Environmental Engineering Reference
In-Depth Information
6.7
Schematic illustration of Hub and PoD system (Banks, 2011).
Farm-based digestion was chosen as the best option as most of the
feedstock is generated on the farm and the digestate is spread on its land
area. To minimise risks of the transmission of animal or plant disease the
concept of a Hub and PoD (points of digestion) was developed (Fig. 6.7),
where blending and sanitisation of the urban-generated waste feedstock
takes place before export onto the farms. Although the digesters are located
on farms they do not necessarily have to be operated by farmers, who could
sub-contract this to a single operating company.
The model is based on
.
an average food waste generation rate of 180 kg per household per year
.
dairy cow slurry production of 19.3 tonnes per year
.
recommended farm fertiliser application rates in a nitrogen vulnerable
zone
.
GHG emissions calculated using the IPCC methodology (IPCC, 2006)
.
the values of Kongshaug (1998) for indirect energy use in fertiliser
production
.
biogas yields from co-digestion mixes taken from Banks and Zhang
(2010)
.
farm and herd sizes from the farm business survey (Defra, 2010)
.
population statistics for the region
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