49 research outputs found
Effect of the pig slurry separation techniques on the characteristics and potential availability of N to plants in the resulting liquid and solid fractions
Solid-liquid separation of slurry is used to obtain a solid (SF) and liquid fraction (LF), both
used as organic fertilisers. Previous works showed that the separation technique used
influences the composition of the resulting SF but no data are available relative to the LF.
Four commonly used separation processes were considered e centrifugation, sieving,
enhanced settling by the addition of cationic polyacrylamide (PAM-), and sediment settling
as well as a recent sequential process e sieving followed by PAM addition to the resulting
LF. The resulting LFs and SFs were comprehensively characterised and the amount of N
potentially available for plants after incorporation to soil was also evaluated. Except for
slurry that was only sieved which was very similar in composition to whole slurry (WS), the
SFs and LFs had, respectively, higher and lower, concentrations of nutrients and organic
matter (OM) than the WS. The ratio of ammoniacal to total N in the LFs varied from 0.33 to
0.92 whereas the values in the SFs varied between 0.16 and 0.31. The N:P:K ratio was also
significantly influenced by the separation technique. Less than 10% of the total N applied in
the WS, SFs or LFs was found to be potentially available for plants and, in some LFs, N
immobilisation occurred after soil application. Since separation technique strongly influences
nutrient distribution between LF and SF, as well as N speciation, the choice of the
technique has to consider the final use of the resulting fractions as well as acquisition and
operating costs
Assessment of CO2 emissions during acidification, storage and after incorporation to soil of pig slurry
RAMIRAN International ConferenceLarge amounts of pig slurry are produced each year in Portugal leading to environmental problems such as water
and air pollution. Previous studies have reported that livestock production is the main source of anthropogenic
ammonia (NH3) emissions in Europe (Kai et al., 2008) and an important source of greenhouse gases (Weiske and
Petersen, 2006). Effluent treatment has been promoted to improve slurry management and to reduce its
environmental impact (Sommer and Hutchings, 2001, Fangueiro et al., 2008a). Solid-liquid separation of slurry is a
useful tool at the farm level producing valuable fractions, a liquid that can be used for direct fertilisation and a solid
fraction that can be composted (Fangueiro et al., 2008b). Alternatively, acidification of slurry has been proposed to
reduce ammonia (NH3) emissions during storage and field application (Kai et al., 2008). Previous works
(Misselbrook et al., 2005; Fangueiro et al., 2008a) reported that higher NH3 emissions occurred during storage of
liquid fraction of slurry or manure with low dry matter content, probably due to a reduced crust formation that
decreases NH3 emissions. Hence, acidification of the liquid fraction of slurry is strongly recommended. Slurry
acidification is common practice in The Netherlands and Denmark (Schils et al., 1999; Eriksen et al., 2008) but this
technology still needs to be improved to avoid hazards. It is expected that this technology will be used in more
countries since the European Directive (2001/81/CE) demands a decrease of atmospheric pollutants such as NH3:
targets for lower NH3 emissions have been already set in Spain (Castrillon et al., 2009). Nevertheless, the
acidification process leads to significant carbon dioxide (CO2) emissions (Vandré and Clemens, 1997). Such CO2
release is problematic when a closed system of slurry acidification is used (when acidified slurry is flushed back to
pig houses) since it may lead to foam formation (Vandré and Clemens, 1997; Borst, 2001). Nevertheless, Fangueiro
et al. (2010) reported that acidification of slurry or derived fractions led to a decrease in CO2 emissions following
soil addition relative to non acidified materials.
The aim of the present work was to measure the CO2 emissions during the acidification process of the
liquid fraction of pig slurry and its subsequent impact during storage and after soil incorporation
Impact of cattle slurry treatment by separation and acidification on gaseous emissions after soil application
Objectives: Cattle-slurry management became a priority in many livestock farms and slurry treatment is used
to increase the fertilizer value of slurry and/or minimize its environmental impact. Indeed, significant
emissions of ammonia (NH3) and greenhouse gases (GHG) as nitrous oxide (N2O), carbon
dioxide (CO2) and methane (CH4) can occur during and after slurry application to soil. Application
of acidified slurry or liquid fraction (LF) obtained by solid-liquid separation are two alternatives to
raw slurry application that have proven to be efficient to minimize ammonia emissions. However,
few is known about its effect on GHG emissions.
The aim of the present work was to assess the efficiency of cattle slurry treatment by acidification
and/or solid liquid separation to mitigate ammonia (NH3) and greenhouse gases (GHG) emissions
following surface application to a sandy loam soil
Tidal Venuses: Triggering a Climate Catastrophe via Tidal Heating
Traditionally stellar radiation has been the only heat source considered
capable of determining global climate on long timescales. Here we show that
terrestrial exoplanets orbiting low-mass stars may be tidally heated at high
enough levels to induce a runaway greenhouse for a long enough duration for all
the hydrogen to escape. Without hydrogen, the planet no longer has water and
cannot support life. We call these planets "Tidal Venuses," and the phenomenon
a "tidal greenhouse." Tidal effects also circularize the orbit, which decreases
tidal heating. Hence, some planets may form with large eccentricity, with its
accompanying large tidal heating, and lose their water, but eventually settle
into nearly circular orbits (i.e. with negligible tidal heating) in the
habitable zone (HZ). However, these planets are not habitable as past tidal
heating desiccated them, and hence should not be ranked highly for detailed
follow-up observations aimed at detecting biosignatures. Planets orbiting stars
with masses <0.3 solar masses may be in danger of desiccation via tidal
heating. We apply these concepts to Gl 667C c, a ~4.5 Earth-mass planet
orbiting a 0.3 solar mass star at 0.12 AU. We find that it probably did not
lose its water via tidal heating as orbital stability is unlikely for the high
eccentricities required for the tidal greenhouse. As the inner edge of the HZ
is defined by the onset of a runaway or moist greenhouse powered by radiation,
our results represent a fundamental revision to the HZ for non-circular orbits.
In the appendices we review a) the moist and runaway greenhouses, b) hydrogen
escape, c) stellar mass-radius and mass-luminosity relations, d) terrestrial
planet mass-radius relations, and e) linear tidal theories. [abridged]Comment: 59 pages, 11 figures, accepted to Astrobiology. New version includes
an appendix on the water loss timescal
Wave Number of Maximal Growth in Viscous Magnetic Fluids of Arbitrary Depth
An analytical method within the frame of linear stability theory is presented
for the normal field instability in magnetic fluids. It allows to calculate the
maximal growth rate and the corresponding wave number for any combination of
thickness and viscosity of the fluid. Applying this method to magnetic fluids
of finite depth, these results are quantitatively compared to the wave number
of the transient pattern observed experimentally after a jump--like increase of
the field. The wave number grows linearly with increasing induction where the
theoretical and the experimental data agree well. Thereby a long-standing
controversy about the behaviour of the wave number above the critical magnetic
field is tackled.Comment: 19 pages, 15 figures, RevTex; revised version with a new figure and
references added. submitted to Phys Rev
Tidal torques. A critical review of some techniques
We point out that the MacDonald formula for body-tide torques is valid only
in the zeroth order of e/Q, while its time-average is valid in the first order.
So the formula cannot be used for analysis in higher orders of e/Q. This
necessitates corrections in the theory of tidal despinning and libration
damping.
We prove that when the inclination is low and phase lags are linear in
frequency, the Kaula series is equivalent to a corrected version of the
MacDonald method. The correction to MacDonald's approach would be to set the
phase lag of the integral bulge proportional to the instantaneous frequency.
The equivalence of descriptions gets violated by a nonlinear
frequency-dependence of the lag.
We explain that both the MacDonald- and Darwin-torque-based derivations of
the popular formula for the tidal despinning rate are limited to low
inclinations and to the phase lags being linear in frequency. The
Darwin-torque-based derivation, though, is general enough to accommodate both a
finite inclination and the actual rheology.
Although rheologies with Q scaling as the frequency to a positive power make
the torque diverge at a zero frequency, this reveals not the impossible nature
of the rheology, but a flaw in mathematics, i.e., a common misassumption that
damping merely provides lags to the terms of the Fourier series for the tidal
potential. A hydrodynamical treatment (Darwin 1879) had demonstrated that the
magnitudes of the terms, too, get changed. Reinstating of this detail tames the
infinities and rehabilitates the "impossible" scaling law (which happens to be
the actual law the terrestrial planets obey at low frequencies).Comment: arXiv admin note: sections 4 and 9 of this paper contain substantial
text overlap with arXiv:0712.105
Habitable Climates: The Influence of Obliquity
Extrasolar terrestrial planets with the potential to host life might have
large obliquities or be subject to strong obliquity variations. We revisit the
habitability of oblique planets with an energy balance climate model (EBM)
allowing for dynamical transitions to ice-covered snowball states as a result
of ice-albedo feedback. Despite the great simplicity of our EBM, it captures
reasonably well the seasonal cycle of global energetic fluxes at Earth's
surface. It also performs satisfactorily against a full-physics climate model
of a highly oblique Earth-like planet, in an unusual regime of circulation
dominated by heat transport from the poles to the equator. Climates on oblique
terrestrial planets can violate global radiative balance through much of their
seasonal cycle, which limits the usefulness of simple radiative equilibrium
arguments. High obliquity planets have severe climates, with large amplitude
seasonal variations, but they are not necessarily more prone to global snowball
transitions than low obliquity planets. We find that terrestrial planets with
massive CO2 atmospheres, typically expected in the outer regions of habitable
zones, can also be subject to such dynamical snowball transitions. Some of the
snowball climates investigated for CO2-rich atmospheres experience partial
atmospheric collapse. Since long-term CO2 atmospheric build-up acts as a
climatic thermostat for habitable planets, partial CO2 collapse could limit the
habitability of such planets. A terrestrial planet's habitability may thus
depend sensitively on its short-term climatic stability.Comment: Minor changes, references added. 34 pages, 13 figures, accepted by
Ap
Effect of the stellar spin history on the tidal evolution of close-in planets
We investigate how the evolution of the stellar spin rate affects, and is
affected by, planets in close orbits, via star-planet tidal interactions. To do
this, we used a standard equilibrium tidal model to compute the orbital
evolution of single planets orbiting both Sun-like stars and 0.1 M\odot
M-dwarfs. We tested two stellar spin evolution profiles, one with fast initial
rotation (P=1.2 day) and one with slow initial rotation (P=8 day). We tested
the effect of varying the stellar and planetary dissipation and the planet's
mass and initial orbital radius. Conclusions: Tidal evolution allows to
differentiate the early behaviors of extremely close-in planets orbiting either
a rapidly rotating star or a slowly rotating star. The early spin-up of the
star allows the close-in planets around fast rotators to survive the early
evolution. For planets around M-dwarfs, surviving the early evolution means
surviving on Gyr timescales whereas for Sun-like stars the spin-down brings
about late mergers of Jupiter planets. In light of this study, we can say that
differentiating between one spin evolution from another given the present
position of planets can be very tricky. Unless we can observe some markers of
former evolution it is nearly impossible to distinguish the two very different
spin profiles, let alone intermediate spin profiles. Though some conclusions
can still be drawn from statistical distributions of planets around fully
convective M-dwarfs. However, if the tidal evolution brings about a merger late
in its history it can also entail a noticeable acceleration of the star in late
ages, so that it is possible to have old stars that spin rapidly. This raises
the question of better constraining the age of stars
Parametric Forcing of Waves with Non-Monotonic Dispersion Relation: Domain Structures in Ferrofluids?
Surface waves on ferrofluids exposed to a dc-magnetic field exhibit a
non-monotonic dispersion relation. The effect of a parametric driving on such
waves is studied within suitable coupled Ginzburg-Landau equations. Due to the
non-monotonicity the neutral curve for the excitation of standing waves can
have up to three minima. The stability of the waves with respect to long-wave
perturbations is determined a phase-diffusion equation. It shows that the
band of stable wave numbers can split up into two or three sub-bands. The
resulting competition between the wave numbers corresponding to the respective
sub-bands leads quite naturally to patterns consisting of multiple domains of
standing waves which differ in their wave number. The coarsening dynamics of
such domain structures is addressed.Comment: 23 pages, 6 postscript figures, composed using RevTeX. Submitted to
PR
The role of chaotic resonances in the solar system
Our understanding of the Solar System has been revolutionized over the past
decade by the finding that the orbits of the planets are inherently chaotic. In
extreme cases, chaotic motions can change the relative positions of the planets
around stars, and even eject a planet from a system. Moreover, the spin axis of
a planet-Earth's spin axis regulates our seasons-may evolve chaotically, with
adverse effects on the climates of otherwise biologically interesting planets.
Some of the recently discovered extrasolar planetary systems contain multiple
planets, and it is likely that some of these are chaotic as well.Comment: 28 pages, 9 figure