Efforts are underway to transform regulatory toxicology and chemical safety assessment from a largely empirical science based on direct observation of apical toxicity outcomes in whole organism ...toxicity tests to a predictive one in which outcomes and risk are inferred from accumulated mechanistic understanding. The adverse outcome pathway (AOP) framework provides a systematic approach for organizing knowledge that may support such inference. Likewise, computational models of biological systems at various scales provide another means and platform to integrate current biological understanding to facilitate inference and extrapolation. We argue that the systematic organization of knowledge into AOP frameworks can inform and help direct the design and development of computational prediction models that can further enhance the utility of mechanistic and in silico data for chemical safety assessment. This concept was explored as part of a workshop on AOP-Informed Predictive Modeling Approaches for Regulatory Toxicology held September 24-25, 2015. Examples of AOP-informed model development and its application to the assessment of chemicals for skin sensitization and multiple modes of endocrine disruption are provided. The role of problem formulation, not only as a critical phase of risk assessment, but also as guide for both AOP and complementary model development is described. Finally, a proposal for actively engaging the modeling community in AOP-informed computational model development is made. The contents serve as a vision for how AOPs can be leveraged to facilitate development of computational prediction models needed to support the next generation of chemical safety assessment.
Based on previous reports, UV/sulfite process is generally used as an advanced reduction process (ARP) since eaq− and/or ∙H, both with strong reduction potential, could be substantially generated ...herein. Very recently, the combination of UV and sulfite as an advanced oxidation process (AOP) or an oxidation-reduction coupling process has attracted increasing interest due to the yield of SO4∙− and/or HO∙. Herein, the application of UV/sulfite as an ARP and AOP (or oxidation-reduction coupling process) during water and wastewater treatments is reviewed respectively. (1) In the absence of O2, UV/sulfite works as an ARP. The generation mechanism of reactive reduction species and various contaminants removal (including degradation kinetics and efficiency, decomposition mechanisms, effects of some factors, etc.) is summarized in detail and systematically. Moreover, both the application of different types of UV lights and the economic evaluation are summarized systematically. (2) In the presence of O2, UV/sulfite could be used as an AOP or oxidation-reduction coupling process. The generation mechanism of reactive oxidation species and influencing factors is also presented in detail. Moreover, two ways (including homogeneous and heterogeneous activation) used to enhance the UV/sulfite oxidation potential are summarized respectively. Moreover, several knowledge gaps and research needs for further research are proposed. Overall, this review provides an overview for in-depth understanding of UV/sulfite as an ARP or AOP (oxidation-reduction coupling process) during water and wastewater treatments.
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•The performance of UV/sulfite as an ARP was discussed in detail.•The application of various UV lights during UV/sulfite as an ARP was reviewed.•The energy evaluation of UV/sulfite as an ARP was summarized systematically.•UV/sulfite as an AOP or oxidation-reduction coupling process was presented.
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Nowadays, pharmaceuticals are the center of significant environmental research due to their complex and highly stable bioactivity, increasing concentration in the water streams and high persistence ...in aquatic environments. Conventional wastewater treatment techniques are generally inadequate to remove these pollutants. Aiming to tackle this issue effectively, various methods have been developed and investigated on the light of chemical, physical and biological procedures. Increasing attention has recently been paid to the advanced oxidation processes (AOPs) as efficient methods for the complete mineralization of pharmaceuticals. Their high operating costs compared to other processes, however, remain a challenge. Hence, this review summarizes the current and state of art related to AOPs, biological treatment and their effective exploitation for the degradation of various pharmaceuticals and other emerging molecules present in wastewater. The review covers the last decade with a particular focus on the previous five years. It is further envisioned that this review of advanced oxidation methods and biological treatments, discussed herein, will help readers to better understand the mechanisms and limitations of these methods for the removal of pharmaceuticals from the environment. In addition, we compared AOPs and biological treatments for the disposal of pharmaceuticals from the point of view of cost, effectiveness, and popularity of their use. The exploitation of coupling AOPs and biological procedures for the degradation of pharmaceuticals in wastewater was also presented. It is worthy of note that an integrated AOPs/biological system is essential to reach the complete degradation of pharmaceuticals; other advantages of this hybrid technique involve low energy cost, an efficient degradation process and generation of non-toxic by-products.
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•Pharmaceutical compounds in different water matrices contribute to ecotoxicity.•Water treatment plants are efficient to reduce but not remove pharmaceuticals present in water.•Removal of pharmaceuticals by advanced oxidation processes (AOPs) from wastewater appears efficient.•Biological processes are promising techniques in the removal of pharmaceuticals.•The hybrid AOPs/biological system is economical and efficiency for complete degradation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ
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•UV/chlorine degrading CBZ gave similar DBP formation and genotoxicity and decreased cytotoxicity compared to UV/H2O2.•UV/chlorine degrading ATZ slightly increased DBP formation but ...decreased toxicity compared to UV/H2O2.•The DBP formation and toxicity were correlated with the NOM alteration induced by AOPs.
This study compares the influences of UV/chlorine and UV/H2O2 advanced oxidation of natural organic matter at the equivalent degradation of two model micropollutants on the formation of disinfection by-products (DBPs) and toxicity during post-chlorination. At 90% degradation of carbamazepine, the UV/chlorine advanced oxidation process (AOP) at pH 6.0 (3.0 mg/L chlorine and 280 mJ/cm2) resulted in comparable yields of dichloroacetic acid, trichloroacetic acid, chloroform, chloral hydrate, dichloroacetonitrile, trichloropropanone and total organic chlorine (TOCl) during the post-chlorination, compared to the UV/H2O2 AOP (8.0 mg/L H2O2 and 280 mJ/cm2). The UV/chlorine AOP increased the chloroacetic acid yields by 28–43% at pH 7.0 and 8.0. The cytotoxicity with the UV/chlorine AOP was 32% lower than with the UV/H2O2 AOP, however, the genotoxicity was similar. At the 90% degradation of atrazine, the UV/chlorine AOP (6.0–13.9 mg/L chlorine and 750–1000 mJ/cm2) increased the chloroacetic acid yields by 35–81% but did not increase the yields of other four known DBPs and TOCl, compared to the UV/H2O2 AOP (8.0–12.9 mg/L chlorine and 750–1000 mJ/cm2). The cytotoxicity and genotoxicity with the UV/chlorine AOP at pH 6.0 were 22–27% lower than those with the UV/H2O2 AOP, likely due to the selective destruction of the precursors of cytotoxic and genotoxic DBPs by RCS. The TOCl yields were positively correlated to the decreases in the specific UV absorbance at 254 nm and humic-like fluorescence. The TOCl yields exhibited a linear relationship with the genotoxicity (R2 = 0.81) but were weakly correlated with the cytotoxicity (R2 = 0.40). Although the UV/chlorine AOP increases the formation of some DBPs under certain circumstances, compared to the UV/H2O2 AOP, it does not enhance the genotoxicity and even decreases the cytotoxicity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Advanced oxidation using UV/free chlorine and UV/chloramines are being considered as alternatives to UV/H2O2 for treatment of reverse osmosis (RO) permeate in treatment trains for the potable reuse ...of municipal wastewater. This pilot-scale comparison of the three advanced oxidation processes (AOPs) evaluated three factors important for selecting among these alternatives. First, the study characterized the speciation of oxidants serving as the source of radicals within the AOPs to facilitate process modeling. Kinetic modeling that included consideration of the chloramines occurring in RO permeate accurately predicted oxidant speciation. Modeling of the UV/free chlorine AOP indicated that free chlorine is scavenged by reactions with ammonia and monochloramine in RO permeate, such that oxidant speciation can shift in favor of dichloramine over the short (∼30 s) timescale of AOP treatment. Second, the order of efficacy for degrading the target contaminant, 1,4-dioxane, in terms of minimizing UV fluence was UV/free chlorine > UV/H2O2 ≫ UV/chloramines. However, estimates indicated that the UV/chloramines and UV/H2O2 AOPs could be similar on a cost-effectiveness basis due to savings in reagent costs by the UV/chloramines AOP, provided the RO permeate featured >3 mg/L as Cl2 chloramines. Third, the study evaluated whether the use of chlorine-based oxidants within the UV/free chlorine and UV/chloramines AOPs enhanced disinfection byproduct (DBP) formation. Even after AOP treatment and chloramination, total halogenated DBP formation remained low at <15 μg/L for all three AOPs. DBP formation was similar between the AOPs, except that the UV/free chlorine AOP promoted haloacetaldehyde formation, while the UV/H2O2 and UV/chloramines AOPs followed by chloramination increased chloropicrin formation. However, total DBP formation on a toxic potency-weighted basis was similar among the AOPs, since haloacetonitriles and haloacetamides were the dominant contributors and did not differ significantly among the AOPs.
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•Mixtures of oxidants occur in AOPs at potable reuse facilities.•A kinetic model could predict oxidant speciation in these AOPs.•The order of efficacy for 1,4-dioxane loss was UV/HOCl > UV/H2O2 ≫ UV/chloramines.•Halogenated DBP concentrations were similar for these AOPs.
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•Unexpected nitration processes led to formation of several nitro-derivatives.•Nitrogen fixation importantly contributes to formation of reactive nitrogen species in ...sonolysis.•Denitration and renitration processes in persulfate based AOPs causes nitration of intermediates.•Post-treatment and nitro-derivatives monitoring are important in AOPs.•Risk of low water quality in case of unexpected nitration during treatment process.
Chemical compounds containing nitro group (nitro-products) are a one of toxic by-products, that can be formed during wastewater treatment processes. In case of presence of nitrite or nitrate ions, the formation of nitro-products during advanced oxidation processes (AOPs) is very common. It is caused by the reactive nitrogen species (RNs) such as nitrate radical (NO3•), nitrite radical (NO2•), nitrogen oxide radical (NO•) and peroxynirite (ONOO–). In fact, the oxidative degradation of N-containing pollutants releases nitrate, nitrite and ammonium ions. In some cases, secondary reactions of mineralised nitrogen species (nitrate and nitrite ions) with the parent or intermediate compound generate next several nitro-products. The nitro-products are more toxic comparing to the primary pollutants and act as the precursors of the nitrogenous disinfection by-products. Moreover, some studies reported unexpected nitro-products formation during the oxidative degradation. In case of such processes a special attention should be made to monitor and minimize these effects. De-nitration of the initial nitro-compounds induces the formation of various nitro-products in AOPs. It was observed for UV light driven, Fenton and persulfate based AOPs. The sonochemical nitrogen fixation is a key mechanism for the formation of nitro-compounds in ultrasounds based AOPs. Therefore, this paper is focused on comparison of various AOPs in terms of nitro-products formation mechanisms and the associated environmental issues.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
The adverse outcome pathway (AOP) framework provides a practical means for organizing scientific knowledge that can be used to infer cause-effect relationships between stressor events and ...toxicity outcomes in intact organisms. It has reached wide acceptance as a tool to aid chemical safety assessment and regulatory toxicology by supporting a systematic way of predicting adverse health outcomes based on accumulated mechanistic knowledge. A major challenge for broader application of the AOP concept in regulatory toxicology, however, has been developing robust AOPs to a level where they are peer reviewed and accepted. This is because the amount of work required to substantiate the modular units of a complete AOP is considerable, to the point where it can take years from start to finish. To help alleviate this bottleneck, we propose a more pragmatic approach to AOP development whereby the focus becomes on smaller blocks. First, we argue that the key event relationship (KER) should be formally recognized as the core building block of knowledge assembly within the AOP knowledge base (AOP-KB), albeit framing them within full AOPs to ensure regulatory utility. Second, we argue that KERs should be developed using systematic review approaches, but only in cases where the underlying concept does not build on what is considered canonical knowledge. In cases where knowledge is considered canonical, rigorous systematic review approaches should not be required. It is our hope that these approaches will contribute to increasing the pace at which the AOP-KB is populated with AOPs with utility for chemical safety assessors and regulators.
Advanced oxidation using UV and hydrogen peroxide (UV/H2O2) has been widely applied to degrade contaminants of emerging concern (CECs) in wastewater for water reuse. This study investigated the ...degradation kinetics of mixed CECs by UV/H2O2 under variable H2O2 doses, including bisphenol A, estrone, diclofenac, ibuprofen, and triclosan. Reverse osmosis (RO) treated water samples from Orange County Water District’s Groundwater Replenishment System (GWRS) potable reuse project were collected on different dates and utilized as reaction matrices with spiked additions of chemicals (CECs and H2O2) to assess the application of UV/H2O2. Possible degradation pathways of selected CECs were proposed based on high resolution mass spectrometry identification of transformation products (TPs). Toxicity assessments included cytotoxicity, aryl hydrocarbon receptor-binding activity, and estrogen receptor-binding activity, in order to evaluate potential environmental impacts resulting from CEC degradation by UV/H2O2. Cytotoxicity and estrogenic activity were significantly reduced during the degradation of mixed CECs in Milli-Q water by UV/H2O2 with high UV fluence (3200 mJ cm−2). However, in GWRS RO-treated water samples collected in April 2017, the cytotoxicity and estrogen activity of spiked CEC-mixture after UV/H2O2 treatment were not significantly eliminated; this might be due to the high concentration of target CEC and their TPs, which was possibly affected by the varied quality of the secondary treatment influent at this facility such as sewer-shed and wastewater discharges. This study aimed to provide insight on the impacts of post-UV/H2O2 CECs and TPs on human and ecological health at cellular level.
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•Present resulting toxicity during single CEC degradation by UV/H2O2.•Show resulting toxicity of spiked CECs degraded by UV/H2O2 in RO samples.•Possible degradation pathways of selected CECs were proposed.•Toxicity analysis at cellular level shows the risk of post-UV/H2O2 on human and wildlife.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ
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•The sluggish FeIII/FeII cycles restrict Fe-based system from practical application.•Accelerating the FeIII/FeII redox centres is an innovative strategy.•Fe3+/MgAl-MoS4/PMS system was ...more reactive than the reported system.•Regeneration of Fe2+ was responsible for good PMS utilization and activity.•The unsaturated S2− and Mo4+ were disclosed to fuel electron to reduce Fe3+.
The slow transformation of Fe3+ back to Fe2+ restrict the practical application of Fe-based catalytic treatment of organic pollutants. Herein, we report a new findings of MgAl-MoS4 to accelerate the redox cycle of Fe3+/Fe2+ in Fe3+/PMS system. Based on the degradation of 4-chlorophenol (4-CP) profile, the rate constant of Fe3+/MgAl-MoS4/PMS system was 40 to 42 folds higher than MgAl-CO3/PMS, MgAl-MoS4/PMS and Fe3+/PMS respectively. Moreover, Fe3+/MgAl-MoS4/PMS system was superior both in the degradation efficiency of pollutants as well as in the stoichiometric efficiency of oxidants from the recently reported Fe3+/WS2/PMS, Fe3+/MoS2/PMS or other well-known nano-catalysts systems. This co-catalytic effect of MgAl-MoS4 on the studied redox metals falls in the order of Fe3+ > V5+ > Cu2+ > Mn2+~Ag+. Furthermore, the Fe3+/PMS/MgAl-MoS4 system shows smooth degradation over a wide pH (3.0–7.0) and complete stabilities in the recycled studies. Additionally, the presence of excessive amounts of inorganic anions or organic matters also did not influence the degradation profile. In mechanism studies, both the unsaturated S2− and Mo4+ of MgAl-MoS4 were disclosed to fuel electron continuously during the reduction of Fe3+ ions, and thus accelerate the rate limiting step (Fe3+/Fe2+). Additionally, the layered structure, memory effect and suitable surface charge of LDH material also concentrates the reactants molecules and hence, the boosted effect of MgAl-MoS4 was associated with the better adsorption of Fe3+ ions, the faster PMS decomposition, and the acceleration of Fe3+/Fe2+ redox cycle. This work indicates a breakthrough in the field of classical homogenous Fe/PMS system, offers the very first report on the role of Mo6+ and S2− to modulate the redox behaviour of homogenous Fe ions in persulfate based advanced oxidation processes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•UV fluence and •OH exposure were calculated from abatements of two micropollutants•The abatement of other micropollutants was predicted within ±20 %•The model allowed estimations of k•OH and kUV of ...co-existing micropollutants•A sensitivity analysis showed limited effect of analytical errors if probe compounds were abated > 50%
Organic micropollutants (MPs) are increasingly detected in water resources, which can be a concern for human health and the aquatic environment. Ultraviolet (UV) radiation based advanced oxidation processes (AOP) such as low-pressure mercury vapor arc lamp UV/H2O2 can be applied to abate these MPs. During UV/H2O2 treatment, MPs are abated primarily by photolysis and reactions with hydroxyl radicals (•OH), which are produced in situ from H2O2 photolysis. Here, a model is presented that calculates the applied UV fluence (Hcalc) and the •OH exposure (CT•OH,calc) from the abatement of two selected MPs, which act as internal probe compounds. Quantification of the UV fluence and hydroxyl radical exposure was generally accurate when a UV susceptible and a UV resistant probe compound were selected, and both were abated at least by 50 %, e.g., iopamidol and 5-methyl-1H-benzotriazole. Based on these key parameters a model was developed to predict the abatement of other MPs. The prediction of abatement was verified in various waters (sand filtrates of rivers Rhine and Wiese, and a tertiary wastewater effluent) and at different scales (laboratory experiments, pilot plant). The accuracy to predict the abatement of other MPs was typically within ±20 % of the respective measured abatement. The model was further assessed for its ability to estimate unknown rate constants for direct photolysis (kUV,MP) and reactions with •OH (k•OH,MP). In most cases, the estimated rate constants agreed well with published values, considering the uncertainty of kinetic data determined in laboratory experiments. A sensitivity analysis revealed that in typical water treatment applications, the precision of kinetic parameters (kUV,MP for UV susceptible and k•OH,MP for UV resistant probe compounds) have the strongest impact on the model's accuracy.
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