Real Water Research Articles

Enhanced long-term stability of stained microplastics with carbon nitride fluorescent polymer for tracking

Fluorescent labeling and imaging is a useful tool to track the temporal and spatial distribution of microplastics (MPs) with size and shape features. However, the limited fluorescently labeled MPs spheres, photo-bleaching and leaching of organic small molecular dyes hamper the tracking of MPs in the environment. In this work, phenyl-modified carbon nitride (PMCN) fluorescent polymer was prepared and applied for the staining of eight different types of MPs. The interface interaction mechanism between PMCN fluorescent polymer and MPs was investigated by the desorption experiments. The long-time photo-stability of the stained MPs against ultraviolet (UV) light irradiation, freeze-thaw cycles, various environmental factors and real environmental water samples was evaluated. The MPs stained with PMCN fluorescent polymer showed more robust stability than the common dye (Nile red) against the damage when exposure to UV light for 72 h, treatment with freeze-thaw cycles for 60 days, exposure to strong acid, strong alkali, high salinity, freshwater (river and lake) or seawater for 60 days. Results indicate PMCN fluorescent polymer is promising as a convenient, efficient and universal fluorescent tracer for visually tracking the migration and distribution of MPs in environmental water system.

Unconventional fluorescence behavior of ε-polylysine: Selective and sensitive detection of Cu2+ in real water samples, test paper strips, living cells, and anticounterfeiting applications

Herein, we report the clustering-triggered emission (CTE) behavior of ε-PL and its various applications. The CTE properties of ε-PL in solution were confirmed from the SEM analysis, DLS data, and the observation of the Tyndall effect. We explored these unique and unconventional photophysical characteristics of ε-PL for the selective detection of Cu2+ with a LOD of as low as 0.45 ppb (7.11 nM), which is much less than the safe limit set by the WHO for Cu2+ in drinking water (2 ppm). The quantum yield of ε-PL reduced from 0.24 to 0.008 upon Cu2+ addition, and the quenching was found to be dynamic in nature. Further, ε-PL was able to detect Cu2+ in real water samples (tap and lake water) as well as in living cells (MCF-7). For real-time applications, ε-PL-coated paper strips and silica gel were fabricated for rapid and convenient detection of Cu2+. The anti-counterfeiting application of ε-PL has also been demonstrated. These findings highlight an efficient method for the selective detection of Cu2+ by ε-PL, an unconventional fluorescent polymer without any chemical modifications, and its real-time applications in Cu2+ sensing and as an anti-counterfeit material. This potentiates its use in agriculture, waste management, medicine, and related fields.

Application of catalytic wet peroxide oxidation for sunscreen agents breakdown

Sunscreen agents are chemical compounds widely used nowadays for skin protection from UV sunlight. Recently, their ubiquitous occurrence in aquatic systems has been evidenced, which poses a high risk for the environment and human health as they are associated with endocrine disrupting activity, reproductive toxicity, and genotoxicity. In this work, the feasibility of an economically and environmentally friendly catalytic system based on the thermally modified natural magnetite and hydrogen peroxide (Fe3O4-R400/H2O2), has been evaluated for the degradation of two representative sunscreen agents: benzophenone-3 (BP-3) and 4-aminobenzoic acid (PABA) in wastewater. The experiments were conducted under circumneutral pH (pH0 = 5), with temperature control (25 °C). Both compounds (500 μg L−1) were successfully removed from water by using a relatively low catalyst concentration (0.5 g L−1) and the theoretical stoichiometric H2O2 dose for their complete oxidation (∼2.3 mg L−1). Afterwards, a complete operating condition study was performed with BP-3, given its predominant occurrence in fresh waters, analysing the influence of H2O2 dose (1.2–4.6 mg L−1), catalyst concentration (0.1–0.5 g L−1), and temperature (25–45 °C). From the evolution of the identified by-products, a reaction pathway was proposed according to which oxidation of BP-3 gives rise to several aromatic intermediates, which finally evolve to short-chain organic acids. The generation of such aromatic by-products led to a considerably ecotoxicity increase in the initial stages of the reaction, but non-toxic effluents were ultimately achieved. Notably, the mineralization yield reached was above 60%. As a proof of concept, the feasibility of the system was finally demonstrated in real water matrices (WWTP effluent and surface water).

Efficient removal of 17α-ethinylestradiol by algae-based red mud catalyst activated persulfate: Removal mechanism and defect of quenching

The synthesis and optimization of carbon-based materials, derived from various solid waste sources to activate peroxydisulfate (PDS), offer a practical approach that addresses both the recycling of solid waste resources and the removal of recalcitrant organic pollutants. In this study, stacked algae sludge and discarded red mud solid waste were repurposed to synthesize an algae-based red mud catalyst (AR-BC) using the carbon-thermal reduction technique. The obtained AR-BC catalyst exhibited efficient adsorption and degradation capabilities for 17α-ethinylestradiol (EE2). The results showed that AR-BC can adsorb 42.67 % of EE2 at equilibrium, with a maximum capacity of 8.0 mg/g. After the activation of PDS by the AR-BC catalyst, it was observed that EE2 was completely degraded within 20 min. The superior activation ability is mainly attributed to the presence of Fe3O4 and oxygen-containing functional groups in AR-BC. Both free radicals and non-free radicals coexisted in the AR-BC/PDS system, with the former predominantly influencing the EE2 degradation process. And hydroxyl radical was identified as the primary reactive oxygen species. Moreover, AR-BC exhibited robust adaptability and reusability in real water for efficient adsorption and degradation of EE2. This study presents a viable solution by seamlessly integrating resource recycling with pollutant removal, offering an innovation approach.

A Novel Thin-Layer Flow Cell Sensor System Based on BDD Electrode for Heavy Metal Ion Detection.

An electrochemical sensor based on a thin-layer flow cell and a boron-doped diamond (BDD) working electrode was fabricated for heavy metal ions determination using anodic stripping voltammetry. Furthermore, a fluidic automatic detection system was developed. With the wide potential window of the BDD electrode, Zn2+ with high negative stripping potential was detected by this system. Due to the thin-layer and fluidic structure of the sensor system, the electrodepositon efficiency for heavy metal ions were improved without using conventional stirring devices. With a short deposition time of 60 s, the system consumed only 0.75 mL reagent per test. A linear relationship for Zn2+ determination was displayed ranging from 10 μg/L to 150 μg/L with a sensitivity of 0.1218 μA·L·μg-1 and a detection limit of 2.1 μg/L. A high repeatability was indicated from the relative standard deviation of 1.60% for 30 repeated current responses of zinc solution. The system was applied to determine Zn2+ in real water samples by using the standard addition method with the recoveries ranging from 92% to 118%. The system was also used for the simultaneous detection of Zn2+, Cd2+, and Pb2+. The detection results indicate its potential application in on-site monitoring for mutiple heavy metal ions.

Electrochemical detection of paracetamol using zeolitic imidazolate framework and graphene oxide derived zinc/nitrogen-doped carbon

A composite of zeolitic imidazolate frameworks and graphene oxide (ZIF-GO) derived 3D–2D Zn/N-doped carbon (ZnNC-rGO) was developed for the electrochemical detection of the analgesic paracetamol (PCT). The pyrolysis of ZIF-GO led to the formation of a nanoscale structure featuring ZnNC cubes embedded in rGO sheets. The Zn0-to-ZnO phase transition was found to mediate electrons during the reversible paracetamol redox reactions, which contributed to the sensing current response. Upon 800 °C heating under a N2 atmosphere, the mesoporosity of ZnNC-rGO(800) was significantly enhanced, thereby increasing the electrochemical surface area and charge transfer efficiency. The electrode sensitivity was optimized at a calibration linearity of 0.526 μA μM−1) with detection limit (0.077 μM) in the range of 0.5 – 70 μM using differential pulse voltammetry mode (DPV). The precision of analytical recovery for trace paracetamol concentrations was maintained based on the excellent reproducibility and selectivity trials in the presence of interference chemicals and in real water samples.

Ultrasensitive ECL immunosensor for trenbolone detection based on double-assisted signal amplification strategy of Nb2O5-decorated TiO2 nanorods and Co3O4-Co3(PO4)2 nanosheets

Trenbolone (TB) is used for treating malnutrition in livestock and increasing their muscle mass. However, its excessive intake can lead to metabolic and reproductive disorders in animals. In addition, it causes adverse effects in humans even at very low concentrations. Herein, an innovative electrochemiluminescence (ECL) immunosensor based on a double-assisted signal amplification strategy has been proposed for the sensitive detection of TB. Nb2O5-decorated TiO2 nanorods, with a large surface area, good biocompatibility, and excellent catalytic properties, were used as the substrates for the effective loading of TB antibodies. In addition, Co3O4-Co3(PO4)2 nanosheets, used as labels, improved the ECL signals and were used to incorporate TB antigens for designing competitive ECL immunosensors. Various experimental factors, such as the pH of the phosphate buffer solution, concentration of the co-reactant, and time of incubation, were examined. The proposed ECL immunosensor exhibited high sensitivity, good repeatability, and high stability for TB concentration and was successfully implemented for the analysis of real water samples. Under optimal conditions, the proposed immunosensor responded linearly to relevant concentrations of TB from 1.0 × 10−3 to 1.0 × 103 ng/mL, with a detection limit of 0.39 × 10−3 ng/mL (S/N = 3). Notably, this study fabricated a simple and ultrasensitive TB detection system with novelty of practical application in environmental monitoring.

ISFME extraction of As species from some real water samples using an imidazolium-based task-specific ionic liquid (TSIL): Synthesis and characterization

ABSTRACT To determine of arsenic species in real water samples using electrothermal atomic absorption spectrometry, a high-performance in-situ solvent formation microextraction technique has been developed using homogenous liquid – liquid microextraction concepts. The developed method was based on the use of a synthesized imidazolium-based ionic liquid (IL) modified with ammonium pyrrolidine dithiocarbamate as a task-specific ionic liquid (TSIL), which was chelated with As(III) and then converted to a hydrophobic IL using ammonium hexafluorophosphate in anion exchange reactions. As(V) was reduced to As(III), using a satisfied reducing agent, and the total amount of As was analyzed using ETAAS. TSIL acts simultaneously as an extracting solvent and a chelating agent. The characterization of the synthesized TSIL was performed using13CNMR and FTIR analyses. When optimal conditions were met, linear dynamic ranges of 0.5–50 µg/L and 0.5–20 µg/L were obtained in the determination of As(III) and total As, respectively. The limits of detection (LOD) and quantitation (LOQ) were determined to be 0.021 µg/Land 0.064 µg/L for the determination of As(III) (for concentration 20 µg/L), respectively, and the standard deviation (RSD%, n = 7) was 2.0%. To evaluate the validity of the method, it was successfully applied for As species determination in different real water samples.

A polydiacetylene (PDA) based dual-mode optical sensor for the ppb level selective detection of biogenic polyamines

Biogenic polyamines (BPAs), specifically spermine and spermidine, play vital roles in cellular physiology, influencing processes like cell growth and proliferation. Beyond their cellular implications, these amines serve as biomarkers for cancer and aging-related diseases. This study presents a dual-output optical sensor for BPAs using polydiacetylene (PDA). The sensor utilizes alendronate's phosphate groups as recognition units for BPAs in liquid and solid phases. Ammonium groups of BPAs interact with negatively charged alendronate-modified PDA (PDAPH) liposomes causing a color change from blue to red accompanied by a gradual increase in fluorescence output at λmax 622 nm. The sensor exhibits high sensitivity with low detection limits of 4.3 ppb and 5.1 ppb for spermine and spermidine in colorimetric analysis, and lower limits of 1.6 and 1.4 ppb in fluorimetric measurements respectively, demonstrating its dual output ability. PDAPH liposomes also respond to cadaverine and putrescine indicating the probe's ability to detect key BPAs. The sensor shows minimal responses to interfering species, confirming its selective affinity towards BPAs. Practical validation in real water, urine, and serum samples demonstrates the sensor's efficiency. Immobilization of PDAPH liposomes into sodium alginate results in the creation of PDA beads. These beads exhibit a discernible color change when exposed to BPA concentrations exceeding 0.3 μM with a sufficiently low detection limit of 11.7 ppb in the solid phase. These findings highlight the efficiency of the PDAPH liposome sensor for accurate and reliable biogenic polyamine detection.

Electrochemical Sensing of Cadmium and Lead Ions in Water by MOF-5/PANI Composites.

For the first time, composites of metal-organic framework MOF-5 and conjugated polymer polyaniline (PANI), (MOF-5/PANI), prepared using PANI in its conducting (emeraldine salt, ES) or nonconducting form (emeraldine base, EB) at various MOF-5 and PANI mass ratios, were evaluated as electrode materials for the electrochemical detection of cadmium (Cd2+) and lead (Pb2+) ions in aqueous solutions. Testing of individual components of composites, PANI-ES, PANI-EB, and MOF-5, was also performed for comparison. Materials are characterized by Raman spectroscopy, scanning electron microscopy (SEM) and dynamic light scattering (DLS), and their electrochemical behavior was discussed in terms of their zeta potential, structural, morphology, and textural properties. All examined composites showed high electrocatalytic activity for the oxidation of Cd and Pb to Cd2+ and Pb2+, respectively. The MOF/EB-1 composite (71.0 wt.% MOF-5) gave the highest oxidation currents during both individual and simultaneous detection of two heavy metal ions. Current densities recorded with MOF/EB-1 were also higher than those of its individual components, reflecting the synergistic effect where MOF-5 offers high surface area for two heavy metals adsorption and PANI offers a network for electron transfer during metals' subsequent oxidation. Limits of detection using MOF/EB-1 electrode for Cd2+ and Pb2+ sensing were found to be as low as 0.077 ppm and 0.033 ppm, respectively. Moreover, the well-defined and intense peaks of Cd oxidation to Cd2+ and somewhat lower peaks of Pb oxidation to Pb2+ were observed at voltammograms obtained for the Danube River as a real sample with no pretreatment, which implies that herein tested MOF-5/PANI electrodes could be used as electrochemical sensors for the detection of heavy metal ions in the real water samples.

Green batch prepared a novel C/P co-doping urchin-like TiO2 for enhanced photocatalytic degradation and mineralization of trimethoprim

In advancing the practical application of photocatalytic degradation for pollutant removal, batch preparation of environmentally friendly photocatalysts plays a crucial role. Herein, we prepared C/P co-doped urchin-like TiO2 (C/P–TiO2) through a straightforward room temperature impregnation and atmospheric annealing process. Phytic acid served as the dopant precursor for introducing C and P onto the TiO2 surface. This doping process was verified through energy dispersive X-ray spectroscopy (EDX), electron spin resonance (ESR), and X-ray photoelectron spectroscopy (XPS) analysis. The C/P–TiO2 photocatalyst exhibited exceptional efficiency in degrading the target compound trimethoprim (TMP), achieving a degradation of 98% TMP within 60 min and a mineralization of 40% TMP within 120 min, which were respectively 2.4 and 1.6 times higher than that of pristine TiO2. The intermediate products of TMP were detected, and a plausible degradation pathway was proposed. Photoelectric characterization results also confirmed that C/P co-doping could effectively enhance the carrier separation efficiency of C/P–TiO2. The catalysts prepared using the scaled-up impregnation system and reusing the phytic acid solution consistently demonstrated stable catalytic performance, which confirmed the viability of the method for green and batch preparation of C/P co-doped TiO2. Notably, the obtained catalyst consistently exhibited high degradation efficacy in various real water bodies, highlighting its substantial potential for practical application. The green and batch preparation method of C/P–TiO2 introduces a novel approach to the practical application of photocatalysis technology in treatment of water contaminants.

The enrichment and separation of lanthanides ions from wastewater using solvent sublation coupled with high speed countercurrent chromatography

Rare earth elements are non-renewable resources. During their processing, a lot of wastewater are produced, which poses a danger to human beings and the environment. Herein, the enrichment method of solvent sublation for La (III), Ce (III), Gd (III) and Er (III) was designed and established. Enrichment parameters pH, flotation time, extractant concentration and air flow rate were optimized. The result showed that the highest recovery of La (III) reached up to 92.33 % under the optimized conditions of pH 8, 10 min of flotation time, 0.15 mol L-1 of the extractant 2-ethylhexyl phosphate acid-2-ethylhexyl ester and 30 mL min−1 of air flow rate. The light rare earth element Ce (III) and heavy rare earth elements Gd (III) and Er (III) were also examined and obtained with maximum recovery. The stability of the extractant complexation with rare earth ions and the mechanism of competitive extraction were studied by density functional theory calculations. The extraction ability was following sequence of La (III) < Ce (III) < Gd (III) < Er (III). The enrichment of rare earth elements from real water samples was investigated and obtained result was consistent with the experiment result of synthetic solutions. The established high speed countercurrent chromatography method was used to successfully separate La (III), Ce (III), Gd (III) and Er (III) from the solution of rare earth ions enriched by solvent sublation.

A Simple Method for Synthesizing Nitrogen-Doped Carbon Quantum Dots for Fluorescent "Turn off" Mercury (II) Ion Sensing.

Here, straightforward and environmentally friendly fluorescent nitrogen doped carbon quantum dots (N-CQDs) with a high blue fluorescence emission at 455nm are used for ultrasensitive Hg2+ ion detection. Folic acid and urea are used as carbon sources in the carbonization process. Two broad absorption bands at around 280 and 370nm from UV-Vis spectrum and characteristic absorption peaks from infrared spectrum confirms the successful synthesis of the N-CQDs. Energy dispersive X-Ray analysis confirmed the elemental composition of the N-CQDs. Transmission electron microscopy showed the homogeneous globular morphology of the N-CQDs with an average particle size of 65nm. Zeta potential measurement established the stability and surface charge of N-CQDs. Dynamic light scattering measurement showed the average size of N-CQDs. With the addition of Hg2+ ion to N-CQDs, the blue fluorescence emission is quenched. Moreover, the N-CQDs can be applied to real water sample such as pond water, river water, and tap water. The detection limit is approximately calculated to be 12 nM and linear range is 0-30 parts per billion.

Facile synthesis of sub-10 nm Cu-MOF nanofibers as electrochemical sensor element for picomolar chloramphenicol detection

Precise detection of antibiotics in aquatic environments is significant for human health and ecological environment development due to the excessive use of antibiotics. However, the accurate detection of ultralow-level antibiotics, such as picomolar level, has always been an extremely challenging task. Herein, we synthesized the sub-10 nm copper-based metal–organic framework nanofibers (Cu-MOF NFs) with a large specific area and high conductivity for achieving the electrochemical detection of picomolar-level chloramphenicol (CAP) in real water samples. As a result, by optimization of synthesis time and detection conditions, Cu-MOF NFs with a diameter of about 5 nm exhibited the ultralow limit of detection with 0.03 pM and wide detection range with 0.1––1.0 × 106 pM for CAP detection, as well as the designed sensor electrode has the excellent specificity, reproducibility, and stability. Importantly, the prepared sensor electrode exhibits reliable analytical results for CAP in real water samples, such as tap water, bottled water, and milk, indicating that designed sensor electrode has great application potential for the precise detection of antibiotics in practical samples.

OPTIMAL CONDITIONS FOR LIME TREATMENT OF MINE WASTEWATER FROM POLYMETALLIC ORE MINES

Mine waters of polymetallic mines are multicomponent systems containing ions of heavy non-ferrous metals, calcium, magnesium, iron, ammonium, as well as chlorides, sulfates, fluorides and other components in a wide range of concentrations. As a rule, water purification of this type is carried out by the lime method, which provides a fairly high degree of extraction of the most toxic pollutants (metals), with relatively small material costs. Taking into account the large volume, complexity and variation of the composition of mine waters, the tasks of optimizing reagent consumption, methods of its supply and effective control of the purification process still do not lose their relevance. The article presents the results of laboratory studies to determine the optimal conditions for processing model solutions that provide the maximum degree of purification for specific conditions of the Irtysh mine (East Kazakhstan). Experimental data obtained on model solutions are confirmed by the results of purification of real mine waste water. The results of experiments with mine water confirmed that the selected pH region of 9.5–10.5 can be accepted as optimal, which will allow achieving a high degree of purification of mine water.

Production of a double cermet coating to treatment of the turbine blades

Turbine blades commonly encounter external defects, such as cracks and high porosity, while in operation. To mitigate these challenges, the method of thermal spraying by flame is utilized for the application of cermet materials, which comprise both metal and ceramics, onto the blades. This process involved incorporating manganese (Mn) into a chromium oxide (Cr2O3) base in varying proportions (3,6,9,12,15)%. Before this, the two blends underwent multiple preparatory stages, such as being combined in a micro-mill for two hours and subsequently dried at 80 °C for thirty minutes to eliminate any moisture in the lab. The coating bases were prepared from an out-of-service turbine bit and shaped into squares with a side length of 1 cm. The bases were then roughened and indented using a paint gun. The resulting models were sintered at a temperature of 1000 °C for two hours. A number of structural and physical tests were carried out for the painted models before and after thermal sintering. Scanning electron microscope tests revealed crystalline regularity and lattice consistency of the outer surface especially at 15%Mn. The observed results of actual density indicated a gradual increase in density with successive additions of manganese. However, there was a consistent decrease in real porosity and water absorption, resulting in lower values at 15%. The hardness and adhesion strength exhibited significant improvements, increasing by approximately 15%. Conversely, the addition of the stiffener led to a continuous decrease in thermal conductivity. Consequently, it was concluded that the ideal coating settings for achieving favorable results were a coating distance of 16cm, a coating angle of 90°, and thermal sintering at 1000 °C.

Microwave synthesis of chitosan-based carbon dots for Al3+ detection and biological application.

Yellow fluorescent carbon dots (Y-CDs) were prepared via microwave method using chitosan and o-phenylenediamine as the main raw materials. The obtained Y-CDs possesses good water solubility, excellent biocompatibility and luminous stability. During the microwave pyrolysis carbonization process, the surface of Y-CDs was modified with the functional groups such as amino and carboxyl, which can bind to Al3+ by forming complexes, further improving the selectivity and sensitivity of the Al3+ detection. And the fluorescence of Y-CDs was quenched by Al3+ by static quenching process. More importantly, Y-CDs as fluorescent sensor was further applied for the determination of Al3+ in the real water samples with high reliability and accuracy. In addition, Y-CDs present potential application in biological imaging. The cultivated zebrafish embryos with Y-CDs displayed clearly in vivo uptake and metabolic fluorescence images, further confirming its low toxicity and excellent biocompatibility.

High enrichment and measurement of heterocyclic aromatic hydrocarbons from environmental waters with magnetic resorcinol-formaldehyde nanocomposites coupled with high performance liquid chromatography

Heterocyclic aromatic hydrocarbons are concerned pollutants with carcinogenic toxicity, which exist universally in various environmental matrices and have great harm to environmental and human health. In present work, magnetic resorcinol-formaldehyde composites (Fe3O4@SiO2@R–F) were fabricated via aldol condensation reaction under alkaline condition. The prepared magnetic materials were examined and analyzed with Fourier transform infrared spectroscopy and other related instruments. The Fe3O4@SiO2@R–F composites were utilized to develop an efficient magnetic solid phase extraction (MSPE) method for extracting six heteropolyclic aromatic hydrocarbons from environmental water samples including carbazole (CB), 7-methylquinoline (7-MQL), 9-methylcarbazole (9-MCB), dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The analytes were analyzed by high performance liquid chromatography-ultraviolet variable wavelength detector (HPLC-VWD). The main factors affecting MSPE were optimized. With the optimal parameters, 9-MCB and 4-MDBT have good linearity over the concentration range of 0.1–300 μg L−1, and 7-MQL, CB, DBT and 4,6-DMDBT have good linearity over the concentration range of 0.5–300 μg L−1. The limits of detection were over the concentration range of 0.012–0.031 μg L−1. This method was successfully employed to measure real waters, and the spiked recoveries ranged from 89.4% to 99.9%. The results confirmed that the developed method was reliable, robust and could be employed as a usefully alternate way for analyzing such pollutants in waters.

Perceived and Real Water Competency and Drowning Risk Among Adults

Traditionally, public understanding of drowning survival has focused on swimming capacity, often measured by how far a person can swim. With respect to the high incidence of adult drowning in high-income countries, using the more inclusive concept of water competency may yield a more comprehensive explanatory framework for understanding the reasons behind these drownings. Any competency base required to survive a drowning situation is dynamic, complex, and multi-faceted. Furthermore, perceptions of risk and capacity to cope with that risk are likely to be pivotal to the avoidance of drowning. Adults’ perceived water competence was measured against their actual water competence in a pool environment. Adults were tested on their competence in entering and exiting water, floating, and swimming. Despite most adults (98%) being unable to swim more than 100 m in open water, more than half (59%) perceived themselves as good swimmers, and more than quarter (27%) thought they could swim more than 200 m at the post-survey. In conclusion, reality gaps were found in water competence among adult groups. Differences between perceived and actual competence suggest that many adults may underestimate the risk of drowning and overestimate their competency. This provides a plausible explanation as to why many adults drown.

Comparison of Acid- and Base-Modified Biochar Derived from Douglas Fir for Removal of Copper (II) from Wastewater

Copper is a non-biodegradable heavy metal, and high levels in water bodies cause serious environmental and health issues. Douglas fir biochar has a higher number of carboxylic, phenolic, and lactonic groups, which provide suitable active sites for copper removal. Douglas fir biochar (BC) was modified using 20% solutions of KOH (KOH/BC), H2SO4, (H2SO4/BC), and Na2CO3 (Na2CO3/BC). All materials were characterized using SEM, SEM-EDS, FTIR, TGA, XRD, BET, and elemental analysis. These modifications were done to compare the activations of those sites by measuring copper removal efficiencies. KOH/BC, H2SO4/BC, and Na2CO3/BC materials gave surface areas of 389.3, 326.7, and 367.9 m2 g−1, respectively, compared with pristine biochar with a surface area of 578.9 m2 g−1. The maximum Langmuir adsorption capacities for Na2CO3/BC, KOH/BC, BC, and H2SO4/BC were 24.79, 18.31, 17.38, and 9.17 mg g−1, respectively. All three modifications gave faster kinetics at 2 mg/L initial copper concentrations (pH 5) compared with pristine BC. The copper removal efficiency was demonstrated in four different spiked real water matrices. The copper removals of all four water matrices were above 90% at 2 mg/L initial concentration with a 2 g/L biochar dosage. The competitive effects of Pb2+, Zn2+, Cd2+, and Mg2+ were studied at equimolar concentrations of Cu2+ and competitive ions for all four materials.