Excessive algae growth has generated conflicts on the use of water supplies; therefore, the focus on new technologies to remove algae from water bodies is demanding. The aim of the present study was to assess the effect of hydrodynamic cavitation on the inactivation of microalgae belonging to genus Scenedesmus. A laboratory-scale experimental apparatus was built in order to accomplish this goal; it consisted of a Venturi device designed to generate the cavitation phenomenon. Suspended microalgae samples were treated for 60 minutes under different cavitation intensities (cavitation number—Cv—ranging from 0.17 to 0.27). Results evidenced that microalgae decay over time can be modeled through first-order kinetics. The maximum removal efficiency (85%) was recorded at the highest cavitation intensity (Cv = 0.17). The removal efficiency decreased as the cavitation number increased. Hydrodynamic cavitation was effective in inactivating Scenedesmus; it produced irreversible damages to cell morphology such as flotation spines removal, cell wall lesions, cytoplasm extravasation, and cavity formation. Assumingly, hydrodynamic cavitation has great potential to treat eutrophic water bodies. Furthermore, it represents a sustainable removal technique, since it does not produce secondary pollution.

Ca-Al layered double hydroxides (LDHs) with different Ca/Al molar ratios were composited at pH ranges, using a co-precipitation method, and were experimented to remove fluoride from wastewater and studied in terms of isotherm models such as Langmuir and Freundlich reactions. The composite LDHs were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA). The results showed that different synthesis conditions of Ca-Al LDHs had an influence on their morphology, layered structure, and particle size distribution, which substantially affected the uptake capacity for aqueous fluoride. LDHs with the Ca/Al molar ratio of 2 and synthesized at the pH of 12 had the highest capacity for the fluoride removal (e.g., 146.6 mg/g) and such reaction reached an equilibrium within 1 h. The Freundlich model was a better fit for this study. The high adsorption method of Ca-Al LDHs can be favorable to removing fluoride from wastewater streams.

This study aimed to investigate a novel method of red mud neutralisation by Ca(NO₃)₂ (NRM), keeping its adsorption capacity in relation to natural red mud (RM) for Ni(II), Pb(II) and Zn(II). Results pointed out that the neutralisation process decreases the pH and electrical conductivity values on NRM due to reaction between the carbonate and bicarbonate alkalinity of red mud and calcium from calcium nitrate to form calcite (CaCO₃). The maximum adsorption capacity values of RM and NRM, respectively, were 1.78 and 1.79 mmol g⁻¹ for Ni(II), 2.13 and 2.23 mmol g⁻¹ for Pb(II) and 1.14 and 1.06 mmol g⁻¹ for Zn(II). Pseudo-second-order model is the main responsible for the adsorption of these metals on RM and NRM. The adsorption reaction is endothermic and these metals have affinity to RM and NRM. Thus, it is possible to neutralise the red mud with Ca(NO₃)₂ without adsorption capacity losses of Ni(II), Pb(II) and Zn(II).

The reaeration coefficient (K ₐ) is an essential parameter to predict the dissolved-oxygen concentration in different aquatic ecosystems. The techniques applied to K ₐ estimates require considerable efforts, since measuring this coefficient is a laborious and expensive task. Thus, the use of predictive equations wherein K ₐ is found through hydraulic flow parameters is common. However, the available prediction equations lead to estimates often different from each other. A new predictive equation is addressed in the present study. The insertion of a dimensionless number resulting from the relation between the RMS (Root Mean Square) of the free-surface vertical velocity and the surface flow velocity is the great innovation of the study. The reaeration experiments and the surface vertical velocity mapping were performed in a circular hydraulic channel. The flow velocity varied from 0.25 to 0.64 m s⁻¹, and depth varied from 0.09 to 0.15 m. The new equation led to more accurate results than the equations based on traditional hydraulic parameters such as the Reynolds and Froude numbers, mainly when it comes to K ₐ values higher than 40 day⁻¹. The sensitivity analysis has shown that the new dimensionless number is the most sensitive parameter of the herein proposed predictive equation and that the influence from the Reynolds and Froude numbers on K ₐ weakens as turbulence gets more intense.

A magnetic chitosan-modified Fe₃O₄@SiO₂ with sodium tripolyphosphate adsorbent (MTPCS) was synthesized by surface modification of Fe₃O₄@SiO₂ with chitosan using sodium tripolyphosphate (STPP) as the cross-linker in buffer solution for the adsorption of Cu(II) ions from aqueous solution. The structure and morphology of this magnetic nanoadsorbent were examined by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), BET surface area measurements, Fourier transform infrared spectrometer (FTIR), and X-ray photoelectron spectroscopy (XPS). The effects of initial pH, adsorbent amount, and initial concentration of heavy metal ions were investigated by batch experiments. Moreover, adsorption isotherms, kinetics, and thermodynamics were studied to understand the mechanism of adsorbing metal ions by synthesized MTPCS. The results revealed that adsorption kinetics was best depicted by the pseudo-second-order rate mode and intraparticle-diffusion models. The adsorption isotherm fitted well to the Langmuir model. Moreover, thermodynamic study verified the adsorption process was endothermic and spontaneous in nature. The maximum adsorption occurred at pH 5 ± 0.1, and the adsorbent could be used as a reusable adsorbent with convenient conditions.

The aim of this study was to investigate the presence of heavy metals/metalloids (Pb, Cd, Hg, Cu, Fe, Zn, As) in the muscle tissue of fish from the Danube River (two locations: Zemun and Grocka). For the purpose of heavy metal determination in fish muscle, 120 samples of six different fish species, Prussian carp, barbel, bream, carp, pike perch, and catfish were collected. For determining heavy metals, we used microwave oven digestion and atomic absorption spectrometer methods. The highest average content of Pb (0.084 ± 0.004 mg kg⁻¹), Cd (0.082 ± 0.003 mg kg⁻¹), Hg (0.466 ± 0.006 mg kg⁻¹), and As (0.333 ± 0.007 mg kg⁻¹) was found in the muscle of carp (an omnivorous fish) from Grocka, while the highest average level of Fe (13.60 ± 0.03 mg kg⁻¹) was deposited in bream (also omnivorous) from Zemun. Also, the average Cu level (1.62 ± 0.13 mg kg⁻¹) was the highest in catfish muscle (a carnivorous fish) from Grocka, while the highest Zn content (11.16 ± 0.17 mg kg⁻¹) was determined in muscle of Prussian carp (an omnivorous fish) from Zemun. The highest content of heavy metals (Cu, Fe, and Zn, respectively) in muscle of the six different types of fish from both locations was symmetrically arranged by species (catfish, barbel, and Prussian carp, respectively). Concentrations of Pb, Hg, and As in the Danube River fish muscle were under the maximum residual levels prescribed by the European Union (EU) and the maximum allowed concentrations (MAC) for Serbia. On the other hand, in all fish muscle from both locations (Zemun and Grocka), higher concentrations of Cd than prescribed (MAC) were found, with the exception of bream and pike perch.

Occurrence of halonitromethanes (HNMs) in drinking water has been a concern recently due to the potentially high human health risks of HNMs. Mechanisms of formation of HNMs during disinfection has remained controversial. The objective of this study was to investigate the effects of nitrite on the formation of trichloronitromethane (TCNM), a dominant HNM species occurring in chlorinated water. Polyhydroxy-phenols (hydroquinone, catechol, resorcinol, and phloroglucinol) and sugars (glucose, maltose, and lactose) were compared as surrogates/model compounds of common organic precursors of humic and non-humic substances in natural organic matter, respectively. The results showed that TCNM was not detectable after chlorinated sugars with the addition of nitrite. Upon chlorinating the polyhydroxy-phenols, TCNM formation varied greatly among different compounds, i.e., resorcinol > phloroglucinol > catechol >> hydroquinone. The results demonstrated that TCNM formation in the presence of nitrite was a function of aromaticity as well as the position and number of hydroxyl groups on the benzene rings of a compound, and the TCNM formation potential of humic substances was greater than that of non-humic substances. For catechol, resorcinol, and phloroglucinol, TCNM formation varied greatly with pH but generally remained stable with the increase of reaction time and temperature.

Mercury (Hg) is an environmental pollutant which is detrimental to the health of living beings due to the toxicity in its all oxidation states. To control mercury pollution development of low cost, efficient and highly sensitive prototype mercury sensor remains a challenge. In the present work, we have proposed a low-cost prototype device based on silver nanoparticle-impregnated poly(vinyle alcohol) (PVA-Ag-NPs) nanocomposite thin film for mercury detection. The thin film, fabricated through a facile protocol, is shown to be a fast, efficient, and selective sensor for Hg²⁺ in aqueous medium with a detection limit of 10 ppb. We have utilized the aggregation and amalgamation of Ag-NPs with Hg²⁺ to develop the low-cost, highly efficient and feasible prototype mercury sensor. In the presence of Hg²⁺, the yellowish thin film turned into colourless due to the loss of intense surface plasmon resonance (SPR) absorption band of the silver nanoparticles (Ag-NPs) through aggregation and amalgamation with mercury. The developed sensor has high selectivity for Hg²⁺ ions over a wide range of other competing heavy metal ions, generally present in water of natural sources. The sensor response is found to be linear over the Hg²⁺ ion concentration regime from 10 ppb to 5 ppm. The developed sensor has shown to determine a trace Hg²⁺ ions in real water samples. Finally, using the proposed technique, we have developed a simple and inexpensive prototype device for monitoring in field environmental mercury pollution. Graphical Abstract ᅟ

Energy development in the Bakken and Three Forks formations of the USA has led to an increase in fugitive dust from unpaved roads. A dust abatement alternative that has been considered in this region is oil-well produced waters. The objectives of this study were to compare dust loading at sites abated with produced water to non-abated control sites and to determine if the elemental constituents in released dust are different compared to control roads. Three previously untreated unpaved roads were selected, and passive dust collectors were placed at 10, 20, 40, and 60 m from the road on the downwind side of the dominant prevailing wind in each mile section. Eighty-four days post-application, two sections treated with produced waters failed to reduce dust when compared to the controls. Dust elemental changes were found on two of the three roads. Elements that were found to have differences included Mo, Mn, Fe, As, Au, and Hg. Overall results indicated that oil-well produced water is not effective at controlling road dust. Results of this study are important to road managers who are contemplating the usage of produced waters to reduce dusts from unpaved roads.

Spontaneous colonization of mine tailing dams by plants is a potential tool for phytostabilization of such reservoirs. However, the physical and chemical properties of each mine tailings deposit determine the success of natural plant establishment. The plant Baccharis linearis is the main native nanophanerophyte species (evergreen sclerophyllous shrub) that naturally colonizes abandoned copper tailings dams in arid to semiarid north-central Chile. This study compare growth of B. linearis against the physical and chemical properties of a Technosol derived from copper mine tailings. Five sites inside the deposit were selected based on B. linearis vegetation density (VD), at two soil sampling depths under the canopy of adult individuals. Physical and chemical properties of tailings samples and nutrient concentrations in tailings and plants were each determined. Some morphological features of the plants (roots and aerial parts) were also quantified. There were significant differences in soil available water capacity (AW) and relative density (Rd) at different VD. Sites with low AW and high Rd had lower nutrient concentrations and higher Zn content in tailings, decreased infection by arbuscular mycorrhizal fungi, and increased fine root abundance and root hair length in individual plants. In contrast, higher AW, which was positively correlated with fine particles and organic matter content, had a positive effect on vegetation coverage, increased N and P contents in tailings, and increased N contents in leaf tissues, even when available N and P levels in tailings were low. Multiple constraints, such as low AW, N, P, and B contents and high Zn concentrations in the tailings restricted vegetation coverage, but no phenotypic differences were observed between individuals. Thus, in order to promote dense coverage by B. linearis, water retention in these tailings must be improved by increasing colloidal particles (organic and/or inorganic) contents, which have a positive effect on colonization by this species.