Fate of organic microcontaminants in wastewater treatment and river systems: An uncertainty assessment in view of sampling strategy, and compound consumption rate and degradability

Abstract

The growing awareness of the relevance of organic microcontaminants on the environment has led to a growing number of studies on attenuation of these compounds in wastewater treatment plants (WWTP) and rivers. However, the effects of the sampling strategies (frequency and duration of composite samples) on the attenuation estimates are largely unknown. Our goal was to assess how frequency and duration of composite samples influence uncertainty of the attenuation estimates in WWTPs and rivers. Furthermore, we also assessed how compound consumption rate and degradability influence uncertainty. The assessment was conducted through simulating the integrated wastewater system of Puigcerdà (NE Iberian Peninsula) using a sewer pattern generator and a coupled model of WWTP and river. Results showed that the sampling strategy is especially critical at the influent of WWTP, particularly when the number of toilet flushes containing the compound of interest is small (≤100 toilet flushes with compound day), and less critical at the effluent of the WWTP and in the river due to the mixing effects of the WWTP. For example, at the WWTP, when evaluating a compound that is present in 50 pulses·d using a sampling frequency of 15-min to collect a 24-h composite sample, the attenuation uncertainty can range from 94% (0% degradability) to 9% (90% degradability). The estimation of attenuation in rivers is less critical than in WWTPs, as the attenuation uncertainty was lower than 10% for all evaluated scenarios. Interestingly, the errors in the estimates of attenuation are usually lower than those of loads for most sampling strategies and compound characteristics (e.g. consumption and degradability), although the opposite occurs for compounds with low consumption and inappropriate sampling strategies at the WWTP. Hence, when designing a sampling campaign, one should consider the influence of compounds' consumption and degradability as well as the desired level of accuracy in attenuation estimations.

Minimizing Errors in RT-PCR Detection and Quantification of SARS-CoV-2 RNA for Wastewater Surveillance

“…Only where wastewater is homogenized, and dilution is limited may grab sampling result in representative samples, e.g., sampling from wastewater systems of airplanes and cruise ships (Ahmed et al 2020f;Albastaki et al, 2021). Sampling of small sewer networks (e.g., buildings or neighbourhoods), where few toilet flushes occur over the course of a day and large short-term fluctuations are expected, would require an increased sampling frequency or peak sampling, e.g., during the morning hours, to capture these shedding events (Aymerich et al, 2017). Passive samplers may be useful alternatives in such cases as they have a demonstrated ability to accumulate pathogens over time, often with greater sensitivity and efficiency than grab samples.…”

Passive Sampling of SARS-CoV-2 for Wastewater Surveillance

“…The collection of spot or grab samples is an option, but the high temporal variability of wastewater flows and pollutant concentrations at these smaller scales 16 , 17 suggest that single grab sampling may reduce sensitivity and miss important information, such as shedding events. 18 Ideally, multiple grab samples could be collected from each site, but this significantly increases costs and safety risks. To account for the dynamics of wastewater at these smaller scales, monitoring stations could be established with autosamplers and flow meters programmed to take frequent flow-proportional or time-proportional samples.…”

“…Although the application of WBE at smaller scales is appealing, collection of representative samples within the sewerage network presents several challenges. The collection of spot or grab samples is an option, but the high temporal variability of wastewater flows and pollutant concentrations at these smaller scales , suggest that single grab sampling may reduce sensitivity and miss important information, such as shedding events . Ideally, multiple grab samples could be collected from each site, but this significantly increases costs and safety risks.…”

“…Ideally, multiple grab samples could be collected from each site, but this significantly increases costs and safety risks. To account for the dynamics of wastewater at these smaller scales, monitoring stations could be established with autosamplers and flow meters programmed to take frequent flow-proportional or time-proportional samples . Apart from requiring specialized skillsets, such installations are difficult at this scale because of (1) installation and maintenance costs, (2) equipment availability, (3) limited space and access to the sampling site, (4) safety concerns, especially as traffic management is commonly required, (5) the absence of a reliable power supply for refrigerated samplers, and (6) excessive sampling depths, which may be more than 10 m and is beyond the capacity of most autosampler pumps.…”

Environmental Footprint of Wastewater Treatment: A Step Forward in the Use of Toxicological Tools

“…Sampling represents a crucial step in the characterization of different streams, hence in the evaluation of plant performance. Several authors have underlined the huge variability of trace pollutants content throughout a day or a week: influent and effluent single grab samples are not representative at all of the actual trends (see, inter alia, [ 15 , 16 , 17 , 18 ]). For these reasons, the duration of every monitoring campaign was set at two weeks, much longer than the hydraulic retention time (HRT).…”