Biosolids

• This nutrient-rich material is then dried to make “biosolids”, which are used to fertilise agricultural soil.
• Unfortunately every kilogram of biosolids also contains thousands of tiny pieces of plastic.
• These pieces are so small they can only be seen under a microscope, so they’re called microplastics.

Biosolids as fertiliser

• The waste becomes a resource, a useful and economically viable fertiliser, rather than ending up in landfill.
• Read more:
  More than 1,200 tonnes of microplastics are dumped into Aussie farmland every year from wastewater sludge

Microplastics in Australian biosolids

• Wastewater treatment plants can capture anywhere from 60% to more than 90% of the microplastics in sewage before the wastewater is discharged.
• We assessed the abundance, characteristics and size ranges of microplastics in biosolids collected from 13 wastewater treatment plants across three states.

• We suspect this corresponds to people washing more synthetic fleece clothing and blankets.
• We estimate Australians release between 0.7g and 21g of microplastics per person into wastewater every year.
• This contributes to the amount of microplastics in biosolids.
• Our biosolid samples contained anywhere from 1kg to 17kg of microplastics per tonne.

What’s the problem?

• While natural weathering processes such as sunshine and rain will slowly break down microplastics into smaller and smaller particles, that only makes matters worse.
• Smaller particles cause more harmful effects to soil organisms.
• Microplastics in soil can be ingested by soil organisms such as earthworms and cause harmful effects on these vital organisms.

Here’s what we can do

• We need to put effective control measures in place to minimise the accumulation of microplastic in productive agricultural soils.
• The most effective way to do this is to reduce the level of microplastics in biosolids at the source.
• Australia’s National Plastics Plan recommends the Australian government work with industry to “phase-in” microfibre filters on all washing machines by 2030.
• Read more:
  'Humanity's signature': study finds plastic pollution in the world's lakes can be worse than in oceans

• This project was co-sponsored by Urban Utilities, Sydney Water, SA Water, Water Corporation (WA) and Eurofins Environment Testing Australia.
• Frederic Leusch receives funding related to this research topic from the Queensland Government through an Advance Queensland Industry Research Project, Water Research Australia, and various Australian water utilities.