What’s in Wastewater and Why is it Dangerous?

TL; DR: Humans use water. Stuff gets in water. Humans treat water. Humans don’t die. Yay.


Water – H2O, agua, whatever you want to call it – is essential to life on Earth. We use it for all kinds of things in the household (such as for drinking, washing our dishes, clothes, and bodies, watering the garden, etc) as well as in industry, hospitals, and so on. In Australia, we expect this water to be of a minimum acceptable standard (ie clear, safe to drink, etc) and have laws to ensure the water utility provides this.

But what happens to it once it’s been used? 

Well, to answer your insightful and conveniently pertinent question, let’s start with a definition.

“Wastewater … is any water that has been adversely affected in quality by anthropogenic influence.” – The Great and Powerful Wikipedia

This basically means once humans have used the water it becomes wastewater. This includes residential sewage, as well as industrial, and municipal water. The water utility (in Perth that’s the Water Corporation) is also responsible for ensuring wastewater is transported to a wastewater treatment plant, where the wastewater is treated (duuhhh) to a quality deemed acceptable for release into the environment, or further treatment for re-use.

Let’s take a closer look at what’s actually in wastewater, and the issues these constituents can create.

Constituents of Concern

What makes untreated wastewater such a disaster?

Another great question, well done! That would be the so-called Constituents of Concern – ooooooooo, scaaaryyyy. Check ’em out in this rad table:

Constituent of Concern Description
Suspended Solids Including plastics, sediments, debris, etc
Biodegradable Organics Biomass, etc
Pathogens Bacteria, viruses, disease-causing nasties
Nutrients Mainly phosphorus and nitrogen
Priority Pollutants The more toxic and potent chemical contaminants
Refractory Organics Poorly biodegraded compounds
Heavy Metals Lead, mercury, etc
Dissolved Inorganics Salts, ions, all your multivitamins that you’ve peed out
Pharmaceuticals Hormones, antibiotics, other medicine products you pee out

If released into the environment or re-used untreated, wastewater constituents can have huge impacts on environmental and human health. (For example, check out this article on how plastic microbeads are making fish toxic to eat!) However, modern treatment processes aim to ensure safe release of wastewater to the environment. Seeing as wastewater is defined as a product of human impact, I think we are morally obligated to take responsibility for the ecological impact it can have if released untreated.

Let’s look at an example.

Mercury (aka all-around bad guy) – A Heavy Metal

Heavy metals – including Mercury (Hg), Lead (Pb), Cadmium (Cd), and others – are poisonous at varying concentrations. They do not biodegrade, nor can they be destroyed, making them a long term hazard if contamination occurs.

Mercury is a naturally occurring planet in the solar system. However, it does not occur naturally in earthly living organisms, having no role in biological or physiological functions. As such, its presence in organisms is a sign of contamination and/or bio-accumulation. This means it has polluted a water or soil source, been consumed by an organism, and made its way up the food chain through predation.

Hg Accumulation

Mercury has widespread industrial applications, and is used in products such as batteries, thermometers, and dental fillings! If these products are not properly disposed of, the mercury can end up in wastewater and, if not treated, do some serious damage (as it did in 1932 in Japan). Various forms of mercury poisoning can cause a multitude of health issues, including damage to the brain and central nervous system, spontaneous abortion, developmental difficulties in children, and more.

I was pretty confronted by the potential for harm that mercury presents, but luckily there are strict environmental policies for the handling of heavy metals.

For more information on heavy metals and their impacts on the environment and human health, I recommend this site.

To Treat or not to Treat?

Have a gander at this vid for more information on the wastewater treatment process. Also check out the Water Corps’ process here. It’s important to note that there are no processes to remove heavy metals from wastewater. Rather, environmental laws restrict the use and disposal of heavy metals, including mercury, to ensure proper disposal so that they do not enter wastewater flows in the first place!

BUT, if mercury does make it in, wastewater treatment plants typically employ the Toho process – adding Potassium Iodide (KI) to precipitate Mercury Iodide (HgI2) – so they can physically remove mercury from the wastewater. This and other methods of mercury removal are explained in all the gory (chemistry intensive) detail here.

Personally, I believe ensuring mercury never enters wastewater is the best solution both now and moving into the future. Prevention of contamination through proper disposal is safer, cheaper, and more efficient than the lazier pour-everything-down-the-drain-and-let-someone-else-deal-with-it approach.

The whole “out of sight, out of mind” mantra that our parents lived by is dead.

With today’s increasing environmental conscience, we are beginning to be much more accountable for the end-of-life management of products, including wastewater. There are many examples of this (like nespresso coffee pods), demonstrating the importance of this kind of thinking moving into the future. I find that life-cycle thinking is an excellent sign of the times and is certainly the way forward for a sustainable society, ensuring positive relationships are developed and maintained between humans and the environment. Check out my last post to read more on this!


Most people’s conceptions of what wastewater is, and what’s in it, is often far from the truth.Far from the truth 2

Greater public awareness of what should and shouldn’t be disposed of through wastewater mediums is required to ensure treatment is adequate and efficient. If people know what to flush, then we can reduce the number of constituents for which we need to screen and treat, and reduce cost and impact of wastewater in the environment.

I’d love to hear your thoughts on this topic! Comment below and I’ll do my best to get back to you.

Until next time,

– SustainableTim


Useful Links and References:













Heavy Metals:





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6 thoughts on “What’s in Wastewater and Why is it Dangerous?

  1. Hey SustainableTim, really enjoyed reading your blog and watching your vlog. That constituents of concern list is very intimidating, we clearly have a lot of work ahead of us if we want to reach our clean water goals. I completely agree with you when you say that “out of sight, out of mind” is dead, we need to work together to make everyone aware of where their water is going. I could never bring myself to wash oil down the sink now that I’ve seen how it accumulates in sewerage systems. Keep up the good work, can’t wait to read/watch next weeks instalment!

    Liked by 1 person

  2. I really liked how you linked your blog and your vlog. It flowed really nicely and really helped when you mentioned a lot of examples in your blog, both recent and old to really cement the idea that it’s not just a new problem. Really good links too by the way!


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