[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.
The Scientific World Journal 01/2014; 2014:930879. · 1.73 Impact Factor
[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: 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.
Chemical Engineering Communications 01/2012; 199(7):849-864. · 1.05 Impact Factor
[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%.
[Show abstract][Hide abstract] ABSTRACT: Mechanism and performances of arsenic(III) [As(III)] and arsenic(V) [As(V)] sorption onto hydrated iron(III) oxide (HFO)-coated materials were investigated at neutral pH where arsenic occurs in both molecular and ionic forms. Arsenic sorption by HFO-coated materials was proven to be a multistage process consisting of both macropore and intraparticle diffusion. Higher mass-transfer velocities were obtained for As(III), which is attributed to the beneficial features of HFO. Equilibrium studies revealed the spontaneous and favorable nature of the arsenic sorption process. The maximum sorption capacity and the Gibbs free energy values indicated that HFO-coated materials exhibit more affinity towards As(III). The Langmuir and Freundlich isotherm models revealed both the chemical and physical nature of the sorption process, while the Dubinin-Radushkevich model indicated that physical sorption is a more dominant process with HFO-coated materials.
Water Environment Research 06/2011; 83(6):498-506. · 1.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A more effective chemical control in the water-steam cycle (WSC) of thermal power plants (TPP) is proposed in this paper. Minimization of corrosion effects by the production of ultra pure water and its strict control is the basis of all the investigated processes. The research involved the analysis of water samples in the WSC through key water quality parameters and by the most convenient analytical tools. The necessity for the stricter chemical control is demonstrated through a concrete example of the TPP Nikola Tesla, Serbia. After a thorough analysis of the chemical control system of the WSC, diagnostic and control parameters were chosen for continuous systematic measurements. Sodium and chloride ions were recognized as the ions which indicate the corrosion potential of the water and give insight into the proper production and maintenance of water within the WSC. Chemical transformations of crucial corrosion elements, iron and silica, were considered and related to their quantitative values.
[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.
Resources Conservation and Recycling 01/2011; 55(12):1139-1145. · 2.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, the performance and the efficiency of physico-chemical effluent treatment in a paper mill was investigated, with the aim of evaluating the treatment rationality and running stability. The effluent treatment plant (ETP) uses alum as a coagulant and polyacrylamide as a flocculant in multi-stage water purification. Inadequate efficiency and some operational problems were observed and their occurrences were investigated. Several simple measures inside the mill and some technical measures can prevent or postpone expensive end-of-pipe treatment investments, such as biological treatment. Chemically enhanced primary treatment under optimal operating conditions can be a stand-alone technique for achieving high quality effluent. Furthermore, reductions in wastewater generation in combination with fiber and filler recovery provide environmental benefits as well as significant economic savings in production. The advantages of the cleaner production approach in existing treatment units compared to expensive biological end-of-pipe technologies are obvious. This study demonstrated that the examined mill could easily and cost-effectively change its water system toward strict discharge limits by continuing to use the existing treatment units.
Journal of Cleaner Production 01/2011; 19:764-774. · 3.59 Impact Factor
[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.
[Show abstract][Hide abstract] ABSTRACT: A simple method for the separation and determination of inorganic arsenic (iAs) species in natural and drinking water was developed. Procedures for sample preparation, separation of As(III) and As(V) species and preconcentration of the total iAs on fixed bed columns were defined. Two resins, a strong base anion exchange (SBAE) resin and a hybrid (HY) resin were utilized. The inductively-coupled plasma-mass spectrometry method was applied as the analytical method for the determination of the arsenic concentration in water. The governing factors for the ion exchange/sorption of arsenic on resins in a batch and a fixed bed flow system were analyzed and compared. Acidity of the water, which plays an important role in the control of the ionic or molecular forms of arsenic species, was beneficial for the separation; by adjusting the pH values to less than 8.00, the SBAE resin separated As(V) from As(III) in water by retaining As(V) and allowing As(III) to pass through. The sorption activity of the hydrated iron oxide particles integrated into the HY resin was beneficial for bonding of all iAs species over a wide range of pH values from 5.00 to 11.00. The resin capacities were calculated according to the breakthrough points in a fixed bed flow system. At pH 7.50, the SBAE resin bound more than 370 microg g(-1) of As(V) while the HY resin bound more than 4150 microg g(-1) of As(III) and more than 3500 microg g(-1) of As(V). The high capacities and selectivity of the resins were considered as advantageous for the development and application of two procedures, one for the separation and determination of As(III) (with SBAE) and the other for the preconcentration and determination of the total arsenic (with HY resin). Methods were established through basic analytical procedures (with external standards, certified reference materials and the standard addition method) and by the parallel analysis of some samples using the atomic absorption spectrometry-hydride generation technique. The analytical properties of both procedures were similar: the limit of detection was 0.24 microg L(-1), the limit of quantification was 0.80 microg L(-1) and the relative standard deviations for samples with a content of arsenic from 10.00 to 300.0 microg L(-1) ranged from 1.1 to 5.8%. The interference effects of anions commonly found in water and some organic species which can be present in water were found to be negligible. Verification with certified reference materials proved that the experimental concentrations found for model solutions and real samples were in agreement with the certified values.
[Show abstract][Hide abstract] ABSTRACT: The surface morphology of gold electrodes on piezoelectric quartz crystals was characterized by scanning electron microscopy and scanning tunnelling microscopy. Sensors with various coating materials as polymers, liquid crystal and nitrocompounds have been employed to demonstrate the importance of surface properties in determining the response of the device. The sensors were evaluated for detection of organophosphorus and nitroaromatic vapours in air.
[Show abstract][Hide abstract] ABSTRACT: The potential ability of a bulk acoustic wave device oscillating in a thickness shear mode (BAWTSM) chemically modified with various compounds (4-amino-antipyrine, poly(vinyl pyrrolidone), Carbowax-20M, Triton X-100) for selective binding and assay of phenol compounds in the vapour phase has been investigated. The sensor was tested in a continuous flow system. The highest sensitivity was achieved with 4-amino-antipyrine as coating. It was estimated that the maximal frequency response was about 100 Hz for 20 μg of coating and for a phenol concentration of 0.05 mg dm−3 in air. The frequency response of the sensor to various phenol derivatives was correlated with adsorption and absorption during a dissolution process onto the surface of the coating sensor.
[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.
Central European Journal of Chemistry 11(9). · 1.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Inorganic arsenic removal from water using low-cost adsorbents is presented in this paper. Selective removal of As(III) and As(V) from water was performed with natural materials (zeolite, bentonite, sepiolite, pyrolusite and limonite) and industrial by-products (waste filter sand as a water treatment residual and blast furnace slag from steel production); all inexpensive and locally available. Kinetic and equilibrium studies were realized using batch system techniques under conditions that are likely to occur in real water treatment systems. The natural zeo-lite and the industrial by-products were found to be good and inexpensive sorbents for arsenic while bentonite and sepiolite clays showed little affinity towards arsenic. The highest maximum sorption capacities were obtained for natural zeolite, 4.07 mg As(V) g -1 , and waste iron slag, 4.04 mg As(V) g -1 .