Coppabella Township Sewage Treatment Plant Upgrade

Our Solution

After completing various projects for Aurizon Holdings Limited, Dowdens won the tender to provide the process design, equipment supply, civil construction, installation, commissioning, and training for the STP plant operators. The project’s construction phase began with extensive civil works undertaken to raise the ground level for the new STP components. The pre-existing STP has historically been subject to flooding during heavy rainfall events due to the site’s proximity to the local creek. Upon surveying the site’s substrate, a water table was discovered 1m below ground level.

Working with local Civil Engineers Cardno, a substantial foundation was designed/laid to ensure the new buildings, plant components and 4,000-tonne water tank would be stable and remain above the floodplain even during heavy rainfall. Once the foundations were laid, Dowdens began construction of the 400,000L lined stainless steel water tank, a new building to house the STP process equipment properly, operators office, laboratory facilities, and a backup generator used to power the entire STP in the event of power loss.

Three Stage Process

Primary treated effluent from the existing STP (Class C quality) is transferred to a 45,000 L Glass Media Filtration (GMF) feed tank via duty/stand-by submersible pumps on demand.

Stage 1

In Stage 1, the clarified effluent from the existing STP process is first dosed with sodium hypochlorite as primary disinfection to reduce biofouling of the Glass Media. It is then passed through the duty/stand-by Glass Media Filters, which reduce particulates, suspended solids and turbidity from the GMF filtrate stream to ensure no large particles damage the UF membranes in stage 2.

Stage 2

In Stage 2, the GMF filtrate is passed through a UF treatment process which incorporates 5% ‘cross-flow to maximise the filtration run-time between back flushes (triggered by high trans-membrane pressure). The system consists of 8 individual outside-in PVDF membranes which reduce turbidity to less than 1 NTU (Nephelometric Turbidity Units) whilst removing any particles greater than 0.0002mm from the permeate stream. The UF feed is again dosed with sodium hypochlorite to assist in cleaning the UF membranes from biological and organic fouling between the backwash and Chemical Enhanced Back Flush (CEBF) cycles.

Stage 3

In Stage 3, the UF filtrate is passed through duty/stand-by Activated Carbon Filters (ACF) on-demand to reduce colour and odour (by removing aromatic compounds) as a final ‘polish’ before being fed to the treated effluent tank. The ACF filtrate is then dosed with sodium hypochlorite as the final disinfection of the treated effluent before entering the treated effluent storage tank for dispersal via above-ground irrigation systems. 

Dowdens provided a centralised, custom-designed and fabricated chemical dosing system for the UF Polishing Plant. This included a 1000 L Chemical Storage tank and a splash-proof racking area housing five individual Chemical Dosing pumps complete with an internal bund and double containment dosing line connections.

400 KL Stainless Steel Effluent Tank

When the treated effluent arrives in the 400 KL stainless steel tank, a recirculation system pumps it through a chlorine analyser and back to the treated effluent tank. The chlorine analyser then controls the residual free chlorine level in the treated water. It will start/stop a chemical dosing pump required to maintain the pre-set residual free chlorine level.

Each of the GMF, UF and ACF processes are periodically backwashed and cleaned, with residual waste being fed to a nearby buffer dam where chlorine is allowed to dissipate. Based on the level in the buffer dam and the level in the treated effluent tank, the water may then be returned to the pump station at the front of the STP for reprocessing.

Key Components

• 400, 000 L Stainless Steel Effluent Tank
• 45,000 L Glass Media Filtration
• UF Treatment
• PVDF Membranes
• Activated Carbon Filters
• Chlorine Analyser
• Chemical Dosing System
• 1000 L Chemical Storage Tank

The upgraded Sewage Treatment Plant is now capable of producing 180KL of treated Class A effluent per day for above-ground irrigation applications. The local Coppabella Golf Course is one area where this treated effluent is used for irrigation.