Photocatalytic degradation of DOM in urban stormwater runoff with TiO2 nanoparticles under UV light irradiation: EEM-PARAFAC analysis and influence of co-existing inorganic ions

Fate of sulfamerazine by synchronous adsorption and photocatalysis dependent on natural organic matter properties

Natural organic matter (NOM) can impede the removal of organic micro-pollutants (OMPs) through several mechanisms, including inner filter effect, competition with the target OMP, and radical scavenging, during synchronous adsorption/photocatalysis of multi-functional composites. In this study, the fate and inhibitory mechanisms of sulfamerazine (SMZ, a model OMP) that occurred in presence of seven different NOM samples (i.e. three standard NOM surrogates, a river water sample, a carbon filter effluent and two different sand filter effluents) during the adsorption/photocatalysis by a composite of Bi2O3-TiO2 supported on powdered activated carbon (Bi2O3-TiO2/PAC, abbreviated as BTP) when exposed to visible light irradiation were revealed. The results indicated that adsorption played a greater attribution than photocatalysis on SMZ removal. The primary impediment to the adsorption and photocatalytic degradation of SMZ was attributed to the presence of terrestrial-derived, humic-like NOM fractions with high aromaticity. The adsorption efficacy of SMZ was weakened by the absorption of NOM and its degradation products onto the BTP surface. The inner filter effect, competition between NOM and SMZ, and radical scavenging were responsible for the reduced photocatalysis of SMZ. In the cases of real water matrices, the presence of inorganic anion and co-existed NOM reduced the removal of SMZ. In summary, the findings of this work offer a comprehensive comprehension of the impact of NOM fractions on photocatalysis, emphasizing the necessity to examine the interplay between NOM and background inorganic constituents in the degradation of OMP via adsorption/photocatalysis.

Progress of photocatalytic oxidation-adsorption synergistic removal of organic arsenic in water

Photocatalytic oxidation-adsorption synergistic treatment of organic arsenic pollutants is a promising wastewater treatment technology, which not only degrades organic arsenic pollutants by photocatalytic degradation but also removes the generated inorganic arsenic by adsorption. This paper compares the results of photocatalytic oxidation-adsorption co-treatment of organic arsenic pollutants such as monomethylarsonic acid, dimethylarsinic acid, phenylarsonic acid, p-arsanilic acid, and 3-nitro-4-hydroxyphenylarsonic acid on titanium dioxide, goethite, zinc oxide, and copper oxide. It examines the influence of the morphology of organic arsenic molecules, pH, coexisting ions, and the role of natural organic matter. The photocatalytic oxidation-adsorption co-treatment mechanism is investigated, comparing the hydroxyl radical oxidation mechanism, the hydroxyl radical and superoxide anion radical cooxidation mechanism, and the hydroxyl radical and hole cooxidation mechanism. Finally, the future prospects of metal oxide photocatalytic materials and the development of robust and efficient technologies for removing organic arsenic are envisioned.

High-throughput experimentation for photocatalytic water purification in practical environments

High-throughput screening instrument was developed for photocatalytic water purification, enabling the simultaneous testing of 132 photocatalytic reactions under uniform visible light irradiation, temperature control, and stirring. The instrument was used to investigate the effects of different catalysts (TiO2, ZnO, α-Fe2O3) and environmental waters (seawater, urban wastewater, and industrial wastewater) on dye degradation. It was observed environmental ions, particularly carbonate and phosphate ions, significantly reduced catalyst activity by inhibiting the adsorption of dye molecules. To develop effective catalysts for dye degradation in industrial wastewater, 15 types of noble metal nanoparticles (NPs) were supported on photocatalysts. The study found that noble metal NPs with high work functions and oxidation resistance, such as Au and Pt, exhibited higher activity even in the industrial wastewater, likely converting environmental ions into active species. These findings, based on 432 test results, demonstrate the effectiveness of the developed high-throughput screening instrument for optimizing photocatalytic water purification.

FT-ICR-MS combined with fluorescent spectroscopy reveals the driving mechanism of the spatial variation in molecular composition of DOM in 22 plateau lakes

Dissolved organic matter (DOM) is the largest carbon pool and directly affects the biogeochemistry in lakes. In the current study, fourier transform ion cyclotron mass spectrometry (FT-ICR-MS) combined with fluorescent spectroscopy was used to assess the molecular composition and driving mechanism of DOM in 22 plateau lakes in Mongolia Plateau Lakes Region (MLR), Qinghai Plateau Lakes Region (QLR) and Tibet Plateau Lakes Region (TLR) of China. The limnic dissolved organic carbon (DOC) content ranged from 3.93 to 280.8 mg L^-1 and the values in MLR and TLR were significantly higher than that in QLR. The content of lignin was the highest in each lake and showed a gradually decreasing trend from MLR to TLR. Random forest model and structural equation model implied that altitude played an important role in lignin degradation while the contents of total nitrogen (TN) and chlorophyll a (Chl-a) have a great influence on the increase of DOM Shannon index. Our results also suggested that the inspissation of DOC and the promoted endogenous DOM production caused by the inspissation of nutrient resulted in a positive relationship between limnic DOC content and limnic factors such as salinity, alkalinity and nutrient concentration. From MLR to QLR and TLR, the molecular weight and the number of double bonds gradually decreased but the humification index (HIX) also decreased. In addition, from the MLR to the TLR, the proportion of lignin gradually decreased, while the proportion of lipid gradually increased. Both above results suggested that photodegradation was dominated in lakes of TLR, while microbial degradation was dominated in lakes of MLR.

SnO2 and CuO anchored on zeolite as an efficient heterojunction photocatalyst for sunlight-assisted degradation of cefixime

The fabrication of heterojunction nanocomposites has been proven as a highly efficient strategy to achieve promising photocatalysts. In this study, tin oxide (SnO₂) and copper oxide (CuO) nanoparticles (NPs) were synthesized in situ using Rosmarinus officinalis and simultaneously anchored on zeolite for the fabrication of zeolite/SnO₂/CuO as a novel heterojunction photocatalyst. The performance of zeolite/SnO₂/CuO was assessed against photodegradation of cefixime as a model pharmaceutical contaminant. A good catalytic potential and synergistic effect was obtained for zeolite/SnO₂/CuO compared to pure SnO₂ and CuO NPs. Under optimum conditions, 89.65% of cefixime was degraded after 2.5 h under natural sunlight. Based on radical quenching experiments, the importance of involved oxidizing species in the photodegradation of cefixime using zeolite/SnO₂/CuO was in order of h⁺ > ^•OH > [Formula: see text]. Among studied anions, the highest inhibitory effect was observed for nitrate ion. Also, the main intermediates of the photodegradation process of cefixime in zeolite/SnO₂/CuO system were determined by HPLC-MS and the possible pathways were suggested. More than 83% cefixime was removed after three catalyst reuse cycles, indicating a cost-effectiveness potential in the reusability of zeolite/SnO₂/CuO. Also, the toxicity and plant growth tests revealed the feasibility of discharging the treated cefixime solutions to irrigate agricultural crops. Overall, the obtained results provide a promising technique with a synergistic feature for the efficient removal of organic pollutants.

Photocatalytic oxidation degradation of tetracycline over La/Co@TiO2 nanospheres under visible light

The oxygen-vacancy-rich La/Co@TiO₂ nanospheres for the photo catalytic degradation of tetracycline were prepared by a simple two-step method. 3 wt%La/Co@TiO₂ nanospheres had better photocatalytic performance of the degradation of tetracycline than that of the other catalysts under visible light may be due to the synergistic effect between La/Co and TiO₂ and nano-confined effect. The catalytic experimental results showed the degradation ratio of tetracycline (40 mg/L) were 100% for 90 min. XPS, Raman, and photoelectrochemical results showed appropriate number of oxygen vacancies existed on the surface of TiO₂, which could improve the activation efficiency of dissolved oxygen in tetracycline solution because they accelerated the electron transfer rate in the system and inhibited the photoelectron-hole pair recombination under visible light. The EPR and radical scavenger tests showed h⁺, O₂^-, and ·OH were the main active species for the degradation of tetracycline. Also, the possible mechanism and intermediates of the tetracycline degradation process were speculated under the visible light. La/Co@TiO₂ nanospheres would be a promising photocatalyst for wastewater treatment.

Remediation of pesticides using TiO2 based photocatalytic strategies: A review

Nowadays, pesticides are regarded as the most dangerous of the various organic pollutants, posing substantial environmental and human threats worldwide. Pesticide contamination has become one of the most crucial environmental issues due to its bio-persistence and bioaccumulation. Different conventional methods are being utilized for pesticide removal, yet pesticides are thought to be significantly present in the environment. The development and application of sophisticated wastewater treatment methods are being pursued to remove contaminants effectively, particularly pesticides. In the past several decades, nanoscience and nanotechnology have emerged as essential tools for the identification, removal, and mineralization of persistent pesticides by employing advanced nanomaterials such as pristine titanium dioxide (TiO₂), doped TiO₂, nanocomposites (NCs) TiO₂, and ternary nanocomposites (TNCs) TiO₂ by advanced oxidation processes (AOPs). Advancement in the characteristics of TiO₂ by doping, co-doping, construction of NCs and TNCs has contributed to the dramatic efficiency up-gradation by reducing band gap, solar active photocatalyst, enhancing PCA, high photostability, chemically inertness and multiple time reusability. Based on previous literature, utilizing La-TiO₂ NCs photocatalyst, the mineralization of pesticide (imidacloprid) attained up to 98.17% that is almost 40-53% greater than pristine TiO₂. The present review attempt to discuss the recent research performed on TiO₂ based nanoparticles (NPs) and NCs for photocatalytic mineralization of various pesticides. The basic mechanism of TiO₂ photocatalysis, types of reactors used for photocatalysis, and optimized experimental conditions of TiO₂ for pesticides mineralization are discussed.

Tracing dissolved organic matter in inflowing rivers of Nansi Lake as a storage reservoir: Implications for water-quality control

Quantitative characterization of dissolved organic matter (DOM) in various aquatic ecosystems has become of increasing importance as its transformation plays a key role in inland water carbon, yet few studies have quantified water DOM inputs to storage lakes for water quality control and safety assurance. This study assessed the quantity and quality of DOM in 21 inflow rivers of Nansi Lake as the important storage lake of large-scale water transfer projects by using excitation-emission matrix spectroscopy coupled with parallel factor analysis (EEM-PARAFAC) and ultraviolet-visible (UV-Vis) spectroscopy. The results showed that DOM contents varied significantly with an average value of 5.8 mg L^-1 in different inflow rivers, and three fluorescence substances (including UVC humic-like, UVA humic-like and tyrosine-like components) were identified by EEM-PARAFAC. The distribution of the DOM components was distinctively different among sampling sites, and UVA humic-like component mainly dominated in Nansi Lake. Meanwhile, DOM components with higher aromaticity and molecular weight were found in the west side of lake. Fluorescence spectral indexes manifested that the source of DOM was mainly from allochthonous or terrestrial input. Moreover, significant correlations between water quality and DOM characteristics were observed in Nansi Lake. These findings would be beneficial to understand the biogeochemical role and impact of DOM in inflowing rivers in the water-quality monitoring and control of storage lakes.

Degradation of Minocycline by the Adsorption-Catalysis Multifunctional PVDF-PVP-TiO2 Membrane: Degradation Kinetics, Photocatalytic Efficiency, and Toxicity of Products

The photocatalytic degradation of minocycline was studied by using polyvinylidene fluoride-polyvinylpyrrolidone-TiO₂ (PVDF-PVP-TiO₂) fiber mats prepared by an electrospinning technology. The influences of the TiO₂ dosage, minocycline concentrations, inorganic anions, pH values, and dissolved organic matter (DOM) concentrations on the degradation kinetics were investigated. A mass of 97% minocycline was degraded in 45 min at 5% TiO₂ dosage. The corresponding decomposition rate constant was 0.069 min^-1. The inorganic anions affected the minocycline decomposition in the order of HCO₃^- > Cl^- > SO₄^2- > NO₃^-, which was confirmed by the results of electron spin resonance (ESR) spectra. The lowest electrical energy per order (E_EO) was 6.5 Wh/L. Over five cycles, there was no change in the photocatalytic performance of the degrading minocycline. Those investigations suggested that effective degradation of minocycline could be reached in the PVDF-PVP-TiO₂ fiber mats with a low energy consumption, good separation and, good recovery. Three photocatalytic decomposition pathways of minocycline were proposed: (i) hydroxyl substitution of the acylamino group; (ii) hydroxyl substitution of the amide group, and (iii) a cleavage of the methyl groups and further oxidation of the amino group by OH. Potential risks caused by TP159 and TP99 should not be ignored, while the TP90 are nontoxic. Tests indicated that the toxicity of the photocatalytic process may be persistent if minocycline and its products were not mineralized completely.

Construction of direct Z-scheme Bi5O7I/UiO-66-NH2 heterojunction photocatalysts for enhanced degradation of ciprofloxacin: Mechanism insight, pathway analysis and toxicity evaluation

Direct Z-scheme Bi₅O₇I/UiO-66-NH₂ (denoted as BU-x) heterojunction photocatalysts were successfully constructed through ball-milling method. Photocatalytic activities of the as-prepared BU-x samples were determined by using a typical fluoroquinolone antibiotic, ciprofloxacin (CIP). All BU-x heterojunctions exhibited better CIP removal performances than that of pristine Bi₅O₇I and UiO-66-NH₂ upon exposure to white light irradiation. In comparison, the heterojunction with UiO-66-NH₂ content of 50 wt% (BU-5) showed excellent structural stability and the optimal adsorption-photodegradation efficiency for the CIP removal. The removal efficiency of CIP (10 mg/L) over BU-5 (0.75 g/L) achieved 96.1% within 120 min illumination. Meanwhile, the effect of photocatalyst dosage, pH and inorganic anions were systemically explored. Reactive species trapping experiments, electron spin resonance (ESR) signals, Mott-Schottky measurements and density functional theory (DFT) simulation revealed that the photo-generated holes (h⁺), hydroxyl radical (·OH) and superoxide radical (·O₂^-) played crucial roles in CIP degradation. This result can be ascribed to that the unique Z-scheme charge transfer configuration retained the excellent redox capacities of Bi₅O₇I and UiO-66-NH₂. Meanwhile, the CIP degradation pathways and the toxicity of various intermediates were subsequently analyzed. This work provided a feasible idea for removing antibiotics by bismuth-rich bismuth oxyhalide/MOF-based heterostructured photocatalysts.

Immobilization of TiO2 Nanoparticles in Cement for Improved Photocatalytic Reactivity and Treatment of Organic Pollutants

Non-point organic pollutants in stormwater are a growing problem in the urban environment which lack effective and efficient treatment technologies. Incorporation of conventional wastewater techniques within stormwater management practices could fundamentally change how stormwater quality is managed because contaminants can be degraded during stormwater transport or storage. This study investigated the photocatalytic reactivity of titanium dioxide functionalized with maleic anhydride (Ti-MAH) within cement pastes when compared to ordinary Portland cement. Preparation of Ti-MAH was performed by permanently bonding maleic anhydride to titanium in methanol, drying and powdering the residual material, and then inter-grinding the preparation with cement during mixing. When compared with OPC, the Ti-MAH cured cement paste is more reactive under a wider range of light wavelengths, possesses a higher band gap, sustains this heightened reactivity over multiple testing iterations, and treats organics effectively (>95% methylene blue removal). Amorphous silica within calcium-silica-hydrate, C-S-H, is theorized to bond to the powdered Ti-MAH during curing. Verification of silicon bonding to the titanium by way of MAH was demonstrated by FTIR spectra, SEM imagery, and XRD. Creating a sustainable and passive photocatalytic cement that precisely bonds silica to Ti-MAH is useful for organic contaminants in urban stormwater, but use can translate to other applications because Ti-MAH bonds readily with any amorphous silica such as glass materials, paints and coatings, optics, and LEDS, among many others.

Degradation of dissolved organic matter in effluent of municipal wastewater plant by a combined tidal and subsurface flow constructed wetland

Dissolved organic matter (DOM) is an important constituent of wastewater treatment plant (WWTP) effluent. A novel combined tidal and subsurface flow constructed wetland (TF-SSF-CW) of 90 L was constructed for a ten-month trial of advanced treatment of the WWTP effluent. Excitation emission matrix (EEM) fluorescence spectroscopy, parallel factor (PARAFAC) analysis and a two end-member mixing model were employed to characterize the composition and removal process of the effluent DOM (EfOM) from the WWTP. The results showed that the TF-SSF-CW performed an efficient EfOM removal with dissolved organic carbon (DOC) removal rate of 88% and dissolved organic nitrogen (DON) removal rate of 91%. Further analysis demonstrated that the EfOM consisted mainly of two protein moieties and two humic-like groups; protein moieties (76%) constituted the main content of EfOM in raw water and humic-like groups (57%) became the dominating contributor after treatment. The EfOM from the WWTP was mainly of aquatic bacterial origin and evolved to a higher proportion of terrigenous origin with higher humification in the TF-SSF-CW effluent. A common controlling treatment-related factor for determining the concentrations of the same kind of substances (protein groups or humic-like groups) was revealed to exist, and the ratio of removal rates between the same substances in treatment was calculated. Our study demonstrates that the TF-SSF-CW can be a novel and effective treatment method for the EfOM from WWTPs, and is helpful for understanding of the character of EfOM in wetland treatment.

Photochemical Reactivity of Humic Substances in an Aquatic System Revealed by Excitation-Emission Matrix Fluorescence

The photochemical reactivity of humic substances plays a critical role in the global carbon cycle, and influences the toxicity, mobility, and bioavailability of contaminants by altering their molecular structure and the mineralization of organic carbon to CO₂. Here, we examined the simulated irradiation process of Chinese standard fulvic acid (FA) and humic acid (HA) by using excitation-emission matrix fluorescence combined with fluorescence regional integration (FRI), parallel factor (PARAFAC) analysis, and kinetic models. Humic-like and fulvic-like materials were the main materials (constituting more than 90%) of both FA and HA, according to the FRI analysis. Four components were identified by the PARAFAC analysis: fulvic-like components composed of both carboxylic-like and phenolic-like chromophores (C1), terrestrial humic-like components primarily composed of carboxylic-like chromophores (C2), microbial humic-like overwhelming composed of phenolic-like fluorophores (C3), and protein-like components (C4). After irradiation for 72 h, the maximum fluorescence intensity (F _max) of C1 and C2 of FA was reduced to 36.01-58.34%, while the F _max of C3 of both FA and HA also decreased to 0-9.63%. By contrast, for HA, the F _max of its C1 and C2 increased to 236.18-294.77% when irradiated for 72 h due to greater aromaticity and photorefractive tendencies. The first-order kinetic model (R ² = 0.908-0.990) fitted better than zero-order kinetic model (R ² = 0-0.754) for the C1, C2, and C3, of both FA and HA, during their photochemical reactivity. The photodegradation rate constant (k ₁) of C1 had values (0.105 for FA; 0.154 for HA) that surpassed those of C2 (0.059 for FA, 0.079 for HA) and C3 (0.079 for both FA and HA) based on the first-order kinetic model. The half-life times of C1, C2, and C3 ranged from 6.61-11.77 h to 4.50-8.81 h for FA and HA, respectively. Combining an excitation-emission matrix with FRI and PARAFAC analyses is a powerful approach for elucidating changes to humic substances during their irradiation, which is helpful for predicting the environmental toxicity of contaminants in natural ecosystems.

Nanocellulosics: Benign, Sustainable, and Ubiquitous Biomaterials for Water Remediation

Water is critical for all lives to thrive. Access to potable and safe water has been argued to rank top among the prerequisites for defining the standard of living of a nation. However, there is a global decline in water quality due to human activities and other factors that severely impact freshwater resources such as saltwater intrusion and natural disasters. It has been pointed out that the millions of liters of industrial and domestic wastewater generated globally have the potential to help mitigate water scarcity if it is appropriately captured and remediated. Among the many initiatives to increase access to clean water, the scientific community has focused on wastewater remediation through the utilization of bioderived materials, such as nanocellulosics. Nanocellulosics, derived from cellulose, have the advantages of being ubiquitous, nontoxic, and excellent adsorbents. Furthermore, the surface properties of nanocellulosic materials can easily be modified. These advantages make them promising materials for water remediation applications. This perspective highlights the most important new developments in the application of nanocellulosics in water treatment technologies, such as membrane, adsorption, sensors, and flocculants/coagulants. We also identify where further work is urgently required for the widespread industrial application of nanocellulosics in wastewater treatment.

Bifunctional Bi12O17Cl2/MIL-100(Fe) composites toward photocatalytic Cr(VI) sequestration and activation of persulfate for bisphenol A degradation

Bifunctional Bi₁₂O₁₇Cl₂/MIL-100(Fe) composite (BMx) was firstly constructed via facile ball-milling method. The optimal BM200 was highly efficient for Cr(VI) sequestration and activation of persulfate (PS) for bisphenol A (BPA) decomposition under white light illumination, which was much more remarkable than the pristine MIL-100(Fe) and Bi₁₂O₁₇Cl₂, respectively. Furthermore, the photocatalytic reduction efficiency can be significantly improved via the addition of some green small organic acids (SOAs). As well, the BPA degradation can be achieved over an extensive initial pH range of 3.0-11.0. When the PS concentration increased to more than 2.0 mM, the BPA degradation efficiency decreased due to the SO₄^-• self-scavenging effect. It was also found that the co-existence of inorganic anions like H₂PO₄^-, HCO₃^-, SO₄^2-, Cl^- and NO₃^- could decelerate the BPA degradation. The excellent photocatalytic Cr(VI) reduction and persulfate activation performances originated from both MIL-100(Fe) with excellent PS activation ability and Bi₁₂O₁₇Cl₂ with a favorable band position, which not only enabled the efficient separation of charges but also accelerated the formation of SO₄^-• radicals. The BM200 displayed prominent stability and recyclability. More importantly, the credible degradation pathway was proposed based on UHPLC-MS analysis and DFT calculation. This research revealed that the Fe-based MOFs/bismuth-rich bismuth oxyhalides (Bi_xO_yX_z, X = Cl, Br and I) composites possessed great potential in wastewater remediation.

Effects of natural organic matter on the photolysis of tetracycline in aquatic environment: Kinetics and mechanism

The residues of tetracycline in environment have raised increasing concern for the deleterious impact on ecological and human health. Natural organic matter (NOM), ubiquitous in natural waters, is unavoidable to encounter tetracycline, which might affect the fate of tetracycline in aquatic environment. In this study, we investigated the effect of natural organic matter (NOM) on the photolytic fate of tetracycline (TC). The photolysis kinetics of TC were evaluated with two representative NOM, tannic acid (TA) and gallic acid (GA). The presence of TA and GA obviously inhibited the removal of TC under UV irradiation with photolysis rate constant at 0.067 h^-1 and 0.071 h^-1, respectively, which were 32.3% and 28.3% less than that without TA and GA (0.099 h^-1). Furthermore, NOM exhibited different impacts on both indirect photolysis and direct photolysis. NOM promoted the formation of hydroxyl radical, induced the generation of triplet-excited state NOM and thus greatly enhanced the indirect photolysis of TC. However, direct photolysis was almost completely inhibited by NOM via inner filter effect and interacting with TC to form ground-state complex with low photoreactive. Moreover, similar intermediates were detected in the presence and absence of NOM, indicating that NOM exhibited limited influence on the degradation pathways of TC. This study reveals the multiple roles of NOM on tetracycline photolysis, contributing to better understand the photolytic fate of antibiotics in natural waters.

Construction of S-doped MgO coupled with g-C3N4 nanocomposites with enhanced photocatalytic activity under visible light irradiation

In the present work, a series of photocatalysts in which S-MgO (SM) was coupled with g-C3N4 (CN) were synthesized and characterized in detail using various characterization techniques.

Photocatalytic degradation of dissolved organic matter under ZnO-catalyzed artificial sunlight irradiation system

This study investigates the photocatalytic degradation of dissolved organic matter (DOM) under ZnO-assisted artificial sunlight system at various conditions (ZnO dosage, pH, and the presence of Cl⁻, SO₄²⁻, and HCO₃⁻). The results show that the degradation of DOM follows a pseudo-first-order kinetics. Fluorescence excitation–emission matrices coupled with parallel factor (EEM-PARAFAC) analysis decomposes DOM into two fluorophores (C1 and C2). The total removals and photodegradation rates calculated with DOC, UV₂₅₄, and the F_max of C1 are similar, increasing with higher ZnO dosages and being highest in pH 7 and lowest in pH 4. ZnO dosage has a similar effect on DOM degradation when assessed using C2, as with C1, but pH effect is not consistent. As for the anions, HCO₃⁻ shows the strongest inhibition for DOC, UV₂₅₄ and C1 while Cl⁻ has the strongest facilitation effect for C2. The total removal and photodegradation rates calculated with the F_max of C1 and C2 are higher than those calculated using DOC and UV₂₅₄. This study demonstrates that the successful application of EEM-PARAFAC analysis in addition to traditional parameters can provide further insight into the photocatalytic degradation mechanisms associated with DOM in conjunction with a ZnO catalyst under artificial sunlight.

Study on the removal of humic acid by ultraviolet/persulfate advanced oxidation technology

Humic acid (HA) in water is the main precursor of disinfection by-products in the chlorination process of drinking water. In this study, an ultraviolet/persulfate (UV/PS) process, in a laboratory-scale system, is successful in the degradation of HA. The results showed that HA was significantly degraded (UV₂₅₄ removal rate of ~ 89%) and partially mineralized (~ 62.5%) by UV/PS treatment at a PS dose of 0.4 mM, pH of 7.12, and UV irradiation time of 160 min. The trihalomethane formation potential (THMFP) was also significantly reduced (THMFP reduction of ~ 85.4%). A strong linear relationship was observed between UV₂₅₄ and dissolved organic carbon. The removal rate of HA at low pH was better than that at high pH conditions, and the inhibition by Cl^- slowed down after an initial increase, and the inhibition was weaker than HCO₃^-. By analyzing the fluorescence spectrum of two humic-like substances, the fluorescent compounds C1 and C2 in HA were significantly degraded, and the change in C1 and C2 concentration was correlated with the decrease of THMFP. The degradation of different fractions of natural organic matter in real-world water samples indicated that UV/PS has significant potential to decrease HA in water.

Adsorption of cyanobacterial extracellular polymeric substance on colloidal particle: Influence of molecular weight

Cyanobacterial extracellular polymeric substances (EPSs) in aquatic environments are easily adsorbed onto colloidal particles, whereas the adsorption behavior as affected by molecular weight (MW) properties remained unknown till now. Herein, the bulk cyanobacterial EPS matrix (<0.45 μm) was fractionated into high MW (HMW-, 1 kDa~0.45 μm) and low MW (LMW-, <1 kDa) fractions, with MW-dependent adsorption heterogeneities onto TiO₂ colloids exploring through batch experiment, UV-Vis and fluorescence spectroscopy, and two dimensional Fourier transform infrared correlation spectroscopy (2D-FTIR-COS). About two-thirds of total organic matters within bulk EPS matrix were distributed in the HMW fraction, leaving one-third in the LMW fraction. Compared to LMW-EPS, the HMW counterpart exhibited higher aromaticity and richness of autochthonous protein-like substances, showing evident MW-dependent differences in abundance and composition. The adsorption capacity based on the measurement of total abundance, UV-Vis and fluorescent spectra all decreased in sequence of HMW- > Bulk > LMW-EPS, demonstrating obvious MW-dependent adsorption heterogeneities. During adsorption, the values of SUVA₂₅₄ in residual supernatants exhibited an initial decrease followed by gradual increase for all samples, suggesting that the preferentially adsorbed aromatic substances can be subsequently replaced by the non-aromatic moieties. 2D-FTIR-COS further revealed that the carboxylic groups of proteins were preferentially adsorbed onto colloidal surface, followed by the CC functional groups and then the CH groups of polysaccharides, which accounted for the variations of SUVA₂₅₄ values in the supernatants. This study demonstrated that the adsorption behavior of EPS matrix was highly MW-dependent, and detailed characterization on size fractionation is thus needed in future studies.

Photocatalytic degradation of organic micropollutants: Inhibition mechanisms by different fractions of natural organic matter

Natural organic matter (NOM) can inhibit the photocatalytic degradation of organic micropollutants (OMPs) through inner filter effect, reactive oxygen species (ROS) scavenging, and competitive adsorption. However, previous studies have focused solely on the bulk properties of NOM and our understanding of the inhibition mechanism by NOM fractions during photocatalytic degradation of OMP is still fragmentary. In this study, five well-characterized different NOM samples (i.e., secondary treated wastewater, river water, and three standard NOM surrogates) were used to elucidate the inhibition mechanisms during photocatalytic degradation of carbamazepine (a model OMP) using TiO₂ and its composites with carbon nanotubes (CNT-TiO₂) under UVC and solar-light irradiation. The results indicated that terrestrially derived NOM with high aromaticity, a low oxygen/carbon atom ratio, and large molecular weight is the major fraction that participates in ROS scavenging, competitive adsorption, and inner filter effect. Furthermore, the modeling analysis suggested that inner filter effect due to NOM and ROS scavenging was the most influential inhibitory mechanism. In the case of secondary treated wastewater, the presence of high concentrations of inorganic species (e.g., PO₄^3-, Cl^-, and NO₃^-) together with NOM significantly reduced the photocatalytic degradation of carbamazepine. Overall, the methods and the results of this study provide a comprehensive understanding of the effects of NOM fractions on photocatalysis and highlight the need to further consider the interplay between NOM and background inorganic constituents in photocatalytic degradation of OMP.

Biochar-induced metal immobilization and soil biogeochemical process: An integrated mechanistic approach

The nature of biochar-derived dissolved organic matter (DOM) has a crucial role in the interactions between biochar and metal immobilization, carbon dynamics, and microbial communities in soil. This study utilized excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) modeling to provide mechanistic evidence of biochar-induced influences on main soil biogeochemical processes. Three biochars produced from rice straw, wood, and grass residues were added to sandy and sandy loam soils and incubated for 473 d. Microbial and terrestrial humic-like fluorescent components were identified in the soils after incubation. The sandy loam soil exhibited a higher DOM with microbial sources than did the sandy soil. All biochars reduced Pb bioavailability, whereas the rice straw biochar enhanced the As bioavailability in the sandy loam soil. The biochar-derived aliphatic-DOM positively correlated with As bioavailability (r = 0.82) in the sandy loam soil and enhanced the cumulative CO₂-C (r = 0.59) in the sandy soil. The promoted cumulative CO₂-C in the sandy soil with all biochars correlated with the enhanced microbial communities, in particular, gram-positive (r = 0.59) and gram-negative (r = 0.59) bacteria. Our results suggest that the integration of EEM-PARAFAC with spectroscopic indices could be useful for a comprehensive interpretation of the soil quality changes in response to the application of biochar.

The Shock Effect of Inorganic Suspended Solids in Surface Runoff on Wastewater Treatment Plant Performance

Previous studies on the water quality of surface runoff often focused on the chemical oxygen demand (COD), nitrogen, phosphorus, and total suspended solid (TSS), but little is known in terms of the inorganic suspended solids (ISS). This research investigated the effects of ISS carried by surface runoff on the treatment efficiency of the pretreatment facilities and the ratio of mixed liquor volatile suspended solid to mixed liquor suspended solid (MLVSS/MLSS) of the activated sludge in a wastewater treatment plant (WWTP) with the anaerobic-anoxic-oxic (AAO) process in Chongqing city, China. The results showed that the surface runoff had a long-lasting impact on the grit removal capacity of the grit chamber, affecting the normal operation after the rainfall. In contrast, the primary sedimentation tank showed strong impact resistance with higher removal rates of COD, TSS, and ISS. Nonetheless, the primary settling tank aggravates the removal of organic carbon in sewage during rainfall, having a negative impact on subsequent biological treatment. The ISS in the surface runoff could increase the sludge concentration and decrease the MLVSS/MLSS ratio. After repeated surface runoff impact, the MLVSS/MLSS ratio in the activated sludge would drop below even 0.3, interrupting the normal operation of WWTP.

Dissolved organic matter in urban forestland soil and its interactions with typical heavy metals: a case of Daxing District, Beijing

As an active substance, dissolved organic matter (DOM) acts a pivotal part in heavy metals (HMs) transportation from urban forestland soil to aquatic ecosystem. In this study, the soil samples from 35 individual subareas were scientifically collected with the aid of geographical information system (GIS) technology. UV-visible (UV-vis) and excitation-emission matrix (EEM)-related parameters suggested that the DOM in urban forestland soil mainly originated from terrestrial and microbial sources. Fluorescence quenching titration associated with parallel factor (PARAFAC) modeling was applied to quantify the complexation ability of four HMs (Cu, Cd, Pb, and Ni) and DOM in urban forestland soil. One fulvic-like (C1), two humic-like (C2 and C3), and one protein-like fluorophores (C4) were identified by EEM-PARAFAC modeling. Considerable differences in fluorescence quenching curves were observed between individual organic constituents and target HMs. Among the four HMs, addition of Cu(II) ions resulted in EEM spectra quenching of each PARAFAC-decomposed organic constituent. However, relatively strong fluorescence quenching phenomena were only detected in humic-like constituents (C2 and C3) with the titration of Pb(II) and Ni(II), which revealed that these types of organic constituent were predominantly responsible for Pb(II) and Ni(II) binding in urban forestland soil-derived DOM. Furthermore, considering the resistant nature of C2 and C3 constituents along with their significant quenching effects for the four target HMs, the concentrations of humic-like constituents in urban forestland soil may be a useful parameter to evaluate the potential risk of HMs immobilization and transformation.