Ozone absorption in raw waters

The ozone absorption in raw water entering the main ozonization step at the Belgrade drinking water supply plant was investigated in a continuous stirred tank reactor (CSTR). A slow chemical reaction rate of dissolved ozone and pollutants present in raw water have been experimentally determined. The modified Hatta number was defined and calculated as a criterion which determines whether and to which extent the reactions of ozone and pollutants influence the rate of the pure physical ozone absorption

Absorption in a three-phase fluidized bed II: Mass transfer investigations

The absorption of carbon dioxide in aqueous diethanolamine solutions was carried out in a three-phase fluidized bed with inert spherical packing. The rate of absorption was calculated on the basis of measuring the concentration change in the liquid phase on-line by a conductivity probe. It was shown that the Danckwerts plot method might be successfully used to simultaneously determine the effective interfacial area and both the gas and liquid-side mass transfer coefficients. While the gas-side mass transfer coefficient is independent of the liquid flow rate, the effective interfacial area and liquid-side mass transfer coefficient increase with increasing liquid flow rate

Ozone absorption in a mechanically stirred reactor

Ozone absorption in water was investigated in a mechanically stirred reactor, using both the semi-batch and continuous mode of operation. A model for the precise determination of the volumetric mass transfer coefficient in open tanks without the necessity of the measurement the ozone concentration in the outlet gas was developed. It was found that slow ozone reactions in the liquid phase, including the decomposition of ozone, can be regarded as one pseudo-first order reaction. Under the examined operating conditions, the liquid phase was completely mixed, while mixing in a gas phase can be described as plug flow. The volumetric mass transfer coefficient was found to vary with the square of the impeller speed

Diffusion of drugs from hydrogels and liposomes as drug carriers

BACKGROUND: The mass transfer of model drugs Lidocaine hydrochloride and Dihydroquercetin from hydrogels (the usual carriers for topical drugs), and hydrogels containing liposomes, as novel drug vehicles, was studied. Diffusion experiments were performed using a Franz diffusion cell. Experimental data were used to calculate drug diffusion coefficients across membranes, and their effective diffusion coefficients from hydrogels and liposome containing hydrogels. For the first time the diffusion resistance of all drug carriers was determined from corresponding diffusion coefficients. The main aim of this work was the study of drug diffusion coefficients from liposomes and their comparison with related diffusion coefficients from hydrogels to find how liposomes contribute to prolonged and controlled drug release. RESULTS: Drug diffusion coefficients were: 1.38 . 10(-8)-m(2) s(-1) for Lidocaine hydrochloride and 5.96 . 10(-9)m(-2) s(-1) for Dihydroquercetin, while corresponding effective diffusion coefficients from hydrogels were: 7.82 . 10(-10)m(2) s(-1) and 7.98 . 10(-10)m(2) s(-1), respectively. Effective diffusion coefficients from liposome-containing hydrogels were:4.82 . 10(-10)m(2) s(-1) (Lidocaine hydrochloride) and 4.305 . 10(-10)m(2) s(-1) (Dihydroquercetin). Diffusion resistances for the two hydrogels were almost the same. Very similar values of diffusion resistances for all liposome dispersions were obtained. CONCLUSION: Calculated diffusion coefficients and resistances demonstrate that liposomes, as drug carriers, significantly affect diffusion rates. The results obtained could be used whenever diffusion-controlled drug release is required