Engineers ‘hit gold’ with innovations that recover heavy metals from biosolids

(Nanowerk News) Engineers in Melbourne have developed a cost-effective and environmentally friendly way to remove heavy metals, including copper and zinc, from biosolids.

The team’s work, led by RMIT University in collaboration with South East Water and Manipal University in India, advances another method of removing heavy metals by recycling the acidic liquid waste generated during the recovery phase, instead of dumping it.

Lead senior researcher Professor Kalpit Shah of RMIT said the heavy metals found in biosolids – treated sewage sludge – could be valuable, and recovery of metals such as copper and zinc could be achieved using the team’s approach.

“Our innovation helps ensure the resulting biosolids do not leach heavy metals into the environment and retain usable nutrients for land applications,” said Shah, Deputy Director (Academic) of the ARC-funded Training Center for Australian Biosolids Transformation Resources at RMIT’s School of Engineering.

“With further processing, biosolids can be turned into high-quality biochar, which is a renewable energy source and has various applications including as fertilizer.”

This research was published in an international journal Hydrometallurgy (“Investigations into closed loop hydrometallurgical processes for heavy metal removal and recovery from biosolids via mild acid pre-treatment”).

How does innovation work?

The overall metal removal process occurs through three stages: extraction, purification and recovery.

Prior to the team’s work, recovery of metals from biosolids had not been fully explored among researchers beyond the first phase.

The first author of the journal article, RMIT PhD researcher Ibrahim Hakeem, said biosolids can contain some metals locked within organic matter, making the purification and recovery of metals difficult.

“We devised an approach where we can recover metals individually and do so with the least damaging closed-loop solution for the environment,” said Hakeem, from RMIT’s School of Engineering.

Co-author from Manipal University, Dr Abhishek Sharma, said this work is beneficial for increasing the overall efficiency of the process during the conversion of biosolids to biochar via pyrolysis.

Shah said the work complements the team’s biochar-producing pyrolysis technology, which is being trialled by South East Water, Intelligent Water Networks (IWN) and Greater Western Water at the Melton Water Recycling Plant.

“Pyrolysis is a process that uses heat to break down organic matter into valuable products and occurs without oxygen to prevent the material from burning. The team used this process to remove emerging pathogens and contaminants from the biosolids.”

Co-author and Deputy Director (Industry) of the ARC-funded Training Center for the Transformation of Australian Biosolid Resources, Dr Aravind Surapaneni, said the water industry globally is considering alternative thermal conversion technologies such as pyrolysis to address concerns over contaminants including springs and poly-fluoroalkyl substances. (PFAS).

The challenge was that the reduction of organic matter via pyrolysis resulted in higher concentrations of heavy metals in the biochar, which the team’s new technique aided.

The application of biosolids to agricultural land in Australia is subject to guidelines and regulations that set limits on heavy metal concentrations, ensuring that biosolids can be used safely as fertilizers.

What’s the next step?

The team aims to work with water authorities to employ heavy metal removal techniques prior to pyrolysis.

“The transition to a circular economy is important for the water industry,” said South East Water Research and Development Manager, Dr David Bergmann.

“We have previously seen our sludge as waste, but now through research like this we can see that cleaning it up and turning it into potentially valuable materials and further applications is possible.”

Shah said the team’s innovation could also be used for other waste streams such as rainwater lagoon sludge and mine tailings.

“We plan to work with South East Water to conduct a techno-economic analysis which will hopefully lead to a pilot trial.

“We are also interested in working with companies that manage stormwater lagoons and mine tailings. The next step of engagement with them could be testing their sample in our lab followed by a pilot trial,” he said.