Impact of nano zero valent iron dosing on biotransformation and adsorption of 20 biomarkers in sewers

Understanding the stability of biomarkers during sewer transport is one of the crucial steps when applying wastewater-based epidemiology (WBE) for assessing consumption or exposure to chemicals. Their stability could be impacted by chemical dosing, a common method used to control the generation of hydrogen sulfide in urban sewer networks. Nano zero valent iron (nZVI) has recently attracted attention due to its effectiveness on sulfide and methane removal. However, the impact of dosing nZVI on the transformation of biomarkers in sewers and the consequent influence on WBE estimation remains unknown. This study investigated the impact of nZVI dosage on adsorption and biotransformation processes of 20 pharmaceutical biomarkers in lab-scale sewer reactors. Dosing nZVI (50 mg Fe/L) effectively inhibited the production of sulfide and changed microbial communities in sewer biofilms. There was no adsorption observed when biomarkers interacted with nZVI only, indicating that adsorption to nZVI dosing was not the main mechanism for biomarker transformation. Meanwhile, the duration and amount of dosing nZVI had no impact on stable biomarkers with less 15% loss (e.g. cotinine, OH-cotinine, benzoylecgonine and acesulfame). In contrast, nZVI dosing affected the transformation of inherently moderately stable biomarkers like methamphetamine, 3,4-methylenedioxymethamphetamine, methylone, carbamazepine, ketamine and atenolol. These findings revealed the complex impacts of nZVI on mediating sewer conditions, biological compositions and in-sewer stability of biomarkers. An evaluation framework was applied to jointly consider the impact of nZVI dosing and hydraulic retention time on biomarker stability, which provides new knowledge for WBE's application in dynamic sewer systems.