Kinetic,equilibrium and thermodynamic studies of thiamethoxam adsorption by multi-walled carbon nanotubes

Because of their high adsorption capacity, carbon nanotubes have caught the attention of the scientific community and a number of experimental results confirmed their ability to adsorb many toxins from water. The aim of this work was to study the kinetics, equilibrium and thermodynamics of thiamethoxam adsorption by multi-walled carbon nanotubes in aqueous solutions. To further elucidate the influence of nanotube structure on the adsorption mechanism, the experiments were performed on both fresh (pristine) and nitric acid-modified multi-walled carbon nanotubes. The results of the kinetic studies were analyzed using three kinetic models, while the adsorption equilibrium was tested against four different adsorption models. Based on the results, and the physico-chemical properties of the adsorbent and adsorbate, it is proposed that the dominant mechanism for thiamethoxam molecules attaching to multi-walled carbon nanotubes is caused by aromatic π–π interactions (electron donor–acceptor interactions). The results of thermodynamic calculations based on the adsorption data indicate the exothermic nature of the process, regardless of the carbon nanotube type used. The decrease in entropy and the consequent negative change in Gibbs free energy, as expected, confirm the spontaneity of thiamethoxam adsorption on both pristine and functionalized multi-walled carbon nanotubes.     

Fungal air contamination in distinct sites within a municipal landfill area

Municipal wastes collected in landfills are a significant source of air contamination and frequently characterize by elevated concentrations of different fungi. Posing a serious health threat to landfill workers and local residents, the fungal aerosol has to be monitored with respect to its quantity and quality. In this study, concentrations of airborne fungi, their particle size distribution, species composition and the presence of cytotoxic strains of Aspergillus fumigatus were assessed in different sites within the landfill area. The quantitative and qualitative changes in the fungal aerosol were determined with respect to a season and landfill activity level (i.e. exploitation or standstill periods). Within the landfill area, particular sites were grouped with regard to airborne fungi concentrations and similarities in species composition. The qualitative analysis indicated that 43 species were shared during both sampling times, and only nine species were characteristic for the standstill period. Among fungal isolates, 21 strains of A. fumigatus revealed cytotoxic activity expressed at different levels, depending on the fungal extract concentrations used in the MTT assay. The results suggested that exposure (especially in summer) to small airborne particles, containing distinct species, may occur not only in the active sector but also in close vicinity to the landfill. Hence, microbial monitoring of the landfill and surrounding area should be carried out taking into account both quantitative aspect supplemented by size distribution analysis and qualitative features, especially of those strains possessing cytotoxic activity.     

Influence of the natural organic matter in the removal of caffeine from water by fixed-bed column adsorption

The removal of caffeine from tap water by F-400 granular activated carbon in fixed-bed adsorption experiments was carried out. Textural and chemical characterization of the adsorbent through N₂ adsorption–desorption isotherms, Fourier transform infrared spectrometry, isoelectric point determination and scanning electron microscopy studies was developed in studies previously reported. Caffeine breakthrough curves and total organic carbon profiles at different operation conditions (inlet concentration, volumetric flow rate and mass of adsorbent) were obtained. These experimental results showed a displacement of the natural organic matter from the active sites exerted by caffeine molecules due to their higher affinity to the surface carbon. This behavior led to an overshooting, a local outlet natural organic matter concentration higher than the feed quantity. A competitive effect seems to be observed in the removal of the target compound, decreasing the efficiency of the process. Axial dispersion coefficients and dimensionless numbers were estimated for the caffeine removal onto F-400 activated carbon. Therefore, the regeneration of the adsorbent by adsorption–desorption cycles was studied.     

Moving bed biofilm reactor to treat wastewater

This review carries out a comparative study of advanced technologies to design, upgrade and rehabilitate wastewater treatment plants. The study analyzed the relevant researches in the last years about the moving bed biofilm reactor process with only attached biomass and with hybrid biomass, which combined attached and suspended growth; both could be coupled with a secondary settling tank or microfiltration/ultrafiltration membrane as a separation system. The physical process of membrane separation improved the organic matter and NH₄ ⁺-N removal efficiencies compared with the settling tank. In particular, the pure moving bed biofilm reactor–membrane bioreactor showed average chemical oxygen demand, biochemical oxygen demand on the fifth day and total nitrogen removal efficiencies of 88.32, 90.84 and 60.17%, respectively, and the hybrid moving bed biofilm reactor–membrane bioreactor had mean chemical oxygen demand, biochemical oxygen demand on the fifth day and total nitrogen reduction percentages of 91.18, 97.34 and 68.71%, respectively. Moreover, the hybrid moving bed biofilm reactor–membrane bioreactor showed the best efficiency regarding organic matter removal for low hydraulic retention times, so this system would enable the rehabilitation of activated sludge plants and membrane bioreactors that did not comply with legislation regarding organic matter removal. As the pure moving bed biofilm reactor–membrane bioreactor performed better than the hybrid moving bed biofilm reactor–membrane bioreactor concerning the total nitrogen removal under low hydraulic retention times, this system could be used to adapt wastewater treatment plants whose effluent was flowed into sensitive zones where total nitrogen concentration was restricted. This technology has been reliably used to upgrade overloaded existing conventional activated sludge plants, to treat wastewater coming from textile, petrochemical, pharmaceutical, paper mill or hospital effluents, to treat wastewater containing recalcitrant compounds efficiently, and to treat wastewater with high salinity and/or low and high temperatures.     

Evaluation of the removal of heavy metals in a natural wetland impacted by mining activities in Mexico

This research is focused on evaluating heavy metals (Cd, Cu, Fe, Mn, Pb, and Zn) uptake and removal by Eleocharis ovata, Cyperus manimae, Typha dominguensis, and Pteridium aquilinum in a natural wetland impacted by mining activities. We analyzed heavy metals content and distribution in native plants, soils, and water of a semipermanent natural wetland in Taxco de Alarcón, Guerrero, and we also determined the physicochemical characteristics of the water. Translocation factor (TF) and bioconcentration factor (BCF) were evaluated. Results showed that physical and chemical conditions are favorable for plants development. Correlation analysis showed a good and positive relation (0.95) between Cu and Pb in soils and plants. In the analyzed matrices: Zn (0.62–2.20 mg/L) exceeded the permissible limits in water, high concentrations of Pb and Zn (26.57–525.67 and 266.67–983.33 mg/kg, respectively) were detected in the studied soils, and Pb exceeded the normal range for E. ovata and P. aquilinum in the analyzed plants. Uptake of heavy metals in the tissues of different species was found in the following order: root > leaf. Data of TF and BCF showed that E. ovata is a tolerant plant with respect to heavy metals exposure since TF value was greater than 1. This study showed that E. ovata could be considered as a bioaccumulator of heavy metals in contaminated soils.     

Metals in tidal flats colonized by microbial mats within a South-American estuary (Argentina)

In this study, we measured the concentrations of metals (Cd, Cu, Pb, Ni, Cr, Zn, Hg, Mn, and Fe) and assessed the characteristics of tidal flats (grain size and organic matter content) in sediments and their overlying microbial mats fractions to evaluate the anthropogenic impact within the Bahía Blanca Estuary (BBE). Puerto Rosales (PR) and Almirante Brown (AB), located in the middle and inner zone of the estuary, respectively, were used as sampling sites. Sediments were composed mainly of silt–clay in AB, whereas first fine-grained particles were coarser in depth in PR. Regarding the concentration of metals in both fractions, we found differences between sites: There were higher concentrations of overall metals in AB relative to PR. In addition, higher concentrations of Cu were recorded in the first centimeters of AB tidal flats, whereas higher concentration of Cd were recorded in microbial mats of PR. Considering that the grain size was similar between sites, these results are consistent with the high concentration of organic matter found in AB, probably because this site is close to a former municipal dump and sewage discharges. Also, the higher Cd content found in PR site would highlight both the influence of untreated urban discharges and port anthropogenic activities. In conclusion, this study allowed identifying high values of some metals in the presence of microbial mats in the BBE, thus suggesting a possible interaction between both, at least for metals like Cu or Cd.     

Metallophilic fungi research: an alternative for its use in the bioremediation of hexavalent chromium

Contamination by hexavalent chromium has had a large impact on modern society and human health. This problem is a consequence of its great industrial applicability to several products and processes. Short-term exposure to hexavalent chromium can cause irritation, ulceration in skin and stomach and in addition to cancer, dermatitis, and damage to liver, renal circulation and nervous tissues, with even death being observed in response to long-term exposures. Many techniques have been used for the remediation of this pollutant, including physical and chemical approaches and, in more recent years, biological methods. Filamentous fungi isolated from contaminated sites exhibit a significant tolerance to heavy metal; hence, they are an important source of microbiota capable of eliminating hexavalent chromium from the environment. However, these microorganisms can do so in different ways, including biosorption, bioreduction, and bioaccumulation, among others. In this review, we explore several of the most documented mechanisms that have been described for fungi/hexavalent chromium interactions and their potential use in bioremediation.     

Dynamic compaction evaluation using in situ tests in Sagunto’s Harbor,Valencia (Spain)

This paper presents an assessment on the use of dynamic compaction as a ground improvement technique in a port’s hydraulic fill in the new southern dock of Sagunto’s Harbor near Valencia (Spain). Soil behavior improvement was monitored by several in situ techniques such as boreholes with SPTs, DPSH, CPTU and CSWS geophysical tests. A total energy between 2188 and 3125 kN/m² (depending the area) was applied to the hydraulic fill by the dynamic compaction procedure. In situ techniques led to evaluate dynamic compaction efficiency, as well as controlling ground modifications that might cause potential damages to adjacent buildings. The dynamic compaction carried out was capable of fulfilling requirements established to use the area, that is, an average deformability modulus (E′) of 30 MPa with a minimum of 20 MPa, in a depth of 10 m. Moreover, dynamic compaction increased hydraulic fill relative density by about 75%.     

Changes in water chemistry along the newly formed High Arctic fluvial–lacustrine system of the Brattegg Valley (SW Spitsbergen,Svalbard)

Changes in water chemistry along the High Arctic fluvial–lacustrine system located in Wedel Jarlsberg Land in the SW Spitsbergen (Svalbard) were investigated during the summer season of 2010 and 2011. The newly formed river–lake system consists of three lakes connected with the Brattegg River. The first bathymetric measurements of these lakes were made by the authors in 2010. The Brattegg River catchment represents a partly glaciered Arctic water system. The studied lakes are characterized by low mineralization and temperature of water. The value of the electrolytic conductivity (EC) ranges from 30.2 to 50.5 μS cm^?1 and the temperature of surface water from 1.5 to 7.8 °C. The temperature increase takes place downstream starting from Upper Lake to the outflow from Myrktjørna Lake. The waters of lakes have higher temperatures than the stream. The predominant ions are HCO₃ ^? (up to 16.5 mg L^?1), Cl^? (6.66–8.53 mg L^?1), Ca²⁺ (2.40–4.45 mg L^?1) and Na⁺ (2.65–3.36 mg L^?1). The highest values of ammonium and DOC found in the lowest Myrktjørna Lake seem to be related to the presence of aquatic organisms and also birds. From the group of 10 analyzed microelements, increased concentrations of aluminum, up to almost 500 μg L^?1, are present in the lakes’ water. Water isotopic composition ranges for δ¹⁸O and δ²H, from ?10.6 to ?10.9‰ and from ?70.8 to ?72.3‰, respectively. The vertical zonality of lake waters is manifested in a decrease in the temperature and increase in EC and chemical elements concentrations.