Environmental Science: Water Research & Technology最新文献

Magnetic flocculation has been gaining interest as a potential method for treating combined sewer overflows (CSOs) because of its short settling time, small footprint, and dense sludge. This study developed a rapid magnetic flocculation method involving 30 s rapid stirring and 90 s slow stirring combined with magnetic sedimentation to treat CSOs. Compared to traditional magnetic coagulation, the entire process had a reaction time of only 2 minutes. Despite the low floc density that was insufficient for settling by gravity alone, the flocs rapidly settled in a magnetic field due to the flocs enveloping magnetic particles, significantly reducing the required reaction and settling time for the treatment. Meanwhile, the optimal parameters of the process were determined. Under optimal conditions, the removal efficiencies of chemical oxygen demand, total nitrogen, and total phosphorus can reach 90%, 75%, and 80%, respectively. Besides, the treatment efficiency of rapid magnetic flocculation–magnetic sedimentation on CSOs under different weather conditions was also investigated to demonstrate the feasibility of the process in practical applications. The results suggest that the rapid magnetic flocculation–magnetic sedimentation technique is a promising strategy for the treatment of CSOs.

The illicit connection of wastewater pipes to stormwater pipes might result in the direct discharge of wastewater into natural water and even drinking water sources. The multiple pollutants in untreated wastewater effluent, including organic matter, nutrients, emerging contaminants (ECs) and disinfection by-product (DBP) precursors, posed risks to ecological safety. Herein, Fe(VI) and Fe(VI)/Fe(III)-based processes were found to be effective in treating overflow wastewater as a combination of coagulation and oxidation. In the presence of Fe(VI) below 200 μM, the addition of Fe(III) could further improve the removal of COD (43.1%), TP (87.9%), and turbidity (95.3%) compared to that by Fe(VI) alone. With respect to ECs, the highly detected paracetamol (PCT) of 10 μM in wastewater can be efficiently degraded by Fe(VI) exceeding 300 μM, which reached approximately 97.2% removal within 22 min. The rapid consumption of Fe(VI) by other organics present in wastewater necessitates the addition of Fe(III) at a low [Fe(III)] : [Fe(VI)] ratio to expedite the oxidation of ECs. For DBPs, the Fe(VI)-based process decreased DBP formation and DBP-associated cytotoxicity by about 50–80% at optimal dosage (300 μM) and prioritize the removal of haloacetaldehyde and haloacetonitrile precursors. This may be attributed to the efficient removal of aromatic protein-like components. However, the addition of Fe(III) may deteriorate the DBP formation control due to interaction between Fe(III) and Fe(VI) reducing the Fe(VI) oxidation capacity on organics. This study demonstrated that Fe(VI) and Fe(VI)/Fe(III)-based processes might be a promising treatment process for simultaneous removal of multiple pollutants in wastewater from illicitly connected urban stormwater systems.

The pharmaceutical industry has been increasing its production, manufacturing, and promotion of various products, resulting in a rise in contaminants in water. Drugs pose a significant threat because they can persist in water for extended periods. To address this issue, a project was initiated to develop a model for predicting the degradation percentage of pharmaceutical contaminants in water using different physicochemical methods. The model is based on artificial neural networks and uses quantitative structure–activity relationship (QSAR) to predict the degradation percentage of drugs in water when subjected to ozonation, ozonation + H₂O₂, activated carbon use, UV radiation, Fenton darkness, and photo-Fenton + H₂O₂. A total of 75 models were developed, and five met the validation criteria. With the help of the validated models, the study predicted the elimination percentages of more prevalent drugs in water sources. The results reveal that ozonation, with or without peroxide, is the best degradation method. The study has successfully verified the predicted results by conducting experiments on the degradation of an aqueous solution of cephalexin using ozonolysis, which resulted in a degradation percentage of 97.8%. The industry can use the ANN-INQA algorithm to select an optimal method for effectively degrading pharmaceutical contaminants, which can help reduce costs and save time.

Water scarcity is a global issue which might feasibly be addressed through the use of solar energy to produce uncontaminated steam from contaminated water. This technique would allow greater efficiency in purifying wastewater, or desalinating seawater, to produce an adequate supply of clean water. This work therefore presents a novel design for a solar receiver in the form of a composite sponge made from iron oxide black and natural rubber, prepared via the Dunlop process, which is commonly applied in the rubber sector. This composite sponge can absorb solar energy across a broad spectrum before focusing that energy directly on the interfacial surface. In tests using simulated seawater, and water containing organic dyes and heavy metals, the condensed steam produced met the required standards for potable water. The composite material involved exhibited durability, producing stable results beyond 20 cycles of evaporation and cooling. Furthermore, iron oxide black is cheap, abundant, and available in commercial quantities, while natural rubber latex and its associated technologies are widely established for large-scale usage. Therefore, solar receivers based on an iron oxide black/natural rubber composite sponge have significant potential in various applications which make use of solar steam generation, for instance, desalination for freshwater production, or even for sterilization.

In activated sludge, the antibiotic resistance genes (ARGs) can be present either in the intracellular (iDNA) or extracellular DNA fraction (exDNA). Recent advances in the exDNA extraction methodology allow a better profiling of the pool of ARGs. However, little is known about how stress conditions modify the distribution of ARGs between both DNA fractions. Here, we performed two batch tests for analyzing the effects of two different stress conditions, namely nutrient starvation and high concentrations of sulfamethoxazole (1, 10 and 150 mg L⁻¹) in activated sludge. We tracked by qPCR the resulting relative abundances of four target genes, namely the universal 16S rRNA gene, the class 1 integron-integrase gene intI1, and the sulfonamide resistance genes sul1 and sul2 in both the iDNA and exDNA fractions. In the exDNA pool, unlike starvation, which provoked a decrease of 1–2 log₁₀ [copies] per ng DNA in the concentration of sul1 and intI1, the presence of sulfamethoxazole did not influence the abundances of sul1 and sul2. However, high concentrations of sulfamethoxazole (150 mg L⁻¹) selected for microorganisms harboring sul1 and, more remarkably, sul2 genes in their iDNA during their exponential growth phase. The abundances of intI1 and sul1 were positively correlated in the exDNA fraction (r > 0.7), whereas no significant correlation (p < 0.05) between the abundance of these two genes was found in the iDNA fraction of the sludge. High SMX concentrations influenced the abundance of ARGs in the iDNA; their abundance in the exDNA was influenced by nutrient limitations. Further studies should consider the profiling of exDNA fractions because of the relationship between ARGs and mobile genetic elements. Besides, the surveillance of antimicrobial resistance is encouraged in wastewater treatment plants facing high antibiotic concentrations.

Anaerobic secondary biological wastewater treatment could increase energy efficiency by avoiding energy-intensive aeration while producing methane that could be harvested for energy production. However, sulfides produced by biological sulfate reduction can inhibit efforts to reuse wastewater by interfering with chlorine or UV disinfection. At laboratory- and pilot-scale, this study compared oxidation of sulfides in a pilot-scale anaerobic secondary effluent by hydrogen peroxide (H₂O₂) or chlorine (NaOCl) and disinfection by UV or NaOCl with respect to meeting water quality guidelines for non-potable reuse applications. Chlorine oxidized sulfides within 6 minutes but required high chlorine doses (∼200 mg-Cl₂ L⁻¹) and formed particulate elemental sulfur at pH ≥ 6.2, necessitating filtration. H₂O₂ oxidized sulfides within 24 min, forming elemental sulfur near pH 7 and thiosulfate at pH >8. UV disinfection at ∼200 mJ cm⁻² average UV fluence achieved <2.2 MPN/100 mL total coliform and 5-log inactivation of bacteriophage MS2, while NaOCl disinfection only controlled total coliform. Initial cost estimates indicated that the lowest cost options (∼$0.40 per m³) to meet water quality goals for non-potable reuse involved sulfide oxidation either at pH 7 followed by filtration or at pH ∼8.3 without filtration, and then UV disinfection at 200 mJ cm⁻² average UV fluence and addition of NaOCl to achieve a 5 mg-Cl₂ L⁻¹ total chlorine residual for distribution.

Orthophosphate (PO₄) is a commonly used corrosion control treatment to reduce lead (Pb) concentrations in drinking water. PO₄ reduces Pb concentrations by forming relatively insoluble lead phosphate (Pb–PO₄) minerals. In some cases, however, Pb–PO₄ minerals have been observed to form nanoparticles, and if suspended in water, these nanoparticles can be mobile and reach consumer taps. Although recent research on Pb–PO₄ particles has been performed, there remains a need to improve our understanding of the nature of Pb–PO₄ nanoparticles. For that reason, Pb precipitation experiments were conducted to generate Pb–PO₄ nanoparticles in bench scale studies for analysis. The study objective was to observe how pH, dissolved inorganic carbon (DIC), and PO₄ impacted the properties of Pb–PO₄ particles. Specifically, particle size, surface charge, mineralogy, and solubility were analysed. Hydrocerussite was precipitated when no PO₄ was present, hydroxypyromorphite (Pb₅(PO₄)₃OH) nanoparticles (<100 nm diameter) were precipitated when excess PO₄ relative to Pb necessary to completely precipitate the mineral was present, and a mixture of the two minerals was precipitated when an insufficient amount of PO₄ was present. Hydroxypyromorphite particles were less soluble than hydrocerussite by up to two orders of magnitude. The estimated K_sp,OH of 10^−66.87 in this work closely aligned with previous K_sp,OH estimates that ranged from 10^−66.77 to 10^−62.79. Hydroxypyromorphite particles would not settle in water which was likely due to their small size and high negative charge. The mobility and size of these particles indicates that there are potential implications for such particulate Pb to remain suspended in water and thus be present in the tap water.

The unregulated use of pesticides, which constitutes organophosphates, demands their continuous monitoring from a human health perspective. The development of efficient, reliable and affordable methods for the effective quantification, removal and detoxification of pesticides is indeed a significant challenge in the fields of agriculture, environmental science and public health. Herein, we designed a simple approach for the construction of a functionalised electrochemical material that includes the following steps: (i) the cation–π induced non-covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with an organic cation IL, and (ii) the complexation of IL@MWCNTs with Hg²⁺ to accelerate electron transfer, apparently enhancing the response of Hg/IL@MWCNTs towards azinphos-methyl, as revealed by cyclic voltammetry. Hg/IL@MWCNTs/GCE exhibits electrocatalytic behaviour towards azinphos-methyl (AZM) with a low detection limit of 1.10 μM and a wide linear range (0.20–180 μM). The degradation of the AZM pesticide was supported by ³¹P NMR titration and mass spectrometry, which confirmed the conversion of AZM into its non-toxic products. Taking into account the aforementioned findings, the functionalised IL@MWCNT composite was fabricated into an ultrathin polyamide layer on a PES support membrane via interfacial polymerisation for practical application. The developed nanocomposite membrane removes the Hg²⁺ metal ion and azinphos-methyl pesticide from contaminated water with a removal efficiency of 95% and 90%, respectively.

Microbial desalination cell (MDC) provides integral solutions for addressing water scarcity and environmental challenges. This research paper investigates a novel MDC with two distinct exoelectrogens, Shewanella putrefaciens MTCC 8104 (MDC – 1) and mixed culture (MDC – 2) at three different NaCl concentrations (10 g L⁻¹, 20 g L⁻¹ and 30 g L⁻¹) and brackish water in the desalination chamber utilizing sago effluent as an anolyte. The maximum chemical oxygen demand (COD) removal and desalination efficiency of 95.1 ± 2% and 13.2 ± 2% were observed for 30 g L⁻¹ NaCl for MDC – 1. Furthermore, the power density obtained at 30 g L⁻¹ NaCl concentration for MDC – 1 was 60.22 ± 0.2 mW m⁻² and 43.09 ± 0.2 mW m⁻² for MDC – 2. The internal resistance of the Shewanella putrefaciens inoculated MDC – 1 was very low compared to MDC – 2. However, the dynamics changed in brackish water treatment, where MDC – 1 faced challenges due to the diffusion of ions other than Na+ and Cl⁻, leading to increased internal resistance and reduced power output. In contrast, the mixed culture in MDC – 2 adapted well to the brackish water ions, showcasing higher oxidation–reduction potential, increased power, and low internal resistance. These findings underscore the superior performance of Shewanella putrefaciens in NaCl desalination, while a mixed culture proves more adaptable and effective in real-time brackish water treatment. As conductivity increases, internal resistance diminishes, suggesting the potential future application of MDC in treating real seawater and brackish water by optimizing volume ratios, biofilm performance and preventing membrane fouling.