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.

Mainstream anaerobic ammonium oxidation (ANAMMOX) offers a promising alternative to conventional nitrogen removal processes in municipal wastewater treatment. However, research has largely focused on its potential to reduce oxygen demand rather than external carbon requirements. This study compared the external carbon demand of mainstream ANAMMOX with that of anaerobic-anoxic-oxic (A2O) and partial denitrification/ANAMMOX (PD/A) processes. Stoichiometric ratios, validated in a laboratory-scale packed-bed biofilm reactor, were implemented in a simulation framework reflecting representative conditions in Korean wastewater treatment plants. A 5 × 5 × 3 × 3 simulation matrix evaluated external carbon demand and its sensitivity to sidestream ammonium concentration (SAC), mainstream ammonium concentration (MAC), mainstream total organic carbon concentration (MTC), and sidestream flow rate (SFR) through gradient-based analysis and regression modeling. Mainstream ANAMMOX reduced external carbon demand by up to ~10.8%-72.2% compared with A2O and ~3.7%-41.2% compared with PD/A, depending on influent loading conditions. SAC and MTC were identified as the dominant drivers of carbon reduction. Notably, higher MAC levels slightly diminished the relative carbon savings due to the increased external carbon requirement for polishing the stoichiometric nitrate byproduct. Three composite indices (sidestream effective nitrogen load index, total effective nitrogen load index, and sidestream contribution ratio [SCR]) were proposed, with SCR exhibiting the highest predictive accuracy. Although the absolute savings are site-specific, these findings suggest that mainstream ANAMMOX can substantially decrease reliance on external carbon sources, and the proposed indices provide practical tools for process evaluation and design optimization.

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.

Groundwater is essential for drinking and irrigation, but its quality is impacted by human activities and rapid urbanization. This study presents a unique assessment of groundwater quality in agroecosystems situated at the rural-urban interface of Bengaluru, an area undergoing rapid land-use change and intensive agricultural practices. Unlike earlier studies that examine only rural or urban zones, this study integrates physicochemical analysis, hydrochemical facies (Piper plot), water quality index (WQI), and principal component analysis (PCA) to provide a comprehensive understanding of seasonal variations in groundwater quality. A total of 60 borewell water samples were collected from the study site and analyzed for various water quality parameters. Results show that groundwater remains within permissible limits set by the Bureau of Indian Standards (BIS). The Piper plot indicates that most samples are of mixed type, with alkaline earths exceeding alkalis, and strong acids surpassing weak acids. Water chemistry is affected by the dominance of evaporation and precipitation. The WQI showed that 50% of the samples were classified as excellent during the post-monsoon period, increasing to 76% in the pre-monsoon period. PCA explains 96.30% and 84.80% of the variance in post- and pre-monsoon conditions, with principal component (PC1) accounting for 49.40% and 48.60%, respectively. Most groundwater is suitable for human use and irrigation. However, the government should monitor contamination sources to enable more comprehensive future assessments of groundwater quality.