Sludge flow indicates thermal process performance

The behaviour of sewage sludge flow may hold the key to optimising the thermal treatment of wastewater, according to research conducted at RMIT University. Tracking sludge flow during the thermal treatment process could help engineers improve treatment plant designs and boost biogas production. The research findings demonstrate that sludge flow can be used as a tool to gauge how quickly organic matter is dissolving at high temperatures, with scope to monitor process performance online.

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

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 the flow.

Lead investigator and Associate Professor Nicky Eshtiaghi from the School of Engineering said that 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,” 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 equations used in the study are based on direct measurement of sludge at conditions that mimic real-world thermal treatment processes. The new technique can measure flow behaviour without destroying the samples, often a big challenge during data collection of concentrated sludge.

Thicker sludge, more biogas

The study showed that varying 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.”

Eshtiaghi, a member of the Water: Effective Technologies and Tools Research Centre at RMIT, said the research could enable more efficient design and troubleshooting of pumps, mixers and heat exchangers in the sludge treatment process.

The study, with lead author and PhD researcher Kevin Hii, is published in Water Research (DOI: 10.1016/j.watres.2019.03.039).

Image credit: ©stock.adobe.com/au/Curioso Photography

Originally published here.