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Suspended matter filtration causes a counterintuitive increase in UV-absorption
Louis Peperzak1, Jan-Berend Willem Stuut2, Hendrik Jan van der Woerd3
1NIOZ Royal Institute for Sea Research, Department of Estuarine & Delta Systems, PO Box 59, NL-1790 AB Den Burg, the Netherlands.
Marine Pollution Bulletin
|August 27, 2022
Summary
Water filtration can increase UV-absorption by creating smaller particles, potentially reducing disinfection effectiveness. While it removes suspended matter mass, this unexpected outcome requires careful consideration for water treatment strategies.
Area of Science:
- Environmental Science
- Water Treatment Technologies
- Analytical Chemistry
Background:
- Filtration is a common pretreatment in water treatment to remove suspended matter (SPM).
- SPM can interfere with chemical and UV disinfection processes.
- The impact of filtration on UV-absorption characteristics of water is not fully understood.
Purpose of the Study:
- To investigate the effect of filtration on UV-absorption in water treatment.
- To test the hypothesis that filtration can increase UV-absorption by altering particle size distribution.
- To evaluate the implications of filtration-induced changes in UV-absorption for disinfection efficacy.
Main Methods:
- Filtration experiments using 25 and 40 μm mesh screens on ballast water.
- Measurement of particle counts and particle-size distributions (PSD) before and after filtration.
- Modeling of the Mass Normalized Beam Attenuation Coefficient (A/SPM) to assess UV-absorption relative to SPM.
- Independent model verification using Arizona test dust suspensions.
Main Results:
- UV-absorption (A, 254 nm) increased after filtration, particularly with the finer mesh screen.
- Filtration led to a shift towards smaller particle sizes in the filtered water.
- The A/SPM ratio increased post-filtration, indicating higher UV-absorption per unit of suspended matter.
- Model predictions for A/SPM were validated with test dust suspensions.
Conclusions:
- Filtration effectively reduces suspended matter mass, making it a suitable pretreatment for chemical disinfection.
- However, filtration can generate smaller particles that increase UV-absorption, potentially hindering UV disinfection performance.
- The study highlights a trade-off between SPM removal and UV-absorption changes during water filtration.
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