From Highlights in Chemical Science (Amaya Camara-Campos):
High quality analysis of raw sewage is crucial to measure pollutants in the environment and the efficiency of wastewater treatments plants. Suspended solids in sewage can block analytical apparatuses and complicate analysis so samples are commonly filtered before analysis. But, appropriate corrections for the filtration step are not always made say Rolf Halden and Randhir Deo at Arizona State University, Tempe.
Some hydrophobic organic compounds adsorb onto these solid filters and disappear from the sample, so the analysis of the resulting aqueous phase does not show the total amount that was present before filtering, explains Halden. Halden and Deo studied reported data for 33 organic compounds in the aqueous phase and found that between 15-60% of some compounds’ mass was adsorbed onto the suspended solids, which led to estimates of organic pollutants being 50% lower than actually present. And at higher pH levels, the underestimation became more frequent.
More wastewater coverage here.