Comparison of ozone and HO· induced conversion of effluent organic matter (EfOM) using ozonation and UV/H2O2 treatment

Online control of UV and UV/H2O2 processes targeted for the removal of contaminants of emerging concern (CEC) by a fluorescence sensor

This study assessed the online and real-time monitoring of contaminants of emerging concern (CEC) using a microbial/tryptophan-like fluorescence sensor in a quaternary AOP (advanced oxidation process) pilot plant installed downstream of a tertiary municipal wastewater treatment plant (WWTP). Real-time fluorescence measurements were validated with lab-scale tryptophan-like fluorescence. Changes in water quality induced by different UV or UV/H2O2 doses were detected by the fluorescence sensor allowing real-time control of processes. The removal of CEC was discussed considering their photo-susceptibility and reactivity with •OH and then classified into three groups based on their reactivity and removal efficiency (RE). Linear models of CEC removal developed using real-time fluorescence removal as a surrogate parameter resulted very accurate (overall R2≥0.90) for most of CEC. Furthermore, real-time fluorescence data were successfully used to predict i) pseudo-observed first-order degradation rate constants of CEC (R2=0.99), and ii) UV doses during both UV and UV/H2O2 processes (R2>0.90). The findings of this study demonstrated that fluorescence sensors can be employed in operational relevant environment to monitor a broad range of CEC and control UV doses during UV-AOPs. Therefore, the implementation of fluorescence sensors is expected for optimizing costs, energy consumption and efficiency of quaternary wastewater treatments.

Catalytic ozonation of reverse osmosis concentrate from coking wastewater reuse by surface oxidation over Mn-Ce/γ-Al2O3: Effluent organic matter transformation and its catalytic mechanism

Degradation of organics in high-salinity wastewater is beneficial to meeting the requirement of zero liquid discharge for coking wastewater treatment. Creating efficient and stable performance catalysts for high-salinity wastewater treatment is vital in catalytic ozonation process. Compared with ozonation alone, Mn and Ce co-doped γ-Al2O3 could remarkably enhance activities of catalytic ozonation for chemical oxygen demand (COD) removal (38.9%) of brine derived from a two-stage reverse osmosis treatment. Experimental and theoretical calculation results indicate that introducing Mn could increase the active points of catalyst surface, and introducing Ce could optimize d-band electronic structures and promote the electron transport capacity, enhancing HO• bound to the catalyst surface ([HO•]ads) generation. [HO•]ads plays key roles for degrading the intermediates and transfer them into low molecular weight organics, and further decrease COD, molecular weights and number of organics in reverse osmosis concentrate. Under the same reaction conditions, the presence of Mn/γ-Al2O3 catalyst can reduce ΔO3/ΔCOD by at least 37.6% compared to ozonation alone. Furthermore, Mn-Ce/γ-Al2O3 catalytic ozonation can reduce the ΔO3/ΔCOD from 2.6 of Mn/γ-Al2O3 catalytic ozonation to 0.9 in the case of achieving similar COD removal. Catalytic ozonation has the potential to treat reverse osmosis concentrate derived from bio-treated coking wastewater reclamation.

Insight into roles of carbon anodes for removal of refractory organic contaminants in electro-peroxone system: Mechanism, performance and stability

Electro-peroxone (EP) is a novel technique for the removal of refractory organic contaminants (ROCs), while the role of anode in this system is neglected. In this work, the EP system with graphite felt anode (EP-GF) and activated carbon fiber anode (EP-ACF) was developed to enhance ibuprofen (IBP) removal. The results showed that 91.2% and 98.6% of IBP was removed within 20 min in EP-GF and EP-ACF, respectively. Hydroxy radical (O⋅H) was identified as the dominant reactive species, contributing 80.9% and 54.0% of IBP removal in EP-ACF and EP-GF systems, respectively. The roles of adsorption in EP-ACF and direct electron transfer in EP-GF cannot be ignored. Due to the differences in mechanism, EP-GF and EP-ACF systems were suitable for the removal of O⋅H-resistant ROCs (e.g., oxalic acid and pyruvic acid) and non-O⋅H-resistant ROCs (e.g., IBP and nitrobenzene), respectively. Both systems had excellent stability relying on the introduction of oxygen functional groups on the anode, and their electrolysis energy consumption was significantly lower than that of EP-Pt system. The three degradation pathways of IBP were proposed, and the toxicity of intermediates were evaluated. In general, carbon anodes have a good application prospect in the removal of ROCs in EP systems.

Removal of ofloxacin using a porous carbon microfiltration membrane based on in-situ generated •OH

This study investigated the removal performance of ofloxacin (OFL) by a novel electro-Fenton enhanced microfiltration membrane. The membranes used in this study consisted of metal-organic framework derived porous carbon, carbon nanotubes and Fe2+, which were able to produce hydroxyl radicals (•OH) in-situ via reducing O2 to hydrogen peroxide. Herein, membrane filtration with bias not only concentrated the pollutants to the level that could be efficiently treated by electro-Fenton but also confined/retained the toxic intermediates within the membrane to ensure a prolonged contact time with the oxidants. After validated by experiments, the applied bias of -1.0 V, pH of 3 and electrolyte concentration of 0.1 M were the relatively optimum conditions for OFL degradation. Under these conditions, the average OFL removal rate could be reach 75% with merely 5% membrane flux loss after 4 cycles operation by filtrating 1 mg/L OFL. Via decarboxylation reaction, piperazinyl ring opening, dealkylation and ipso substitution reaction, etc., OFL could be gradually and efficiently degraded to intermediate products and even to CO2 by •OH. Moreover, the oxidation reaction was preferred to following first-order reaction kinetics. This research verified a possibility for antibiotic removal by electro-enhanced microfiltration membrane.

Dynamic Modelling, Process Control, and Monitoring of Selected Biological and Advanced Oxidation Processes for Wastewater Treatment: A Review of Recent Developments

This review emphasizes the significance of formulating control strategies for biological and advanced oxidation process (AOP)-based wastewater treatment systems. The aim is to guarantee that the effluent quality continuously aligns with environmental regulations while operating costs are minimized. It highlights the significance of understanding the dynamic behaviour of the process in developing effective control schemes. The most common process control strategies in wastewater treatment plants (WWTPs) are explained and listed. It is emphasized that the proper control scheme should be selected based on the process dynamic behaviour and control goal. This study further discusses the challenges associated with the control of wastewater treatment processes, including inadequacies in developed models, the limitations of most control strategies to the simulation stage, the imperative requirement for real-time data, and the financial and technical intricacies associated with implementing advanced controller hardware. It is discussed that the necessity of the availability of real-time data to achieve reliable control can be achieved by implementing proper, accurate hardware sensors in suitable locations of the process or by developing and implementing soft sensors. This study recommends further investigation on available actuators and the criteria for choosing the most appropriate one to achieve robust and reliable control in WWTPs, especially for biological and AOP-based treatment approaches.

Importance of Chain Length in Propagation Reaction on •OH Formation during Ozonation of Wastewater Effluent

During the ozonation of wastewater, hydroxyl radicals (•OH) induced by the reactions of ozone (O3) with effluent organic matters (EfOMs) play an essential role in degrading ozone-refractory micropollutants. The •OH yield provides the absolute •OH formation during ozonation. However, the conventional "tert-Butanol (t-BuOH) assay" cannot accurately determine the •OH yield since the propagation reactions are inhibited, and there have been few studies on •OH production induced by EfOM fractions during ozonation. Alternatively, a "competitive method", which added trace amounts of the •OH probe compound to compete with the water matrix and took initiation reactions and propagation reactions into account, was used to determine the actual •OH yields (Φ) compared with that obtained by the "t-BuOH assay" (φ). The Φ were significantly higher than φ, indicating that the propagation reactions played important roles in •OH formation. The chain propagation reactions facilitation of EfOMs and fractions can be expressed by the chain length (n). The study found significant differences in Φ for EfOMs and fractions, precisely because they have different n. The actual •OH yield can be calculated by n and φ as Φ = φ (1 + n)/(nφ + 1), which can be used to accurately predict the removal of micropollutants during ozonation of wastewater.

Real-time organic compound monitoring in advanced oxidation process (AOP) of anaerobic digestion effluent: introduction of UV-VIS spectrum representative index by discrete Fourier transform

Anaerobic digestion effluent from sewage treatment plants (STP) poses a challenge to the operator because of its high organic matter and inorganic nitrogen concentrations, which require an effective process for biological treatment. This study aimed to introduce a UV-VIS spectrum representative index by discrete Fourier transform (DFT) and apply UV-Vis spectrophotometric techniques for real-time organic compound monitoring in the AOP process using anaerobic digestion tank effluent wastewater. The effect of advanced oxidation on the organic compounds of effluent using ozonation was examined. In this research, after treating secondary treated water with the UV-AOP process and anaerobic digestion effluent with ozone microbubble systems, changes in organic substances were expressed by the UV-Vis spectrum and compared with conventional water quality parameters. The anaerobic digestion process effluent was treated through ozone oxidation, had a high curve, and fell gently from 230 to 667 nm. Discrete Fourier transform (DFT) was applied to obtain representative values from the obtained spectrum. From among the coefficients obtained by analyzing the UV-Vis spectrum through DFT, an expected value was selected, and the correlation between CODMn and a3 was the highest (correlation function = 0.694, RSQ = 0.482). Therefore, a linear regression analysis was performed to determine which water quality factor it was related to.

Enhanced permeation performance of biofiltration-facilitated gravity-driven membrane (GDM) systems by in-situ application of UV and VUV: Comprehensive insights from thermodynamic and multi-omics perspectives

Biofouling is a major challenge limiting the practical application of biofiltration-facilitated gravity-driven membrane (GDM) systems in drinking water treatment. In this study, ultraviolet irradiation, including ultraviolet (UV) and vacuum ultraviolet (VUV) irradiation, was used for in-situ purification of membrane tanks to control membrane biofouling. After using UV and VUV, the permeate flux increased significantly by 26.1% and 78.3%, respectively, which was mainly due to the decreased cake layer resistance (Rc). The permeability of the biofouling layer improved after UV and VUV application, as evidenced by the increased surface porosity and decreased thickness. The contents of loosely bound extracellular proteins (LB-PN) and tightly bound extracellular proteins (TB-PN) in the biofouling layer were reduced after UV and VUV irradiation. The decreased LB-PN and TB-PN improved the interfacial free energy between the fouling itself and between the fouling and the membrane, which contributed to the reduction of interfacial cohesion and adhesion, resulting in a looser and thinner biofouling layer and a cleaner membrane. The concentration of protein-like material in the membrane tank decreased after UV and VUV irradiation, significantly altering the bacterial community structure on the membrane surface (Mantel's r > 0.7, p < 0.05). The changes in the metabolic state were responsible for the differences in the LB-PN and TB-PN contents. The inhibition of "Alanine, aspartate and glutamate metabolism" and "Glycine, serine and threonine metabolism" reduced amino acid biosynthesis, which restricted the secretion of LB-PN and TB-PN. Critical genera in the Proteobacteria phylum, such as Hirschia, Rhodobacter, Nordella, Candidatus_Berkiella, and Limnohabitans, were involved in metabolite transformation. Overall, the in-situ application of UV and VUV can be an effective alternative strategy to mitigate membrane biofouling, which would facilitate the practical application of biofiltration-facilitated GDM systems in drinking water treatment.

Insights into degradation of pharmaceutical pollutant atenolol via electrochemical advanced oxidation processes with modified Ti4O7 electrode: Efficiency, stability and mechanism

A novel active Ce-doped Ti₄O₇ (Ti/Ti₄O₇-Ce) electrode was prepared and evaluated for improvement of the refractory pollutants degradation efficiency in Electrochemical advanced oxidation processes (EAOPs). The results showed that the addition of Ce in Ti/Ti₄O₇ electrode leading to great impact on •OH generation rate and electrode stability compared to pristine Ti/Ti₄O₇ electrode. Ti/Ti₄O₇-Ce electrode presented efficient oxidation capacity for pharmaceutical pollutant atenolol (ATL) in EAOPs, which could be attributed to the improvement of indirect oxidation mediated by electro-generated •OH, as the amount of •OH production was 16.5% higher than that in Ti/Ti₄O₇ within 120 min. The operational conditions greatly influenced the ATL degradation. The degradation efficiency of ATL increased as the current density, the degradation efficiency reached 100% under pH 4, but it just removed 81% of ATL under pH 10 after 120 min treatment. Results also suggested that the inhibiting effect from the ATL degradation was mostly associated with the decreased oxidation capacity induced by water hardness and natural organic matter (NOM). It displayed a satisfactory durability after 40 cycles of experimental detections in this research. The results of study suggested that Ti/Ti₄O₇-Ce was a promising electrode for the efficient degradation of PPCPs-polluted wastewater and provided constructive suggestion for the refractory pollutants of EAOPs.

Exploring impacts of water-extractable organic matter on pre-ozonation followed by nanofiltration process: Insights from pH variations on DBPs formation

This study investigated the influence of pH (4-10) on the treatment of water-extractable organic matter (WEOM), and the associated disinfection by-products (DBPs) formation potential (FP), during the pre-ozonation/nanofiltration treatment process. At alkaline pH (9-10), a rapid decline in water flux (> 50 %) and higher membrane rejection was observed, as a consequence of the increased electrostatic repulsion forces between the membrane surface and organic species. Parallel factor analysis (PARAFAC) modeling and size exclusion chromatography (SEC) provides detailed insights into the WEOM compositional behavior at different pH levels. Ozonation at higher pH significantly reduced the apparent molecular weight (MW) of WEOM in the 4000-7000 Da range by transforming the large MW (humic-like) substances into small hydrophilic fractions. Fluorescence components C1 (humic-like) and C2 (fulvic-like) exhibited a predominant increase/decrease in concentration for all pH conditions during pre-ozonation and nanofiltration treatment process, however, the C3 (protein-like) component was found highly associated with the reversible and irreversible membrane foulants. The ratio C1/C2 provided a strong correlation with the formation of total trihalomethanes (THMs) (R² = 0.9277) and total haloacetic acids (HAAs) (R² = 0.5796). The formation potential of THMs increased, and HAAs decreased, with the increase of feed water pH. Ozonation markedly reduced the formation of THMs by up to 40 % at higher pH levels, but increased the formation of brominated-HAAs by shifting the formation potential of DBPs towards brominated precursors.

Immobilized BiOCl0.75I0.25/g-C3N4 nanocomposites for photocatalytic degradation of bisphenol A in the presence of effluent organic matter

The BiOCl_0.75I_0.25/g-C₃N₄ nanosheet (BCI-CN) was successfully immobilized on polyolefin polyester fiber (PPF) through the hydrothermal method. The novel immobilized BiOCl_0.75I_0.25/g-C₃N₄ nanocomposites (BCI-CN-PPF) were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy EDS, X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy (UV-vis DRS) to confirm that BCI-CN was successfully immobilized on PPF with abundant oxygen vacancies reserved. Under simulated solar light irradiation, 100 % of bisphenol A (BPA) with an initial concentration of 10 mg·L^-1 was degraded by BCI-CN-PPF (0.2 g·L^-1 of BCI-CN immobilized) after 60 min. A similar photocatalytic efficiency of BPA was obtained in the presence of effluent organic matter (EfOM). The photocatalytic degradation of BPA was not affected by EfOM <5 mg-C/L. In comparison, the photocatalytic performance was considerably inhibited by EfOM with a concentration of 10 mg-C/L. Furthermore, photogenerated holes and superoxide radicals predominated in the photocatalytic degradation processes of BPA. The total organic carbon (TOC) removal efficiencies of BPA and EfOM were 75.2 % and 50 % in the BCI-CN-PPF catalytic system. The BPA removal efficiency of 94.9 % was still achieved in the eighth cycle of repeated use. This study provides a promising immobilized nanocomposite with high photocatalytic activity and excellent recyclability and reusability for practical application in wastewater treatment.

New insights into the transformation of effluent organic matter during Fe(II)-assisted advanced oxidation processes: Parallel factor analysis coupled with self-organizing maps

The negative effects of effluent organic matter (EfOM) on receiving aquatic environments and advanced treatment facilities pose significant concerns. However, the effective removal of EfOM is challenging due to its chemically complex nature and its refractory characteristics. In this study, two Fe(II)-assisted oxidation processes including UV/Fe(II)/H₂O₂ and UV/Fe(II)/persulfate (UV/Fe(II)/PS) were investigated to promote EfOM reduction. Fe(II) was essential for promoting EfOM degradation. The mineralization rate of EfOM increased from 7 to 29% with 2 mM Fe(II) addition in the UV/H₂O₂ process and to 23% with 0.8 mM Fe(II) addition in the UV/PS process. A preliminary experiment was conducted to obtain the optimal molar ratio of oxidant to Fe(II) for practical applications based on different indicators. The form of Fe(III) prevalent at different pH values strongly affected Fe(II)/Fe(III) cycling, thus determining the progress of EfOM degradation. A machine learning approach consisting of parallel factor analysis coupled with self-organizing maps (PARAFAC-SOM) was employed with fluorescence spectra to visualize the degradation behavior of EfOM in the different reaction systems. Four components (i.e., two humic-like substances, one fulvic acid, and one tryptophan-like substance) were eventually identified, and their reductions reached more than 62% during the Fe(II)-assisted oxidation processes. The degradation orders for each component in the different oxidation processes were initially evaluated by SOM analysis with F_max percentage data. The degradation behavior of EfOM in the UV/Fe(II)/H₂O₂ and UV/Fe(II)/PS systems exhibited different trends based on the best matching unit map and component planes. The humic-like component was more refractory than the other three components in both oxidation processes. The microbial humic-like and high-molecular-weight fulvic acid substances showed higher reactivity with SO·₄^- than with ·OH, while the tryptophan-like substance was more reactive in the UV/Fe(II)/H₂O₂ system than in the UV/Fe(II)/PS system. The outcomes of this study provide new insights into the degradation behavior of EfOM, promoting the development of advanced wastewater treatments.

Effects of DOM characteristics from real wastewater on the degradation of pharmaceutically active compounds by the UV/H2O2 process

The characteristics of dissolved organic matter (DOM) can significantly affect the degradation of target compounds by the advanced oxidation processes. In this study, the effects of the different hydrophobicity/hydrophilicity fractions, molecular weight (MW) fractions, fluorescence components and molecular components of DOM extracted from municipal wastewater on the degradation of 4 pharmaceutically active compounds (PhACs), including carbamazepine, clofibric acid, atenolol and erythromycin by the UV/H₂O₂ process were investigated. The results showed that the degradation rate constants of 4 PhACs decreased dramatically in the presence of DOM. The linear regressions of 4 PhACs degradation as a function of specific fluorescence intensity (SFI) are exhibited during the degradation of 4 PhACs and the SFI may be used to evaluate effect of DOM on target compounds in wastewater. The hydrophobic acid (HPO-A) exhibited the strongest inhibitory effect on degradation of 4 PhACs during oxidation process. The small MW fractions of DOM significantly inhibited the degradation of 4 PhACs during oxidation process. Among three fluorescence components, hydrophobic humic-like substances may significantly inhibit the degradation of 4 PhACs during oxidation process. At the molecular level, the formulas may be derived from terrestrial sources. CHO compound may significantly inhibit the degradation of 4 PhACs during oxidation process on formula classes. The unsaturated hydrocarbons, carbohydrates and tannins compounds may significantly inhibit the effectiveness of the UV/H₂O₂ process on compound classes.

Photolysis of Chlorine Dioxide under UVA Irradiation: Radical Formation, Application in Treating Micropollutants, Formation of Disinfection Byproducts, and Toxicity under Scenarios Relevant to Potable Reuse and Drinking Water

Conversion of potable reuse water utilities and drinking water utilities from a low-pressure UV/H₂O₂ (LPUV/H₂O₂) advanced oxidation process (AOP) to alternative AOPs in which oxidants can effectively absorb photons and rapidly generate radicals has attracted great interest. Herein, we propose a novel UVA/ClO₂ AOP for different water treatment scenarios because of reduced photon absorption by the background matrix and high molar absorptivity for ClO₂ at UVA wavelengths. While the photolysis of ClO₂ produces ^•Cl + O₂ or ^•ClO + O(³P) via distinct product channels, we determined the parameters needed to accurately model the loss of oxidants and the formation of byproducts and combined a kinetic model with experimental data to determine quantum yields (Φ). Modeling incorporating the optimized Φ simultaneously predicted oxidant loss and the formation of major products -HOCl, Cl^-, and ClO₃^-. We also systematically investigated the removal of three contaminants exhibiting different radical reactivities, the formation of 35 regulated and unregulated halogenated disinfection byproducts (DBPs), DBP-associated toxicity, and N-acetylcysteine thiol reactivity in synthetic or authentic RO permeates/surface waters treated by different AOPs. The kinetic model developed in this study was used to optimize operating conditions to control undesired products and improve contaminant removal efficiency. The results indicate that UVA/ClO₂ can outperform LPUV/H₂O₂ in terms of electrical energy per order of contaminant degradation, disinfection byproduct formation, and toxicity indices.

Enhanced removal of refractory humic- and fulvic-like organics from biotreated landfill leachate by ozonation in packed bubble columns

Biotreated landfill leachate contains much refractory organics such as humic and fulvic acids, which can be degraded by O₃. However, the low O₃ mass transfer and high energy cost limit its wide application in landfill leachate treatment. Previous studies proved that packed bubble columns could enhance the O₃ mass transfer and increase the synthetic humic acids wastewater degradation, but the performance of packed bubble columns in real wastewater treatment has not been investigated. Therefore, this study aims to evaluate the feasibility of application of packed bubble column in the real biotreated landfill leachates treatment and provide insights into the transformation of organic matters in leachates during ozonation. Packed bubble columns with lava rocks or metal pall rings (LBC or MBC) were applied and compared with a non-packed bubble column (BC). At an applied O₃ dose of 8.35 mg/(L_{water sample} min), the initial COD (400 mg/L) was only removed for 26% in BC and 32% in MBC while this was 46% in LBC, indicating LBC has the best performance. GC-MS analysis shows that raw biotreated leachate contains potential endocrine disruptors such as di(2-ethylhexyl) phthalate (DEHP). 61% of DEHP was removed in LBC and the least intermediate oxidation products from humic- and fulvic-like organics was detected in LBC. The highest O₃ utilization efficiency (89%) and hydroxyl radical (OH) exposure rate (3.0 × 10^-10 M s) were observed in LBC with lowest energy consumption (E_EO) for COD removal of 18 kWh/m³. The enhanced ozonation efficiency in LBC and MBC was attributed to the improved O₃ mass transfer. Besides, LBC had additional adsorptive and catalytic activity that promoted the decomposition of O₃ to generate OH. This study demonstrates that a packed bubble column increases removal and decreases energy use when treating landfill leachate, thus promoting the application of ozonation.

Catalytic Ozonation for Effective Degradation of Coal Chemical Biochemical Tail Water by Mn/Ce@RM Catalyst

An Mn/Ce@red mud (RM) catalyst was prepared from RM via a doping–calcination method. Scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to characterize the surface morphology, crystal morphology, and elemental composition of the Mn/Ce@RM catalyst, respectively. In addition, preparation and catalytic ozonation conditions were optimized, and the mechanism of catalytic ozonation was discussed. Lastly, a fuzzy analytic hierarchy process (FAHP) was adopted to evaluate the degradation of coal chemical biochemical tail water. The best preparation conditions for the Mn/Ce@RM catalyst were found to be as follows: (1) active component loading of 3%, (2) Mn/Ce doping ratio of 2:1, (3) calcination temperature of 550 °C, (4) calcination time of 240 min, and (5) fly ash floating bead doping of 10%. The chemical oxygen demand (COD) removal rate was 76.58% under this preparation condition. The characterization results suggested that the pore structure of the optimized Mn/Ce@RM catalyst was significantly improved. Mn and Ce were successfully loaded on the catalyst in the form of MnO2 and CeO2. The best operating conditions in the study were as follows: (1) reaction time of 80 min, (2) initial pH of 9, (3) ozone dosage of 2.0 g/h, (4) catalyst dosage of 62.5 g/L, and (5) COD removal rate of 84.96%. Mechanism analysis results showed that hydroxyl radicals (•OH) played a leading role in degrading organics in the biochemical tail water, and adsorption of RM and direct oxidation of ozone played a secondary role. FAHP was established on the basis of environmental impact, economic benefit, and energy consumption. Comprehensive evaluation by FAHP demonstrated that D3 (with an ozone dosage of 2.0 g/H, a catalyst dosage of 62.5 g/L, initial pH of 9, reaction time of 80 min, and a COD removal rate of 84.96%) was the best operating condition.

Advanced treatment of secondary effluent organic matters (EfOM) from an industrial park wastewater treatment plant by Fenton oxidation combining with biological aerated filter

This study investigated the advanced treatment of secondary effluent organic matters (EfOM) from an industrial park wastewater treatment plant (IPWTP) by Fenton oxidation process and its combination with biological aerated filter (BAF). The constituents of EfOM were characterized by using fluorescence excitation-emission matrix, and the results showed that the major components included aromatic proteins, soluble microbial products, humic and fulvic acid-like substances, and compounds associated with fluorescent region of Ex 250-300 nm/Em 600-700 nm. The EfOM was strongly resistant to biodegradation (biochemical oxygen demand (BOD₅):chemical oxygen demand (COD) ratio at 0.11), resulting in less than 15% dissolved organic carbon (DOC) removal efficiency by the BAF reactor. The advanced treatment of EfOM by Fenton oxidation process led to maximum ~50% mineralization efficiency of EfOM under the optimal conditions of 2.0 mM Fe^II, 10 mM H₂O₂, pH 3.0 and 3.0 h of the reaction time. Particularly, Fenton oxidation treatment effectively improved the biodegradability of EfOM in the IPWTP secondary effluents, e.g., increasing the BOD₅:COD ratio from 0.11 to 0.42. A synergistic combination of Fenton oxidation process with the BAF reactor offered desirable mineralization efficiencies of EfOM (>70%) at lower dosages of Fenton's reagents. The present results suggest that Fenton oxidation process combining with the BAF reactor can be a promising strategy for the advanced treatment of EfOM in IPWTP secondary effluents. This study provides guidance for the characterization and advanced treatment of EfOM in IPWTP secondary effluents for practical purpose.

Surrogates for on-line monitoring of the attenuation of trace organic contaminants during advanced oxidation processes for water reuse

The large number of trace organic contaminants (TrOCs) in wastewater has resulted in severe concerns to human health. Ozonation and UV/H₂O₂ are widely used to remove TrOCs in wastewater treatment process. Owing to the trace concentrations of TrOCs in wastewater, real-time monitoring of the abatement efficiency of TrOCs through ozonation and UV/H₂O₂ is quite challenging. Instead of a direct measurement of all the TrOCs, the research community has begun to use different surrogates to monitor the attenuation of TrOCs during AOPs. Various surrogates have been developed over the past few decades. In this review, the different types of surrogates are summarized, including ultraviolet spectroscopy and fluorescence spectroscopy. Strong linear correlations have been found for the removal of TrOCs using AOPs, and the abatement of UV absorption spectroscopy at 254 nm or total fluorescence (TF). Moreover, a two-phase linear correlation can better describe the ozone-resistant TrOCs compared with a single linear correlation. Two different kinds of predictive models exist that use surrogates as the input for ozonation: the regression model and kinetic model. The development of the models requires a further understanding of the impacts of water quality, seasonal variations, and storm events on the kinetic parameters. For the in situ monitoring system, the light-emitting diode (LED) is one of the most promising light sources, although the sensitivity and accuracy still need to be improved.

Advances in the characterization and monitoring of natural organic matter using spectroscopic approaches

Natural organic matter (NOM) is ubiquitous in environment and plays a fundamental role in the geochemical cycling of elements. It is involved in a wide range of environmental processes and can significantly affect the environmental fates of exogenous contaminants. Understanding the properties and environmental behaviors of NOM is critical to advance water treatment technologies and environmental remediation strategies. NOM is composed of characteristic light-absorbing/emitting functional groups, which are the "identification card" of NOM and susceptive to ambient physiochemical changes. These groups and their variations can be captured through optical sensing. Therefore, spectroscopic techniques are elegant tools to track the sources, features, and environmental behaviors of NOM. In this work, the most recent advances in molecular spectroscopic techniques, including UV-Vis, fluorescence, infrared, and Raman spectroscopy, for the characterization, measurement, and monitoring of NOM are reviewed, and the state-of-the-art innovations are highlighted. Furthermore, the limitations of current spectroscopic approaches for the exploration of NOM-related environmental processesand how these weaknesses/drawbacks can be addressed are explored. Finally, suggestions and directions are proposed to advance the development of spectroscopic methods in analyzing and elucidating the properties and behaviors of NOM in natural and engineered environments.

Characterization of wastewater effluent organic matter with different solid phase extraction sorbents

Effluent organic matter (EfOM) from municipal wastewater treatment plants (WWTPs) has received increasing attention due to its impacts on natural and engineered aquatic systems. A comprehensive understanding of molecular compositions of EfOM is crucial for controlling its negative effects and effective removal of it. Fourier transform-ion cyclotron resonance mass spectrometry (FTICR MS) is a powerful method to characterize molecular compositions of EfOM. However, application of this powerful technique is very depending on the sample preparation procedures (i.e. solid phase extraction, SPE) for enrichment and desalting. In this study, a systematic comparison of the difference in molecular compositions of the EfOM extracted using eighteen different SPE sorbents (Envicarb, PPL, ENV, HLB, C18, C18OH, C8, PH, CH, WAX, WCX, MAX, MCX, CBA, C2, CN-E, NH2, and SI) was investigated. Molecular characterization using FTICR MS showed that non-polar sorbents (Envicarb, PPL, ENV, HLB, C18, C18OH) and mixed mode sorbents (WAX, WCX, MAX, MCX) prefer to extract more aromatic and unsaturated molecules, while strongly-polar (SI), mid-polar (CBA, NH2), and weakly non-polar (C2, CN-E) sorbents prefer to extract more aliphatic components. In addition, it is found that combining extracts of CBA, ENV, and EnviCarb sorbents might be a practical way to provide a comprehensive information of molecular composition of EfOM. The results reported in this study provide valuable information on molecular compositions of EfOM and the selectivity of EfOM by different SPE sorbents.

Molecular-Level Transformation of Dissolved Organic Matter during Oxidation by Ozone and Hydroxyl Radical

Ozonation of drinking and wastewater relies on ozone (O₃) and hydroxyl radical (^•OH) as oxidants. Both oxidants react with dissolved organic matter (DOM) and alter its composition, but the selectivity of the two oxidants and mechanisms of reactivity with DOM moieties are largely unknown. The reactions of O₃ and ^•OH with two DOM isolates were studied by varying specific ozone doses (0.1-1.3 mg-O₃/mg-C) at pH 7. Additionally, conditions that favor O₃ (i.e., addition of an ^•OH scavenger) or ^•OH (i.e., pH 11) were investigated. Ozonation decreases aromaticity, apparent molecular weight, and electron donating capacity (EDC) of DOM with large changes observed when O₃ is the main oxidant (e.g., EDC decreases 63-77% for 1.3 mg-O₃/mg-C). Both O₃ and ^•OH react with highly aromatic, reduced formulas detected using high-resolution mass spectrometry (O:C = 0.48 ± 0.12; H:C = 1.06 ± 0.23), while ^•OH also oxidizes more saturated formulas (H:C = 1.64 ± 0.26). Established reactions between model compounds and O₃ (e.g., addition of one to two oxygen atoms) or ^•OH (e.g., addition of one oxygen atom and decarboxylation) are observed and produce highly oxidized DOM (O:C > 1.0). This study provides molecular-level evidence for the selectivity of O₃ as an oxidant within DOM.

Fenton reaction induced in-situ redox and re-complexation of polyphenol-Cr complex and their products

In this study, in-situ Fenton oxidation was used for the de-complexation and degradation of tannin-Cr(III) complexes. Cr(III) can be oxidized into free Cr(VI) under the effect of ·OH and oxidation products of tannin can be used as reductant for Cr(VI) to establish a redox cycle of Cr(III)-Cr(VI)-Cr(III). Thus, it is crucial to investigate the interactions of Cr(III) with tannin derived oxidation products due to negligible accumulation of Cr(VI) during Fenton oxidation treatment. Here, sequential filtration/ultrafiltration was applied to reveal the distribution characteristics of TOC and Cr fractions during the oxidation of tannin-Cr(III). As the increase of colloidal size of tannic acid products, residual TOC and Cr mainly distribute in larger size range after the oxidation of tannin-Cr(III) which can be ascribed to re-complexation between oxidation products and Cr(III). Besides, analytical results indicate that carboxyl group and hydroxyl group in oxidation products may cause the re-complexation of Cr(III), resulting in the formation of highly conjugated materials containing Cr(III). It can be concluded that due attention should be paid to the efficient removal technology and mechanism for polymer-Cr complexes, as well as the oxidation intermediates in the role of conversion and removal of Cr species.

Characterization of dissolved organic matter in wastewater during aerobic, anaerobic, and anoxic treatment processes by molecular size and fluorescence analyses

Changes in the characteristics of dissolved organic matter (DOM: the dissolved fraction of natural organic matter) during a series of wastewater treatment plant (WWTP) processes were investigated by using a combination of molecular size analysis and excitation emission matrix (EEM) spectroscopy coupled with parallel factor analysis. The characteristics of DOM were compared following aerobic, anoxic, and anaerobic treatments. Three peaks at about 100,000 Da (high-molecular-size DOM, Peak 1) and about 900-1,100 Da (intermediate-molecular-size DOM, Peak 2; low-molecular-size DOM, Peak 3 as the shoulder of Peak 2) were observed in the distribution of total organic carbon molecular sizes in the influent of the WWTPs. In this study, five fluorescent components (C1 to C5) were identified in the EEM spectra. Molecular size analysis and molecular size fractionation revealed that the C3 (humic-like) and C5 (specific to sewage) fluorophores had intermediate or low molecular sizes. Comparison of the changes of the concentrations of dissolved organic carbon in each reaction tank and investigation of the removal selectivity of each treatment (aerobic, anaerobic, and anoxic) suggested that the heterogenous compounds present in DOM of the influent were homogenized into intermediate-molecular-size DOM with high hydrophobicity and aromaticity, or into C4 fluorophores (DOM-X), during anaerobic or anoxic treatment. DOM-X was able to be transformed or removed by aerobic treatment. The results suggested that introduction of aerobic treatment at the appropriate stage of wastewater treatment or inclusion of physical or chemical treatment should be an effective way to optimize DOM removal.

Effect of pH on effluent organic matter removal in hybrid process of magnetic ion-exchange resin adsorption and ozonation

It is essential to mitigate the risk of exposure to effluent organic matter (EfOM) in aquatic environments to ensure safe wastewater recycling. Magnetic ion-exchange (MIEX) resin adsorption combined with ozonation could provide EfOM removal. However, the poor understanding of the influences of the parameters and mechanisms in the hybrid process has restricted the applications. In this study, the response surface methodology was used to reveal the interactions of the major operation parameters. The degradation behaviour of the EfOM was investigated by using spectroscopy combined with mathematical methods. The effect of the pH on the EfOM removal was also analysed. The maximum efficiency of the removal of dissolved organic carbon (DOC) was 59.77% at the optimal MIEX resin dosage of 7.97 mL/L, ozone concentration of 8 mg/L, agitation speed of 199.84 r/min, and pH of 9.98. The ozonation was superior to resin adsorption in the removal of 1054-Da compounds, while the resin adsorption was advantageous in the removal of 4168-Da compounds. Three fluorescent components (C1, C2, and C3) were more easily subjected to external perturbation than the DOC and ultraviolet absorbance at 254 nm in the oxidation processes. The MIEX resin exhibited low efficiencies of removal of the fluorescent substances. A synchronous fluorescence analysis coupled with a two-dimensional correlation analysis revealed that the variation in EfOM followed the order of fulvic-to humic-like substances in the hybrid process of MIEX and the following ozonation. The pH was the most significant influencing factor in the hybrid process.

Orthophosphate vs. bicarbonate used as a buffering substance for optimizing the bromide-enhanced ozonation process for ammonia nitrogen removal

Bromide-enhanced ozonation (BEO) process can be a fast and effective solution for the complete removal of total nitrogen (TN) from wastewaters containing from moderate to high concentrations of ammonia nitrogen (AN). Like the traditional biological process of AN oxidation, even BEO requires the presence of buffering agents, in order to oppose the progressive acidification induced by the reaction. This study compares the effect of two buffering substances (namely bicarbonate and mixtures of orthophosphates) in hindering the acidification caused by AN oxidation and, consequently, optimizing the overall efficiency of the process. Tests were carried out with on-purpose made solutions containing concentrations of AN of 5-10 mM. The range of [Br^-]/[O₃] ratio values was from 12 to 18, so as to make ozone the limiting factor in HOBr generation. The results of this study proved that, in the absence of natural buffering agents, mixtures of orthophosphates must be preferred to the more traditionally employed bicarbonate to control the pH evolution of BEO process. In fact, orthophosphates proved to be capable to guarantee an initial pH of the wastewater in the order of 7.5, thus making the zero-order AN removal rates 15% faster than those observed in the presence of bicarbonate. Furthermore, in the presence of mixtures of orthophosphates, the generation of ozonation byproducts in the oxidized form (nitrate, bromate) was reduced by over 70%. Finally, the fine control of pH obtained with orthophosphates in the BEO of AN makes that process an attractive solution for the treatment of effluents containing AN, thus preventing the discharge of residual nitrogen into aquatic environments and avoiding eutrophication of receiving water bodies.

Combination of catalytic ozonation by regenerated granular activated carbon (rGAC) and biological activated carbon in the advanced treatment of textile wastewater for reclamation

Wastewater reclamation in the textile industry has attracted considerable attention. In this study, catalytic ozonation by regenerated granular activated carbon (rGAC) and its combination with biological activated carbon (BAC) was investigated for the reclamation of a real bio-treated dyeing and finishing wastewater (BDFW). Catalytic ozonation by rGAC (O₃/rGAC) was 1.6-2.0 times more efficient than ozonation alone for pollutants degradation. Although iron oxide loaded rGAC (rGAC-Fe) improved the performance of catalytic ozonation by 14%-25%, but was labile (<2 days) compared to stable rGAC (>20 days). Catalytic ozonation improved the generation of ^•OH, contributing 1.1-1.7 times faster of chromophores decomposition and 0.24-0.55 times more increase of biodegradability than ozonation. However, catalytic ozonation increased the acute toxicity of BDFW by two times. The combination of O₃/rGAC and BAC can synergistically reduce COD, chromophores, and color in BDFW during 45-day's continuous operation, the improvements than O₃/rGAC being 21.0%, 18.8%, and 13.6%, respectively. Moreover, although O₃/rGAC of BDFW increased the toxicity from 98.3 to 146.5 μg-HgCl₂/L, post BAC significantly reduced the toxicity to 13.1 μg-HgCl₂/L. Engineering practice of water reclamation by O₃/rGAC-BAC was approved to be feasible based on both the water quality of treated water and the operation cost.

Identification of oxidative stress and estrogenic activity induced by polarity fractions of effluent organic matter

This study evaluated oxidative stress and estrogenic activity induced by hydrophobic (HP), transphilic (TP), and hydrophilic (HL) fractions of effluent organic matter (EfOM) from municipal and industrial wastewater treatment plants. Fluorescence regional integration (FRI) analysis indicated that EfOM showed higher FRI distribution in regions II (aromatic protein-like) and IV (soluble microbial products, SMPs) than Suwannee River natural organic matter (SRNOM), which was primarily in regions III (fulvic acid-like) and V (humic acid-like). The HP and HL fractions of industrial EfOMs significantly increased catalase (CAT) and glutathione S-transferase (GST) activity and lipid peroxidation compared with those of the control (p <  0.05). Estrogenic activity was the highest in industrial EfOM followed by municipal EfOM, and both were significantly higher than that of SRNOM and the control (p <  0.05). FRI distribution in region II was significantly related to CAT, GST, and estrogenic activity (r = 0.7142, 0.7786, and 0.8107, respectively) for the HL fraction of EfOM. For the HP fraction of EfOM, regions II and IV were significantly related to estrogenic activity (r = 0.7221 and 0.6707, respectively). These findings suggest that aromatic protein-like substances and SMPs in EfOM were responsible for the observed oxidative stress and estrogenic activity.

Development of correlation spectroscopy (COS) method for analyzing fluorescence excitation emission matrix (EEM): A case study of effluent organic matter (EfOM) ozonation

Two-dimensional correlation spectroscopy (2DCOS) has been used as a powerful tool for analyzing spectral features, but it has never been applied to fluorescence excitation-emission matrix (EEM) data due to the incompatible dimensions. This study first investigated EEM-COS by reducing the dimensions of the EEM (using parallel factor analysis, PARAFAC) for fitting to 2DCOS (EEM-PARAFAC-COS). The fluorescence changes of effluent organic matter (EfOM) during ozonation were studied using EEM-COS and synchronous fluorescence (SF)-2DCOS. The conventionally used SF-2DCOS proved to be biased due to the intrinsic drawback of SF, while the EEM-PARAFAC-COS gave accurate and trustworthy results. Homo-EEM-PARAFAC-COS indicated that the fluorescence protein-like and fulvic-like substances in EfOM were preferentially ozonated compared to humic-like substances. Hetero-EEM-PARAFAC-COS analyses on the EEM, FTIR, UV-vis absorbance, and size-exclusion chromatography showed that the fluorescence protein-like and fulvic-like substances in EfOM were associated with lower molecular weight (MW, ∼0.95 kDa), UV absorbance at ∼280 nm, and more electron-enriched aromatics (with amide and phenolic groups), which explained their ozonation preference, while humic-like substances were related to carboxylic groups, UV absorbance at ∼255 nm, and organics at MW of ∼4.50 kDa. This work demonstrated the great potential of EEM-PARAFAC-COS in studying fluorescence change and correlating fluorescence with other spectra.

Potential of the integration of coagulation and ozonation as a pretreatment of reverse osmosis concentrate from coal gasification wastewater reclamation

Combination of coagulation and ozonation was used to treat brine derived from a three-stage reverse osmosis (RO) process during coal gasification wastewater reclamation. Effects of operating parameters on the removals of total organic carbon (TOC), color and UV absorbance at 254 nm (A₂₅₄) were investigated during coagulation and ozonation. All the removal efficiencies of TOC, A₂₅₄ and color of FeCl₃ coagulant are about twice those of AlCl₃ coagulant at the same molar dose since almost all the molecular weight fractions of RO concentrate (ROC) could be removed effectively by FeCl₃ coagulant while only the fractions of molecular weight > 3 k Da could be removed effectively by AlCl₃ coagulant. The TOC removal increases with the increasing of ozone dose and reaction temperature during ozonation of ROC after coagulation pretreatment. TOC and color of ROC after pretreated by coagulation could be further removed effectively during ozonation since ozonation can significant reduce the fluorescence response of all the fractions of effluent organic matter in ROC. It is unexpectedly found that the increase of A₂₅₄ is observed after ozonation, this is because the intensity of absorbance at 254 nm by the low molecular weight transformation products (<2 k Da) increases significantly with the reaction time after 30 min. The coagulation coupling with ozonation is efficient in the removals of both TOC and color of ROC.

Residual micro organic pollutants and their biotoxicity of the effluent from the typical textile wastewater treatment plants at Pearl River Delta

This work investigated the biotoxicity and the residual dissolved organic matter (DOM) of the effluents from nine typical full-scale textile plants located at Pearl River Delta (PRD) in Guangdong province, China. The fluorescence regional integration (FRI) analysis showed that the tryptophan-like (II), soluble microbial product-like (IV) and fulvic acid-like substances (III) were the dominant compounds in the DOM. The acute toxicity test showed toxic effects still remained in most textile effluents, which might attribute to the undegraded dyes or aromatic compounds. Combining with the results from multiple methods, it indicated that the selected nine textile wastewater treatment plants (tWWTPs) all contained some residual micro organic pollutants in their effluents, and the residual benzene-derived products or aromatic amines were probably the toxicity-causing substances. Both ozonization and membrane filtration were capable of further decreasing the content of residual DOM, but by comprehensively considering the effects of removing DOM and biotoxicity, membrane filtration was better than ozonization.

Membrane-based separation of potential emerging pollutants

The potential emerging pollutants (PEPs) such as hazardous chemicals, toxic metals, bio-wastes, etc., pose a severe threat to human health, hygiene and ecology by way of polluting the environment and water sources. The PEPs are originated from various industrial effluent discharges including pharmaceutical, food and metal processing industries. These PEPs in contact with water may pollute the water and disturb the aquatic life. Innumerable methods have been used for the treatment of effluents and separating the toxic chemicals/metals. Of these methods, membrane-based separation processes (MBSPs) are effective over the conventional techniques for providing clean water from wastewater streams at an affordable cost with minimum energy requirement. Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), and forward osmosis (FO) methods as well as hybrid technologies are discussed citing the published results of the past decade.

Catalytic micro-ozonation by Fe3O4 nanoparticles @ cow-dung ash for advanced treatment of biologically pre-treated leachate

In this work, the biologically pre-treated leachate was subjected to catalytic micro-ozonation using cow-dung ash composites loaded with Fe₃O₄ nanoparticles (nano-Fe₃O₄@CDA) as the catalyst. The optimal conditions used were nano-Fe₃O₄@CDA dosage of 0.8 g/L, input ozone of 3.0 g/L, and reaction time of 120 min. This environment yielded the following results: The COD and color number (CN) removal reached 53% and 89%, respectively, and the BOD₅/COD increased from 0.05 to 0.32. The catalytic micro-ozonation partially degraded the refractory substances into intermediates with lower molecular weight. The percentage of phenolic compounds decreased sharply from 28.08% to 8.56%, largely due to the opening of the ring as well as to the formation of organic intermediates with a low molecular weight. Based on the results culled from the electron paramagnetic resonance (EPR), it is evident that the nano-Fe₃O₄@CDA catalyst can accelerate in order to generate OH. This was the main mechanism involved in its excellent ability to degrade refractory pollutants. These results demonstrated the potential use of nano-Fe₃O₄@CDA as a catalyst in the catalytic micro-ozonation process.

Characterization of effluent organic matter from different coking wastewater treatment plants

Effluent organic matter (EfOM) in bio-treated wastewater generally has negative impacts on advanced wastewater treatment processes. Thus, a comprehensive characterization of EfOM would help determine feasibility of wastewater treatment. The aim of this work was to characterize EfOM originating from four coking wastewater treatment plants (WTPs) in China, using specific UV absorbance (SUVA), EfOM fractionation, size exclusion chromatography, and excitation-emission matrix (EEM) fluorescence spectroscopy. It was found that the predominant species in all the EfOM samples were hydrophobic compounds with high SUVA values. The molecular weight (MW) distribution of the sampled EfOM was in the range of 300-1500 Da, and stronger UV absorbance was observed in the high MW (＞ 500 Da) region. The EEM fluorescence spectra showed that aromatic compounds accounted for a large proportion of the sampled EfOM based on the fluorescence regional integration technique. The abovementioned analysis highlights the similarities in the characteristics of the EfOM originating from different coking WTPs, regardless of treatment plant design. Meanwhile, significant differences between the characteristics of the EfOM in coking wastewater and municipal wastewater were observed.

Insight into the characteristics, removal, and toxicity of effluent organic matter from a pharmaceutical wastewater treatment plant during catalytic ozonation

Changes in the characteristics, removal efficiency, and toxicity of pharmaceutical effluent organic matter (EfOM) after catalytic ozonation were investigated in this study. After a 90-min treatment with a catalytic ozonation process (COP) in the presence of MnO₂ ceramsite, the total organic carbon (TOC), UV₂₅₄, colority, protein, and humic acid removal rates were 13.24%, 60.83%, 85.42%, 29.36% and 74.19%, respectively. The polysaccharide content increased by 12.73 mg/L during the COP for reaction times between 0 and ~50 min and decreased by 6.97 mg/L between 50 and ~90 min. Furthermore, 64.44% of the total colority was detected in the hydrophobic organic matter (HOM) fraction, and after the COP, and 88.69% of the colority in the HOM was eliminated. Meanwhile, only 59.18% of the colority in the hydrophilic organic matter (HIM) fraction was removed. GC-MS analysis showed that 38 organic pollutant species were completely removed, 8 were partially removed, and 7 were generated. After 90 min of COP treatment, the pharmaceutical EfOM toxicity was effectively reduced based on the higher incubation and lower mortality rates.

Dynamic validation of online applied and surrogate-based models for tertiary ozonation on pilot-scale

New robust correlation models for ozonation, based on UVA₂₅₄ and fluorescence surrogate parameters and developed considering kinetic information, have been applied at pilot-scale. This model framework is validated with the aim for operators to control the ozone dose for the removal of trace organic contaminants (TrOCs) in effluents from full-scale municipal wastewater treatment plants. The inflected correlation model between ΔTrOCs and the surrogates predicts the removal of TrOCs (based on statistical evidence) solely using the 2nd order reaction rate constant with ozone (k_O3) and in a more adequate manner than similar single correlation models. This allows the use of this new model for current and future TrOCs under investigation which is highly interesting when imposed discharge limits might include more and other TrOCs in future. The use of UVA₂₅₄ might be preferable at the current timing for online monitoring of TrOC abatement as the model showed a good predictive power (based on statistical evidence and visual confirmation). Reliable online sensors are more widespread (and commercially) available compared to fluorescence sensors which are still under development, with the exception of a few examples. Nevertheless, the data processing of the fluorescence signals, isolating the different intensities associated with moieties reacting similarly to ozone might even increase the predictive power, given the lower degree of interference (i.e. less scattering).

Advanced oxidation processes for the removal of natural organic matter from drinking water sources: A comprehensive review

Natural organic matter (NOM), a key component in aquatic environments, is a complex matrix of organic substances characterized by its fluctuating amounts in water and variable molecular and chemical properties, leading to various interaction schemes with the biogeosphere and hydrologic cycle. These factors, along with the increasing amounts of NOM in surface and ground waters, make the effort of removing naturally-occurring organics from drinking water supplies, and also from municipal wastewater effluents, a challenging task requiring the development of highly efficient and versatile water treatment technologies. Advanced oxidation processes (AOPs) received an increasing amount of attention from researchers around the world, especially during the last decade. The related processes were frequently reported to be among the most suitable water treatment technologies to remove NOM from drinking water supplies and mitigate the formation of disinfection by products (DBPs). Thus, the present work overviews recent research and development studies conducted on the application of AOPs to degrade NOM including UV and/or ozone-based applications, different Fenton processes and various heterogeneous catalytic and photocatalytic oxidative processes. Other non-conventional AOPs such as ultrasonication, ionizing radiation and plasma technologies were also reported. Furthermore, since AOPs are unlikely to achieve complete oxidation of NOM, integration schemes with other water treatment technologies were presented including membrane filtration, adsorption and others processes.

Molecular characterization of effluent organic matter in secondary effluent and reclaimed water: Comparison to natural organic matter in source water

Municipal wastewater reclamation is becoming of increasing importance in the world to solve the problem of water scarcity. A better understanding of the molecular composition of effluent organic matter (EfOM) in the treated effluents of municipal wastewater treatment plants (WWTPs) is crucial for ensuring the safety of water reuse. In this study, the molecular composition of EfOM in the secondary effluent of a WWTP in Beijing and the reclaimed water further treated with a coagulation-sedimentation-ozonation process were characterized using a non-target Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) method and compared to that of natural organic matter (NOM) in the local source water from a reservoir. It was found that the molecular composition of EfOM in the secondary effluent and reclaimed water was dominated by CHOS formulas, while NOM in the source water was dominated by CHO formulas. The CHO formulas of the three samples had similar origins. Anthropogenic surfactants were responsible for the CHOS formulas in EfOM of the secondary effluent and were not well removed by the coagulation-sedimentation-ozonation treatment process adopted.

Surrogate-Based Correlation Models in View of Real-Time Control of Ozonation of Secondary Treated Municipal Wastewater-Model Development and Dynamic Validation

New robust correlation models for real-time monitoring and control of trace organic contaminant (TrOC) removal by ozonation are presented, based on UVA₂₅₄ and fluorescence surrogates, and developed considering kinetic information. The abatement patterns of TrOCs had inflected shapes, controlled by the reactivity of TrOCs toward ozone and HO^• radicals. These novel and generic correlation models will be of importance for WRRF operators to reduce operational costs and minimize byproduct formation. Both UVA₂₅₄ and fluorescence surrogates could be used to control ΔTrOC, although fluorescence measurements indicated a slightly better reproducibility and an enlarged control range. The generic framework was validated for several WRRFs and correlations for any compound with known kinetic information could be developed solely using the second order reaction rate constant with ozone (k_O3). Two distinct reaction phases were defined for which separate linear correlations were obtained. The first was mainly ozone controlled, while the second phase was more related to HO^• reactions. Furthermore, parallel factor analysis of the fluorescence spectra enabled monitoring of multiple types of organic matter with different O₃ and HO^• reactivity. This knowledge is of value for kinetic modeling frameworks and for achieving a better understanding of the occurring changes of organic matter during ozonation.

Spectroscopic descriptors for dynamic changes of soluble microbial products from activated sludge at different biomass growth phases under prolonged starvation

In this study, the spectroscopic indices of soluble microbial products (SMP) were explored using absorption and fluorescence spectroscopy to identify different distinctive biomass growth phases (i.e., exponential phase, pseudo-endogenous phase, and endogenous phase) and to describe the microbial activity of activated sludge in a batch type bioreactor under prolonged starvation. The optical descriptors, including UV absorption at 254 nm (UVA254), spectral slope, absorbance slope index (ASI), biological index (BIX), humification index (HIX), and the ratio of tryptophan-like to humic-like components (C1/C2), were examined to describe the dynamic changes in SMP. These indices were mostly associated with dissolved organic carbon (DOC) of SMPs and specific oxygen uptake rate (SOUR). Among those, ASI was the most strongly correlated with the SOUR data for the pseudo-endogenous and the endogenous periods. Although the three microbial phases were well discriminated using the spectral slope, BIX, and the C1/C2 ratio, the C1/C2 ratio can be suggested as the most preferable indicator as it can also trace the changes of the relative abundance of proteins to humic-like substances in SMPs. The suggested spectroscopic descriptors were reasonably explained by the general trends of decreased large-sized biopolymer fractions (e.g., proteins) and increased humic substrates (HS) with starvation time, which were detected by size exclusion chromatography. This study provides a novel insight into the strong potential of using optical descriptors to easily probe microbial status in biological treatment systems.

Enhanced treatment of secondary municipal wastewater effluent: comparing (biological) filtration and ozonation in view of micropollutant removal, unselective effluent toxicity, and the potential for real-time control

Ozonation and three (biological) filtration techniques (trickling filtration (TF), slow sand filtration (SSF) and biological activated carbon (BAC) filtration) have been evaluated in different combinations as tertiary treatment for municipal wastewater effluent. The removal of 18 multi-class pharmaceuticals, as model trace organic contaminants (TrOCs), has been studied. (Biological) activated carbon filtration could reduce the amount of TrOCs significantly (>99%) but is cost-intensive for full-scale applications. Filtration techniques mainly depending on biodegradation mechanisms (TF and SSF) are found to be inefficient for TrOCs removal as a stand alone technique. Ozonation resulted in 90% removal of the total amount of quantified TrOCs, but a post-ozonation step is needed to cope with an increased unselective toxicity. SSF following ozonation showed to be the only technique able to reduce the unselective toxicity to the same level as before ozonation. In view of process control, innovative correlation models developed for the monitoring and control of TrOC removal during ozonation, are verified for their applicability during ozonation in combination with TF, SSF or BAC. Particularly for the poorly ozone reactive TrOCs, statistically significant models were obtained that correlate TrOC removal and reduction in UVA₂₅₄ as an online measured surrogate parameter.

Enhanced WWTP effluent organic matter removal in hybrid ozonation-coagulation (HOC) process catalyzed by Al-based coagulant

A novel hybrid ozonation-coagulation (HOC) process was developed for application in wastewater reclamation. In this process, ozonation and coagulation occurred simultaneously within a single unit. Compared with the conventional pre-ozonation-coagulation process, the HOC process exhibited much better performance in removing dissolved organic matters. In particular, the maximal organic matters removal efficiency was obtained at the ozone dosage of 1mgO₃/mg DOC at each pH value (pH 5, 7 and 9). In order to interpret the mechanism of the HOC process, ozone decomposition was monitored. The results indicated that ozone decomposed much faster in the HOC process. Moreover, by using the reagent of O₃-resistant hydroxyl radical (OH) probe compound, para-chlorobenzoic acid (pCBA), and electron paramagnetic resonance (EPR) analysis, it was observed that the HOC process generated higher content of OH compared with pre-ozonation process. This indicates that the OH oxidation reaction as the key step can be catalyzed and enhanced by Al-based coagulants and their hydrolyzed products in this developed process. Thus, based on the catalytic effects of Al-based coagulants on ozonation, the HOC process provides a promising alternative to the conventional technology for wastewater reclamation in terms of higher efficiency.

Investigation of ozone and peroxone impacts on natural organic matter character and biofiltration performance using fluorescence spectroscopy

Impacts of ozonation alone as well as an advanced oxidation process of ozone plus hydrogen peroxide (H₂O₂ + O₃) on organic matter prior to and following biofiltration were studied at pilot-scale. Three biofilters were operated in parallel to assess the effects of varying pre-treatment types and dosages. Conventionally treated water (coagulation/flocculation/sedimentation) was fed to one control biofilter, while the remaining two received water with varying applied doses of O₃ or H₂O₂ + O₃. Changes in organic matter were characterized using parallel factors analysis (PARAFAC) and fluorescence peak shifts. Intensities of all PARAFAC components were reduced by pre-oxidation, however, individual humic-like components were observed to be impacted to varying degrees upon exposure to O₃ or H₂O₂ + O₃. While the control biofilter uniformly reduced fluorescence of all PARAFAC components, three of the humic-like components were produced by biofiltration only when pre-oxidation was applied. A fluorescence red shift, which occurred with the application of O₃ or H₂O₂ + O₃, was attributed to a relative increase in carbonyl-containing components based on previously reported results. A subsequent blue shift in fluorescence caused by biofiltration which received pre-oxidized water indicated that biological treatment readily utilized organics produced by pre-oxidation. The results provide an understanding as to the impacts of organic matter character and pre-oxidation on biofiltration efficiency for organic matter removal.

Contaminant Removal from Source Waters Using Cathodic Electrochemical Membrane Filtration: Mechanisms and Implications

Removal of recalcitrant anthropogenic contaminants from water calls for the development of cost-effective treatment technologies. In this work, a novel electrochemical membrane filtration (EMF) process using a conducting microfiltration membrane as the cathode has been developed and the degradation of sulphanilic acid (SA) examined. The electrochemical degradation of SA in flow-by mode followed pseudo-first-order kinetics with the degradation rate enhanced with increase in charging voltage. Hydrogen peroxide as well as oxidants such as HO^• and Fe(IV)O²⁺ were generated electrochemically with HO^• found to be the dominant oxidant responsible for SA degradation. In addition to the anodic splitting of water, HO^• was formed via a heterogeneous Fenton process with surface-bound Fe(II) resulting from aerobic corrosion of the steel mesh. In flow-through mode, the removal rate of SA was 13.0% greater than obtained in flow-by mode, presumably due to the better contact of the contaminant with the oxidants generated in the vicinity of the membrane surface. A variety of oxidized products including hydroquinone, p-benzoquinone, oxamic acid, maleic acid, fumaric acid, acetic acid, formic acid, and oxalic acid were identified and an electrochemical degradation pathway proposed. These findings highlight the potential of the cathodic EMF process as an effective technology for water purification.

Ozonation effects on emerging micropollutants and effluent organic matter in wastewater: characterization using changes of three-dimensional HP-SEC and EEM fluorescence data

The degradation of effluent organic matter (EfOM) in a municipal wastewater treated by ozonation was characterized using the methods of high-performance size-exclusion chromatography (HP-SEC) and excitation/emission matrix (EEM) fluorescence combined with parallel factor analysis (PARAFAC). The removal of 40 diverse trace-level contaminants of emerging concern (CEC) present in the wastewater was determined as well. Ozonation caused a rapid decrease of the absorbance and fluorescence of the wastewater, which was associated primarily with the oxidation of high and low apparent molecular weight (AMW) EfOM fractions. PARAFAC analysis also showed that components C1 and C2 decreased prominently in these conditions. The EfOM fraction of intermediate molecular weight ascribable to a terrestrial humic-like component (C3) tended to be less reactive toward ozone. Relative changes of EEM fluorescence were quantified using F _max values of PARAFAC-identified components (∆F/F ⁰_max). Unambiguous relationships between ∆F/F ⁰_max values and the extent of the degradation of the examined CECs (∆C/C₀) were established. This allowed correlating main parameters of the ∆C/C₀ vs. ∆F/F ⁰_max relationships with the rates of oxidation of these CECs. The results demonstrate the potential of online measurements of EEM fluorescence for quantitating effects of ozonation on EfOM and micropollutants in wastewater effluents.

Removal of pharmaceuticals from secondary effluents by an electro-peroxone process

This study compared the removal of pharmaceuticals from secondary effluents of wastewater treatment plants (WWTPs) by conventional ozonation and the electro-peroxone (E-peroxone) process, which involves electrochemically generating H2O2 in-situ from O2 in sparged O2 and O3 gas mixture (i.e., ozone generator effluent) during ozonation. Several pharmaceuticals with kO3 ranging from <0.1 to 6.8 × 10(5) M(-1) s(-1) were spiked into four secondary effluents collected from different WWTPs, and then treated by ozonation and the E-peroxone process. Results show that both processes can rapidly remove ozone reactive pharmaceuticals (diclofenac and gemfibrozil), while the E-peroxone process can considerably accelerate the removal of ozone-refractory pharmaceuticals (e.g., ibuprofen and clofibric acid) via indirect oxidation with OH generated from the reaction of sparged O3 with electro-generated H2O2. Compared with ozonation, the E-peroxone process enhanced the removal kinetics of ozone-refractory pharmaceuticals in the four secondary effluents by ∼40-170%, and the enhancement was more pronounced in secondary effluents that had relatively lower effluent organic matter (EfOM). Due to its higher efficiency for removing ozone-refractory pharmaceuticals, the E-peroxone process reduced the reaction time and electrical energy consumption required to remove ≥90% of all spiked pharmaceuticals from the secondary effluents as compared to ozonation. These results indicate that the E-peroxone process may provide a simple and effective way to improve existing ozonation system for pharmaceutical removal from secondary effluents.

A Comparative Electrochemical-Ozone Treatment for Removal of Phenolphthalein

The degradation of aqueous solutions containing phenolphthalein was carried out using ozone and electrochemical processes; the two different treatments were performed for 60 min at pH 3, pH 7, and pH 9. The electrochemical oxidation using boron-doped diamond electrodes processes was carried out using three current density values: 3.11 mA·cm−2, 6.22 mA·cm−2, and 9.33 mA·cm−2, whereas the ozone dose was constantly supplied at 5±0.5 mgL−1. An optimal degradation condition for the ozonation treatment is at alkaline pH, while the electrochemical treatment works better at acidic pH. The electrochemical process is twice better compared with ozonation.

A study on the reactivity characteristics of dissolved effluent organic matter (EfOM) from municipal wastewater treatment plant during ozonation

The reactivity of dissolved effluent organic matter (EfOM) in the process of ozonation was examined. Under different ozone dosages (0.42 ± 0.09, 0.98 ± 0.11 and 2.24 ± 0.17 mgO3/mg DOC), the EfOM before and after ozonation could be classified into four fractions according to their hydrophobicities. By ozonation, the hydrophobic fractions, especially hydrophobic acid (HOA) and hydrophobic neutral (HON), were found to undergo a process of transformation into hydrophilic fractions (HI), of which the HOA were first transformed into HON, and then the majority of the HON fraction was later converted to HI by further ozonation. It was noticeable that after ozonation, the fluorescence intensity in the humic-like and protein-like regions decreased as indicated by the excitation and emission matrix (EEM) spectra for the hydrophobic fractions. By coupling the EEM spectra with the molecular size analysis using high performance size exclusion chromatography (HPSEC), the difference between the characteristic distributions of the humic-like and protein-like fluorophores were further revealed. It could thus be extrapolated that ozone might have preferentially reacted with the protein-like hydrophobic fraction with molecular weight (MW) less than 100 kDa. Moreover, by X-ray photoelectron spectroscopy (XPS) analysis, it was identified that with increasing ozone dosage (from 0 to 2.24 ± 0.17 mgO3/mg DOC), the aromaticity of HON decreased dramatically, while aliphatics and ketones increased especially at the low ozone dose (0.42 ± 0.09 mgO3/mg DOC). Of the EfOM fractions, the HON fraction would have a higher content of electron enriched aromatics which could preferentially react with ozone rather than the HOA fraction.