An innovative and energetic research team led by Professor Bing-Jie Ni and Dr Wei Wei from the University of Technology Sydney (UTS) are now converting sludge from a wastewater treatment plant into valuable liquid bioenergy.
Prof Ni is a worldwide pioneer in modelling and wastewater management. Dr Wei is a young lecturer at the School of Civil and Environmental Engineering. She is a renowned pioneer in revolutionizing the science and practice of sewage sludge management.
“As the by-product of mainstream biological wastewater treatment, waste-activated sludge (WAS) has attracted much attention,” Prof Ni said. “This is due to the considerable financial burden posed on wastewater treatment plants (WWTPs). For Australia alone, around 3.6×105 tons of carbon-rich sludge is generated annually. It represents a substantial but largely untapped renewable energy resource. Therefore, sludge reduction with energy recovery is crucial and has gained increasing attention.”
“Anaerobic fermentation is a proven sludge treatment technology. Short-chain fatty acids (SCFAs) with carbon atoms from 2 to 5 are the traditional products attained from sludge via anaerobic fermentation. Previous studies were mainly focused on enhancing SCFAs outputs via sludge management. This was despite these end products only attaining lower economic value and limited application scope. To improve the carbon recovery value and efficiency, carboxylates and alcohols with longer carbon chains then attracted our attention,” said Dr Wei.
Medium-chain fatty acids vital for bioenergy
“Medium-chain fatty acids (MCFAs) are carboxylates with longer carbon chains. They are upgraded from SCFAs via chain elongation platform,” she said. “MCFAs carry more energy and have better separability than SCFAs. Additionally, MCFAs can be used as the building block for more fields.”
Dr Wei’s team is also looking at a different waste by-product.
“Long-chain alcohols (LCAs) are the other group of liquid bioenergy we focus on when fermenting sludge anaerobically. Butanol and hexanol are the common LCAs attained from the fermentation system. They can be treated as a superior biofuel than ethanol due to their higher hygroscopicity and higher energy density,” said Dr Wei.
Dr Wei realized the great value and potential of generating MCFAs and LCAs massively. She and her team have been using WAS as the primary feedstock, as WAS is easily accessible and a carbon-rich substrate. She believes the sludge-derived MCFAs and LCAs should relieve Australia’s reliance on fossil fuels. It will also assist the development of a circular economy in the foreseeable future, which definitely needs more attention from academia and industry.
“We have already done a lot to improve the liquid bioenergy recovery from sludge by optimizing the interactions among various metabolism steps while shifting microbial community structure towards the desired direction. Easy and technically feasible strategies have been tested to ensure high and stable WAS-derived MCFA productions from fermentation system,” Dr Wei added. “We are now focusing on developing a more economically feasible technique to encourage MCFAs production by reducing or eliminating the need for electron donor.” This new and conceptual idea has been proven viable at a lab scale.
Further applications for sludge to bioenergy
Dr Wei also expects to apply the technique for liquid bioenergy recovery from sludge to other kinds of organic waste, such as food waste, chicken manure and microalgae.
“Some researchers from our team have already started this research topic, such as Lan Wu, a soon graduate PhD candidate from UTS,” she said. “Promising MCFAs and LCAs have been obtained by Miss Lan using the technique earlier applied in sludge fermentation. More publications concerning liquid bioenergy recovery will be available shortly.”
The liquid bioenergy production derived from sludge provides a new paradigm of transforming waste sludge into assets to bring significant economic benefits to WWTPs.
“Our sludge treatment technology represents an eco-friendly and cost-effective solution that not only reduces CO2 emissions but also lowers disposal costs. This technology serves as an exemplary model for transitioning wastewater treatment plants (WWTPs) from a ‘linear economy’ to a ‘circular economy,’ aligning with industrial needs.” said Dr Wei. “The outcomes can be applied in existing anaerobic sludge fermentation infrastructure, as well as to develop new applications in diverse industries for addressing escalating energy demands.”
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