Agriculture Reference
In-Depth Information
liquid stream to oils and char for separation and
use as a fuel). The fuels that are products of
pyrolysis and gasification can be used in boilers
and engines. By-products from pyrolysis, such
as biochar, are also being investigated as a soil
amendment for C storage. Cost estimates for
these technologies vary widely and do not
always include the costs of pretreatment, dry-
ing and fuel preparation, or post-treatment, gas
clean-up, electrical generation, and emissions
controls. In general, it appears the value of the
heat and energy alone does not provide suffi-
cient financial incentive for a thermochemical
conversion facility. Additional income streams
that might make the technology more economi-
cally appealing do not currently exist but could
include a combination of tipping fees collected
for accepting manure solids, renewable power
production tax incentives and the recovery of
value from the ash. Liquid manures can also be
used in thermochemical conversion to produce
energy via direct liquefaction, aqueous-phase
gasification and combined pyrolysis/gasification
(Cantrell
et al
., 2007).
of human pathogens, which could restrict
the use of vermicompost as an organic fertilizer
(Aira
et al
., 2011). To circumvent this problem,
thermophilic composting as a pretreatment to
vermicomposting is also being used to reduce
pathogens. Mupondi
et al
. (2011) reported that a
pre-composting period of 1 week was found to be
ideal for the effective vermicomposting of dairy
manure.
In order to increase the bulk density, nutri-
ent density and particle size uniformity of
manures there has been interest in
pelletization
.
By pelletizing manures, a more nutrient-dense
product is available for transport, thereby ena-
bling a larger land area to be utilized for land
application (Hammac
et al
., 2007). Pelletization
of manures can be done with dry manures such
as poultry litter or liquid manures with the addi-
tion of dry substances (Heinze, 1989). In 2001,
the world's largest pelletization plant, Perdue-
AgriRecycle Poultry Manure Pelletization Plant,
was opened on the Delmarva Peninsula to pro-
cess 95,000 t of manure a year. This was a joint
effort between Perdue, one of the largest US
poultry producers, and the State of Delaware to
help address regional nutrient accumulation
issues. The product produced in the pelletization
process is shipped around the world for use as
fertilizer and fish feed. In Ireland, technology
was developed to blend composted biodegrad-
able farm wastes such as pig manure, spent
mushroom compost and poultry litter with
dried blood or feather meal with mineral sup-
plements, which was then pelletized to produce
an organo-fertilizer with specific N:P:K target
ratios that was pathogen free (Rao
et al.
, 2007).
These designer organo-fertilizers are one way
to add additional nutrient value to manure and
increase their marketability.
Solid manures can also be used for
thermo-
chemical conversion
to produce biogas. Tech-
nologies that burn manure to produce energy or
treat manure to produce fuels are classified as
'thermochemical conversion', and include direct
combustion (burning with excess air to produce
heat), pyrolysis (thermal treatment in the
absence of air, resulting in the production of
pyrolysis oil and a low-BTU gas), gasification
(thermal treatment at higher temperatures in an
oxygen-restricted environment to produce a
low- to medium-BTU gas) and hydrothermal
liquefaction (thermal conversion of solids in a
Slurry and liquid manure systems
Livestock production facilities that house ani-
mals in confinement buildings typically generate
large amounts of both slurry and liquid manure.
In many cases, slurry and liquid manure
undergoes some form of
solid-liquid separation
(removal of organic and inorganic matter) prior
to storage. Objectives for removing solids include
removal of nutrients for transport off-site,
removal of larger particles to make liquid trans-
fer more efficient, and removal of organic mate-
rial to reduce volatile emissions. Separation
efficiency depends on the particle size distribu-
tion in the influent, the characteristics of the
treatment technology and the treatment time.
Separation devices can utilize gravity flow, have
few moving parts and require little management
effort, or they can utilize pumps and motors
and require intensive management. Mechani-
cal separators include: stationary inclined
screen; vibrating screen; rotating flighted cylin-
der; rotating cone; piston; liquid cyclone; and
roller, belt, screw or filter presses. Gravity sepa-
rators include settling basins, ponds and weep-
ing walls.
