AquaNL day 1: nitrous oxide, legionella and nature-based solutions

Nitrous oxide emissions in wastewater treatment plants – Kees Roest

I had the opportunity to give a presentation about nitrous oxide emissions from wastewater treatment plants. This is a pretty specific subject but the high attendance showed that it is quite a hot topic. Laughing gas (N₂O) is a strong greenhouse gas (273 times stronger than CO₂) and, as a result of the use of more and more sustainable energy, the direct emissions are becoming even more apparent. A lot of monitoring is going on at the moment but, in the end, we obviously want to limit emissions. To do that, we need to understand the processes involved. The biokinetic models are still not ideal in that respect. AI models are achieving impressive results for the prediction of nitrous oxide emissions in the short term. At KWR, we are working on hybrid models, combining biokinetic and AI modelling. In that way, we can contribute to controlling the process and the limitation of nitrous oxide emissions. We will be working on this further in a planned TKI Water Technology project. That will include focusing on destruction techniques for captured gas streams containing N₂O from, for example, side-stream processes. Interested parties can still sign up quickly to join in.

Kees Roest gave a presentation on ‘Advanced monitoring, modelling and process optimisation for the management of N2O emissions in wastewater treatment plants’

A little bit of nature in the tech world – Maria Lousada Ferreira

AquaNL always makes me both excited and nervous. The aim is to talk, to share, to network, and to show what you have done and plan to do. You might think that this isn’t very different from a scientific congress. But it isn’t the same. This is a professional world full of pumps, pipes and machines, with a smaller section set aside for consultancy and knowledge institutes. It’s a man’s world: you see very few women walking around. In front of the KWR stand, there was a demonstration robot for underwater inspections in a water tank. I felt exactly like that robot: I was fully immersed in the Benelux water world. Doing my best to speak only Dutch. And as if all this wasn’t challenging enough, this time I was talking about nature-based systems (NbS) for concentrate management. I had brought a bit of nature into the world of technology. What could go wrong?

An empty auditorium was waiting for me when I went to upload my presentation a few minutes before the start. There was one person there fidgeting with his phone. He left when he realised I was about to start. My presentation was at 12:30, which is perilously close to lunch time.

But then current and former KWR colleagues turned up and a few people sat down at the back. I asked them to move closer (which they were happy to do) and started. I told them that KWR is involved in more and more nature-based projects, that our shareholders (the drinking water utilities from the Netherlands and one from Belgium) are asking us to investigate solutions that not only have technical, social and environmental benefits but also potentially positive effects on biodiversity. That reserve osmosis (RO) concentrate from wastewater is already being treated with NbS. That companies like Holland Sensor are interested in developing sensors that can also monitor NbS. That we have drafted a TKI water project proposal in which drinking water concentrate is being treated in constructed wetlands, with support from PWN, Dunea and Holland Sensor.

The next time I looked out at the auditorium, it was half full. There were a few questions followed by fascinating conversations and a post from Blueprofs referred to the PPT. I was happy.

What I realised on the way home was that I was thinking in Dutch. Probably not the first time after twenty years in the Netherlands but definitely the first time I realised it was happening. One of the benefits of immersion!

Maria Lousada Ferreira gave her presentation on ‘Material-based concentrate management’

Legionella still requires attention – Frank Oesterholt

KWR gave two presentations on the topic of Legionella on Tuesday. The topical relevance of this subject was demonstrated by the interest during both presentations. It was nice and busy in auditorium 2! I opened my presentation with the statement that Legionella still requires serious attention, including in tap water systems. I did make it clear that the focus should be more on cooling water systems and wastewater treatment plants. My presentation was linked to a reprint of four articles on Legionella from the 2025 E&W Installatietechniek journal. The editors of E&W and KWR provided that Legionella dossier free of charge for anyone interested in the subject. Unfortunately, the QR code in the presentation didn’t work but, luckily, the reprint is easy to find on our website or using this link.

The second Legionella presentation was about an ongoing TKI study looking at the reliable detection and control of Legionella pneumophila in wastewater. Nikki van Bel of KWR introduced the study. It was conducted in collaboration with the partners to look at alternative, faster detection methods for Legionella in the difficult wastewater matrix. I gave a brief description of the background to the Legionella problem, which is linked to specific types of treatment or treatment processes with warm, nutrient-rich, wastewater. Finally, Jordi Moreno of CEW looked at the research approach in a little bit more detail, emphasising that, alongside the detection methods, the study is also looking at Legionella management in WWTPs, for example with “predictive modelling” based on existing data. The idea here is that good predictive models allow you to implement real-time controls to prevent potential risk situations. The study will be completed this year.

Frank Oesterholt gave a presentation on ‘Legionella continues to demand serious attention’

Nikki Bel spoke with Jordi Moreno about ‘Reliable detection and control of Legionella pneumophila in wastewater’