past projects

Finishing of the floor pour of the SBRs seen through 4.5m-high walling reinforcement.

In 2005, Whyalla (population 21, 600) was SA’s second largest city. For 40 years then, its treated wasterwater had been going into a creek that emptied into the Spencer Gulf. In July that year, a radical change happened when owner/operator SA Water completed a $14.3m water reuse scheme for the city. Below is an extract from a water reuse scheme report (released that year) outlining what was done during that time to address the issue of wastewater.

The scheme will collect water collected from about 6500 Whyalla properties – or about 75% of the city. A new water reclamation plant and associated infrastructure has been built to intercept the existing sewer and treat the water to Class B quality. Most of the recycled water will be used to irrigate the local golf course, city parks, gardens and ovals. This will ensure minimal or no discharge of treated wastewater into Spencer Gulf for more than four months each year. The state government is committed to phasing out discharges into the marine environment wherever economically and environmentally sustainable. The reuse scheme is part of its $300m ongoing program of wastewater treatment plant upgrades. Parsons Brinkerchoff designed the resuse scheme. The $6m civil works contract had a civil workforce on site that peaked at 30. The equipment included excavators, garders and rollers, and the job required large areas of concrete formwork.

The new reclamation plant occupies a rectangular area bounded by a landscaped (trees) security fence near the Anderson Racecourse on the city’s southern edge. Other aspects included: Three new pipelines (from 450mm down to 350mm diameter) running for 6km. These take raw wastewater to the new plant, treated wastewater to the golf course, and sludge from the treatment process back to the original wastewater treatment plant (WWTP) – a series of open lagoons completed in 1965 and a short distance away downstream. An upgrade of the WWTP. Modifications involved the recommissioning of lagoons 3, 5, and 6, and new connection pipes. Lagoons 1, 3, 5, and 6 would be online for the summer months.

The new plant out at the racecourse will have a capacity of 3.15ML/day. It incorporates two parallel sequencing batch reactors (SBRs) for biological nitrogen removal and two parallel balancing ponds each capable of holding 1.3ML of recycled water. (An overflow line discharges excess treated effluent to the existing WWTP.) The balancing ponds have a HDPE liner to prevent infiltration loss and soil/groundwater contamination. The SBRs measure 40m x 30m overall and contain 10 individual compartments of varying capacities. A total length of 280m of 4.5m high walling was constructed of 400mm thick concrete and 250t of steel.

The biggest challenge was working to the very exacting standards of SA Water both for concrete manufacture and placement. The concrete is a relatively high strength and low shrinkage product, the design of which although ideal for water retaining structures having durability and resistance to attack in a wastewater environment, is difficult to both pour and finish. The slump is low and setting times are short. Super plasticisers must be added to achieve the slumps required for both pumping and pouring in high-lift situations. Pouring of concrete was generally commenced at 2am and completed by 10am to avoid the daytime temperatures of up to 48 degrees which are common to this area.

Walling of the SBRs basin with inlet pipework inserts. WHAT IS HAPPENING NOW? Wingtip view showing the water reclamation plant (centre rectangle), the racing track top right and a spill stockpile left foreground. SA Water’s Whyalla Recycled Water Plant (built in 2008), currently supplies around 2.5 million litres of recycled water per day. In early October, SA Water released new upgrade plans for the plant as part of the utility’s $200,000 investment to enhance sewage treatment and the plant’s overall performance. More than 1,300 diffusers in both of the plant’s treatment basins would be replaced to improve the efficiency of the biological process that breaks down nutrients in the sewage. These diffusers distribute a constant supply of oxygen to help microorganisms remove the nutrients, which is an important step in recycling sewage. The treatment plants are now rich resource recovery centres capable of creating sustainable sources of recycled water. When sewage is treated, the solid organic material is separated from water. The recycled water can be used by the local council to help irrigate and green the city’s ovals and parks, while helping keep the golf courses’ playing surface looking lush. Measures are already in place to manage any temporary increases in sewer odour from the plant during the upgrade.