Bondi Sewage Treatment Plant Reliability Improvement and Modernisation Program, Sydney, Australia


Located beside one of the world's most iconic beaches, the Bondi sewage treatment plant (STP) – Sydney's third largest coastal facility – takes wastewater from half a million of the area's inhabitants and discharges 130 million litres/day of treated effluent into the ocean.

Originally commissioned in the 1950s, the facility has undergone a major reliability improvement and modernisation program (RIAMP) designed to renew and enhance the plant to ensure continued, reliable performance for the future.

The project, which was completed in early 2007, as part of Sydney Water's Water Plan 21 and Coastal Wastewater Strategy, forms a key element in the utility's ongoing work to protect the region's ocean and beach environments.

"The project forms a key element in the utility's ongoing work to protect the region's ocean and beach environments."

The work has included addressing issues of wastewater distribution and flow control, sludge management and discharge pumping, improving the collection, handling and disposal of screenings/grit and refurbishing the plant's four digesters.

Upgrades to the ventilation, electrical and control systems were also made, along with increasing the level of automation to improve working conditions and further enhancing the operational reliability of the plant.

The project cost was AUS$95m.

BACKGROUND

Bondi STP is one of ten coastal treatment plants operated by Sydney Water – a statutory, state corporation, wholly owned by the people of New South Wales, providing water and wastewater services to over four million people in Sydney, Illawarra and the Blue Mountains.

A high-rate primary treatment plant, it originally discharged effluent from the cliff face, but public concern over the effect of this approach on the water quality of local beaches led to the construction of a deep water ocean outfall, which was commissioned in 1991. At a maximum water depth of 63m and with a 512m diffuser zone, this now effectively disperses the effluent 2.2km out from the shore.

Treatment is conventional; screenings and grit are removed and the flow then enters sedimentation tanks. The effluent – an average daily dry weather discharge of 130 million litres – is pumped to the ocean outfall. Digesters stabilise the settled material, which eventually leaves the site to be mixed with other organic matter for use as a soil conditioner in agriculture and forestry in the central west region of New South Wales. Screenings and grit are landfilled.

Although the plant had successfully protected what is probably the most famous beach in Australia and served Sydney, together with the municipalities of Waverley, Woollahra, Randwick, Leichhardt and Marrickville, it was beginning to show its age.

After more than fifty years of operation and despite various updates over its life, parts of the facility inevitably needed renewal and modernisation. Additionally, advances in automation offered significant potential benefits in reliability and workforce welfare to a treatment works originally designed with a heavy reliance on manual operation.

In January 2004, construction work began on the three-year programme to safeguard the plant's ability to meet the needs of the region into the future.The project site preparation actually began in October 2003.

IMPROVEMENT AND MODERNISATION

The project brings improvements to six main areas of the plant: flow distribution and control; collection, management and disposal of screenings and grit; sludge and scum handling; digestion and dewatering; ocean discharge pumping; plant ventilation, odour management utilities and control systems.

Since most of the Bondi plant is housed in chambers cut into the sandstone some 40–50m below ground, the project includes an element of tunnelling to extend the existing area to allow the new processing equipment to be accommodated. Although much of the work is underground, some also took place on the surface.

The plant layout consists of four sections, each comprising identical grit and sedimentation tanks. To enable continuity of operation throughout the improvement programme, each is to undergo the necessary demolition, electrical work and construction in sequence, leaving the three remaining sections in service to ensure safe and effective treatment. The existing screening equipment was replaced with a new, finer and more efficient system – the first of its kind to be installed in Australia.

In the same way, the programme called for each of the plant's four digesters – located above ground between the Hugh Bamford Reserve and the Bondi Beach Golf Course – to be emptied and refurbished in turn. In addition to grit blasting and painting the digesters, the sealed areas around the digesters themselves were resurfaced.

Removing and refurbishing the large valves – each one over a metre across – fitted to the six ocean outfall pumps represented one of the most challenging aspects of the project.

By timing the work to coincide with a low tide early in the morning, when plant flows are low, and having one of the sedimentation tanks empty and on standby to receive excess effluent, the work was completed safely while the plant continued to operate. Each valve was removed in turn, returned to the supplier for rehabilitation and then reinstalled as favourable tides permitted.

In the closing phases of the programme, the below-ground odour scrubber was refurbished and the potential installation of a digester-gas-powered electrical generator was investigated. In addition to the improvement scheme, some essential repair was also carried out on the sludge dewatering building.

"A recycled effluent system is being installed in a series of phases, to reclaim water for use within the plant for screen washing and other processes."

The electrical systems were upgraded with the installation of around 90km of new cable, the removal of some 100km of redundant cabling, switchboard replacement and the substitution of two new transformers – with twice the capacity. In addition, upon completion of the project, 250 new monitoring and control instruments have enabled the automation of many routine aspects of plant operation.

Also as part of the improvement project, a recycled effluent system was installed in a series of phases, to reclaim water for use within the plant for screen washing and other processes. This amounts to around 3 million litres/day of treated wastewater.

Although Sydney Water treats and recycles more than 15 billion litres of treated wastewater annually for home use, irrigation, agriculture and industrial purposes, the potential outlets around the Bondi plant are too limited to justify the higher levels of treatment required.

ENVIRONMENTAL IMPROVEMENTS TO THE RESERVE

With the RIAMP, Sydney Water also undertook to carry out improvements to the Hugh Bamford Reserve where the facility is situated. The improvements include replanting of the Military Road embankment, new vehicle access from Wentworth Street, drainage improvements at Wentworth Street and Military Road, a New Military road footpath, a new lookout on the cliff, extension of the coastal walk through the reserve and general rehabilitation of the reserve. Pan Civil was responsible for the work to restore Hugh Bamford Reserve at completion. Weed control was done by Earth Repair and Restoration.

KEY PLAYERS

Sydney Water is the plant owner and project sponsor. Joint venture partners CH2M Hill and Sinclair Knight Merz were responsible for the program concept design and were joined by a consortium of Walter Construction Group (WCG), Golder Associates and United Group Infrastructure in 2003 to undertake the construction work. However, in February 2005, WCG entered voluntary administration and played no further part in the project. The discharge licensing and monitoring authority is the Department of Environment and Conservation.