Effluent Organic Matter Fractions Research Articles

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.

UV/chlorine and chlorination of effluent organic matter fractions: Tracing nitrogenous DBPs using FT-ICR mass spectrometry

UV/chlorine process is a promising advanced treatment to eliminate pathogen and remove refractory micropollutants for reclamation of municipal secondary effluent. However, effluent organic matter (EfOM) featuring high organic nitrogen content serves as a potential precursor for nitrogenous disinfection byproducts (N-DBPs) of health concern. The molecular-level alteration of a hydrophobic (HPO) EfOM fraction and a transphilic (TPI) EfOM fraction isolated from the same municipal effluent and the formation of N-DBPs in the UV/chlorine were tracked by ultrahigh-resolution mass spectrometry. Compared with chlorination, UV/chlorine induced a significantly greater modification on the molecular composition of EfOM and resulted in formation of unique formulae and chlorinated molecules with higher degree of oxidation, lower aromaticity, and less carbon number due to the involvement of reactive radical species. For both EfOM fractions, UV/chlorine formed more diverse DBPs with higher intensity and Cl-incorporation than chlorination. The TPI fraction of EfOM characterized by higher O/C and N/C ratios generated more N-DBPs with higher intensity clustered in the high O/C region than the HPO fraction of EfOM by both UV/chlorine and chlorination. Totally, 207 and 117 nitrogen-containing chlorinated formulae were recorded after UV/chlorine treatment of TPI and HPO, respectively. Precursor tracking found a greater number of DBPs were originated from raw EfOM through electrophilic substitution pathway rather than chlorine addition. Toxicity bioassays demonstrated that DBPs can trigger oxidative stress-induced DNA damage, while HPO fraction of EfOM dominated the induction of cytotoxicity. However, no correlation could be established between the diversity/abundance of N-DBPs and the level of DNA damage. A total of 22 DBPs with a significant rank correlation with DNA damage were identified, while C8H6O5NCl was found as the N-DBP with the strongest correlation. The potential toxic chlorine-containing formula with the most abundant intensity was assigned to C5HO3Cl3. This study suggests that the character and transformation of EfOM and associated toxicity is critical to evaluate the UV/chlorine process toward practical application.

Changes in the structural characteristics of EfOM during coagulation by aluminum chloride and the effect on the formation of disinfection byproducts

The effects of coagulation on the removal efficiency of different fractions of effluent organic matter (EfOM) from wastewater treatment plants were investigated to identify changes in their structural characteristics and the influences on trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP). The results indicated that coagulation performed better for the removal of hydrophobic base (HOB) and hydrophobic neutral (HON) fractions than hydrophilic (HI) and hydrophobic acid (HOA) fractions. The removal efficiency was higher under neutral than under acidic conditions for all fractions. As a result, lower levels of THMFP and HAAFP were detected at pH7. The excitation-emission matrix spectra indicated that the HI fraction contained humic acid-like substances that reacted with chlorine to form THMs. The HON fraction contained soluble microbial byproduct-like substances with a higher potential to create HAAs. The results of Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and high-pressure size exclusion chromatography (HP-SEC) of the raw and coagulated water indicated that a higher molecular weight, α-carbon, COOH, aromatic structures, and polysaccharides were associated with a higher production of disinfection byproducts (DBP). These results elucidate the coagulation efficiencies of EfOM fractions associated with different mechanisms and facilitate the prediction of DBP formation by each fraction based on specific structural characteristics.

Adsorptive removal of propranolol under fixed-bed column using magnetic tyre char: Effects of wastewater effluent organic matter and ball milling

We investigated the competitive effects of different fractions of wastewater treatment plant effluent organic matter (EfOM) on adsorption of an organic micro pollutant (OMP), propranolol (PRO), in a fixed bed column packed with magnetic tyre char (MTC). The results showed that the presence of EfOM inhibited PRO adsorption in wastewater leading to decreased PRO adsorption capacity from 5.86 to 2.03 mg/g due to competitive effects and pore blockage by smaller EfOM fractions. Characterization of EfOM using size exclusion chromatography (LC-OCD) showed that the principal factor controlling EfOM adsorption was pore size distribution. Low molecular weight neutrals had the highest adsorption onto MTC while humic substances were the least interfering fraction. Effect of important parameters such as contact time, linear velocity and bed height/diameter ratio on MTC performance was studied in large-lab scale columns. Linear velocity and contact time were found to be effective in increasing adsorption capacity of PRO on MTC and delaying breakthrough time. Increase in linear velocity from 0.64 cm/min to 1.29 cm/min increased mass transfer and dispersion, resulting in considerable rise of adsorbed amount (5.86 mg/g to 22.58 mg/g) and increase in breakthrough time (15.8–62.7 h). Efficiency of non-equilibrium Hydrus model considering dispersion and mass transfer mechanism was demonstrated for real wastewater and scale up purposes. Ball milling for degradation of adsorbed PRO and regeneration of MTC resulted in 79% degradation of PRO was achieved after 5 h milling (550 rpm), while the addition of quartz sand increased the efficiency to 92%.

Discovery of Polar Ozonation Byproducts via Direct Injection of Effluent Organic Matter with Online LC-FT-ICR-MS.

Effluent organic matter (EfOM), a major ozone consumer during wastewater ozonation, is a complex mixture of natural and anthropogenic organic molecules. Ozonation of EfOM adds to molecular complexity by introducing polar and potentially mobile ozonation byproducts (OBPs). Currently, nontargeted direct infusion (DI) ultrahigh resolution mass spectrometry (e.g. FT-ICR-MS) is used to study OBPs but requires sample extraction, limiting the accessible polarity range of OBPs. To better understand the impact of ozonation on EfOM and the formation of polar OBPs, nonextracted effluent was analyzed by direct injection onto a reversed-phase liquid chromatography system (RP-LC) online hyphenated with an FT-ICR-MS. Over four times more OBPs were detected in nonextracted EfOM compared to effluent extracted with solid phase extraction and measured with DI-FT-ICR-MS (13817 vs 3075). Over 1500 highly oxygenated OBPs were detected exclusively in early eluting fractions of nonextracted EfOM, indicating polar OBPs. Oxygenation of these newly discovered OBPs is higher than previously found, with an average molecular DBE-O value of -3.3 and O/C ratio of 0.84 in the earliest eluting OBP fractions. These polar OBPs are consistently lost during extraction but may play an important role in understanding the environmental impact of ozonated EfOM. Moreover, 316 molecular formulas classified as nonreactive to ozone in DI-FT-ICR-MS can be identified with LC-FT-ICR-MS as isomers with varying degrees of reactivity, providing for the first time experimental evidence of differential reactivity of complex organic matter isomers with ozone.

Assessing the role of cold temperatures on irreversible membrane permeability of tertiary ultrafiltration treating municipal wastewater

A comprehensive assessment of the effects of temperature on hydraulically irreversible membrane permeability in tertiary ultrafiltration of municipal wastewater was conducted through bench scale testing. The influence of temperature was differentiated into impacts on SBR effluent characteristics, water rheological properties, and intrinsic membrane properties, which all subsequently affected the development of hydraulically irreversible permeability. When filtration tests were conducted at 20 °C with the effluents from sequencing batch reactors (SBRs) that were operated at 8, 14 and 20 °C, hydraulically irreversible permeability declined by 38%, 22% and 17%, respectively, during the steady period. The greater decline was attributed to higher generation of effluent organic matter (EfOM) at low SBR operating temperatures. When filtration tests were conducted at the corresponding SBR operating temperature, the hydraulically irreversible permeability with the effluents from SBRs operated at 14 and 8 °C further decreased. The water viscosity and intrinsic membrane resistance were observed to be responsible for 20–29% of the total decrease in hydraulically irreversible permeability. These declines established the upper limit to which fouling mitigation strategies could enhance hydraulically irreversible permeabilities at low temperature. The hydraulically irreversible permeability decline with low filtration temperature beyond that associated with changes in viscosity and intrinsic membrane resistance was attributed to narrowed membrane pores that retained additional EfOM fractions and modified membrane-foulant interactions. The novel approach in differentiating the effects of temperature on secondary treatment and filtration processes developed in the present study provides insights into hydraulically irreversible fouling development and the results from the present study can be employed to understand the limits of tertiary fouling control under challenging conditions.

New insights into the fractionation of effluent organic matter on diagnosis of key composition affecting advanced phosphate removal by Zr-based nanocomposite

The influence of effluent organic matter (EfOM) on phosphate removal by adsorption plays an important role in evaluating the applicability of adsorbents. Currently, molecular understanding of EfOM regarding its impact on adsorption is insufficient due to a lack of appropriate EfOM fractionation/characterization protocols, as associated with the specific structure-function property of adsorbents. In this work, a combined method coupling DEAE/XAD fractionation with molecular characterization was proposed, targeting the versatile structure-function characters of nanocomposite, to reveal the composition of EfOM as well as its impact on phosphate removal by nanocomposite during long-term adsorption/regeneration runs. Zirconium-based polystyrene anion exchanger (HZO-201) was selected as a representative nanocomposite, featuring with porous networking matrix, positively charged surface and multiple adsorptive sites. The EfOM samples from three biologically treated sewage effluent sources were separated into fractions of negatively charged organic acid (OA) and hydrophobic-, transphilic-, hydrophilic-neutral/base (HPO-n/b, TPI-n/b and HPI-n/b). The combined method enables effective differentiation of the charge, aromaticity, molecular weight and functionalities of the fractions, matching the multiple structural/surface characteristics of HZO-201 and favoring the evaluation on the impact of the EfOM fractions. The interference sequence of the EfOM fractions on phosphate removal followed an order of OA > HPO-n/b > TPI-n/b > HPI-n/b. The OA fraction, characterized by negatively charged, aromatic functionalities and broad molecular weight distribution (1–5 kDa and 14 kDa), was recognized as the key interfering fraction, presumably due to its multiple adsorption pathways (i.e., ion exchange, π-π interactions and pore filling). Particularly, the low-molecular-weight OA moieties (1–4 kDa) progressively accumulated onto the nanocomposite via irreversible adsorption, causing a continuous phosphate-capacity loss by 32.70% over multiple cycles. We believe the combined fractionation/characterization method may be extended to other complex water systems to identify key influential organic matters in polishing treatment of various pollutants by adsorption.

Characterizing the molecular weight distribution of dissolved organic matter by measuring the contents of electron-donating moieties, UV absorbance, and fluorescence intensity

Electron-donating moieties (EDM) have recently been used to characterize the redox properties and treatability of dissolved organic matter during water and wastewater treatment. In this study, size exclusion chromatography followed by a derivatization-spectrometric method was developed to determine the molecular weight (MW) distribution of EDM in dissolved organic matter. The relationships between EDM concentration and chromophore content (indicated by UVA254), fluorophore content (indicated by fluorescence), and dissolved organic carbon (DOC) concentration were analyzed for different MW fractions. In general, natural organic matter (NOM) showed higher total EDM concentration and higher EDM average MW than effluent organic matter (EfOM). For NOM, fractions with MW between 1.8 k and 6.9 k Da accounted for most of the EDM (45.4%–48.6%), followed by the fractions with MW < 1.8 k Da (25.6%–42.4%). By contrast, the EDM in EfOM occurred predominantly in fractions with MW < 1 k Da (51.8%–58.6%), with lower concentrations in fractions with MW > 1.8 k Da (<20.2%). The heterogeneous MW distribution of EDM was strongly correlated to the presence of chromophores, but not DOC or fluorophores. The EDM difference between MW fractions suggested that the fraction with MW 1.8–6.9 k Da (40.7%–47.1%) and the fractions with MW < 1 k Da (50.2%–58.8%) should be the dominant oxidant consumers in NOM and EfOM, respectively. When the EDM was normalized by the DOC for each MW fraction (EDMMW/DOCMW), the EDMMW/DOCMW of relatively high-MW fractions (>1.8 k Da) is 1.2–1.9 times of relatively low-MW (<1 k Da) fractions for both NOM and EfOM, which indicates that higher-MW fractions are more susceptible to chemical oxidations. The relationship between EDM change and UVA254 change varied for different MW fractions during advanced ozonation treatment, because of the different oxidation mechanisms in operation for MW fractions. The ozonation of EfOM fractions with higher MW (>1.8 k Da) and lower MW (<1 k Da) preferentially resulted in benzoquinone formation and ring-cleavage, respectively.

A fluorescence-based indicator for nanofiltration fouling propensity caused by effluent organic matter (EfOM)

Effluent organic matter (EfOM) is one of the major foulants responsible for the occurrence of membrane fouling during advanced wastewater treatment using nanofiltration (NF) technology. In this present study, we have reported a simple fouling indicator based on the properties of fractional fluorescence and molecular weight, termed as fluorescence-size-index (FSI), to predict the fouling propensity of NF when filtrating EfOM. Specifically, EfOM collected from twenty-one real sewage samples were first analyzed to quantify their fluorescent compositions and concentrations. The results showed that the EfOM consisted mainly of humic-like substances, soluble organism metabolites and fulvic-like substances, characterized by small-molecule organic matters (<5 kDa) and hydrophobic fractions. Second, the major NF fouling fractions of EfOM were determined based on their fluorescent properties. It was observed that small-molecule hydrophobic components with humic-like fluorescence properties continuously influenced the flux decline rate throughout the whole operation, while macromolecular hydrophilic components with fluorescent properties of apparent aromatic hydrocarbon proteins were primarily responsible for the initial, rapid flux decline. Furthermore, the constructed FSI has proven to be useful in guiding the selection of pretreatment methods for preventing NF fouling.

Characterization and fate of EfOM during ozonation applied for effective abatement of recalcitrant micropollutants

Alterations occurring in the effluent organic matter (EfOM) during ozonation could be detrimental depending on the final application of the treated effluent. In this work, the fate of EfOM in different ozonized wastewaters was assessed through the monitoring of general water quality parameters and organic fractions determined through size-exclusion chromatography combined with organic carbon detection (SEC-OCD) analysis. These different components of EfOM were distinguished based on relative molecular weights and assigned to fractions named as biopolymers, humic substances, building blocks and low molecular weight neutrals and acids. The significant abatement (60–90%) of an ozone-refractory micropollutant (MP) was employed as reference to simulate potential scenarios in which also the presence of these species is wanted to be attenuated. Ultraviolet absorbance at 254 nm (UVA254) and chemical oxygen demand (COD) reductions ranged from 40 to 80% and from 10 to 45%, respectively, for ozone doses between 0.6 and 1.0 mM, depending on the organic matter content (both dissolved and suspended) and alkalinity of the effluents. Dissolved organic carbon (DOC) analysis showed 21–27% reductions in Membrane bioreactor (MBR) effluents, whereas for conventional activated sludge (CAS) samples this value increased (6–35%) during the oxidative treatment. This was attributed to the continuous solubilization of humic substances, according to SEC-OCD results. Moreover, accumulation of lower molecular weight fractions such as building blocks or acids was observed in all the tested effluents, and attributed to the breakdown of largest EfOM fractions, mainly humic substances. Relationships proposed in this work between humic substances evolution, water quality (UVA254) and process parameters (immediate ozone demand (IOD), IOD-normalized hydroxyl radical exposure (∫[OH]dt/IOD) and transferred ozone dose (TOD)) might be useful for EfOM variations estimations along ozonation.

Characterizing property and treatability of dissolved effluent organic matter using size exclusion chromatography with an array of absorbance, fluorescence, organic nitrogen and organic carbon detectors.

In this study, size exclusion chromatography with an array of absorbance, fluorescence, organic nitrogen and organic carbon detectors was used for characterizing property and treatability of effluent organic matter (EfOM) from 12 wastewater treatment plants. According to their apparent molecular weight (AMW), EfOM fractions were assigned to biopolymers (>20 kDa), humic substances that comprise sub-fractions of humic-like acids (HA-I & HA-II, 2.3-7.0 kDa) and fulvic-like acids (FA, 1.5-2.3 kDa), building blocks (0.55-1.5 kDa) and low molecular weight neutral substances (<550 Da). The fractions of biopolymers and low molecular weight neutral substances didn't show humic-like fluorescence, while the fractions of HA-II, FA and building blocks usually had signatures of both humic-like and protein-like fluorescence. Humic substances generally contributed the largest proportion of dissolved organic carbon and nitrogen (DOC & DON) in effluents. Coagulation removed EfOM fractions following the order of biopolymers > HA subfraction > FA subfraction > building blocks, while little removal of protein-like fluorescence in HA-II and FA subfractions was detected. Anion exchange treatment could effectively reduce DOC and DON concentrations; the sequence of the treatment efficiency was humic substances > biopolymers > building blocks. Increasing O3 doses caused DOC and DON of EfOM to be gradually transformed from large AMW fractions into small AMW fractions, while chromophores and fluorophores in HA subfractions were relatively more refractory than those in the other fractions. Size exclusion chromatography with multiple detectors are suggested to be an informative technique for estimating treatability of EfOM by advanced wastewater treatment processes.

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.

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.

The interaction between effluent organic matter fractions and Al2(SO4)3 identified by fluorescence parallel factor analysis and FT-IR spectroscopy

Colloidal organic matter (OC fraction), hydrophobic organic matters (HPO fraction), transphilic matters (TPI fraction) have been extracted and fractionated from Effluent Organic Matter (EfOM). FT-IR spectroscopy and Fluorescence Excitation-Emission Matrix parallel factor (EEM-PARAFAC) analysis have been performed to characterize the chemical structure of fractions. The coagulation performance of EfOM fractions with Al2(SO4)3 was investigated in terms of turbidity reduction and dissolved organic carbon (DOC) removal. FT-IR spectroscopy and Fluorescence have also been introduced to identify the interaction between fractions and Al2(SO4)3. The results showed the main component in different fractions and that HPO fractions can be representative of natural organic matter (NOM), whereas OC fractions is representative of EfOM. The dissolved organic matters (DOMs) like HPO fraction showed better removal efficiency during coagulation. The relationship between zeta potential and DOC removal suggested that the coagulation mechanism of EfOM fractions were different. A new intensity peak showed up in Region V and the enhancement of Fluorescence intensity in humic-like substance exhibited after coagulation, which due to the complex with aluminum salts. The –COO–Al asymmetric stretch in FT-IR spectroscopy confirmed the complexation between aluminum salts and carboxyl groups. As the interaction of Effluent Organic Matter can cause enhancement in fluorescence intensity, fluorescence-EEM was not an appropriate method to evaluate the coagulation performance of secondary effluent with aluminum salts.

Biosorption performance evaluation of heavy metal onto aerobic granular sludge-derived biochar in the presence of effluent organic matter via batch and fluorescence approaches

In present study, the biosorption process of Cu(II) onto aerobic granular sludge-derived biochar was evaluated in the absence and presence of effluent organic matter (EfOM) by using batch and fluorescence approaches. It was found that EfOM gave rise to enhancement of Cu(II) removal efficiency onto biochar, and the sorption data were better fitted with pseudo-second order model and Freundlich equation, in despite of the absence and presence of EfOM. According to excitation-emission matrix (EEM), EfOM was mainly comprised by humic-like substances and fulvic-like substances and their intensities were reduced in the addition of biochar and Cu(II) from batch biosorption process. Synchronous fluorescence spectra coupled to two-dimensional correlation spectroscopy (2D-COS) further implied that a successive fluorescence quenching was observed in various EfOM fractions with the increasing Cu(II) concentration. Moreover, fulvic-like fraction was more susceptibility than other fractions for fluorescence quenching of EfOM.

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 0max). Unambiguous relationships between ∆F/F 0max 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 0max 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.

Role of polarity fractions of effluent organic matter in binding and toxicity of silver and copper

This study evaluates the effect of the physicochemical properties of effluent organic matter (EfOM) from industrial and sewage wastewater treatment plants (WWTPs) on the binding and toxicity of Ag and Cu. EfOM was isolated into hydrophobic, transphilic, and hydrophilic fractions depending on its polarity, and was characterized by elemental, specific ultraviolet absorbance, and fluorescence excitation-emission matrix analyses. Our results suggest that the EfOM consists of microbially derived non-humic substances that have lower aromaticity than the Suwannee River natural organic matter (SR-NOM). The Freundlich model was better at explaining the binding of Ag and Cu onto both SR-NOM and EfOM than the Langmuir model. In particular, the hydrophilic fractions of sewage EfOM showed higher binding capacities and affinities for Ag and Cu than the corresponding hydrophobic fractions, resulting in better reduction of the acute toxicity of Ag and Cu towards Daphnia magna. However, in the case of both SR-NOM and industrial EfOM, the hydrophobic fractions were more efficient at reducing metal toxicity. These findings suggest that the EfOM has different physicochemical properties compared with NOM and that the binding and toxicity of heavy metals are largely dependent on the polarity fractions of EfOM.

Influence of activated carbon preloading by EfOM fractions from treated wastewater on adsorption of pharmaceutically active compounds

In this study, the preloading effects of different fractions of wastewater effluent organic matter (EfOM) on the adsorption of trace-level pharmaceutically active compounds (PhACs) onto granular activated carbon (GAC) were investigated. A nanofiltration (NF) membrane was employed to separate the EfOM by size, and two GACs with distinct pore structures were chosen for comparison. The results showed that preloading with EfOM substantially decreased PhAC uptake of the GACs; however, comparable PhAC adsorption capacities were achieved on GACs preloaded by feed EfOM and the NF-permeating EfOM. This indicates that: (1) the NF-rejected, larger EfOM molecules with an expectation to block the PhAC adsorption pores exerted little impact on the adsorbability of PhACs; (2) the smaller EfOM molecules present in the NF permeate contributed mainly to the decrease in PhAC uptake, mostly due to site competition. Of the two examined GACs, the wide pore-size-distributed GAC was found to be more susceptible to EfOM preloading than the microporous GAC. Furthermore, among the fourteen investigated PhACs, the negatively charged hydrophilic PhACs were generally subjected to a greater EfOM preloading impact.

Novel strategies for diagnosing the cause of short-term organic fouling in ultrafiltration

ABSTRACTThe main objective of this study was to demonstrate the usefulness of a multi-strategic approach for identifying the extent and mechanism of fouling in the ultrafiltration (UF) of wastewater effluent organic matter (EfOM). In this study, we combined EfOM fractionation with spectroscopic autopsies for clean and fouled UF membranes. The EfOM fractions were sequentially removed from the wastewater effluent using relatively gentle techniques (neutral pH and no extractions). The residual EfOM samples were then used in UF tests. This work showed that resistance to filtration was partially reduced with the removal of particles (>20 nm), but almost all of the short-term fouling was eliminated with the removal of organic acids, which constitute 22% of the total organic carbon. The membrane autopsies were conducted using attenuated reflectance infrared spectroscopy for the top and bottom fouled membranes, and comparison was made with the infrared spectra of a clean membrane. Hydrophilic base/neutrals were the dominant EfOM constituents at the top of the fouled membranes. Hydrophobic acids were adsorbed onto the pore walls deep inside the membranes, which coincided with the permeability recovery of fouled membranes. The fouling mechanisms were examined by measuring the resistance to filtration as a function of permeate flux using various operational conditions and by investigating the effectiveness of hydraulic and chemical cleaning on the restoration of membrane permeability.

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.