Fourth cycle of Robustness Research for surface water treatment underway

New compounds are continuously being put on the market and ultimately also often ending up in (surface) water, for example, as organic micropollutants. The presence of these compounds in drinking water is not desirable. Accordingly, the four Dutch dune water utilities (Dunea, PWN, Waternet and Evides) are continuously on the alert to ensure that their treatment processes are sufficiently robust to remove organic micropollutants and other compounds. To this end, they have since 2005 conducted Robustness Research within their collective DPWE research programme.

Robustness Research

KWR, Het Waterlaboratorium (HWL) and the DPWE water utilities carry out the Robustness Research in collaboration. They use pilot plants at the water utilities to test how well the different treatment stages remove a set of extra added pollutants. The Robustness Research runs in five-year cycles, each of which begins with a selection of the currently relevant pollutants, and the design of the research set-up for the dosing (or ‘spiking’) of this mix in the different pilot plants.

KWR researcher Bas Wols: ‘The selection of the pollutants to be added depends among other things on their (potential) occurrence in the sources, their toxicity and the analysis possibilities. The research in the pilot plants is also constantly adjusted to the current needs and wishes of the water utilities. These investigations are carried out in the third and fourth year, and in the fifth year the data are analysed, so that the water utilities can draw on the new knowledge in designing and operating their treatment processes.’

Bioassays

Last year the test set-up and the compounds to be tested in the fourth cycle were determined, and in 2022 and 2023 the experiments are being carried out with added compounds, partly in existing and partly in new pilot plants, which the utilities are now building. This cycle will also study the use of bioassays before and after the spike experiments: effect-based biological measurement methods, in which the reaction of living cells or organisms provides a measure of the presence of (mixes of) compounds that impact the biological processes and thus, potentially, also human and environmental health. KWR researcher Astrid Reus: ‘We now have a range of bioassays available with which we can signal the effects on different biological systems and processes, such as the endocrine system, the DNA, the nervous system or the immune system. At the moment we are studying which bioassays are expected to respond to the twenty compounds chosen for the Robustness Research. From these we will select the bioassays for the spike experiments. We naturally want to cover as many different effects and mechanisms as possible.’

Broader picture of water quality

Wols: ‘The addition of bioassays to the Robustness Research, along with non-target screening and target compound analysis, gives us a broader picture of the water quality. We began doing this in the previous cycle, but in the current one we are doing it more extensively. We include bioassays in experiments without added compounds, to test whether the background produces any signals, but also in the spike experiments, to trace any transformation products that might have formed during the oxidative processes in the treatment. In most cases, smaller, more degradable compounds do appear, and they are in fact very effectively removed through additional carbon filtration, for instance. But we have to always be alert to compounds that can arise during the treatment.’

Genotoxicity

Reus, together with Corine Houtman of HWL, is also currently starting another DPWE research initiative into bioassays, which involves experiments that could potentially link up with the Robustness Research. ‘DNA damage can result from different mechanisms. One compound that causes one of these damaging mechanisms might therefore produce a signal in one genotoxicity bioassay, but not in another. We want to acquire a better understanding about which genotoxicity tests are sensitive for water-relevant compounds, so that we can properly select which set would be best for us to use in safeguarding the water treatment.’

Twenty years captured in data

‘The evaluation after the third cycle of the Robustness Research indicated that the surface water utilities would like to continue with this years-long research,’ says Wols. ‘It produces important information for the design and operation of surface water treatment processes. This research has also built up a valuable 20-year database on surface water quality and 80 relevant compounds, from which we can still extract a great deal of scientific information.’