Most people flush their wastewater down the drain without giving much thought to sewage treatment. But this service is a prerequisite for clean water, one of the most valuable resources in our society. The cost of inaction is too great, writes Emma Undeman.
Emma Undeman is an environmental chemist and researcher at Stockholm University.
Our society is experiencing a chemical intensification where the use pattern has changed from the use of few chemicals in large quantities, often from point sources, to the use of many chemicals in small quantities, such as chemicals in consumer products, and from diffuse sources.
Identifying hazardous substances and legislating one-by-one takes too much time. So acting on incomplete evidence following the precautionary principle should be seen as an alternative.
One such precautionary approach is advanced wastewater treatment which can significantly reduce the emissions of both known and unknown substances to the aquatic environment.
Chemicals enter the sewage system for example when we wash textiles, wash off personal care products or flush down pharmaceuticals that have passed through our bodies. Wastewater contains thousands of compounds with human origin and collects many of the urban chemical flows.
But the majority of urban wastewater treatment plants in the EU today are not designed to remove these so called micropollutants.
If we want to ensure long-term sustainable exploitation of marine and freshwater resources it is important that the end wastewater does not contain high levels of harmful substances. The starting point needs to be to limit the use of harmful chemicals at the production stage.
As we are exposed via multiple pathways, having a source control approach and ensuring enforcement of the polluter pays principle is crucial to protect human and wildlife health.
It also facilitates the transition to a circular economy as the presence of problematic chemicals in products impedes optimal recycling of materials, as well as reuse of water and sludge.
But is this enough?
To minimise health and environmental risks there are several European legislative efforts to limit the use of harmful chemicals, the REACH regulation being the main one.
However, our world is undergoing a rapid chemical intensification with larger volumes and a greater number of chemicals being used in our society. Banned chemicals are often substituted with substances having similar properties, which can be as problematic as the original compounds.
The evaluation and regulatory process is struggling to keep even speed with the ever-increasing number of replacements or new areas of use for chemicals. Also, the number of substances with unknown harmful effects most likely exceeds those with known harmful effects.
Compared to the slow process of regulating and phasing out individual chemicals, advanced wastewater treatment technology can be implemented relatively fast. Removing a wide spectrum of contaminants also reduces the risk of chemical cocktail effects in the aquatic system.
Some aquatic systems are more sensitive than others to the input of pollutants commonly present in wastewater. The Baltic Sea for example is a shallow sea with a slow water exchange with the North Sea through the narrow Danish straits.
The long residence time of water coupled with sensitive marine organisms and the wide spectrum of pollutants emitted from the 85 million inhabitants in the Baltic Sea catchment put this system under high environmental pressure.
If they are emitted in large quantities or not easily degraded, chemical pollutants present in wastewater may accumulate in the marine environment and lead to negative effects on aquatic organisms. In that respect the Baltic Sea could be likened to an aquatic landfill or a waste tank.
Currently there is no perfect one-size-fits-all technology available for removal of micropollutants from wastewater. And even if the sensitivity of the recipient waters is what should justify the investment, for smaller treatment plants the costs in terms of money and energy might prove difficult.
But for treatment plants collecting sewage from larger urban areas additional treatment steps are less costly. This can provide an opportunity to maximise the environmental benefit of investment by enabling removal of a wide range of known and unknown contaminants, hence reducing the chemical load to both nearby and downstream drinking water reservoirs and the sea.
In cases of wastewater reuse for agricultural irrigation or groundwater recharge, it is important to ensure that the risk of contamination from both known and unknown chemical substances is kept to a minimum as the contamination of groundwater and soil may remain for a long time.
It is difficult to estimate the total benefit of implementing advanced treatment to, for instance, the Baltic Sea. For known pollutants with multiple entry pathways the total load reduction and relief of negative effects are difficult and costly to determine. For currently unknown contaminants and effects it is in practice impossible.
But this also means that the cost of inaction is difficult to estimate. The question is perhaps instead to what extent we are prepared to risk contamination of invaluable water resources.
As the Commission’s revision of a number of water related legislation is currently underway, such as the water framework directive and water reuse regulation, the effective tool that advanced wastewater treatment could and should be investigated further.
Both as a way to follow the precautionary principle and as a means to reach acceptable environmental concentrations of prioritised chemicals for which other options are scarce. With its unselective and effective nature additional treatment of wastewater can be a good complement to other measures to limit the chemical pollution of our freshwater and seas.