The Banora Point Wastewater Treatment Plant uses a biological Nutrient Removal process for the treatment of raw sewage.   The plant was upgraded in 1995 at a cost of $18 million to service a population of 50 000 people and since has received minor upgrades to currently achieve 62,500 people.

To expand the capacity to 75 000 people another upgrade commenced in 2010.   The upgrade will include a balance tank, upgraded odour control or deodorising facilities, alum dosing, modifications to existing biological reactors, an additional clarifier, disk filters for treated effluent before UV radiation

Step Screen at inlet of WWTP

Primary Treatment

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 1 cubic metre is removed a day. 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 average dry weather flow into the treatment plant is approximately 14 ML / 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

Raw sewage combines with returning activated sludge and 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

Bioreactor

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^-).

Aerobic Zone in Bioreactor

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

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.   At Banora Point, the detention time in the clarifier is currently about 10 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.

Clarifier

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 14 ML 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.

Current Licence Limits

EPA licence limits for Banora Point WWTP (3717)

Parameter	Units	90 Percentile Concentration	100 Percentile Concentration
Requirements for environmental discharge (to Terranora Inlet)
Volume Limit	kL/day	75 000
Biological Oxygen Demand	mg/L	15	35
Total Nitrogen	mg/L	10	20
Total Phosphorus	mg/L	5	10
Total Suspended Solids	mg/L	20	40
Oil & Grease	mg/L		10
Faecal coliforms	cfu/ 100 mL		10 000
pH	-	Range 6.5 to 8.5

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, i.e. the water content of the sludge is reduced. Initially the sludge is only about 0.3% solids, by adding a polymer the solids percentage is increased to 3% 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% solids.

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

In 2011 a second belt press has been completed to allow the plant to cope with increased loads.

Sludge Disposal

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 when available.

The plant produces around 30 m³ of dried sludge a day.