Sampling for representative micropollutant loads in sewer systems

• Published in: Water science and technology Vol. 54; no. 6-7; pp. 169 - 176
• Main Authors: Ort, C., Gujer, W.
• Format: Journal Article
• Language: English
• Published: England IWA Publishing 01.01.2006
• Subjects: Ammonium; Ammonium compounds; Benzotriazole; Carbamazepine; Carbamazepine - analysis; Continuous flow; Corrosion prevention; Detergents - analysis; Environmental Monitoring; Household chemicals; Households; Load; Micropollutants; Models, Theoretical; Samplers; Sampling; Sewage; Sewer systems; Triazoles - analysis; Wastewater; Water Pollutants, Chemical - analysis; Watersheds
• ISBN: 1843395746; 9781843395744
• ISSN: 0273-1223; 1996-9732
• DOI: 10.2166/wst.2006.591

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.