Photodegradation of metoprolol in the presence of aquatic fulvic acids. Kinetic studies, degradation pathways and role of singlet oxygen, OH radicals and fulvic acids triplet states

Photodegradation of bisphenol A (BPA) in coastal aquaculture waters: Influencing factors, products, and pathways

Bisphenol A (BPA), an endocrine-disrupting contaminant, is ubiquitous in the environment due to its presence in plastics, wastewater, and agricultural runoff. This study investigated the photodegradation behavior of BPA in coastal aquaculture waters near Qingdao, China. Lower salinity promoted BPA photodegradation, while higher salinity has an inhibitory effect, suggesting slower degradation in seawater compared to ultrapure water. Triplet-excited dissolved organic matter (3DOM*) was identified as the primary mediator of BPA degradation, with additional contributions from hydroxyl radicals (•OH), singlet oxygen (1O2), and halogen radicals (HRS). Alepocephalidae aquaculture water exhibited the fastest degradation rate, likely due to its high DOM and nitrate/nitrite (NO3-/NO2-) content, which are sources of 3DOM* and •OH. A positive correlation existed between NO3-/NO2- concentration and the BPA degradation rate. Ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) analysis identified the primary BPA photodegradation products, formed mainly through oxidative degradation, hydroxyl substitution, nitration, and chlorination pathways. Elucidating these photodegradation mechanisms provides valuable insights into the environmental fate and potential ecological risks of BPA in aquaculture environments. This knowledge can inform strategies for marine environmental protection and the development of sustainable practices.

Transformation of metoprolol in UV/PDS process: Role and mechanisms of degradation and polymerization

Advanced oxidation processes for the treatment of organic pollutants in wastewater suffer from difficulties in mineralization, potential risks of dissolved residues, and high oxidant consumption. In this study, radical-initiated polymerization is dominated in an UV/peroxydisulfate (PDS) process to eliminate organic pollutant of pharmaceutical metoprolol (MTP). Compared with an ideal degradation-based UV/PDS process, the present process can save four fifths of PDS consumption at the same dissolved organic carbon removal of 47.3%. Simultaneously, organic carbon can be recovered from aqueous solution by separating solid polymers at a ratio of 50% of the initial chemical oxygen demand. The chemical structure of products was analyzed to infer the transformation pathways of MTP. Unlike previous studies on simple organic pollutants that the polymerization can occur independently, the polymerization of MTP is dependent on the partial degradation of MTP, and the main monomer in polymerization is a dominant degradation product (4-(2-methoxyethyl)-phenol, denoted as DP151). The separated solid polymers are formed by repeated oxidation and coupling of DP151 or its derivatives through a series of intermediate oligomers. This proof-of-concept study demonstrates the advantage of polymerization-dominated mechanism on dealing with large organic molecules with complex structures, as well as the potential of UV/PDS process for simultaneous organic pollution reduction and organic carbon recovery from aqueous solution.

Photochemical fate of β-blocker pindolol in riverine and its downstream coastal waters

Pindolol (PIN) is a commonly used β-blocker drug and has been frequently detected in various natural waters. Comprehensive understanding of its environmental photochemical transformation is necessary to assess its environmental risk. In this study, the photodegradation kinetics and mechanisms of PIN in both freshwater and coastal water were investigated for the first time. The photodegradation experiments were carried out by steady-state photochemical experiment under simulated sunlight irradiation. The results showed that the photodegradation rate of PIN in the freshwater of the Pearl River estuary was significantly faster than that in its downstream coastal water. In river water, PIN can undergo both direct photolysis and indirect photolysis induced by riverine dissolved organic matter (DOM) mainly through excited triplet-state of DOM and singlet oxygen, while direct photolysis dominated its degradation in coastal water. The promotion effect was found to be much greater for Suwannee River Natural Organic Matter (SRNOM) than that of the sampled riverine DOM, due to its high steady-state concentrations of reactive species. Interestingly, coastal DOM in northern and southern China were found to have similar promotion effects on PIN photodegradation for the first time, but both less than that of riverine DOM. A total of seven degradation products of PIN resulting from hydroxylation, hydrogen abstraction and cleavage of ether bond were identified. Biological toxicity of one products were found to be higher than that of PIN. These results are of significance for knowing the persistence and ecological risk of PIN in natural waters.

Formation of reactive intermediates in paddy water from different temperature zones for the promotion of abiotic ammonification

The paddy field is a hot area of biogeochemical process. The paddy water has a large capacity in photo-generation of reactive intermediates (RIs) due to abundant photosensitive dissolved organic matter (DOM), which is influenced by the spatial heterogeneity of paddy soils but rarely been explored. Our work presents the first investigation of the role of soil properties on photochemistry in paddy water. Soil organic matter (SOM), determined by the temperature, was the dominant factor for the photo-generation of RIs in paddy water of main rice producing areas. The RI concentrations generated with abundant SOM from cool regions are 0.05-8.71 times higher than those for the warm regions in China. The humic-like substance and aromatic-like compounds of DOM plays an essential role in RIs generation, which is abundant in paddy soils rich in SOM from Chinese cool regions. In addition, RIs can efficiently accelerate the photo-ammonification of urea and free amino acids by 15.2 %-164 %, leading to 0.13-0.17 mmol/L/d photo-produced ammonium after fertilization, which is preferentially absorbed by rice. The findings of this study will extend our knowledge of the geochemistry of global paddy field ecosystem. The potential role of RIs in nitrogen cycle should be highlighted in the agroecosystem.

Photocatalytic Degradation of Quinolones by Magnetic MOFs Materials and Mechanism Study

With the rising incidence of various diseases in China and the constant development of the pharmaceutical industry, there is a growing demand for floxacin-type antibiotics. Due to the large-scale production and high cost of waste treatment, the parent drug and its metabolites constantly enter the water environment through domestic sewage, production wastewater, and other pathways. In recent years, the pollution of the aquatic environment by floxacin has become increasingly serious, making the technology to degrade floxacin in the aquatic environment a research hotspot in the field of environmental science. Metal-organic frameworks (MOFs), as a new type of porous material, have attracted much attention in recent years. In this paper, four photocatalytic materials, MIL-53(Fe), NH2-MIL-53(Fe), MIL-100(Fe), and g-C3N4, were synthesised and applied to the study of the removal of ofloxacin and enrofloxacin. Among them, the MIL-100(Fe) material exhibited the best photocatalytic effect. The degradation efficiency of ofloxacin reached 95.1% after 3 h under visible light, while enrofloxacin was basically completely degraded. The effects of different materials on the visible photocatalytic degradation of the floxacin were investigated. Furthermore, the photocatalytic mechanism of enrofloxacin and ofloxacin was revealed by the use of three trappers (▪O2-, h+, and ▪OH), demonstrating that the role of ▪O2- promoted the degradation effect of the materials under photocatalysis.

Ti3C2-MXene/NiO Nanocomposites-Decorated CsPbI3 Perovskite Active Materials under UV-Light Irradiation for the Enhancement of Crystal-Violet Dye Photodegradation

Ti3C2-MXene material, known for its strong electronic conductivity and optical properties, has emerged as a promising alternative to noble metals as a cocatalyst for the development of efficient photocatalysts used in environmental cleanup. In this study, we investigated the photodegradation of crystal-violet (CV) dye when exposed to UV light using a newly developed photocatalyst known as Ti3C2-MXene/NiO nanocomposite-decorated CsPbI3 perovskite, which was synthesized through a hydrothermal method. Our research investigation into the structural, morphological, and optical characteristics of the Ti3C2-MXene/NiO/CsPbI3 composite using techniques such as FTIR, XRD, TEM, SEM-EDS mapping, XPS, UV-Vis, and PL spectroscopy. The photocatalytic efficacy of the Ti3C2-MXene/NiO/CsPbI3 composite was assessed by evaluating its ability to degrade CV dye in an aqueous solution under UV-light irradiation. Remarkably, the Ti3C2-MXene/NiO/CsPbI3 composite displayed a significant improvement in both the degradation rate and stability of CV dye when compared to the Ti3C2-MXene/NiO nanocomposite and CsPbI3 perovskite materials. Furthermore, the UV-visible absorption spectrum of the Ti3C2-MXene/NiO/CsPbI3 composite demonstrated a reduced band gap of 2.41 eV, which is lower than that of Ti3C2-MXene/NiO (3.10 eV) and Ti3C2-MXene (1.60 eV). In practical terms, the Ti3C2-MXene/NiO/CsPbI3 composite achieved an impressive 92.8% degradation of CV dye within 90 min of UV light exposure. We also confirmed the significant role of photogenerated holes and radicals in the CV dye removal process through radical scavenger trapping experiments. Based on our findings, we proposed a plausible photocatalytic mechanism for the Ti3C2-MXene/NiO/CsPbI3 composite. This research may open up new avenues for the development of cost-effective and high-performance MXene-based perovskite photocatalysts, utilizing abundant and sustainable materials for environmental remediation.

Nickel-iron-driven heterogenous bio-electro-fenton process for the degradation of methylparaben

Discharge of emerging contaminants such as parabens in natural water bodies is a grievous concern. Among parabens, methylparaben (MP) is most prevalent due to its extensive usage in personal care and food products and has been purported to trigger hormonal-related diseases. In this regard, the bio-electro-Fenton (BEF) process garners attention for remediating refractory compounds because of its ability to generate in situ hydroxyl radicals (•OH) utilising the energy harvested from electroactive microorganisms. In the present investigation, a Ni-Fe-driven heterogenous BEF system (BEF-MFC) was used to degrade MP from different matrices. At neutral catholyte pH, 99.54 ± 0.22% of MP was removed from an initial concentration of 10 mg/L in 240 min of retention time with an estimated treatment cost of about 1.01 $/m3. The removal rate ameliorated when the catholyte pH was dropped to 3.0 and by imposing an external voltage of 0.5 V, requiring just 120 min to achieve comparable MP removal efficiencies. However, catalyst leaching was higher at acidic pH (leaching of Fe ions = 0.44 mg/L and Ni ions = 0.06 mg/L) and applying external voltage increased the treatment cost slightly to 1.08 $/m3. Further, treatment of 10 mg/L MP-spiked real wastewater at pH of 7.0 with the BEF-MFC attained 85.70 ± 3.30% and 56.50 ± 1.70% reduction in MP and total organic carbon, respectively, in 240 min. In addition, a maximum power density of 205.90 ± 2.27 mW/cm2 was harvested in the BEF-MFC; thus, portraying the dual benefit of Ni-Fe heterogeneous catalyst. Even though, Ni-Fe performed reasonably well as Fenton-cum-cathode catalyst, future endeavours should be poised to fine-tune catalysts to accelerate H2O2 and •OH generation, which will reinforce the scalability of this system.

Degradation of metoprolol by UV/sulfite as an advanced oxidation or reduction process: The significant role of oxygen

The degradation of metoprolol (MTP) by the UV/sulfite with oxygen as an advanced reduction process (ARP) and that without oxygen as an advanced oxidation process (AOP) was comparatively studied herein. The degradation of MTP by both processes followed the first-order rate law with comparable reaction rate constants of 1.50×10^-3sec^-1 and 1.20×10^-3sec^-1, respectively. Scavenging experiments demonstrated that both e_aq^- and H• played a crucial role in MTP degradation by the UV/sulfite as an ARP, while SO₄^•- was the dominant oxidant in the UV/sulfite AOP. The degradation kinetics of MTP by the UV/sulfite as an ARP and AOP shared a similar pH dependence with a minimum rate obtained around pH 8. The results could be well explained by the pH impacts on the MTP speciation and sulfite species. Totally six transformation products (TPs) were identified from MTP degradation by the UV/sulfite ARP, and two additional ones were detected in the UV/sulfite AOP. The benzene ring and ether groups of MTP were proposed as the major reactive sites for both processes based on molecular orbital calculations by density functional theory (DFT). The similar degradation products of MTP by the UV/sulfite process as an ARP and AOP indicated that e_aq^-/H• and SO₄^•- might share similar reaction mechanisms, primarily including hydroxylation, dealkylation, and H abstraction. The toxicity of MTP solution treated by the UV/sulfite AOP was calculated to be higher than that in the ARP by the Ecological Structure Activity Relationships (ECOSAR) software, due to the accumulation of TPs with higher toxicity.

Enhanced degradation of few-layer black phosphorus by fulvic acid: Processes and mechanisms

The oxidation of the emerging nanomaterial black phosphorus (BP) affected by pH and oxygen has been carefully documented. However, in natural waters, there is a large amount of chemically reactive organic matters like fulvic acid (FA), whose impacts on degradation and stability of few-layer BP or BP nanosheets (BPNS) are scarcely disclosed. Hence, we investigated the kinetics of BPNS degradation products (H₂PO₂^-, HPO₃^2-, and PO₄^3-) in the presence of FA. The results showed that the apparent reaction rate constants of BPNS were 0.026, 0.050, and 0.060 d^-1 under oxygen-and-light condition and 0.005, 0.016, and 0.023 d^-1 under hypoxia-and-darkness condition at FA gradients of 0, 2.5, and 5 mgC/L, respectively. Microscopic observations, simple molecular simulation experiment, and density functional theory computation explained that FA significantly enhanced the degradation of P atoms on the BPNS surface through the indirect pathway of reducing the energy barrier of O₂ dissociative adsorption and the direct pathway of chemical adsorption, which caused the P-P bond on the BPNS surface to break down and formed P-O bonds or C-P bonds. This study revealed for the first time the degradation mechanism of BPNS in the presence of FA, which is a chemical mechanism of the BPNS transformation behavior. It helps to make a more scientific risk assessment of BP in natural waters.

Applying fulvic acid for sediment metals remediation: Mechanism, factors, and prospect

Fulvic acid (FA) has been shown to play a decisive role in controlling the environmental geochemical behavior of metals. As a green and natural microbial metabolite, FA is widely used in environmental remediation because of its good adsorption complexation and redox ability. This paper introduces the reaction mechanism and properties of FA with metals, and reviews the progress of research on the remediation of metal pollutant by FA through physicochemical remediation and bioremediation. FA can control the biotoxicity and migration ability of some metals, such as Pb, Cr, Hg, Cd, and As, through adsorption complexation and redox reactions. The concentration, molecular weight, and source are the main factors that determine the remediation ability of FA. In addition, the ambient pH, temperature, metal ion concentrations, and competing components in sediment environments have significant effects on the extent and rate of a reaction between metals and FA during the remediation process. Finally, we summarize the challenges that this promising environmental remediation tool may face. The research directions of FA in the field of metals ecological remediation are also prospected. This review can provide new ideas and directions for the research of remediation of metals contaminants in sediments.

Roles of humic substances redox activity on environmental remediation

Humic substances (HS) as representative natural organic matters and the most common organic compounds existing in the environment, has been applied to the treatment and remediation of environmental pollution. This review systematically introduces and summarizes the redox activity of HS for the remediation of environmental pollutants. For inorganic pollutants (such as silver, chromium, mercury, and arsenic), the redox reaction of HS can reduce their toxicity and mobilization, thereby reducing the harm of these pollutants to the environment. The concentration and chemical composition of HS, environmental pH, ionic strength, and competing components affect the degree and rate of redox reactions between inorganic pollutants and HS significantly. With regards to organic pollutants, HS has photocatalytic activity and produces a large number of reactive oxygen species (ROS) under the light which reacts with organic pollutants to accelerate the degradation of organic pollutants. Under the affection of HS, the redox of Fe(III) and Fe(II) can enhance the efficiency of Fenton-like reaction to degrade organic pollutants. Finally, the research direction of HS redox remediation of environmental pollution is prospected.

Fate and transport of pharmaceuticals in water systems: A processes review

Pharmaceuticals are globally consumed by humans and animals to support daily health and to treat disease. Following consumption, they may reach the aquatic environment either directly through the discharge of untreated wastewater to water bodies, or indirectly via treated wastewater as a result of their incomplete removal from wastewater treatment plants. This paper reviews the processes that control the occurrence and fate of pharmaceuticals in water systems, including sorption, photodegradation, hydrolysis and biodegradation. The degree to which these four processes occur is influenced by pharmaceutical types and their chemical structure as well as environmental factors such as sunlight, water depth, organic matter content, water chemistry, sediment properties, and type and abundance of microorganisms. Depending on the complex interactions of these factors, pharmaceutical compounds may be mineralized, partially degraded, or remain intact because they are resistant to degradation. Kinetic rate parameters and the half-life of a variety of pharmaceutical products are provided herein for the above processes under different environmental conditions. Usually, photodegradation and biodegradation represent dominant reaction processes, while hydrolysis only affects some pharmaceuticals, particularly antibiotics. The identified sorption and reaction rate parameters can be incorporated into a concise modeling framework to assess and predict longitudinal concentration profiles of pharmaceutical products in the manmade and natural systems, particularly when large amounts of pharmaceuticals are discharged during abnormal events such as a virus outbreak. Finally, future research is suggested, including the fate of transformed products (intermediates) in water systems.

Effects of dissolved organic matter characteristics on the photosensitized degradation of pharmaceuticals in wastewater treatment wetlands

Wastewater treatment wetlands are aquatic systems where diverse dissolved organic matter (DOM) compositions physically interact. Complex photochemical behaviors ensue, leading to uncertainties in the prediction of indirect photodegradation rates for organic contaminants. Here, we evaluate the photosensitization ability of whole water DOM samples from a treatment wetland and wastewater treatment plant (WWTP) in North Carolina to photodegrade target pharmaceuticals. Optical characterization using ultraviolet-visible and excitation-emission matrix spectroscopy shows that wetland DOM has higher aromaticity than WWTP DOM and that WWTP secondary treatment processes increase aromaticity, overall molecular weight, and humic character of wastewater DOM. Our application of a reversed-phase HPLC method to assess DOM polarity distinctly reveals that a subset of the wetland samples possesses an abundance of hydrophobic DOM moieties. Hydroxyl radicals (˙OH) mediate the majority (>50%) of the indirect photodegradation for amoxicillin (AMX), atenolol (ATL), and 17α-ethinylestradiol (EE2), while singlet oxygen (¹O₂) is presumed to be solely responsible for the photodegradation of cimetidine (CME). Our findings suggest that hydrophobic interactions and improved accessibility to photogenerated reactive intermediates lead to significant increases in photosensitization efficiencies and overall indirect photodegradation rates of AMX, ATL, and EE2 for the hydrophobic wetland samples. In contrast, CME photosensitization yields are unaffected by polarity and trend positively with optical indicators of sunlight-induced DOM photobleaching and humification, suggesting that wetland processing favors faster ¹O₂ photogeneration. These relationships highlight the uncertainties in photosensitization yields and effects of DOM optical properties and polarity on the photochemical fate of organic contaminants.

Atmospheric chemical processes of microcystin-LR at the interface of sea spray aerosol

Microcystins are the most toxic toxins released by cyanobacteria and they have adverse effects on aquatic ecosystems and even human health. Although the removal and detoxification of microcystins in various water bodies have been extensively studied, the interaction mechanism and reaction process of microcystins once they enter the atmosphere are largely unknown, especially at the organic-enriched sea spray aerosol (SSA) interface. Herein, using the surface technique of Langmuir trough coupled in-situ infrared reflection-absorption spectra, we studied the interfacial behavior of microcystin-LR (MC-LR) in artificial seawater containing humic acid and typical surfactants in the presence or absence of UV-irradiation. Zwitterionic 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and anionic stearic acid (SA) were chosen as typical film-forming species, results obtained from the surface pressure-area isotherms showed that MC-LR caused greater expansion of the DSPC monolayer. The comparable results of MC-LR in DSPC/SA-containing systems indicated that the interaction ability was closely related to the monolayer molecular structure and was regulated by electrostatic interaction. Furthermore, the presence of humic acid (HA) could enhance the interaction between microcystin and monolayer molecules. UV-irradiation experiments showed that the photosensitized reaction greatly promoted the removal of microcystin embedded in the SSA surface compared with the direct photolysis effect in the absence of HA. These findings highlight that the toxic effects of microcystins after entering the atmosphere may be weakened by photochemical reactions.

Mechanistic Study of the Effects of Agricultural Amendments on Photochemical Processes in Paddy Water during Rice Growth

The photochemical properties of paddy water might be affected by the commonly used amendments in rice fields owing to the associated changes in water chemistry; however, this important aspect has rarely been explored. We examined the effects of agricultural amendments on the photochemistry of paddy water during rice growth. The amendments significantly influenced the photogenerated reactive intermediates (RIs) in paddy water, such as triplet dissolved organic matter (³DOM*), singlet oxygen, and hydroxyl radicals. Compared with control experiments without amendments, the application of straw and lime increased the RI concentrations by up to 16.8 and 11.1 times, respectively, while biochar addition had limited effects on RI generation from paddy water in in situ experiments under sunlight. Fluorescence emission-excitation matrix spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry, and structural equation modeling revealed that upon the addition of straw and lime amendments, humified DOM substances contained lignins, proteins, and fulvic acids, which could produce more RIs under irradiation. Moreover, the amendments significantly accelerated the degradation rate of 2,4-dichlorophenol but led to the ³DOM*-mediated formation of more toxic and stable dimeric products. This study provides new insights into the effects of amendments on the photochemistry of paddy water and the pathways of abiotic degradation of organic contaminants in paddy fields.

Photoinactivation of Phage Phi6 as a SARS-CoV-2 Model in Wastewater: Evidence of Efficacy and Safety

The last two years have been marked by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. This virus is found in the intestinal tract; it reaches wastewater systems and, consequently, the natural receiving water bodies. As such, inefficiently treated wastewater (WW) can be a means of contamination. The currently used methods for the disinfection of WW can lead to the formation of toxic compounds and can be expensive or inefficient. As such, new and alternative approaches must be considered, namely, photodynamic inactivation (PDI). In this work, the bacteriophage φ6 (or, simply, phage φ6), which has been used as a suitable model for enveloped RNA viruses, such as coronaviruses (CoVs), was used as a model of SARS-CoV-2. Firstly, to understand the virus's survival in the environment, phage φ6 was subjected to different laboratory-controlled environmental conditions (temperature, pH, salinity, and solar and UV-B irradiation), and its persistence over time was assessed. Second, to assess the efficiency of PDI towards the virus, assays were performed in both phosphate-buffered saline (PBS), a commonly used aqueous matrix, and a secondarily treated WW (a real WW matrix). Third, as WW is generally discharged into the marine environment after treatment, the safety of PDI-treated WW was assessed through the determination of the viability of native marine water microorganisms after their contact with the PDI-treated effluent. Overall, the results showed that, when used as a surrogate for SARS-CoV-2, phage φ6 remains viable in different environmental conditions for a considerable period. Moreover, PDI proved to be an efficient approach in the inactivation of the viruses, and the PDI-treated effluent showed no toxicity to native aquatic microorganisms under realistic dilution conditions, thus endorsing PDI as an efficient and safe tertiary WW disinfection method. Although all studies were performed with phage φ6, which is considered a suitable model of SARS-CoV-2, further studies using SARS-CoV-2 are necessary; nevertheless, the findings show the potential of PDI for controlling SARS-CoV-2 in WW.

Activation of organic chloramine by UV photolysis: A non-negligible oxidant for micro-pollutant abatement and disinfection by-product formation

Due to the wide-presence of organic amines in natural waters, organic chloramines are commonly formed during (pre-)chlorination. With the increasing application of UV disinfection in water treatment, both the activation mechanism of organic chloramine by UV photolysis and its subsequent impact on water quality are not clear. Using sarcosine (Sar) as an amine group-containing compound, it was found that organic chloramines (i.e., Cl-Sar) would be firstly formed during chlorination even in the presence of natural organic matter. Compared with self-decay of Cl-Sar, UV photolysis accelerated Cl-Sar decomposition and induced NCl bond cleavage. Using metoprolol (MTP) as a model micro-pollutant, UV-activated Cl-Sar (UV/Cl-Sar) can accelerate micro-pollutant degradation, attributed to reactive radicals formation. HO^• and Cl^• were important contributors, with a total contribution of 45%‒64%. Moreover, the degradation rate of MTP by UV/Cl-Sar was pH-dependent, which monotonically increased from 0.044 to 0.065 min^‒1 under pHs 5.5‒8.5. Although the activation of organic chloramine by UV could accelerate micro-pollutant degradation, UV/Cl-Sar treatment could also enhance disinfection by-products formation. Trichloromethane (TCM) formation was observed during MTP degradation by UV/Cl-Sar. After post-chlorination, TCM, 1,1-dichloropropanone, 1,1,1-trichloropropanone, and dichloroacetonitrile were detected. Their individual and total concentrations were all positively proportional to UV/Cl-Sar treatment time. The total concentration with 30 min treatment (66.93 μg L^‒1) was about 2.3 times that with 1 min treatment (28.76 μg L^‒1). Finally, the accelerated effect was verified with Cl-glycine and Cl-alanine. It is expected to unravel the non-negligible role of organic chloramine on water quality during UV disinfection.

Separation of Photochemical and Non-Photochemical Diurnal In-Stream Attenuation of Micropollutants

For a better process understanding of in-stream attenuation of trace organic contaminants (TrOCs), quantitative comparisons between field studies under different environmental conditions and controlled laboratory experiments are important to separate different processes. However, this is hampered by the challenge to transfer kinetics from the laboratory to different field conditions due to the lack of good quantitative measures to account for different boundary conditions. For phototransformation, in situ light conditions in a river are difficult to determine because light is reduced, for instance, by absorption, scattering on suspended particles, and shading effects. In this study, we present an approach to separate photochemical from non-photochemical diurnal in-stream attenuation based on rate constants relative to diclofenac, as a reference compound, to account for the difference in the in situ light conditions combined with laboratory experiments. 12 out of 45 detected target TrOCs showed a diurnal attenuation at a selected river stretch. A non-photochemical process, potentially biotransformation, was responsible for the diurnal attenuation of bisoprolol, metoprolol, O-desmethylvenlafaxine, tramadol, and venlafaxine. Attenuation of amisulpride, flufenamic acid, hydrochlorothiazide, naproxen, and xipamide can be quantitatively explained by phototransformation, partially for sotalol. Attenuation rate constants of hydrochlorothiazide at different field sites from this study and from published data range over 2 orders of magnitude. Differences can be quantitatively explained by different light exposures but not by water chemical parameters.

Antimicrobial Photodynamic Approach in the Inactivation of Viruses in Wastewater: Influence of Alternative Adjuvants

Pathogenic viruses are frequently present in marine and estuarine waters, due to poor wastewater (WW) treatments, which consequently affect water quality and human health. Chlorination, one of the most common methods used to ensure microbiological safety in tertiarily treated effluents, may lead to the formation of toxic chemical disinfection by-products on reaction with organic matter present in the effluents. Antimicrobial photodynamic therapy (aPDT) can be a promising disinfecting approach for the inactivation of pathogens, without the formation of known toxic by-products. Additionally, some studies have reported the potentiator effect on aPDT of some compounds, such as potassium iodide (KI) and hydrogen peroxide (H2O2). In the present study, the aPDT efficiency of a PS formulation constituted of five cationic porphyrins (Form) in the inactivation of E. coli T4-like bacteriophage, a model of mammalian viruses, in different aqueous matrices with different organic matter content, was evaluated. Photoinactivation studies were performed at different concentrations of Form and in the presence of the adjuvants KI and H2O2. The results showed that the efficiency of bacteriophage photoinactivation is correlated with the Form concentration, the amount of the organic matter in WW, and the adjuvant type. Form can be an effective alternative to controlling viruses in WW, particularly if combined with H2O2, allowing to significantly reduce PS concentration and treatment time. When combined with KI, the Form is less effective in inactivating T4-like bacteriophage in WW.

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.

Photooxidation mechanism of As(III) by straw-derived dissolved organic matter

Straw return-to-field is a common agronomic practice that would affect the physicochemical characteristics of the paddy soil and overlying water, but few studies have focused on the possible impacts of straw return on the conversion of pollutants. In this study, the photooxidation of As(III) in aqueous solution by straw-derived dissolved organic matter (S-DOM) was investigated. The results showed that dissolved organic matter derived from wheat straw (DOMws) and rape straw (DOMrs) exhibited good spectroscopic features and could efficiently oxidize As(III) under irradiation at pH 5.0, with the k_obs values of As(III) oxidation being 0.15 h^-1 and 0.17 h^-1 for DOMws and DOMrs, respectively. Quenching studies indicated that hydroxyl radical (OH) dominated the oxidation of As(III) for both types of dissolved organic matter (DOM), though singlet oxygen (¹O₂) also played a role in the DOMrs system. Since acidic conditions are favorable for the formation of OH, As(III) oxidation decreased with an increase of pH value. Additionally, the oxidation efficiency of As(III) was inhibited in the presence of NO₃^- (0.2-2 mM) while enhanced in the presence of Fe(III) (5-50 μM). This study is of great significance for understanding the removal/transformation behavior of pollutants in paddy fields that receive straw return.

Lignocellulose Biomass as a Multifunctional Tool for Sustainable Catalysis and Chemicals: An Overview

Today, the theme of environmental preservation plays an important role within the activities of the scientific community and influences the choices of politics and the common population. In this context, the use of non-fossil substances should be promoted for different reasons: to avoid the depletion and damage of the areas involved in the fossil fuel extraction, decrease the impact of emissions/by-products related to the industrial transformation of fossil-based products and possibly exploit residual biomasses as sources of carbon. This latter aspect also can be viewed as a way to revalorize lignocellulose waste, generally destined to dump as putrescible matter or to be incinerated. In this review, we are aiming to present a concise overview of the multiple functions of lignocellulose biomass in the broad field of catalysis for a sustainable development. The originality of the approach is considering the lignocellulose-derived matter in three different aspects: (i) as a precursor to convert into platform molecules, (ii) as an active material (i.e., humic-like substances as photosensitizers) and (iii) as a green support for catalytic applications. We find that this perspective can widen the awareness level of scientists involved in the catalysis field for the exploitation of residual biomass as a valuable and complementary resource.

Multiple roles of dissolved organic matter released from decomposing rice straw at different times in organic pollutant photodegradation

Rice straw returning causes a considerable amount of dissolved organic matter (DOM) release into aquatic croplands in a relatively short-term. The presence of rice straw-derived DOM in cropland waters may alter the photochemical behaviors of organic pollutants. However, the photochemical activity and photosensitization role of the DOMs are poorly understood. Here, eight DOM samples were extracted from decomposing rice straw at different times in 49 days to explore their photosensitizing capacities toward diuron (DIU), 17β-estradiol (E2), and sulfamethoxazole (SMX). All of the DOMs were photosensitive and mainly composed of tryptophan-, tyrosine- and fulvic-like substances. Over the decomposition period, the amount of photochemically produced reactive intermediates (PPRIs) by the DOMs peaked on days 7 and 14. The evolution of the DOM photosensitizing capacity towards DIU and E2 was consistent with the variations of PPRIs, and HO· was confirmed as a critical factor. However, the influence of the DOMs on SMX photodegradation was opposite to that on DIU and E2. The positive role of the DOMs in SMX photodegradation was attributed to the tryptophan-like components. The results suggest that straw-derived DOM is an important photosensitizer and that its photosensitization towards organic pollutants is dependent on straw decomposing time and pollutant type.

Aqueous photodegradation of okadaic acid and dinophysistoxin-1: Persistence, kinetics, photoproducts, pathways, and toxicity evaluation

Diarrhetic shellfish poisoning (DSP) toxins are a class of natural organic contaminants that pose a serious threat not only to marine ecosystems and fisheries but also to human health. They are widely distributed in coastal and offshore waters around the world. However, the persistence and photochemical degradation characteristics of DSP in an aqueous environment are still unclear. This study aimed to elucidate the photochemical fate of two representative DSP toxins, namely, okadaic acid (OA) and dinophysistoxin-1 (DTX1). Results showed that photo-mediated chemical reactions play a crucial role in eliminating DSP toxins in seawater. However, the degradation of OA and DTX1 was relatively slow under natural solar radiation, with a removal efficiency of 90.0% after exposure for more than 20 days. When the reaction solutions of OA and DTX1 were exposed to Hg lamp radiation, their degradation followed pseudo-first-order kinetics, and was remarkably influenced by seawater pH and metal-ion concentration. A total of 24 tentative transformation products (TPs) of OA and DTX1 were identified via liquid chromatography high-resolution mass spectrometry. C12 (C₄₃H₆₆O₁₁) and C24 (C₄₄H₆₈O₁₁) were the main TPs. The following possible photodegradation pathways were proposed: decarboxylation, photoinduced hydrolysis, chain scission, and photo-oxidation. Toxicity assays via protein phosphatase 2A inhibition proved that photochemical processes could significantly reduce the DSP toxicity of irradiated solutions by approximately 88%. This work provides an enhanced understanding of the fate of DSP toxins in the aqueous environment, allowing for an improved assessment of their environmental impacts.

Phototransformation of biochar-derived dissolved organic matter and the effects on photodegradation of imidacloprid in aqueous solution under ultraviolet light

Dissolved organic matter (DOM) strongly influences the photodegradation of organic pollutants, varying depending on the structure of DOM. With the wide application of biochar, increasing amounts of DOM is released from biochar to the environment, which has different structural characteristics compared to natural DOM. In this study, DOM was derived from maize straw (MS) and pig manure (PM) and biochars by pyrolyzing MS and PM at 300 °C and 500 °C and the optical characteristics of DOM before and after phototransformation were explored via ultraviolet-visible spectroscopy and excitation-emission matrix fluorescence. Photodegradation of an insecticide, imidacloprid (IMI) in the presence of DOM was examined. The results showed that DOM derived from biochar obtained by pyrolyzing MS and PM mainly contained two identified fluorescent components and high pyrolysis temperature (500 °C) was associated with low molecular weight, small light-screening effects and great aromaticity of the DOM. After exposure to UV light, the aromaticity and molecular weight of the DOM declined due to phototransformation. Significant enhancement was observed in IMI photodegradation in the presence of biochar-derived DOM, and the enhancement was the greatest with DOM derived from pig manure biochar pyrolyzed at 500 °C. In addition to the light shielding effect, the ¹O₂ generated from DOM played an important role in the phototransformation of IMI and DOM. The loss of the nitro group and oxidation at the imidazolidine ring were the main photodegradation pathways for IMI. This study expands our understanding of the fate of biochar-derived DOM and its effects on the fate of coexisting organic pollutants.