Suspended matter filtration causes a counterintuitive increase in UV-absorption

• Published in: Marine pollution bulletin 2022-10, Vol.183, p.114012-114012, Article 114012
• Main Authors: Peperzak, Louis, Stuut, Jan-Berend Willem, van der Woerd, Hendrik Jan
• Format: Article
• Language: English
• Subjects: Absorbance; Ballast water; Filtration; Hill model; Particle-size distribution; Suspended matter
• ISSN: 0025-326X; 1879-3363
• DOI: 10.1016/j.marpolbul.2022.114012

In water treatment, filtration is often a first step to avoid interference of chemical or UV-disinfection with suspended matter (SPM). Surprisingly, in testing a ballast water filter with 25 and 40 μm mesh screens, UV-absorption (A, 254 nm) of filtered water increased with the largest increase in the finest screen. The hypothesis that filtration partly removes large particles and partly replaces them with small unfiltered ones, leading to an overall increase in absorption, was tested by measuring particle counts, particle-size distributions (PSD) and by modeling the Mass Normalized Beam Attenuation Coefficient (A/SPM) before and after filtration. An independent model verification was made by measuring and modeling A/SPM of three differently sized Arizona test dust suspensions. It is concluded that filtration is a good pretreatment for chemical disinfection systems because it removes the suspended matter mass, but that the production of smaller particles increases UV-absorption and hence may reduce disinfection performance. •The process of filtration does not result in a decrease but, counter-intuitively, to an increase in UV-absorption.•Filtration causes large particles to be partly removed, partly reduced to smaller particles.•The increase in smaller particles causes increased UV-absorption.