Transformation and Sorption of Illicit Drug Biomarkers in Sewer Systems: Understanding the Role of Suspended Solids in Raw Wastewater

Abstract

Sewer pipelines, although primarily designed for sewage transport, can also be considered as bioreactors. In-sewer processes may lead to significant variations of chemical loadings from source release points to the treatment plant influent. In this study, we assessed in-sewer utilization of growth substrates (primary metabolic processes) and transformation of illicit drug biomarkers (secondary metabolic processes) by suspended biomass. Sixteen drug biomarkers were targeted, including mephedrone, methadone, cocaine, heroin, codeine, and tetrahydrocannabinol (THC) and their major human metabolites. Batch experiments were performed under aerobic and anaerobic conditions using raw wastewater. Abiotic biomarker transformation and partitioning to suspended solids and reactor wall were separately investigated under both redox conditions. A process model was identified by combining and extending the Wastewater Aerobic/anaerobic Transformations in Sewers (WATS) model and Activated Sludge Model for Xenobiotics (ASM-X). Kinetic and stoichiometric model parameters were estimated using experimental data via the Bayesian optimization method DREAM. Results suggest that biomarker transformation significantly differs from aerobic to anaerobic conditions, and abiotic conversion is the dominant mechanism for many of the selected substances. Notably, an explicit description of biomass growth during batch experiments was crucial to avoid significant overestimation (up to 385%) of aerobic biotransformation rate constants. Predictions of in-sewer transformation provided here can reduce the uncertainty in the estimation of drug consumption as part of wastewater-based epidemiological studies.

Potential impact of the sewer system on the applicability of alcohol and tobacco biomarkers in wastewater‐based epidemiology

“…The faster degradation is probably due to the presence of biofilms on the walls of RM and GS. These results are in agreement with previous studies where selected chemicals degraded faster in the presence of sewer biofilms or suspended than in wastewater …”

“…For EtG, biofilm activities in both the RM and GS reduced its stability in very similar ways (Figure b). The results obtained from the CR indicated that suspended microbes could also affect the stability of EtG, but not that of EtS, in the wastewater alone over the studied experimental period, a phenomenon that was reported recently by Ramin et al…”

“…These results are in agreement with previous studies where selected chemicals degraded faster in the presence of sewer biofilms or suspended than in wastewater. 13,14,18,30…”

Microbial biotransformation of five pyrrolidinophenone‐type psychoactive substances in wastewater and a wastewater isolated Pseudomonas putida strain

“…Before identifying consumption or discharge, it is important to know the analytical targets of the drugs in wastewater formed after biotransformation in humans or by microbes in the wastewater environment . Microbial processes in sewer models have been identified to cause substantial degradation of human metabolites of drugs of abuse and thus analytical targets of relevance for WBE . Identification of transformation products (TPs) in biological samples can be performed using mass spectrometry (MS) and/or nuclear magnetic resonance (NMR) .…”

“…[7] Microbial processes in sewer models have been identified to cause substantial degradation of human metabolites of drugs of abuse and thus analytical targets of relevance for WBE. [7][8][9] Identification of transformation products (TPs) in biological samples can be performed using mass spectrometry (MS) and/or nuclear magnetic resonance (NMR). [10] Liquid chromatography-high resolution-mass spectrometry (LC-HR-MS) allows for identification of low levels of TPs.…”