Effluent Organic Matter Research Articles

Variation in organic matter characteristics and mitigation of ultrafiltration membrane fouling by chlorine and UV/chlorine pre-oxidation in secondary effluent treatment

Membrane fouling caused by effluent organic matter (EfOM) limits its further application in wastewater reuse. In this study, the effect of UV/chlorine pretreatment on membrane fouling was investigated in treating secondary effluent by ultrafiltration (UF) process. The relation between organic matter changes and fouling alleviation after UV/chlorine pretreatment was also studied according to the molecular weight (MW) changes in various resin fractions derived from EfOM. Results showed that UV/chlorine pretreatment effectively alleviated irreversible fouling, whereas chlorine pre-oxidation primarily mitigated reversible fouling. UV/chlorine pre-oxidation reduced 18% of reversible membrane fouling and 38% of irreversible membrane fouling at a chlorine dosage of 8 mg/L, indicating better performance in membrane fouling mitigation than chlorine pre-oxidation. UV/chlorine pre-oxidation also decreased dissolved organic matter in the UF permeate. The hydrophobic acidic (HPO-A) fraction caused dominant membrane fouling, while the hydrophilic (HPI) fraction contained most of high MW organic matter. Pre-oxidation changed the polarity of organic matter in the HPO-A fraction and decomposed the organics of high MW in the HPI fraction, which alleviated membrane fouling. These results showed that UV/chlorine pre-oxidation was a prospective pretreatment process prior to UF in wastewater reclamation.

Critical review of fluorescence and absorbance measurements as surrogates for the molecular weight and aromaticity of dissolved organic matter.

Dissolved organic matter (DOM) is ubiquitous in aquatic environments and challenging to characterize due to its heterogeneity. Optical measurements (i.e., absorbance and fluorescence spectroscopy) are popular characterization tools, because they are non-destructive, require small sample volumes, and are relatively inexpensive and more accessible compared to other techniques (e.g., high resolution mass spectrometry). To make inferences about DOM chemistry, optical surrogates have been derived from absorbance and fluorescence spectra to describe differences in spectral shape (e.g., E2:E3 ratio, spectral slope, fluorescence indices) or quantify carbon-normalized optical responses (e.g., specific absorbance (SUVA) or specific fluorescence intensity (SFI)). The most common interpretations relate these optical surrogates to DOM molecular weight or aromaticity. This critical review traces the genesis of each of these interpretations and, to the extent possible, discusses additional lines of evidence that have been developed since their inception using datasets comparing diverse DOM sources or strategic endmembers. This review draws several conclusions. More caution is needed to avoid presenting surrogates as specific to either molecular weight or aromaticity, as these physicochemical characteristics are often correlated or interdependent. Many surrogates are proposed using narrow contexts, such as fractionation of a limited number of samples or dependence on isolates. Further study is needed to determine if interpretations are generalizable to whole-waters. Lastly, there is a broad opportunity to identify why endmembers with low abundance of aromatic carbon (e.g., effluent organic matter, Antarctic lakes) often do not follow systematic trends with molecular weight or aromaticity as observed in endmembers from terrestrial environments with higher plant inputs.

Effect of pure oxygen aeration on soluble microbial products production in activated sludge system under the toxic condition of phenol

Soluble microbial products (SMP) contribute most of effluent organic matter (EfOM) in biological treatment processes. These products cause membrane fouling and generate disinfection by-products. This study investigated the effect of pure oxygen aeration on the production and characteristics of SMP under the toxic condition of phenol. Two sequencing batch reactors with pure oxygen (O-SBR) and air (A-SBR) aeration were used in the experiments. Results showed that the effluent chemical oxygen demand values of O- and A-SBR were 36.11 ± 1.54 and 42.44 ± 1.42 mg/L, respectively. SMP was the dominant component of EfOM. The various aeration types caused differences in the contents of extracellular polymeric substances (EPS) and SMP in the two SBRs. The content of loosely bound EPS (LB-EPS) in A-SBR was higher than that in O-SBR by 25%, whereas the tightly bound EPS content in A-SBR was lower than that in O-SBR by 19%. Pure oxygen aeration decreased 15% of humic acids, 42% of polysaccharides, and 29% of protein contents of SMP compared with air aeration, but it did not change the functional groups of SMP. SMP concentration was positively correlated with LB-EPS. Pure oxygen aeration caused the low contents of LB-EPS and SMP. This study showed the effect of pure oxygen aeration on SMP reduction, which can be useful for toxic industrial-wastewater biological treatment.

Quantitative source tracking for organic foulants in ultrafiltration membrane using stable isotope probing approach

Quantitatively identifying the primary sources of organic membrane fouling is essential for the effective implementation of membrane technology and optimal water resource management prior to the treatment. This study leveraged carbon stable isotope tracers to estimate the quantitative contributions of various organic sources to membrane fouling in an ultrafiltration system. Effluent organic matter (EfOM) and aquatic natural organic matter (NOM), two common sources, were combined in five different proportions to evaluate their mixed effects on flux decline and the consequent fouling behaviors. Generally, biopolymer (BP) and low molecular weight neutral (LMWN) size fractions - abundantly present in EfOM - were identified as significant contributors to reversible and irreversible fouling, respectively. Fluorescence spectroscopy disclosed that a protein-like component notably influenced overall membrane fouling, whereas humic-like components were predominantly responsible for irreversible fouling rather than reversible fouling. Fluorescence index (FI) and biological index (BIX), common fluorescence source tracers, showed promise in determining the source contribution for reversible foulants. However, these optical indices were insufficient in accurately determining individual source contributions to irreversible fouling, resulting in inconsistencies with the observed hydraulic analysis. Conversely, applying a carbon stable isotope-based mixing model yielded reasonable estimates for all membrane fouling. The contribution of EfOM surpassed 60 % for reversible fouling and increased with its content in DOM source mixtures. In contrast, aquatic NOM dominated irreversible fouling, contributing over 85 %, regardless of the source mixing ratios. This study emphasizes the potential of stable isotope techniques in accurately estimating the contributions of different organic matter sources to both reversible and irreversible membrane fouling.

Synergistic roles of oxidation and self-aggregation in efficient ultrafiltration membrane fouling alleviation using a flow-through Sb-SnO2 anode during wastewater reclamation

The application of ultrafiltration (UF) in wastewater reclamation alleviates the demand for limited water supplies. However, the membrane fouling caused by the effluent organic matter (EfOM) becomes a major obstacle for UF application. In this study, a pre-oxidation strategy for UF using a Sb-SnO2 (ATO) anode in flow-through mode was proposed with the hopes to improve the performance of UF during wastewater reclamation. The results indicated that this flow-through ATO (FA) anode significantly outperformed a boron-doped diamond (BDD) anode in terms of EfOM degradation and membrane fouling control. It is noteworthy that apart from oxidation, the self-aggregation behavior of foulants was also involved in the mechanisms of membrane fouling mitigation. On the one hand, FA pre-oxidation relieved the burden of membrane fouling by decomposing the macromolecular EfOM into small molecular organic matter, and even mineralizing it. The effective destruction of unsaturated EfOM by FA pre-oxidation made a remarkable contribution to fouling mitigation due to the strong correlation between the total fouling index and UV254. On the other hand, the surface morphology of membrane and interface properties of foulants revealed the self-aggregation behavior of foulants. FA pre-oxidation made the foulants aggregate spontaneously and reduced the potential of forming a dense cake layer on the membrane surface, which was conductive for water permeation. Overall, FA pre-oxidation proved to be a feasible and chemical-free option for UF pretreatment to simultaneously produce high-quality reused water and alleviate membrane fouling during wastewater reclamation.

Molecular insight of dissolved organic matter and chlorinated disinfection by-products in reclaimed water during chlorination with permanganate preoxidation

Permanganate is a common preoxidant applied in water treatment to remove organic pollutants and to reduce the formation of disinfection by-products. However, the effect of permanganate preoxidation on the transformation of dissolved effluent organic matter (dEfOM) and on the formation of unknown chlorinated disinfection by-products (Cl-DBPs) during chlorination remains unknown at molecular level. In this work, the molecular changes of dEfOM during permanganate preoxidation and subsequent chlorination were characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Permanganate preoxidation was found to decrease the DBE (double bond equivalent) and AImod (modified aromaticity index) of the dEfOM. The identity and fate of over 400 unknown Cl-DBPs during KMnO4-chlorine treatment were investigated. Most Cl-DBPs and the precursors were found to be highly unsaturated aliphatic and phenolic compounds. The Cl-DBPs precursors with lower H/C and lower O/C were preferentially removed by permanganate preoxidation. Additionally, permanganate preoxidation decreased the number of unknown Cl-DBPs by 30% and intensity of unknown Cl-DBPs by 25%. One-chlorine-containing DBPs were the major Cl-DBPs and had more CH2 groups and higher DBEw than Cl-DBPs containing two and three chlorine atoms. 60% of the Cl-DBPs formation was attributed to substitution reactions (i.e., +Cl–H, +2Cl–2H, +3Cl–3H, +ClO–H, +Cl2O3–2H). This work provides detailed molecular level information on the efficacy of permanganate preoxidation on the control of overall Cl-DBPs formation during chlorination.

Effective control of DBPs formation and membrane fouling in catalytic ozonation membrane reactor for municipal wastewater reclamation

This study aimed to evaluate the performance of different ceramic membranes, namely CuMn2O4 (CMO), g-C3N4 (CN), and CuMn2O4/g-C3N4 (CMO/CN) ceramic membrane (CM), in a catalytic ozonation membrane reactor (COMR) for municipal wastewater reclamation. The results demonstrated that CMO/CM and CMO/CN/CM used in the COMR exhibited high performance in terms of flux, removal efficiency of effluent organic matter (EfOM), control of disinfection by-products formation potential (DBPs-FP), and mitigation of membrane fouling. Notably, catalytic ozonation by CMO/CM showed superior reduction in DBPs formation (40.6 % of nitrogenous DBPs, 83.4 % of halogenated hydrocarbons, 36.6 % of haloacetic acids). Furthermore, significant inhibition of both organic fouling and biofouling was observed in the COMR. The addition of O3 altered the membrane fouling mechanism from gel layer formation to intermediate blocking. Ozonation primarily reduced the physically reversible fouling while catalytic ozonation additionally mitigated physically irreversible fouling. In addition to the almost complete removal of total cells and proteins, catalytic ozonation by CMO/CM further cleaned the α-polysaccharides and β-polysaccharides on the membrane surface, resulting in a 55.3 % reduction in biofilm thickness and demonstrating strong self-cleaning properties. These findings have important implications for enhancing the overall performance and durability of COMR systems in municipal wastewater reclamation.

Evaluation of the fate of wastewater effluent organic matter in receiving water: Effect of sequential photochemical and biological processes

Effluent organic matter (EfOM) discharged from wastewater treatment plants (WWTPs) carry substantial risks to river ecosystems. The fate and role of EfOM in the receiving water is affected by its exposure to sunlight and microbial processes, but the extent of these processes remains unclear. In this study, three-phase sequence of irradiation and microbial incubation with EfOM were conducted to compare the behavior of EfOM with that of natural organic matter in receiving rivers (RNOM). The dissolved organic carbon (DOC) in EfOM was degraded by 23% after three sequential phases, while that in RNOM was degraded by 19%. In the first phase, the irradiation of EfOM stimulated microbial respiration and growth by producing easily metabolizable less aromatic lignin-type molecules, leading to a 21% increase in biodegradation. Conversely, the irradiation of RNOM removed biodegradable lignin-type molecules, causing a 50% decreased in biodegradation. The second and third irradiation phases of EfOM and RNOM produced biodegradable lignin-type molecules, making their molecular compositions increasingly similar. The acute toxicity of EfOM decreased by 55%, and differences in microbial species composition between EfOM and RNOM waters decreased by 82% after the three-phase sequence. These findings can improve understanding of the fate of EfOM discharged into receiving rivers.

Effects of alternative disinfection methods on the characteristics of effluent organic matter and the formation of disinfection byproducts

The characteristics of effluent organic matter (EfOM) and the type of disinfection methods are closely related to the formation of disinfection byproducts (DBPs) in reclaimed water. In this study, five disinfection methods, i.e., chlorination, ultraviolet (UV) followed by chlorination (UV + Cl), UV/chlorine (UV/Cl), chloramination, and chlorine dioxide (ClO2), were applied to investigate the changes in the properties of EfOM, the formation of DBPs, and the relationship between EfOM properties and DBP formation during the disinfection of four secondary biological effluents. The results showed that EfOM with medium molecular weight (MW) (0.5–6 kDa) was the dominant fraction for all WWTPs. From a fluorescence perspective, the EfOM of the AAO process was rich in humic matter, while the EfOM of the oxidation ditch (OD) process was rich in protein matter. Disinfectants tended to transfer EfOM with high molecular weight (MW) (>6 kDa) to those with low MW (<0.5 kDa). Chlorination, UV + Cl and UV/Cl were more reactive to humic matter, while chloramination and chlorine dioxide were more reactive to protein matter. The formation of known DBPs was mainly dependent on humic matter, while protein matter was more likely to generate unknown DBPs. N-DBPs only accounted for 5.7%–17.7% of the total DBPs, but contributed more than 70% of the calculated toxicity, among which bromochloroacetonitrile (BCAN), dichloroacetonitrile (DCAN), and monobromoacetamide (MBAcAm) were the most important contributors to the calculated cytotoxicity. Monobromoacetic acid (MBAA) and MBAcAm were the primary drivers of the calculated genotoxicity. Overall, UV + Cl was the suggested optimal disinfection method for WWTPs.

Understanding molecular-level reactions between permanganate/ferrate and dissolved effluent organic matter from municipal secondary effluent

Permanganate (Mn(VII)) and ferrate ((Fe(VI)) oxidations are well-recognized as advanced treatment processes to degrade organic components detected in secondary effluents from municipal wastewater treatment plant (WWTP). However, Mn(VII) or Fe(VI) reactions are sensitive to the water matrix components, especially the dissolved effluent organic matter (EfOM) contained in secondary effluent. Here, we found that Mn(VII) or Fe(VI) hardly mineralize EfOM, but do change its molecular-level composition. Tests with representative trace organic contaminants (TrOCs) spiked to EfOM-rich wastewater effluent showed that Mn(VII) and Fe(VI) preferentially oxidize phenolic TrOCs. UV–vis and fluorescence spectroscopy analyses suggested that molecular properties associated with optical characteristics of reaction solutions are altered by treatment, including decreases in aromaticity, molecular weight, and electron-donating capacity of EfOM. At the molecular-level, the observed phenomenon is ascribed to preferential oxidation of aromatic structures and electron-rich functional groups (e.g., phenolic structures and hydroxyl groups) within EfOM, as well as the transformation and decomposition of macromolecular sulfur- and nitrogen-containing compounds (most likely proteins or microbial byproduct-like material). These findings advance the application of Mn(VII) and Fe(VI) for optimization and proper control of EfOM of emerging concern within treatment trains being developed for advanced treatment facilities.

Comparative molecular transformations of dissolved organic matter induced by chlorination and ammonia/chlorine oxidation process

The ammonia/chlorine oxidation process can greatly degrade PPCPs in water. However, its effect on molecular transformations of natural organic matter (NOM) and effluent organic matter (EfOM) are still poorly understood. In this study, molecular transformations of NOM and EfOM occurring during ammonia/chlorine were explored and compared with those occurred during chlorination, using spectroscopy and mass spectrometry. Phenolic and highly unsaturated aliphatic compounds together with aliphatic compounds were found to be predominant in both NOM and EfOM samples, all of which were significantly degraded after two processes. The ammonia/chlorine process led to greater decreases in the molecular weights of such components but lower reductions in aromaticity. Compared with chlorination, ammonia/chlorine was found to be more likely to degrade compounds while remaining fluorophores or chromophores. The CH(N)O(S) precursors were found to be similar for both processes but their products were quite different. The CH(N)O(S) precursors that only found in ammonia/chlorine had higher molecular weights and greater degrees of oxidation but lower degrees of saturation. In contrast, the unique CH(N)O(S) products that only found in ammonia/chlorine exhibited lower molecular weights and lower degrees of oxidation degrees together with higher degrees of saturation. Lower total abundance of chlorinated byproducts was found by ammonia/chlorine compared with chlorination, although the former process provided a richer diversity. In all water samples, chlorinated byproducts were mainly generated by substitution reactions during ammonia/chlorine and chlorination. Overall, the findings of this study could provide new insights into the transformations of NOM and EfOM induced by ammonia/chlorine and chlorination.

Simulated-sunlight enhances membrane aerated biofilm reactor performance in sulfamethoxazole removal and antibiotic resistance genes reduction

Membrane aerated biofilm reactors (MABRs) can be used to treat domestic wastewater containing sulfamethoxazole (SMX) because of their favorable performance in the treatment of refractory pollutants. However, biologics are generally subjected to antibiotics stress, which induces the production of antibiotic resistance genes (ARGs). In this study, a simulated-sunlight assisted MABR (L-MABR) was used to promote SMX removal and reduce ARGs production. The SMX removal efficiency of the l-MABR system was 9.62 % superior to that of the MABR system (83.13 %). In contrast from MABR, in the l-MABR, only 28.75 % of SMX was removed through microbial activity because functional bacteria were inactivated through radiation by simulated sunlight. In addition, photolysis (64.61 %) dominated SMX removal, and the best performing indirect photolysis process was the excited state of effluent organic matters (3EfOMs*). Through photolysis, ultraviolet (UV) and reactive oxygen species (ROS) enriched the SMX removal route, resulting in the SMX removal pathway in the l-MABR no longer being limited by enzyme catalysis. More importantly, because of the inactivation of functional bacteria, whether in the effluent or biofilm, the copy number of ARGs in the l-MABR was 1–3 orders of magnitude lower than that in the MABR. Our study demonstrates the feasibility of utilizing simulated-sunlight to enhance the antibiotic removal efficiency while reducing ARG production, thus providing a novel idea for the removal of antibiotics from wastewater.

Spectroscopic analysis on effluent organic matter (EfOM) evolution in different UV-based advanced oxidation processes

The effluent organic matter (EfOM) removal performance of the advanced wastewater treatment process has drawn great attention owing to the potential ecological risk of EfOM in the receiving aquatic environments. However, the EfOM evolution process is still unclear in the various advanced wastewater treatment processes. In this study, the EfOM evolution process in terms of components, structures, and functional groups was investigated in four kinds of UV-based advanced oxidation processes (AOPs). The overall EfOM removal performances were in the order: UV/NaClO > UV/PMS > UV/H2O2 > UV. According to the spectroscopic analysis results, simple aliphatics/aromatic/acetylenes compounds with C–O, =C–H, amides, or amino structures deriving from protein-like substances, are easily destroyed under UV irradiation. Apart from these structures, microbial metabolic was strongly sensitive to a reactive chlorine species (RCS)-dominated system, especially nutrients, amino acids, and small peptides with ester. Total of 22 species of halogen by-products with high biotoxicity (acetonitrile-based chlorinated EfOM, chlorinated acetate, chlorinated methane) were detected in the UV/NaClO group. In contrast, the reactive oxygen species (ROS)-dominated systems exhibited strong structure selectivity for ester (UV/H2O2) and carbonyl (UV/PMS) in all of the EfOM components, exhibiting strong reaction activity with EfOM at different stages. The results reveal the EfOM evolution in different UV-based AOPs, providing a strategy for selecting suitable UV-based AOPs in the advanced wastewater treatment process in terms of high-efficiency removal of EfOM.

Photo-transformation of wastewater effluent organic matter reduces the formation potential and toxicity of chlorinated disinfection byproducts

Sunlight exposure can degrade and transform discharged wastewater effluent organic matter (EfOM) in aquatic systems, potentially enhancing the feasibility of reusing wastewater for drinking purposes. However, there remains a lack of comprehensive understanding regarding the sunlight-induced changes in the molecular-level composition, characteristics, and chlorine reactivity of EfOM. Herein, we investigated the impact of sunlight on the optical properties, chemical composition, and formation of disinfection byproducts of EfOM using multiple spectroscopic analyses, high-resolution mass spectrometry, chlorination experiments, and in vitro bioassays. Upon natural sunlight exposure, we observed significant decreases in ultraviolet–visible absorbance and fluorescence intensity of EfOM, indicating the destruction of chromophores and fluorophores. Photolysis generally yields products with lower molecular weight and aromaticity, and with higher saturation and oxidation levels. Moreover, a shift within the EfOM from condensed aromatic-like compounds to tannin-like components was observed. Furthermore, sunlight exposure reduced the reactivity of EfOM toward the formation of trihalomethanes and haloacetonitriles during chlorination, while there was a slight increase in the specific formation potential of haloketones. Importantly, the disinfection byproducts resulting from chlorination of the irradiated EfOM exhibited reduced microtoxicity. Overall, this study provides new insights into alterations in EfOM under sunlight exposure and aids in predicting the health risks of effluent discharge in water environments.

Novel insight into secondary effluent quality improvement and ultrafiltration fouling mitigation by UV/peracetic acid pretreatment

Ultrafiltration (UF) technology is widely used in the treatment for deep purification of municipal secondary effluent, however, the membrane fouling and low removal of N, P, and organic matter during actual operation have been the main bottlenecks limiting its wide-spread application. To address the above problems, this study employed peracetic acid (PAA) and UV/PAA to evaluate the effects of PAA-based pre-oxidation on ultrafiltration membrane fouling and secondary effluent water quality. The results demonstrated that the activated PAA pre-oxidation could prominently enhance the hydrophilicity of effluent organic matter, effectively destroy the high molecular weight organic matter and mineralize the low molecular weight organic matter. PAA and its metabolites, as well as the by-products of EfOM, increased the C/P ratio in water samples from 118 to 563 and the C/N ratio from 0.86 to 8.53. After UV/20 mg/L PAA pretreatment, the reversible and irreversible membrane fouling resistance significantly decreased by 55.97 % and 65.67 %, respectively. Moreover, the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory showed lower adhere potential of the foulants to the membrane surface. In general, UV/PAA as ultrafiltration pretreatment has a huge potential for secondary effluent treatment for membrane fouling mitigation and water quality improvement.

Using Fe(II)/Fe(VI) activated peracetic acid as pretreatment of ultrafiltration for secondary effluent treatment: Water quality improvement and membrane fouling mitigation

Ultrafiltration (UF) is a technology commonly used to treat secondary effluents in wastewater reuse; however, it faces two main challenges: 1) membrane fouling and 2) inadequate nitrogen (N), phosphorus (P), and organic micropollutants (OMPs) removal. To address these two issues, in this study, we applied peracetic acid (PAA), Fe(VI)/PAA, and Fe(II)/PAA as UF pretreatments. The results showed that the most effective pretreatment was Fe(II)/200 μM PAA, which reduced the total fouling resistance by 90.2%. In comparison, the reduction was only 29.7% with 200 μM PAA alone and 64.3% with Fe(VI)/200 μM PAA. Fe(II)/200 μM PAA could effectively remove fluorescent components and hydrophobic organics in effluent organic matter (EfOM), and enhance the repulsive force between foulants and membrane (according to XDLVO analysis), and consequently, mitigate pore blocking and delay cake layer formation. Regarding pollutant removal, Fe(II)/200 μM PAA effectively degraded OMPs (>85%) and improved P removal by 58.2% via in-situ Fe(Ⅲ) co-precipitation. The quencher and probe experiments indicated that FeIVO2+, •OH, and CH3C(O)OO•/CH3C(O)O• all played important roles in micropollutant degradation with Fe(II)/PAA. Interestingly, PAA oxidation produced highly biodegradable products such as acetic acid, which significantly elevated the BOD5 level and increased the BOD5/total nitrogen (BOD5/TN) ratio from 0.8 to 8.6, benefiting N removal with subsequent denitrification. Overall, the Fe(II)/PAA process exhibits great potential as a UF pretreatment to control membrane fouling and improve water quality during secondary effluent treatment.

Comparison of molecular characteristics between commercialized and regional natural organic matters

Natural organic matter (NOM) is a ubiquitous substance in natural aquatic ecosystems that is a significant component in any experiment involving water. However, experimentally simulating the aquatic conditions using NOMs from natural sources remains difficult. As a result, previous experimental studies have predominantly relied on commercialized NOMs. This study aimed to comprehensively compare the characteristics of two commercialized NOMs (Suwannee River NOM: SRNOM, Mississippi River NOM: MRNOM) and two regional NOMs (Nakdong River NOM: NDNOM, effluent organic matter: EfOM) using various analytical methods during water dissolution. Both commercialized NOMs showed low conductivity (SRNOM: 28.6 &lt;i&gt;μ&lt;/i&gt;S/cm, MRNOM: 35.4 &lt;i&gt;μ&lt;/i&gt;S/cm) and were highly humidified (SRNOM: HIX 14.22, MRNOM: HIX 11.44), whereas NOMs from natural water had relatively higher conductivity (NDNOM: 365.7 &lt;i&gt;μ&lt;/i&gt;S/cm, EfOM: 398.8 &lt;i&gt;μ&lt;/i&gt;S/cm) and lower humification (NDNOM: HIX 2.47, EfOM: HIX 2.50). The SRNOM and MRNOM contained large amounts of tannin-like substances (SRNOM: 43.5%, MRNOM: 43.1%). The NDNOM had a humidification state similar to that of the EfOM, except for the portion of protein-like biopolymer, which was smaller. The different characteristics of the samples can be critical in selecting appropriate NOMs for use in future studies because they can significantly influence the experimental chemical reaction.

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.

Superior performance of catalytic ozonation on molecular-level transformation of effluent organic matter and self-cleaning property in catalytic ozonation membrane reactor

Catalytic ozonation membrane reactor (COMR) is one of the most promising technologies for municipal wastewater reclamation. Herein, we evaluated superior performance of catalytic ozonation in COMR through filtration of effluent organic matter (EfOM) using the origin and three catalytic membranes. We found that filtration primarily contributed to rejection of protein-like fluorescence enriched in relatively high-oxygen compounds (O/C >0.4) with high molecular weight and catalytic ozonation further removed humic-like materials and highly unsaturated, aromatic and reduced compounds (O/C<0.4; H/C<1.3), demonstrating complementary function of catalytic ozonation and filtration. The superior performance of catalytic ozonation than ozonation is reflected in higher removal of medium molecular weighted humic-like materials and S-containing compounds, enhancing the mineralization and reaction extent of EfOM. Additionally, catalytic ozonation exhibited strong self-cleaning property and eliminated irreversible membrane fouling. Our findings provide molecular-level insights into the reaction mechanism governing the COMR towards municipal wastewater reclamation.

Reactivity of dissolved effluent organic matter (EfOM) with hydroxyl radical as a function of its isolated fractions during ozonation of municipal secondary effluent

Dissolved effluent organic matter (EfOM) plays an important role in ozonation decomposition and hydroxyl radical (·OH) scavenging in ozonation for the degradation of trace organic contaminants (TrOCs) in municipal secondary effluents. The properties of EfOM have been considered a major concern in this process because EfOM fractions act differently as initiator, promoter or inhibitor of ozone decomposition and ·OH scavenging, which further impacts the degradation effectiveness of TrOCs. This study isolated EfOM from three wastewater treatment plants into six fractions (HoA, HoB, HoN, HiA, HiB and HiN) to understand the reaction kinetics as a function of EfOM and its isolated fractions. Their reaction rate constants with ·OH (kEfOM-·OH), and their roles as the initiator, promoter and inhibitor in the ·OH chain reactions in ozone decomposition were further quantified. The results showed that kEfOM-·OH of hydrophilic fractions (HiF) (accounting for 17%) reached up to 10 times as high as that for hydrophobic fractions (HoF) (accounting for 83%) (7.92 × 108 M−1 s−1 versus 0.78 × 108 M−1 s−1), suggesting the dominating role of HiF in ·OH scavenging. Hydrophilic base (HiB) was the most important fraction dominating the ozone decomposition and reaction with ·OH due to its highest rate constants of initiation and promotion. This study quantifies the kinetics and contribution of EfOM fractions in ·OH scavenging, which will guide the optimization implementation of ozonation and other ·OH-mediated AOPs toward wastewater effluents.