and breaks up the DNA of the micro organisms reducing their ability to reproduce. The water then flows to the effluent lagoon where the sunlight and lack of food result in further die off of bacteria.

Discharge of effluent

The water from this effluent pond is discharged into the Terranora Inlet on the high and outgoing tides. During dry weather about 12 ML or 12 million litres are discharged daily. Some effluent is reticulated around the plant for washing down and irrigation and Coolangatta Tweed Golf Course utilises some effluent for irrigation.

The Filter Belt Press

A portion of the biological mixture of micro-organisms (activated sludge) is taken out each day. At the belt press the sludge is dewatered, ie the water content of the sludge is reduced. Initially the sludge is only about 0.3 per cent solids, by adding a polymer the solids percentage is increased to three per cent and after being forced between the two belts of the belt press more water is extracted and the solids percentage increases to approximately 14 - 17 per cent solids.

The extracted liquid is returned to the start of the treatment process and the sludge is dried and stored.

Sludge Disposal

Sludge produced from biological phosphorus removal plants is unstable. It is odorous, biologically active, can not be stockpiled and is very difficult and expensive to process into a reusable form.

Options that have been considered include:

  • Soil conditioner or fertilizer - this is the ideal use for the sludge
  • Incineration
  • Very large drying beds
  • Heating - electric or gas / steam drying to above 60 per cent solids
  • Aerobic digestion / drying beds
  • Worm farms
  • Soil injection
  • Mixing with soil to produce top soil
  • Composting - various forms
  • Burial
  • Cement / lime / stabilisation

Currently, most of the sludge from the Banora Point Wastewater Treatment Plant is being transported to the Toowoomba area where it is being used as a soil conditioner for land crops and some is also used locally on cane farms.

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