Chemicals’ pathways to the sea
Chemicals reach the Baltic Sea via several different pathways: deposition from air, via surface runoff, eroded soil, rivers, direct emissions along the coast or at sea - and from outgoing water of wastewater treatment plants (WWTPs).
From urban areas, thousands of these so-called micropollutants flow via WWTPs to surrounding waters making these facilities major collection points for chemical flows in society. The micropollutants enter the sewage system for example when we wash clothes, rinse off personal care products or flush pharmaceuticals that have passed through our bodies.
Today, conventional WWTPs are not designed to remove these chemicals. In particular pharmaceuticals are often poorly removed as many are by design highly water-soluble compounds that are resistant to biodegradation.
By upgrading conventional WWTPs with more advanced treatment technology, specifically designed to remove micropollutants, the chemical emissions to the Baltic Sea could be significantly decreased.
50% load reduction in coastal zone possible
Out of the 615 WWTPs close to the Baltic Sea coast, 45 plants receive wastewater from more than 100 000 connected persons and together treat wastewater from almost 70% of the coastal population.
Upgrading these large WWTPs with advanced treatment technologies would on average remove 70-80% of the micropollutants in outgoing water, reducing the total load from all coastal WWTPs by approximately 50%. This measure has potential to significantly lower concentrations of a wide range of micropollutants in seawater, thereby enhancing the protection of this sensitive water body.
A general reduction of the total chemical load to the Baltic Sea can be seen as a precautionary measure to lower the risk of what today remain unanticipated adverse effects. This is particularly important for persistent and water soluble chemicals since they easily escape conventional WWTPs, spread in waterways and accumulate in aquatic “end-stations” such as the Baltic Sea.
Costs are lower for large treatment plants
Advanced wastewater treatment is today most commonly used for purification of drinking water and treatment of industrial wastewater. With the exception of forerunners found in Germany and Switzerland, this technology is rarely used in Europe to treat municipal wastewater.
There is a range of different available technologies that can be used to remove micropollutants from wastewater. Oxidation of chemicals with ozone or adsorption onto activated carbon are the two technologies mainly tested and implemented in full scale. The choice between the two is case dependent, depending on existing infrastructure, how sludge is to be treated, composition of the wastewater and which chemicals one wants to target. Removal efficiencies differ between them as some chemicals are best removed by ozonation and some by activated carbon.
No technology is capable of removing all chemicals but full scale implementations of advanced treatment technologies show that, with reasonable costs (ca 0.1-0.3 euro/m3) and energy demand (ca 0.01-0.3 kWh/m3), chemical concentrations can on average be decreased by approximately 70-80%. Costs and energy demand per cubic meter are lower for large facilities, and are also likely to decrease as technologies develop and prices drop with increasing market demand.
The costs of additional treatment should be weighed against the benefit of removing chemicals from wastewater, as well as having the cost-effectiveness compared with that of other measures with the same goal.
Source control is key
The key principle for reducing chemical emissions in wastewater is to regulate use of harmful chemicals already at the production stage. This source control approach protects all environmental compartments and enables enforcement of the polluter-pays-principle. It also facilitates the transition to a circular economy, enabling optimal recycling of materials, and safe reuse of sludge as fertiliser and wastewater for irrigation and aquifer recharge.
Several treaties, directives and regulations are in place to manage chemical risk, but the speed and scope of regulation, success of implementation and extent of compliance are unfortunately insufficient. There is neither adequate information on environmental levels and effects of the majority of chemical substances used, nor cost efficient measures to manage risks.
A number of fundamental challenges still have to be met before effective and satisfactory source control is achieved (see box here below). Even if these challenges are met, measures for regulating production and use may still be insufficient in protecting the aquatic environment since:
- the realistic emission reduction potential may not suffice to reduce environmental levels below relevant toxicity thresholds, such as Environmental Quality Standards.
- there are difficulties in regulating and reducing use of environmentally concerning substances with invaluable benefits for humans such as pharmaceuticals and efficient firefighting foams.
- several banned chemicals, such as PCBs and DDT, are still circulating in the environment, despite the fact that primary emissions of these chemicals have already been radically reduced.
These circumstances mean end-of-pipe measures, such as advanced wastewater treatment, are required to sufficiently reduce environmental levels of many hazardous substances.