The Kingscliff Wastewater Treatment Plant (WWTP) was designed to treat sewage collected from the Kingscliff Sewerage Catchment.

The Kingscliff Wastewater Catchment includes:

• Kingscliff
• Fingal
• Chinderah
• Cudgen
• South Kingscliff (Salt)
• Casuarina

The treatment plant was commissioned in February 2008.  The plant replaced an out dated and under sized treatment facility.  The facility is located in Cudgen to service a population of 25,000 people.  The design flow rate through the plant is 6.0 ML/D.

The effluent quality discharged achieves very low nutrient limits making it a world class treatment facility.  An educational facility, the Sustainable Living Centre, has been incorporated into the plant control building to provide both static and interactive displays to explain the treatment process.

The overall project costs for the new facility was $45,000,000.   

Aerial Photo of Kingscliff WWTP February 2008

Treatment Process

The treatment process for the Kingscliff WWTP is required to meet stringent effluent discharge requirements that were determined during the Environmental Impact Study for the plant. 

A further requirement was that the process needed to be simple to operate and extremely robust to guard against shock loads on the plant. 

The selected process for Kingscliff WWTP is a chemically enhanced biological nutrient removal (CEBNR) process incorporating the following stages:

• Primary Treatment
  • Fine Screening
  • Grit Removal
  • Odour Control
• Secondary Treatment
  • Anaerobic Reactor
  • Oxidation Tank
  • Secondary Anoxic Zone
  • Secondary Aerobic Zone
  • Clarification
• Tertiary Treatment
  • Secondary Effluent Pump Station
  • Filtration
  • Chlorination
  • De-chlorination
• Sludge Management
  • Sludge Lagoons
  • Sludge Dewatering
  • Beneficial Reuse
• Effluent Reuse
  • Chinderah Golf Course

Effluent Standards

The effluent standards adopted for Kingscliff WWTP are consistent with best practice treatment technologies. 

EPA Licence limits for Kingscliff WWTP (12684) February 2008

 Primary Treatment

Raw sewage flows are pumped to the inlet channel via twin 500 mm pipelines that receive pumped flows from the Kingscliff Sewerage Catchment.  Inlet flows are monitored via flowmeters installed on each pipeline.

Fine Screening

The raw sewage passes through a step screen to allow debris to be removed from the flow.  Automatic screening is provided by a 3mm step screen where screenings are “stepped” up the screen and discharged through a chute into the screenings screw conveyor.  The screenings are washed, compressed and discharged directly from the screw wash press to the storage bin.

Raw sewage can bypass the step screen if blocked or off-line and flow via an overflow weir with a manual screen. 

Grit Removal

The grit removal system comprises a vortex grit chamber and a classifier.  Grit is settled in the vortex chamber by centrifugal flow within the tank.

Settled grit, collected in the base of the grit tank, is periodically removed via a grit pump to a classifier where the grit is washed and dewatered prior to discharge to a storage bin

Odour Control

Odour control is used to minimise odours from the inlet works.  The inlet works are completely covered to contain odourous gases produced within the sewerage system.  An extraction fan to removes the odour from within the inlet works to the odour control unit.

The odour control unit treats the odour in a two stage process involving a biological trickling system followed by an activated carbon system.  This system is designed to remove 99.9% of all odours within the system.

Secondary Treatment

The Kingscliff WWTP secondary process is based on the 5-stage Phoredox Process (“Modified Bardenpho”), in the form of an oxidation tank design.  Magnesium Hydroxide (MHL) and Alum are also dosed to ensure that the specified effluent quality is achieved

Kingscliff WWTP Secondary Process Diagram

Anaerobic Reactor

Sewage enters the first chamber of the compartmentalised anaerobic reactor (total of four chambers), where it is mixed with return activated sludge, magnesium hydroxide (MHL), and alum.  Four submersible mixers (one per anaerobic chamber) ensure that the raw sewage, return activated sludge (RAS) and chemicals are completely mixed.   The anaerobic reactor is designed to reduce biological phosphorus. 

Oxidation Tank

Aeration in the oxidation tank is provided by three (2 No. duty/1 No. standby) surface aerators fitted with variable speed drives.  Dissolved oxygen (DO) concentrations in the oxidation tank are monitored by two DO probes.  Controlling the amount of air provided to the system (by changing the aerator speeds), results in optimised nitrogen removal capabilities.

Waste activated sludge and scum is withdrawn from the oxidation tank, adjacent to the secondary aerobic reactor.  Kingscliff WWTP has been designed to operate at an average sludge age of 25 days.

Secondary Anoxic and Aerobic Zone

Mixed liquor transfers from the oxidation tank, to the secondary anoxic reactor.  A submersible mixer located in the anoxic reactor ensures that the contents are fully mixed, and solids settling is prevented.  Mixed liquor flows to the secondary aerobic chamber, where two submersible aerators ensure that residual ammonia-nitrogen is converted to nitrate-nitrogen in order to meet the stringent ammonia-nitrogen licence conditions.

Clarification

Mixed liquor is distributed evenly between two circular clarifiers via a centre feed well.  The clarifiers contain a scraper that concentrates the return activated sludge (RAS) in the centre of the clarifier’s base where it is extracted and returned to the anaerobic reactor.  Effluent overflows the clarifier launders to the filter feed (secondary effluent) pump station.

Return Activated sludge pump station

Tertiary Filtration

The filter feed pumps transfer the secondary effluent from the clarifiers to the micro-screening filtration system.  The flow is evenly split between two filter units.  Effluent passes through the 20 micron filter medium, and particulates are trapped on the surface of the medium.  Periodically a backwash cycle is initiated, which cleans the filter medium.  Backwash water is returned back to the plant inlet works where it is retreated.

Chlorination

Filtered effluent flows under gravity to the chlorine contact tank (CCT).  Sodium hypochlorite is dosed at the inlet to the CCT distribution chamber.  Chlorinated effluent flows through the CCT, which provides contact time to ensure disinfection is achieved.

Service water is used on-site for washing down equipment and flushing lines. 

Dechlorination

Final effluent (being filtered and disinfected) flows from the Chlorination Contact Tank to the dechlorination chamber.   Sodium bisulphite is dosed into the chamber to dechlorinate the effluent prior to release to the discharge point. 

Once fully treated, effluent is reused or is pumped to the Tweed River outfall.

Sludge Management

Waste activated sludge is pumped from the oxidation tank to the anaerobic sludge lagoons. Biosolids are further stabilised using 4 anaerobic sludge lagoons. Each lagoon has a volume of approximately 3,900m³.  Stabilisation also reduces odour in the dewatered sludge.

Sludge lagoons

Supernatant (clear water on top) from the lagoon is recycled via a site utility pump station to inlet works.

Sludge from the lagoons is pumped into averaging tanks then pumped to the centrifuge and dewatered.  The dewatering process is based on centrifugal force. To help the sludge coagulate, polymer is fed into the process.  After the water has been separated from the sludge the water is drained off from one end.

The dewatered sludge is fed to the sludge bin loading conveyer which feeds the sludge cake storage hopper.  Centrate is continuously decanted and flows via gravity to the site drainage pump station.

Sludge cake storage hopper holds 50m³ of dewatered sludge that can be reused on cane fields or broad acre farms as a soil conditioner. 

The Tweed Valley has sufficient area of cane fields available to allow the sludge to be beneficially reused in a sustainable manner.   To ensure that no nuisance odours occur, the biosolids are incorporated into the top soil within 2 hours of application.

Effluent Reuse

The chlorinated effluent is sent to Chinderah Golf Course for beneficial reuse as well as being used onsite .

Aerial Photo of Kingscliff WWTP and surrounding area 2008