Sludge flow research opens the door for more energy efficient treatment processes

Flow properties of sewage sludge are subject to change with time, recent research from RMIT University has revealed – a finding that’s likely to bolster energy efficiency in sewage treatment methods.

RMIT University Associate Professor Nicky Eshtiaghi said the research outcomes would support more efficient treatment processes and help create more liveable and sustainable cities. 

“Accurate estimation of the flow properties of sewage sludge is the key factor in the efficient design and optimisation of wastewater treatment processes,” she said. 

“In this work, we developed a novel model that accurately predicts sludge flow properties with time, hence enabling treatment processes design to be more energy efficient.

“Due to the simplicity of the model developed, its implementation in simulation software is simple, which in return facilitates process optimisation due to the prediction of optimal flow properties.”

Eshtiaghi said considering the time-dependent behaviour of sludge is crucial in creating more efficient processes.

“We showed that the flow properties of sewage sludge (including viscosity) are subjected to change with time. These properties reduce with time when sludge is flowing but increase with time when sludge is stagnant,” she said. 

 “We showed that it is necessary to consider this variation in engineering of the wastewater treatment processes otherwise these processes cannot be designed efficiently.

 “Without considering the time-dependent behaviour of sludge, process equipment design would be very inaccurate.” 

Developing a model

The research team developed a simple and practical model that accurately predicts change of sewage sludge flow properties over time and at different concentrations. 

“Our model can be used in process simulation for engineering and optimisation of sewage sludge transportation and mixing processes,” Eshtiaghi said.  

“[The] model parameters are invariant to solid concentration, hence make it easy to use for engineering treatment processes at various solid concentrations. 

The model can be utilised by engineers and operators to conveniently obtain flow properties of sludge for troubleshooting, Eshtiaghi said.

“Engineering consulting companies also can use it for designing new sludge treatment processes more efficiently,” she said. 

“In the future, the models developed in this study will be used in simulation software to develop a GUI [graphical user interface]-based application for easily finding sludge flow behaviour at different concentrations as a function of time to predict pressure drop as a result.

“Designing energy-efficient processes will bring several advantages including reduction in operation cost for water utilities and the service cost for consumers, while reducing greenhouse gas emissions and helping to tackle climate change. 

“This means, ultimately, improving the liveability of cities.”