Biological conversion of micropollutants in drinking water treatment

The basic research question addressed in this project is whether and how the removal of micropollutants can be improved/optimised through the use of biological treatment processes. The researchers are also focussing on making the technology application-ready.

More insight into mechanisms behind the degradation of organic micropollutants

The recent examples of pyrazole and GenX show that it is very likely that more and more ‘new’ substances will be turning up in drinking water sources in the years ahead. Furthermore, it has long been known that these sources (groundwater, river water) can contain low concentrations (ng/L – μg/L) of organic micropollutants (OMPs). The concentrations of these substances in the water sources will also probably increase as a result of population aging/ climate change. It is therefore extremely important to effectively remove these substances – as well as inorganic micropollutants such as arsenic. Various scientific studies have shown that biological processes, such as rapid sand filtration (SF), river-bank filtration, biological granular activated carbon filtration (BAC), and slow sand filtration (SSF), can remove a range of organic micropollutants. It also seems possible that inorganic micropollutants (like arsenic) can be biologically converted in rapid sand filters. Biological processes are not very energy-intensive and thus constitute a sustainable and environmentally-friendly solution for the removal of OMPs. An additional benefit is that biological treatment processes, such as SF, BAC and SSF, are already present in many Dutch treatment plants. Implementing a new process therefore (often) does not involve any significant additional investment.

However, the underlying mechanisms responsible for the biological conversion are not yet fully understood. It also remains unclear why one substance is biodegradable while another is not. By acquiring more insight into these mechanisms, we would be able to better manage these processes or to optimise the OMP degradation.

The basic research question addressed in this project is whether and how the removal of micropollutants can be improved/optimised through the use of biological treatment processes. This requires deeper insight into which bacteria/enzymes are responsible for the conversion of specific micropollutants. In addition, research questions like: How much seeding material is needed to seed a filter? and Could other seeding techniques be applicable? will be tackled for the purpose of making the technology application-ready.

Which bacteria are responsible for the degradation of micropollutants?

The basic research question addressed in this project is whether and how the removal of micropollutants can be improved/optimised through the use of biological treatment processes. This requires greater insight into which bacteria/enzymes are responsible for the conversion of specific micropollutants. The research aims to achieve this through a combination of measurements in full-scale filters (SF, BAC or SSF) and in lab-scale column and accumulation experiments. In the first instance, the study focuses on a single filter medium selected on the basis of the full-scale data and in consultation with the supervisory group.

There is in addition the matter of the operational application of this concept. Earlier research shows that it is possible to seed a filter to improve the removal of specific OMPs (e.g., pyrazole and metformin). This involves using a filter medium from a filter that can in fact remove the specific OMP. But a large amount of seeding material (50%) was needed to achieve this result. The expectation is that this seeding concept could be relevant to a much broader range of OMPs, and possibly also for inorganic micropollutants like arsenic.

The basic question concerning which bacteria are responsible for the degradation of micropollutants is by nature more in-depth, while research questions like: How much seeding material is needed to seed a filter? and Could other seeding techniques be applicable? are related to making the technology application-ready.

The research outcomes

The outcomes of the research will be:

• information and knowledge about the bacteria responsible for the removal of micropollutants;
• information and knowledge about which organic micropollutants can be biologically degraded in an effective manner and which display persistent behaviour;
• information about biological degradation pathways of an inorganic micropollutant – that has yet to be selected – in drinking water treatment processes;
• information and knowledge about the possibilities of seeding filters to improve or optimise the degradation of micropollutants; and
• a report, or a publication, that describes the insights obtained as well as their practical application for micropollutants.

The project’s outcomes will also be shared externally in congresses, and a scientific paper on the research will be published.