Table 4.3 lists simplified gas-yield values for cattle and pigs. A more accurate estimate can be
arrived at by combining the gas-yield values from, say, table 3.5 with the correction factors for
digester temperature and retention time shown in figure 5.2.
GYT,RT = mGy x fT,RT
GYT,RT = gas yield as a function of digester temperature and retention time
mGy = average specific gas yield, e.g. 1/kg VS (table 3.5)
fT,RT = multiplier for the gas yield as a function of digester temperature and retention time (cf. fig.
5.2)
As a rule, it is advisable to calculate according to several different methods, since the available
basic data are usually very imprecise, so that a higher degree of sizing certainty can be achieved by
comparing and averaging the results.
Establishing the plant parameters
The degree of safe-sizing certainty can be increased by defining a number of plant parameters:
Specific gas production (Gp)
i.e. the daily gas-generation rate per m³ digester volume (Vd), is calculated according to the
following equation:
Gp = G: Vd (m³ gas/m³ Vd x d)
Digester loading (Ld)
Ld - TS (VS) input/m³ digester volume (kg TS (VS)/m³ Vd x d)
Then, a calculated parameter should be checked against data from comparable plants in the region
or from pertinent literature.
Table 4.3: Simplified gas-yield values for substrate from cattle and pigs (digesting
temperature: 22-27 °C) (Source: OEKOTOP)
Type of housing/
manure
24-h stabling
- dung only
(moist),unpaved
floor (10% losses)
- dung and
urine,concrete
floor
- stable manure
(dung + 2 kg litter),
concrete floor
Cattle, live wt. 200 - 300
kg
manu Gas yield (I/d)
re
yield
(kg/d) RT=60 RT=80
9-13
300-
450
20-30 350-
510
22-32 450-
630
350-500
450-610
530-730
Buffalo, live wt. 300 -
450 kg
manu Gas yield
re (I/d)
yield
(kg/d) RT=60 RRT
=80
14-18 450-
540
300-
620
30-40 450-
600
5440-
710
32-42 550-
740
630-
890
Pigs, live wt 50 - 60 kg
man
ure
yield
(kg/d
)
Gas yield (l/d)
RT=40 RT=60
--
-
2.5- 120-
3.0 140
--
150-180
-
34