Micro-environments and mass transfer phenomena in biofilms studied with microsensors

1999 ◽  
Vol 39 (7) ◽  
pp. 173-178 ◽  
Author(s):  
Dirk de Beer ◽  
Andreas Schramm
Keyword(s):  
Mass Transfer ◽  
Liquid Flow ◽  
Microbial Population ◽  
In Situ Hybridisation ◽  
Molecular Techniques ◽  
Complex Structures ◽  
Microbial Composition ◽  
Direct Observations ◽  
Direct Measurements

Direct observations on chemical micro-environment and microbial composition in biofilms are rare. The combination of microsensor and molecular techniques is highly useful for studies on the microbial ecology of biofilms. We shortly describe some applications of microsensors to study mass transfer phenomena and microbial processes in biofilms. It has recent been recognized that biofilms are not always flat layers of cells, but can consist of complex structures allowing liquid flow. Thus the classical view, that transport in biofilms is diffusional, is challenged. In laboratory grown biofilms the effect of convection on mass transfer was demonstrated. The microsensor technique has improved, so that direct in situ measurements in living biofilms are possible. By direct measurements of liquid flow with microsensors we show that in biofilms grown in bioreactors heterogeneity and convectional transport must also be taken into account. For the description of the microbial population we use molecular techniques, such as in situ hybridisation with 16S rRNA-targeted oligonucleotide probes. In a nitrifying-denitrifying biofilm we found a complex nitrifying community consisting of members of the genera Nitrosomonas, Nitrosospira, Nitrobacter and Nitrospira. Their occurrence was correlated with nitrification activity as determined by microsensor measurements.

Structure and microbial composition of nitrifying microbial aggregates and their relation to internal mass transfer effects

2004 ◽  
Vol 50 (10) ◽  
pp. 213-220 ◽  
Author(s):  
B.-M. Wilén ◽  
D. Gapes ◽  
L.L. Blackall ◽  
J. Keller
Keyword(s):  
Mass Transfer ◽  
In Situ Hybridisation ◽  
Gas Analysis ◽  
Microbial Consortia ◽  
Fish Analysis ◽  
Fluorescence In Situ Hybridisation ◽  
Internal Mass ◽  
Microbial Composition ◽  
Transfer Resistance ◽  
Internal Mass Transfer

This paper presents an analysis of the structure and microbial composition of nitrifying aggregates, formed as either flocs or granules, in sequencing batch reactors (SBR) operated with a high ammonium load. The structure and microbial community of the aggregates was determined by fluorescence in situ hybridisation (FISH). The aggregate structure and size was related to mass transfer limitations observed by measurements of OURs measured by either a titrimetric and off-gas analysis sensor (TOGA) or by microsensors. The FISH analysis showed that the spatial arrangement of the microbial consortia correlated well with the oxygen gradients inside the aggregates. In the larger aggregates, the ammoniumand nitrite-oxidising bacteria were mainly concentrated to the outer 100–200 μm, whereas in the floc system, the bacteria were distributed throughout the entire aggregate. This indicates that the internal mass transfer resistance is considerably larger when the aggregate size increases which is directly supported by TOGA measurements.

Biofilm reactor technology for low temperature anaerobic waste treatment: microbiology and process characteristics

2005 ◽  
Vol 52 (7) ◽  
pp. 107-113 ◽  
Author(s):  
S. McHugh ◽  
G. Collins ◽  
T. Mahony ◽  
V. O'Flaherty
Keyword(s):  
Population Structure ◽  
Low Temperature ◽  
Microbial Population ◽  
High Strength ◽  
Biofilm Reactor ◽  
Molecular Techniques ◽  
Cod Removal ◽  
Successful Implementation ◽  
Microbial Composition ◽  
Reactor Technology

The microbial composition, methanogenic activity and architecture of particulate and fixed biofilms within four anaerobic hybrid reactors, R1–R4, operating at psychrophilic temperatures were investigated. The reactors treated low-strength (1 g COD l−1; R1) and high-strength (10 g COD l−1; R2–R4) wastewaters from the food-processing sector (R1, R2 – whey; R3 – sucrose; R4 – volatile fatty acids). Successful start-up and long-term psychrophilic operation was observed for all four reactors, with COD removal efficiencies of 80–99% achieved at 12–20 °C at organic loading rates of 1.3–20 kg COD m−3 d−1. The formation and maintenance of a well-settling granular sludge bed and an attached biofilm were shown to occur under psychrophilic conditions, an important consideration for the successful implementation of low temperature biofilm reactor technology. Culture-independent molecular techniques (terminal restriction fragment length polymorphism, clone library analysis and 16S rRNA gene sequencing) revealed that microbial population structure could be a key factor in reactor performance, with changes in the community structure of the three high-strength reactors preceding granular instability and a subsequent decline in COD removal efficiency. Biomonitoring of microbial population structure and dynamics within anaerobic reactors may, therefore, allow for the early recognition of potential operational problems.

Direct Observations of the Epitaxial Growth of Sputtered Ag on Si

1973 ◽  
Vol 31 ◽  
pp. 122-123
Author(s):  
J. S. Maa ◽  
Thos. E. Hutchinson
Keyword(s):  
Epitaxial Growth ◽  
Film Growth ◽  
Ion Beam ◽  
Ion Beam Sputtering ◽  
Microscopy Technique ◽  
Direct Observations ◽  
In Situ Electron Microscopy ◽  
Beam Sputtering ◽  
The Subject

The growth of Ag films deposited on various substrate materials such as MoS2, mica, graphite, and MgO has been investigated extensively using the in situ electron microscopy technique. The three stages of film growth, namely, the nucleation, growth of islands followed by liquid-like coalescence have been observed in both the vacuum vapor deposited and ion beam sputtered thin films. The mechanisms of nucleation and growth of silver films formed by ion beam sputtering on the (111) plane of silicon comprise the subject of this paper. A novel mode of epitaxial growth is observed to that seen previously.The experimental arrangement for the present study is the same as previous experiments, and the preparation procedure for obtaining thin silicon substrate is presented in a separate paper.

Bio-P and non-bio-P bacteria identification by a novel microbial approach

1999 ◽  
Vol 39 (6) ◽  
pp. 13-20 ◽  
Author(s):  
Philip L. Bond ◽  
Jürg Keller ◽  
Linda L. Blackall
Keyword(s):  
In Situ Hybridisation ◽  
Microbial Populations ◽  
Biological Phosphorus Removal ◽  
Gram Positive Bacteria ◽  
P Content ◽  
Identification Of Bacteria ◽  
Widespread Belief ◽  
Biological Phosphorus ◽  
P Removal

Culturing bacteria from activated sludge with enhanced biological phosphorus removal (EBPR) has strongly implicated Acinetobacter with the process. However, using fluorescent in-situ hybridisation (FISH) probing to analyse microbial populations, we have shown evidence opposing this widespread belief. We describe the phosphorus (P) removing performance and microbial population analyses of sludges obtained in a laboratory scale EBPR reactor. Two sludges with extremely high P removing capabilities were examined, the P content of these sludges was 8.6% (P sludge) and 12.3% (S sludge) of the MLSS. Identification of bacteria using FISH probing indicated both sludges were dominated by microbes from the beta proteobacteria and high mol% G+C Gram positive bacteria. Acinetobacter could make up only a small proportion of the cells in these sludges. Sludge with extremely poor P removal (P content of 1.5%, referred to as T sludge) was then generated by reducing the P in the influent. Bacteria resembling the G-bacteria became abundant in this sludge and these were identified using FISH probing. The anaerobic transformations of the T and P sludges correlated well with that of the non-EBPR and EBPR biological models respectively, indicating that bacteria in the T sludge have the potential to inhibit P removal in EBPR systems.

The role of (bio)surfactant sorption in promoting the bioavailability of nutrients localized at the solid-water interface

1999 ◽  
Vol 39 (7) ◽  
pp. 91-98 ◽  
Author(s):  
Ryan N. Jordan ◽  
Eric P. Nichols ◽  
Alfred B. Cunningham
Keyword(s):  
Mass Transfer ◽  
Cell Membrane ◽  
Substrate Concentration ◽  
Water Interface ◽  
Industrial Systems ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Surfactant Sorption

Bioavailability is herein defined as the accessibility of a substrate by a microorganism. Further, bioavailability is governed by (1) the substrate concentration that the cell membrane “sees,” (i.e., the “directly bioavailable” pool) as well as (2) the rate of mass transfer from potentially bioavailable (e.g., nonaqueous) phases to the directly bioavailable (e.g., aqueous) phase. Mechanisms by which sorbed (bio)surfactants influence these two processes are discussed. We propose the hypothesis that the sorption of (bio)surfactants at the solid-liquid interface is partially responsible for the increased bioavailability of surface-bound nutrients, and offer this as a basis for suggesting the development of engineered in-situ bioremediation technologies that take advantage of low (bio)surfactant concentrations. In addition, other industrial systems where bioavailability phenomena should be considered are addressed.

The effect of two-phase flow regime on hydrodynamics and mass transfer in a horizontal-tube gas-liquid reactor

1985 ◽  
Vol 50 (3) ◽  
pp. 745-757 ◽  
Author(s):  
Andreas Zahn ◽  
Lothar Ebner ◽  
Kurt Winkler ◽  
Jan Kratochvíl ◽  
Jindřich Zahradník
Keyword(s):  
Mass Transfer ◽  
Pressure Drop ◽  
Flow Regime ◽  
Liquid Flow ◽  
Horizontal Tube ◽  
Liquid Holdup ◽  
Two Phase ◽  
Flow Rates ◽  
Type Relation ◽  
Good Agreement

The effect of two-phase flow regime on decisive hydrodynamic and mass transfer characteristics of horizontal-tube gas-liquid reactors (pressure drop, liquid holdup, kLaL) was determined in a cocurrent-flow experimental unit of the length 4.15 m and diameter 0.05 m with air-water system. An adjustable-height weir was installed in the separation chamber at the reactor outlet to simulate the effect of internal baffles on reactor hydrodynamics. Flow regime maps were developed in the whole range of experimental gas and liquid flow rates both for the weirless arrangement and for the weir height 0.05 m, the former being in good agreement with flow-pattern boundaries presented by Mandhane. In the whole range of experi-mental conditions pressure drop data could be well correlated as a function of gas and liquid flow rates by an empirical exponential-type relation with specific sets of coefficients obtained for individual flow regimes from experimental data. Good agreement was observed between values of pressure drop obtained for weirless arrangement and data calculated from the Lockhart-Martinelli correlation while the contribution of weir to the overall pressure drop was well described by a relation proposed for the pressure loss in closed-end tubes. In the region of negligible weir influence values of liquid holdup were again succesfully correlated by the Lockhart-Martinelli relation while the dependence of liquid holdup data on gas and liquid flow rates obtained under conditions of significant weir effect (i.e. at low flow rates of both phases) could be well described by an empirical exponential-type relation. Results of preliminary kLaL measurements confirmed the decisive effect of the rate of energy dissipation on the intensity of interfacial mass transfer in gas-liquid dispersions.

Absorption of oxygen into solutions of polymers

1986 ◽  
Vol 51 (10) ◽  
pp. 2127-2134 ◽  
Author(s):  
František Potůček ◽  
Jiří Stejskal
Keyword(s):  
Mass Transfer ◽  
Aqueous Solutions ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Flow Rate ◽  
Liquid Flow ◽  
Flow Curve ◽  
Liquid Flow Rate ◽  
Polymer Concentration ◽  
Newtonian Liquids

Absorption of oxygen into water and aqueous solutions of poly(acrylamides) was studied in an absorber with a wetted sphere. The effects of changes in the liquid flow rate and the polymer concentration on the liquid side mass transfer coefficient were examined. The results are expressed by correlations between dimensionless criteria modified for non-Newtonian liquids whose flow curve can be described by the Ostwald-de Waele model.

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