Do drinking water plants retain microplastics? An exploratory study using Raman micro-spectroscopy

Area of Science:

• Environmental Science
• Water Treatment Technology
• Analytical Chemistry

Background:

• Microplastic (MP) contamination is a growing concern in drinking water sources.
• Understanding the removal efficiency of water treatment plants is crucial for public health.
• Previous studies have often focused on larger microplastic particles.

Purpose of the Study:

• To quantify the removal of microplastics (MPs) down to 1 μm by a Danish drinking water treatment plant.
• To assess the efficiency of MP removal based on both particle counts and mass.
• To investigate the influence of MP size on retention efficiency.

Main Methods:

• Raman micro-spectroscopy (μRaman) was used for MP quantification.
• Water samples were collected from the inlet and outlet over five consecutive days.
• A custom-made filtration device with 1 μm steel filters was employed to process approximately 1 m³ of water per sample.

Main Results:

• Treated water contained an average of 1.4 MP counts/L (4 pg/L).
• Overall treatment efficiency was 43.2% for MP counts and 75.1% for MP mass.
• Retention efficiency decreased significantly for smaller MPs (41.1% below 5 μm) compared to larger ones (79.6% above 10 μm).
• Variability in MP retention suggested potential release of small MPs from plant components.

Conclusions:

• The drinking water treatment plant demonstrated moderate efficiency in removing microplastics.
• Smaller microplastic particles (<5 μm) pose a greater challenge for removal.
• Potential release of nanoplastics (NPs) from internal plant components warrants further investigation.