Sydney utility cogeneration trials reveal the pros and cons
Sydney Water is working to better predict the downstream effects of adding food waste to its cogeneration facilities – and plans to share the findings with the rest of the industry.
In collaboration with the University of Wollongong, Sydney Water began its three-year trial by adding beverage waste, including beer, wine and alcopops, and will move on to higher protein food waste before testing fat, oil and grease (FOG) waste.
“The project is feeding both digesters the same wastewater sludge, but with the experimental digester a certain percentage of the sludge is removed and replaced with food or beverage waste; we then monitor the outputs in terms of how much extra biogas is generated,” said Sydney Water's Service Planning Analyst Brendan Galway.
“At the moment with the 10% beverage we've put through, we're generating about a 30% increase in biogas.”
Sydney Water Principal Scientist – Treatment Dr Heri Bustamante added: “One aspect of the Shellharbour research, which is believed to be a world first, is that the project will develop a tool that will predict the biogas production of a range of food wastes.
“The research will enable Sydney Water to determine exactly the correct amounts of different types of food waste to be added in a variety of mixtures, to maximise energy production and to ensure that there are no downsides to the process.”
The trial involves two 1000L mini-research digesters and will also look at the impacts on biosolids and centrate.
“Some of the impacts we would be concerned with are increases in nitrogen and phosphorous and where that ends up,” Galway said.
“If it ends up in the biosolids that's not a bad thing, but if it ends up in the centrate and our sidestreams that puts pressure onto the plant in terms of increased energy and chemical costs.
“Or if a product is not readily digestible, then it's going to come through in a lower-quality biosolid, and therefore we might need to use more poly to help the dewatering process.”
Sydney Water is currently co-digesting fruit and vegetable waste at its Cronulla wastewater treatment plant. It has a further eight facilities that are currently doing cogeneration, but not co-digestion.
The research findings will help inform the expansion of Sydney Water's co-digestion program and others.