Degradation Of Natural Organic Matter Research Articles

VUV coupled with low-dose H2O2 as pretreatment prior to UF: Performance, mechanisms, DBPs formation and toxicity evaluation

Ultrafiltration (UF) is widely used in drinking water plants; however, membrane fouling is unavoidable. Natural organic matter (NOM) is commonly considered as an important pollutant that causes membrane fouling. Herein, we proposed VUV/H2O2 as a UF pretreatment and used UV/H2O2 for comparison. Compared to UV/H2O2, the VUV/H2O2 system presented superior NOM removal. In the VUV/H2O2 system, the steady-state concentration of HO• was approximately twice that in the UV/H2O2 system, which was ascribed to the promoting effect of the 185 nm photons. Specifically, 185 nm photons promoted HO• generation by decomposing mainly H2O at a low H2O2 dose or by decomposing mainly H2O2 at a high H2O2 dose. The VUV/H2O2 pretreatment also demonstrated better membrane fouling mitigation performance than did UV/H2O2. An increase in the H2O2 dose promoted HO• generation, thereby enhancing the performance of NOM degradation and membrane fouling alleviation and shifting the major membrane fouling mechanism from cake filtration to standard blocking. The VUV/H2O2 (0.60 mM) pretreatment effectively reduced disinfection byproducts (DBPs) formation during chlorine disinfection. Additionally, the oxidant H2O2 affected the membrane surface morphology and performance but had no evident effect on the mechanical properties. In actual water treatment, the VUV/H2O2 pretreatment exhibited better performance than the UV/H2O2 pretreatment in easing membrane fouling, ameliorating water quality, and reducing DBPs formation and acute toxicity.

Monitoring natural organic matter in drinking water treatment with photoelectrochemical oxygen demand

AbstractConventional metrics such as total organic carbon (TOC) and ultraviolet absorbance at 254 nm (UV254) may oversee aspects of natural organic matter (NOM) reactivity in drinking water treatment. The novel photoelectrochemical oxygen demand (peCOD) analyzer indirectly measures the oxygen consumed during NOM oxidation with photo‐ and electrochemical methods, quantifying NOM reactivity. peCOD was valuable for tracking NOM degradation in nine drinking water treatment facilities, particularly in processes where conventional metrics failed to capture changes in NOM from partial oxidation (e.g., biofiltration and oxidation). However, peCOD exhibited moderate correlations with TOC (R2 = 0.67) and UV254 (R2 = 0.48), indicating the need for its concurrent use with conventional methods. While peCOD was not a significant predictor of disinfection by‐product formation potential (R2 < 0.20), its inclusion alongside standard NOM metrics improved the performance of multivariable regression models. Thus, peCOD provided a rapid, standardized, operator‐friendly, environmentally conscious, concentration‐based approach for evaluating NOM characteristics in drinking water samples.

Excessive Ozonation Stress Triggers Severe Membrane Biofilm Accumulation and Fouling.

The established benefits of ozone on microbial pathogen inactivation, natural organic matter degradation, and inorganic/organic contaminant oxidation have favored its application in drinking water treatment. However, viable bacteria are still present after the ozonation of raw water, bringing a potential risk to membrane filtration systems in terms of biofilm accumulation and fouling. In this study, we shed light on the role of the specific ozone dose (0.5 mg-O3/mg-C) in biofilm accumulation during long-term membrane ultrafiltration. Results demonstrated that ozonation transformed the molecular structure of influent dissolved organic matter (DOM), producing fractions that were highly bioavailable at a specific ozone dose of 0.5, which was inferred to be a turning point. With the increase of the specific ozone dose, the biofilm microbial consortium was substantially shifted, demonstrating a decrease in richness and diversity. Unexpectedly, the opportunistic pathogen Legionella was stimulated and occurred in approximately 40% relative abundance at the higher specific ozone dose of 1. Accordingly, the membrane filtration system with a specific ozone dose of 0.5 presented a lower biofilm thickness, a weaker fluorescence intensity, smaller concentrations of polysaccharides and proteins, and a lower Raman activity, leading to a lower hydraulic resistance, compared to that with a specific ozone dose of 1. Our findings highlight the interaction mechanism between molecular-level DOM composition, biofilm microbial consortium, and membrane filtration performance, which provides an in-depth understanding of the impact of ozonation on biofilm accumulation.

Chemical-free vacuum ultraviolet irradiation as ultrafiltration membrane pretreatment technique: Performance, mechanisms and DBPs formation

Membrane fouling induced by natural organic matter (NOM) has seriously affected the further extensive application of ultrafiltration (UF). Herein, a simple, green and robust vacuum ultraviolet (VUV) technology was adopted as pretreatment before UF and ultraviolet (UV) technology was used for comparison. The results showed that control effect of VUV pretreatment on membrane fouling was better than that of UV pretreatment, as evidenced by the increase of normalized flux from 0.27 to 0.38 and 0.73 after 30 min UV or VUV pretreatment, respectively. This is related to the fact that VUV pretreatment exhibited stronger NOM degradation ability than UV pretreatment owing to the formation of HO•. The steady-state concentration of HO• was calculated as 3.04 × 10−13 M and the cumulative exposure of HO• reached 5.52 × 10−10 M s after 30 min of VUV irradiation. And the second-order rate constant between NOM and HO• was determined as 1.36 × 104 L mg−1 s−1. Furthermore, fluorescence EEM could be applied to predict membrane fouling induced by humic-enriched water. Standard blocking and cake filtration were major fouling mechanisms. Moreover, extension of UV pretreatment time increased the disinfection by-products (DBPs) formation, the DBPs concentration was enhanced from 322.36 to 1187.80 μg/L after 210 min pretreatment. However, VUV pretreatment for 150 min reduced DBPs content to 282.57 μg/L, and DBPs content continued to decrease with the extension of pretreatment time, revealing that VUV pretreatment achieved effective control of DBPs. The variation trend of cytotoxicity and health risk of DBPs was similar to that of DBPs concentration. In summary, VUV pretreatment exhibited excellent effect on membrane fouling alleviation, NOM degradation and DBPs control under a certain pretreatment time.

Comparative study of UV/chlorine and VUV/chlorine as ultrafiltration membrane pretreatment techniques: Performance, mechanisms and DBPs formation

Membrane fouling, primarily resulting from natural organic matter (NOM) widely existing in water sources, has always been a chief hindrance for the prevalent application of ultrafiltration (UF). Thus, vacuum ultraviolet (VUV)/chlorine process was proposed as a strategy for UF membrane fouling control and ultraviolet (UV)/chlorine process was used for comparison. VUV/chlorine process exhibited more excellent performance on NOM removal than UV/chlorine process. [HO•]ss and [Cl•]ss were calculated as 1.26 × 10−13 and 3.06 × 10−14 M, respectively, and ClO• might not exist under the conditions of 0.08 mM chlorine and 30 min VUV irradiation. [HO•]ss, [Cl•]ss and [ClO•]ss were not available and the formation of reactive radicals was unsustainable in UV/chlorine system. Moreover, VUV/chlorine pretreatment also showed better performance on the reversible and irreversible membrane fouling control than UV/chlorine pretreatment. The dominated fouling mechanism in the final stage of filtration was cake filtration. Additionally, the amount of detected disinfection by-products (DBPs) in VUV/chlorine system was significantly lower than that in UV/chlorine system. During subsequent chlorination disinfection, the yield of DBPs with VUV/chorine pretreatment was higher than that with UV/chlorine pretreatment. VUV/chlorine pretreatment could effectively control DBPs formation when the pretreatment time was extended to 120 min. In summary, VUV/chlorine system presented a most excellent performance on membrane fouling control, NOM degradation and DBPs control.

Controlling ultrafiltration membrane fouling in surface water treatment via combined pretreatment of O3 and PAC: Mechanism investigation on impacts of technological sequence

In this research, the effects of combined powdered activated carbon (PAC)-ozone (O3) pretreatment on ultrafiltration (UF) performance were comprehensively examined and compared with the conventional O3-PAC pretreatment. The performance of pretreatments on mitigating membrane fouling caused by Songhua River water (SHR) was evaluated by specific flux, membrane fouling resistance distribution, and membrane fouling index. Moreover, the degradation of natural organic matter in SHR was investigated by UV absorbance at 254 nm (UV254), dissolved organic carbon (DOC), and fluorescent organic matter. Results showed that the 100PAC-5O3 process was the most effective in improving the specific flux, with 82.89 % and 58.17 % reductions in the reversible fouling resistance and irreversible fouling resistance respectively. Additionally, the irreversible membrane fouling index was reduced by 20 % relative to 5O3-100PAC. The PAC-O3 process also exhibited superior performance in the degradation of UV254, DOC, three fluorescent components, and three micropollutants in the SHR system compared to O3-PAC pretreatment. The O3 stage played a major role in mitigating membrane fouling, while PAC pretreatment enhanced the oxidation in the subsequent O3 stage during the PAC-O3 process. Furthermore, the Extended Derjaguin-Landau-Verwey-Overbeek theory and pore blocking-cake layer filtration model fitting analysis were employed to explain the mechanisms of membrane fouling mitigation and fouling patterns transformation. It was found that PAC-O3 significantly increased the repulsive interactions between the foulants and the membrane, which restrained the formation of the cake layer filtration stage. Overall, this study evidenced the potential of PAC-O3 pretreatment in surface water treatment applications, providing new insights into the mechanism of controlling membrane fouling and improving the permeate quality.

Degradation of natural organic matter and disinfection byproducts formation by solar photolysis of free available chlorine

Environment disinfection effectively curbs transmission of the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). However, elevated concentration of free available chlorine (FAC) in disinfectants can be discharged into surface water, generating toxic disinfection byproducts (DBPs). The impact of solar photolysis of FAC on natural organic matter (NOM) to form DBPs has not been well studied. In this work, solar photolysis of FAC was found to result in higher formation of DBPs, DBPs formation potential (DBPsFP), total organic chlorine (TOCl) and lower specific ultraviolet absorbance at 254 nm (SUVA254), compared to dark chlorination. In solar photolysis of FAC, formation of total DBPs was promoted by pH=8, but hindered by the addition of HCO3−, radical scavenger or deoxygenation, while addition of NO3−and NH4+both enhanced the formation of nitrogenous DBPs. Differences in the formation of DBPs in solar photolysis of FAC under various conditions were influenced by reactive species. The formation of trichloromethane (TCM) and haloacetic acids (HAAs) in solar photolysis of FAC positively correlated with the steady-state concentrations of ClO• and O3. The steady-state concentrations of •NO and •NH2 positively correlated with the formation of halonitromethanes (HNMs). HAAs and haloacetonitriles (HANs) mainly contributed to calculated cytotoxicity of DBPs. This study demonstrates that solar photolysis of FAC may significantly impact the formation of DBPs in surface water due to extensive use of disinfectants containing FAC during SARS-CoV-2 pandemic.

Cobalt oxide decorated activated carbon/peroxymonosulfate pretreatment for ultrafiltration membrane fouling control in secondary effluent treatment: Insights into interfacial interaction and fouling model transformation

To control the ultrafiltration (UF) membrane fouling caused by the secondary effluent, cobalt oxide loaded activated carbon (CoOx-PAC) activating peroxymonosulfate (PMS) was applied as a pretreatment. The degradation of natural organic matter (NOM) and membrane fouling mitigation performance for the CoOx-PAC/PMS pretreatment were comprehensively investigated. The dissolved organic carbon (DOC), fluorescent organics, and phenol in the secondary effluent system were utilized to evaluate the removal effect of the CoOx-PAC/PMS process on the organic matter. Results showed that 100 mg/L 0.5 %CoOx-PAC combined with 2 mM PMS (0.5 %CoOx-PAC/PMS) had an excellent degradation on NOM, removing 84.92 % of DOC, and above 97 % of fluorescent organics within 120 min. The catalytic activity of phenol in this process was even superior to that of homogeneous catalysis (Co2+/PMS). Moreover, the normalized specific flux and membrane fouling resistance were employed to verify the influences of the CoOx-PAC/PMS on membrane fouling. The 0.5 %CoOx-PAC/PMS system significantly improved the specific flux, with a 94.26 % decline in reversible membrane fouling resistance and a 53.05 % reduction in irreversible fouling resistance. O2•− and 1O2 were involved in the reaction as crucial reactive oxide species according to electron paramagnetic resonance and quenching tests. They changed the physicochemical properties of NOM, which decomposed the high molecular weight organics into low molecular weight hydrophilic fractions, thereby delaying the formation of cake layers and alleviating membrane fouling. The Extended Derjaguin-Landau-Verwey-Overbeek theory was used to assess the interaction between the foulants and the UF membranes. The transformation of fouling models was analyzed and found that the intricate membrane fouling filtration mechanisms were transformed into a single standard blocking mode after 0.5 %CoOx-PAC/PMS pretreatment.

New insights into interfacial interaction and nanoconfinement effect in synergistic oxidation-filtration via CoFe2O4-ceramic membrane activated peroxymonosulfate

Ceramic membranes incorporating CoFe2O4 (CoFeCM) were synthesized to activate peroxymonosulfate (PMS), and the performance and mechanisms of its oxidation-filtration were comprehensively investigated. The catalytic filtration performance of CoFeCM/PMS was evaluated by degradation of organic pollutants and the mitigation of membrane fouling. Results indicated that CoFeCM/PMS effectively removed toxic micropollutants, including phenol (82.56%), atrazine (93.42%), and carbamazepine (87.40%), ensuring the permeate quality and safety. Also, this synergistic process notably improved the degradation of natural organic matter (NOM) in the secondary effluent and Songhua River water. CoFeCM/PMS filtration effectively mitigated membrane fouling caused by three typical model organics, reducing their irreversible membrane fouling resistance by 70.85–83.62%, and increasing the normalized flux to 48.74–82.61%. The membrane fouling derived from two actual water systems was also greatly alleviated by CoFeCM/PMS. Based on the Extended Derjaguin-Landau-Verwey-Overbeek theory analysis, NOM was oxidized by reactive oxide species into hydrophilic small molecular fractions, resulting in remarkably increased repulsive interaction between NOM and CoFeCM surface. Density functional theory calculation results confirmed the nanoconfinement effect in CoFeCM pores, which can slow down the growth of foulants in pores and effectively alleviate irreversible membrane fouling. Consequently, standard blocking transformed into the dominant membrane fouling pattern due to the synergistic effects of nanoconfinement catalysis (in membrane pores) and repulsive interactions (on membrane surface) during oxidation-filtration.

Water Purification and Electrochemical Oxidation: Meeting Different Targets with BDD and MMO Anodes

The complex composition of natural organic matter (NOM) can affect drinking water treatment processes, leading to perceptible and undesired taste, color and odor, and bacterial growth. Further, current treatments tackling NOM can generate carcinogenic by-products. In contrast, promising substitutes such as electrochemical methods including electrooxidation (EO) have shown safer humic acid and algae degradation, but a formal comparison between EO methods has been lacking. In this study, we compared the Boron-doped diamond (BDD) electrode electrolysis performance for Suwannee River NOM degradation using mixed-metal oxide (MMO) anodes under different pH (6.5 and 8.5) representative of the high and low ranges for acidity and alkalinity in wastewater and applied two different current densities (10 and 20 mA cm−2). BDD anodes were combined with either BDD cathodes or stainless steel (SS) cathodes. To characterize NOM, we used (a) total organic compound (TOC), (b) chemical oxygen demand (COD), (c) specific ultraviolet absorbance (SUVA), and (d) specific energy consumption. We observed that NOM degradation differed upon operative parameters on these two electrodes. BDD electrodes performed better than MMO under stronger current density and higher pH and proved to be more cost-effective. BDD-SS electrodes showed the lowest energy consumption at 4.4 × 103 kWh kg COD−1. while obtaining a TOC removal of 40.2%, COD of 75.4% and SUVA of 3.4 at higher pH and current. On the contrary, MMO produced lower TOC, COD and SUVA at the lower pH. BDD electrodes can be used in surface water as a pre-treatment in combination with some other purification technologies to remove organic contaminants.

Magnetic visible-light activated photocatalyst CuFe2O4/Bi2WO6/mpg-C3N4 for the treatment of natural organic matter

Despite growing interest in research on visible-light-driven photocatalysts, reusable photocatalysts have not been extensively developed for the treatment of natural organic matter (NOM), because such development requires an understanding of the complex NOM structures. In this study, we combined the individual benefits of CuFe2O4, Bi2WO6, and mesoporous graphitic carbon nitride (mpg-C3N4) to prepare a magnetic, visible-light-driven photocatalytic composite, CBC-5, for effectively removing NOM in a short period of time. The degradation mechanisms were further explored at the molecular level through ultra-high-resolution mass spectrometry. Broad light absorbance and charge transmission based on a dual S-scheme pathway allowed CBC-5 to generate multiple active agents, OH (49.7 %), O2− (27.6 %), and h+ (24.8 %), which ultimately led to the removal of 7.9 mgC of NOM per 0.9 g of CBC-5 in 6 h. Humic-like fluorophores were preferentially degraded, followed by the generation of simple phenolic components as by-products. Molecular-level investigation revealed that the NOM structures with high degree of unsaturation and functionalization were preferentially attacked by the radicals. Oxygenic groups were formed upon the oxidation of the unsaturated bonds and the functional groups having a low oxidation state of carbon (OSc) before the degradation of the carboxyl-rich alicyclic molecules. NOM degradation was prioritized in the following order: CHON > CHO > CHOS. Oxidative deamination is attributed to the preferential degradation of N-containing compounds, which are partially transformed to CHO compounds. CHOS compounds enriched with aliphatic organosulfates were recalcitrant to photocatalytic oxidation. Thus, CBC-5 demonstrated convenient magnetic recovery, stable performance, and high recyclability and can be applied as a promising NOM treatment agent.

Mechanisms of iodine enrichment in the pore-water of fluvial/lacustrine aquifer systems: Insight from stable carbon isotopes and batch experiments

• High iodine groundwater occurs in discharge area of fluvial/lacustrine aquifer systems. • Local transformation of sediment Fe minerals explains the enrichment of pore-water iodine in the deep sediments. • Iodine-rich pore-water in the shallow sediments near the coastal area is related to the marine transgressions. The wide occurrence of high iodine groundwater is posing negative effects on human health. The land subsidence due to groundwater over-exploitation causes the release of iodine-rich pore-water trapped in clayey sediment into groundwater, however, the mechanisms of iodine enrichment in pore-water were still unclear. In this study, we selected the Datong Basin (DB) and North China Plain (NCP) with few and severe land subsidence, respectively, to understand the contributions of complex hydro-biogeochemical processes on the enrichment of iodine in groundwater and pore-water by using the inorganic/organic carbon isotope and batch experiments. The results showed that at the DB, the range of groundwater iodine was 4–2175 µg/L, and the enrichment of groundwater iodine is mainly related to the transformation of iron oxyhydroxides triggered by microbial degradation of organic matter, which was reflected by the more depleted δ 13 C DIC signatures of groundwater and gradual increasing trend of ratio of HCl-extractable Fe(II)/sediment Fe total and sediment δ 13 C DOC signatures with depth. In comparison, groundwater iodine at the NCP had the range of 2–1106 µg/L, and pore-water rich in iodine preserved in the clayey sediment serves as the main source. The depth profiles of sediment iron mineral fractions and δ 13 C DOC signatures suggested that the NCP sediments experienced lower degree of reductive transformation of iron minerals and microbial degradation of natural organic matter. At some specific depths higher than 300 m, the evident higher ratios of HCl-extractable Fe(II)/sediment Fe total indicate that the local transformation of iron minerals can explain the pore-water rich in iodine at deep sediments, which was supported by the results of microbial batch experiments. The pore-water with high iodine concentration preserved in the shallow sediment is more likely related to the marine transgressions. This study helps to improve our understanding of the mechanisms of high iodine groundwater, which may provide some new insights on further groundwater management.

Spectroscopic characteristics and disinfection byproduct formation during UV-assisted photoelectrochemical degradation of humic acid

UV-assisted photoelectrochemical processes (UV/E) that produce reactive species are extensively used for degrading pollutants in water, such as natural organic matter (NOM). However, the consequence of the chlorinated disinfection byproducts (DBPs) from smaller compounds broken down is not clear in the UV/E. In this study, excitation-emission matrices (EEM) and parallel factor analysis (PARAFAC) were applied to determine the products formed during decomposition and the influence of UV/E processes on the formation of DBPs. In comparison with UV photochemical and electrochemical processes, the deterioration rate of NOM in the UV/E process rose by 68.45% and 54.47% in 70 min, while it increased up to 48.85% under the electrochemical process in 23 h. Not only does the reaction time affect the degradation, but the electrolyte concentration and current density also disturb it. The EEM peak locations were 275 nm/495 nm (Component 1), 275 nm/410 nm (Component 2), 230 nm/405 nm (Component 3), and <220 nm/290 nm (Component 4), which were considered to humic acids, hum-like compounds, fulvic acid-like compounds, and aromatic proteins, respectively. C1 and C2 were well relevant to dissolved organic carbon (DOC) and UV254 (r = 0.925–0.963, p < 0.01) and the formation of MCAA, DCAA, and TCAA were strongly interrelated with UV254 and DOC (r = −0.711 to −0.584). The generation of DBPs has a good correlation with C2 (r = – 0.673, p < 0.01). DBPs formation and calculated theoretical cytotoxicity were significantly suppressed by the UV/E process with a higher degradation of NOM. A similar amount of DBPs formation was obtained while 52.6% and 82.90% of the DOC was reduced under the electrochemical process and the UV/E process, indicating that a lower DBPs production and higher degradation efficiency in the UV/E process. It was supposed that the UV/E process could be an alternative for natural organic matter oxidation with properly controlled DBP formation.

Copper doped Fe-N-C as an excellent Fenton-like catalyst for membrane fouling mitigation against natural organic matters at neutral pH

The presence of humic substances as a component of natural organic matter (NOM) may cause inefficiency towards drinking water treatment processes, especially the membrane fouling during filtration process. Therefore, to enhance the efficiency of the conventional membrane filtration process, several copper doped Fe-N-C bimetallic heterogeneous Fenton-like catalysts (Cux@FeNC) were prepared and evaluated by executing their catalytic degradation performance against NOM. Results indicated that humic acid (HA, 10 mg/L) could be significantly degraded (95%) within 30 min application of Cu5p@FeNC-Fenton under neutral pH, which was relatively higher than of FeNC-Fenton (70%) under identical conditions. The macromolecular organic matters in NOM could be destroyed more effectively while the overall mineralization degree also became relatively higher. Meanwhile, a lower membrane fouling of UF (PES 20 kDa)/NF (DOW 270) and highest flux recovery after backwash were observed with Cu5p@FeNC-Fenton treatments. Characterization and chemical analysis further explored the introduction of Cux in FeNC was responsible for the rapid reactive oxygen species (ROS) generation and efficient degradation of NOM. Additionally, a possible copper-iron synergetic mechanism in Fenton-like system was proposed. This work gives a deep insight into the potential NOM degradation using Fenton-like Cux@FeNC catalysts and ensures the membrane fouling mitigation for effective water treatment processes.

Laccase-Coated Polyethersulfone Membranes for Organic Matter Degradation and Removal

Natural organic matter (NOM) removal from water is getting progressively significant for water treatment plants not only to improve drinking water aesthetics such as taste and smell, but also to avoid disinfection by-products (DBPs) formed during disinfection by chlorine. This study applies the catalytic properties of the wood degrading laccase enzyme produced by white rot fungi (WRF) on breaking down and removing organic matter in drinking water. White rot fungi isolates were collected and examined for their ability to degrade humic acid (HA), a NOM model compound. Highly permeable polyethersulfone (PES) membrane was prepared following the phase inversion process and used as material to support the immobilization of the lignin-degrading enzymes extracted from Perenniporia sp. and Polyporaceae sp. for NOM degradation and removal. A 52 % humic acid removal was recorded for the Polyporaceae sp. The addition of laccase substrate 4-hydroxybenzoic acid showed a great impact on the hydrophilicity of the membranes as a decrease in contact angle measurements of <60 was achieved. Moreover, modified membrane’s immobilization yield and enzyme activity also improved. The modified membrane achieved a rejection of greater than 90 % for the model compound. Enzyme activity was a function of contact time and substrate type. The attained results revealed that catalytic membranes can be an efficient alternative for NOM removal and membrane fouling alleviation during water treatment.

A simple ZVI-Fenton pre-oxidation using steel-nails for NOM degradation in water treatment

The feasibility of a heterogeneous Fenton Process (ZVI/H2O2) using commercial low-carbon-steel nails as the Zero-Valent Iron (ZVI) source was evaluated for the first time for the removal of natural organic matter (NOM) from natural surface waters with distinct physico-chemical characteristics. The synergistic effect of ZVI nails and H2O2 on the process was confirmed. Results showed similar removal efficiencies of NOM in water samples from Thames river and Regent's Park lake (both in London, UK) (under initial pH 3.5 and 100% excess of H2O2 dosage), reaching dissolved organic carbon (DOC) removals of 61.6% ± 3.0 and 59.6% ± 4.7, and UV254 removals of 79.9% ± 0.6 and 77.3 ± 6.2, respectively with 60 min of batch reaction time. ZVI nail surface characterization by scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), and X-ray photoemission spectroscopy (XPS) revealed the formation of a passivating oxide-hydroxide layer on the nail during the reaction, which reduces its surface activity with 20% in continuous use. Results indicate that ZVI/H2O2 process using commercial iron nails is a promising pre-oxidation step for drinking water treatment. The low cost of commercial nails together with the facility of separating them from the water are the main advantages for the application of this process in remote regions with limitations in infrastructure and/or finance.

Iron-doped zinc oxide for photocatalyzed degradation of humic acid from municipal wastewater

Degradation of natural organic matter especially Humic acid is a big challenge, while its byproducts are carcinogenic, which is a threat to life. Here, Fe3+:ZnO has been deployed on ceramic plats (CP) using SILAR method for solar photocatalytic mineralization of HA in municipal wastewater. Structural results show that ZnO and Fe3+:ZnO deployed over CP have an average crystallite size of 47.43 nm and 29.54 nm, respectively. Further, Fe3+ doping increased the conductivity of ZnO due to enhanced photon capturing ability and effective surface area. Almost 90% HA photodegradation was achieved at the reaction parameters optimized by response surface methodology. Owing to the strong interaction between negatively charged HA and positive zeta potential of ZnO@CP (24 mV) and Fe3+:ZnO@CP (26 mV). Moreover, a significant reduction in BOD (~73%), COD (~76%) and TOC (~63%) have been observed after solar photocatalytic treatment of municipal wastewater. In comparison, ZnO@CP hybrid removed HA (400 mgL−1) at the rate of 3.3 kgm−3d−1 with a lower reduction in BOD (~57%), COD (~45%) and TOC (~57%) than Fe3+:ZnO@CP, confirming that the Fe doping has tuned the bandgap and manipulated the active sites onto the surface of ZnO. Moreover, direct coating of photocatalyst over CP provided exceptional stability and reusability as a photocatalyst which maintained ~80% of its activity even after 14 cycles of wastewater treatment and only lose 29% of its activity after 22 cycles. Hence, by designing a photocatalyst adhered directly onto the ceramic (substrate) present the novel sustainable photocatalyst supported wastewater treatment systems at a large scale.

Degradation of natural organic matter using Ag-P25 photocatalyst under continuous and periodic irradiation of 405 and 365 nm UV-LEDs

Removal of natural organic matter (NOM) in drinking water is an important objective imposed by water utilities due to plant operational problems, taste and odor issues. Photocatalysis using titanium dioxide (TiO2) has been increasingly explored in water treatment studies as a potential technology to remove NOM, with most studies employing 365 nm UV light. However, photocatalysis under this wavelength limits the application of UV/TiO2 to larger scales as it is not cost-effective and energy-efficient. We approached this limitation by exploring the impact of switching between periodic and continuous irradiation when removing NOM under both non-visible and visible light exposure (365 and 405 nm). In addition, we used silver (Ag) to increase the photocatalytic efficiency of TiO2 in the visible region. The optimum concentration of Ag was first investigated by comparing the surface area, and hydroxyl radical (˙OH) formation rate of Ag-P25 with different Ag:P25 ratios. Of the Ag:P25 ratios explored, 1.29% Ag-P25 was found to be the optimal based on high surface area and ˙OH formation rate. The effect of periodic irradiation on Suwanee River NOM removal using two wavelengths was then investigated. Dissolved organic carbon (DOC) concentrations and UV absorbance at 254 nm (UV254) indicated that the 1.29% Ag-P25 was more efficient than P25 at a higher irradiation cycle of 365 nm. The electrical energy per order (EEO) values calculated for each treatment further indicated that using 1.29% Ag-P25 resulted in a lower energy requirement for removing DOC and UV254 than P25.

H2O2-assisted photocatalysis for removal of natural organic matter using nanosheet C3N4-WO3 composite under visible light and the hybrid system with ultrafiltration

In this study, a nano-sheet C3N4-WO3 composite (nsCW21) was applied as a visible-light active photocatalyst to degrade natural organic matter (NOM). The nsCW21 photocatalyst exhibited a higher removal efficiency for NOM than the bare host and other composite counterparts due to the effective separation of the charge carriers in the Z-scheme pathway. The addition of H2O2 resulted in the enhanced photocatalytic performance via the generation of hydroxyl radicals from the catalyst with an NOM removal rate of up to 71% for 5 h. The catalyst showed a considerable stability, which held a good NOM degradation efficiency during five cycle runs. The complex NOM removal behavior was unraveled by using a fluorescence excitation emission matrix-parallel factor analysis and a two-dimensional correlation spectroscopy (2D-COS) combined with Fourier-transform infrared spectroscopy (FT-IR). The large sized and the terrestrial humic-like component exhibited a high adsorption tendency toward the catalyst and was degraded primarily by h+, while a typical humic-like component, which is mainly removed by .OH, displayed a high degradation rate constant (k = 0.159 h−1). The 2D-COS revealed the sequence of the preferable removal among the different NOM functional groups in the nsCW21 system with H2O2 addition, which occurred in the order of open ring reaction > oxygenated functional groups > the transformation into aliphatic compounds/inorganic moieties. Meanwhile, the hybrid system that employed ultrafiltration as a post-treatment demonstrated synergetic effects on the improved effectiveness for NOM removal in the overall system, which was a total of 91%, of the residuals from the precedent photocatalysis as well as alleviating the membrane fouling.

Enrichment of Geogenic Ammonium in Quaternary Alluvial-Lacustrine Aquifer Systems: Evidence from Carbon Isotopes and DOM Characteristics.

Geogenic ammonium in groundwater owing to mineralization of natural organic matter (NOM) has been reported in different geologic settings, but detailed mechanisms responsible for high ammonium concentration levels are poorly understood. To this end, we chose Quaternary high ammonium aquifer systems in central Yangtze River basins and used carbon isotopes in both dissolved organic carbon and inorganic carbon together with characterization of dissolved organic matter (DOM) and groundwater chemistry to reveal mechanisms related to the genesis of ammonium. The results indicate that high levels of geogenic ammonium (up to 33.50 mg/L as N) occur due to long-term water-rock interactions in a relatively sluggish hydrogeological environment with abundant organic matter that is rich in both C and N. The stable carbon isotope data suggest that ammonium in the groundwater is released from intensive degradation of organic matter with higher contents of ammonium associated with methanogenesis. The optical signatures of DOM indicate ammonium in the groundwater is mostly associated with terrestrial humic-like components rather than protein-like components. Molecular characterization of DOM by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) shows that, compared to low ammonium groundwater, high ammonium groundwater has larger mass weights, greater abundance of CHO+N compounds, higher percentages of lignin- and condensed-hydrocarbon-like components, lower H/C ratios, higher nominal oxidation state of carbon (NOSC) values and more double bonds, rings, and aromatic structures. Strong degradation of NOM and preferential utilization of energetically more favorable, terrestrial humic-like components (lignin-like as the main class) with high NOSC values facilitates the formation of high ammonium groundwater. To the best of our knowledge, this is the first effort to use carbon isotopes and DOM characteristics to identify enrichment mechanisms for geogenic ammonium in alluvial-lacustrine aquifer systems.