Water Environment Research最新文献

The development of effective and environmentally friendly bacterial attachment media remains a challenge in aquaculture wastewater treatment, particularly for systems with high organic loading such as Clarias macrocephalus ponds. In this study, a bentonite-acrylic acid hydrogel was synthesized by gamma irradiation and evaluated as a bacterial attachment medium for aquaculture wastewater treatment. The effects of composition ratio and irradiation dose on gel-forming ability, swelling behavior, and solubility were investigated to determine optimal preparation conditions. The hydrogel prepared at a bentonite-to-acrylic acid ratio of 10:1 (g/mL) and an irradiation dose of 25 kGy exhibited favorable gel properties and structural stability, making it suitable for bacterial immobilization. Two bacterial strains (B4 and B5) demonstrated strong adhesion to the attachment media and stable immobilization behavior. When applied to wastewater treatment, the combined system achieved high removal efficiencies of 99.44% COD, 99.40% BOD₅, 93.20% TP, 98.14% ammonia, 88.39% SS, and 85.21% color meeting the discharge limits of Vietnamese standards. These results indicate that the bentonite-acrylic acid hydrogel synthesized by irradiation is a promising attachment medium for enhancing biological treatment efficiency in aquaculture wastewater systems.

Microplastics (MPs) are pervasive carriers of aquatic pollutants, yet their adsorption behaviors, especially after environmental aging, remain incompletely understood. This study systematically investigated the adsorption of bisphenol A (BPA) onto four common MPs: polyvinyl chloride (PVC), polyolefin resin (PO), polypropylene (PP), and polyethylene (PE), and their ultraviolet (UV)-aged counterparts. We found that UV aging universally enhanced the adsorption capacity, with increases of up to 19% compared to pristine MPs. Aged PVC (A-PVC) exhibited the highest overall affinity. Adsorption mechanisms diverged: PO, PP, A-PVC, and A-PE followed multilayer chemical adsorption, whereas PE, A-PO, and A-PP exhibited monolayer chemical adsorption; only pristine PVC followed monolayer physical adsorption. Importantly, UV aging altered these adsorption mechanisms by modifying the surface physicochemical properties of MPs. Environmental factors significantly modulated adsorption, which increased with contact time and initial BPA concentration but decreased with higher MPs dosage and pH, peaking at 25°C and remaining unaffected by salinity. These results reveal that UV aging not only intensifies adsorption capacity but can also alter the fundamental adsorption mechanism, thereby reshaping the role of MPs as transport vectors for endocrine-disrupting compounds like BPA in aquatic environments. This study provides crucial insights for ecological risk assessment of coexisting MPs and organic pollutants.

A significant advantage of membrane capacitive deionization (MCDI) lies in its ability to achieve medium to high water recovery rates. A prototype of MCDI unit demonstrated a recovery around 68% while consistently achieving salt removal efficiencies of ≥ 90% from feed water with a total dissolved solids (TDS) concentration of 1490 mg/L. However, the presence of coagulant-derived multivalent ions, particularly Fe²⁺, Fe³⁺, and Al³⁺, poses a challenge to long-term salt rejection efficiency. When Fe³⁺ or Al³⁺ was present at concentrations near 10 mg/L in feed water with a TDS of ~400 mg/L, the residual iron or aluminum concentration in the treated water exceeded the permissible limits defined by drinking water standards. Despite high removal efficiencies (> 90%) for key cations including Na⁺, Ca²⁺, Mg²⁺, Al³⁺, Fe²⁺, and Fe³⁺, regeneration studies revealed a distinct desorption trend: Mg²⁺ > Na⁺ > Ca²⁺ > Al³⁺ > Fe²⁺ ≈ Fe³⁺. This trend indicates that Fe³⁺ and Fe²⁺ are the most strongly retained and thus the most scale-forming ion in MCDI systems, followed by Al³⁺. Salt adsorption capacity of NaCl is 0.66-4.14 mg/g and modeled using the modified Donnan model effectively described the nonlinear adsorption behavior and also for all other systems with and without coagulant ions. Due to the presence of divalent ions, Donnan potential decreased compared to NaCl system without coagulant ions. The presence of coagulant ions further decreased the Donnan potential. Energy consumed 68.2-78.6 kT/ion and mostly increased to 60.6-101.3 kT/ion during partially choked condition. Post-operational surface analyses using x-ray photoelectron spectroscopy (XPS) and energy-dispersive spectroscopy (EDS) confirmed the accumulation of these metal ions on the carbon electrode surfaces. The observed deposition of oxide and hydroxide of coagulant ions significantly impacts long-term MCDI performance, underscoring the need for pretreatment strategies and electrode material optimization to enhance the sustainability and effectiveness of MCDI in domestic water purification applications.

Groundwater serves as an indispensable freshwater source in arid high-altitude urban basins. This study investigates the western Xining city on northern Tibetan Plateau, to elucidate the hydrochemical characteristics, genetic mechanisms, and resource implications of its groundwater in arid urban basins. A comprehensive approach integrating hydrochemical and statistical analyses, the entropy-weighted water quality index, and irrigation suitability evaluation was employed. The results show groundwater in the present arid high-altitude urban basin is generally neutral to weakly alkaline, exhibiting marked spatial variability in total dissolved solids (TDS), with 47.83% exceeding drinking water standards. Along the groundwater flow path, the hydrochemical facies evolve from HCO₃-Ca type to mixed Cl-Mg·Ca type and ultimately to Cl-Ca type, reflecting a clear salinization trend. Groundwater chemistry is mainly governed by silicate weathering, with secondary contributions from carbonate and evaporite dissolution, accompanied by limited cation exchange. Anthropogenic influences, particularly agricultural fertilization, have caused extensive nitrate enrichment, affecting 96% of the samples. River water exhibits excellent quality and is suitable for direct consumption, whereas only 56.5% of the groundwater meets drinking water standards, with the remainder classified as medium to poor quality. Regarding irrigation suitability, river water is highly favorable, and most groundwater is also acceptable. However, certain localities show elevated salinity and sodium hazards, highlighting the need for enhanced management to ensure sustainable water resource utilization. This study elucidates the hydrochemical genesis of groundwater in fragile plateau urban environments and contribute to sustainable local water resource management.

Exergy analysis provides a unified framework for assessing environmental, technical, and economic aspects in energy terms, enabling the identification of irreversibilities that reduce process efficiency. In wastewater treatment, its application remains limited, focusing on municipal effluents and chemical exergy derived from chemical oxygen demand. This study proposes an advanced exergy analysis model for wastewater treatment, structured in three phases: (i) system data, (ii) exergy analysis, and (iii) optimization through exergoenvironmental, exergoeconomic, and exergotechnical indicators, statistically assessed using the desirability function approach (DFA). The model was validated using a case study of a leachate treatment system that combined coagulation-flocculation, three photo-Fenton configurations, and activated sludge. The highest desirability (0.59) in exergy terms for the pretreatment was achieved with 1 g L^-1 iron chloride at pH 5, while DFA was 0.74 in the photo-Fenton process involved pretreated leachate with residual iron (0.08 g L^-1 of iron) and a single 2.5 g L^-1 dose of hydrogen peroxide followed by biological treatment. Irreversibilities were greatest in the biological stage due to electricity demand followed by influent composition, reagent consumption, and sludge generation. The model offers robust criteria for optimizing treatment design and supports the achievement of Sustainable Development Goals 6, 11, and 12.

Macrophytes such as Pistia stratiotes and Pontederia crassipes can release allelopathic compounds and reduce cyanobacteria biomass. Cyanobacterial cells interact with heterotrophic bacteria, which contribute to nutrient uptake and antioxidative responses, among other functions. However, the role of microbial communities in allelopathic interactions between macrophytes and cyanobacteria remains unexplored. We investigated how the bacterial community associated with Microcystis aeruginosa influences the effects of aqueous macrophyte extracts. Both extracts inhibited cyanobacterial growth and photosynthetic activity (99% for P. stratiotes and 55% for P. crassipes) while increasing bacterial abundance (threefold). The composition of the bacterial communities stimulated by extracts shifted: whereas original cultures were rich in Methyloversatilis and Rhodobacter, the P. stratiotes extract promoted the growth of Shinella, Flavobacterium, and Comamonadaceae, and the P. crassipes extract favored Enterobacterales. When these stimulated communities were reintroduced into M. aeruginosa cultures, allelopathic inhibition was reduced (40% for P. stratiotes and 12% for P. crassipes). We concluded that the growth of the associated microbiota attenuated the allelopathic effects, partially preserving cyanobacterial cells. Bacterial groups favored by the treatments may participate in allelochemical degradation and antioxidant protection or activate other types of metabolism beneficial to cyanobacteria, mitigating the harmful effects of the extracts. These results highlight the importance of considering the role of microbial communities in cyanobacterial allelopathic interactions.

Achieving ultra-low phosphorus levels (< 0.05 mg L^-1) in wastewater effluents is a critical engineering challenge for mitigating eutrophication. This study developed a coupled microflocculation and micro-nanobubble flotation process for enhancing phosphorus removal. Comprehensive screening determined that 50 mg L^-1 polyaluminum chloride coupled with 1.0 mg L^-1 cationic polyacrylamide provided optimal microflocculation performance. Orthogonal experiments confirmed that a hydraulic retention time of 15 min, aeration rate of 200 L h^-1, and dissolved air pressure of 0.60 MPa resulted in the highest TP removal efficiency. The process was able to reduce TP in actual secondary effluent from 0.86 to 0.036 mg L^-1, achieving an average removal efficiency of 95.8% over 30 days of continuous operation. Mechanistic analysis revealed that high dissolved air pressure (0.60 MPa) was critical for generating a dense, bimodal distribution of micro- and nanobubbles with extended residence times, dramatically increasing bubble-floc collision and electrostatic attachment efficiency. This study establishes a highly efficient technology for meeting increasingly stringent phosphorus discharge standards in municipal wastewater treatment.

The sustainability of sand is becoming more uncertain; therefore, a critical need exists to identify alternative materials for green infrastructure that meet desirable, site-specific functions. Technosol rain gardens (glass, shale, and shell) were tested for their ability to infiltrate and filter stormwater of chemical pollutants. Technosols had similar infiltration rates as sand, while large particle sizes of technogenic materials led to significantly higher saturated hydraulic conductivities (111-211 cm h^-1) compared to sand (37.3 cm h^-1). Technosols decreased all pollutant concentrations, except Zn, compared with the synthetic stormwater. Shale (0.0461 mg L^-1), shell (0.0544 mg L^-1), and sand (0.0306 mg L^-1) had comparable effluent NH₄-N. Compared with sand, shale removed 27.8% more Cu, while glass, shale, and shell removed 58.9%, 85.3%, and 57.7% more Pb, respectively. Glass and shell demonstrate potential for increasing long-term runoff capture under saturated conditions while removing > 50% of chemical pollutants like NH₄-N, P, Cu, and Pb.

This study used density functional theory to study the reaction pathways and intermediates associated with the oxidation of salicylic acid (SA). The analysis was carried out for each of the three SA charge states (i.e., 0, -1, -2) that are observed in aqueous solution. SA can be oxidized to the three primary byproducts, 2,3 DHBA, 2,5 DHBA, and catechol, via cyclohexadienyl radical intermediate formation. A second mechanism consists of an initial H• radical abstraction, which produces organic radicals that react with hydroxyl radicals, but this pathway does not form a catechol. Activation energy calculations confirmed that 2,3 DHBA is the most thermodynamically favored byproduct, followed by 2,5 DHBA and catechol. Formation of uncommon byproducts was also investigated. The operational implications for water treatment processes are discussed. To the author's knowledge, this is the first study to use the electronic properties of SA to elucidate the oxidation pathways across the full range of pH values found in water.

Microplastics have garnered global attention due to their widespread presence in the environment, significant ecological impacts, and potential human health risks. This study was conducted in the Gulf of Bejaia (Algeria), focusing on three representative beaches: Sidi Ali Labher, Aokas, and Oueddas. Sampling was carried out between April and May 2024 across 100 m² transects at each site, subdivided into 50 cm × 50 cm quadrats, yielding 20 replicates under calm weather conditions. Microplastics (MPs) were separated using NaCl flotation and vacuum filtration on gridded cellulose ester filters. Quantitative analyses included MPs density (items/m²), ANOVA for abundance and size differences, and visualizations via Python libraries. Three indices were computed: the Microplastics Pollution Index (MPPI), the Pellets Pollution Index (PPI), and the Fibers Ingestion Potential Index (FIPI). The distribution of MP types showed that fragments were the most prevalent, followed by fibers, foams, films, and pellets. The MPPI indices revealed high abundance at Aokas (MPPI total = 17.18), moderate abundance at Sidi Ali Lebhar (MPPI total = 9.28), and low abundance at Oueddas (MPPI total = 4.22). The FIPI values for Aokas, Sidi Ali Labher, and Oueddas were 0.09, 0.10, and 0.11, respectively, indicating minimal to low potential for fiber pollution from beaches. This study highlights the significant variation in microplastic distribution across the studied beaches and suggests that fibers ingested by biota in these regions are not predominantly from beach pollution.