This is the 100-kilolitre, purpose-built holding tank being used in an innovative project to convert fruit and vegetable waste from Sutherland Shire shops into power.
Leader readers asked for more information about the process following our recent report on the trial of the scheme.
Six hundred wheelie bins a day of fruit and vegetable waste no longer goes to landfill but, instead, is converted into power to help run the Cronulla sewage treatment plant.
The renewable energy process will provide more than 60 per cent of the plant’s power needs.
A Sydney Water spokesman said seven shire businesses were taking part in the three year trial.
They are Cronulla Fruit Fair, Sylvania Best Fresh, Gymea Fresh, Caringbah Best Fresh, Sydney's Best Fresh Engadine, Sutherland Best Fresh and Fruit Ezy Miranda.
Sydney Water provided the following detailed explanation of the process:
“Recycling food waste company Pulpmaster provides processing machines, which are like large blenders to local fruit and vegetable retailers.
“These machines grind the food waste and add enough water to allow the waste to be pumped to a holding tank.
“Pulpmaster tanker trucks collect the waste when the tank is full.
“The tanker trucks then deliver the waste to Cronulla Wastewater Treatment Plant.
“The waste is pumped into a purpose built holding tank.
“From there it is blended with sewage sludge before being added to an anaerobic digester (a large enclosed tank).
“The bacteria in the aerobic digester work to “digest” the food waste and sewage sludge (similar to what happens in a human stomach).
“This digestion process produces large amounts of methane, which we collect in the digester and then send to a biogas co-generation engine that combusts it and turns it into electricity.
“Waste heat from the biogas engine is used to heat the digesters, hence the term ‘cogeneration’.
“The Cronulla plant uses the electricity and the excess heat, while the solids remaining from the digestion process go to farmlands as an organic fertiliser.
“This whole process is contained from start to finish to eliminate odour.
“The plant will self-supply more than 60 per cent of its electricity demand from food waste and sewage sludge once the trial is in full swing.”
