Browsing by Author "Koumanova B."
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Item Adsorptive removal of carbamazepine from wastewaters by activated charcoals(2013-11-05) Stoykova M.; Koumanova B.; Mörl L.The capacity of activated charcoals for the adsorption of Carbamazepine, an antiepileptic drug, from aqueous solutions was studied. The charcoals were activated with water steam at different temperatures prior to adsorption experiments. Langmuir and Freundlich models were used for the description of the adsorption equilibrium of Carbamazepine on different activated beech-charcoals. The uptake of the adsorbents was directly proportional to their specific surface area. The adsorbents, activated at higher temperatures (480-740°C; 360-630°C and 650-700°C) had a higher adsorption capacity for Carbamazepine (14,49 mg g-1; 13,97 mg g-1 and 11,81 mg g-1, respectively) than those activated at lower temperatures (220-655°C and 7,45 mg g-1; 185-450°C and 4,46 mg g-1, respectively). All adsorbents showed quick and full adsorption at the lower concentration range.Item Anaerobic co-digestion of wasted vegetables and activated sludge(2009-01-01) Saev M.; Koumanova B.; Simeonov I.Anaerobic co-digestion of activated sludge (AS) and wasted vegetables (wasted cucumbers (WC) and wasted tomatoes (WT)) was carried out at mesophilic conditions (34 ± 0.5°C). A continuously stirred bioreactor with volume of 5 dm3 (3 dm3 working volume) was used. The digestion was examined in semi-continuous mode and 30 days hydraulic retention time. Total solids, volatile solids, COD and volatile fatty acids (VFA) were determined according to the standard methods. Daily the total biogas production as well as CH4 and CO2 content were determined using a graduated gasholder and an infrared sensor, respectively. pH was measured with Seibold pH-meter. The initial AS/WC ratio of the mixture used was 90/10. The average biogas production was 0.150 dm3 dm−3 d1. The VFA concentrations were low during the process. After 127 days WT was added to the mixture. The AS/WC/WT ratio was 80/10/10. The CH4 and CO2 content in the biogas varied in the range of 64 - 72 % and 13 - 25 %, respectively. The data obtained during this study confirm that the co-digestion of the vegetables with AS is more favourable compared to the single digestion of the vegetables. © 2009 Taylor and Francis Group, LLC.Item Dynamic studies of nitrophenols sorption on perfil in a fixed-bed column(2008-01-01) Yaneva Z.; Marinkovski M.; Markovska L.; Meshko V.; Koumanova B.The adsorption of two substituted nitrophenols, namely 4-nitrophenol (4-NP) and 2,4-dinitrophenol (2,4-DNP), from aqueous solutions onto perfil was studied using a fixed bed column. The theoretical solid diffusion control (SDC) model describing single solute adsorption in a fixed bed based on the Linear Driving Force (LDF) kinetic model was successfully applied to the investigated systems. The model parameters of solid diffusion coefficient, DS, axial dispersion coefficient, DL, and external mass transfer coefficient, kf, for the investigated systems were estimated by the means of a best fit approach. Some deviations were found between the predicted and the experimental data which reflect the fact that the assumptions of the model were not quite fulfilled for these experiments. It is necessary to adjust the values of the solid diffusion coefficient, the axial dispersion coefficient and the external mass transfer coefficient in order to obtain a satisfactory agreement between the simulated and the experimental breakthrough curves. A Biot number was used as an indicator for the intarparticle diffusion. The Biot number was found to decrease with the increase of bed depth, indicating that the film resistance increased or the intraparticle diffusion resistance decreased.Item Heterogeneous fenton and photo-fenton oxidation for paracetamol removal using iron containing ZSM-5 zeolite as catalyst(2017-02-01) Velichkova F.; Delmas H.; Julcour C.; Koumanova B.Paracetamol is commonly found in wastewaters, as a consequence of its high consumption and incomplete elimination by conventional treatments. Homogenous (photo-)Fenton oxidation has proved efficient for its remediation, but it suffers from uneasy dissolved iron recovery. Therefore this work examines the performance and stability of an iron containing zeolite (Fe/MFI) as catalyst for this reaction. Effects of reaction parameters (pH, temperature, catalyst and H2O2concentrations, UV/vis irradiation) are investigated in batch conditions, by comparing the pollutant and Total Organic Carbon disappearance rates in solution, as well as the overall mineralization yield (including solid phase) and oxidant consumption. At near neutral pH paracetamol can be fully converted after 5 h, while TOC removal reaches up to 60%. Finally, thanks to good catalyst stability (low leaching), a continuous process coupling oxidation and membrane filtration is proposed, showing constant TOC conversion over 40 h and iron loss in the permeate <0.3 ppm. © 2016 American Institute of Chemical Engineers AIChE J, 63: 669–679, 2017.Item Heterogeneous Fenton oxidation of paracetamol using iron oxide (nano)particles(2013-12-01) Velichkova F.; Julcour-Lebigue C.; Koumanova B.; Delmas H.100 mg L-1 paracetamol aqueous solutions were treated by heterogeneous Fenton oxidation at acidic pH (2.6). Three types of iron oxides - nano- and submicro-structured magnetite, nanostructured maghemite - were tested as catalysts for that purpose. For each system, the paracetamol conversion and mineralization yield (Total Organic Carbon removal) were evaluated, as well as the catalyst stability upon recycling. The influence of reaction parameters such as temperature, iron amount, and hydrogen peroxide dosage was also investigated. Paracetamol mineralization was improved by high temperature and low oxidant dosage due to radical scavenging effects. In best conditions (two times the stoichiometric amount of H2O2, a temperature of 60 C, a catalyst concentration of 6 g L-1), paracetamol was fully degraded after 5 h, but total mineralization was not yet achieved: TOC removal reached about 50% when magnetite powders were used as catalysts. All iron oxides exhibited low iron leaching (<1%) and stable catalytic activity upon first recycling. © 2013 Elsevier Ltd. All rights reserved.Item Linear and nonlinear regression methods for equilibrium modelling of p-nitrophenol biosorption by Rhizopus oryzae: Comparison of error analysis criteria(2013-01-01) Yaneva Z.; Koumanova B.; Georgieva N.The study assessed the applicability of Rhizopus oryzae dead fungi as a biosorbent medium for p-nitrophenol (p-NP) removal from aqueous phase. The extent of biosorption was measured through five equilibrium sorption isotherms represented by the Langmuir, Freundlich, Redlich-Peterson, multilayer and Fritz-Schlunder models. Linear and nonlinear regression methods were compared to determine the best-fitting equilibrium model to the experimental data. A detailed error analysis was undertaken to investigate the effect of applying seven error criteria for the determination of the single-component isotherm parameters. According to the comparison of the error functions and to the estimation of the corrected Akaike information criterion (AI C C), the Freundlich equation was ranked as the first and the Fritz-Schlunder as the second best-fitting models describing the experimental data. The present investigations proved the high efficiency (94) of Rhizopus Oryzae as an alternative adsorbent for p-NP removal from aqueous phase and revealed the mechanism of the separation process. © 2013 Zvezdelina Lyubenova Yaneva et al.Item Study of the mechanism of nitrophenols sorption on expanded perlite - Equilibrium and kinetics modelling(2012-01-01) Yaneva Z.; Koumanova B.; Georgieva N.The adsorption behavior of 2-nitrophenol (2-NP) and 2,4-dinitrophenol (2,4-DNP) on expanded perlite (EP) at equilibrium and kinetic conditions was investigated. The experimental equilibrium data were interpreted by Langmuir, Freundlich, Redlich-Peterson, Temkin and the multilayer isotherm models. Both the Temkin and the multilayer models gave the most satisfactory representation of the experimental data for 2-NP sorption on EP covering the whole concentration range, presuming high initial sorption rate, presence of adsorbent-adsorbate chemical interactions and multilayer adsorption, as the basic characteristics featuring the equilibrium behavior of the system studied. The experimental kinetic results were analyzed by the pseudo-first, pseudo-second order models, Bangham's model, intra-particle diffusion model, and Elovich kinetic equation. The values of the calculated rate, mass transfer parameters and correlation coefficients proved that chemisorptions/intraparticle diffusion could be outlined as the basic rate controlling mechanisms during 2-NP/2,4-DNP sorption on expanded perlite. Uptake of nitrophenols increased in the order 2-NP < 2,4-DNP.Item Treatment of wastewaters containing Fe, Cu, Zn and as by microbial hydrogen sulfide and subsequent emoval of COD, N and P(2018-01-01) Bratkova S.; Lavrova S.; Angelov A.; Nikolova K.; Ivanov R.; Koumanova B.Acid drainage wastewaters (pH 2.6 - 2.8) contaminated with Fe 200 mg/l, Cu 25 mg/l, Zn 25 mg/l, and As 15 mg/l were treated in a laboratory-scale installation. The installation design includes an anaerobic sulfidogenic bioreactor, a chemical reactor, an aerobic activated sludge reactor, an anaerobic biofilter and a vertical flow constructed wetland reactor, connected in series. Sulfate-reducing bacteria were adhered in biofilm, which is immobilized on zeolite particles in the anaerobic bioreactor. The bacteria were cultivated on a medium containing lactate as a source of carbon and energy. The influence of TOC/SO42- ratios 0.43, 0.54 0.64 on the rate of the microbial sulfate-reduction was determined. Pollutants removal was achieved in a chemical reactor by sedimentation with microbially produced H2S. SEM/EDS data and X-ray diffraction analyses proved that the precipitated heavy metals are mainly in forms of relevant insoluble sulfides. The design of the lab-scale installation makes possible efficient removal of the residual organic compounds and hydrogen sulfide as well as the processes of nitrification and denitrification to occur. The reported treating method allows the removal of heavy metals, COD, N and P from wastewaters below the permeable level for water intended for use in the agriculture and/or industry.