Microplastics and PAHs mixed contamination: An in-depth review on the sources, co-occurrence, and fate in marine ecosystems.

Microplastics (MPs) and polycyclic aromatic hydrocarbons (PAHs) are toxic contaminants that have been found in marine ecosystems. This review aims to explore the sources and mechanisms of PAHs and MPs mixed contamination in marine environments. Understanding the released sources of PAHs and MPs is crucial for proposing appropriate regulations on the release of these contaminants. Additionally, the mechanisms of co-occurrence and the role of MPs in distributing PAHs in marine ecosystems were investigated in detail. Moreover, the chemical affinity between PAHs and MPs was proposed, highlighting the potential mechanisms that lead to their persistence in marine ecosystems. Moreover, we delve into the various factors influencing the co-occurrence, chemical affinity, and distribution of mixed contaminants in marine ecosystems. These factors, including environmental characteristics, MPs properties, PAHs molecular weight and hydrophobicity, and microbial interactions, were critically examined. The co-contamination raises concerns about the potential synergistic effects on their degradation and toxicity. Interesting, few studies have reported the enhanced photodegradation and biodegradation of contaminants under mixed contamination compared to their individual remediation. However, currently, the remediation strategies reported for PAHs and MPs mixed contamination are scarce and limited. While there have been some initiatives to remove PAHs and MPs individually, there is a lack of research specifically targeting the removal of mixed contaminants. This deficiency highlights the need for further investigation and the development of effective remediation approaches for the efficient remediation of PAHs and MPs from marine ecosystems.

Disinfection by-products control in wastewater effluents treated with ozone and biological activated carbon followed by UV/Chlor(am)ine processes.

Sequential utilization of ozone (O3) and biological activated carbon (BAC) followed by UV/chlor(am)ine advanced oxidation process (AOP) has drawn attention in water reuse. However, the formation of disinfection by-products (DBPs) in this process is less evaluated. This study investigated the DBP formation and the relevant toxicity during the O3-BAC-UV/chlor(am)ine treatment of sand-filtered municipal secondary effluent. DBP formation in UV/chlorine and UV/dichloramine (NHCl2) processes were compared, where the impact of key operational parameters (e.g., UV wavelength, pH) on DBP formation were comprehensively evaluated. O3-BAC significantly reduced DBP formation potential (DBPFP) (58.2 %). Compared to UV/chlorine AOP, UV/NHCl2 AOP reduced DBP formation by 29.7 % in short-time treatment, while insignificantly impacting on DBPFP (p > 0.05). UV/NHCl2 AOP also led to lower calculated cytotoxicity (67.7 %) and genotoxicity (55.9 %) of DBPs compared to UV/chlorine AOP. Compared to 254 nm UV light, the utilization of 285 nm UV light decreased the formation of DBPs in wastewater treated with the UV/chlorine AOP and UV/NHCl2 AOP by 31.3 % and 19.2 %, respectively. However, the cytotoxicity and genotoxicity in UV/NHCl2 AOP using 285 nm UV light increased by 83.4 % and 58.5 %, respectively, compared to 254 nm. The concentration of DBPs formed in the UV/NHCl2 AOP at pH 8 was 54.3 % lower than that at pH 7, suggesting a better control of DBPs at alkaline condition. In the presence of bromide, UV/NHCl2 AOP tended to generate more brominated DBPs than UV/chlorine AOP. Overall, UV/NHCl2 AOP resulted in lower concentration and toxicity of DBPs compared to UV/chlorine AOP.

Mineralization characteristics and behavior of polyethylene microplastics through ozone-based treatment.

The elimination of microplastics (MPs) has become an urgent issue due to their large quantities and imperfect treatment technologies. In this work, polyethylene (PE), which is ubiquitous in the environment, was selected to study its removal by ozone-based treatment. Catalysts including α-MnO2 and α-FeOOH were synthesized for catalytic ozonation to improve efficiency. The study focused on simulating the conversion of CO2 in the off-gas via the detection of inorganic carbon produced. The morphology and structure of the remaining PE MPs were characterized using scanning electron microscope and Fourier-transform infrared spectroscopy-attenuated total reflection. Our results confirmed that fragmentation and oxidation occurred in the remaining PE MPs, which enhanced the adsorption capacity of ofloxacin (OF). Besides, the 20 mM α-FeOOH could better improve the mineralization efficiency by 3.27 folds with more production of •OH (1.09*10-12 M). Moreover, possible products identified by liquid chromatography-time-of-flight mass spectrometer confirmed the decomposition of main chains of MPs into low-molecular-weight organic compounds with functional groups such as C-OH, C-O-C, and CO. The finding that photoaged PE MPs could be efficiently mineralized under the attack of O3/•OH provides a solid foundation for the removal of natural MPs in the environment.

Analyzing disinfection by-products yield and mechanisms in UV/Cl2 using response surface methodology and quantitative structure-activity relationship models.

The study aimed to investigate the formation of halogenated disinfection byproducts (DBPs) during applying UV/chlorine (UV/Cl2) and unravel the interactive impacts of critical operational parameters and the mechanisms behind DBPs formation. Response surface methodology and quantitative structure-activity relationship models were developed to evaluate the contribution of electrophilic, nucleophilic, and free radical reactions to the formation of DBPs in UV/Cl2. The study found that Cl2 and its interactions dominated the total DBPs and non-Br-DBPs formation, while Br- and the Cl2-Br- interaction played a decisive role in the Br-DBPs formation. The study also observed significant interactions of Br, Cl2, and pH on chloroform, bromodichloromethane, dichloroacetonitrile, 1,1-dichloro-2-propanone, trichloroactic acid, and chlorodibromoacetic acid formations, while no evident interaction on chloral hydrate, dibromochloromethane, trichloroacetone, dibromoacetic acid, and bromodichloroacetic acid formations. The electrophilic substitution of HOBr mainly controlled the formation of trihalomethanes, and the contribution of nucleophilic, electrophilic, and free radical (•OH, Cl•, Cl2•- and ClO•) reactions depended on the molar ratio of Cl2 to Br, and pH-determined hydrolysis rate constants of DBPs and the types of free radicals. Overall, the response surface methodology and quantitative structure-activity relationship models provided a reference for revealing DBPs formation mechanisms in other disinfection processes.

Cu(II) assisted peroxymonosulfate for antibiotic resistant bacteria inactivation: A potential disinfection technology in swimming pool.

Alternative disinfection technology to chlorination is required to control the risk of antibiotic resistance in swimming pools. In this study, copper ions (Cu(II)), which often exist in swimming pools as algicides, were used to activate peroxymonosulfate (PMS) for the inactivation of ampicillin-resistant E. coli. Cu(II) and PMS showed synergistic effects on E. coli inactivation in weak alkaline conditions, obtaining 3.4 log inactivation in 20 min with 10 µM Cu(II) and 100 µM PMS at pH 8.0. Quenching experiments indicated that radicals (i.e., OH and SO4-) were not the main disinfectors for E. coli inactivation. Based on the structure of Cu(II) and density functional theory calculations, the Cu(II)-PMS complex (Cu(H2O)5SO5) was recommended as the active species for E. coli inactivation. Under the experimental conditions, the PMS concentration had a greater influence on E. coli inactivation than the Cu(II) concentration, possibly because increasing PMS concentration accelerates ligand exchange reaction and facilitates active species generation. By forming hypohalous acids, halogen ions could improve the disinfection efficiency of Cu(II)/PMS. The addition of HCO3- concentration (from 0 to 1.0 mM) and humic acid (0.5 and 1.5 mg/l) did not significantly inhibit the E. coli inactivation. The feasibility of adding PMS to waters containing Cu(II) for the inactivation of antibiotic-resistant bacteria was validated in actual swimming pool waters, where 4.7 log inactivation of E. coli was achieved in 60 min.

Characteristics and behaviors of microplastics undergoing photoaging and Advanced Oxidation Processes (AOPs) initiated aging.

The fact that 94% of microplastics (MPs) ubiquitous in the environment are subject to natural weathering makes the aging study currently a research hotspot. This review summarized the physicochemical characteristics of MPs undergoing natural and artificial aging and evaluated current analytical methods used in aging studies. Besides, the differences in photoaging and aging induced by advanced oxidation processes (AOPs) were discussed, leading to a conclusion that AOPs composed of oxidant and ultraviolet (UV) irradiation can better facilitate the alteration of MPs compared to UV irradiation alone. In addition, the environmental behavior of aged MPs was outlined and their adsorption properties for organics and metals were highlighted as a result of combined effects of hydrophobic, π-π, diffusion, and hydrogen bond interaction. Furthermore, the mechanisms of photoaging and AOPs-initiated aging were analyzed, mainly the role of reactive oxygen species (ROS) and environmentally persistent free radicals (EPFRs). Finally, the applications of two-dimensional correlation spectroscopy (2D-COS) and three-dimensional fluorescence spectra using excitation emission matrix-parallel factor analysis (EEM-PARAFAC) were discussed for the aging process analysis. This overview plays an important role in explaining the aging characteristics of MPs and provides a theoretical foundation for further investigations into their toxicity and removal.

Ozonation facilitates the aging and mineralization of polyethylene microplastics from water: Behavior, mechanisms, and pathways.

Microplastics (MPs) are ubiquitous in the environment, of which 94 % undergo the aging process. Accelerated aging induced by advanced oxidation processes (AOPs) is significant in explaining the formation pathway of secondary MPs and enables possible mineralization. In this study, ozonation coupled with hydrogen peroxide (O3/H2O2), a type of AOPs, was applied for the aging of MPs (polyethylene, PE). Physiochemical properties of aged PE MPs were analyzed through scanning electron microscope, Fourier-transform infrared spectroscopy-attenuated total reflection, and X-ray photoelectron spectroscopy. The mechanism regarding the contribution of reactive oxygen species (•OH) was determined using chemical probe (p-chlorobenzoic acid) and quencher (tert-butanol). Possible transformation pathways were modeled via two-dimensional correlation spectroscopy. Mineralization of MPs, associated with aging was also studied, with the percentage of PE degradation determined by mass loss. Our results confirmed that ozonation promoted fragmentation of PE, with 20 mM H2O2 facilitating the production of •OH. The growth of oxygen-containing functional groups on the surface of PE was consistent with the alteration of the oxygen-to­carbon atom ratio, revealing the formation of CO, CO, and C-O-C. The enhanced adsorption property of aged PE for triclosan was due to the increased specific surface area and negative charges on the surface. Moreover, the percentage of PE degradation was higher at lower concentrations, and the mass loss reached 32.56 % at a PE concentration of 0.05 g/L after 8-h ozonation. These results contribute to revealing the long-term aging behavior of MPs and providing significant guidance for employing AOPs to achieve efficient removal.

Degradation of organics and formation of DBPs in the combined LED-UV and chlorine processes: Effects of water matrix and fluorescence analysis.

Combined processes of light-emitting diodes ultraviolet (LED UV) and chlorination (Cl2) are alternative disinfection technologies in drinking water, while the formation of disinfection by-products (DBPs) needs to be evaluated. This study investigated the impacts of critical water matrix factors on the DBP formation in the combined processes. Moreover, the correlation between the degraded natural organic matter (NOM) and the formed DBP was studied. Simultaneous UV/Cl2 outperformed single Cl2 and sequential combined processes in degrading humic acids (HA) and resulted in the highest DBP yield. Iodide at 5-20 µg/L and bromide at 0.05-0.2 mg/L slightly affected the degradation of organics, while increased the formation of brominated DBPs up to 36.6 µg/L. pH 6 was regarded as the optimum pH, achieving high efficiency of HA degradation and a lower level of total DBP formation than pH 7 and 8 by 11 % and 24 %, respectively. Compared to HA samples (46.8-103.9 µg/L per mg/L DOC), NOM in canal water were less aromatic and yielded fewer DBPs (19.6 and 21.2 µg/L per mg/L DOC). However, the extremely high bromide in site 1 samples (18.6 mg/L) shifted the chlorinated DBPs to their brominated analogues, posting around 1 order of magnitude higher levels of toxicities than HA samples. The reduction of absorbance at 254 nm (UV254) correlated with all DBP categories in HA samples, while the correlation coefficients were compromised when included in the canal samples. For the first time, this study found that parallel factor analysis (PARAFAC) would neglect the fluorescence change caused by iodide/bromide in UV/Cl2, while the changes could be captured by self-organising map (SOM) trained with full fluorescence spectra. Fluorescence Ex/Em pairs were proposed to predict DBP formation, suggesting a potential method to develop an online monitoring system for DBPs.

Performance analysis of a stormwater green infrastructure model for flow and water quality predictions.

Nature-based solutions or Green infrastructure (GI) used for managing stormwater pollution are growing in popularity across the globe. Stormwater GI models are important tools to inform the planning of these systems (type, design, size), in the most efficient and cost-effective manner. MUSIC, an example of such a tool, uses regression and first order decay models. Studies validating MUSIC model performance are, however, scarce, hindering future model development and transferability of the model for systems operating under different design and climatic conditions. To close this gap, this paper evaluates MUSIC for a field scale bioretention system, stormwater wetland and vegetated swale operating under Singapore tropical climate. The treatment modules were able to simulate outflows and effluent pollutant concentrations reasonably well for cumulative event volumes (mostly within ±25%) and cumulative TP and TN loads (within ±30%). Outflow TSS loads were significantly under-estimated as a result of greater variability in measured TSS concentrations across events. The findings indicate that simple empirical models such as MUSIC can be transferred to different regions provided that management decisions are based on long-term modelling efforts. The modules generally simulated the outflow hydrographs and pollutographs of the different inflow and drying/wetting conditions relatively poorly.

Investigation of the efficacy of the UV/Chlorine process for the removal of trimethoprim: Effects of operational parameters and artificial neural networks modelling.

The UV/Cl2 process (also known as chlorine photolysis, which is the combination of chlorine and simultaneous irradiation of UV light) is conventionally applied at acidic mediums for drinking water treatment and further treatment of wastewater effluents for secondary reuse. This is because the quantum yield of HO• from HOCl (ϕHO•, 254 = 1.4) is greater than the one from OCl- (ϕHO•, 254 = 0.278) by approximately 5 times. Moreover, chlorine photolysis in acidic mediums also tends to have lower radical quenching rates than that of their alkaline counterparts by up to 1000 times. The aim of this research is to investigate the applicability of the UV/Cl2 process by assessing its efficacy on the removal of trimethoprim (TMP) at not only acidic to neutral conditions (pH 6-7), but also alkaline mediums (pH 8-9). At alkaline pH, free chlorine exists as OCl- and since OCl- has a higher molar absorption coefficient as compared to HOCl at higher wavelengths, there would be higher reactive chlorine species (RCS) formation and contribution. TMP removal followed pseudo-first order kinetics and depicted that a maximum fluence based constant (kf' = 0.275 cm2/mJ) was obtained using 42.25 µM (3 mg/L) of chlorine at pH 9, with an irradiation of 275 nm. At alkaline conditions, chlorine photolysis performance followed the trend of UV (275)/Cl2 > UV (265)/Cl2 > UV (310)/Cl2 > UV (254)/Cl2. RCS like Cl•, Cl2-• and ClO• contributed to the degradation of TMP. When the pH was increased from 6 to 8, contribution from hydroxyl radicals (HO• ) was decreased whilst that of RCS was increased. Application of UV (310)/Cl2 had the highest HO• generation, contributing to TMP removals up to 13% to 48% as compared to 5% to 27% in UV (254, 265, 275)/Cl2 systems at pH 6-9. Artificial neural networks modelling was found to be able to verify and predict the contribution of HO• and RCS conventionally calculated via the general kinetic equations in the UV/Cl2 system at 254, 265, 275 and 310 nm.

Efficient bio-refractory industrial wastewater treatment with mitigated membrane fouling in a membrane bioreactor strengthened by the micro-scale ZVI@GAC galvanic-cells-initiated radical generation and coagulation processes.

Micro-scale ZVI@GAC-based iron-carbon galvanic-cells (ZVI@GACs) were prepared with the Ca-Si-H/Ca-H formation process and first applied to initiate radical generation and coagulation processes in MBR for treating bio-refractory industrial wastewater (IWW). Batch tests revealed the H2O2 production (0.19-0.28 mg/L) and •OH generation (p-CBA decay, k1 = 0.040 min-1) in ZVI@GACs-dosed system (packing volume of 5%) under aeration. Adoption of ZVI@GACs into aerobic activated sludge process (ZVI@GACs/AS) enhanced TOC degradation (k2) and phenolic compounds (PHENs) destruction (k3). ZVI@GACs/AS at ZVI@GACs packing volume of 5%, 10% and 20% improved k2 from 0.11 h-1 (bare AS) to 0.17, 0.21 and 23 h-1 and k3 from 0.24 h-1 to 0.36, 0.49 and 0.57 h-1, respectively. The oxygen uptake rate (OUR) and 15-min acute bio-toxicity demonstrated that the bio-toxicity of IWW was reduced and the activity of biomass was enhanced in the ZVI@GACs/AS system. In MBR, ZVI@GACs at packing volume of 10% enhanced COD and PHENs removal by 14% and 22%, respectively. Membrane fouling cycle was prolonged by 71%. The accumulations of EPS-proteins, EPS-polysaccharides, SMP-proteins and SMP-polysaccharides were reduced by 6%, 67%, 27% and 60%, respectively. Fourier transform infrared spectroscopy (FTIR) confirmed the oxidation of SMP-polysaccharides in ZVI@GACs-MBR. The iron ions released from ZVI@GACs showed inhibition on the secretion of SMP-/EPS-proteins. Floc particle size distribution (PSD) and X-ray diffraction (XRD) spectrum confirmed that the coagulation effects of Fe(OH)3 and FeOOH triggered by Fe3+ increased the sludge floc size and contributed to membrane fouling mitigation. Genus Enterococcus was enriched in MBR with the destruction of PHENs by the ZVI@GACs-initiated radical generation process. The findings of this study confirmed successful development and adoption of ZVI@GACs into MBR for bio-refractory IWW treatment. It also provided an in-depth understanding on the mechanisms of ZVI@GACs-MBR system.

Degradation of carbamazepine by UVA/WO3/hypochlorite process: Kinetic modelling, water matrix effects, and density functional theory calculations.

The rapid recombination of electron/hole pairs is a major setback in the application of WO3-based photocatalysis in water treatment. In this study, hypochlorite (ClO-) was used as an electron acceptor to enhance the photocatalytic degradation of carbamazepine (CBZ) using UVA-excited WO3. The results showed that CBZ degradation in the UVA/WO3/ClO- system followed a pseudo-first order reaction kinetic model. The addition of 0.1 mM ClO- to the UVA/WO3 system at pH values of 8.2 and 6.2 increased the rate constant (kobs) of the degradation process 5.3- and 11.5-fold, respectively. Further, increasing the WO3 dosage or decreasing the initial CBZ concentration resulted in an increase in kobs. However, at high concentrations, ClO- inhibited CBZ degradation. Based on the kinetic model, it could be suggested that ClO played a dominant role in the degradation process. Furthermore, the water matrix effects were as follows: the optimal pH was 6.2; humic acid, chloride, bicarbonate, and ammonium exhibited inhibitory effects on CBZ degradation; and sulfate ion significantly enhanced the degradation. Density functional theory (DFT) calculations indicated a strong affinity between ClO- and the WO3 surface. Specifically, the electrical energy per order that was associated with the use of ClO- varied in the range of 0.100-1.617 kWh/m3. In summary, this study shows that ClO- is an excellent electron acceptor for excited WO3, while clarifying the CBZ degradation-enhancing effect of ClO- as well as the kinetic model and DFT calculations. These findings can be employed in the degradation of recalcitrant contaminants in a cost-effective manner, while being significant for the development of more effective catalysts of UV-assisted advanced oxidation processes.

Enhancing the degradation of carbamazepine by UVA-LED/WO3 process with peroxydisulfate: Effects of light wavelength and water matrix.

In this study, peroxydisulfate (PDS) was used as electron acceptor to improve the photocatalytic activity of WO3. The results indicated that the degradation of carbamazepine by UVA-LED/WO3/PDS process followed pseudo-first order and PDS addition significantly enhanced the degradation rate by inhibiting the recombination of electrons and holes. The observed pseudo-first order rate constant (kobs) was in linear relationship with the dosage of WO3, while inversely proportional to the initial concentration of CBZ. PDS decreased the kobs slightly when its concentration exceeded 0.5 mM. The 365 nm UVA-LED performed much better than 385 nm or 405 nm even though its energy efficiency was the lowest. Based on the steady-state kinetic model, sulfate radical was the dominant radical. The effects of water matrix were complex: bicarbonate ion and humic acid showed strong inhibitory effect; increasing the pH above 7 led to significant drop in CBZ removal; sulfate ion slightly decreased the kobs while 5 mM chloride ion more than doubled the kobs. The interactions between anions and WO3 surface were theoretically analysed to explain the effects of anions. The electrical energy per order values suggest that UVA-LED/WO3/PDS process is suitable for water with low organic carbon.

The optimal method for peroxydisulfate quenching: A comparison of commonly used reductants.

Peroxydisulfate-based advanced oxidation process has drawn increasing interest recently. Quenching the residual peroxydisulfate is essential for the accurate measurement of the concentration of target pollutants. However, it was rarely discussed which reductant is best for peroxydisulfate quenching. In this study, how the quenching of peroxydisulfate by four commonly used quenchers (methanol, ascorbic acid, sodium thiosulfate and sodium sulfite) affected the concentration of carbamazepine was investigated. Sodium sulfite reacted with carbamazepine directly, with the highest removal rate up to 39%. Higher carbamazepine removal rate was achieved by peroxydisulfate/sodium sulfite than by sodium sulfite alone. SO3•- and SO5•- rather than SO4•- played the major role in carbamazepine removal by sodium sulfite or peroxydisulfate/sodium sulfite. Methanol was found unable to reduce peroxydisulfate. Ascorbic acid, when used with a concentration more than three times higher than that of peroxydisulfate, was the best quencher with the lowest carbamazepine removal rate observed at a pH range of 3.5-10.0. Sodium thiosulfate was unfit for peroxydisulfate quenching at pH 3.5 as it was decomposed and formed bisulfite under strong acidic condition. The results of this study provided valuable guidance to the selection of proper quenchers for peroxydisulfate-related advanced oxidation processes.

FeOx@GAC catalyzed microbubble ozonation coupled with biological process for industrial phenolic wastewater treatment: Catalytic performance, biological process screening and microbial characteristics.

Phenolic compounds are common ccontaminants in industrial effluents. In this study, a combined catalytic microbubble ozonation and biological process was developed and applied for efficient industrial phenolic wastewater (PWW) treatment. Catalytic activity of an iron-oxides (FeOx) doped granular activated carbon (GAC) catalyst (FeOx@GAC) in microbubble ozonation for PWW treatment was investigated. The results demonstrated that the FeOx@GAC catalyzed microbubble ozonation (O3/FeOx@GAC) obtained significantly higher reaction rate constant (k1 = 0.023 min-1) in TOC removal compared to the bare GAC catalyzed microbubble ozonation (O3/GAC, k1 = 0.013 min-1) and ordinary microbubble ozonation (k1 = 0.008 min-1). Destruction rate constant of phenolic compounds (k2) was improved from 0.014 min-1 (ordinary microbubble ozonation) to 0.025 min-1 (O3/FeOx@GAC). The 60-min pretreatment of PWW by O3/FeOx@GAC process enhanced BOD5/COD ratio from 0.31 to 0.76 and reduced the acute bio-toxicity by 79.2%. Screening and characterization of biological post-treatment processes were conducted among activated sludge process (ASP), up-flow anaerobic sludge blanket (UASB) and membrane bioreactor (MBR). UASB and ASP showed limited phenolic compounds removal of 35.4% and 57.0% with lower bio-toxicity resistance than MBR (94.9% phenolic compounds removal). The combined process O3/FeOx@GAC-MBR was thus developed and achieved high COD removal (98.0%) and phenolic compounds degradation (99.4%). PWW pretreatment by O3/FeOx@GAC process decreased membrane fouling rate of MBR by 88.2% by reducing proteins/polysaccharides accumulation in both extracellular polymeric substances and soluble microbial products. 16S rRNA high-throughput sequencing revealed the predominance of phylum Proteobacteria, class Alphaproteobacteria and genera Mycobacterium, Gordonia, Pedomicrobium & Defluviimonas in biological PWW treatment bio-systems. Pearson correlation coefficient and ANOVA analysis verified that Mycobacterium possessed high bio-toxicity resistance and was the main contributor to the biodegradation of phenolic compounds.

Photocatalytic transformation fate and toxicity of ciprofloxacin related to dissociation species: Experimental and theoretical evidences.

Chemical speciation of ionizable antibiotics greatly affects its photochemical kinetics and mechanisms; however, the mechanistic impact of chemical speciation is not well understood. For the first time, the impact of different dissociation species (cationic, zwitterionic and anionic forms) of ciprofloxacin (CIP) on its photocatalytic transformation fate was systematically studied in a UVA/LED/TiO2 system. The dissociation forms of CIP at different pH affected the photocatalytic degradation kinetics, transformation products (TPs) formation as well as degradation pathways. Zwitterionic form of CIP exhibited the highest degradation rate constant (0.2217 ± 0.0179 min-1), removal efficiency of total organic carbon (TOC) and release of fluoride ion (F-). Time-dependent evolution profiles on TPs revealed that the cationic and anionic forms of CIP mainly underwent piperazine ring dealkylation, while zwitterionic CIP primarily proceeded through defluorination and piperazine ring oxidation. Moreover, density functional theory (DFT) calculation based on Fukui index well interpreted the active sites of different CIP species. Potential energy surface (PES) analysis further elucidated the reaction transition state (TS) evolution and energy barrier (ΔEb) for CIP with different dissociation species after radical attack. This study provides deep insights into degradation mechanisms of emerging organic contaminants in advanced oxidation processes associated to their chemical speciation.

Water treatment residual: A critical review of its applications on pollutant removal from stormwater runoff and future perspectives.

In recent years, many studies have been conducted on using different filter media in bioretention systems for stormwater runoff treatment. This critical review paper provides a comprehensive review on the current state of water treatment residual (WTR), a recycled material that can be used as bioretention filter media for removals of key stormwater runoff pollutants (especially phosphorus) and future perspectives with innovative modification on WTR applied for pathogen removal from stormwater runoff. This review paper comprised (i) a brief summary of the reported WTR characteristics, (ii) a thorough evaluation of WTR performance on major pollutants removal from stormwater runoff (iii) a discussion on phosphorus removal mechanisms by WTR applied in the stormwater runoff treatment, and (iv) a review of the future perspectives of WTR for pathogen removal and other potential practical application in the field of stormwater treatment. As outlined in this review, WTR in stormwater runoff treatment has yet to be fully explored. The possible enhancements, especially metal surface modification on WTR are reviewed to bring about the widespread use of WTR in stormwater reuse practices.

Photoelectrocatalytic degradation of organics and formation of disinfection byproducts in reverse osmosis concentrate.

The high content of organics in municipal reverse osmosis concentrate (ROC) requires proper treatment. Here, this study applied the photoelectrocatalysis (PEC) to reduce the concentration of organics in ROC. Meanwhile, the formation of disinfection byproducts (DBPs) was investigated. Participation of primary oxidants in organics removal and DBPs formation was revealed at different anodic potentials and pHs. The results showed that PEC process effectively oxidized the organics in ROC, achieving the highest mineralization rate of 63%. Increasing anodic potential from 0 to 1.0 V enhanced the oxidations of bulk organics (i.e., dissolved organic carbons (DOC), UV254, fluorescence, large molecular weight compounds) and trace-level pharmaceuticals. Raising anodic potential to higher than 1.0 V slightly benefited the oxidations of bulk organics, owing to the relatively stable formation of hydroxyl radicals (OH•) and radical reactive chlorine species (r-RCS). The continuously rising concentration of free chlorine (FC) accelerated the decompositions of pharmaceuticals at ≥ 1.0 V. However, the generated FC raised the concentration of DBPs up to 10.36 µmol/L at 3.0 V. Lowering initial pH from 7-9 to 4-6 improved the mineralization rates by around 20% due to the higher formation of OH• at pH 4-6. Further decreasing initial pH from 6 to 4 enhanced the breakdown of large molecular weight compounds as well as the decomposition of pharmaceuticals. This came from the strengthened formation of FC and r-RCS at lower pHs. The intense participation of FC and r-RCS resulted in a higher total DBP concentration at pH 4-6 than that at pH 7-9. However, the individual species of DBPs changed differently toward the pH shift. The results of this study show that PEC could be an alternative for organics oxidation in ROC with proper control of DBPs formation.

Effect of alpha-hydroxy acids on transformation products formation and degradation mechanisms of carbamazepine by UV/H2O2 process.

The role of dissolved organic matters (DOM) in the matrix of water on the degradation of refractory pharmaceutical has aroused broad concerns. However, The effect of alpha-hydroxy acids as vulnerable aliphatic acids in the water on the degradation of Carbamazepine (CBZ) has been lack of research. The decomposition kinetics and transformation products (TPs) of CBZ by UV/H2O2 process were studied in the existence of glycolic acid (GA) and lactic acid (LA) and the degradation pathways were proposed. Both GA and LA had significantly negative effects on the decomposition kinetics and mineralization of CBZ by UV/H2O2 process. The declination of steady-state OH concentration in the presence of GA and LA justified the negative effects. GA was demonstrated to be stronger at scavenging and competing OH with CBZ, compared with LA, with the rate constant of slightly less than the common OH scavenger methanol. One-step dosing mode of H2O2 was better than multi-step dosing mode for CBZ decomposition, especially in the presence of GA and LA. The identification of TP253a, TP253b, TP271a, TP271b, TP226, and TP180 in the absence and presence of GA and LA were performed by HPLC-MS/MS and two main degradation pathways were presented. Except for TP271a and TP271b, GA and LA retarded the abundance peaks of other four TPs, of which the formation kinetics rates and decay kinetics rates were negatively affected. Tailing peaks of all TPs caused by GA and LA inevitably resulted in the toxicity of the treated effluent of UV/H2O2 process even when CBZ was decomposed completely. Therefore, alpha-hydroxy acids play important roles in determining the fate and transformation of refractory pharmaceuticals in AOPs treatment.

Role of metal modified water treatment residual on removal of Escherichia coli from stormwater runoff.

Extensive studies have been conducted on bioretention filter media applied in best management practices for stormwater runoff treatment. To date, more reported studies are focused on pollutants elimination such as suspended solids and nutrients. There has been limited research on pathogen removal from stormwater runoff. More focused studies on pathogen removal are therefore required if the intended stormwater is harvested for indirect potable use. In this study, water treatment residuals (WTR), a recycled biofilter media was surface-modified with metals to assess its potential for E. coli removal from stormwater runoff. To achieve this goal, four types of modified WTRs, prepared using iron, copper, platinum, and silver as antibacterial agents, were tested in parallel batch tests. After the cost-effectiveness evaluation among the four modified WTRs for bacterial removal, Fe2O3- and CuO-WTRs were shortlisted for further mechanism and stability studies. Stable antibacterial performances (E. coli log removal of 0.58 ±â€¯0.04 and 0.90 ±â€¯0.04, respectively) were achieved using the Fe2O3- and CuO-WTRs under intermittent synthetic and natural stormwater runoff conditions. No significant metal leaching was observed over prolonged continuous treatment. The experimental results showed the bio-adsorption onto the surface modified Fe2O3- and CuO-WTR was a key mechanism for E. coli removal followed by E. coli inactivation at solid-liquid interface caused by the antibacterial effect of metal coatings (where CuO was reported to have higher biotoxicity than Fe2O3). These findings clearly suggested the potential of CuO-modified WTR for pathogen removal in stormwater treatment practices.