South East Water's shorter storage period for biosolids

South East Water has received approval from the Victorian Environment Protection Authority (EPA) to shorten the minimum drying and storage period for biosolids at two of its treatment plants. The reduction in storage time is expected to deliver significant savings in cost and storage, enabling the utility to meet the needs of a rapidly growing population in Melbourne’s south-east.

South East Water produces around 3000 dry tonnes of biosolids per annum and operates treatment processes that convert the sludge into biosolids-based fertiliser, which farmers then use to improve soil quality and structure. Treatment processes are tightly regulated by the EPA, which requires that specific steps are taken to ensure potentially harmful pathogens are not allowed to contaminate the end product.

“Our treatment plants have a finite space for stockpiling biosolids,” said Rex Dusting, infrastructure general manager at South East Water. “The three-year storage requirement meant that sooner or later we will run out of space, and that would require significant capital expenditure unless we found a way to do things differently.”

Scientists at South East Water initially examined existing research in which Imperial College London and RMIT had explored alternative methods to treat biosolids and reduce pathogenic risk. The team then set out to validate this research with a project of its own, based on testing at its Somers and Boneo treatment plants.

Over a 12-month period, the reduction in E. coli, Salmonella and enteric viruses was found to meet and exceed the EPA log reduction requirements. Its treatment process was validated, documented and formalised in a quality management system certified to the HACCP food safety standard; in December, South East Water was granted approval by the EPA for one-year stockpiling of sludge at Boneo and Somers while maintaining the highest quality grade of biosolids.

The move to one-year stockpiling will increase the nutrient value of biosolids fertilisers used by local farmers, with beneficial elements such as nitrogen, phosphorus and organic carbon present in significantly higher levels compared with product stored for three years. Meanwhile, South East Water’s annual cost savings at the two treatment plants will run into the tens of thousands.

Not only is the need to regularly turn stockpiles using heavy equipment significantly less, and the cost of weed control and stockpile segregation dramatically reduced, but the change to process will free up almost 20,000 m² of storage. This will enable South East Water to cope with the expected growth in sludge in the years ahead, without the need to construct new stockpile areas or acquire new buffer zones.

South East Water will now seek approval to reduce stockpile durations at other treatment plants and is also examining longer-term opportunities to reduce the one-year requirement to a matter of months, unlocking further savings in operating and capital expenditure across the organisation.