Environmental Engineering Reference
In-Depth Information
Table 13.1
Composition of selected substrates suitable for digestion
Substrate
Total
solids
(g/kg)
Volatile
solids
(g/kg)
Total N
(g/kg)
Ammonium
nitrogen
(NH 4 + -N)
(g/kg)
Total P
(g/kg)
Animal manures
Liquid dairy manure
110 ± 23 90 ± 21
3.9 ± 0.9
1.7 ± 0.8
0.7 ± 0.3
Poultry broiler manure
452 ± 30 256 ± 25 20.1 ± 3.1 12.5 ± 2.3
1.2 ± 0.4
Swine manure slurry a
N/A b
37
4.0
2.7
1.3
Horse dung
230 ± 28 190 ± 33 1.1 ± 0.3
0.7 ± 0.1
0.4 ± 0.1
Crops
Corn silage c
472 ± 10 445 ± 11 1.8 ± 0.3
0.9 ± 0.1
0.2 ± 0.1
Switchgrass c
461 ± 17 435 ± 14 4.3 ± 1.4 N/A
0.4 ± 0.1
Agri-food industry wastes
Waste grease
228 ± 43 202 ± 45 1.4 ± 0.8
0.3 ± 0.1
0.2 ± 0.1
Grocery food waste
169 ± 35 138 ± 54 1.7 ± 0.7
1.3 ± 0.4
0.3 ± 0.2
Corn thin stillage
(ethanol brewery waste)
108 ± 22 92 ± 19
1.9 ± 0.4
0.1 ± 0.0
0.9 ± 0.5
a OMAFRA (2011).
b Not available.
c Total N, NH 4 + -N and total P concentrations based on air-dried mass of
substrate.
Note: Mean concentrations reported on wet mass basis ± standard deviation
unless stated otherwise.
Source: Data collected by University of Guelph.
Animals are typically inefficient at digesting nutrients from dietary feed
and excrete high proportions of these nutrients, resulting in animal manures
with relatively high proportions of N and P (Van Horn et al., 1996;
Lukehurst et al., 2010). The composition of animal manures is not only
affected by the digestive system (ruminant vs. omnivore) and age of the
animal but also by farm practices (bedding type, washwater volume, manure
storage, etc.). Table 13.1 demonstrates that the N composition in solid
manure (e.g. poultry broiler) can be as much as five times greater than liquid
manure (e.g. liquid dairy). The variability in manure nutrient composition
has a significant influence on the digestion process, thereby influencing the
nutrient content in the digestate.
Co-substrates, which can include crops or agri-food industry wastes, are
added to manure to enhance biogas yields. These co-substrates typically
have much higher organic matter content, measured as volatile solids (VS),
with respect to nutrients. The addition of these co-substrates to manure
drives the C:N ratios of the mixture to optimum digestion values ranging
between 20:1 and 30:1 (Burke, 2001; Gerardi, 2003; Sakar et al., 2009). Some
co-substrates used in manure digestion may introduce heavy metals or other
contaminants that are not biodegraded during digestion. Because these
￿ ￿ ￿ ￿ ￿ ￿
 
Search WWH ::




Custom Search