Treated wastewater in Victoria is still contaminated, according to a study. So are we and the environment safe?


Wastewater is a by-product of humanity that is produced all day, every day. In the home, wastewater is used water that disappears when you flush the toilet, empty the sink or empty the washing machine.


Industrial processes also produce wastewater. In the world, 359 billion cubic meters of wastewater are produced every year, equal to 144 million Olympic swimming pools.

In Australia, some of this water is treated and reused. This so-called recycled water is used, for example, to wash cars, irrigate crops and gardens. The treated water is also released into rivers as waste, which is regulated by an operator license.

So is treated wastewater safe? Our research, published today, has found that treating wastewater removes many particles, but some contaminants remain. While not sufficient to affect human health, the effects on the environment are less clearly established.


Read more: We now treat half of the world’s wastewater and can make inroads into the other half

Purple recycled water tap and hose with no drinking sign
Recycled water is commonly used to irrigate gardens and crops.

Making the most of our water

Water is a precious and limited resource. There is no such thing as new water. Our planet’s water dates back 4.5 billion years and is constantly being recycled by Earth’s systems.


As the earth’s population grows and the climate dries out, we need all the water we can get.

In light of this challenge, the state of Victoria has a plan to make better use of treated wastewater. Other Australian states and territories have similar plans.


Read more: Where to get more water: Eight unconventional resources to tap into

Wastewater comes from homes, businesses, industrial sites and farms, as well as any rainwater or groundwater that enters the sewage system.

Specialized treatment plants process this wastewater. A combination of technologies is used to achieve treatment goals, based on the character of the raw wastewater and the use of the treated wastewater. These processes include primary, secondary and tertiary treatment.


Wastewater treatment seeks to remove:

  • organic substances (proteins, hydrocarbons, oils and fats)

  • suspended solids (small particles)

  • bacteria (eg Escherichia coli).

In Victoria, as elsewhere in Australia, wastewater must meet stringent standards. Water companies achieve this by implementing stringent procedures and processes and monitoring water quality.

But even after treatment, some contaminants can remain. These can be divided into emerging and pre-existing contaminants.


Emerging contaminants include pharmaceuticals, pesticides, phthalates (used to make plastics stronger), industrial chemicals and chemicals in personal care products.

They are described as emerging due to the limited information we have about them, the risks they pose and dose-response effects, especially at low and ultra-trace concentrations.

Traditional contaminants include, for example, PFAS, trace metals and insecticides such as DDT.


So should we be concerned about contaminants in treated wastewater? Our new research has looked into this question.

Read more: PFAS at dinner? Studying the accumulation of “chemicals forever” in livestock points to ways to reduce the risks


What did the study find?

EPA scientists collaborated with the Victorian Department of Energy, Environment and Climate Action and 13 state water companies to investigate emerging contaminants in wastewater. As a science-based regulator, EPA undertakes research based on pollution and waste issues to protect the health of the Victorian community and environment. Use the data and evidence from studies like these to guide future action.

We collected 230 samples of treated and untreated water at a variety of wastewater treatment plants. We screened them for the presence of 414 emerging and pre-existing contaminants.

Outflow from a wastewater treatment plant
For the study, 230 samples of treated and untreated water from wastewater treatment plants were collected.
Image: EPA, Author provided

We have detected 180 contaminants in treated and untreated water. These included:


  • 48 chemicals found in pharmaceuticals and personal care products
  • 5 chemicals that disrupt the endocrine system
  • 21 per- and polyfluoroalkyl substances (PFAS)
  • 34 herbicides
  • 8 insecticides
  • 7 fungicides
  • 12 industrial compounds
  • 7 phenols
  • 28 disinfection byproducts.

None of the contaminant levels in the treated water exceeded human health guidelines for drinking water and water used for recreational activities.

As might be expected, the concentrations of most emerging contaminants were lower in treated water than in untreated water. However, some contaminants remained in the treated water. Examples included the antidepressant venlafaxine and the anticonvulsant drug carbamazepine.


Read more: A Fishy Problem: How Antidepressants Can Affect the Health of Our Aquatic Ecosystems

So which treatment method is best? Based on our study, it is one that combines all of the following:

  • an activated sludge process, which can be aerobic or anaerobic if aerobic, air is required and is introduced into the mixed liquid by aeration devices or natural diffusion

  • prolonged aeration using a mechanical device to aerate the water

  • ultraviolet light disinfection, which uses UV radiation to break down the DNA of pathogens

  • microfiltration, a membrane process that removes particles larger than 0.1 microns

  • reverse osmosis, which is another membrane process and removes most of the salt and large molecules, producing water with very low dissolved content

  • disinfection with chlorination, zoning or UV disinfection.

But treatment that combines all of the above processes is relatively rare. It is used by only four out of 200 wastewater treatment plants in Victoria. These plants produce the highest grade of recycled water.


Read more: ‘Cuck factor’ pushes premier towards desalination once again, but history suggests time for recycled water has come

What does this mean for the environment?

None of the contaminants we detected in the treated wastewater violated human health guidelines. However, we must not forget the environment.


Pharmaceutical pollution, in particular, is a pressing global problem. A recent study found pharmaceuticals in 258 rivers in 104 countries on all continents. Pharmaceutical chemicals degrade rapidly in the environment, but are continually replenished.

According to the World Health Organization, traces of pharmaceuticals in drinking water are very unlikely to pose any risk to human health. But information on potential environmental effects remains limited.


To find out more: 80% of domestic water goes to waste, we have to recover it

You can make a difference

Environmental authorities regulate how business and industry use, store and dispose of their waste. However, your actions at home, no matter how small, can mean fewer contaminants make it to wastewater treatment plants.

Actions you can take include:


  • take medicines only as directed and return unwanted and expired medicines to a pharmacy

  • choose chemical-free cleaning products

  • minimize the use of pesticides in the garden and insect sprays in the house

  • If you have a wastewater management system at home, such as for gray or black water, maintain it regularly and avoid using strong chemicals.

Next steps

Further research is underway involving the Victorian EPA, water companies and research institutes. It aims to build our understanding of what, if and how emerging contaminants are present in soil and absorbed by crops irrigated with recycled water.

Ultimately, the work will reduce the potential risks posed by wastewater to people and the environment by ensuring that official advice is up-to-date and evidence-based.

The authors of the reports are EPA scientists Minna Saaristo, Simon Sharp, Shanli Zhang and Mark P. Taylor.


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