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Abstract

Biological regeneration of water and organic sorbents used in the absorption of hydrophilic and hydrophobic pollutants, respectively, was studied. In both cases biodegradation takes place in a membrane bioreactor. In the case of organic sorbents regeneration of the biodegradation process is integrated with the extraction of a given pollutant to water phase. In experiments carried out in this work, the proposed systems were tested using a strain of Pseudomonas fluorescens. For hydrophilic compounds experiments were performed using alcohols (1-butanol and 2-propanol) as model substrates. Applying the mathematical model of a membrane bioreactor elaborated previously, the values of pollutant concentration were determined and positively verified in the experiments. This system of water sorbent regeneration is fully satisfying. The process of biodegradation integrated with extraction was analysed on the basis of model compounds such as benzene and toluene. The study confirmed a possibility of organic sorbent (silicone oil) regeneration. However, due to a very high partition coefficient of benzene or toluene between the organic and aqueous phases, the process could be considered only for the case of their high concentrations in the gas directed to absorption.
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Abstract

In this study, β-galactosidase enzyme from Kluyveromyces fragilis was immobilised on a commercial polyethersulfone membrane surface, 10 kDa cut-off. An integrated process, concerning the simultaneous hydrolysis-ultrafiltration of whey lactose was studied and working conditions have been fixed at 55°C and pH 6.9, the same conditions that are used for the industrial process of protein concentration. For the immobilisation, best results were obtained using 5% (v/v) of glutaraldehyde solution and 0.03 M galactose; the total activity recovery coefficient (TARC) was 44.2%. The amount of immobilised enzyme was 12.49 mg with a total activity of 86.3 LAU at 37°C, using 5% (w/v) lactose solution in phosphate buffer (100 mM pH 6.9). The stability of the immobilised enzyme was approximately 585 fold higher in comparison with the stability of free enzyme. Multipoint covalent immobilisation improves the stability of the enzyme, thereby enhancing the decision to use the membrane as a filtering element and support for the enzyme immobilisation.
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Abstract

Two types of submerged membrane bioreactors (MBR): hollow fiber (HF) and hollow sheet (HS), have been studied and compared in terms of energy consumption and average shear stress over the membrane wall. The analysis of energy consumption was made using the correlation to determine the blower power and the blower power demand per unit of permeate volume. Results showed that for the system geometries considered, in terms the of the blower power, the HF MBR requires less power compared to HS MBR. However, in terms of blower power per unit of permeate volume, the HS MBR requires less energy. The analysis of shear stress over the membrane surface was made using computational fluid dynamics (CFD) modelling. Experimental measurements for the HF MBR were compared with the CFD model and an error less that 8% was obtained. For the HS MBR, experimental measurements of velocity profiles were made and an error of 11% was found. This work uses an empirical relationship to determine the shear stress based on the ratio of aeration blower power to tank volume. This relationship is used in bubble column reactors and it is extrapolate to determine shear stress on MBR systems. This relationship proved to be overestimated by 28% compared to experimental measurements and CFD results. Therefore, a corrective factor is included in the relationship in order to account for the membrane placed inside the bioreactor.
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