The Victorian Environmental Protection Authority (EPA) have officially given South East Water the approval to reduce the minimum drying and storage period for biosolids at two of its treatment plants from three years to one.

This will now pave the way for significant cost savings while improving the nutrient value of its biosolids-based fertilizer product.

The reduction in storage time is expected to deliver tens of thousands of dollars in annual cost savings, and free up 20,000㎡ of storage, enabling the utility to meet the needs of a rapidly growing population in Melbourne’s south-east.

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.

In 2015, South East Water completed a rigorous 12-month testing program at its Boneo and Somers treatment plants, and submitted research to the EPA that demonstrated it could achieve the same microbial safety levels after one-year of stockpiling, compared with the mandated three-year requirement.

Biosolids are a major byproduct from the water treatment process and are made up of waste sewage sludge, which has typically undergone treatment to remove pathogens (bacteria, parasites and viruses) and volatile organic matter.

South East Water produces around 3000 dry tonnes of biosolids per annum, and in line with its commitment to 100 per cent beneficial reuse, 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 such as E. coli, salmonella and enteric viruses are not allowed to contaminate the end product.

South East Water Infrastructure General Manager, Rex Dusting, said South East Water expects the sludge volumes it services to triple in the next three decades so reducing the minimum storage time will provide more storage space for the future.

“Our treatment plants have a finite space for stockpiling biosolids. 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,” Mr Dusting said.

Scientists at South East Water initially examined existing research commissioned by the Victorian Smart Water Fund, in which Imperial College London and Melbourne’s RMIT had explored alternative methods to treat biosolids and reduce pathogenic risk.

The team then set out to validate this research with a one-year project of its own, based on testing at Somers and Boneo.

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, so South East Water submitted the research for peer review and further examination.

Its treatment process was validated, documented and formalised in a quality management system certified to the HACCP food safety standard.

“This is a significant breakthrough in how we manage and treat solid waste at South East Water,” Mr Dusting said.

“It shows how high quality research and development can drive important change in our industry, and deliver greater efficiency and better environmental outcomes.”

Local farmers will now be able to take advantage of better quality biosolids fertilisers, and in larger quantities, while South East Water’s annual cost savings at the two treatment plants will run into the tens of thousands.

The need to regularly turn stockpiles using heavy equipment will now be reduced and the cost of weed control and stockpile segregation is also dramatically reduced.

The new storage space 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.

“By further reducing stockpiling requirements, we hope to achieve even greater streamlining and operational efficiencies, and deliver more savings back to our customers,” Mr Dusting said. 

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