Adsorption of methyl tertiary butyl ether on granular zeolites: Batch and column studies.

Methyl tertiary butyl ether (MTBE) has been shown to be readily removed from water with powdered zeolites, but the passage of water through fixed-beds of very small powdered zeolites produces high friction losses not encountered in flow through larger sized granular materials. In this study, equilibrium and kinetic adsorption of MTBE onto granular zeolites, a coconut shell granular activated carbon (CS-1240), and a commercial carbon adsorbent (CCA) sample was evaluated. In addition, the effect of natural organic matter (NOM) on MTBE adsorption was evaluated. Batch adsorption experiments determined that ZSM-5 was the most effective granular zeolite for MTBE adsorption. Further equilibrium and kinetic experiments verified that granular ZSM-5 is superior to CS-1240 and CCA in removing MTBE from water. No competitive adsorption effects between NOM and MTBE were observed for adsorption to granular ZSM-5 or CS-1240, however there was competition between NOM and MTBE for adsorption onto the CCA granules. Fixed-bed adsorption experiments for longer run times were performed using granular ZSM-5. The bed depth service time model (BDST) was used to analyze the breakthrough data.

Quantifying the adhesion and interaction forces between Pseudomonas aeruginosa and natural organic matter.

Atomic force microscopy (AFM) was used to characterize interactions between natural organic matter (NOM), and glass or bacteria. Poly(methacrylic acid) (PMA), soil humic Acid (SHA), and Suwannee River humic Acid (SRHA), were adsorbed to silica AFM probes. Adhesion forces (Fadh) for the interaction of organic-probes and glass slides correlated with organic molecular weight (MW), but not with radius of the organic aggregate (R), charge density (Q), or zeta potential (zeta). Two Pseudomonas aeruginosa strains with different lipopolysaccharides (LPS) were chosen: PAO1 (A+B+), whose LPS have common antigen (A-band) + O-antigen (B-band); and mutant AK1401 (A+B-). Fadh between bacteria and organics correlated with organic MW, R, and Q, but not zeta. PAO1 had lower Fadh with silica than NOM, which was attributed to negative charges from the B-band polymers causing electrostatic repulsion. AK1401 adhered stronger to silica than to the organics, perhaps because the absence of the B-band exposed underlying positively charged proteins. DLVO calculations could not explain the differences in the two bacteria or predict qualitative or quantitative trends in interaction forces in these systems. Molecular-level information from AFM studies can bring us closer to understanding the complex nature of bacterial-NOM interactions.

Adhesion of Aureobasidium pullulans is controlled by uronic acid based polymers and pullulan.

Aureobasidium pullulans is a potentially pathogenic microfungus that produces and secretes the polysaccharide pullulan and other biomacromolecules, depending on the microbe's physiological state. The role of these macromolecules in mediating adhesion and attachment were examined. Interfacial forces and adhesion affinities of A. pullulans were probed for early-exponential phase (EEP) and late-exponential phase (LEP) cells, using atomic force microscopy (AFM). Biochemical assays showed that A. pullulans produces both pullulan and a uronic acid based polymer. The pullulan is not produced until the LEP, and it can be removed by treatment with pullulanase. Both adhesion forces between the microbe and the AFM tip (silicon nitride) and attachment of the cells to quartz sand grains were controlled by the density of the uronic acid polymer. Uronic acid polymers doubled in density between the EEP and the LEP and were unaffected by the enzyme pullulanase. Retention to quartz in a packed column was quantified using the collision efficiency (alpha), the fraction of collisions between the microbes, and the sand grains, that result in attachment. Adhesion forces and retention on glass were well correlated, with these values being higher for EEP cells (F(adh) = 7.65 +/-4.67 nN; alpha = 1.15) than LEP (F(adh) = 2.94 +/- 0.75; alpha = 0.49) and LEP + pullulanase cells (F(adh) = 2.33 +/-2.01 nN; alpha = 0.43). Steric interactions alone do not describe the adhesion behavior of this fungus, but they do provide information regarding the length and density of the macromolecules studied.