Dissolved Organic Matter Removal Research Articles

Capabilities of Microbial Consortia from Disparate Environment Matrices in the Decomposition of Dissolved Organic Matter by Biofiltration

Dissolved organic matter (DOM) plays a pivotal role in drinking water treatment, influencing the performance of unit processes and final water quality (e.g. disinfection byproduct risk). Biofiltration is an effective method of reducing DOM, but currently lacks a comprehensive appreciation of the association between microbial profiles and biofiltration performance. In this study, bench-scale biofiltration units inoculated with microbial consortia from river and soil matrices were operated successively for comparing their efficacy in terms of DOM removal. The results showed that biofiltration units receiving soil microbes were significantly superior (p<0.05) to those receiving river inoculated microbes in terms of decomposing DOM recalcitrant fractions and reducing DBP formation potential, resulting in DOC and DBP precursor removals of up to 58.4% and 87.9%, respectively. Characterization of the taxonomic composition revealed that differences in the microbial assembly of the two biofilter groups were subject to deterministic rather than stochastic factors. Furthermore, more complicated interspecific relationships and niche structures in soil inoculated biofilters were deciphered by co-occurrence network, providing a plausible profile on a taxonomic division of labor in DOM stepwise degradation. Accordingly, the contribution of microbial compositions was found to be of greater importance than the GAC mass and biomass attached to the media. Thus, this study has advanced the understanding of microbial-mediated DOM decomposition in biofiltration, and also provided a promising strategy for enhancing the process for water use via developing appropriate engineered consortia of bacteria.

Purifying surface water contaminated with azo dyes using nanofiltration: Interactions between dyes and dissolved organic matter

In this research, the interactions of two azo dyes, Methyl Orange (MO) and Eriochrome Black T (EBT), with dissolved organic matter (DOM) in surface water were studied, emphasizing their removal using nano-filtration membranes (NF-270 and NF-90). High-Performance Size Exclusion Chromatography (HPSEC) findings indicated that the dyes' molecular weight in deionized (DI) water ranged from 500 to 15k Dalton (Da), adjusting peak intensities with Jingmi River (JM) water Beijing. Notably, when dyes were diluted in JM water, ultraviolet (UV533 &466, and UV254), together with total organic carbon (TOC) parameters, revealed color removal rates of 99.49% (EBT), 94.2% (MO), 87.6% DOM removal, and 86% TOC removal for NF-90. The NF-90 membrane demonstrated a 75% flux decline for 50 mL permeate volume due to its finer pore structure and higher rejection effectiveness. In contrast, the NF-270 membrane showed a 60% decline in flux under the same conditions. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) analysis of dye-treated membranes in JM water revealed that the NF-270 showed a CC bond peak at 1660 cm−1 across various samples, while analyzing NF-90, the peaks at 1400 cm−1, 1040 cm−1, 750 cm−1, and 620 cm−1 disappeared for composite sample removal. The hydrophobicity of each membrane is measured by the contact angle (CA), which identified that initial CAs for NF-270 and NF-90 were 460 and 700, respectively, that were rapidly declined but stabilized after a few seconds of processing. Overall, this investigation shows that azo dyes interact with DOM in surface waters and enhance the removal efficiency of NF membranes.

Constructing S-scheme Au/g-C3N4/BiVO4 heterojunction with peroxymonosulfate-enhanced photocatalytic activity and mechanism insight

Dissolved organic matter (DOM) in black-odorous water can cause excessive growth of plants and algae, leading to deterioration of water quality. Herein, an S-scheme Au/g-C3N4/BiVO4 heterojunction was constructed using a three-step method for DOM degradation in real black-odorous water in the presence of peroxymonosulfate (PMS). 4Au/g-C3N4/BiVO4/PMS exhibited highly efficient photocatalytic performance, and the DOM removal rate could reach 92.9 %, which was 19.1 and 9.9 times higher than that of g-C3N4/PMS and BiVO4/PMS, respectively. The changes of fluorescence components in DOM were detected using synchronous fluorescence spectra and two-dimensional correlated spectroscopy analysis, and the toxicity of catalytically treated black-odorous water was evaluated by growth inhibition of Escherichia coli. A reasonable S-scheme mechanism was suggested by theoretical calculations and photoelectrochemical tests. The S-scheme mechanism and the synergistic effect of photocatalysis and hybrid advanced oxidation process (HAOP) increased the catalytic activity of Au/g-C3N4/BiVO4/PMS.

The removal of pathogenic bacteria and dissolved organic matter from freshwater using microporous membranes: insights into biofilm formation and fouling reversibility

Pathogenic bacteria in drinking-water pose a health risk to consumers, as they compromise the quality of portable water. Chemical disinfection of water containing dissolved organic matter (DOM) causes harmful disinfection by-products. In this work, 4-hydroxybenzoic acid (4-HBA) blended polyethersulfone membranes were fabricated and characterised using microscopic and spectroscopic techniques. The membranes were evaluated for the removal of bacteria and DOM from synthetic and environmental water. Permeate flux increased from 287.30 to 374.60 l m−2 h−1 at 3 bars when 4-HBA increased from 0 to 1.5 wt.%, suggesting that 4-HBA influenced the membrane’s affinity for water. Furthermore, 4-HBA demonstrated antimicrobial properties by inhibiting bacterial growth. The membrane with 1 wt.% 4-HBA recorded 99.4 and 100% bacteria removal in synthetic and environmental water, respectively. Additionally, DOM removal of 55–73% was achieved. A flux recovery ratio (FRR) of 94.6% was obtained when a mixture of bacteria and humic acid was filtered, implying better fouling layer reversibility during cleaning. Furthermore, 100% FRR was achieved when a multimedia granular filtration step was installed prior to membrane filtration. The results illustrated that the membranes had a high permeate flux with low irreversible fouling. This indicated the potential of the membranes in treating complex feed streams using simple cleaning protocols.

Comparison on molecular transformation of dissolved organic matter during Fenton and activated carbon adsorption processes for chemical cleaning wastewater treatment

This study employed Fenton oxidation and powdered activated carbon (PAC) adsorption processes for the removal of recalcitrant dissolved organic matter (DOM) in chemical cleaning wastewater (CCW) to meet discharge standards. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to identify resistant compounds and investigate the transformation characteristics of DOM. CCW mainly contained surfactant exhibiting heteroatom-rich characteristics, and both processes exhibited effective DOM removal but distinct selectivity towards different subclasses of formulas. PAC adsorption significantly decreased the number of DOM compounds and more effective in aromatic compounds than Fenton oxidation. The aliphatic compounds (AImod ≤ 0.5, 1.5 ≤ H/C ≤ 2.0) predominantly with saturated and reduced states were resistant to PAC adsorption, and particularly a specific CHONSP formula was the predominant contributor to residual DOM in the effluent. In contrast, Fenton oxidation degraded most substances in the CCW except for a few saturated and reduced compounds primarily consisting of CHO, resulting in an increase in DOM number. Two unsaturated subclasses, carboxylic-rich alicyclic molecules/lignin-like structures (primarily CHON) and carbohydrates (primarily CHONP and CHONSP), were prominently produced after Fenton oxidation. The major mechanisms governing Fenton oxidation of surfactant in CCW primarily involved dealkylation (25.2 %), oxygen addition (21.2 %), and decarboxylation (19.8 %). Given the unique removal preferences and resistance observed in Fenton and PAC processes, a combination approach could be explored in the future to achieve advanced overall performance.

Activation of iron oxide minerals in an aquifer by humic acid to promote adsorption of organic molecules

In aquifers, the sequestration and transformation of organic carbon are closely associated with soil iron oxides and can facilitate the release of iron ions from iron oxide minerals. There is a strong interaction between dissolved organic matter (DOM) and iron oxide minerals in aquifers, but the extent to which iron is activated by DOM exposure to active iron minerals in natural aquifers, the microscopic distribution of minerals on the surface, and the mechanisms involved in DOM molecular transformation are currently unclear. This study investigated the nonbiological reduction transformation and coupled adsorption of iron oxide minerals in aquifers containing DOM from both macro- and micro perspectives. The results of macroscopic dynamics experiments indicate that DOM can mediate soluble iron release during the reduction of iron oxide minerals, that pH strongly affects DOM removal, and that DOM is more efficiently degraded at low rather than high pH values, suggesting that a low pH is conducive to DOM adsorption and oxidation. Spherical aberration-corrected scanning transmission electron microscopy (SACTS) indicates that the reacted mineral surfaces are covered with large amounts of carbon and that dynamic agglomeration of iron, carbon, and oxygen occurs. At the nanoscale, three forms of DOM are found in the mineral surface agglomerates (on the surfaces, inside the surface agglomerates, and in the polymer pores). The microscopic organic carbon and iron mineral reaction patterns can form through oxidation reactions and selective adsorption effects. Fourier transform ion cyclotron resonance mass spectra indicate that both synergistic and antagonistic reactions occur between DOM and the minerals, that the release of iron is accompanied by DOM decomposition and humification, that large oxygen- and carbon-containing molecules are broken down into smaller oxygen- and carbon-containing compounds and that more molecules are produced through oxidation under acidic rather than alkaline conditions. These molecules provide adsorption sites for sediment, meaning that more iron can be released. Microscopic evidence for the release of iron was acquired. These results improve the understanding of the geochemical processes affecting iron in groundwater, the nonbiological transformation mechanisms that occur at the interfaces between natural iron minerals and organic matter, groundwater pollution control, and the environmental behavior of pollutants.

Unraveling the characteristics of dissolved organic matter removed by aluminum species based on FT-ICR MS analysis

Given the complexity of dissolved organic matter (DOM) and its interactions with coagulant chemicals, the mechanisms of DOM removal by aluminum (Al) coagulants remains a significant unknown. In this study, six test waters containing DOM with molecular weight (MW, <1 kDa, 1–10 kDa and >10 kDa) and hydrophobicity (hydrophilic, transphilic and hydrophobic) were prepared and coagulated with Al0, Al13 and Al30. The molecular-level characteristics of DOM molecules that were removed or resistant to removal by Al species were analyzed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results showed that at the molecular level, saturated and reduced tannins and lignin-like compounds containing abundant carboxyl groups exhibited higher coagulation efficiency. Unsaturated and oxidized lipids, protein-like, and carbohydrates compounds were relatively resistant to Al coagulation due to their higher polarity and lower content of carboxyl groups. Al13 removed molecules across a wider range of molecular weights than Al0 and Al30, thus the DOC removal efficiency of Al13 was the highest. This study furthers the understanding of interactions between Al species and DOM, and provides scientific insights on the operation of water treatment plants to improve control of DOM.

Purification of dredged water by magnetic coagulation: Response surface optimization and dissolved organic matter removal characteristics.

In the present study, magnetic coagulation was used to treat dredged water and the response surface method was used to optimize process parameters. The dissolved organic matter (DOM) removal characteristics were characterized by three-dimensional fluorescence spectrometry and ultra-high resolution mass spectrometry. During the magnetic coagulation process, the suspended solids (SS) removal rate increased initially and then decreased under conditions of increasing magnetic powder dosage and stirring rate. After magnetic coagulation and precipitation for 20 min, the contents of SS, ammonia nitrogen, chemical oxygen demand, and total phosphorus in the treated dredged water met the requirements of the discharge standard (GB8978-1996, China). Three-dimensional fluorescence results showed that magnetic coagulation selectively removed fulvic acids and humic acid substances. After magnetic coagulation with precipitation for 10min and 20 min, the total relative content of lignins, tannins, proteins, lipids, aminosugars, unsaturated hydrocarbons, condensed aromatic structures, and carbohydrates decreased by 26.3% and 39.4%, respectively. After magnetic coagulation, the distribution range of small molecule DOM shifted to the low H/C and high O/C regions. This study provides a novel perspective for studies on the removal of DOM in dredged water by magnetic coagulation. PRACTITIONER POINTS: SS and DOM removal were significantly enhanced by the use of magnetic coagulation. SS removal efficiency was affected by stirring rate and magnetic powder dosage. Magnetic coagulation selectively removed fulvic acids and humic acid substances. DOM molecule shifted to low H/C and high O/C regions after magnetic coagulation.

The combined effects of lanthanum-modified bentonite and Vallisneria spiralis on phosphorus, dissolved organic matter, and heavy metal(loid)s

The use of lanthanum-modified bentonite (LMB) combined with Vallisneria spiralis (V∙s) (LMB + V∙s) is a common method for controlling internal phosphorus (P) release from sediments. However, the behaviors of iron (Fe) and manganese (Mn) under LMB + V∙s treatments, as well as the associated coupling effect on P, dissolved organic matter (DOM), and heavy metal(loid)s (HMs), require further investigations. Therefore, we used in this study a microelectrode system and high-resolution dialysis technology (HR-Peeper) to study the combined effects of LMB and V∙s on P, DOM, and HMs through a 66-day incubation experiment. The LMB + V∙s treatment increased the sediment DO concentration, promoting in-situ formations of Fe (III)/Mn (IV) oxyhydroxides, which, in turn, adsorbed P, soluble tungsten (W), DOM, and HMs. The increase in the concentrations of HCl-P, amorphous and poorly crystalline (oxyhydr) oxides-bound W, and oxidizable HMs forms demonstrated the capacity of the LMB + V∙s treatment to transform mobile P, W, and other HMs forms into more stable forms. The significant positive correlations between SRP, soluble W, UV254, and soluble Fe (II)/Mn, and the increased concentrations of the oxidizable HMs forms suggested the crucial role of the Fe/Mn redox in controlling the release of SRP, DOM, and HMs from sediments. The LMB + V∙s treatment resulted in SRP, W, and DOM removal rates of 74.49, 78.58, and 54.78 %, which were higher than those observed in the control group (without LMB and V∙s applications). On the other hand, the single and combined uses of LMB and V·s influenced the relative abundances of the sediment microbial communities without exhibiting effects on microbial diversity. This study demonstrated the key role of combined LMB and V∙s applications in controlling the release of P, W, DOM, and HMs in eutrophic lakes.

Removal of dissolved organic matter via a combination of UV/persulfate oxidation and biological activated carbon (BAC) process

The combination process of UV/peroxydisulfate (UV/PDS) oxidation and BAC (UV/PDS-BAC) is examined as an advanced treatment for conventional drinking water treatment through a continuous flow experimental apparatus with actual sand filter effluent as feed water. The effect of three key parameters (UV dosage, PDS dosage, and water temperature) on dissolved organic matter (DOM) is evaluated via long-term monitoring data. The removal behavior of DOM in the UV/PDS-BAC process is also compared with that in the O3-BAC process. Further, this study delves into the mechanisms behind the enhanced DOM removal achieved by UV/PDS-BAC. The achieved results reveal that impressive removal rates of 42.1 % for total organic carbon (TOC) and 62.9 % for UV254 could be achieved in the presence of specific conditions: a UV input of 200 mJ/cm2 and a PDS dosage of 0.5 mM. The efficiency of DOM removal by UV/PDS-BAC exhibits a positive correlation with the UV dosage ranging from 50 to 200 mJ/cm2, and the water temperature in the range of 4–30 ℃. While increasing the PDS dosage from 0.01 to 0.5 mM results in improved DOM removal, any further increase yields reduced removal efficiency. In comparison, subjected to similar operating conditions, UV/PDS-BAC outperforms O3-BAC in removing DOM. The superior DOM removal achieved by the UV/PDS-BAC process can be essentially attributed to several factors: firstly, it exhibits excellent mineralization capacity for low molecular weight organics (<1 kDa) and leads to increased biodegradable fraction of organics by oxidatively degrading DOM with a molecular weight >3 kDa. Secondly, the appropriate exposure of activated carbon pores is chiefly maintained by suitably controlling the biomass. Lastly, the enhanced biodegradability of BAC influent stimulated the growth of bacteria proficient in degrading DOM.

Coagulation pretreatment coupled with indigenous microalgal-bacterial consortium system for on-site treatment of rural black wastewater

Improper treatment of rural black wastewater (RBW) presents substantial challenges, including the wastage of resource, environmental contamination, and economic consequences. This study proposed an integrated process for RBW treatment, consisting of coagulation/flocculation (C/F) pretreatment and subsequent inoculation of indigenous microalgal-bacterial consortium (IMBC) for nitrogen recovery, namely C/F-IMBC process. Specifically, the optimal C/F conditions (polyaluminium chloride of 4 g/l, polyacrylamide of 50 mg/l, and pH of 6) were determined through a series of single-factor experiments, considering CN, turbidity, and dissolved organic matter (DOM) removal, economic cost, and potential influence on the water environment. Compared to the sole IMBC system for RBW treatment, the proposed C/F-IMBC process exhibited a remarkable 1.23-fold increase in microalgal growth and a substantial 17.6–22.6 % boost in nitrogen recovery. The altered RBW characteristic induced by C/F pretreatment was supposed to be responsible for the improved system performance. In particular, the abundance of DOM was decreased and its composition was simplified after C/F pretreatment, based on the analysis for excitation-emission matrices with parallel factor and gas chromatography–mass spectrometry, thus eliminating the potential impacts of toxic DOM components (e.g., Bis(2-ethylhexyl) phthalate) on IMBC activity. It should also be noted that C/F pretreatment modified microbial community structure as well, thereby regulating the expression of nitrogen-related genes and enhancing the system nitrogen recovery capacity. For instance, the functional Cyanobacteria responsible for nutrient recovery was enriched by 1.95-fold and genes involved in the assimilatory nitrate reduction to ammonia pathway were increased by 1.52-fold. These fundamental findings are expected to offer insights into the improvement of DOM removal and nitrogen recovery for IMBC-based wastewater treatment system, and provide valuable guidance for the development of sustainable on-site RBW treatment technologies.

RETRACTED: Enhanced biofiltration coupled with ultrafiltration process in marine recirculating aquaculture system: Fast start-up of nitrification and long-term performance

In marine recirculating aquaculture systems (RAS), the biological nitrification system usually suffers from long time start-up and proliferation of potential pathogenic bacteria under the high salinity stress. This study aims to develop a strategy for fast start- up and long-term biosecurity of marine RAS by using a combined biofiltration system (ceramic rings (CR) - granular activated carbon (GAC) - ultrafiltration (UF) process) in an actual marine RAS for selenotoca multifasciata. The ammonia nitrogen and dissolved organic matter (DOM) removal performance, membrane fouling characteristics and microbial communities during long-term operation (200 days) were investigated. The CR-GAC-UF process minimized the start-up time of the nitrification system to 14 days under low ammonia concentrations (below 2 mg/L). Long-term operation of the marine RAS with ammonia and nitrite nitrogen stabilized below 0.1 mg/L with a daily ammonia nitrogen removal rate of 91.7 %. The UF membranes were operated at fluxes at 15 LHM and the protein/polysaccharide ratios of soluble microbial products (SMP) and extracellular polymeric substances (EPS) on the membranes were stable below 0.5 with low fouling levels. A number of bacterial genera that have the potential to degrade protein and humic-like substances were recognized, which was related to the long-term DOM removal. Candidatus_Nitrosopumilus, Nitrosomonas_sp. and Nitrospira sp. ENR4 were detected as the core nitrifiers in CR-GAC-UF process, which were closely related to the amoABC, hao and nxrA genes (p < 0.05). With the multi-stage barrier of CR-GAC-UF, the heterotrophic plate count in therecirculating water was kept at 3 ± 1 CFU/mL and the relative abundance of potential pathogens declined gradually below 0.81 %. Taken together, this study provides a theoretical basis for the wider application of marine RAS.

New insights into the adsorptive characteristics of trihalomethane precursors from surface water using magnetic powdered activated carbon

Powdered activated carbon (PAC) can effectively eliminate dissolved organic matter (DOM) as a precursor of trihalomethane (THM), but its application has raised concerns regarding its separation and the overelevated formation of brominate THM species in treated water after chlorination. Although magnetic PAC (Mag-PAC) has been proposed as an easily separable adsorbent for water treatment, its removal by Mag-PAC remains unknown. In this study, a novel Mag-PAC adsorbent for removing DOM and controlling THM formation from surface water was fabricated, evaluated using batch experiments, and compared with PAC. Our results found that Mag-PAC blended the advantages of PAC and magnetic particles, having an efficient removal performance toward DOM with an adsorption capacity of 2.84–3.69 mg-C/g and good magnetic separability of 10.15 emu/g. The iron oxide coating on the carbon matrices was predominantly distributed in the presence of crystalline goethite and magnetite structures. Chemisorption was the dominant mechanism of DOM adsorption by Mag-PAC. The sorption rate of DOM was influenced by the impregnation of iron oxide, but such impregnation did not significantly affect the DOM adsorption capacity. Aromatic DOM, humic-acid and fulvic-acid like compounds were efficiently adsorbed by the Mag-PAC. Compared with PAC, Mag-PAC exhibited a higher reduction in lifetime cancer risks from THMs through the ingestion pathway by decreasing the formation potential of trichloromethane and bromodichloromethane, which generated high unit risks among various THM species. These findings highlight the potential of Mag-PAC as an effective sorbent for DOM removal to control the formation of THM in surface water.

MIEX resin and enhanced coagulation treatment of high-bromide natural water: Chlorine reactivity and DBP precursors removal

Both organic and inorganic constituents play a major role in the formation and speciation of disinfection by-products (DBPs) under chlorination. In this study, the removal of organic and inorganic precursors to DBPs by ion exchange and coagulation was examined, and the relationships between characteristics of dissolved organic matter (DOM), chlorine reactivity, and the formation of DBPs in high-bromide natural water were investigated. Formation potential tests were conducted for trihalomethanes (THMs) and haloacetronitriles (HANs) before and after the different treatments (coagulation, magnetic ion exchange (MIEX) resin, and combined MIEX/coagulation). At a low resin dose, MIEX was more effective than coagulation for DOM removal. The advantages of the MIEX resin were more prominent at a high resin dose because substantial amounts of DOM and bromide were simultaneously removed. The maximum bromide uptake on the MIEX resin was 0.02 mg-Br/mL. A 4-component PARAFAC model was developed using a dataset of 148 fluorescence excitation-emission matrices (EEMs) generated from pre-chlorinated and post-chlorinated samples. The maximum fluorescence intensities of humic-like components were found to be strongly correlated to THMs formation (R2 = 0.79–0.89). The MIEX treatment substantially lowered the formation of THMs (19–51%) and HANs (70–95%) due to its ability to remove humic-like DOM and bromide. The fluorescence loss for humic-like DOM was found to increase over a chlorination time of 3 days, suggesting that these compounds had stronger reactivity to chlorine compared to protein-like DOM. The chlorine reactivity of protein-like DOM increased after treatments as the residual chlorine was able to react with the less reactive fractions of DOM after chlorine-reactive compounds were removed.

Effect of granular activated carbon adsorption on mitigating microfiltration membrane fouling by algal organic matter

Abstract Algal blooms can seriously affect the operation of water treatment processes including low-pressure (micro- and ultrafiltration) and high-pressure (nanofiltration and reverse osmosis) membranes mainly due to the accumulation of algae-derived organic matter (AOM). This study investigated the effect of granular activated carbon (GAC) pretreatment on PVDF microfiltration performance for the removal of AOM. Dissolved organic matter (DOM) solution of commercial humic acid, extra- and intracellular organic matter from two species of algae, and Cyanobacteria were used for the investigation of the fouling potential of the membrane. A comparison study of different DOM removal and fouling behaviors of microfiltration (MF) after GAC adsorption as pretreatment was evaluated under variable GAC dosage and solution pH. Almost 15–20% improvement in flux and decline in irreversible fouling occurred due to the pretreatment using 1.0 g/L of GAC for an hour. The intracellular material caused higher membrane fouling than humic acid due to the hydrophilic nature of the AOM. Membrane fouling and decline in flux increased with increasing pH in the range of 5.0–8.0. The comparison results might help to provide insights into the real challenge of dealing with the treatment of algal-laden water.

Removal performance of dissolved organic matter from municipal secondary effluent by different advanced treatment processes and preventing the formation of disinfection by-products.

Various advanced treatment processes including ultrafiltration (UF), ozonation, enhanced coagulation, and biological aerated filter (BAF) have been applied to reduce dissolved organic matter (DOM) from the secondary effluent of municipal wastewater treatment plants (MWTPs). In this study, DOM were characterized and the relationship between DOM characteristics and disinfection by-products (DBPs) generation was investigated systematically. Results showed that BAF and ozonation processes could significantly affect DOM characteristics in the treated effluents and the following DBP generation. UF and enhanced coagulation reduced the production of DBPs by removing large molecular hydrophobic organics. The removal of low molecule DOM by BAF resulted in a 67.6% reduction in trihalomethanes (THMs) production. Ozonation could oxidize large hydrophobic DOM into small hydrophilic molecules containing aldehyde and ketone groups, leading to 54% increase of halogenated aldehydes (HALs) and halogenated ketones (HKs). Humic acid (HA) was the main organic type in DOM and important precursor for THMs and dichloroacetonitrile (DCAN) formation. The generation of trichloromethane (TCM) showed a significant positive correlation (R2 = 0.987) with the specific ultraviolet absorbance at 254nm (SUVA). Large molecule hydrophobic DOM devoted the most to the formation of carbonaceous disinfection by-products and [Formula: see text]-N content was an important factor affecting the generation of nitrogenous disinfection by-products. These results are important for the optimization of advanced treatment process in MWTPs, and controlling DBPs should consider the removal of low MW hydrophobic DOM and the reduction of SUVA.

The effect and spectral response mechanism of dissolved organic matter (DOM) in Pb(II) adsorption onto biochar

This study investigated the interaction of biochar-derived dissolved organic matter (DOM) and metal pollutant Pb(II) during adsorption. Research data showed that the adsorption capacity of biochar and residual biochar (after removal of DOM) was 277.62 and 204.47 mg g−1, respectively, indicating that DOM played a significant role in enhancing the adsorption efficiency of Pb(II). The results indicated that the adsorption process of Pb(II) on biochar and residual biochar followed the pseudo-second-order kinetic equation (R2 > 0.99), and the adsorption isotherm was much closer Freundlich model. A combination of three-dimensional excitation-emission matrix (3D-EEM), synchronous fluorescence, Fourier transform infrared spectroscopy (FT-IR), and two-dimensional correlation spectroscopy (2D-COS) was employed to investigate the interaction between DOM and Pb(II). 3D-EEM indicated the presence of four major components of DOM, namely two protein-like substances, one humic acid-like substance, and one fulvic acid-like substance. The synchronous fluorescence revealed a gradual quenching of the fluorescence of the DOM sample with an increase in Pb(II) concentration, indicating a static quenching mechanism between DOM and Pb(II). FTIR-2D-COS analysis showed a specific sequence of DOM binding with Pb(II) is as follows: 1500 > 1010 > 880 > 1390 > 1260 cm−1. This findings have significant implications for the role of DOM in environmental science and have potential applications in various fields.

Removing DOM from chloride modified hydrochar could improve Cu2+ adsorption capacity from aqueous solution

The behavior and composition of hydrochar-based dissolved organic matter (DOM) would affect the efficiency of copper (Cu) removal from wastewater through adsorption. In this study, the reed was hydrolyzed in the presence of feedwater with and without ZnCl2, FeCl3, and SnCl4 to produce pristine hydrochars (PHCs), which were named H2O-HC, ZnCl2-HC, FeCl3-HC, and SnCl4-HC. After removal of DOM, washed hydrochars (WHCs) were obtained, labelled as W–H2O-HC, W-ZnCl2-HC, W-FeCl3-HC, and W-SnCl4-HC. The release dynamics of DOM from PHCs were analyzed, and the adsorption behaviors of Cu2+ on both PHCs and WHCs were investigated. The results showed that chloride-modifications were beneficial for the porosity, specific surface area (SSA), and functional groups of WHCs. Meanwhile, the quantity of hydrochar-based DOM was significantly affected by chloride-modifications. In particular, the relative contents of Ar–P and Fa-L in the DOM released from hydrochars varied with time and modification. Furthermore, the Qe of Cu2+ adsorption on WHCs followed the order of W-SnCl4-HC > W-FeCl3-HC > W-ZnCl2-HC > W–H2O-HC at 15 °C. Compared to PHCs, the adsorption capacity of Cu2+ on WHCs was improved by 7.15–119.77% at the temperature of 35 °C. Simultaneously, the adsorption capacity of Cu2+ in WHCs showed a significant correlation with the SSA via physical adsorption (P < 0.05). Moreover, XPS analysis revealed that Cu2+ adsorption also occurred via complexation and chelation through newly formed Cu–O group between W-SnCl4-HC and Cu2+. Notably, the increase of Cu2+ adsorption in WHCs was significantly correlated with the release of Fa-L and Ar–P from PHCs (P < 0.05). This study found that the content and composition of hydrochar-based DOM could be a major driving factor for Cu2+ adsorption.

Effects of dissolved organic matter removal and molecular transformation in different water treatment processes on formation of disinfection byproducts

Alterations in molecular composition of dissolved organic matter (DOM) during water treatments can influence the composition and toxicity of disinfection by-products (DBPs) in subsequent chlorination disinfection process. In this study, the impacts of DOM composition after various water treatment techniques (coagulation, adsorption, nanofiltration, biological aerated filter (BAF), and their integrated processes) on the generation mechanisms of DBPs were comprehensively explored by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in combination with GC–MS and LC-MS analysis. The results indicated that coagulation preferentially removed unsaturated (low H/C) and oxidized (high O/C) compounds, whereas adsorption was prone to remove the reduced (low O/C) component that was more reactive with chlorine, leading to lower yields (μg DBP/mg DOC) of trihalomethanes (THMs) and haloacetic acids (HAAs) during subsequent chlorination. The coagulation-adsorption technique exhibited a relatively high removal of both known and unknown DBPs, demonstrating that coagulation and adsorption were complementary for DOM removal at the molecular level. Nanofiltration selectively removed molecules with relatively high O/C, however, those with very low O/C that were more reactive with chlorine could pass through the nanofiltration membrane, resulting in the highest yields of THMs and HAAs. Although BAF was inefficient in removing DBPs precursors, it could convert molecules with low degree of oxidation and unsaturation into highly oxidized and unsaturated ones, thereby significantly enhancing the removal of DBPs precursors in the subsequent coagulation-adsorption process. These findings are instrumental in developing and selecting more effective techniques to minimize the formation of DBPs in water treatment.

Chemodiversity transformation of organic matters in a full scale MBR-NF wastewater reclamation plant

Membrane bioreactor (MBR) and nanofiltration (NF) process has been attractive in wastewater reclamation, and was set as the target process in this study. Dissolved organic matter (DOM) and trace organic contaminants (TrOCs), closely associated with water safety, are noteworthy pollutants. Though the general DOM characteristics and TrOCs removal in MBR-NF reclamation process have been reported in lab‐/pilot-scale experiment, the molecular characteristics of DOM revealed by high resolution mass spectrometry, and the correlation between DOM and TrOCs have been rarely studied in full-scale MBR-NF wastewater reclamation plant. In this work, biological and NF processes contributed significantly to the removal of DOM and TrOCs, while MBR filtration contributed slightly. Spectroscopic analyses revealed that DOM with higher aromaticity and lower molecular weight were more recalcitrant along the treatment. Aromatic protein-like substances were preferentially removed comparing to humic-like substances. Fourier transform ion cyclotron resonance mass spectrometry was applied to investigate DOM transformation at molecular level. DOM molecules with higher H/C and lower O/C, especially the aliphatics and peptides, were readily biodegraded into higher‑oxygenate, highly unsaturated, and aromatic compounds. The generated species mainly included condensed aromatics, polyphenols, and highly unsaturated compounds. Filtration in MBR tended to reject higher oxygenated molecules. NF effectively removed most of the DOM molecules, especially higher oxygenated molecules with low H, N and S. The residual TrOCs in the NF effluent, including sulfamethoxazole, ofloxacin, and bisphenol A, still displayed above medium environmental risk. Significant correlations were found among organic compounds, spectral indices, and peptides molecules. Positive correlation between most of the TrOCs and several DOM parameters implied that they were synchronously removed in biological and membrane filtration processes. SUVA and FI might be potential indexes in monitoring the performance of MBR-NF process in both DOM and TrOC removal. These findings would expand the understanding of DOM and TrOCs behavior in wastewater reclamation process and simplify an in-depth system monitoring.