Acknowledgements

This PhD research would not have happened without the help of many people, but by far the most important for me was Mario Pronk. Friend, colleague, co-promotor, Mario mixed all these roles in a mixture of inspirational debates and discussions. We spent hours and hours discussing the observations in our research (or what is better, road cycling or mountain biking). When we first met in 2014, I presented a model, which now can be seen as the first prototype of the granulation model from chapter On the mechanisms. Afterwards Mario came to me, a little bit surprised, saying he thought these types of models were only made at the university. From then on, we had a mutual understanding - as similar minds. Together we have set up the R&D for Nereda^® at Royal HaskoningDHV and it was Mario in the end convincing me to start with my PhD research. Many, many, many thanks for all of this.

I learned that intuition is important in scientific research. Most research starts with a feeling that something might be interesting. I think Mark van Loosdrecht combines a well-developed intuition with a broad experience in the field, which makes Mark a unique person. There is a bit of a rebel in Mark, ignoring authority and decorum, always going the route he thinks is best. I recognize that ‘stubbornness’ in myself and that made we had a good mutual understanding from the start. From every meeting I had with Mark there was a takeaway, and I really learned a lot from working with Mark. I am very grateful to have had Mark as a promotor.

There is one person, that has been very important to this research, although he did not contribute anything to the research itself. Helle van de Roest was awakening the interest in science in me, in the years before I started my PhD research. I worked closely together with Helle, and he constantly challenged me to deeper understand the Nereda^® process and to avoid ‘superficial knowledge’. Although Helle retired in the year I started my PhD research, his legacy echoed into it constantly. So, Helle, many thanks for the all the valuable lessons.

My PhD research was a unique opportunity for me, with great support from RHDHV. It was the ‘Nereda director’ René Noppeney, who initiated the whole thing and supported me along the way. During the 5 years of this research, I had two bosses at RHDHV, Hugo van Gool and Joãao Tiago de Almeida. Both were 100 % supportive and helped me through the more difficult episodes of this research. Thank you both for your support and dedication to my journey.

There are more (former) colleagues at RHDHV that were important for me in this research, especially the colleagues in the R&D team. In de first years, Tim van Erp was my go-to, when I needed something built for my research at the PNU. With his practical skills he could make anything happen. Valerie Sels already contributed during her bachelor thesis to this research, looking at the bulk settling behaviour of AGS. After this thesis, Valerie kept connected to AGS research and after her graduation she became a valuable colleague. Especially her contribution to the research on the settling properties of AGS (chapter Settling behaviour) was invaluable. Pascalle Vermeulen started with an internship, looking at granulation in the PNU. We recognized talent and after her graduation she became our colleague in the R&D team, helping us greatly in all the ongoing research projects. The internal review of my four papers was done by Andreas Giesen. He helped greatly by spending many hours reviewing and correcting my papers.

Our research facility in Utrecht, the PNU played an important role in this PhD research. Two operators, Jan Cloo and Mark Stevens from HDSR supported us with the daily operations. Already in 2014 it was Mark, doing the official sampling of the PNU, noticing that elevated levels of effluent suspended solids were going to be a problem for AGS technology, thus triggering the research presented in chapter Effluent suspended solids, helping to overcome this problem. The level of dedication of Jan and Mark was unique and very much appreciated. Several other people for Dutch district water authorities helped me along the way: by sampling, helping with experiments, discussion and in many other ways. Special thanks go to Erik Rekswinkel, Philip Schyns, Henri Scheurs and Meinard Eekhof.

One of the greatest benefits of my PhD research was being on the university, discussing with knowledge driven people. I especially enjoyed the discussions with my room mates: Viktor Haaksman, Jure Zlopasa and Morez Jafari. Many afternoons were filled with drawing on the whiteboard, having fierce discussions. I learned that having an open mindset is the only thing you need to have a fruitful discussion on any topic. The three of you really helped me to feel part of the team at the university.

Over the years I supervised many students, contributing in some way to this PhD research. Some these students later became my colleagues at RHDHV. Special thanks go to Struan Robertson, Jimmy van Opijnen, Suellen Espindola, Eline van der Knaap, Pieter Brorens, Jelle Langedijk, Isabelle Schroeten, Amanda Vierwind and Lindsey Carver. Working with students helped me to focus on specific research topics, forcing me to take a break from the daily routine at the office.

Finally, I want to thank my family, Ankie, Julius and Maurits. You always fully supported this journey I started, and especially in the more difficult moments you helped me in so many ways. We celebrated together when a new paper was published, but there was also the sometimes-necessary distraction to get my mind of my work. We made this journey together and I could not have done it without you!

Thank you all!