Biosolids – timing is everything
When Benjamin Franklin popularised the term ‘time is money’ back in 1748, it’s unlikely that sewage sludge was on his mind, but ask anyone involved in the processing of biosolids, and they’ll tell you that time is a big factor.
The major by-product in the water treatment process, biosolids are made up of waste sewage sludge, which has typically undergone treatment to remove pathogens (bacteria, parasites and viruses) and volatile organic matter. Once stabilised, it’s a product with a broad range of applications – from fertiliser, compost and road base to biofuel, glass manufacture and jewellery.
As you’d expect, all biosolids applications are regulated and in Australia, those regulatory regimes are some of the strictest in the world.
South East Water currently produces around 3000 dry tonnes of biosolids each year across four of its eight treatment plants in Melbourne’s south-east and on the Mornington Peninsula. This Victorian Government utility is committed to 100 percent beneficial use of its biosolids, and operates treatment processes that convert the sludge into biosolids-based fertiliser. The product is then shipped to local farms where it’s used to improve soil quality and structure, most commonly for cattle pasture.
These treatment processes are tightly regulated by Victoria’s Environmental Protection Agency (EPA), which requires that specific steps are taken to ensure that potentially harmful pathogens such as E. coli, salmonella and enteric viruses are not allowed to contaminate the end product.
For South East Water that means a rigorous program of testing and analysis and a minimum drying and storage period of three years in order to achieve the highest quality grade (Treatment Grade T1) which, from a microbiological perspective, is suitable for ‘unrestricted’ use on local farms.
With sludge volumes set to rise significantly in the coming years, however, this mandatory storage period is presenting South East Water with a major headache.
“South East Water services some of Melbourne’s fastest growing regions, and we expect sludge volumes to triple in the next three decades,” says product quality scientist Dr Aravind Surapaneni.
“Our treatment plants have a finite space for stockpiling biosolids. The three-year storage requirement means that sooner or later we will run out of space, and that will require significant capital expenditure, unless we find a way to do things differently.”
With the company’s commitment to the beneficial use of biosolids non-negotiable, Surapaneni and his team undertook a project to examine the possibility of reducing the storage period of biosolids without compromising their ‘unrestricted’ classification.
“We set out to prove that the reduction in a range of pathogen quantities required by the EPA could be achieved after one year of stockpiling rather than three.
They began by examining research commissioned by the Smart Water Fund, an initiative established by the Victorian water industry in 2002 to help address the ongoing challenges posed by climate change and water scarcity.
The fund’s research, which involved Imperial College London and RMIT in Melbourne, explored alternative methods to treat biosolids and reduce the pathogenic risk. Surapaneni and his team set out to validate this research with a one-year R&D project of their own, based at South East Water’s Boneo and Somers treatment plants.
“We set out to prove through rigorous sampling and monitoring that the reduction in a range of pathogen quantities required by the EPA could be achieved after one year of stockpiling rather than three,” says Surapaneni.
From November 2014, fortnightly samples of raw sewage and waste-activated sludge were taken. Samples were also taken at drying pans (Boneo and Somers), solar dryer sheds (Boneo), and one-year stockpile stages, and measured against equivalent samples from the three-year process.
Over the 12-month testing period, the reduction in enteric viruses, E. coli and salmonella bacteria was found to meet and exceed the EPA log reduction requirements. The removal of the parasite Ascaris ova could not be proven, as it is not endemic in Australia and could not be detected in sewage. South East Water submitted the research for peer review and further examination.
“It was clear that both the aerobic and anaerobic drying processes we operate at Boneo and Somers could achieve the same microbial safety levels after one year of stockpiling,” says Surapaneni.
“We also found from literature and RMIT research that the beneficial elements in the biosolids – particularly nitrogen, phosphorus and organic carbon – degraded over time and were significantly higher in product stored for one year than in product stored for three.”
South East Water took its research and findings to the EPA and, in December 2015, was granted approval for one-year stockpiling of sludge at Boneo and Somers using the now validated treatment process to achieve Treatment Grade T1.
The validated treatment process has been documented and formalised in a quality management system certified to the HACCP (hazard analysis and critical control points) food safety standard. A commitment has also been made to the EPA that periodic monitoring of sewage for the presence of Ascaris ova will continue in case the incidence of this parasite increases as a result of changes in demographics.
“This is a game-changer for how we manage our biosolids programs,” says Surapaneni. “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 are obvious beneficiaries. Growers across the south-east region of Melbourne will be able to take advantage of better quality biosolids fertilisers, and in larger quantities.
For South East Water though, annual cost savings at the two treatment plants will run into the tens of thousands. The need to regularly turn stockpiles using heavy equipment is significantly less, while the cost of weed control and stockpile segregation is dramatically reduced.
Across Boneo and Somers almost 20,000 square metres of storage will be freed up to cope with the expected growth in sludge in the years ahead. There is no 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.
“Further reductions in storage will mean even greater streamlining and operational efficiencies, and I’m hopeful we can deliver more savings back to our customers,” says Surapaneni.
Franklin was right, even after all these years. Time is money after all.
The author, Matt Mollett, is spokesperson for South East Water in Victoria. This article also appears in Issue 1 of Corporate Waste Solutions.