Simulation of turbulence and dissolved oxygen concentration profiles over biofilm using k–ɛ turbulence model

The objective of this study is to investigate the flow structure over biofilm experimentally and theoretically. Velocity and turbulence profiles over biofilm measured by a laser Doppler velocimetry were compared to simulated profiles using the k–ɛ turbulent model. Also, dissolved oxygen concentration profiles over biofilm are measured using a micro DO sensor. The k–ɛ turbulence model was proved to be a useful tool for the understanding of mass transfer inside and outside biofilm. Dissolved oxygen concentration profile inside and outside biofilm showed the existence of turbulent diffusion inside biofilm.

Development of a respirometric assay to measure the transient load response of activated sludge to individual organic chemicals

This study described a new respirometric technique to monitor the transient response of activated sludge systems to individual synthetic organic compounds (SCOs). The assay used a fed-batch reactor system which contained mixed liquor from the parent reactor and received a biogenic feed and the target SOC at the same F/M ratio as was applied to the parent reactor. The fed-batch reactor was oxygenated using a hollow-fiber reaeration module to meet the steady-state oxygen demand. The reaeration module was characterized by means of KL a studies. The assay monitored the dissolved oxygen concentration profile after application of a shock load achieved by switching to a fed-batch feed with the target SOC at an elevated concentration. Mathematical descriptions of the transient profiles were derived and the experimentally observed dissolved oxygen profiles were subsequently compared to profiles predicted using extant kinetic parameters for SOC removal measured using an earlier developed assay. The use of the assay were complicated by the difficulty in maintaining a reaeration capacity at constant and low capacity. As a result, the adequacy of the measured extant kinetic parameters as predictors of the transient response could not be confirmed.

Atom Probe Microanalysis of Superconducting YBa2Cu3O7−x

ABSTRACTSuperconducting YBa2Cu3O7−x needles prepared from hot-pressed discs of oxide powders were analyzed in a long drift-tube type atom probe. An analyses was made from a randomly located area about 2 nm in diameter. Most of the oxygen field-evaporated as O2+ ions. The measured composition agreed well with that of YBa2Cu3O6.5 except for yttrium which was found to be too high. The oxygen concentration profile showed fluctuations about 2.5 nm apart which must still be clarified.