The average person in the UK uses 149 litres of water per day – but what happens to it once it goes down the drain? Our wastewater can reveal far more than you’d expect.
You may not be surprised to hear that sewage shows high levels of antihistamines in the spring, antibiotics in the winter and illicit drugs such as MDMA at weekends, but how about the fact that alcohol also spikes on Wednesdays?
“It’s really surprising to see that no matter where we live, as a society we do really similar things,” says Professor Barbara Kasprzyk-Hordern from our Department of Chemistry. “We think we are all different, and I’m sure we are when we look at individuals, but as communities we are alike.”
Taking a fingerprint
Barbara’s research focuses on wastewater fingerprinting, where samples of water from rivers and treatment plants are tested using a process called mass spectrometry. This can detect levels of chemicals at incredibly low levels, giving an overview of what’s going on in our bodies and households at a town or city level.
For example, Barbara has found that weekends yield more of a chemical called 3-PBA, which is made when the body breaks down certain types of pesticides. She attributes this to the fact that people are more likely to cook from scratch and eat more vegetables on weekends.
Far from just being a source of interesting facts, though, Barbara’s research has a strong environmental and public health angle. “While the goal is always to make water cleaner, this requires an input of energy – and competing with that is the climate change dimension, which ideally requires the water utility process to be less energy intensive,” she explains.
“This gave us an opportunity to look at treating the source. So instead of investing in new technology for treating wastewater, how about we influence when pharmaceuticals are actually used?”
Flushing it out
The water testing carried out by Barbara’s team is sensitive enough to pick up when people have flushed excess medication down the toilet to get rid of it – something that can prove hazardous to the environment. Observations such as this could indicate a need for a public education campaign about how to safely dispose of unused prescriptions.
Barbara is also working with a team from across the University in a bid to change how GPs prescribe medicines for non-infectious diseases, such as diabetes and mental health conditions. This could mean a move to ‘green prescribing’ – spending time outside has been shown to help in mild cases of depression – or recommending medicines that have less of an impact on our ecosystems.
She adds: “I think people tend to forget that they are part of the environment – they think the environment is here and public health is there, but the simple truth is that we are part of it, and if we affect the environment it will fire back.”
Source of resources
Wastewater can also provide us with more than just information: it can act as a source of materials, enabling us to recover and reuse resources rather than look for or produce new ones. When the water we discard is treated, it is first sieved and filtered to remove any solid matter, and is then treated using a ‘sludge’ of helpful bacteria that break down dissolved organic material.
“Wastewater treatment is performed by a community of microorganisms,” explains Viviane Runa, a PhD student in our Centre for Sustainable & Circular Technologies (CSCT). “These communities are very complex, and it can be hard to identify what are the key bacteria – removing nutrients, carbon or other pollutants and contaminants. One of the aims of my project is to find ways to study these organisms, and better understand the interactions that take place in their communities.”
Viviane is focusing on a process to remove phosphorus from our wastewater. Phosphorus is a scarce resource, but one that is vital for growing crops. Some organisms in the water-purifying sludge can accumulate and store the phosphates from sewage. She says: “We can harvest the cells and use this waste sludge as a fertiliser, which can help to mitigate the phosphorus scarcity.”
Bacteria to bioplastics
Bioplastics – plastics made from renewable sources – can also be produced from sludge. The various stages of wastewater treatment can take place across both anaerobic (without oxygen) and aerobic (with oxygen) environments. “At the anaerobic stage, the bacteria in the sludge have a lot of carbon available to them from the wastewater,” explains Viviane. “However, as they don’t have oxygen present to enable them to grow, they simply take up all the carbon and store it.”
The cells store carbon in chains called PHAs – which are often plentiful in sludge when it is collected at the end of the anaerobic treatment phase. PHAs have similar properties to the plastic used for items such as water bottles, but with the added bonus of being biodegradable.
Viviane is examining the communities of bacteria found in wastewater treatment plants across the UK to compare their makeups and the amounts of nutrients and bioplastics that can be recovered from them. She is hoping that better understanding their composition could lead to greater yields of desirable chemicals, making water treatment greener than ever before.
“If we operate treatment plants in a different way, we can favour the growth of organisms that are actually more efficient,” she says. “This could enable recovery of other valuable resources.” While PHAs are the type of plastic that’s a positive to find in our wastewater, there are others that aren’t so welcome.
A minuscule menace
Microbeads are tiny spheres of plastic often measuring less than 0.5mm in diameter, even smaller than a grain of sand. Their use is incredibly widespread – from cosmetics, through to paints and agricultural products. It’s estimated that a whopping 250,000 tons of these particles make their way to the oceans each year, and into the food chain.
“The challenge with plastic microbeads is related to their size,” says Davide Mattia, Professor of Chemical Engineering. “They’re too small to be captured by wastewater treatment plants, so they end up in the oceans or in soil. Fish eat them or plants absorb them via their roots, so then we eat them. Microbeads are found in the fat tissue of our bodies; we are full of microplastics because of this cycle. The only way to address this problem is to stop using them.”
A partial ban
Unfortunately, the reality isn’t as straightforward. Although the UK government has banned the sale of ‘wash-off’ products such as shower gels and toothpastes containing plastic microbeads, their use is still permitted in many other products, including those that are left on the skin. There are also only a handful of other countries across the world who have implemented similar legislation. “The legal definition for what is banned is very narrow at the moment,” Davide observes.
A team, led by Professor Emeritus Janet Scott and including Davide and Professor Karen Edler, developed a method for creating a biodegradable alternative to microbeads by forcing a solution of a sugar called cellulose through a membrane. These beads are then washed off using vegetable oil before being fixed in an antisolvent solution. As cellulose is what plants are made of, it is a renewable, sustainable resource – offering further advantages over plastic.
The natural alternative
In 2018, the spin-off company Naturbeads was founded, which is working to scale-up the manufacturing process. “The company is now commercialising the technology,” he says. “The idea is that in one or two years’ time, there will start to be commercial products that use the cellulose beads.” What’s more, the beads can be tailored to mimic the properties of many different types of plastic microbeads for various uses – whether they’re opaque or translucent, rough or smooth.
“Once traditional microbeads are in the environment, you can’t remove them,” concludes Davide. “You would have to treat the entire ocean with a very fine-toothed comb. It’s just impossible.” While the use of these plastics sadly can’t be undone, the commercial adoption of a cellulose alternative would prevent further damage to the ecosystem.
“That’s the thing about studying wastewater,” Barbara sums up, “it provides an overall understanding of where the problems are and how they can potentially be solved.”