Agriculture Reference
In-Depth Information
Figure 3.10
Typical DAF installation (by courtesy of Enisca, Cookstown, Northern Ireland).
(return activated sludge) which settles out at the base of
the clarifier is returned to the reactor vessel to maintain
the critical concentration of biomass. The remainder
(waste activated sludge) is drawn off to be concentrated
and may require further treatment before disposal.
Where sludges are to be applied to land which is fallow
or is to be seed-bed for arable crops, the application is
unlikely to become a problem unless the land is close to
urban development, when odours may cause a nuisance.
Low-trajectory agricultural slurry spreaders can be used.
When sludges are to be applied to grassland, there is a
greater risk of grazing stock ingesting any pathogens
present. In the United Kingdom, a minimum holding
period of 4-6 weeks is required for animal slurries.
However, in some EU member states, a period of 6
months is mandatory. Alternatively, sludge can be
injected into the soil; application rates will vary with soil
type, field capacity and type of crop. Rates in excess of
120 m
3
/ha are most likely to lead to run-off by leaching
or via land drains.
Figure 3.11
Fine bubble diffused air systems (by courtesy of
Enisca, Cookstown, Northern Ireland).
The dissolved organic matter, colloidal residues and
fine solids are oxidised to carbon dioxide and water.
Proteins are broken down into nitrates and sulphates
by a mixed culture of micro-organisms in the reactor.
The major product of the process is new cells (biomass).
The biomass, together with material which has resisted
biodegradation, is separated out from the treated efflu-
ent in settling tanks (clarifiers). The supernatant liquor
from the clarifier is discharged over a weir for disposal or
further treatment, if required. A proportion of sludge
Further reading
Food and Agriculture Organization (FAO) Standard design for small
scale modular slaughterhouses, www.fao.org/docrep/003/t0034e/
T0034E01.htm (accessed on 9 April 2014).
MLC Industry Consulting, Slaughterhouse Design Manual, March
2007.
Recommended Animal Handling Guidelines and Audit Guide, 2007
Edition, American Meat Institute Foundation.
