From pure cultures to flocs: a bottom-up approach for microbial ecology studies of biological wastewater treatment

Promovendus/a: Laurens Parret

Promotor(en): Prof. dr. ir. Ilse Smets, Prof.dr.ir. Jo De Vrieze

Every day, huge amounts of wastewater are produced all over the world. If this water is not cleaned properly, it can harm the environment and for example lead to the loss of biodiversity. Luckily, nature itself provides us with inspiration for cleaning up this waste: in wastewater treatment plants, microorganisms team up to form sticky clumps called "flocs" that are able to purify the water.

But how do these microorganisms work together, and what makes them stick? Scientists still do not fully understand the details, which means that fixing problems with the formation of these flocs often relies on trial and error. This thesis takes a closer look at the black box of microbial teamwork by building a simplified community of only five (key) species found in wastewater treatment. By studying these bacteria alone as well as in groups, and using tools like microscopes and DNA analysis, we can map how they interact and what helps them aggregate into strong flocs.

One highlight is the use of alginate (gel) beads to force the bacteria together, which helps them form spherical colonies similar to those found in real treatment plants. The research also shows that some bacteria behave differently depending on who else is around—sometimes they do not behave in the way we expect unless they are part of a mixed group.

To make these experiments possible, an open-source reactor was built, allowing for precise control of the experimental parameters, and promoting the sharing of laboratory setups (and experience) with other researchers. The results show that it is possible to grow and monitor a model bacterial community over time (using this reactor platform), paving the way for a deeper understanding and intensified engineering of biological wastewater treatment plants.

In short, this work opens the black box of microbial floc formation, offering a bottom-up approach to microbial ecology that could help make water treatment more reliable and environmentally friendly.