[show abstract][hide abstract] ABSTRACT: The microbiological colonisation of buildings and man-made structures often occurs on the walls of plumbing systems; therefore, monitoring of opportunistic pathogens such as Legionella pneumophila (L. pneumophila), both in water distribution mains and in consumers' plumbing systems, is an important issue according to the international and national guidelines that regulate the quality of drinking water. This paper investigates the presence of L. pneumophila in the Dalmatian County of Croatia and the relationship between L. pneumophila presence and heavy metals concentrations, free residual chlorine and water temperature in hot water distribution systems (WDS). Investigations were performed on a large number of hot water samples taken from taps in kitchens and bathrooms in hotels and homes for the elderly and disabled in the Split region. Of the 127 hot water samples examined, 12 (9.4%) were positive for Legionella spp. with median values concentration of 450 cfu × L(-1) . Among positive isolates, 10 (83.3%) were L. pneumophila sg 1, and two of them (16.6%) belonged to the genera L. pneumophila sg 2-14. The positive correlation between the water temperature, iron and manganese concentrations, and L. pneumophila contamination was proved by statistical analysis of the experimental data. On the contrary, zinc and free residual chlorine had no observed influence on the presence of L. pneumophila. The presence of heavy metals in water samples confirms the corrosion of distribution system pipes and fittings, and suggests that metal plumbing components and associated corrosion products are important factors in the survival and growth of L. pneumophila in WDS.
Annals of agricultural and environmental medicine: AAEM 09/2012; 19(3):431-6. · 3.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: In the present study, the sorption of lead by the natural and Fe(III)-modified zeolite (clinoptilolite) is described. The characterization of the natural zeolite-rich rock and the Fe(III)-modified form was performed by chemical analysis, point of the zero charge (pHpzc), X-ray powder diffraction, applying the Rietveld/RIR method for the quantitative phase analysis, and scanning electron microscopy. The effects of sorbents dose and the initial lead concentrations on its sorption by two sorbents were investigated. For both sorbents, it was determined that at lower initial concentrations of lead, ion exchange of inorganic cations in zeolites with lead, together with uptake of hydrogen dominated, while at higher initial lead concentrations beside these processes, chemisorption of lead occurred. Significantly higher sorption of lead was achieved with Fe(III)-modified zeolite. From sorption isotherms, maximum sorbed amounts of lead, under the applied experimental conditions, were 66 mg/g for the natural and 133 mg/g for Fe(III)-modified zeolite. The best fit of experimental data was achieved with the Freundlich model (R2 ≥ 0.94).Highlights► In this paper sorption of lead by the natural and Fe(III)-modified zeolite was investigated. ► Fe(III)-modified zeolite was synthesized under strongly basic conditions. ► The effects of sorbents dose and the initial lead concentrations on its sorption by two sorbents were studied. ► Much higher sorption of lead was achieved with Fe(III)-modified zeolite (natural zeolite – 66 mg/g; Fe(III)-modified zeolite – 133 mg/g). ► The best fit of experimental data was obtained with Freudlich sorption model.
[show abstract][hide abstract] ABSTRACT: The purpose of this study was to compare the quality of hot water between eleven hotels in the Split-Dalmatia County, Croatia that are open year round and 10 summer season hotels and retirement homes with irregular use of water. We took 122 samples between May and December 2009. Water temperature and free residual chlorine were measured in situ. Physical and chemical analysis included pH, electrical conductivity, and concentrations of iron, manganese, copper, zinc, calcium, and magnesium that were measured using atomic absorption spectrophotometry, while the Legionella species were determined using a cultivation method on buffered charcoal yeast extract agar. Differences in metal concentrations between the seasonal and year-round accommodation facilities were negligible, save for zinc that was higher in year-round (0.341 mg L(-1)) than in seasonal facilities (0.130 mg L(-1)). Samples from all year-round and six summer season hotels were negative to the Legionella species, but four seasonal facilities turned up with positive samples to Legionella pneumophila. Our study has demonstrated that water quality differs between year-round and seasonal accommodation facilities. These findings suggest that metal plumbing components and associated corrosion products are important factors in the survival and growth of Legionella species in water distribution systems.
Archives of Industrial Hygiene and Toxicology 12/2011; 62(4):335-40. · 0.67 Impact Factor
[show abstract][hide abstract] ABSTRACT: The effect of zeolite bed depth on lead removal from aqueous solutions by the column method has been examined. The results indicate that the increase of bed depth delays the breakthrough point and exhaustion point, and increases the contact time of the zeolite – lead solution, and the height of the mass transfer zone, hz. The increase of the bed depth lowers the effect of axial dispersion on the mass transfer process. In order to predict the time necessary for exceeding the defined effluent concentration for a constant bed depth, the bed depth service time (BDST) approach has been used. Experimentally obtained breakthrough curves for the flow rate of 1 ml/min were used to derive the BDST approach equations. These equations were successfully used for modelling of the system for flow rates of 2 and 3 ml/min. The BDST equations have yielded modelled linear equations used for calculation of hz. The increase of the flow rate increases hz, which indicates that the zeolite–solution contact time is not sufficient. This may be attributed to the affect of axial dispersion on mass transfer on the solid-liquid interface.
Separation Science and Technology - SEPAR SCI TECHNOL. 01/2009; 44(13):3113-3127.
[show abstract][hide abstract] ABSTRACT: The column method using a fixed bed of zeolite clinoptilolite was applied to remove lead and zinc ions from binary metal ions solutions. The raw zeolite sample used in this study was obtained from the Vranjska Banja deposit (Serbia) and contained more than 80% of clinoptilolite. The breakthrough curves have an S-shape for the total as well as for the single metal ions in binary solution. Lead and zinc ions bind simultaneously on the zeolite bed, and as the service cycle progresses lead ions displace a great portion of bound zinc. During the regeneration cycle, the quantity of lead desorbed is =15 times higher than the quantity of zinc, which means that mostly lead ions were bound on the zeolite. Breakthrough curves have been interpreted quantitatively by means of the Michaels method, and the results calculated have been compared with the results for single metal ions solutions.
Studies in Surface Science and Catalysis - STUD SURF SCI CATAL. 01/2008; 174:509-512.
[show abstract][hide abstract] ABSTRACT: The removal of lead ions from aqueous solutions by means of a fixed bed of natural zeolite clinoptilolite has been investigated. Isothermal column experiments were performed under a constant inlet concentration and bed depth, and different flow rates. The capacities of the breakthrough and exhaustion points do not change significantly with the increase of the flow rate, while the time needed to reach breakthrough is significantly shorter. To determine the kinetic constants, the equation by Yoon and Nelson was applied to the experimental results. The rate proportionality constant KYN increases and the time τ decreases with the increase of the lead solution flow. Based on these parameters the modelled breakthrough curves have been obtained, and they are in agreement with the corresponding experimental data. The parameters of the Yoon–Nelson model have been successfully used for scaling up the bed depth of the examined system, and a satisfactory agreement of experimental and predicted breakthrough curves has been obtained.
Microporous and Mesoporous Materials - MICROPOROUS MESOPOROUS MAT. 01/2007; 105(3):298-304.
[show abstract][hide abstract] ABSTRACT: The kinetics of zinc and lead ions removal by modified zeolite-clinoptilolite has been investigated. The rate of the ion exchange process for lead ions is faster than for zinc ions, as well as the time needed to reach the equilibrium. The ion exchange capacity of zeolite of lead ions is doubly higher than that of zinc ions. Diffusion models according to the Vermeulen's approximation, the parabolic diffusion model and the homogeneous diffusion model have been tested with the experimental data of ion exchange for zinc and lead. For both systems examined, the best fit of the models proposed with the experimental data was shown by the Vermeulen's approximation and the homogeneous diffusion model with t-->t(infinity). The diffusion coefficients are calculated from kinetic models of lead ions they are of the order of 10(-6)cm(2)/min, constant for all examined initial concentrations and not dependent on time. The diffusion coefficients in the system of zinc ions is of the order of 10(-8)cm(2)/min, also independent of initial concentrations, but decreasing with time from the beginning of ion exchange to the equilibrium.
Journal of Hazardous Materials 09/2006; 136(3):938-45. · 3.93 Impact Factor
[show abstract][hide abstract] ABSTRACT: The kinetics of uptake of zinc ions from aqueous solutions by natural zeolitic tuff has been investigated. Batch experiments at constant temperature and hydrodynamic conditions have been performed. A decrease in the initial zinc concentration in aqueous solutions prolongs the time needed for equilibrium. Various kinetic models including the film-diffusion model, the surface diffusion model and the heterogeneous diffusion model have been tested for the description of the experimental results of zinc concentration in the solution over time. Diffusion through the film and diffusion through the surface of the particle could be the rate limiting steps at the initial reaction time. However, the heterogeneous diffusion model seems to be the best model providing a satisfactory fitting of the experimental results from the beginning of the process to the point of equilibrium, particularly at lower initial zinc concentrations.
Journal of Environmental Management 06/2006; 79(3):298-304. · 3.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: The aim of this investigation is removal of lead ions from aqueous solutions using the column method with more successive service and regeneration cycles. The experiments were performed at constant temperature and dimensions of column and fixed bed of zeolite, with variation of zeolite particle sizes and flows through the bed, concentrations of lead solutions and the regenerate. Eight service and regeneration cycles were performed without changes of the breakthrough and exhaustion capacity. The highest effectiveness of the column performance has been attained for the zeolite particle size of 0.6–0.8 mm, at the initial concentration of 212.5 mg Pb/L and the flow rate of 2 mL/min. At these experimental conditions, the optimal values of the empty bed contact time and high of the mass transfer zone have been achieved.
[show abstract][hide abstract] ABSTRACT: An uptake of zinc (Zn), copper (Cu), and lead (Pb) from aqueous solutions by ion exchange on natural zeolitic tuff has been studied. The Croatian zeolite clinoptilolite from the Donje Jesenje deposit has been used as a natural ion exchanger. The efficiency of removal is higher for Pb and Cu than for Zn ions. Measured concentrations of Si in the liquid phase identify the detachment of the aluminosilicate structure during ion exchange in the presence of H(+) and OH(-) ions. The adsorption isotherm equations; Langmuir-Freundlich, Redlich-Petersen, Toth, Dubinin-Radushkevich, modified Dubinin-Radushkevich, and Lineweawer-Burk were derived from the basic empirical equations, and used for calculation of ion exchange parameters. The best fitting of experimental results to the proposed isotherms was observed in models that assume that ionic species bind first at energetically most favorable sites, with multi-layer adsorption taking place subsequently.
Water Research 05/2004; 38(7):1893-9. · 4.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: The possibility of removing Zn2+ cations from wastewater by ion exchange using natural zeolites as exchangers has been investigated. The process of binding of zinc ions into zeolite structure has been established by several reaction mechanisms as a fast chemical reaction of ion exchange, accompanied by slower adsorption of different ionic species and possible precipitation or coprecipitation with the zeolite structure. The physicochemical phenomena such as hydrolysis and dissolution of surface layers are the result of interaction of zeolite with hydrogen or hydroxyl ions from the solution. Complexation of OH- with Zn2+ to form the zinc-hydroxy species strongly depends on pH value and affect the uptake mechanism as to lower dissolution of surface aluminosilicate layers. Structure imperfections as a surface property of mineralogical nonhomogeneous zeolitic grains can lead to formation of sorption surface sites with different energy, which affects the nonuniform distribution of different zinc species adsorbed. It is particularly possible in zeolitic tuff samples with relatively high content of aluminosilicates as minor mineralogical components, which is characteristic of Croatian deposits.
Journal of Colloid and Interface Science 05/2003; 260(1):166-75. · 3.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: The influence of calcium nitrate on the process of carbon dioxide absorption in aqueous monoethanolamine (MEA) solution has been considered. The experimental data obtained under typical conditions used for the industrial precipitation of calcium carbonate has been used to determine the speciation in solution and the supersaturation profile in the bulk liquid by means of a specially developed algorithm as well as the kinetic regime of the absorption process in a pure aqueous solution and in the presence of calcium species at 30 °C using equilibrium and kinetic data from the literature. As expected, in pure MEA solution carbon dioxide reacts with MEA yielding ethanolammonium carbamate, whereas in the presence of calcium nitrate the process shifts towards CaCO30 ion pair formation, resulting in a continuous increase of the supersaturation generated during the “induction period” of calcium carbonate precipitation. The proposed reaction mechanism is supported also by the precipitate morphology determined by SEM analysis.
[show abstract][hide abstract] ABSTRACT: Calcium carbonate was precipitated by carbonation of calcium nitrate and monoethanolamine solution. The influence of various organic admixtures on the crystallization, crystal morphology, and polymorphism of calcium carbonate has been studied using different techniques. Our results show that sucrose and fructose present even at very high concentrations do not affect the duration or mechanism of the carbonation process at a higher degree, what is attributed to the specific quality of the ethanolamine process. At high concentration citric acid and ethylenediamine-tetrakis-N,N,N,N-(methylenephosphonic acid) had some effect on the process mechanism, phase composition, morphology and crystal aggregation of the calcium carbonate precipitated.
[show abstract][hide abstract] ABSTRACT: Hydrolysis of a natural zeolite and of the same zeolite converted into its Na+ form by conditioning with 2M NaCl, has been carried out with high purity ion-free water by means of the batch method. The process of hydrolysis was monitored by continuous measurements of changes in pH values and in electrical conductivity in the zeolite-water suspension. The results obtained for the hydronium ion exchange have been analysed kinetically according to the heterogeneous diffusion model and the first-order rate model.
Studies in surface science and catalysis 01/1999; 125:761-767.
[show abstract][hide abstract] ABSTRACT: Morphological development in calcium carbonate precipitation by the ethanolamine process at 30 and 60°C has been examined using different techniques (quantitative image analysis, laser diffraction, XRD, and FT-IR). The initially grown phase is of vaterite modification that at higher temperatures (60°C) transforms to a more stable aragonite phase within the reactor itself. A comparison of the form and structure of calcium carbonate particles obtained during the process leads to a conclusion that crystal aggregation is the mechanism that determines the overall particle size at lower temperatures (30°C), while crystal growth dominates at higher temperatures. The results show that crystal characterization by quantitative image analysis permits a better understanding of the phenomena taking place in the reactor.
[show abstract][hide abstract] ABSTRACT: Extra-pure calcium carbonate was obtained in the laboratory by carbonation of a solution of calcium nitrate and monoethanolamine with carbon(IV) oxide under various operating conditions. The particle size and shape of the samples obtained were characterized by image analysis. The results show that the method of quantitative morphological characterization using defined shape descriptors enables us to get a better insight into the relationship of the mineralogical composition and particle size/shape to precipitation conditions.
[show abstract][hide abstract] ABSTRACT: High-purity precipitated calcium carbonate has been produced in the laboratory by carbonation of a solution of calcium nitrate and monoethanolamine. The process was traced by measurements of the change in Ca concentration and in electrical conductivity of the solution. The κ−t and cCu−t curves were analyzed to determine the effect of temperature and concentration of carbon(IV) oxide on the process of carbonation. The samples obtained were mainly of aragonite and vaterite crystal modifications with traces of calcite. The relationship between the mineralogical composition and particle size (morphology) and operating conditions was examined as well.
[show abstract][hide abstract] ABSTRACT: The phase composition of mineral aragonite and synthetic vaterite samples was determined qualititavely by using IR-spectrophotometric and X-ray diffraction analyses. The transformation of aragonite, A, and vaterite, V, into the stable modification calcite, C, was followed using differential scanning calorimetry analysis. In order to determine the kinetics and mechanisms of these phase transformations, a number of experimental DSC curves were elaborated mathematically and the stationary point theory was applied. The activation energy, Ea, and the enthalpy, ΔH, were found to be, respectively, 234.5 ± 5.6 kJ mol−1 and 122 Jg−1 for the phase transformation A → C, and 252.8 ± 48.7 kJ mol−1 and −21.2 Jg−1 for the V → C transformation.
[show abstract][hide abstract] ABSTRACT: The dehydroxylation of gibbsite into boehmite was investigated by means of DSC analysis under non-isothermal conditions in the temperature range 453–673 K at heating rates from 2.5 to 20.0 K min−1. Mathematical analysis of the experimental DSC curves revealed the mechanism and kinetics of the gibbsite dehydroxylation process. The kinetic curvesα=f(t) andα=f(T) are sigmoidal in shape; their inflection points and the νm point of the curvesν=f(T) andν=f(T) are interrelated and are defined by the concept of a stationary point. The activation energy for the first stage of gibbsite dehydroxylation in the temperature range 453–673 K is 132.92±8.33–142.26±8.33 kJ mol−1.
Journal of Thermal Analysis 01/1996; 46(5):1339-1347.