Transformation and Sorption of Illicit Drug Biomarkers in Sewer Biofilms

Abstract

In-sewer transformation of drug biomarkers (excreted parent drugs and metabolites) can be influenced by the presence of biomass in suspended form as well as attached to sewer walls (biofilms). Biofilms are likely the most abundant and biologically active biomass fraction in sewers. In this study, 16 drug biomarkers were selected, including the parent forms and the major human metabolites of mephedrone, methadone, cocaine, heroin, codeine, and tetrahydrocannabinol (THC). Transformation and sorption of these substances were assessed in targeted batch experiments using laboratory-scale biofilm reactors operated under aerobic and anaerobic conditions. A one-dimensional model was developed to simulate diffusive transport, abiotic and biotic transformation, and partitioning of drug biomarkers. Model calibration to experimental results allowed estimating biotransformation rate constants in sewer biofilms, which were compared to those obtained for suspended biomass. Our results suggest that sewer biofilms can enhance the biotransformation kinetics of most selected compounds. Through scenario simulations, we demonstrated that the estimation of biotransformation rate constants in biofilm can be significantly biased if the boundary layer thickness is not accurately estimated. This study complements our previous investigation on the transformation and sorption of drug biomarkers in the presence of only suspended biomass in untreated sewage. A better understanding of the role of sewer biofilms-also relative to the in-sewer suspended solids-and improved prediction of associated fate processes can result in more accurate estimation of daily drug consumption in urban areas in wastewater-based epidemiological assessments.

Experimental Investigation and Modeling of the Transformation of Illicit Drugs in a Pilot-Scale Sewer System

“…except for KET with closer distributions of at minor levels. This could be ′ explained by the stronger biological activities of biofilms in the pilot sewer pipes and the sewer reactors of Li et al 10 compared to biofilms in the reactors of McCall et al 14 and/or Ramin et al 16 Moreover, and/or appear to be generally equivalent…”

“…(h -1 ) represents the processes in the bulk liquid wastewater, mainly μ chemical hydrolysis assuming that the sorption to suspended solids or biofilm is limited for investigated biomarkers 5,14,16,33 and the biological activity of suspended solids is negligible compared to the sewer biofilms or sediments. [34][35][36] It is further postulated that remains the same under aerobic and anaerobic conditions, according to the findings of McCall et al 14 To calibrate the transformation model, experimental datasets obtained from the pilot rising main pipe (Day and 2) and the pilot gravity sewer (Day 4 and 5) pipe were used to estimate and , respectively, through a Bayesian procedure ′ ′ described in Li et al 10 The datasets of Day 3 (rising main) and Day 6 (gravity sewer)…”

“…To date, several lab-scale studies have assessed the in-sewer stability of illicit drug biomarkers and estimated the transformation coefficients under their specific testing conditions. 10,14,16 Table S3.2), and their prediction capabilities are jointly compared under the conditions of the pilot-scale sewer system. Multiple prediction scenarios (mean with 95% confidence bounds) under the conditions of the pilot rising main and the gravity sewer are generated for each investigated biomarker (Table S3.…”

“…[2][3][4][5] In order to improve the accuracy of back-estimation, researches have been widely conducted to address the uncertainties associated with sampling method and chemical analysis, [5][6][7][8][9] while a comprehensive understanding of biomarkers stability in real sewers is still ongoing. [10][11][12][13][14][15][16][17] Biomarkers are subjected to physiochemical and biological processes during their transport in rising main and gravity sewer pipes, where the hydraulic retention time (HRT) may last for hours. 18 Neglecting the biomarkers transformation (e.g., the degradation or formation in sewers) will lead to an under-or over-estimation of drug consumption in a catchment.…”

Systematic evaluation of biomarker stability in pilot scale sewer pipes

“…Many laboratory experiments used bulk liquid wastewater in a container to represent the sewer conditions (Ostman et al 2014, Senta et al 2014, and other studies utilized sewer reactors that have biofilms (Gao et al 2017, O'Brien et al 2017, Ramin et al 2017, Thai et al 2014. These studies have found, for example, that the relatively fast degradation of cocaine and 6monoacetylmorphine compromised their usability as biomarkers in WBE.…”