High-quality organic biosolids could be more readily available for Australian farmers as the result of an important SA Water study confirming a faster timeframe to eliminate nasty pathogens, offering significant benefits to both Australian agriculture and water industries.
Collected and safely treated at SA Water’s wastewater treatment plants, around 30,000 tonnes of organic biosolids matter is produced every year and provided free to primary producers to improve soil quality for dry land crops like cereals, or irrigated permanent crops such as citrus or vines.
Current guidelines require high-grade biosolids to be stored for three years to ensure all pathogenic microorganisms are inactive before the end product.
Speaking ahead of today’s Ozwater ‘19 conference in Melbourne, SA Water’s Senior Manager of Water Expertise Dr Daniel Hoefel said a pathogenic die off validation project had demonstrated a better-quality biosolid product could be achieved in just a third of the time.
“While the practical benefits of more quickly recycling and reusing biosolids are clear, we wanted to ensure that any changes to the treatment and storage process does not compromise the end result, as untreated product can potentially contain pathogens like bacteria, viruses and protozoa,” Dr Hoefel said.
“Following an intensive monitoring program for both fresh and aged biosolids of up to 30 months, we detected no additional improvement in the guideline requirements of biosolids tested by extending the stockpiling period beyond 12 months.
“This is a significant outcome for both farmers and water utilities across the country, as on-site storage is a costly process and requires specialist infrastructure such as sludge drying lagoons and specifically-engineered hardstands to age the stockpiles over a long-term period.
“The overall agronomic quality of biosolids for use in agriculture also deteriorates the longer it remains in storage, which means cutting the long-term stockpiling by as much as two-thirds is likely to see a higher-quality end product for farmers.”
Treating wastewater sludge into reusable biosolids at wastewater treatment plants can involve gravity thickening and dissolved air floatation thickeners, before anaerobic digestion is used to speed up the breakdown of organic matter. The output is then required to undertake lagoon storage for at least one year and stockpiling for a further three years before the biosolids can be collected from site by primary producers.
According to 2017 statistics, the amount of dry biosolids produced in Australia was 327,000 tonnes per year, with an overwhelming majority used in the agriculture sector.
The project’s exciting results have now been successfully submitted to the local regulatory authorities, South Australia’s Environmental Protection Authority and SA Health to seek to officially reduce the on-site stockpiling guidelines from three years to one year for Grade A biosolids, and to six months for Grade B biosolids.
“Having a quicker turnover of biosolids means an ability to decrease the storage areas required for treatment, which we estimate could potentially lead to significant operational savings across our wastewater treatment plants,” Dr Hoefel said.
‘SA Water’s experience in reducing storage times to achieve Grade A biosolids’ will be presented at OzWater’19 - Australia’s international water conference and exhibition - at the Melbourne Convention Exhibition Centre.
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