Behind the PhD-degree: Rebeca Pallarés Vega and Thomas Prot

The world is in disbalance. Human prosperity has caused major problems worldwide, but brave scientists are up for a challenge of global proportions. Meet Rebeca and Thomas – a biologist researching how to combat antibiotic resistance to save lives and a chemical engineer preventing political and economic crises by magnetically lifting iron-phosphate crystals. Both took a closer look at our wastewater in a fight for a better planet and a better life.

Discover what this couple of young scientists discovered about their research and how they got there. The people behind the science, and the science behind the people.

Menacing microbes and molecules

While wastewater treatment plants are major filters regulating human output into the environment, they still leach molecules and microbes that can harm – albeit not at first sight. Rebeca and Thomas explain the routes of these minuscule pollutants and how they cause significant troubles.

One of these ways is one of the super bacteria. Bacteria are everywhere, including all over you. They usually cause no problems. But sometimes, we get badly infected. Resulting in a lethal outcome. “Normally, we treat these harmful bacteria using antibiotics, but more and more are becoming resistant,” Rebeca explains. “Some of us already have some antibiotic-resistant bacteria in our body.

While our immune system is working, they are controlled. But if our immune system is down, we might become sick. If these bacteria causing the illness happen to be resistant to antibiotics, the treatment might not work.

Increasingly worrying are the so-called superbugs. Those bacteria are resistant to multiple antibiotics. “If they cause an infection, we cannot treat the patient anymore,” she says.

For a while, it has been considered that the microbes can gain this super ability at a bacterial rendezvous point we call a wastewater treatment plant, after which they seep into the environment, polluting the natural systems with resistant microbes.

Similarly, the leaching of phosphorus-rich compounds into surface waters causes an imbalance in the surrounding ecosystems. “In Europe, we flush up to 25% of our phosphorus needs down the toilet because it was contained in our food, through its use as a fertilizer for plants,” Thomas says.

“Excessive phosphate concentrations in surface waters cause algal blooms, ruining ecosystems they come in touch with,” the chemical engineer explains, “and the phosphorus reserves are limited and not well-distributed worldwide. For example, Europe has very few phosphorus reserves, so a phosphorus shortage could really cause a political crisis.”

Mobile DNA

Both scientists researched the prevention of these crises in their own ways.

Rebeca first established how widespread resistant genes in wastewater are. “We checked for DNA, for antibiotic-resistant genes by taking samples from the Dutch wastewater treatment plants,” she states, “and we saw that they were doing a fair job removing the genes – around 100 times less in the output than in the input.”

Which sounds like a great outcome, but more has to be done. Rebeca: “they do quite some nice work, but still, there is a constant release of antibiotic-resistant genes from the wastewater. Especially when it rains, the plants are doing worse in removing the genes.” Real troublesome in a country with a history of heavy rains.

On top of that, Rebeca has researched the inter-exchange of these resistant genes through mobile DNA – plasmids – that can transfer from one bacterium to the other. Rebeca: “Even when we know how to deal with one species, the resistant genes could persist in the others.” Some of which keep building up all sorts of different gene clusters, including resistant DNA to other compounds such as disinfectants.

“They do quite some nice work, but still, there is a constant release of antibiotic-resistant genes from the wastewater

In the end, this breeds a race of multiple antibiotic-resistant super bacteria. Given a selection pressure – such as antibiotic presence – the superbugs survive and proliferate. “As we’ve seen with COVID,” she explains, “the best-fit variants – i.e., the delta variant – will take over.

Rebeca was happy to contribute to the genetic arms race. “In the end, we figured out data that can help to assess the risk of antibiotic-resistant discharges and studied how plasmids spread through a complicated environment such as in wastewater.  Some of the findings are baby steps, but we gained insights into the unknown.”

Mining for phosphorus in wastewater

For Thomas, the risks of phosphorus discharge were already clear as day. But once again, too little is done in wastewater treatment plants to prevent crises. Thomas: “Current in-place methods can only recover up to 30% of the phosphorus from sludge.”

They do so in the form of a mineral called struvite. “Phosphorus likes to attach to certain metals. By adding magnesium to sludge, grains of phosphorus-rich struvite can form and be harvested,” he explains.

But there is another strategy. Iron is commonly added to remove phosphorus in wastewater treatment plants, and the resulting iron phosphate is easier to recover. Thomas: “It was discovered that phosphorus binds even better to iron – creating a magnetic mineral called vivianite that ends up in the sludge.”

In total, we will be able to extract more than 60% of the phosphorus from wastewater. More than twice as much as with struvite.

The chemical engineer researched how to scale the formation and extraction of the magnetic grains to pilot scale. “To get all the vivianite out, we used strong magnets – industrial mining equipment. And could pull out most of it,” he says, “in total, we will be able to extract more than 60% of the phosphorus from wastewater. More than twice as much as with struvite.”

And Thomas and his team further improved the process. “We checked whether we could make more vivianite by adding more iron and whether we could form it in different parts of the wastewater treatment plant,” he explains. Indeed, with little effort, the process could be further improved.

“The strategy can work for any wastewater treatment plant as long as sufficient iron is present, which is commonly the case in regions with stringent phosphorus discharge limits like in North European countries,” Thomas says. And it is a necessity. “In Germany, at least 50% of the phosphorus should be recovered by in-place methods in a few years, which was simply not possible with the old methods.”

A couple of scientists

While adventurously looking to gain experience abroad, Thomas and Rebeca first met at Wetsus. Next to finding their love for science here, both scientists fell for each other too.

But when Rebeca was about to return home – as there seemed to be no further place for her at Wetsus – she got a surprise call, telling that she suited the position of a new Ph.D. candidate. “I figured we would not be together, I was about to fly back to Spain, but I stayed around for Thomas’s birthday, as I got the call…” she explains laughingly, “well, I ended up staying, we are still here together.”

Happy as ever, they just succesfully defended their Ph.D.’s on the same day.

“Which is great,” Thomas says, “as we had quite some overlap and we wanted to invite a lot of people.” For him, that is what the last few years have been really about. “I like the science, but the people drive me. I never expected to do a Ph.D. in the first place, but the atmosphere in the phosphate theme convinced me.” “And,” Rebeca says, “some people think Thomas stayed around for me, but it was actually because of the love for Leon, his supervisor.”

“I never expected to do a Ph.D. in the first place, but the atmosphere in the phosphate theme convinced me

Rebeca had already taken her interest in science at a younger age. “In Spain, we go home during lunchtime, and it’s a well-known fact that after eating, Spanish dads fall asleep – have a siesta – with the sound of wildlife documentaries,” she says, “as I watched the animals, plants, oceans, everything really, always inspired me. And I still like all these different aspects of biology.” After her education, a Ph.D. was a logical choice.

Now Rebeca is continuing her research in the UK. “I want to contribute further. We try to improve the antibiotic resistance conditions in India.”

Thomas will still stick around at Wetsus. “I will help supervise some Ph.D.’s and will focus on writing European projects.”

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