5 research outputs found
Influence of synthetic packing materials on the gas dispersion and biodegradation kinetics in fungal air biofilters
The biodegradation of toluene was studied in two
lab-scale air biofilters operated in parallel, packed respec-
tively with perlite granules (PEG) and polyurethane foam
cubes (PUC) and inoculated with the same toluene-
degrading fungus. Differences on the material pore size,
from micrometres in PEG to millimetres in PUC, were
responsible for distinct biomass growth patterns. A compact
biofilm was formed around PEG, being the interstitial
spaces progressively filled with biomass. Microbial growth
concentrated at the core of PUC and the excess of biomass
was washed-off, remaining the gas pressure drop compar-
atively low. Air dispersion in the bed was characterised by
tracer studies and modelled as a series of completely stirred
tanks (CSTR). The obtained number of CSTR (
n
) in the
PEG packing increased from 33 to 86 along with the
applied gas flow (equivalent to empty bed retention times
from 48 to 12 s) and with operation time (up to 6 months).
In the PUC bed,
n
varied between 9 and 13, indicating that
a stronger and steadier gas dispersion was achieved.
Michaelis
–
Menten half saturation constant (
k
m
) estimates
ranged 71
–
113 mg m
−
3
, depending on the experimental
conditions, but such differences were not significant at a
95% confidence interval. The maximum volumetric elim-
ination rate (
r
m
)variedfrom23to50gm
−
3
h
−
1
.
Comparison between volumetric and biomass specific
biodegradation activities indicated that toluene mass trans-
fer was slower with PEG than with PUC as a consequence
of a smaller biofilm surface and to the presence of larger
zones of stagnant air
Microbial renewable feedstock utilization: A substrate-oriented approach
Increasingly lignocellulosic biomass hydrolysates are used as the feedstock for industrial fermentations. These biomass hydrolysates consist of complex mixtures of different fermentable sugars, but also contain inhibitors and salts that affect the performance of the product-generating microbes. The performance of six industrially relevant microorganisms, i.e., two bacteria (Escherichia coli and Corynebacterium glutamicum), two yeasts (Saccharomyces cerevisiae and Pichia stipitis) and two fungi (Aspergillus niger and Trichoderma reesei) were compared for their ability to utilize and grow on different feedstock hydrolysates (corn stover, wheat straw, sugar cane bagasse and willow wood). Moreover, the ability of the selected hosts to utilize waste glycerol from the biodiesel industry was evaluated. P. stipitis and A. niger were found to be the most versatile and C. glutamicum, and S. cerevisiae were shown to be the least adapted to renewable feedstocks. Clear differences in the utilization of the more abundant carbon sources in these feedstocks were observed between the different species. Moreover, in a species-specific way the production of various metabolites, in particular polyols, alcohols and organic acids was observed during fermentation. Based on the results obtained we conclude that a substrate-oriented instead of the more commonly used product oriented approach towards the selection of a microbial production host will avoid the requirement for extensive metabolic engineering. Instead of introducing multiple substrate utilization and detoxification routes to efficiently utilize lignocellulosic hydrolysates only one biosynthesis route forming the product of interest has to be engineered