The aim of this work was to investigate the biosorption of a cationic dye (methylene blue (MB)) by Salvinia minima. Biomass was characterized using the point of zero charge and scanning electron microscopy. The effects of pH (2–10), biosorbent dose (1–6 g/L), initial MB concentration (49.14 ± 1.03, 99.60 ± 0.67, 148.91 ± 2.00, 198.24 ± 1.91, 243.74 ± 2.32 mg/L), and time (20, 40, 60, 120, 180, 240, 300, 360 min) on MB biosorption and removal were evaluated. The MB biosorption kinetics were analyzed using pseudo-first- and pseudo-second-order kinetic models, as well as Elovich and intraparticle diffusion models, and Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms were used to analyze the equilibrium biosorption. A positive effect of pH on MB biosorption and removal was observed when pH was increased from 2 to 4 (28.18 ± 0.30 and 110 ± 0.05 mg/g, 23.20 ± 0.27 and 90.50 ± 0.01 %, respectively), while an increase in the biomass dose from 1 to 6 g/L reduced biosorbent efficiency from 157.30 ± 2.59 to 38.23 ± 0.02 mg/g. The adsorption kinetic data fit the pseudo-second-order equation, suggesting that chemisorption was the rate-determining step during MB biosorption by S. minima biomass. Equilibrium biosorption was described by the Freundlich model, implying that MB multilayers form on the heterogeneous surface of the biomass. S. minima biomass can be used as a biosorbent for the removal and adsorption of cationic dyes from water or wastewater.

The textile industry often releases effluents into the environment without proper treatment or complete dye removal. Azo dyes, which are characterized by azo groups (―N═N―), are frequently used in the textile industry. Among the different wastewater treatment methods available, biological treatment has been extensively studied. The aim of the present study was to compare the biodegradation of the azo dye Direct Blue 71 by the fungi Phanerochaete chrysosporium and Aspergillus oryzae in paramorphogenic form using a 100 μg/ml dye solution. Biodegradation tests were performed within 240 h. The absorbance values obtained with UV-VIS spectrophotometry were used to determine the absorbance ratio and the percentage of dye discoloration following the biodegradation test. FTIR analysis allowed the identification of molecular compounds in the solution before and after biodegradation. Both A. oryzae and P. chrysosporium demonstrated considerable potential regarding the biodegradation of dyes in wastewater. These results may contribute toward improving effluent treatment systems in the textile industry.

Clay minerals have been utilized for the remediation of heavy metal-polluted soil. However, information on the remediation stability of various clay minerals with different performances is limited. In this study, a kind of palygorskite (PAL) with a sorption amount for Cd²⁺about 40 mg/g, which is much larger than common minerals, was selected as amendment for in situ immobilization field demonstration. Besides, sorption stability which is essential for remediation was investigated in an ideal solid solution system by sorption and desorption behaviors of Cd²⁺on PAL, including isotherms, kinetics, and various stimulated environmental factors such as pH, temperature, and background electrolytes. The calculated thermodynamic parameters confirmed the sorption process was endothermic and driven by entropy changes. Only minimal desorption was caused by stimulated irrigation or runoff and acid rain. The temperature, pH, and background electrolyte dependence confirmed that the sorption of Cd²⁺on PAL was stable. Various characterization results including X-ray photoelectron spectroscopy (XPS), scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) mapping, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) confirmed the sorption mechanisms were surface precipitation of CdCO₃and surface complexation with hydroxyl groups.

Adsorption onto powdered activated carbon (PAC) is a promising option to remove organic micro-pollutants (OMP) from drinking water sources or wastewater. Since this treatment option requires continuous PAC dosing, sufficient contact time and subsequent separation of the PAC, the integration into existing process chains is challenging. In the present investigation, the pre-loading of a deep bed filter with PAC used as fixed bed adsorber was investigated. The retention and distribution of an exemplary PAC in a pumice rapid filter were determined. Gravimetry combined with combustion of the PAC at 550 °C was applied to differentiate between PAC and filter material residues and revealed comparably high PAC immobilization in the upper third of the pumice filter. Comparative adsorption experiments in batch with suspended PAC and continuous filtration tests with immobilized PAC showed advantageous results for immobilized PAC with regard to the removal of OMP and the sum parameters dissolved organic carbon and UV light absorption at 254 nm wavelength. The results indicate that a conventional rapid filter together with PAC can be effectively utilized as fixed bed adsorption filter.

The increased industrial and economic developments that have occurred in recent decades, particularly in mining, agricultural and metal recycling activities have decisively contributed to the increased concentration of heavy metals in soil. This study was carried out to evaluate the performance of Sorghum bicolor and Chrysopogon zizanioides in the citric acid-assisted phytoextraction of Pb in a field experiment setup in an area contaminated by automotive battery waste. Two soils amendments were used and they were dolomitic limestone and silicate slag at doses of 4.74 and 12.80 t ha⁻¹, respectively. Commercial citric acid was applied in each experimental parcel on the 63rd day of the cultivation in order to enhance Pb solubilisation and plant availability. Citric acid, which was applied at a dose of 40 mmol kg⁻¹of soil, was efficient in the solubilisation of Pb in soil and in the induction assisting of the removal of Pb from soil by the both species tested. Commercial citric acid is indicated for use in the area, due to its low cost and high biodegradability. Due to the low natural solubility of Pb and the large amount of time required, i.e. more than 900 years, phytoextraction without the application of chelating agents is not viable for remediation of the study area. Sorghum grown in soil amended with silicate slag combined with the application of the chelating agent commercial citric acid is the recommended phytoextraction programme for the remediation of an area with moderate Pb contamination.

Carbonaceous material obtained from industrial sewage sludge and Na-zeolitic tuff were used to adsorb cadmium from aqueous solutions in column systems. The Bohart, Thomas, Yoon–Nelson, and mass transfer models were successfully used to fit the adsorption data at different depths, and the constant rates were evaluated. The parameters such as breakthrough and saturation times, bed volumes, kinetic constants, adsorption capacities, and adsorbent usage rates (AUR) were determined. The results show that the breakthrough time increases proportionally with increasing bed height. The adsorption capacity for cadmium for Na-zeolitic tuff was higher than carbonaceous material. The results indicated that the Na-zeolitic tuff is a good adsorbent for cadmium removal.

The disposal of cyanogenic residues from the processing of cassava, during the flour production in certain regions of the Brazilian northeastern, has been a cause of concern in recent years, since this practice may lead to environmental imbalances. The results obtained in this work show a possible impact caused by the release of this kind of waste into water bodies, as well as its potential use as biofertilizer, mainly due to its high nutrient content. Humic substances (HS) from water and soil showed high interaction with cyanide ions (CN⁻), being the main responsible for the bioavailability of these ions into the environment. Furthermore, studies in microcosms propose viable and low-cost alternatives to decrease the levels of CN⁻ions in the liquid waste (called “manipueira”), as well as its potential use as biofertilizer.

The role of the hyporheic zone in mercury (Hg) cycling has received limited attention despite the biogeochemically active nature of this zone and, thus, its potential to influence Hg behavior in streams. An assessment of Hg geochemistry in the hyporheic zone of a coarse-grained island in the Coast Fork Willamette River in Oregon, USA, illustrates the spatially dynamic nature of this region of the stream channel for Hg mobilization and attenuation. Hyporheic flow through the island was evident from the water-table geometry and supported by hyporheic-zone chemistry distinct from that of the bounding groundwater system. Redox-indicator species changed abruptly along a transect through the hyporheic zone, indicating a biogeochemically reactive stream/hyporheic-zone continuum. Dissolved organic carbon (DOC), total Hg, and methylmercury (MeHg) concentrations increased in the upgradient portion of the hyporheic zone and decreased in the downgradient region. Total Hg (collected in 2002 and 2003) and MeHg (collected in 2003) were correlated with DOC in hyporheic-zone samples: r ² = 0.63 (total Hg-DOC, 2002), 0.73 (total Hg-DOC, 2003), and 0.94 (MeHg-DOC, 2003). Weaker Hg/DOC association in late summer 2002 than in early summer 2003 may reflect seasonal differences in DOC reactivity. Observed correlations between DOC and both total Hg and MeHg reflect the importance of DOC for Hg mobilization, transport, and fate in this hyporheic zone. Correlations with DOC provide a framework for conceptualizing and quantifying Hg and MeHg dynamics in this region of the stream channel, and provide a refined conceptual model of the role hyporheic zones may play in aquatic ecosystems.

Micrometer-size poly(vinyl phosphonic acid) (p(VPA)) hydrogel was synthesized by employing UV irradiation of an emulsion containing vinyl phosphonic acid (VPA) and crosslinker, prepared using lecithin as surfactant and gasoline as solvent. The p(VPA) microgels were employed in absorption of UO₂²⁺ions from aqueous environments and have very high and fast absorption capacity. In about 20 min, 670 mg UO₂²⁺ions were absorbed per gram of p(VPA) microgel from the prepared UO₂²⁺ion solution, and the absorption capacity increased up to 900 mg at pH 6. Various parameters affecting UO₂²⁺absorption characteristics of p(VPA) were investigated. It was found that the Langmuir isotherm fitted the absorption characteristics of p(VPA) better than the Freundlich isotherm. Moreover, magnetic ferrite can be prepared within p(VPA) and used as a magnetically responsive p(VPA) microgel composite for externally controlled absorption of UO₂²⁺ions with little decrease in the absorption capacity of the p(VPA) microgel.

While most waste foundry sands (WFSs) are not hazardous, regulatory agencies are often reluctant to permit their beneficial use in agricultural and geotechnical applications due to concerns over metal leaching. The objective of this study was to quantify total and Toxicity Characteristic Leaching Procedure (TCLP) metals in 16 waste sands from Brazilian ferrous foundries then assess their potential to leach to groundwater using a probabilistic model. Total and TCLP metal concentrations in the non-hazardous sands fell within ranges as reported in the literature, although some of the leachate concentrations were found to exceed drinking water and groundwater maximum contaminant levels (MCLs). Leachate values above the MCLs were then used in the model to estimate groundwater concentrations at hypothetical wells up to 400m downgradient from a land application unit. A conservative scenario of 1 ha of land applied WFS, and high annual rainfall totals (low evaporation) suggested that groundwater concentrations of Ba, Hg, Mn, Ni, and Pb could potentially exceed health-based MCLs at most wells. While a wet climate can exacerbate the transport of metals, land application of WFSs in areas with moderate rainfall totals or high rainfall, high evaporation was predicted to be protective of groundwater quality and human health.