Safety assessment of organic micropollutants in reclaimed water: Chemical analyses, ecological risk assessments, and in vivo endocrine-disrupting studies.

Reclaimed water from municipal wastewater has great potential in mitigating the water resource crisis, while the inevitable residue of organic micropollutants (OMPs) challenges the safety of reclaimed water reuse. Limited information was available regarding the overall adverse effects of mixed OMPs in reclaimed water, especially the endocrine-disrupting effects on living organisms. Herein, chemical monitoring in two municipal wastewater treatment plants showed that 31 of 32 candidate OMPs including polycyclic aromatic hydrocarbons (PAHs), phenols, pharmaceuticals and personal care products (PPCPs) were detected in reclaimed water, with a concentration ranging from ng/L to µg/L. Then, based on the risk quotient value, phenol, bisphenol A, tetracycline, and carbamazepine were ranked as high ecological risks. Most PAHs and PPCPs were quantified as medium and low risks, respectively. More importantly, using aquatic vertebrate zebrafish as an in vivo model, the endocrine-disrupting potentials of OMP mixtures were comprehensively characterized. We found that a realistic exposure to reclaimed water induced estrogen-like endocrine disruption and hyperthyroidism in zebrafish, abnormal expression of genes along the hypothalamus-pituitary-thyroid (-gonad) axes, reproductive impairment, and transgenerational toxicity. Based on the chemical analyses, risk quotient calculations, and biotoxicity characterization, this study contributed to understanding the ecological risks of reclaimed water and developing the control standards for OMPs. In addition, application of the zebrafish model in this study also highlighted the significance of in vivo biotoxicity test in water quality evaluation.

Cost-effective electrogeneration of H2O2 utilizing HNO3 modified graphite/polytetrafluoroethylene cathode with exterior hydrophobic film.

Electrochemical 2-electrons oxygen reduction process has been regarded as the effective strategy for H2O2 generation in wastewater treatment. However, its large-scale application is still limited by the relatively high cost of the carbon materials and short-term stability. In this study, a nitric acid modified graphite/polytetrafluoroethylene (PTFE) composite cathode with exterior hydrophobic film was fabricated for cost-effective electrogeneration of hydrogen peroxide (H2O2). Experimental results show that 2 M HNO3 modification rendered the introduction of much more defect sites and oxygen/nitrogen-containing groups on graphite. As a result, H2O2 electrogeneration was 3.0 times as much as that of virgin graphite counterpart at 3 mA cm-2. Moreover, the additional introduction of exterior hydrophobic film on the as-prepared graphite/PTFE cathode did not only further promote H2O2 electrogeneration, but also endowed the cathode with strong hydrophobic stability. As for the modified cathode with exterior hydrophobic film, the influence of mass graphite/PTFE binder ratio (1:1-4:1) and pH (3.0-9.0) on H2O2 electrogeneration was slight, but the current density (3.0-15 mA cm-2) had evident effect on H2O2 electrogeneration. Generally, owing to its low price and being easily available, the modified graphite would be cost-effectively utilized to prepare the gas diffusion cathode for the large-scale electrogeneration of H2O2 in industry.