Desalination plant cleans up

Solid and liquid waste streams managed

The construction of Sydney’s Desalination Plant has been a logistically complex undertaking for project manager the Water Delivery Alliance (WDA) in the management of waste. Being an Environmental Protection Agency (EPA) and Department of Environment and Climate Change (DECC) approved company for the management and permanent disposal of waste streams such as on this project, Worth Recycling was appointed to work on two main sites of the project.

The pipeline in the Tempe area is being built from the banks of the Cooks River in the Tempe Recreation Reserve, close to the site of the former Tempe Tip, which, like most old refuse sites, contained varying levels of contaminated material.

Wallis Constructions, headed up by Nigel Wallis, was contracted by the Water Delivery Alliance to construct a section of the pipeline which produced thousands of cubic metres of solid waste over a four-month excavation period, of which 500 tonnes was hazardous material.

“To excavate an area with material of this sort, the level of scrutiny and control is notably heightened, and we followed rigorous requirements on health, safety and personal protection equipment,” said Nigel.

Geotechnical and environmental engineers sampled the soils and classified waste types within the construction zone, breaking it into sub-sections. Different safety measures were enforced for each sub-section depending on the soil type and associated classification.

Waste was also classified into four holding bays, each concrete lined and securely storing more than 300 tonnes of material behind fenced-off areas within the construction site, with bays identified as general solid waste, restricted solid waste and hazardous waste.

Acid sulfate soils, which need to be treated with lime to minimise health and safety risks, were found across the site and designated treatment bays were constructed to handle this material.

Worth Recycling, which was appointed by Wallis Constructions to manage the transport, handling and treatment of this waste material, used specialised ‘tippers’ which transported it to the Worth Recycling Windsor treatment plant.

The Worth Recycling solids waste immobilisation (SWI) program treated the material by immobilising it through a fixation plant that carries out a high-sheer mixing process that adds reagents to render the material completely safe.

“This was a big job and our highly skilled technical and operational staff worked carefully with Wallis Constructions through all stages of the process from the initial chemical and physical analysis to the safe treatment of the material,” said George Cooper, Commercial Manager of Worth Recycling.

Another project where Worth Recycling has provided waste management support involves the excavation of both solid and liquid waste, with nearly 100% of the liquid waste recycled and re-used in the building materials industry as a direct replacement for potable water.

Energy Australia is constructing a new Kurnell-based, two-storey 1000 m² substation designed to allow existing substation infrastructure to be retired and help ensure a continued secure power supply to the industries around the Kurnell region, including the desalination plant.

In the civil and building construction phase of the project, being managed by Thomas & Coffey Limited, underground water has had to be siphoned from the base of the building in order for the site to remain dry.

A de-watering system has been set up to extract the water from the ground, which is placed in four separate sedimentation holding tanks, each with a capacity to store between 5000 and 20,000 litres of waste and liquid materials.

A filtration system has been designed to extract the water from the waste, with the by-product resulting in a viscous sludge material.

Worth Recycling continues to work on the project, with many hundreds of tonnes of waste material secured from the project thus far with dedicated vacuum tankers on call 24 hours a day to manage the refuse.

The liquid waste has been treated using Worth Recycling’s ceramic membrane ultra filtration system which can filter fluids down to 0.005 µm, removing most if not all contaminants, discharging clean filtered permeate while contaminants are contained and immobilised.

“This project has been a complete success, with the bulk of the refuse, some 500,000 litres of liquid waste, recycled for practical use,” George said.