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Could liquid biosolids help grow Australia's agricultural industry?

Producing biosolids in liquid form could inject new life into Australia’s typically underperforming soils and grow a new market for the wastewater treatment by-product.

According to the Cooperative Research Centre for High Performance Soils (Soil CRC), poor soil quality costs Australian farmers billions of dollars in lost revenue each year. 

But injecting the nutrients and organic matter in biosolids into a plant’s root zone could enhance agricultural productivity and improve soil structure, fertility and function.

This is what Victoria’s South East Water (SEW) hopes to prove by trialling the use of liquid biosolids at its Longwarry Water Recycling Plant.

The trial, which is being conducted in partnership with the Soil CRC and the University of Newcastle, has so far seen a bumper crop of sorghum produced under dryland conditions.

The current method for producing biosolids in Victoria involves a long treatment process to make sure the product meets treatment grade T1, the only type of biosolids deemed safe for unrestricted use as fertiliser on farms. 

This includes storing the product for a minimum of three years before it is used.

SEW Senior Research and Planning Scientist Aravind Surapaneni said the utility aims to show that using biosolids in liquid form – known as treatment grade T2 or T3 – is appropriate for use on agricultural crops.

“This would permit time and cost efficiencies through bypassing conventional drying and stockpiling processes,” Surapaneni said.

“By undertaking this trial, we can assess the impact of using T3 grade liquid biosolids on crops, as well as identifying any potential risks of using this byproduct.”

New South Wales is so far the only state where liquid biosolids are used, and Soil CRC CEO Michael Crawford said the SEW trial is important for Australia’s water and agricultural industries. 

“In addition to addressing an important issue for the water sector, it provides scientists and farmers with an understanding of how the addition of organic matter and nutrients to the subsoil can improve soil productivity and, ultimately, farmer profitability,” Crawford said. 

“The Soil CRC provides the opportunity for effective collaboration between industry and science, as well as a pathway to adoption of new soil management technologies by farmers.”

This isn’t SEW’s first foray into biosolids research. The utility won the Research Innovation Award at the 2019 Australian Water Awards for its project ‘Driving Change from Conservatism to Pragmatism – Better Use of Biosolids and Recycled Water by Using Research to Challenge Guidelines’, which challenged industry guidelines about how long biosolids need to be stored.  

If successful, the trial could influence the Victorian Environmental Protection Agency’s guidelines on liquid injection of T3 grade biosolids in the state, which would provide benefits for water authorities, farmers and their crops. 

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