Browsing by Author "Lavrova S."

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    Drug mass transfer mechanism, thermodynamics, and in vitro release kinetics of antioxidant-encapsulated zeolite microparticles as a drug carrier system
    (2018-10-01) Yaneva Z.; Georgieva N.; Bekirska L.; Lavrova S.
    The aim of the present study was to develop a new vitamin E-zeolite drug carrier system, and investigate the mass transfer mechanism of the antioxidant encapsulation and release on/from the mineral matrix by thermodynamic and kinetics sorption/desorption experiments and mathematical modelling of the experimental data. The surface, morphological and spectral characteristics of the vitamin and the zeolite were determined by Boehm titration, SEM, FTIR and UV/Vis spectrophotometric analyses. Intraparticle diffusion was not the only rate-limiting mechanism, as the mixed-order kinetics model gave the highest regression coefficient (R2) and lowest SSE, MSE, RMSE, and AICC values. The thermodynamic study confirmed the endothermic nature of the spontaneous encapsulation process and increased degrees of randomness at the solid-liquid interface. The in vitro release results were best modelled by the zero-order and sigmoidal models. The results obtained are essential for the development of innovative vitamin E-carrier systems for application in human and veterinary medicine.
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    Treatment of landfill leachate in two stage vertical-flow wetland system with/without addition of carbon source
    (2016-01-01) Lavrova S.
    The aim of this study was to investigate the treatment efficiency of two laboratory scale vertical-flow wetland systems (VFWS) with/without additional carbon source to affect the denitrification of landfill leachate, taken from an active 15 years old landfill for municipal solid wastes. The BOD/COD ratio of the leachate was 0.26, which means predominance of slowly biodegradable substances. During the experiments the parameters COD, BOD, [NH4-N], [NO2-N], [NO3-N] and total phosphorus were determined. Significant removal efficiency according to COD (94.69 ± 2.5 %) and BOD (95.96 ± 2.5 %) was achieved. Complete nitrification of ammonium nitrogen into nitrite and nitrate occurred in both systems. Denitrification occurred only in the wetland system when methanol was added.
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    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.