Tracking sludge flow for better wastewater treatment

A new way of tracking how sewage sludge flows during thermal treatment could help engineers design better wastewater treatment plants and boost the production of biogas.

Researchers at RMIT University have demonstrated how the flow behaviour of sludge can be used as a tool to gauge how quickly organic matter is dissolving at high temperatures, suggesting the potential for online monitoring.

Traditional methods of assessing thermal treatment performance require time-consuming sampling and chemical analysis, rheology calculations however – which measure and detail how liquids flow – can be done in real time online.

The study, published in Water Research, found a correlation between how sludge dissolves and changes in its flow behaviour, indicating it may be possible to monitor thermal treatment performance simply by tracking flow.

Lead investigator Associate Professor Nicky Eshtiaghi 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,” Ms Eshtiaghi said.

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

The new technique can measure flow behaviour without destroying samples, often a big challenge for concentrated sludge data collection.

The study also shows that varying the thickness of sludge has little impact on the effectiveness of thermal treatment, meaning plant operators could potentially increase biogas production 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,” Ms 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.”