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Calretinin-22k (CR-22k. Together, our data suggest the presence of an allosteric conformational unit encompassing sites I-III for CR-22k and I-IV for CR, with a very similar conformation and conformational changes for both proteins. In the allosteric unit of CR, site IV is fully active, whereas in CR-22k this site has a 80-fold decreased affinity, due to the decreased amphiphilic properties of the C-terminal helix of this site. Some very specific Ca 2؉ -dependent conformational changes suggest that both CR and CR-22k belong to the "sensor"-type family of Ca 2؉ -binding proteins.

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The impact of membrane fouling by natural organic matter (NOM) on the behavior of micropollutants during ultrafiltration (UF) was investigated. Batch experiments with radioactively labeled estradiol and ibuprofen in the presence of NOM model compounds (alginate, Nordic aquatic and Aldrich humic acid) were performed using a hydrophilic and a hydrophobic membrane. The results indicate that the impact of the NOM fractions studied on micropollutant retention correlated with the fouling mechanism of the individual NOM fractions. NOM substances of high molecular weight such as alginate and Aldrich HA that foul the membrane by pore blocking and cake/gel formation had a greater impact than the Nordic aquatic humic acid of lower molecular weight. The effect of cake formation was attributed partly to micropollutant-NOM partitioning and subsequent NOM retention and partly to the effect of the fouling layer itself acting as a kind of second membrane. Fouling by NOM cake/gel formation led to a significantly increased retention of estradiol, whereas the impact of fouling on ibuprofen retention was negligible due to significantly lower Log Koc values of ibuprofen compared to estradiol. Moreover, NOM adsorption on the membrane can lower the adsorption of hydrophobic micropollutants. Membrane adsorption of estradiol was in the order of mg/m 2 and was largely reversible with caustic solutions. The results of this study may prove useful for predicting the mass flow of micropollutants in UF applications.

Fouling is one of the most critical aspects of membrane technology and is strongly influenced by natural water characteristics.This studyfocuses on a mechanistic understanding of the impact of interactions between natural organic matter (NOM) and particles on fouling. The model substances used were humic acid, alginate (polysaccharide), and kaolinite. NOM-kaolinite adsorption experiments, particle characterization, and dead-end ultrafiltration (UF) batch experiments were performed. The adsorption experiments indicated particle stabilization at low NOM equilibrium concentrations, whereas calcium induced significant aggregation, especially with alginate. UF experiments implicated a synergistic fouling effect of particle-NOM combinations, which was greatly reduced by calcium. Moreover, irreversible NOM fouling was only prevented by particles in the presence of calcium. On the basis of our results, we present a mechanistic model suggesting that synergistic fouling effects occur due to particle stabilization by NOM adsorption, especially shown for HA, and antagonistic effects due to particle destabilization by calcium. However, synergistic fouling can also be based on sterical interferences between larger NOM in the form of polysaccharides and particles during simultaneous pore blocking and cake formation. A heterogeneous NOM-particle fouling layer is ultimately formed with membrane associations dominated by NOM. The combined fouling is conclusively determined bythe type of NOM, its specific fouling mechanisms, and its particle interactions prior to and during the filtration process.