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In wastewater treatment plants (WWTPs), aeration is the major energetic cost, thus its minimisation will improve the cost-effectiveness of the process. This study shows that both the dissolved oxygen (DO) concentration and aerobic hydraulic retention time (HRT) affect the competition between polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs). At low DO levels, Accumulibacter PAOs were shown to have an advantage over Competibacter GAOs, as PAOs had a higher oxygen affinity and thus largely maintained their aerobic activity at low DO levels, while GAO activity decreased. Bioreactor operation at low DO levels was found to increase the PAO fraction of the sludge. Furthermore, an increase in aerobic HRT (at a DO level of 2 mg O2/L), promoted the proliferation of GAOs over PAOs, decreasing the EBPR efficiency. Overall, this study shows that low aeration can be beneficial for EBPR performance through selecting for PAOs over GAOs, which should be incorporated into WWTP models in order to minimise energetic costs and improve WWTP sustainability.

Angle-scanned X-ray photoelectron diffraction (XPD) and scanning tunneling microscopy (STM) are used to characterise the structure of TiO2 nanoparticles grown on a Pt(111) single crystal surface. The nanoparticles grow over a well-ordered oxide interfacial layer that displays a (square root 43 x square root 43) - R7.6 degrees superstructure with a unit cell (18.2 x 18.2 A), as demonstrated by STM and low-energy electron diffraction (LEED). Our XPS Ti 2p core level spectra suggest a significant contribution from reduced titanium ions within the interfacial layer. On the contrary, according to XPS binding energy data, the nanoparticles are mostly composed of Ti(IV) ions. During the initial stage of the growth, the nanoparticles are on the average 2 nm high and about some tens of nm wide, and show a flat on-top surface, while the interparticle region show the structure of the ordered interfacial layer. During later stages of the deposition, the particles become larger and they show a more irregular, globular-like shape as well as coalescence. But, even at this stage of the growth, large interparticle regions are present. Moreover, the nanoparticles produce a distinct XPD pattern which demonstrates that they grow with a preferential azimuthal orientation with respect to the substrate surface. A simple geometrical analysis of the XPD data in terms of forward scattering events suggests that the particles crystallize in the rutile TiO2 structure and expose the (100) surface. This hypothesis is supported by means of multiple scattering simulations of the XPD patterns.

No abstract

in Wiley InterScience (www.interscience.wiley.com).The simulated-moving bed (SMB) is now a well established adsorption process for obtaining high-purity products at a similarly high-recovery. In principle the SMB process can be applied to gases, and has been, but application has been limited. Here, we reexamine the SMB process for separation of gaseous components in the light of recent developments in novel cyclic operating schemes and advanced optimization tools. A novel single-column experimental setup is employed to demonstrate the feasibility of the process, explore the effect of its major operating parameters, and illustrate the performance enhancements that are obtained by using an advanced cyclic operation scheme, such as the asynchronous shifting of the inlet/outlet ports. The experimental feasibility and effectiveness of gas-phase SMB are assessed by running and comparing optimized configurations for the separation of CH 4 /CO 2 over activated carbon using nitrogen as carrier gas. For this separation, the asynchronous configuration always outperforms the classical SMB scheme, both in productivity and eluent consumption, except at very low-feed throughput where both schemes are coincident. At higher-feed flow rates, the asynchronous scheme quickly diverges from a four-zone, closed-loop configuration towards a three-zone, open-loop process with a 50.6% increase in feed throughput, and 10% reduction on eluent gas consumption.