Reducing waste to landfill
HUBER RoSF4 grit washing is an economic and innovative sewage treatment technology which produces up to 90% dry solids with less than 3% of residual organics.
The technology, which has been standard in Europe since the 1990s, due to a lack of landfill space, streamlines the sewage treatment process and makes a plant more efficient by replacing conventional classifiers and producing, what is claimed to be, the driest grit with the lowest amount of residual organics.
The Huber RoSF4, which is available in four different sizes to cater to all different size sewage treatment plants, was used at the initial installation at Australia’s largest and oldest sewage treatment plant which runs 100 m below north Bondi. The plant has been in existence since the early settlement of Sydney.
The plant was removing naturally occurring sand in grit traps but once the slurry was removed from thousands of litres per hour of sewage, plant operators were left with large quantities of a foul smelling soil which had to be transported for disposal at landfill.
To make the plant more efficient, Sydney Water contacted Ovivo to deliver three HUBER RoSF4 grit washing plants to replace the 25-year-old conventional classifiers, which were producing just 50% dry solids.
Ovivo were contracted to achieve more than 80% dry solids at the Bondi plant but they consistently and significantly exceeded the performance guarantee, achieving 90% solids, all of the time, with residual organics under 3%. This resulted in half the amount of grit having to be trucked out of Bondi, and accordingly, less disposal costs and fewer truck movements in a busy urban area.
Since the completion of the Bondi plant, most Australian water authorities have adopted the technology. Ovivo, who are the sole agents for Huber in Australia, have supplied two more plants to Sydney Water and a large plant to Melbourne Water. South Australia Water has also bought the equipment and the Water Corporation in WA, as well as numerous authorities in Queensland, have also adopted the Huber technology.
The key to the HUBER RoSF4 design is the dimensioning of the conical settlement tank, Coanda inlet system, fluidised bed mechanism for washing and the control strategy for operation of the discharge screw.
The unit is available in a number of sizes, typically 8-32 L/s, to cover a range of hydraulic and solids throughput. Fabrication is from 304 or 316 stainless steel.
These recent installations have improved the perception of grit washing in Australia. Achieving greater than 90% DS results in reduced truck movements, lower disposal costs, greater organic return to the plant and the possibility to reuse the grit as road base.