Dutch technical study maps advanced treatment technologies

According to the new Urban Wastewater Treatment Directive, advanced or quaternary treatment will be mandatory for many WWTPs in the future. In the Dutch Innovation Programme for Micropollutants from Wastewater Treatment Plant Effluent (IPMV), twenty alternatives for removing micropollutants have been investigated. “Thanks to this programme, water authorities now have more than ten water treatment technologies to choose from”, says Cora Uijterlinde from the Dutch Foundation for Applied Water Research STOWA.  

The research programme IPMV mainly focused on combining proven technologies (activated carbon, ozone, and filtration) with each other or with new technologies. “It turned out that using lower doses of activated carbon or ozone can also remove nutrients and stimulate biological processes,” Uijterlinde explains. The Dutch water authorities, who are responsible for wastewater treatment in the Netherlands, submitted ideas for new and combinations of existing technologies.

Efficiency was key

The technologies were evaluated based on removal efficiency, CO₂ footprint, and costs. A condition for participation was that the technology had already been proven at lab-scale. Another important condition was that the technology could be implemented by 2027. “That’s a tight deadline if you’re working with completely new technology. That’s why the focus has often been on further research into optimizing activated carbon and ozone,” says Uijterlinde.

Promising results

The most promising technologies are now being applied at demo scale. Examples include combinations of biological removal and ozone, combinations of activated carbon and ozone, and a combination of biological removal and granular activated carbon. It has become clear that when you place a biofilm with bacteria—already present in wastewater—under the right conditions, the fossil-based activated carbon lasts longer. After this research programme, water boards now have a much wider range of technologies to choose from. The choice of a specific technology depends on the composition of the influent.

Upscaling technologies

None of the currently available techniques has yet exceeded Technology Readiness Level (TRL) 6. Technology readiness levels are a method for estimating the maturity of technologies. Uijterlinde: “Now that the programme has ended, we must move towards successful demos (TRL 7). Water boards can receive funding for this through an acceleration programme. During the IPMV programme, which was coordinated by STOWA, 50 to 100 people continuously exchanged knowledge. As a result, broad expertise now exists within the water boards regarding micropollutant removal.”

Failures identified

Some techniques proved unsuccessful during the innovation program. Uijterlinde: “It turned out not to be possible to replace existing zeolites in detergents with ones that not only soften water but also remove pharmaceutical residues through adsorption. Unfortunately, that didn’t work. Another technology that failed involved adding iron to activated carbon. And in a small pilot, filtration using enzymes also proved ineffective. The enzymes were supposed to break down micropollutants, but this did not work in practice either.”

Tailored solutions

Back in 2015, STOWA conducted an initial exploration into technologies used abroad for removing micropollutants. “At the time, this was mainly activated carbon in Germany and ozone in Switzerland. In the Netherlands, we chose not to copy these proven technologies because the composition of our wastewater differs from that abroad. For instance, bromide levels in our wastewater are higher. If you then use ozone, you risk forming harmful degradation products such as bromate. So, the composition of wastewater is crucial in determining the right technology.”

Advanced treatment

Under the new Urban Waste Water Treatment Directive, quaternary treatment removing a broad spectrum of micropollutants will be mandatory for all plants over 150.000 population equivalent (p.e.) and over 10.000 p.e. based on a risk assessment by 2045. In addition, known viruses, emerging pathogens, chemical pollutants (including per- and polyfluoroalkyl substances or PFAS), microplastics, and antimicrobial resistance will be strictly monitored.