From source to user: how chemicals end up in our waters via the wastewater system

Deltares is studying routes, risks and solutions for three WWTPs in the south of the Netherlands

Working with a consortium, Deltares looked at three WWTPs in the south of the Netherlands to see how these substances move from the source, via the WWTP, to the places where water users may be affected.

The consortium partners are: RIWA-Maas, Schone Maaswaterketen, KWR, Evides Waterbedrijf, Evides Industriewater, DOW Benelux B.V., the Provincial Authority of Noord-Brabant, Free University of Amsterdam, Wageningen University and Research Centre, and Radboud University Nijmegen.

How do substances move through the water system?

We mapped out the route of the treated wastewater for the Heeswijk-Dinther, Heugem and Bath WWTPs: how the water spreads, which substances were transported with it, and the consequences for the receiving waters, in this case the Meuse and the Western Scheldt.

These WWTPs are of interest because, for example, the Meuse supplies water for drinking water preparation and because the Western Scheldt is a Natura 2000 area.

The study by Deltares drew on existing water quality data to provide a picture in graphs and maps of the spread of the substances from the sources, through sewers, WWTPs and smaller watercourses to the Meuse and Western Scheldt (report on distribution and effects (in Dutch)).

To establish the route substances take, to see where they end up and who uses the water at that location, several parties along the routes were involved in the study, including water authorities, drinking water utilities, Rijkswaterstaat, provincial authorities, environmental services, companies, and other key stakeholders, such as Maastricht University Medical Center (Maastricht UMC+) near the Heugem WWTP.

Maps were produced with them, as well as visualisations of the routes taken by the substances from the sources to the locations where there are possible effects on water users. That process also addressed questions from water users and how to improve water quality.

How do you draw up a list of known and unknown substances?

To tackle pollutants in the water system in a structured and consistent way, it is necessary to get to grips better with the substances present in discharges to the wastewater system.

The study by Deltares and KWR included a roadmap to arrive at a list of known and unknown industrial substances (suspects) (report on list of substances (in Dutch)).

This roadmap was processed in the online SPOT tool (Substances Prioritization & Detection Tool) and it helps not only to draw up of lists of substances but also to determine the possible origins of substances found in surface water or wastewater.

Using this roadmap, a comprehensive list was established for each of the three WWTPs of substances that may enter wastewater in discharges to sewers that is destined for treatment.

It proved difficult here to obtain complete permit data. Tools such as the ZZS Navigator are useful but they could be further developed and improved.

Overarching conclusions

• WWTPs do not remove all substances from wastewater: some are transported by the treated wastewater to surface water.
• Climate affects water quality; dry periods and extreme precipitation result in fluctuations in water levels. In dry conditions, substances from treated wastewater may have a stronger impact.
• It is important for stakeholders to be aware of the possible effects of substances from treated wastewater, and to engage in discussions about how to improve water quality. The discussion pictures and system maps from the study can be used for this purpose.
• Finally, it was striking that there is a general paucity of monitoring data for the substances and their metabolites along the route from the source via the wastewater treatment plant to the receiving (surface) water. That makes it difficult to determine the effects precisely.

We make the following recommendations:

• More monitoring, but above all in smart locations. At sources, at WWTP intake and discharge points, and downstream in watercourses – including flow measurements.
• Awareness-raising with the discussion pictures (report on distribution and effects) and more monitoring data. Work together and share your knowledge (water authorities, hospitals, agriculture, industry and government authorities).
• Know the sources of substances, track them down. Existing tools and information can be used for this purpose, as collected in the SPOT tool (report on list of substances).
• Monitor water quality and also monitor during dry periods. In addition, divert treated wastewater to watercourses with little water since concentrations of substances can increase there.

What do the three locations demonstrate?

Heeswijk-Dinther

This WWTP treats the wastewater from households and several businesses in the region. The treated wastewater is discharged via smaller surface waters to the Meuse.

At the Heeswijk-Dinther WWTP, the effects in the surface water of substances from treated wastewater vary due to differences in how the water is routed during the year. This water is used by agriculture, for leisure and for drinking water.

We looked at the normal situation and the situation in dry conditions in the summer months. The concentrations are highest during dry summers when the treated wastewater is diverted to the Wambergse Beek. There is dilution on the way to the Meuse. More details can be found in the report (report on distribution and effects).

The discussion picture showing the situation around the wastewater treatment plant allows for a discussion of possible measures with stakeholders: reducing the use of pollutants, for example, or supplying more water during dry periods and continuing the sound monitoring of water quality.

Heugem

This WWTP processes wastewater from households and the Maastricht University Medical Centre (Maastricht UMC+). The treated wastewater is discharged through a small watercourse that empties into the Meuse. The focus here was on pharmaceutical residues and other medical substances that enter the WWTP via Maastricht UMC+.

A number of substances were tracked along the routes they take, see the report (report on distribution and effects). These substances end up in the wastewater system because they are not broken down in the human body, or only partially so.

They enter the surface water via the sewers and the WWTP. They also do not break down, or only partially, in the WWTP. They are diluted and sometimes break down further in the surface water. The flow rate, the amount of water in the Meuse, often determines concentration levels.

This therefore depends on dry periods and precipitation. The water here is mainly used for nature, leisure and drinking water.

Our advice is to use the discussion picture about the distribution and effect of pharmaceutical residues in the environment to initiate dialogue with suppliers and users of medicines.

Bath

This WWTP processes wastewater from a large wastewater pipeline to which households and various chemical industries (including Moerdijk) are connected.

The treated wastewater is discharged into the Western Scheldt. The central question at this location is whether the treated wastewater from the WWTP contributes to pollution of the Western Scheldt, which is an important nature area.

The available data, see the report (report on distribution and effects), indicate that the concentration of the investigated substances in the Western Scheldt is relatively high. The Western Scheldt is affected by many other sources.

Given this background, the role of substances from the WWTP does not stand out separately. It is important to focus on these emissions from the WWTP, however, because any additional burden in an estuary that is already under pressure is relevant for the water quality and the ecosystem.

The effects are difficult to study because not enough data are available for the same substances along the entire route from the source to the Western Scheldt. However, it is possible to use the SPOT method to draw up lists of substances (report on list of substances) to identify the sources of certain substances.

This research is part of a Top Consortium for Knowledge and Innovation (TKI) project: “Integrated Approach to Industrial Problem Substances in Surface Water: ‘From Source to Effect’”.