Aquatic photolysis of high-risk chemicals of emerging concern from secondary effluent mediated by sunlight irradiation for ecological safety and the enhanced methods.

Natural sunlight can reduce the chemicals of emerging concern (CECs) and biological effects from the discharged domestic wastewater. But the aquatic photolysis and biotoxic variations of specific CECs detected in secondary effluent (SE) were not clear. In this study, 29 CECs were detected in the SE, and 13 medium- and high-risk CECs were identified as target chemicals based on their ecological risk assessment. To comprehensively explore the photolysis properties of the identified target chemicals, the direct and self-sensitized photodegradation of the target chemicals, even the indirect photodegradation in the mixture, were investigated and compared with these photodegradation in the SE. Of the 13 target chemicals, only five chemicals (including dichlorvos (DDVP), mefenamic acid (MEF), diphenhydramine hydrochloride (DPH), chlorpyrifos (CPF), and imidacloprid (IMI)) underwent direct and self-sensitized photodegradation processes. The removal of DDVP, MEF, and DPH was attributed to self-sensitized photodegradation, which was mainly mediated by •OH; CPF and IMI primarily relied on direct photodegradation. Synergistic and/or antagonistic actions that occurred in the mixture improved/decreased the rate constants of five photodegradable target chemicals. Meanwhile, the biotoxicities (acute toxicity and genotoxicity) of the target chemicals (including individual chemicals and the mixture) were significantly reduced, which can explain the reduction of biotoxicities from SE. For the two refractory high-risk chemicals, atrazine (ATZ) and carbendazim (MBC), algae-derived intracellular dissolved organic matter (IOM) on ATZ, and IOM and extracellular dissolved organic matter (EOM) on MBC had slightly promotion for their photodegradation; while peroxysulfate, and peroxymonosulfate served as sensitizers were activated by natural sunlight and effectively improved their photodegradation rate, and then reduced their biotoxicities. These findings will promote the development of CECs treatment technologies based on sunlight irradiation.

The impact of natural sunlight irradiation on the biotoxicities of different molecular sizes EfOM/SRNOM and its relationship with spectral and molecular level parameters.

Natural sunlight irradiation is regarded as an efficient and low-carbon method for controlling the biotoxicity of effluents from domestic wastewater treatment plants (WWTPs). Dissolved organic matter in WWTPs effluent (EfOM) is responsible for the non-specific biotoxicity of effluent. In the present study, the variation in spectral characteristics, molecular composition, luminescent bacteria toxicity, and genotoxicity of EfOM of different molecular sizes (MOSs) during natural sunlight irradiation were investigated from a systematic perspective, and the standard natural organic matter from the Suwannee River (SRNOM) was synchronously assessed for comparative purposes. To further explore the cause of the biotoxicity changes, the relationships between the spectral or molecular level parameters (obtained from FT-ICR MS analysis) and biotoxicity were assessed using correlation analysis. The molecules in <1 kDa EfOM with lower molecular weight, higher unsaturation degree, and higher humification and fluorescence had higher luminescent bacteria toxicity under sunlight irradiation. However, in the <1 kDa SRNOM, the molecules which were characterized by higher humification and fluorescence had higher luminescent bacteria toxicity. The notable genotoxicity reduction of EfOM under sunlight irradiation was attributed to the photochemical degradation of components with a high unsaturation degree. Such findings could enable ecological safety improvement of aquatic environments using natural sunlight.

Micropollutants and biological effects as control indexes for the operation and design of shallow open-water unit ponds to polish domestic effluent.

Additional control indexes should be considered for the operation and design of post-treatment systems, as the wastewater treatment objectives are developing toward protecting the safety of ecological environments. In this study, two control indexes were selected and examined systematically in pilot-scale shallow open-water unit (SOWU) ponds for domestic effluent polishing: micropollutants and biotoxicities. The total risk quotient (RQTotal ≤ 1) and effect-based trigger value (EBT) were set as the thresholds for known micropollutants and biological effects, respectively. The results showed that RQTotal of micropollutants (n = 46) could be mitigated to an acceptable level and the luminescent bacteria toxicity was in compliance with the EBT after SOWU polishing in the warm season. The reduction of micropollutants and biotoxicities in the SOWUs both fit the k-C* model well (R2 > 0.9) in the warm and cold seasons. Finally, the k-C* model integrated with the control indexes was developed to design the SOWU dimensions, and the results indicated that a pond area of 21.7-108.5 m2 was required for every 1 m3/d of effluent when micropollutants were set as the control index, while a pond area of 3.6-18.2 m2 was required when luminescent bacteria toxicity was set as the control index.

Sunlight-induced changes in naturally stored reclaimed water: Dissolved organic matter, micropollutant, and ecotoxicity.

Natural sunlight is a vital environmental element and plays a significant role in the ecological storage of reclaimed water (RW), but its impacts on RW quality are poorly understood. In this study, sunlight-induced changes in RW with a focus on dissolved organic matter (rDOM) and 52 residual micropollutants were investigated in the field during the summer and winter seasons. The results indicated that sunlight exposure led to the dissipation of chromophoric DOM (CDOM) in the summer (55% loss) and winter (19% loss) after 14 consecutive sunny days. During open storage of RW, CDOM absorption in UVC regions was preferentially removed in the summer, while during the winter there was preferential removal of CDOM in UVA regions. The results also showed higher fluorescent DOM (FDOM) removal in summer than in winter (49% and 28%, respectively). Results in both seasons indicated that humic acid-like compounds were the most photolabile fractions and were preferentially removed under sunlight exposure. Sunlight also induced attenuation of micropollutants in the summer and winter at reductions of 66% and 24% from the initial values, respectively. Significant attenuation (>75%) was only observed for endocrine-disrupting chemicals, pharmaceuticals, and sunscreens in the summer, but they accounted for 76% of the total concentrations. Vibrio fischeri toxicity tests demonstrated that sunlight constantly decreased the luminescent bacteria acute toxicity of RW, which was estimated to be caused mainly by the sunlight-induced changes of FDOM and CDOM, while the detected micropollutants could only explain 0.02%-2% of acute toxicity. These findings have important implications regarding our understanding of the ecological storage of reclaimed water and the contribution of management strategies.