Environmental Science: Water Research & Technology最新文献

In this study, we investigated pervaporative hydrogen isotope separation behaviors in proton-conductive membranes. Perfluorosulfonic acid (Nafion) and polybenzimidazole membranes exhibited similar hydrogen isotope separation factors, with varying water permeation fluxes based on membrane type and thickness. Increasing temperature improved water permeation flux, while the H/D separation factor remained unaffected. The highest H/D separation factor (1.086) was achieved with a single layer of Nafion at reduced vacuum, surpassing the ¹⁶O/¹⁸O separation factor (1.015). The observed H/D separation behavior is attributed to the mobility difference between hydrons (H⁺ and D⁺) rather than bulk water diffusion (H₃O⁺ and H₂DO⁺). Experiments with heavy metal-exchanged Nafion membranes suggested a negligible contribution of direct H/D ion exchange of sulfonic acid to the overall H/D separation factor. Additionally, water pervaporation through two membranes increased the H/D separation factor.

Access to clean and potable groundwater is paramount for sustaining human health and ecological balance. Traditional groundwater purification techniques often fall short in addressing emerging contaminants and increasing water scarcity challenges. As per the World Health Organization (WHO), around 2 billion individuals worldwide rely on a drinking water source that is contaminated with faeces. In India, approximately 163 million individuals do not have access to potable water, rendering it a notable concern. Advanced membrane technologies have emerged as promising solutions for groundwater purification due to their efficiency, cost-effectiveness, and adaptability. In recent years, the incorporation of nanomaterials such as graphene, carbon nanotubes, metal nanoparticles, and nanocomposites into membrane structures has revolutionized the field of groundwater purification. These nanomaterials offer unique properties, including a high surface area, tuneable surface chemistry, and exceptional mechanical strength, which significantly enhance membrane separation processes. Their application has resulted in improved removal efficiencies for various contaminants, including heavy metals, organic pollutants, and microorganisms. This review provides an overview of recent advancements in membrane-based groundwater purification, with a specific focus on the integration of nanomaterials to enhance membrane performance. It explores the key mechanisms by which nanomaterial-enhanced membranes enhance groundwater purification, including increased adsorption capacity, reduced fouling, and improved selectivity. Moreover, the environmental sustainability of these advanced membranes is discussed, highlighting their potential to reduce energy consumption and chemical usage compared to conventional purification methods. Additionally, this review sheds light on the challenges and prospects associated with implementing nanomaterial-enhanced membranes at a larger scale, considering factors such as scalability, cost-effectiveness, and regulatory compliance. It also emphasizes the need for interdisciplinary research collaborations among materials scientists, engineers, and environmental experts to address these challenges effectively.

Due to the growing demand for water in human society, the shortage of water resources has become the bottleneck of ecological civilization construction and social and economic sustainable development. Therefore, the circulation and development of water resources are important measures to ensure water resources and water security. Capacitive deionization technology (CDI) offers numerous advantages, including high efficiency, energy savings, ease of operation, and renewability. It has been actively developed as a promising new technology. Following decades of research, the application of CDI has become increasingly widespread. Most of the existing literature reviews, however, are only related to seawater desalination. Consequently, this paper mainly emphasizes the most current research progress in various application fields of CDI in water treatment. The focus of this paper is on the application principles and progress of CDI in water treatment, introducing and analyzing potential research findings of CDI in water desalination, water softening, removal of heavy metals, purification of industrial wastewater, and removal of nutrients. The summary and comparison include CDI and other ion treatment technologies, such as reverse osmosis, electrodialysis, and membrane distillation. Secondly, the latest research progress on CDI coupling technology is discussed. Finally, some suggestions on the presentation present the progress of CDI technology and the prospects for the future.

Nitrate is a common groundwater contaminant, primarily caused by the leaching of fertilizers. It poses a risk to human health, prompting the USEPA to set a drinking water limit of 10 mg L⁻¹. Membrane-based bioelectrochemical systems (MBES) are effective treatment mechanisms for remediation of nitrate-rich groundwater. However, there is a knowledge gap surrounding how chloride ions as competing ions impact nitrate removal mechanisms and kinetics. In this study, nitrate-rich groundwater was fed into the cathode side of an MBES equipped with an anion exchange membrane (AEM). Nitrate ions were subsequently transported to the anolyte, where microbe-mediated reduction to N₂ was achieved. The system performance was evaluated under varied catholyte nitrate and chloride concentrations as well as with different applied current densities. The MBES consistently achieved nitrate removal efficiencies of at least 85% with catholyte nitrate concentrations ranging from 14 mg L⁻¹ NO₃⁻-N to 56 mg L⁻¹ NO₃⁻-N. Notably, the highest nitrate removal rate of 8.28 ± 0.01 mg NO₃⁻-N L⁻¹ h⁻¹ was achieved when the catholyte influent nitrate concentration was 56 mg L⁻¹ NO₃⁻-N. The nitrate removal behavior in the MBES can be characterized as a pseudo-first-order reaction. The presence of chloride ions, acting as model competing ions to nitrate, was found to decrease the rate of nitrate removal. Additionally, we found that diffusion is the primary driving force for nitrate removal, with electromigration slightly enhancing nitrate transport across the membrane in the MBES. When actual groundwater was used as the catholyte, 90.6 ± 12.1% nitrate was removed and the removal rate reached 5.3 ± 0.4 mg L⁻¹ h⁻¹ NO₃⁻-N, demonstrating the high efficiency of this MBES in treating nitrate-contaminated groundwater.

As widely used industrial ingredients and products of the biodegradation of benzalkonium chloride disinfectants, benzylamines are expected to occur in municipal wastewater effluents and other wastewater-impacted waters, but their fate during chlorine or chloramine disinfection is unclear. This study characterized the degradation pathways of benzylamine, N-methylbenzylamine and N,N-dimethylbenzylamine during chlorination and chloramination. The dominant reaction pathways during chlorination involved chlorine transfer to the benzylamine nitrogen followed by hydrochloric acid elimination to form an imine and hydrolysis of the imine to form an aldehyde and lower order amine. Benzylamine formed benzaldehyde in preference to benzonitrile. For N-methylbenzylamine and N,N-dimethylbenzylamine, hydrochloric acid elimination between the benzyl nitrogen and the methyl substituent formed formaldehyde and either benzylamine or N-methylbenzylamine, while elimination between the nitrogen and the benzyl substituent formed benzaldehyde and either monomethylamine or dimethylamine. Similar products were observed during chloramination, but over longer timescales. Formation of products involving halogenation of the aromatic ring was not observed. Of highest toxicological concern was the 34% molar yield of NDMA that formed during chloramination of N,N-dimethylbenzylamine in concert with benzyl alcohol by a pathway occurring in parallel to the imine formation and hydrolysis pathway. Based on these reaction pathways, a strategy to reduce NDMA formation within potable reuse facilities was validated using laboratory-scale versions of the reverse osmosis and ultraviolet light processes used in potable reuse trains. The strategy involved treating fully nitrified wastewater influents to these facilities with free chlorine for 5 min to degrade N,N-dimethylbenzylamine and other potent NDMA precursors prior to the addition of ammonia to form chloramines used to control biofouling within these facilities.

Biological oxidation of manganese (Mn) by bacteria results in the formation of biogenic Mn oxides (MnOx), which are known to be strong oxidants and effective catalysts. Manganese-oxidizing bacteria (MnOB) often develop in engineered systems for water treatment under oligotrophic conditions. In this study, we investigated the MnOB within biofilms sampled in two different seasons from full-scale oxygen-supplemented biological activated carbon (BAC) filters performing the complete removal of Mn from wastewater. By applying a novel batch enrichment approach ensuring the continuous presence of soluble Mn, after 42 days the start-up microbial community grew into thick, floccular biofilms efficiently oxidizing Mn²⁺ into numerous black nodules. The amount of Mn oxidized was quantified using inductively coupled plasma optical emission spectroscopy (ICP-OES). X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) revealed that the MnOx formed was a birnessite-type (δ-MnO₂) with a crystalline, nanoflower structure. Comparison of the microbial community composition before and after the enrichment by means of 16S rRNA gene amplicon sequencing showed increases of members of the orders Rhizobiales and Burkholderiales, and identified among the most abundant some bacterial groups which have rarely or never been associated with Mn oxidation before (Rhodococcus, Ellin6067, Planctomycetota Pir4 lineage, Rhizobiales A0839 and Amb-16S-1323). This study unravels the potential of production of crystalline MnOx by mixed-microbial communities which uniquely generate in a man-made biofilter. The new insights provided implement the knowledge in the field, with the perspective to design innovative biotechnologies to remove recalcitrant compounds where MnOB find optimal growth conditions to produce catalytic forms of MnOx.

Lead (Pb²⁺) is one of the toxic pollutants that poses hazardous and severe risks to human health and the environment globally. Lead toxicity issues can be addressed primarily by the detection of Pb. Thus, the requirement for accurate sensors for lead detection in environmental samples is tremendously increasing across the globe. Fluorescence-based detection of lead in water samples can serve as a stepping stone towards achieving goals such as point-of-care, portable, and on-site detection. In the present study, a selective fluorometric chemical sensor developed from dithizone and carbon quantum dots (CQDs) embedded in chitosan polymer thin films was evaluated for Pb²⁺ detection in various natural water resources. The fluorescent chemical sensors were characterized using FTIR spectroscopy, XPS, XRD, TEM, CLSM, UV spectroscopy, and fluorescence spectroscopy. Pb²⁺ ions were detected employing a fiber optic spectrophotometer (FOS) paired with a reflectance probe. Two river water samples and household tap water samples were evaluated for the presence of Pb²⁺ ions, and spiking studies were carried out to measure the accuracy of detection. The sensing and analytical results indicated that lead detection with a limit of detection of 18.3 nM was possible in the 0–100 μM range of concentration with a response time of 1 minute. The spiking of Pb²⁺ concentration in the various water resources led to an accurate estimation with a maximum error of 1.4%, indicating an interference-free detection of Pb²⁺. The estimation of Pb²⁺ based on Micro-plasma Atomic Emission Spectroscopy was used as a reference method. The results indicate that the developed fluorescent chemical sensor based on dithizone-CQD-impregnated chitosan thin films coupled with a fiber optic spectrometer device shows tremendous potential for point-of-care and real-time monitoring of Pb²⁺ ions in real water samples.

A novel and highly efficient photocatalyst, g-C₃N₄/Bi₂MoO₆/clinoptilolite nanocomposite (CNBC), was synthesized by a hydrothermal method and acted as a Z-scheme heterojunction for efficient activation of peroxydisulfate (PDS) to degrade oxytetracycline (OTC) under visible light (vis) irradiation. The morphology and structure of the photocatalyst were determined by XRD, FT-IR, FE-SEM, EDX, BET, TGA, UV-vis DRS, PL, and XPS. The results showed that CNBC-30 had the best photocatalytic performance with an OTC removal efficiency of more than 87% within 120 min under the conditions of [OTC] = 20 mg L⁻¹, [catalyst] = 500 mg L⁻¹, [Na₂S₂O₈] = 1.26 mM, and pH = 4 at room temperature, which was much better than those of pure g-C₃N₄, Bi₂MoO₆, and CNB composites. This superiority is due to the excellent adsorption ability of clinoptilolite that effectively forms the g-C₃N₄/Bi₂MoO₆ heterojunctions, thus improving the ability to separate charge carriers while decreasing the recombination rate of electron–hole pairs. Furthermore, the effect of catalyst dosage, oxidant concentration, initial pollutant concentration, solution pH, and coexisting anions on the OTC degradation was comprehensively studied. The results showed that the CNBC-30/PDS system had high reusability and adaptability at different pH levels (3.0–11.0). Quenching tests showed that ¹O₂, O₂˙⁻, and h⁺ played the main roles in OTC degradation. In addition, OTC intermediates were identified and degradation pathways were proposed based on the results of MS analysis. DFT calculations successfully predicted the positions on the OTC molecule with high Fukui numbers that are suitable for attack by oxidants. CNBC-30 was stable for OTC degradation after four cycles with a degradation efficiency of above 78%, demonstrating its durability and potential for practical applications. This study provides insight into PDS activation in the visible light region by a clinoptilolite-based Z-scheme heterojunction for organic pollutant degradation.

This study reports a sustainable and green method for phosphorus (P) extraction and recovery from waste activated sludge (WAS) using glycine as a P-extraction agent. Glycine showed an extraordinary ability to induce P release from waste-activated sludge at a rate of 8.7 mg P per L per h without being consumed. The P-extraction rate was linearly related to the mixed liquor suspended solid concentration and was not affected by the temperature in the range of 25–35 °C. After extraction, the released P was recovered via calcium precipitation, resulting in high P-content (48%, as phosphate) products (dominated by amorphous calcium phosphate). An unparallel advantage of the method is the high recyclability of glycine. Repetitive experiments showed <10% glycine loss over four P-extraction–P-recovery–glycine-reuse cycles. Additionally, extremely low heavy metal contents were observed in the P-recovery products in comparison to the acid/alkali-assisted P extraction, indicating its environmental friendliness as a sustainable strategy for P recovery from WAS.

As non-sewered toilets are now the most commonly used sanitation facilities, the faecal sludge management (FSM) sector is starting to be recognised as an important actor for global carbon management. The development of systematic strategies to calculate avoided emissions and carbon storage opportunities is currently constrained by a lack of understanding of carbon flows during faecal sludge treatment. This study investigated carbon sequestration potential for faecal sludge treatment systems that involve co-pyrolysis of human faeces (HF) and wood biomass (WB) at different blending ratios HF : WB (100 : 0, 75 : 25, 50 : 50, 25 : 75, 0 : 100) and temperatures (450, 550, 650 °C). The systematic investigation of analytical biochar stability parameters and the quantification of carbon flows among pyrolysis products were carried out for the first time in the context of faecal sludge. The stability of the produced biochars was assessed based on their remaining volatility, carbon structure (H/C and O/C ratios, SEM and FTIR analyses) and oxidation resistance (chemical oxidation by H₂O₂ and thermal degradation by thermogravimetric analysis [R₅₀ index]). Overall, co-pyrolysis of HF and WB improved carbon fixation and biochar stability, enhancing carbon sequestration potential compared to pyrolysis of pure faecal feedstocks. Biochars produced from 50 : 50 HF : WB blends at 550 °C had the highest carbon retention (41.1%); this feedstock blending ratio corresponds to ∼30 g dry wood added in toilets as a cover material (per user per day), based on the expected daily excretion quantities. For these conditions, the H/C, O/C ratios, H₂O₂ oxidation and R₅₀ index values suggest that the produced biochars have developed an aromatic structure and are suitable for long-term carbon storage. The biochar characteristics were found to be more dependent on feedstock composition than pyrolysis temperature – provided that the temperature reached was sufficient to ensure completion of the main pyrolytic reactions (≥500 °C) – while carbon flows to the bio-oil and non-condensable gas fractions were significantly influenced by pyrolysis operational parameters (retention time and inert gas flow rate). The formation of CaCO₃ was observed via SEM/EDX and can be further investigated as a potential additional carbon storage mechanism in FSM. The findings of this research can be used to create a methodological dataset to inform carbon assessments and future modelling applications, paving the way towards the establishment of carbon-negative FSM.