Relationship between fluorescence excitation-emission matrix properties and the relative degree of DOM hydrophobicity in wastewater treatment effluents

Spectral and molecular insights into the characteristics of dissolved organic matter in nitrate-contaminated groundwater

The characteristics of dissolved organic matter (DOM) serve as indicators of nitrate pollution in groundwater. However, the specific DOM components associated with nitrate in groundwater systems remain unclear. In this study, dual isotopes of nitrate, three-dimensional Excitation emission matrices (EEMs) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were utilized to uncover the sources of nitrate and their associations with DOM characteristics. The predominant nitrate in the targeted aquifer was derived from soil organic nitrogen (mean 46.0%) and manure &sewage (mean 34.3%). The DOM in nitrate-contaminated groundwater (nitrate-nitrogen >20 mg/L) exhibited evident exogenous characteristics, with a bioavailable content 2.58 times greater than that of uncontaminated groundwater. Regarding the molecular characteristics, DOM molecules characterized by CHO + 3N, featuring lower molecular weights and H/C ratios, indicated potential for mineralization, while CHONS formulas indicated the exogenous features, providing the potential for accurate traceability. These findings provided insights at the molecular level into the characterization of DOM in nitrate-contaminated groundwater and offer scientific guidance for decision-making regarding the remediation of groundwater nitrate pollution.

Insight into spatial variations of DOM fractions and its interactions with microbial communities of shallow groundwater in a mesoscale lowland river watershed

Dissolved organic matter (DOM) plays a crucial role in driving biogeochemical processes and determining water quality in shallow groundwater systems, where DOM could be susceptible to dynamic influences of surface water influx. This study employed fluorescence excitation-emission matrix (EEM) spectroscopy combined with principal component coefficients, parallel factor analysis (PARAFAC), co-occurrence network analysis and structural equation modeling (SEM) to examine changes of DOM fractions from surface water to shallow groundwater in a mesoscale lowland river basin. Combining stable isotope and hydrochemical parameters, except for surface water (SW), two groups of groundwater samples were defined, namely, deeply influenced by surface water (IGW) and groundwater nearly non-influenced by surface water (UGW), which were 50.34 % and 19.39 % recharged by surface water, respectively. According to principal component coefficients, reassembled EEM data of these categories highlighted variations of the tyrosine-like peak in DOM. EEMs coupled with PARAFAC extracted five components (C1-C5), i.e. C1, protein-like substances, C2 and C4, humic-like substances, and C3 and C5, microbial-related substances. The abundance of the protein-like was SW > IGW > UGW, while the order of the humic-like was opposite. The bacterial communities exhibited an obvious cluster across three regions, which hinted their sensitivity to variations in environmental conditions. Based on co-occurrence, SW represented the highest connectivity between bacterial OTUs and DOM fractions, followed by IGW and UGW. SEM revealed that microbial activities increased bioavailability of the humic-like in the SW and IGW, whereas microbial compositions promoted the evolution of humic-like substances in the UGW. Generally, these results could be conducive to discern dissimilarity in DOM fractions across surface water and shallow groundwater, and further trace their interactions in the river watershed.

Role of low-proportion, hydrophobic dissolved organic matter components in inhibiting methylmercury uptake by phytoplankton

Uptake of methylmercury (MeHg), a potent neurotoxin, by phytoplankton is a major concern due to its role as the primary pathway for MeHg entry into aquatic food webs, thereby posing a significant risk to human health. While it is widely believed that the MeHg uptake by plankton is negatively correlated with the concentrations of dissolved organic matter (DOM) in the water, ongoing debates continue regarding the specific components of DOM that exerts the dominant influence on this process. In this study, we employed a widely-used resin fractionation approach to separate and classify DOM derived from algae (AOM) and natural rivers (NOM) into distinct components: strongly hydrophobic, weakly hydrophobic, and hydrophilic fractions. We conduct a comparative analysis of different DOM components using a combination of spectroscopy and mass spectrometry techniques, aiming to identify their impact on MeHg uptake by Microcystis elabens, a prevalent alga in freshwater environments. We found that the hydrophobic components had exhibited more pronounced spectral characteristics associated with the protein structures while protein-like compounds between hydrophobic and hydrophilic components displayed significant variations in both distributions and the values of m/z (mass-to-charge ratio) of the molecules. Regardless of DOM sources, the low-proportion hydrophobic components usually dominated inhibition of MeHg uptake by Microcystis elabens. Results inferred from the correlation analysis suggest that the uptake of MeHg by the phytoplankton was most strongly and negatively correlated with the presence of protein-like components. Our findings underscore the importance of considering the diverse impacts of different DOM fractions on inhibition of phytoplankton MeHg uptake. This information should be considered in future assessments and modeling endeavors aimed at understanding and predicting risks associated with aquatic Hg contamination.

The application of chitosan quaternary ammonium salt to replace polymeric aluminum ferric chloride for sewage sludge dewatering

Inorganic coagulants such as poly aluminum ferric chloride (Al/Fe) are applied conventionally to sewage sludge dewatering and can be retained in the sludge cake, causing its conductivity to increase and generate secondary pollution. To reduce these disadvantages, there is a need to develop alternative, more sustainable chemicals as substitutes for conventional inorganic coagulants. In the present investigation, the application of a polymeric chitosan quaternary ammonium salt (CQAS) is explored as a complete, or partial, replacement for Al/Fe in the context of sludge dewatering processes. Laboratory experiments using digested sewage sludge showed that CQAS could effectively substitute for over 80 % of the Al/Fe inorganic coagulant in the sludge dewatering process. This substitution resulted in a reduction of sludge cake conductivity by more than 50 %. Simulation of sludge dewatering curves and imaging of the sludge surface indicated that the addition of CQAS led to an increase in nanosized pores, and a decrease in the specific resistance of the sludge filter cake as the dosage of Al/Fe decreased to around 30 %. The variations of fluorescence emission, quantum yield and carboxylic and amino groups, suggested that the chelating of Al/Fe decreased due to the bridging effects of CQAS. The CQAS had different flocculation bridging effects on various EPS fractions, which varied the amount of protein chelated with Al/Fe in each fraction. This study provides new information about the benefits of replacing conventional inorganic coagulants with natural organic polymers for sewage sludge dewatering, in terms of reduced sludge cake conductivity and greater dry solids content.

Photo-induced leaching behaviors and biodegradability of dissolved organic matter from microplastics and terrestrial-sourced particles

Recent studies have increasingly focused on the occurrence of plastic leachate and its impacts on aquatic ecosystems. Nonetheless, the environmental fate of this leachate in the presence of abundant natural organic matter (NOM)-a typical scenario in environments contaminated with plastics-remains underexplored. This study investigates the photo-induced leaching behaviors of dissolved organic matter (DOM) from terrestrial-sourced particles (forest soil and leaf litter) and microplastics (MPs), specifically polystyrene (PS) and polyvinyl chloride (PVC), over a two-week period. We also examined the biodegradability and spectroscopic characteristics of the leached DOM from both sources. Our results reveal that DOM from microplastics (MP-DOM) demonstrates more persistent leaching behavior compared to terrestrial-derived DOM, even with lesser quantities per unit of organic carbon. UV irradiation was found to enhance DOM leaching across all particle types. However, the photo-induced leaching behaviors of fluorescent components varied with the particle type. The MP group exhibited a broader range and higher biodegradability (ranging from 19.7% to 61.6%) compared to the terrestrial-sourced particles (ranging from 3.7% to 16.5%). DOM leached under UV irradiation consistently showed higher biodegradability than that under dark conditions. Furthermore, several fluorescence characteristics of DOM, such as the protein/phenol-like component (%C2), terrestrial humic-like component (%C3), and humification index (HIX)-traditionally used to indicate the biodegradability of natural organic matter-were also effective in assessing MP-DOM (with correlation coefficients R2 = 0.6055 (p = 0.003), R2 = 0.5389 (p = 0.007), and R2 = 0.4640 (p = 0.015), respectively). This study provides new insights into the potential differences in environmental fate between MP-DOM and NOM in aquatic environments heavily contaminated with MPs.

Co-influence of biochar-supported effective microorganisms and seasonal changes on dissolved organic matter and microbial activity in eutrophic lake

DOM (dissolved organic matter) play a crucial role in lakes' geochemical and carbon cycles. Eutrophication evolution would influence nutrient status of waters and investigating the DOM variation helps a better understanding of bioremediation on environmental behavior of DOM in eutrophic lakes. In our study, the contents, compositions and characteristics of systematic DOM&SOM (sediment organic matter) were greatly influenced by seasonal changes. But the effective bioremediations obviously reduced the DOM concentration and thus mitigated the eutrophication outbreak risks in water bodies due to the increased MBC (microbial biomass carbon), microbial activity and metabolism. In early summer, the overall DOM in each treatment were readily low levels and derived from both autochthonous and exogenous origins, dominated by fulvic acid-like. In midsummer, the DOM contents and characteristics in each treatment increased significantly as phytoplankton activity improved, and the majority of DOM were humic acid-like and mainly of biological origin. The greatest differences of enzymes, MBC, microbial metabolism and DOM&SOM removal among different treatments were observed in summer months. In autumn, the systematic DOM&SOM slightly reduced due to the deceased microbial activity, in which the microbial humic acids were main component and derived from endogenous sources. Additionally, the gradually decreased SOM with cultivated time in each treatment was a result of microbiological conversion of SOM into DOM. For various treatments, BE, BE.A, BE.C and BE.E increased the MBC, enzymatic and microbial activities due to the application of biochar-supported EMs. Among these, BE and BE.A, especially BE.A with oxygen supplement, achieved the most desirable effect on reducing systematic DOM&SOM levels and increasing enzymatic and microbial activities. The group of EM also reduced the levels of DOM&SOM as improved degradation of EMs for DOM. However, BC, BE.C and BE.E finally did not achieved the desirable effect on reducing DOM&SOM due to the suppression of microbial activities, respectively, from high dose of biochar, weakening of dominant species and additional introduction of EMs in low liveness.

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.

Simultaneous removal of phosphate, calcium, and ammonia nitrogen in a hydrogel immobilized reactor with bentonite/lanthanum/PVA based on microbial induced calcium precipitation

In recent years, it is urgent to solve nitrogen and phosphorus pollution in domestic wastewater. The target strain Pseudomonas sp. Y1 was immobilized using polyvinyl alcohol (PVA) matrix coupled with bentonite and lanthanum (La), respectively, to fabricate four hydrogel materials that used to construct bioreactors. The optimal operating parameters and dephosphorization mechanism were discussed, and the effects of hydrogel materials and different loads on the performance of the bioreactor were contrastively analyzed. The results manifested that when the hydraulic retention time (HRT) was 6.0 h, the C/N was 6.0, and the Ca²⁺ concentration was 100.0 mg L^-1, the bioreactors had the best heterotrophic nitrification-aerobic denitrification (HNAD) and biomineralization capacity, and the maximum removal efficiencies of Ca²⁺, PO₄^3--P, and NH₄⁺-N were 82.57, 99.17, and 89.08%, respectively. The operation data indicated that the addition of bentonite significantly promoted HNAD, and the bioreactor had stronger dephosphorization ability in the presence of La. The main phosphorous removal mechanisms were confirmed to be adsorption and co-precipitation. Finally, high-throughput sequencing results indicated that Pseudomonas accounted for the paramount proportion in the bioreactor, and the prediction of functional genes indicated that the C/N of 6.0 is more favorable for the expression of nitrogen removal-related functional genes in the bioreactor system. This study highlights the superiority of microbial induced calcium precipitation (MICP) combined with PVA hydrogel, and provides a theoretical basis for simultaneous nitrogen and phosphate removal of wastewater.

Improved fractionation method using amphipathic NDAM for the efficient separation of disinfection by-product precursors in natural organic matter

The hydrophilic substances in natural organic matter (NOM) are the main precursor of disinfection by-products (DBPs) formed during disinfection processes. The fractionation of the components in NOM based on hydrophilicity contributes to elaborating the behavior of NOM during disinfection. However, the traditional NOM fractionation method using two hydrophobic resins of DAX-8 and XAD-4 lays emphasis on the separation of hydrophobic substances, limiting the thorough study of the hydrophilic components in NOM. In this work, the amphiphilic resin NDAM was employed as a replacement of XAD-4 to realize more thorough separation of the hydrophilic substances. Compared with the divinylbenzene (DVB) structure of XAD-4, the NDAM possesses a more hydrophilic skeleton of N-vinylpyrrolidone (NVP) and DVB which favors the adsorption of hydrophilic components in NOM. The two fractionation methods of DAX-8 + XAD-4 and DAX-8 + NDAM were applied to fractionate NOM, and the obtained fractions were characterized via fluorescence spectra, UV spectra, acid-base titration, the partition coefficients of aqueous two-phase systems(ATPs), and 1H nuclear magnetic resonance (1H-NMR). The results showed that the transphilic fractions separated by XAD-4 accounted for 11.09% of NOM, while the proportion increased to 20.33% with the method of NDAM fractionation. Besides, the hydrophilic components enriched by NDAM not only have more π-conjugated systems and more aromatic structure but also contain more oxygen-containing and nitrogen-containing functional groups. In addition, the hydrophilic fractions separated by NDAM contained more DBP precursors. The NDAM separates more NOM which can produce bromine-containing DBPs into HPIA, and the DBP productivity of HPIN is significantly higher than that of XAD-4. In general, the NOM fractionation method proposed in this study utilizing NDAM resin could fractionate the hydrophilic fractions in NOM more thoroughly, showing application potential in the analysis and control of DBPs formed from NOM.

Unravelling relationships between fluorescence spectra, molecular weight distribution and hydrophobicity fraction of dissolved organic matter in municipal wastewater

The characteristics of dissolved organic matter (DOM) in the influent and secondary effluent from 6 municipal wastewater treatment plants (WWTPs) were investigated with a size exclusion chromatogram (SEC) coupled with multiple detectors to simultaneously detect ultraviolet absorbance, fluorescence, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) as a function of molecular weight (MW). The SEC chromatograms showed that biopolymers (>6 kDa) and humic substances (0.5-6 kDa) comprised the significant fraction in the influent, while humic substances became the abundant proportion in the secondary effluent. Direct linkages between MW distribution and hydrophobicity of DOM in the secondary effluent were further explored via SEC analysis of XAD resin fractions. DON and DOC with different hydrophobicity exhibited significantly distinct MW distribution, indicating that it was improper to consider DOC as a surrogate for DON. Different from DOC, the order of averaged MW in terms of DON was hydrophobic neutral ≈ transphilic neutral > hydrophobic acid > transphilic acid > hydrophilic fraction. Fluorescence spectral properties exhibited a significant semi-quantitative correlation with MW and hydrophobicity of DOC, with Pearson's coefficients of -0.834 and 0.754 (p < 0.01) for biopolymer and humic substances. Meanwhile, regional fluorescence proportion was demonstrated to indicate the MW and hydrophobicity properties of DON at the semi-quantitative level. The fluorescence excitation-emission matrix (EEM) could be explored to provide a rapid estimation of MW distribution and hydrophobic/hydrophilic proportion of DOC and DON in WWTPs.

Synchronous removal of ammonia nitrogen, phosphate, and calcium by heterotrophic nitrifying strain Pseudomonas sp. Y1 based on microbial induced calcium precipitation

Pseudomonas sp. Y1, a strain with superior synchronous removal ability of ammonia nitrogen (NH₄⁺-N), phosphate (PO₄^3--P), and calcium (Ca²⁺) was isolated, with the removal efficiencies of 92.04, 99.98, and 83.40 %, respectively. Meanwhile, the chemical oxygen demand (COD) was degraded by 90.33 %. Through kinetic analysis, the optimal cultivated conditions for heterotrophic nitrification-aerobic denitrification (HNAD) and biomineralization were determined. The growth curves experimental results of different nitrogen sources indicated that strain Y1 could remove NH₄⁺-N through HNAD. The results of excitation-emission matrix (EEM) proved that the appearance of extracellular polymeric substances (EPS) promoted the precipitation of phosphate minerals. Finally, the characterization results of the bioprecipitates showed that the HNAD process produced the alkalinity required for microbial induced calcium precipitation (MICP), resulting in the removal of PO₄^3- via adsorption and co-precipitation. This study provides a theoretical basis for the application of microorganisms to achieve synchronous nutrient removal and phosphorus recovery in wastewater.

Advanced oxidation processes and selection of industrial water source: A new sight from natural organic matter

Natural organic matter (NOM) refers to the dissolved organic matter in natural water that can pass through 0.45 μm filter membrane. As a pivotal role in the surface water body, it has a significant effect on the efficiency of AOPs. In this study, Excitation emission matrix - parallel factor (EEM-PARAFAC) analysis is used to elucidate the changes of NOM fluorescence peaks after electrochemical oxidation process, two-dimensional correlation spectroscopy (2D-FTIR-COS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) are utilized to clarify the molecular characteristics of NOM in surface water and the effects of electrochemical oxidation on NOM molecules. The results indicate that parts of NOM molecules are mineralized into simple compounds and precursors of refractory organic matters produced by some NOM molecules after AOPs. It is concluded that the precursors of these refractory organic matters may belong to terrestrial humus (C2). Therefore, for the purpose of avoiding more refractory organic pollutants produced by NOM which can reduce the performance of AOPs in the water treatment process, factories should choose water sources with less humus as industrial water supply, or degrade humus by physical or chemical methods before industrial water supply.

Fluorescence excitation-emission matrix as a novel indicator of assimilable organic carbon in wastewater: Implication from a coal chemical wastewater study

Assimilable organic carbon (AOC) is recognized as an important parameter to evaluate the biostability of water. Studies have been carried out to investigate the easier and faster AOC detection methods in recent years. In our study, the relationship between AOC and excitation-emission matrix (EEM) was investigated through analysis of wastewater from a coal chemical industrial corporation, including biochemical effluent, ultrafiltration effluent, and reverse osmosis concentrate. Considering the influence of water sample properties on AOC distribution, these water samples were fractionated according to their hydrophilicity and acid/base properties. Neutrals and hydrophobic acids were major components of total organic carbon and AOC concentration of these fractions was measured. EEM spectra of water samples were divided into five regions according to fluorescence peaks. Distribution of fluorescence region integration (FRI) of water samples was also calculated, as well as other fluorescence parameters. Statistical analysis showed that the concentration of AOC presented high positive correlation with the FRI in region H2, with R² = 0.696. Monte Carlo simulation also proved that the proportion of significant R² (p < 0.05) was high at 89.1%, suggesting that the model was reliable at least at the qualitative level. In that case, FRI in Region H2 could be an indication for AOC concentration in water samples. Our findings focus on fundamental insights into establishing relationship between spectroscopy method and AOC in wastewater and provide an easier way of accessing AOC in coal chemical industrial wastewater. Further investigation could be oriented to the dynamic analysis of AOC transformation and tracing.

Spectroscopic fingerprints to track the fate of aquatic organic matter along an alpine headstream on the Tibetan Plateau

The fragile aquatic ecosystem on the Tibetan Plateau is severely threatened by human activities and climate change. Dissolved organic matter (DOM) is a vital indicator of surface water quality; however, its comprehensive molecular analysis is challenged due to its low concentration (total organic carbon less than 0.5 mg/L) in alpine areas. This study proposes the fluorescence excitation-emission matrix (FEEM) to fingerprint DOM in a typical headstream in the Namco basin, one of the largest lake regions in Tibet. We found that the FEEM can sensitively detect low-concentration pollution traces and the variation of DOM along the flow from the ice sheet, through the wetland, eventually to the estuary of the lake. The fluorescence intensity indices for biodegradable carbon (f_T/C) and humification (HIX_em) responded drastically along the flow. Fluorescence regional integrals (FRIs) clearly reflected the overall increase of protein-like substances and decrease of humus-like substances along the flow, whereas this tendency was reversed when passing through the wetland. The FRIs-derived secondary parameters (HPP, HMP, WLP and SSP) further sensed likely variations in hydrophobicity, humification degree, excited-state fluorophore energy and Stokes shift. Parallel factor analysis (PARAFAC) and two-dimensional correlation spectroscopy (2DCOS) of the FEEM signals witnessed the trade-off among tyrosine-like organics (C1 peak), tryptophan-like byproducts (C2 peak) and humus-like remains (C3 peak) along the flow. The C1 component can be traced back to the vicinity of the ice sheet exit, presumably due to human and animal activities. The wetland can absorb or convert part of the C1 component into C2 or C3 products, demonstrating the function of regulating water quality and buffering environmental impacts. The spectroscopic indicators evaluated in this study may provide tools for diagnosing early traces of water pollution and ecological instability in alpine areas.

Potential release of dissolved organic matter from agricultural residue-derived hydrochar: Insight from excitation emission matrix and parallel factor analysis

Potential release quantity and quality of dissolved organic matter (DOM) from hydrochar (HDOM) in various environmental conditions were investigated. Corn cobs were utilized as model agricultural residue to prepare the hydrochar. Four extracts, ultra-pure water, acid solution, alkali solution and salt solution, and two temperatures, 20 °C and 60 °C, were adopted to imitate various environmental conditions. Excitation-emission spectrophotometry with parallel factor analysis was used to evaluate the chemical properties of HDOM. The results showed that the dissolved organic carbon in the HDOM was high, ranging from 46 to 268 mg g^-1. Four components were confirmed in the HDOM: mixed substances of humic-like and protein-like components, marine humic-like substances, terrestrial humic-like substances and tyrosine-like substances. Alkalinity and high temperature conditions could enhance the leaching amount of HDOM, particularly humic-like substances, and change the relative proportion of components and the chemical quality. In addition, values of the fluorescence indexes indicated that the HDOM was high microbial availability. Released HDOM may result in significant impacts in ecosystem functionality. These findings reveal the potential release characteristics of HDOM in the environment, opening new doors to understanding the environmental impacts of hydrochar and guiding its rational application.

A year-long cyclic pattern of dissolved organic matter in the tap water of a metropolitan city revealed by fluorescence spectroscopy

Delivering drinking water with stable quality in metropolitan cities is a big challenge. This study investigated the year-long dynamics of dissolved organic matter (DOM) in the tap water and source water of a metropolitan city in southern China using fluorescence spectroscopy. The DOM detected in the tap water, and source water of Shenzhen city was season and location-dependent. A year-long cyclic trend of DOM was found with predominate protein-like fluorescence in the dry season compared to the humic-like enriched DOM in the wet season. A general DOM pattern was estimated by measuring the shift in dominant fluorescence regions on the excitation-emission matrix (EEM). The difference in fluorescent DOM (FDOM) composition (in terms of the ratio of protein-like to humic-like fluorescence) was above 200% between wet and dry seasons. The taps associated with reservoirs receiving water from the eastern tributary of Dongjiang River showed significant changes in protein-like contents than the taps with source water originating from the western part of the river. This study highlights the importance of optimizing drinking water treatment plants' operational conditions after considering seasonal changes and source water characteristics.

Using excitation-emission matrix fluorescence to evaluate the performance of water treatment plants for dissolved organic matter removal

This study is aimed at assessing the performance of water treatment plants (both wastewater and drinking water treatment plants) for dissolved organic matter (DOM) removal using excitation-emission matrix fluorescence (EEMF) as the monitoring technique. The influent from the wastewater treatment plant (WWTP) of Burgos (Spain) is characterized from the presence of protein-like peaks (T1 and T2) and humic-like peaks (A and C), T2 and A showing the highest fluorescence intensity. The percentages of total removal in the effluent were in the following order: peak T1 (65%) > peak A (45%) > peak C (34%) > peak T2 (26%). The humic-like peaks were the most removed at the primary sedimentation stage, whereas peak T1 was by far the most removed in the biological reactor. Protein-like peaks T1 and T2 experienced a slight increase in the final effluent in comparison to their fluorescence at the previous stage (the exit of the biological reactor), an increase that can be explained by the release of SMP (soluble microbial products) from the biomass in the secondary clarifier. A poor correlation was obtained between peak T2 fluorescence and COD, BOD (r² = 0.34-0.38). The natural water from the Úzquiza reservoir in Burgos (Spain) is characterized by the only presence of humic substances: a majority peak A (fulvic-like) and a weak peak C (humic-like). The whole fluorescent DOM was removed by coagulation-flocculation but a low fluorescence peak T2 appeared at the final stage, coming from protein-like SMPs released by the biomass attached to the filters.

Monitoring dissolved organic matter in wastewater and drinking water treatments using spectroscopic analysis and ultra-high resolution mass spectrometry

Dissolved organic matter (DOM) plays a critical role in determining the quality of wastewater and the safety of drinking water. This is the first review to compare two types of popular DOM monitoring techniques, including absorption spectroscopy and fluorescence excitation-emission matrices (EEMs) coupled with parallel factor analysis (PARAFAC) vs. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), for the applications in wastewater and drinking water treatments. The optical techniques provide a series of indices for tracking the quantity and quality of chromophoric and fluorescent DOM, while FT-ICR-MS is capable of identifying thousands of DOM compounds in wastewater and drinking water at the molecule level. Both types of monitoring techniques are increasingly used in studying DOM in wastewater and drinking water treatments. They provide valuable insights into the variability of DOM composition in wastewater and drinking water. The complexity and diversity of DOM highlight the challenges for effective water treatments. Different effects of various treatment processes on DOM are also assessed, which indicates that the information on DOM composition and its removal is key to optimize the treatment processes. Considering notable progress in advanced treatment processes and novel materials for removing DOM, it is important to continuously utilize these powerful monitoring tools for assessing the responses of different DOM constituents to a series of treatment processes, which can achieve an effective removal of DOM and the quality of treated water.