225 research outputs found
Effect of lipids on biomass development in anaerobic fixed-bed reactors treating a synthetic dairy waste
The aim of this work was to follow the evolution in
quantity and quality of the biomass developed
during the operation of two anaerobic fixed bed
reactors treating a synthetic dairy waste with
different lipid contents. The feasibility of a special
reactor design that allowed the biomass withdrawal
with minimum operation disturbances was tested.
The HRT was maintained at 1.5 days and the
influent concentration was gradually increased from
3 to 12 g COD/l. Initially, one reactor was loaded
with skim milk and the other one with whole milk,
with equal organic loading rates (OLR). The effect
of lipids was evaluated in terms of reactor
performance, total, adhered and entrapped biomass
and evolution of biomass quality determined in
batch assays by: (i) measuring of potential specific
methanogenic activity against direct (acetate,
H2/CO2) and indirect (propionate and butyrate)
substrates; (ii) measuring of the resistance of
acetoclastic bacteria to the presence of sodium
oleate. The lipids reduced the adhered fraction of
biomass. The methanogenic activity against butyrate
was enhanced in the presence of lipids, but no
significant effect was detected on the other
measured activities. The biomass taken from the
reactor fed with lipids was more susceptible to the
presence of sodium oleate, but, over the operation
period, this susceptibility was reduced
Effect of lipids and oleic acid on biomass development in anaerobic fixed-bed reactors. Part I: biofilm growth and activity
Two similar anaerobic fixed-bed bioreactors which allowed the biomass to be periodically
withdrawn were run in parallel. After feeding each digester with synthetic dairy wastes of different lipid
content (Period I), both digesters were fed with increasing sodium oleate concentrations with skim milk
as co-substrate (Period II) and oleate as the sole carbon source (Period III). In Period I, the digester
fed with lipids was more effcient and exhibited lower levels of volatile fatty acids than the digester fed
without lipids. The biofilm built up in the presence of lipids was thinner, but more resistant to the
presence of oleate than the biofilm formed in the absence of lipids, which lost 53% of its solids after
contacting with oleic acid. The specific methanogenic activity with butyrate as substrate was enhanced
in the presence of lipids, but no significant effect was detected on the acetoclastic and hydrogenophilic
activities, which remained similar for both digesters along the trial period
Effects of lipids and oleic acid on biomass development in anaerobic fixed-bed reactors. Part II : oleic acid toxicity and biodegradability
Oleic acid toxicity and biodegradability were followed during long-term operation of two
similar anaerobic fixed-bed units. When treating an oleate based effluent, the sludge from the bioreactor
that was acclimated with lipids during the first operation period, showed a higher tolerance to oleic
acid toxicity (IC50=137 mg/l) compared with the sludge fed with a non-fat substrate (IC50=80 mg/l).
This sludge showed also the highest biodegradation capacity of oleic acid, achieving maximum methane
production rates between 33 and 46 mlCH4_(STP)/gVS.day and maximum percentages of methanization
between 85 and 98% for the range of concentrations between 500 and 900 mg oleate/l. When oleate
was the sole carbon source fed to both digesters, the biomass became encapsulated with organic matter,
possibly oleate or an intermediate of its degradation, e.g. stearate that was degraded at a maximum
rate of 99 mlCH4_(STP)/gVS.day. This suggests the possibility of using adsorption-degradation cycles for
the treatment of LCFA based effluents. Both tolerance to toxicity and biodegradability of oleic acid
were improved by acclimatization with lipids or oleate below a threshold concentration
Influence of lipid acclimatization on the oleic acid toxicity towards methanogenic acetoclastic bacteria
Instituto de Biotecnologia e Química Fina (IBQF)
Influence of lipid acclimatization on the support matrix colonisation in anaerobic filters treating oleic acid
Instituto de Biotecnologia e Química Fina (IBQF)
A new method to study interactions between biomass and packing material in anaerobic filters
A new anaerobic, random-packed, fixed-bed reactor, where the fixed bed matrix is distributed between up to 36 independent mini-bioreactors, has been developed to investigate biomass-support interactions in anaerobic filters.
Glass, Plexiglas and polyvinyl chloride (PVC) of three sizes all gave similar results though entrapped biomass was maximal at 3 g/L of matrix void volume for the smallest size and a maximum of 1 g adhered biomass per m2 was obtained for the largest size. In a second run, by periodically removing 3 mini-bioreactors, potential specific
methanogenic activities against individual substrates were determined along the time and a continuous growth of the adhered biomass was observed, achieving a maximum of 40% of the total biomass.Comunidade Europeia - Human Capital and Mobility grant
Revealing the structure of the outer disks of Be stars
Context. The structure of the inner parts of Be star disks (20 stellar radii)
is well explained by the viscous decretion disk (VDD) model, which is able to
reproduce the observable properties of most of the objects studied so far. The
outer parts, on the ther hand, are not observationally well-explored, as they
are observable only at radio wavelengths. A steepening of the spectral slope
somewhere between infrared and radio wavelengths was reported for several Be
stars that were previously detected in the radio, but a convincing physical
explanation for this trend has not yet been provided. Aims. We test the VDD
model predictions for the extended parts of a sample of six Be disks that have
been observed in the radio to address the question of whether the observed
turndown in the spectral energy distribution (SED) can be explained in the
framework of the VDD model, including recent theoretical development for
truncated Be disks in binary systems. Methods. We combine new multi-wavelength
radio observations from the Karl. G. Jansky Very Large Array (JVLA) and Atacama
Pathfinder Experiment (APEX) with previously published radio data and archival
SED measurements at ultraviolet, visual, and infrared wavelengths. The density
structure of the disks, including their outer parts, is constrained by
radiative transfer modeling of the observed spectrum using VDD model
predictions. In the VDD model we include the presumed effects of possible tidal
influence from faint binary companions. Results. For 5 out of 6 studied stars,
the observed SED shows strong signs of SED turndown between far-IR and radio
wavelengths. A VDD model that extends to large distances closely reproduces the
observed SEDs up to far IR wavelengths, but fails to reproduce the radio SED.
... (abstract continues but did not fit here)Comment: 20 pages, 8 figure
Covariant conservation of energy momentum in modified gravities
An explicit proof of the vanishing of the covariant divergence of the
energy-momentum tensor in modified theories of gravity is presented. The
gravitational action is written in arbitrary dimensions and allowed to depend
nonlinearly on the curvature scalar and its couplings with a scalar field. Also
the case of a function of the curvature scalar multiplying a matter Lagrangian
is considered. The proof is given both in the metric and in the first-order
formalism, i.e. under the Palatini variational principle. It is found that the
covariant conservation of energy-momentum is built-in to the field equations.
This crucial result, called the generalized Bianchi identity, can also be
deduced directly from the covariance of the extended gravitational action.
Furthermore, we demonstrate that in all of these cases, the freely falling
world lines are determined by the field equations alone and turn out to be the
geodesics associated with the metric compatible connection. The independent
connection in the Palatini formulation of these generalized theories does not
have a similar direct physical interpretation. However, in the conformal
Einstein frame a certain bi-metricity emerges into the structure of these
theories. In the light of our interpretation of the independent connection as
an auxiliary variable we can also reconsider some criticisms of the Palatini
formulation originally raised by Buchdahl.Comment: 8 pages. v2: more discussio
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