Research from UNSW Sydney has assessed a range of contaminants that may warrant closer monitoring to help protect the environment and maintain the benefits of biosolid reuse.
UNSW engineers have identified a number of contaminants that may warrant closer attention to help water utility companies and regulators make informed decisions about the management of biosolids.
Biosolids are treated sewage sludge – that is wastewater from household kitchens, laundries and bathrooms which has been processed to create a product suitable for beneficial use.
About 80% of biosolids produced in Australia are reused on farmland since it provides valuable nutrients and organic matter that can improve soil quality and support plant growth.
However, biosolids can also contain the remnant traces of chemicals entering the system from everyday household activities such as washing, cleaning and taking medicines.
A new study, led by UNSW researchers, has now examined what happens to some of those chemicals when biosolids are applied to farmland, including how long they can remain in the environment and whether their concentrations could potentially affect plants and animals.
Their findings, published in the Journal of Hazardous Materials, provides a framework for identifying contaminants that may need closer attention to ensure regulators can continue to utilise the benefits of biosolids.
Professor Denis O’Carroll, from the Water Research Laboratory in UNSW’s School of Civil and Environmental Engineering, said: “It is important that biosolids can continue to be applied to the land to act as a fertiliser and get nutrients into the soil.
“What this research has shown is that there are some potential contaminants of concern because of their concentration or how they persist in soil.
“And we hope this work can be the first step in a multi-staged plan to mitigate against the problem.”
Environmental screening assessment
Importantly, the study is an environmental screening assessment.
It does not demonstrate that the chemicals examined are causing harm on farms, that food grown using biosolids is unsafe, or that people are being exposed to harmful levels of contaminants.
However, the researchers did identify several chemicals that could persist in soil for months or even years. These include some per-and-polyfluoroalkyl substances (PFAS), carbamazepine (a medicine used to treat conditions such as epilepsy), triclocarban and triclosan (antimicrobial chemicals in personal care products) and galaxolide and tonalide (fragrance chemicals).
“Whenever people flush their toilet or their water goes down the sink, all of that ultimately ends up at a wastewater treatment plant,” says Dr Calvin He, author of the paper.
“That wastewater can be treated and the resulting biosolid can be applied to farmland as a fertiliser. But if there are still contaminants present then they can stay in the soil.
“Even though biosolids have a really amazing benefit of being full of carbon, nitrogen and phosphorus, there is also a downside in that you’re potentially applying these contaminants.”
For their study, the UNSW team examined 47 chemicals, including pharmaceuticals, personal care products, industrial chemicals, hormones and other substances that have previously been detected in biosolids.
These included commonly used medicines, antimicrobial ingredients found in some personal care products, and chemicals used in industrial and consumer applications.
