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  • 1
    Electronic Resource
    Electronic Resource
    Abrasion of suspended biofilm pellets in airlift reactors: Importance of shape, structure, and particle concentrations (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 88-99 
    Details
    ISSN: 0006-3592
    Keywords: biofilm structure ; detachment ; abrasion ; collisions ; airlift-reactor ; hydrodynamics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The detachment of biomass from suspended biofilm pellets in three-phase internal loop airlift reactors was investigated under nongrowth conditions and in the presence of bare carrier particles. In different sets of experiments, the concentrations of biofilm pellets and bare carrier particles were varied independently. Gas hold-up, bubble size, and general flow pattern were strongly influenced by changes in volume fractions of biofilm pellets and bare carrier particles. In spite of this, the rate of biomass detachment was found to be linear with both the concentration of biofilm pellets and the bare carrier concentration up to a solids hold-up of 30%. This implies that the detachment rate was dominated by collisions between biofilm pellets and bare carrier particles. These collisions caused an on-going abrasion of the biofilm pellets, leading to a reduction in pellet volume. Breakage of the biofilm pellets was negligible. The biofilm pellets were essentially ellipsoidal, which made three-dimensional size determination necessary. Calculating particle volumes from two-dimensional image analysis measurements and assuming a spherical shape led to serious errors. The abrasion rate was not equal on all sides of the biofilm pellets, resulting in an increasing flattening of the pellets. This flattening was oriented with the basalt carrier inside the biofilm and independent of the absolute abrasion rate. These observations suggest that the collisions causing abrasion are somehow oriented. The internal structure of the biofilms showed two layers, a cell-dense outer layer and an interior with a low biomass density. Taking this density gradient into account, the washout of detached biomass matched observed changes in volume of the biofilm pellets. No gradient in biofilm strength with biofilm depth was indicated. © 1997 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Dynamics of biofilm detachment in biofilm airlift suspension reactors (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 45 (1995), S. 481-487 
    Details
    ISSN: 0006-3592
    Keywords: biofilms ; detachment ; substrate loading ; airlift reactor ; abrasion ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The dynamic change in the overall detachment rate of spherical biofilms in a biofilm airlift suspension reactor was measured after a downshift of the substrate loading rate to zero while all other conditions remained constant. In contrast to the expectations, the overall detachment rate decreased rapidly to a nearly stable level. Correlations available from literature were not able to describe this phenomenon. Concepts were formulated which can describe the observations from this study. Research under dynamic conditions and careful monitoring of the biofilm surface area and biofilm morphology are necessary to elucidate and discriminate biofilm detachment mechanisms. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260450604
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Detachment of biomass from suspended nongrowing spherical biofilms in airlift reactors (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 46 (1995), S. 258-269 
    Details
    ISSN: 0006-3592
    Keywords: biofilm ; detachment ; abrasion ; breakage ; airlift reactor ; hydrodynamics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In three-phase internal loop airlift reactors, the detachment of biomass from suspended biofilm pellets in the presence of bare carrier particles was investigated under nongrowth conditions. The detachment rate was dominated by collisions between bare carrier particles and biofilm pellets. The concentration of bare carrier particles and the carrier roughness strongly influenced the detachment rate. A change in flow regime from bubbling to slug flow considerably increased the detachment rate. Otherwise, the superficial gas velocity did not directly affect the detachment rate. The influence of particle size was not clear. The bottom clearance did not affect the detachment rate within the tested range. Other aspects of reactor geometry might be important. The main detachment processes were abrasion and breakage of biofilm pellets. During the detachment process, two phases could be distinguished. In the first phase the detachment was relatively high, and both breakage and abrasion of biofilm pellets occurred. During the second phase, breakage dominated and the detachment rate was lower. The two-phase behavior is explained by differences in strength between the inner and outer biofilm layers, possibly caused by variations in local growth rates during biofilm formation. Differences in growth history might also explain the various detachment rates observed with different biofilm batches. © 1995 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260460309
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    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Influence of biomass production and detachment forces on biofilm structures in a biofilm airlift suspension reactor (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 58 (1998), S. 400-407 
    Details
    ISSN: 0006-3592
    Keywords: abrasion ; airlift reactor ; biofilm ; structure ; density ; surface shape ; thickness ; shear ; carrier concentration ; substrate loading ; detachment ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The influence of process conditions (substrate loading rate and detachment force) on the structure of biofilms grown on basalt particles in a Biofilm Airlift Suspension (BAS) reactor was studied. The structure of the biofilms (density, surface shape, and thickness) and microbial characteristics (biomass yield) were investigated at substrate loading rates of 5, 10, 15, and 20 kg COD/m3 · day with basalt concentrations of 60 g/L, 150 g/L, and 250 g/L. The basalt concentration determines the number of biofilm particles in steady state, which is the main determining factor for the biofilm detachment in these systems. In total, 12 experimental runs were performed. A high biofilm density (up to 67 g/L) and a high biomass concentration was observed at high detachment forces. The higher biomass content is associated with a lower biomass substrate loading rate and therefore with a lower biomass yield (from 0.4 down to 0.12 gbiomass/gacetate). Contrary to general beliefs, the observed biomass detachment decreased with increasing detachment force. In addition, smoother (fewer protuberances), denser and thinner compact biofilms were obtained when the biomass surface production rate decreased and/or the detachment force increased. These observations confirmed a hypothesis, postulated earlier by Van Loosdrecht et al. (1995b), that the balance between biofilm substrate surface loading (proportional to biomass surface production rate, when biomass yield is constant) and detachment force determines the biofilm structure. When detachment forces are relatively high only a patchy biofilm will develop, whereas at low detachment forces, the biofilm becomes highly heterogeneous with many pores and protuberances. With the right balance, smooth, dense and stable biofilms can be obtained. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 58:400-407, 1998.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 5
    Electronic Resource
    Electronic Resource
    Adhesion and biofilm development on suspended carriers in airlift reactors: Hydrodynamic conditions versus surface characteristics (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 880-889 
    Details
    ISSN: 0006-3592
    Keywords: biofilm ; airlift reactor ; adhesion ; detachment ; surface characteristics ; Pseudomonas putida ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Adhesion and biofilm formation by Pseudomonas putida was studied using suspended carriers in laboratory airlift reactors. Standard, roughened, hydrophobic, and positively charged glass beads, sand, and basalt grains were used as carriers. The results clearly show that in airlift reactors hydrodynamic conditions and particle collisions control biofilm formation. In the reactors, on surfaces subjected to different shear levels, biofilm formation differed considerably. This could be described by a simple growth and detachment model. Increased surface roughness promoted biofilm accumulation on suspended carriers. The physicochemical surface characteristics of the carrier surface proved to be less important due to the turbulent conditions in the airlift reactors. Adhesion of P. putida to glass beads was poor, and results of an adhesion test under quiescent conditions were not predictive for adhesion and subsequent biofilm formation under reactor conditions. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55:880-889, 1997.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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