Sampling for PPCPs in Wastewater Systems: Comparison of Different Sampling Modes and Optimization Strategies

Abstract

The aim of this study was to assess uncertainties associated with different sampling modes when evaluating loads of pharmaceuticals and personal care products (PPCPs) in sewers and influents to sewage treatment plants (STPs). The study demonstrates that sampling uncertainty can range from "not significant" to "far greater than the uncertainty due to chemical analysis", which is site- and compound-specific and depends on the (in)accuracy of the analytical method. Conventional sampling devices operated in common time- or flow-proportional sampling modes, and applying traditional sampling intervals of 30 min or longer can result in the collection of nonrepresentative samples. At the influent of a STP, wastewater may appear as a continuous stream, but it is actually composed of a number of intermittently discharged, individual wastewater packets from household appliances, industries, or subcatchments in pressurized sewer systems. The resulting heterogeneity can cause significant short-term variations of pollutant loads. We present different experimental results and a modeling approach showing that the magnitude of sampling uncertainty depends mainly on the number of pollutant peaks and the sampling frequency; sampling intervals of 5 min or shorter may be required to properly account for temporal PPCP variations in influents of STPs. A representative sample is a prerequisite for providing meaningful analytical results and cannot be compensated with a large number of samples, accurate chemical analysis, or sophisticated statistical evaluation. This study highlights that generalizing from one case to another is difficult and hence a careful systems analysis of the catchment under investigation, or precautionary choice for a sophisticated sampling mode, is necessary to prove reproducibility.

Impact of approach used to determine removal levels of drugs of abuse during wastewater treatment

“…Consequently, since advanced analytical methodologies for the detection of emerging micropollutants are now available, unsuitable sampling increasingly represents a major source of inaccuracy (Ort et al, 2010b). Ort et al (2010a) assessed how sampling strategies were addressed in numerous studies and found that only few provided justification for the choice of sampling technique, duration, mode and frequency. Most studies that have monitored the levels of DOAs in wastewater used grab samples or isolated 24-h composite samples of the influent and effluent of the WWTP (Bones et al, 2007;Mazzella et al, 2007;Postigo et al, 2008b) and did not consider the HRT or mixing in the treatment tanks for the estimation of full-scale removal efficiencies.…”

Estimating surface water concentrations of “down-the-drain” chemicals in China using a global model

“…where r is the proportion of chemical removed in a WWTP, which ideally should be commensurate with monitoring data (Ort et al, 2010) but which can also be estimated from the results of standard laboratory biodegradation tests (e.g. Struijs et al, 1991;European Commission, 2003) and DF is the dilution factor which can be defined as:…”

Assessment of Domestic Wastewater Disposal in Some Selected Wards of Maiduguri Metropolis, Borno State, Nigeria

“…Further consideration should be given to (e) the sample size and sampling method. The relatively low number of pharmaceutical users in the two WWTP catchments, and the Benson WWTP catchment in particular, leaves model estimates of antibiotic users highly susceptible to systematic errors, as previously described [50]. The heterogeneity in the content of wastewater associated with low flush events, typical of low flow periods in the middle of the night, are a major factor influencing variations in analyte recovery over much of the sampling period [51][52][53].…”

“…This higher variability can be witnessed by the higher standard deviation in hourly measures of OC in Benson (4336472 ng/L) as compared to Oxford (358660 ng/L). The Oxford and Benson sewer systems receive flow from a number of pumping stations that contribute to the mixing of discrete flushing events, however, the problems associated with sampling small populations would be more effectively alleviated with more intensive sampling (every 5-15 minutes) [50]. And finally, the wastewater epidemiology approach for antibiotics will likely be highly sensitive to (f) variability in environmental temperatures and precipitation, where low temperatures will likely retard biodegradation and high precipitation will dilute potentially inhibitory levels of drug while also resuspending sediment that can subsequently influence the drug's fate.…”