Sampling for representative micropollutant loads in sewer systems.
Most commercially available auto-sampling devices do not support a continuous flow-proportional sampling mode, which would conceptually be the best for collecting representative composite samples. Instead different discrete sampling modes are available. Household chemicals can show considerable random short-term variations. With the anticorrosive benzotriazole, relating to a middle-frequent household activity, we show that, besides an accurate flow meter, mainly three factors are decisive for the representativeness of a substance's average load: the substance's load pattern, the sampling frequency and the length of the composite sample. When the sampling intervals are 10 minutes or longer, errors in the order of +/-40% (standard deviation) or more have to be accepted, if the substance of interest is contained in a low number of wastewater pulses (i.e., the level of household activity). This particularly holds true for specific pharmaceuticals e.g. carbamazepine. Ammonium would be less critical, because it relates to a larger number of sources in the same catchment.
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Swiss Federal Institute of Aquatic Science and Technology, Eawag, CH-8600 Dübendorf and Institute of Environmental Engineering, ETH Zurich, CH-8093 Zurich, Switzerland. christoph.ort@eawag.ch
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D002220:Carbamazepine / Q000032:analysis; D003902:Detergents / Q000032:analysis; D004784:Environmental Monitoring; D008962:Models, Theoretical; D012722:Sewage; D014230:Triazoles / Q000032:analysis; D014874:Water Pollutants, Chemical / Q000032:analysis*
D003902:Detergents; D012722:Sewage; D014230:Triazoles; D014874:Water Pollutants, Chemical; D002220:Carbamazepine; C012771:benzotriazole