In Asturias (north of Spain), mercury mining has been identified as a potential source of trace elements such as As, Sb, Pb, and Hg. In particular, at Los Rueldos mine site, some of these contaminants are dissolved in acidic mine drainage (AMD). Here we treated this leachate by means of nanofiltration to remove some of its pollutants. In order to improve our understanding of the geochemical factors involved in nanofiltration, we analyzed sediment geochemistry and the origin of acidic waters. In coherence with the observation of similar behaviors of As, Fe, and Al in the nanofiltration tests, a clear geochemical association between As, Sb, S, and Fe both in sediments and in the occurrence of AMD was detected. The FILMTEC™ NF-2540 membrane used in this study proved to be highly suitable for the treatment and concentration of the metallic and semimetallic contaminants in the acidic water, even at low pH and moderate pressures.

Dual-effects of adsorption and photodegradation over titania, silica embedded titania, silica and commercial Degussa P-25 samples were studied for the decolourization of methylene blue in aqueous medium. Silica embedded titania and silica were prepared using inexpensive polymeric version of ethyl silicate as a source of silica. Catalysts were characterized by X-ray diffraction, scanning electron microscopy, UV-Vis spectroscopy and low temperature (77 K) nitrogen adsorption measurements. Among all the catalysts, silica embedded titania has exhibited faster decolourization of methylene blue solution on account of the enhancement of adsorption followed by degradation. An amount of the catalyst and the initial dye concentration of MB solution were found to influence the decolourization activity. Compared to titania catalyst, silica embedded titania and Degussa P-25 have shown the red shift in their UV-Vis spectrum. The experimental data of the reaction fitted well to the pseudo first order kinetic model. In present studies, the adsorption mechanism for the decolourization of MB solution was found to be applicable for an intra particle diffusion model. © 2013 Springer Science+Business Media Dordrecht.

Finding an environmentally safe and cost-effective method which is efficient enough to meet the regulatory standards of potable and industrial wastewater presents unique challenges. In this work, Moringa stenopetala seed powder which had particle size of 300 μm was characterized; ash content 4.7 %, bulk density 0.531/cm3, particle density 0.88 g/cm3, color yellowish, and pH 4.5. Fourier transform infrared spectroscopy analysis showed the multifunctionality of the M. stenopetala seed powder. M. stenopetala seed powder was assessed for percentage chromium removal and milligrams per gram chromium uptake as a function of contact time, pH, and dose of the adsorbent and initial concentration. The maximum percent removal was 99.74 %. Sorption kinetics of chromium adsorption by M. stenopetala seed powder was predicted reliably using a pseudo-second order model. An intra-particle diffusion model revealed that the biosorption of metals proceeds through various processes. Equilibrium uptakes were evaluated using Langmuir, Freundlich, Temkin, and the Dubinin-Radushkevich adsorption isotherm models. Even though the correlation coefficient was not as high as the Langmuir and Freundlich models for Temkin adsorption isotherm model, the metal uptake which was predicted by the model is comparable with the experimental value. Generally, the seed powder of M. stenopetala was found to be effective in the removal of chromium from tannery wastewater. © 2013 Springer Science+Business Media Dordrecht.

Atmospheric deposition occurs in a variety of forms and is crucial for the evaluation of nutrient budgets, critical loads, and pollution inputs across space and time. Atmospheric wet deposition is typically quantified by analyzing the chemistry of precipitation that is collected in some type of container with a lid that opens in response to precipitation. However, collectors can vary in shape as well as in the sensor that signals when precipitation is occurring. Here, we compare the collectors made by Aerochem Metrics and N-CON Systems Company Inc. The former has been widely used for several decades, while the latter is relatively new and has been used in a variety of configurations depending on the solute of interest. Event-based samples were collected from August 2007 to October 2008 and analyzed for nitrate, ammonium, sulfate, chloride, and dissolved organic carbon (DOC). A variety of approaches were used to assess the comparability of the two collectors. Regressions of concentration versus concentration from the two collectors were strong, and the slope did not differ from 1 for nitrate, ammonium, or sulfate. The median concentrations of nitrate, ammonium, and sulfate were, however, significantly higher in the N-CON collector, while there were no overall differences between collectors for chloride or DOC. Although we have observed some statistically significant differences between solute concentrations of samples collected from the two collectors, our mixed results suggest that these differences are relatively small.

Papaya seed was used as biosorbent for removal of tannery dye (Direct Black 38) from aqueous solution. The papaya seed was characterized, and it posseses macro/mesoporous texture, large pore size, and a surface containing various organic functional groups. The initial dye concentration, contact time, and pH significantly influenced the adsorption capacity. Equilibrium data were analyzed by the Langmuir and Freundlich isotherm models. The equilibrium data were best represented by the Langmuir isotherm, with a high adsorption capacity of 440 mg g⁻¹. Adsorption kinetic data were fitted using the pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Boyd models. The adsorption kinetics for the dye onto papaya seed was best described by second-order kinetic equation. The adsorption process mechanism was found to be controlled by both external mass transfer and pore diffusion, but the external diffusion was the dominating process. Papaya seeds showed to be a promising material for adsorption of Direct Black 38 dye from aqueous solution.

To evaluate cadmium (Cd) remediation capacity of gray poplar (Populus × canescens Sm. referred to the hybrid of Populus tremula L. × Populus alba L.), the glasshouse experiment was conducted in hydroponics, and the effects of Cd (0, 10, 30, 50, and 70 μM) on plant growth as well as Cd uptake and translocation were investigated. The growth rate of all tissues in P. × canescens decreased slowly with an increase in Cd concentrations. Among different tissues, the root exhibited the highest level of bio-concentration factor (BCF), followed by leaves, bark, and wood. BCFs in bark and wood significantly decreased with an increase in Cd concentrations. The translocation factor in different tissues firstly increased and then declined with an increase in Cd concentrations, respectively. The translocation factor in different tissues decreased slowly with an increase in Cd concentrations. Cd accumulation rates significantly increased and reached about sevenfold the level after 70 μM than that observed after 0 μM (control) for 28 days. These results indicated that P. × canescens have good tolerance against Cd stress, varying in Cd accumulation and translocation. These properties need to be taken into account in selecting species for the phytoremediation of orefield.

Recently, metal nanoparticles have attracted attention as promising peroxygen activators for the rapid and effective remediation of organic contaminants. In this work, a one-dimensional physical model experiment was designed to investigate the mobility of the metal nanoparticles in porous media and the potential use of metal nanoparticles as peroxygen activators for in situ treatment of source zones. We found that our synthesized nano-Pd-Fe0 particles were mobile in a non-geological porous medium and relatively immobile in a geological porous medium. In addition, we observed that iron-based bimetallic nanoparticles were able to remain in suspension in an ideal aqueous system much longer (>6 weeks) than iron-based monometallic nanoparticles (<1 h). To overcome the nano-Pd-Fe0 particle delivery issue in geological porous media, an activation zone approach was adopted. Nano-Pd-Fe0 particles were injected in order to create a zone to activate persulfate for the treatment of a trichloroethylene source zone. Trichloroethylene mass destruction was only 9 % higher in the nano-Pd-Fe 0 activated persulfate system compared to the non-activated persulfate system as revealed by a short-duration chloride concentration spike in the effluent. In addition, the nano-Pd-Fe0 activation zone was rapidly deactivated after being exposed to persulfate as visually observed by a color change, indicating that the longevity of the activation zone is limited. © 2013 Springer Science+Business Media Dordrecht.

Anaerobic digestion is one of the most effective means for the stabilisation of sludge. However, it has a very slow rate-limiting hydrolysis phase which is attributed to the low biodegradability of cell walls and the presence of extracellular biopolymers. This study aims at investigating the effect of ultrasonic, microwave and combined microwave–ultrasonic treatment on biogas production, solids removal and dewaterability of anaerobically digested sludge. A comparison was made between the three pretreatment techniques conducting the digestion tests under similar conditions on the same synthetic sludge sample inoculated by digested sewage sludge. The experimental results depict that the combined microwave–ultrasonic treatment (2,450-MHz, 800-W and 3-min microwave treatment followed by 0.4-W/ml and 10-min ultrasonication) resulted in better digester performance than ultrasonic or microwave treatment. Mesophilic digestion of combined microwave–ultrasonic-pretreated sludge produced a significantly higher amount of methane (147 ml) after a sludge retention time of 17 days, whereas the ultrasonic- and microwave-treated sludge samples produced 30 and 16 ml of methane, respectively. The combined microwave–ultrasonic treatment resulted in total solids reduction of 56.8 % and volatile solid removal of 66.8 %. Furthermore, this combined treatment improved dewaterability of the digested sludge by reducing the capillary suction time (CST) down to 92 s, as compared to CST of 331 s for microwave-treated and 285 s for ultrasonically treated digested sludge samples. Optimisation tests were also carried out to determine the best combination.

The adsorption mechanism of Ni(II) and Zn(II) onto activated carbon fiber (ACF) cloth and felt plain and oxidized was investigated in this work. The adsorption equilibrium data were obtained in a batch adsorber. The concentration of acidic and basic sites on the ACFS was determined by an acid-base titration method. The experimental adsorption equilibrium data were interpreted with the Redlich-Peterson isotherm, which fitted the data reasonably well. The ACF was oxidized with HNO3 solution and the concentration of acidic sites increased during oxidation, whereas that of the basic sites diminished. The adsorption capacity of the oxidized ACF was higher than that of the plain ACF because the oxidation of ACF formed more acidic sites on the surface where the metal cations can be adsorbed. The adsorption capacity of the plain and oxidized ACFs was linearly dependent upon the concentration of carboxylic sites. The adsorption of Ni(II) and Zn(II) on the ACFs was due to both electrostatic interactions and cation-π interactions. The contribution of ion exchange to the overall adsorption of Zn(II) and Ni(II) on ACFs was less than 3.3 % and can be considered negligible. © 2013 Springer Science+Business Media Dordrecht.

Stormwater is a potential and readily available alternative source for potable water in urban areas. However, its direct use is severely constrained by the presence of toxic pollutants, such as heavy metals (HMs). The presence of HMs in stormwater is of concern because of their chronic toxicity and persistent nature. In addition to human health impacts, metals can contribute to adverse ecosystem health impact on receiving waters. Therefore, the ability to predict the levels of HMs in stormwater is crucial for monitoring stormwater quality and for the design of effective treatment systems. Unfortunately, the current laboratory methods for determining HM concentrations are resource intensive and time consuming. In this paper, applications of multivariate data analysis techniques are presented to identify potential surrogate parameters which can be used to determine HM concentrations in stormwater. Accordingly, partial least squares was applied to identify a suite of physicochemical parameters which can serve as indicators of HMs. Datasets having varied characteristics, such as land use and particle size distribution of solids, were analyzed to validate the efficacy of the influencing parameters. Iron, manganese, total organic carbon, and inorganic carbon were identified as the predominant parameters that correlate with the HM concentrations. The practical extension of the study outcomes to urban stormwater management is also discussed.