A new method of tracking how sewage sludge flows during thermal treatment could help engineers design more efficient wastewater treatment plants and increase biogas production.

Traditional ways of assessing the performance of thermal treatment require time consuming sampling and chemical analysis.

But researchers at RMIT University have shown rheology calculations, which measure and detail how liquids flow, can be used in real-time to gauge how quickly organic matter is dissolving at high temperatures

The study, published in Water Research, found a correlation between how sludge dissolves and changes in its flow behaviour. This indicates it might be possible to monitor thermal treatment performance just by tracking the flow.

Lead investigator Associate Professor Nicky Eshtiaghi, from RMIT’s School of Engineering, said correctly estimating the rheological parameters of sludge is critical to efficient process design.

“Our technique enables engineers and plant operators to conveniently obtain these parameters without having to perform the measurements at high temperatures themselves,” she said.

“We hope the research encourages more serious consideration of flow behaviour in optimising and designing high-pressure and high-temperature sludge handling.”    

The equations in the study are based on direct measurement of sludge in conditions that mimic real-world treatment processes.

Boosting biogas

The researchers also found that changing the thickness of sludge has little impact on the effectiveness of thermal treatment.

This means plant operators could increase biogas production downstream by increasing the solid content of sludge during initial treatment processes.

“Thicker sludge can be beneficial for both optimising efficiency overall and for producing more biogas,” Eshtiaghi said.

“With our discovery that the thickness of sludge makes no difference, this research gives plant operators more flexibility in designing processes that can better exploit the renewable energy potential of wastewater sludge treatment.”  

For more on improving wastewater treatment, don't miss the Wastewater Treatment and Optimisation Stream at Ozwater'19 on Wednesday, 8 May. View the full program here.