[Show abstract][Hide abstract] ABSTRACT: This study is focused on the surface modifications of the materials that are used for antimicrobial water treatment. Sorbents of different origin were activated by Ag+-ions. The selection of the most appropriate materials and the most effective activation agents was done according to the results of the sorption and desorption kinetic studies. Sorption capacities of selected sorbents: granulated activated carbon (GAC), zeolite (Z), and titanium dioxide (T), activated by Ag+-ions were following: 42.06, 13.51 and 17.53 mg/g, respectively. The antimicrobial activity of Ag/Z, Ag/GAC and Ag/T sorbents were tested against Gram-negative bacteria E. coli, Gram-positive bacteria S. aureus and yeast C. albicans. After 15 min of exposure period, the highest cell removal was obtained using Ag/Z against S. aureus and E. coli, 98.8 and 93.5%, respectively. Yeast cell inactivation was unsatisfactory for all three activated sorbents. The antimicrobial pathway of the activated sorbents has been examined by two separate tests – Ag+-ions desorbed from the activated surface to the aqueous phase and microbial cell removal caused by the Ag+-ions from the solid phase (activated surface sites). The results indicated that disinfection process significantly depended on the microbial-activated sites interactions on the modified surface. The chemical state of the activating agent had crucial impact to the inhibition rate. The characterization of the native and modified sorbents was performed by X-ray diffraction technique, X-ray photoelectron spectroscopy and scanning electron microscope. The concentration of adsorbed and released ions was determined by inductively coupled plasma optical emission spectroscopy and mass spectrometry. The antimicrobial efficiency of activated sorbents was related not only to the concentration of the activating agent, but moreover on the surface characteristics of the material, which affects the distribution and the accessibility of the activating agent.
[Show abstract][Hide abstract] ABSTRACT: Determination of total halogens in coal was investigated with oxygen bomb combustion followed by ion chromatography. Experimental parameters were optimized by fractional factorial design and response surface methodology. Fractional factorial design was employed in screening experiments to evaluate the influence of the oxygen pressure, catalyst, absorption solution, reduction reagent, bomb cooling time, and a combustion aid on the combustion of coal in an oxygen bomb. Response surface methodology was conducted to further refine the results obtained by fractional factorial design and to define parameters for the procedure. The accuracy and precision of combustion with ion chromatography were evaluated by the use of two certified reference materials and by fortified in-house coal standards. The limits of detection and quantification for total halogens were 0.84 and 2.80 milligrams per kilogram, respectively, for 500 milligram samples. Ion chromatography provided relative standard deviations less than 4 percent, recoveries exceeding 95 percent, and was convenient. This method is recommended for routine determination of total halogens in coal because of its reliability.
Full-text · Article · Jun 2015 · Analytical Letters
[Show abstract][Hide abstract] ABSTRACT: Natural minerals, such as quartz, clinoptilolite and calcite, are useful as sorbents for various applications, but their content of heavy metals ions is the most problematic obstacle to their application. Before their (re)use, the minerals must be purified. In this work, the subject was desorption of lead from a natural multi-component mineral sample consisting of a mixture of silicates (mainly quartz and clinoptilolite) and calcite formations. Besides deionized water, different extraction solutions were tested: NaCl, KCl, CaCl2, MgCl2, HCl, HNO3, EDTA, EDTA/HCl, EDTA/NaOAc–HOAc, HOAc, NaOAc and NaOAc–HOAc. Several parameters were varied in order to obtain the optimal conditions for the desorption process: the concentration of the extraction solution, the ratio of the mass of the sample and volume of the extractant, and the pH value of the suspension. The best purification effect in one desorption cycle was obtained when 0.1 M EDTA, at a pH value of 3.5 (0.2 M EDTA was mixed with 0.01 M acetic buffer, at pH value 3.0, in ratio 1:1) was applied. Sequential extraction (5 consecutive iterations) was performed to provide a more efficient purification process. The lead content (58.20 mg/kg) was decreased by: 20% (using HOAc), 21% (using EDTA) and by more than 50% (using EDTA/NaOAc–HOAc). The pH value and conductivity were measured at all critical points to clarify the mechanism of the desorption process. The formation of Pb–EDTA complex is the result of two parallel phenomena, complexing and ion-exchange. An enhanced adsorption capacity and an improved microelement profile for the purified samples were also attained. The mineralogical and radiochemical performances of the sample were determined by the X-ray diffraction and gamma spectrometry techniques. Microelement analyses of the native and purified samples were performed by inductively coupled plasma optical emission spectroscopy (ICP-OES).
Full-text · Article · Oct 2014 · Applied Surface Science
[Show abstract][Hide abstract] ABSTRACT: Analysis and monitoring of arsenic is still a challenging analytical task. Due to its complex behaviour (different forms of arsenic that can be present depending on pH and oxidation states of arsenic) as well as demanding analytical procedures and instrumental tools for control of arsenic concentration in drinking water which is set to 10 mu g L-1, there are still some open questions and issues when arsenic is the scientific topic. In this paper the idea was to use a multivariate statistical approach to identify the key variables and their relation to high arsenic concentration in surface waters of Serbia. The main idea was to identify and connect the key water quality parameters with arsenic concentration and to suggest adequate treatment technologies for water purification and arsenic removal. The data set for multivariate statistical approach were water quality parameters of surface water samples from Serbia. The artificial neural network (ANN) was applied for data analysis. After applying ANN the results showed strong relation between arsenic concentration and P-tot, SO42-, COD, carbonate, N-org, DO, and SiO2 content. What could be concluded from the obtained results is that high concentration of organic matter, proportional to nutrients (nitrogen and phosphorus), silica (SiO2) and dissolved oxygen highly correlates with the dissolved arsenic which implies that the most adequate technology for the water treatment could be precipitation, which in general includes coagulation. What remains unquestioned and needs to be performed is arsenic speciation analysis.
[Show abstract][Hide abstract] ABSTRACT: Micro-electro-mechanical systems (MEMS) are miniaturized devices that can sense the environment, process and analyze information, and respond with a variety of mechanical and electrical actuators. MEMS consist of mechanical elements, sensors, actuators, electrical and electronics devices on a common silicon substrate. Micro-electro-mechanical systems are becoming a vital technology for modern society. Some of the advantages of MEMS devices.are: very small size, very low power consumption, low cost, easy to integrate into systems or modify, small thermal constant, high resistance to vibration, shock and radiation, batch fabricated in large arrays, improved thermal expansion tolerance. MEMS technology is increasingly penetrating into our lives and improving quality of life, similar to what we experienced in the microelectronics revolution. Commercial opportunities for MEMS are rapidly growing in broad application areas, including biomedical, telecommunication, security, entertainment, aerospace, and more in both the consumer and industrial sectors on a global scale. As a breakthrough technology, MEMS is building synergy between previously unrelated fields such as biology and microelectronics. Many new MEMS and nanotechnology applications will emerge, expanding beyond that which is currently identified or known. MEMS are definitely technology for 21st century.
[Show abstract][Hide abstract] ABSTRACT: Numerous regression approaches to isotherm parameters estimation appear in the literature. The real insight into the proper modeling pattern can be achieved only by testing methods on a very big number of cases. Experimentally, it cannot be done in a reasonable time, so the Monte Carlo simulation method was applied. The objective of this paper is to introduce and compare numerical approaches that involve different levels of knowledge about the noise structure of the analytical method used for initial and equilibrium concentration determination. Six levels of homoscedastic noise and five types of heteroscedastic noise precision models were considered. Performance of the methods was statistically evaluated based on median percentage error and mean absolute relative error in parameter estimates. The present study showed a clear distinction between two cases. When equilibrium experiments are performed only once, for the homoscedastic case, the winning error function is ordinary least squares, while for the case of heteroscedastic noise the use of orthogonal distance regression or Margart's percent standard deviation is suggested. It was found that in case when experiments are repeated three times the simple method of weighted least squares performed as well as more complicated orthogonal distance regression method.
Full-text · Article · Jan 2014 · The Scientific World Journal
[Show abstract][Hide abstract] ABSTRACT: The sorption of inorganic arsenic species, As(III) and As(V), from water by sepiolite modified with hydrated iron(III) oxide was investigated at 25 degrees C through batch studies. The influence of the initial pH value, the initial As concentration, the contact time and the type of water on the sorption capacity was investigated. Two types of water were used, deionised and groundwater. The maximal sorption capacity for As(III) dissolved in deionised water was observed at an initial and final pH value 7.0, while the bonding of As(V) was observed to be almost pH independent for pH value in the range from 2.0 to 7.0, while a significant decrease in the sorption capacity was observed at pH values above 7.0. The sorption capacity at initial pH 7.0 was about 10 mg g(-1) for As(III) and 4.2 mg g(-1) for As(V) in deionised water. The capacity in groundwater was decreased by 40 % for As(III) and by 20 % for As(V). The Langmuir model and pseudo-second order kinetic model revealed good agreement with the experimental results. The results showed that Fe(III)-modified sepiolite exhibits significant affinity for arsenic removal and it has the potential for application in water purification processes.
Full-text · Article · Jan 2014 · Journal of the Serbian Chemical Society
[Show abstract][Hide abstract] ABSTRACT: In this study, removal of arsenic ions using two industrial by-products as adsorbents is represented. Removal of As(III) and As(V) from water was carried out with industrial by-products: residual from the groundwater treatment process, iron-manganese oxide coated sand (IMOCS), and blast furnace slag from steel production (BFS), both inexpensive and locally available. In addition, the BFS was modified in order to minimise its deteriorating impact on the initial water quality. Kinetic and equilibrium studies were carried out using batch and fixed-bed column adsorption techniques under the conditions that are likely to occur in real water treatment systems. To evaluate the application for real groundwater treatment, the capacities of the selected materials were further compared to those exhibited by commercial sorbents, which were examined under the same experimental conditions. IMOCS was found to be a good and inexpensive sorbent for arsenic, while BFS and modified slag showed the highest affinity towards arsenic. All examined waste materials exhibited better sorption performances for As(V). The maximum sorption capacity in the batch reactor was obtained for blast furnace slag, 4040 μgAs(V)/g.
[Show abstract][Hide abstract] ABSTRACT: In this study, a multivariate statistical approach was used to identify the key variables responsible for process water quality in a power plant. The ion species that could cause corrosion in one of the major thermal power plants (TPP) in Serbia were monitored. A suppressed ion chromatographic (IC) method for the determination of the target anions and cations at trace levels was applied. In addition, some metals important for corrosion, i.e., copper and iron, were also analysed by the graphite furnace atomic absorption spectrophotometric (GFAAS) method. The control parameters, i.e., pH, dissolved oxygen and silica, were measured on-line. The analysis of a series of representative samples from the TPP Nikola Tesla, collected in different plant operation modes, was performed. Every day laboratory and on-line analysis provides a large number of data in relation to the quality of water in the water-steam cycle (WSC) which should be evaluated and processed. The goal of this investigation was to apply multivariate statistical techniques and choose the most applicable technique for this case. Factor analysis (FA), especially principal component analysis (PCA) and cluster analysis (CA) were investigated. These methods were applied for the evaluation of the spatial/temporal variations of process water and for the estimation of 13 quality parameters which were monitored at 11 locations in the WSC in different working conditions during a twelve month period. It was concluded that PCA was the most useful method for identifying functional relations between the elements. After data reduction, four main factors controlling the variability were identified. Hierarchical cluster analysis (HCA) was applied for sample differentiation according to the sample location and working mode of the TPP. On the basis of this research, the new design of an optimal monitoring strategy for future analysis was proposed with a reduced number of measured parameters and with reduced frequency of their measurements.
Full-text · Article · Sep 2013 · Central European Journal of Chemistry
[Show abstract][Hide abstract] ABSTRACT: The aim of this study is to investigate the possibilities of removing lead, cadmium, and zinc from air by sorption with natural wool fibers (NWF), thus evaluating the possible application of wool materials in direct protection of air from the influence of heavy metals. Metal detection was performed (before and after the sorption process) by potentiometric stripping analysis. Sorption experiments were done in two ways: by immersing NWF in model solutions (prepared by the working standard solutions and deionized water), and by immersing NWF in solutions of sediments from the air. The influence of mass sorbent, sorption time, pH, and temperature on the sorption of lead, cadmium, and zinc were experimentally examined. Effectiveness of lead, cadmium, and zinc sorption by applying natural wool fibers is shown as the sorption capacity (a ratio between metal concentration before and after sorption and sorbent mass). Sorbent of 0.1 g NWF mass in neutral environment collected: after 10 min 23.9% of lead, 19.0% of cadmium, and 21.3% of zinc, whereas after 30 min 71.5% of lead, 69.6% of cadmium, and 69.4% of zinc was collected. NWF of the same mass in acidic environment showed lower sorption capabilities. For pH 4.5 the effective sorption was: 68.6% of lead, 66.8% of cadmium, and 66.6% of zinc; whereas for pH 2.1 NWF sorption is 54.6% of lead, 53.2% of cadmium, and 52.9% of zinc. The optimal pH range for application of this sorption during the experiment material was 4.5-7.0. The sorption was made in solutions with pH 2.1 due to potentiometric stripping analysis application conditions. Temperature significantly impacted the tested material sorption characteristics. When the temperature slightly increased, regardless of the inflicted damage, NWF kept its functionality. When the temperature was higher than 60 degrees C, the sorbent effectiveness was reduced. The NWF sorption capacity was lowest at 100 degrees C: 11.63 mu g g(-1) for lead, 8.18 mu g g(-1) for cadmium, and 9.41 mu g g(-1) for zinc. The results of the experimental research have shown that a high degree of removal (about 70%) can be achieved provided that the mass of the sorbent rages from 0.06-0.1 g, contact time is long enough (30 min), and that there are no significant effects of temperature and pH.
Preview · Article · Mar 2013 · Hemijska industrija
[Show abstract][Hide abstract] ABSTRACT: Arsenic exists in the form of various chemical species differing in their physicochemical behaviour, toxicity, bioavailability and biotransformation. The determination of arsenic species is an important issue for environmental, clinical and food chemistry. However, differentiation of these species is a quite complex analytical task. Numerous speciation procedures have been studied that include electrochemical, chromatographic, spectrometric and hyphenated techniques. This review presents the relevant research in the field of arsenic speciation analysis with novel applications and significant advances. Stability of arsenic species and each of the analytical steps (sample collection, storage, preservation, extraction) of the arsenic speciation methods is particularly evaluated. Analytical validation and performance of these Methods are also reviewed.
Full-text · Article · Jan 2013 · Journal of the Serbian Chemical Society
[Show abstract][Hide abstract] ABSTRACT: The analytical properties of an analytical method must be evaluated through validation protocols. Beside specificity and/or selectivity, linearity of calibration, repeatability and accuracy, the most important parameters are: LOD (limit of detection) and LOQ (limit of quantification). Through these limits, it is possible to define the smallest concentration of analyte that can be reliably detected and quantified. To establish these limits, an analyst should apply several estimation methods and test a large number of sample replicates. It is difficult to make a compromise between complex statistical programs and the simple analytical demand to have reliable analytical parameters. The differences and equivalency of estimation methods and approaches for analytical limits could be overcome by an experimental comparison. In this paper, the focus is the LOD of inductively coupled plasma-mass spectrometry (ICP-MS) measurements employed for the determination of arsenic. The current approaches for the calculation of the LOD are summarized and critically discussed.
[Show abstract][Hide abstract] ABSTRACT: In this study, acid heat–activated neutralized red mud (AB) was promoted as an efficient sorbent for the removal of inorganic arsenic from water. Three sorbents: neutralized red mud (Bauxsol), acid-treated Bauxsol (aBauxsol), and AB were investigated for arsenic removal. The sorption of arsenic on these adsorbents was studied as a function of contact time, initial arsenic concentration, and adsorbent dosage. The Langmuir isotherm was the best-fit adsorption isotherm model for the experimental data. The adsorption capacity of the activated red mud for As(V) was found to be 1.49 mg g at a pH of water of 7.0. It was observed that AB at a dose of 6.0 g L could effectively remove As(III) and As(V) from water. Anion interference on a molar basis was found to follow the order: phosphate interference was higher than sulfate interference, which was higher than bicarbonate interference.
Full-text · Article · Jul 2012 · Chemical Engineering Communications
[Show abstract][Hide abstract] ABSTRACT: A simple and efficient method for the separation and determination of dimethylarsenate DMAs(V) was developed in this work. Two resins, a strong base anion exchange (SBAE) resin and iron-oxide coated hybrid (HY) resin were tested. By simple adjustment of the pH value of water to 7.00, DMAs(V) passed through the HY column without any changes, while all other arsenic species (inorganic arsenic and monomethylarsonate, MMAs(V)) were quantitatively bonded on the HY resin. The resin capacity was calculated according to the breakthrough point in a fixed bed flow system. At pH 7.00, the HY resin bonded more than 4150 mu g g(-1) of As(III), 3500 mu g g(-1) of As(V) and 1500 mu g g(-1) of MMAs(V). Arsenic adsorption behavior in the presence of impurities showed tolerance with the respect to potential interference of anions commonly found in natural water. DMAs(V) was determined in the effluent by inductively coupled plasma mass spectrometry (ICP-MS). The detection limit was 0.03 mu g L-1 and the relative standard deviation (RSD) was between 1.1-7.5 %. The proposed method was established by application of standard procedures, i.e., using an external standard, certified reference material and by the standard addition method.
Preview · Article · Jan 2012 · Journal of the Serbian Chemical Society
[Show abstract][Hide abstract] ABSTRACT: A simple and efficient method for separation and determination of inorganic arsenic (iAs) and organic arsenic (oAs) in drinking, natural and wastewater was developed. If arsenic is present in water prevailing forms are inorganic acids of As(III) and As(V). oAs can be found in traces as monomethylarsenic acid, MMA(V), and dimethylarsenic acid, DMAs(V). Three types of resins: a strong base anion exchange (SBAE) and two hybrid (HY) resins: HY-Fe and HY-AgCl, based on the activity of hydrated iron oxides and a silver chloride were investigated. It was found that the sorption processes (ion exchange, adsorption and chemisorptions) of arsenic species on SBAE (ion exchange) and HY resins depend on pH values of water. The quantitative separation of molecular and ionic forms of iAs and oAs was achieved by SBAE and pH adjustment, the molecular form of As(III) that exists in the water at pH <8.0 was not bonded with SBAE, which was convenient for direct determination of As(III) concentration in the effluent. HY-Fe resin retained all arsenic species except DMAs(V), which makes possible direct measurements of this specie in the effluent. HY-AgCl resin retained all iAs which was convenient for direct determination of oAs species concentration in the effluent. The selective bonding of arsenic species on three types of resins makes possible the development of the procedure for measuring and calculation of all arsenic species in water. In order to determine capacity of resins the preliminary investigations were performed in batch system and fixed bed flow system. Resin capacities were calculated according to breakthrough points in a fixed bed flow system which is the first step in designing of solid phase extraction (SPE) module for arsenic speciation separation and determination. Arsenic adsorption behavior in the presence of impurities showed tolerance with the respect to potential interference of anionic compounds commonly found in natural water. Proposed method was established performing standard procedures: with external standard, certified reference material and standard addition method. Two analytical techniques: the inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectroscopy-hydride generation (AAS-GH) were comparatively applied for the determination of arsenic in all arsenic species in water. ICP-MS detection limit was 0.2 μg L(-1) and relative standard deviation (RSD) of all arsenic species investigated was between 3.5 and 5.1%.
Full-text · Article · Nov 2011 · Analytica chimica acta
[Show abstract][Hide abstract] ABSTRACT: This paper analyses the utilization of water and recycled fiber from waste paper for the production in one Serbian cardboard mill. Water and fiber consumption, wastewater generation and its characteristics, as well as sludge recirculation were monitored during production of various paper types, with different grade and weight. The aim was to evaluate production rationality and running stability concerning water and fiber utilization and possibilities for their conservation. Cleaner production measures inside the mill and in the effluent treatment plant were suggested for the improvement of wastewater quality and water conservation. Savings in water and fibers were estimated, with the respect to economic and environmental aspects of proposed cleaner production measures.
Full-text · Article · Oct 2011 · Resources Conservation and Recycling
[Show abstract][Hide abstract] ABSTRACT: The coastal area surrounding the lbar river in the North of Kosovo and Metohija, in the region from Kosovska Mitrovica to Leposavic alone, is occupied with seven industrial waste dumps originated from the exploitation and flotation refinement of mineral raw materials, metallurgic refinement of concentrates, chemical industry, industrial refinement and energetic facilities of Trepca. The existing waste dumps, active and passive, are of heterogenic chemical composition. They show its impact onto the river water by the content of heavy metals found in it. Removal of lead, cadmium and zinc, regardless to the any known technology, would be economically unrewarding. The prevailing wooden plant in this area is the white willow. This work is focused on removal of heavy metals (Pb, Cd and Zn) from the water of river lbar using the white willow. Roots of the willow are cultivated using the method of water cultures in individual solution of heavy metals and sample of the river water. The preparation of the samples for analysis was performed by burning the herbal material and dissolving the ash in the appropriate acids. The concentrations of metals were being determined by stripping analysis. In the investigated solutions of heavy metals, the increase of biomass was 25.6% in the lead solution, 27.3% in cadmium and 30.7% in the zinc solution. The increase of biomass in the nutritional solution, without heavy metals, was 32.4% and in sample river water 27.5%. Coefficient of bioaccumulation in solutions with heavy metals was: 1.6% in lead solution, 1.9% in cadmium and 2.2% in zinc solution. Accumulated amounts of the metals from the tested samples were: 18.74 mu g of lead, 20.09 mu g of cadmium and 22.89 mu g of zinc. The coefficient of bioaccumulation of the water samples which contained 44.83 mu g/dm(3) of lead, 29.21 mu g/dm(3) of cadmium and 434.00 mu g/dm(3) of zinc, during 45 days period, was 30.3% for lead, 53.4% for cadmium and 3.9% for zinc. The concentrations of accumulated metals from the river water were 19.01 mu g of lead, 21.85 mu g of cadmium and 23.96 mu g of zinc in grams dry matter. The obtained results indicate that the willow might contribute to the decontamination of moderately contaminated river water from Pb, Cd and Zn.
[Show abstract][Hide abstract] ABSTRACT: In this study, the possibility of monitoring ion species that could cause corrosion processes in the thermal power plant (TPP) using suppressed ion chromatography (SIC) was investigated. An ion chromatography method for the determination of target anions at sub-to-low-μg/L levels in power plant water samples was developed. In this method, the water samples are injected using the large-loop direct injection technique, the analyte anions are separated and detected using the suppressed conductivity detection method. The validation of the analytical method was studied in terms of linearity, sensitivity, precision and accuracy. The method was linear (r > 0.995) over the concentration working range. The detection limits were found to be 0.080, 0.160, 0.180, 0.230 and 0.200 μg/L for F−, Cl−, NO3−, PO43− and SO42−, using Na2CO3/NaHCO3 as the eluent, and 0.077 and 0.082 μg/L for F− and Cl− using NaOH as the eluent, respectively. The relative standard deviations (RSD) of the retention times and peak areas were less than 0.8 and 8%, respectively. The derived data showed that the average recoveries were generally in the range of 60–120%. The performance of the new method was evaluated by analyzing water–steam samples from the thermal power plant “Nikola Tesla”, Serbia.Research highlights► For analysis of anions at trace level high volume suppressed IC method was developed. ► The validation of the IC method was studied in terms of linearity, sensitivity, precision and accuracy. ► The IC method has been successfully evaluated by analyzing water samples from the TPP Nikola Tesla. ► The diagnostic and control parameters were optimized in the water-steam cycle. ► Chloride and sulphate ions were recognized as ions which indicate of corrosion in water steam cycle.