Inaccuracies in published data underestimate the amount of organic pollutants in raw sewage, providing flawed information for environmental policy makers, claim US scientists. 

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 apparatus 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.

'This work addresses a clear issue in the reporting of organic contaminant loading in raw influent entering wastewater treatment facilities,' says Chad Kinney, an expert in wastewater at Colorado State University, Pueblo, US. '[It] shines light on the importance of the solid side of wastewater treatment when considering both removal efficiencies from the aqueous phase as well as total removal,' he adds. 

Halden has outlined specific recommendations for sample processing and data reporting that he says will enhance the accuracy and informational value of future environmental monitoring data. But he concludes that there is a need for 'a close inspection of existing databases to root out erroneous and misleading information that may influence environmental management and regulations.' 

Amaya Camara-Campos 

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