Soil-injected liquid biosolids trial in Victoria

A trial in Victoria is investigating new ways to use biosolids, the by-product of the wastewater treatment process.

Biosolids provide farmers with a nutrient-rich fertiliser to maintain soils and stimulate plant growth, thus increasing agricultural productivity. Water organisations have used liquid biosolids in Australia since 1998, but all applications so far have been limited to New South Wales. The current method for producing biosolids in Victoria involves a long treatment process to ensure the product meets treatment grade T1 — the only type of biosolids deemed safe for unrestricted use as fertiliser on farms. This process involves storing the product for a minimum of three years before use.

In partnership with the University of Newcastle and supported by the Soil Cooperative Research Centre (Soil CRC), researchers from South East Water are studying the effects of soil-injected liquid biosolids on soil structure, fertility and function at their Longwarry Water Recycling Plant in Modella, Victoria.

Approved by EPA Victoria via its research, development and demonstration pathway, the trial has already recorded a bumper crop of summer forage sorghum following the liquid injection of biosolids under dryland conditions.

Soil CRC CEO Dr Michael Crawford believes the project is vital: “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.

“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,” Dr Crawford said.

University of Newcastle environmental remediation researcher and one of the project investigators, Dr Balaji Seshadri, said optimising the use of biosolids will result in high-value products that can enhance agricultural productivity and soil health.

“Delivering nutrients and organic matter in biosolids to the root zone via liquid injection is one novel approach we’re exploring through this joint trial that will ultimately benefit Australia’s farming community,” Dr Seshadri said.

South East Water’s Senior Research and Planning Scientist Dr Aravind Surapaneni said, “We hope to prove that using biosolids in liquid form (known as T2 or T3 treatment grade) is appropriate for use on agricultural crops. This would permit time and cost efficiencies through bypassing conventional drying and stockpiling processes.

“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 by-product,” he said.

If successful, the project may influence EPA guidelines on liquid injection of T3-grade biosolids in Victoria. To celebrate the success of the project so far, South East Water hosted a biosolids field day with more than 100 industry professionals and researchers at the plant.

South East Water had another recent cause for celebration after being declared the winner of the Research Innovation category at this year’s AWA National Awards held in May. Dr Surapaneni accepted the award for a groundbreaking project to drive industry change on the use of biosolids and recycled water based on research.

“At South East Water, we’ve long recognised the role of research in driving industry improvements and greater customer value,” Surapaneni said.

“Using rigorous research methodology and expertise, together with collaboration with industry and stakeholders, our project team was able to deliver regulatory changes that significantly reduced storage requirements for biosolids and recycled water from three years to one year and from 25 days to 18 days respectively,“ he added.

Water authorities around Australia have already adopted results of this research, which has translated into millions of dollars in savings, improved efficiencies at treatment plants and increased recycled water availability to customers.

Image caption: Biosolids field day at Longwarry hosted by South East Water. Image credit: © South East Water.