Bark and biochar in horizontal flow filters effectively remove microplastics from stormwater

Area of Science:

• Environmental Science
• Water Treatment Technologies
• Pollutant Removal

Background:

• Organic materials like bark and biochar show potential for stormwater treatment.
• Microplastics (MPs) are emerging pollutants in stormwater, with limited research on their removal by organic filters.

Purpose of the Study:

• To investigate the efficiency of bark and biochar filters in retaining various microplastic types from stormwater.
• To assess the impact of filter length and material packing on microplastic removal and transport.

Main Methods:

• Horizontal bark and biochar filters of varying lengths (25-100 cm) were loaded with a mixture of microplastic types (polyamide, polyethylene, polypropylene, polystyrene) in different shapes and sizes (25-900 μm).
• Filters were subjected to a constant water flow (5 mL/min) for one week, with effluents analyzed for MPs using μFTIR imaging.
• A detailed analysis of MP distribution within a bark filter was conducted by segmenting the filter material.

Main Results:

• All bark and biochar filters demonstrated high MP retention rates, exceeding 97%.
• Despite high retention, MPs were detected in all effluents, with concentrations ranging from 5-750 MP/L (bark) and 35-355 MP/L (biochar).
• Small-sized polyamide particles constituted over 91% of detected MPs in effluents. MP concentration in effluents decreased with longer filters, possibly due to reduced channeling.

Conclusions:

• Bark and biochar filters are promising for microplastic removal from stormwater.
• Filter packing integrity is crucial to prevent MP breakthrough and minimize environmental emissions.
• Further research should focus on optimizing filter design and installation to enhance MP capture efficiency.