Design of anaerobic plants
The temperature is important. Normally the plants are built for an operational
temperature of approx. 35°C (mesophillic}. Thermophilic processes (at 50-60°C} are
seldom used whereas plants with lower temperatures (15-25°C} are sometimes
used.
9 .3.1 Design of plants with suspended sludge
These plants are normally designed based on the COD volumetric load, the COD
sludge load, or the sludge age.
Design based on the volumetric load
The volumetric load, Bv,coo is defined as follows (symbols from Fig 9.1):
(9.7)
from which the necessary tank volume, V'lJ can be found:
(9.8)
Notice that Ccoo,1is biodegradable COD.
The volumetric load varies with the type of plant as shown in Table 9.3. The
geometric data of the plants and the technical details are given in Table 9.4.
Plant type
Volumetric load
kg COD/(m 3 ·d)
15-25°C
30-35°C
50-60°C
Contact plant
0.5-2
2-6
3-9
Sludge blanket plant
1-3
3-10
5-15
Fixed filter
1-3
3-10
5-15
Rotating disc
1-3
3-10
5-15
Fluidized filter
1-4
4-12
6-18
Expanded filter
1-4
4-12
6-18
Table 9.3
Volumetric load (biodegradable COD) for anaerobic plants at different temperatures. Treatment efficiency
for COD: 80-90 per cent.
296
Example 9.2
Design of an anaerobic sludge blanket plant by means of the volumetric load.
1 ,200 m 3 of wastewater/d is to be treated. The content of organic matter in the wastewater is divided into fractions, see Expression (2.4):
S1 = 0.1 kg COD/m 3
Ss = 2.5 kg COD/m 3
X1 = 0.2 kg COD/m 3