Urban wastewater treatment directive

Urban wastewater collection and treatment has been regulated in the EU since 1991. In 2019 the European Commission evaluated the Urban Wastewater Treatment Directive and found only 42% of the 1.7 million kilometres of European rivers and streams were in a good ecological status. Among multiple stressors, urban wastewater is the most significant anthropogenic point.

In October 2022 the Commission adopted a proposal to revise its directive to address the shortcomings and align with the objectives of the European Green Deal. A study was conducted to investigate the following:

• How wastewater from households and small industries affects the ecological health of European streams.
• Identify the reason behind European Streams not meeting the requirements of the European Water Framework Directive (WFD) even after imposing regulatory laws.
• Identify a percentage threshold of wastewater discharge to water flow, above which ecological damage can occur.

What was Studied in Wastewater Treatment?

• The researchers set up a database which had numerous datasets that contained the ecological status, water flow and the estimated amount of wastewater treatment plant effluent discharge from EU’s 26,523 wastewater treatment plants. They analyzed the threshold percentage of wastewater above which ecological harm can occur.
• They calculated the Urban Discharge Fraction (UDF) an urban waste-water discharge share of stream flow and used UDF spatial data to compare with an existing study on European streams that identified seven known stressors of aquatic ecosystems. This was done to identify if there was any direct correlation between UDF and the stressors. NO direct correlation was found. This led the researchers to conclude that UDF could be an independent and additional stressor.
• Further analysis showed that with the higher urban discharge flow, there would be a negative impact on the ecological status of the European streams and small rivers. Hence concluded that UDF should not exceed 6.5%

Why did the wastewater treatment fail?

1. The entry point of treated wastewater is not always in the best position for dilution.
2. Absence of a system-oriented approach for monitoring the entire waste-water sector.