The relative effect of the different manure removal
strategies was modeled in scenarios with significantly higher and
lower base methane emission. Multiple barn and outside storage simulations
were run by applying the optimized ABM parameter set and varying the
hydrolysis rate (αopt) and substrate conversion rate
of methanogens (qmax,opt) to force various
levels of base methane emission levels. The two parameter values spanned
from 20 to 500% of the optimized parameter values, covering reported
methane emission levels in pig houses (Supporting Information,Table S3 ). Input variables and parameters for
barn simulations were similar to those described for model validation
(but with changes in αopt and qmax,opt). When calculating averaged methane emission on a yearly
basis, predicted emissions between the batch periods (7 days) were
included. The slurry mass effluents and slurry effluent concentrations
of degradable VS and methanogens from the barn simulations were used
as the input for outside storage simulations. The slurry temperature
was altered in monthly intervals according to Danish weather conditions
(Supporting Information,Table S4 ). In
the storage simulations, the slurry was completely removed once a
year in March and 10% of the slurry was removed for field application
in September. The enrichment factor (resid_enrich) was set to zero
due to assumed vigorous agitation of the slurry tank before field
application. The simulated storage was scaled to fit the slurry from
30 pigs by setting the surface area to 20 m2, thereby achieving
an average slurry height of ca. 2 m over a 1 year simulation. The
pH in the storage was set to 7 for all treatments (slightly higher
than in-barn slurry pH) as pH tends to increase slightly during storage.32 (link) Predicted methane emission was normalized to
slurry volume to correct for differences in slurry production between
the sections.
strategies was modeled in scenarios with significantly higher and
lower base methane emission. Multiple barn and outside storage simulations
were run by applying the optimized ABM parameter set and varying the
hydrolysis rate (αopt) and substrate conversion rate
of methanogens (qmax,opt) to force various
levels of base methane emission levels. The two parameter values spanned
from 20 to 500% of the optimized parameter values, covering reported
methane emission levels in pig houses (Supporting Information,
barn simulations were similar to those described for model validation
(but with changes in αopt and qmax,opt). When calculating averaged methane emission on a yearly
basis, predicted emissions between the batch periods (7 days) were
included. The slurry mass effluents and slurry effluent concentrations
of degradable VS and methanogens from the barn simulations were used
as the input for outside storage simulations. The slurry temperature
was altered in monthly intervals according to Danish weather conditions
(Supporting Information,
the storage simulations, the slurry was completely removed once a
year in March and 10% of the slurry was removed for field application
in September. The enrichment factor (resid_enrich) was set to zero
due to assumed vigorous agitation of the slurry tank before field
application. The simulated storage was scaled to fit the slurry from
30 pigs by setting the surface area to 20 m2, thereby achieving
an average slurry height of ca. 2 m over a 1 year simulation. The
pH in the storage was set to 7 for all treatments (slightly higher
than in-barn slurry pH) as pH tends to increase slightly during storage.32 (link) Predicted methane emission was normalized to
slurry volume to correct for differences in slurry production between
the sections.
