Condensed rotational separation

Condensed Rotational Separation is based on partial condensation of components of gas-gas mixtures. Condensation is induced by flash evaporation or pressure distillation. The rotational particle separator removes the micron sized particles formed by condensation from the gas. Yields and purities are enhanced by adding a next stage of liquid flash and relooping the gas to the first stage. A great improvement in separation performance, in both yields and purities, is achieved by allowance for operation of CRS within the vapour-liquid-solid region. Condensed rotational separation is shown to be an economically attractive process for upgrading sour gas fields contaminated with CO2 and/or H2S

Condensed rotational separation

Condensed Rotational Separation is based on partial condensation of components of gas-gas mixtures. Condensation is induced by flash evaporation or pressure distillation. The rotational particle separator removes the micron sized particles formed by condensation from the gas. Yields and purities are enhanced by adding a next stage of liquid flash and relooping the gas to the first stage. A great improvement in separation performance, in both yields and purities, is achieved by allowance for operation of CRS within the vapour-liquid-solid region. Condensed rotational separation is shown to be an economically attractive process for upgrading sour gas fields contaminated with CO2 and/or H2S

Influence of medium composition on the characteristics of a denitrifying biofilm formed by alcaligenes denitrificans in a fluidised bed reactor

The influence of the ratio carbon/nitrogen and phosphorus concentration on the performance of a biofilm fluidised bed reactor used for denitrification and on the properties of the biofilm was studied. Although the removal efficiencies of C and N reached steady-state values, the thickness of the biofilm steadily increased. The dry density of the biofilm did not seem to be dependent on the loading conditions, although a denser biofilm was obtained when there was no nutrient limitation that corresponded to the complete removal of nitrate and carbon. The composition of the biofilm in terms of proteins and polysaccharides changed with the C/N ratio and P concentrations. Higher denitrifying activities, which were obtained with increasing P concentrations, were related with higher protein content, since metabolism was shifted from polysaccharide production towards cell production. The thickness and the density of the biofilms were related mainly with the shear stress in the reactor and the composition of biofilms was dependent on the composition of the medium and related with higher activities of the microorganisms.Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XXI . Instituto de Biotecnologia e Química Fina (IBQF)

Designing an observation instrument for assessment for learning practice

In Assessment for Learning (AfL), assessment is a tool used to support students’ learning. In the last decades, research has shown the potential of AfL on student learning. Implementation of AfL in practice however, has proven to be complicated and a concrete discriminative operationalization of AfL practice is lacking. Aim of this study is to support the implementation of AfL and to operationalize AfL in an observation instrument for AfL practice. For the design of the observation instrument, a literature search was conducted to find an applicable theoretical framework for AfL and to describe teachers’ activities in AfL practice in concrete processes. The search resulted in the identification of the three main processes of AfL for teachers, students and peers: 1) identifying where learners are going; 2) where they are in their learning and 3) how to get there, as the theoretical framework for the design of the observation instrument. Theory on feedback (dialogues) and monitoring and scaffolding was used to describe teachers’ activities in the three main processes of AfL. The resulting observation instrument is presented in this paper. To determine if the instrument meets its intended goals, the instrument was tested in observing teachers in their practice. Results show that the instrument is appropriate to identify and discriminate between AfL practices and that the instrument is suitable for coaching teachers in their change to AfL

Hydrodynamic considerations on optimal design of a three-phase airlift bioreactor with high solids loading

The hydrodynamic study of a three-phase airlift (TPAL) bioreactor with an enlarged gas–liquid dual separator was carried out. Different lengths and diameters of the draft tube were tested to show how the design of the separator zone affects the hydrodynamic performance of the TPAL reactor. Ca-alginate beads with entrapped yeast biomass at different loadings (0, 7, 14 and 21% v/v) were used in order to mimic the solid phase of conventional high cell density systems, such as those with cells immobilized on carriers or flocculating cells. Important information on multiphase flow and distribution of gas and solid phases in the internal-loop airlift reactor (ALR) with high solids loading was obtained, which can be used for suggesting optimal hydrodynamic conditions in a TPAL bioreactor with high solids loading. It is finally suggested that the ALR with a dual separator and a downcomer to riser cross-sectional area ratio (AD/AR) ranging from 1.2 to 2.0 can be successfully applied to batch/continuous high cell density systems, where the uniform distribution of solid phase, its efficient separation of particles from the liquid phase, and an improved residence time of air bubbles inside the reactor are desirable.European Community - ‘Improving Human Research Potential’ - Marie Curie Fellowship - contract number HPMF-CT-2002-01643

Nitrifying and heterotrophic population dynamics in biofilm reactors: effects of hydraulic retention time and the presence of organic carbon

Two biofilmreactors operated with hydraulic retention times of 0.8 and 5.0 h were used to study the links between population dynamics and reactor operation performance during a shift in process operation from pure nitrification to combined nitrification and organic carbon removal. The ammonium and the organic carbon loads were identical for both reactors. The composition and dynamics of the microbial consortia were quantified by fluorescence in situ hybridization (FISH) with rRNA-targeted oligonucleotide probes combined with confocal laser scanning microscopy, and digital image analysis. In contrast to past research, after addition of acetate as organic carbon nitrification performance decreased more drastically in the reactor with longer hydraulic retention time. FISH analysis showed that this effect was caused by the unexpected formation of a heterotrophic microorganism layer on top of the nitrifying biofilm that limited nitrifiers oxygen supply. Our results demonstrate that extension of the hydraulic retention time might be insufficient to improve combined nitrification and organic carbon removal in biofilm reactors.Ministério da Ciência, Tecnologia e Ensino Superior. Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XXI BD/15943/98). Deutscher Akademischer Austauschdienst (A/99/06961). European Comission - T.M.R. BioToBio project. Deutsche Forschungsgemeinschaft