Environmental Engineering Reference
In-Depth Information
Table 5.2 Methane yields for selected crops
Crop
Yield(l) CH
4
/kg VS
Maize (whole crop)
205-450
Wheat (grain)
384-426
Grass
298-467
Clover
300-350
Oilseed rape
240-340
Potatoes
276-400
Fodder beet
420-500
Source: Murphy et al. (2011)
Table 5.3 Solubility of some relevant gases in water
(millilitres of gas reduced to 0
o
C and 760mmHg per litre of
water when the partial pressure is 760mmHg)
Temperature (
o
C)
0
10
20
30
CH
4
55.6
41.8
33.1
27.6
N
2
23
18.5
15.5
13.6
O
2
49.3
38.4
33.4
26.7
CO
2
1710
1190
878
665
solubility difference between methane and carbon dioxide is utilised in gas
upgrading.
Anaerobic digestion usually takes place within three temperature ranges
.
thermophilic, 55-60
8
C
.
mesophilic, 35-40
8
C
.
psychrophilic,
<
20
8
C
In the mesophilic range, gas production decreases at 43
8
C and inhibition
sets in. Similar occurrences take place at 63
C in the thermophilic range
(Pfeffer, 1979). It is recommended (WPCF, 1987) that fluctuations of 1
8
Cor
greater do not occur in digesters as this has an unsettling effect on the
microbial community.
8
5.5
Reactor configuration
5.5.1 Types of reactors
The optimal reactor design and configuration is a function of the feedstock
characteristics. The feedstock must be assessed for characteristics, including
DS content, volatility of solids, biodegradability, density, functional specific
gravity (potential to float) and particle size. Reactors may be dry or wet,
batch or continuous, one-step or multi-step and one-phase or multi-phase
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