Design of anaerobic plants
Organic matter in wastewater dominated
Removal rate
by:
rx,M, kg COD(S}/(kg COD(B) d)
15-25°C
30-35°C
50-60°C
Acetic acid
0.7-1.5
2.5-5
3.5-7.5
Dissolved, easily degradable matter
0.3-0.7
1.2-2.5
1.5-3
Suspended slowly degradable matter
0.05-0.15
0.25-0.5
0.5-1.0
Table 9.7
Sludge specific removal rate, rx,M, anaerobic plants.
Example 9.4
The design of a fixed anaerobic filter for the treatment of the wastewater used in Examples 9.2 and 9.3. The effluent concentration is assumed to correspond to that in Example 9.3. The volume of the filter is found from Expression (9.14):
V2 = 01 · (C1 - Ss.3)/(rx,M · X2)
From Example 9.3 we have:
0 1 = 1 ,200 m 3 /d
C1 = 2.7 kg COD/m 3
Ss,3 = 0.2 kg COD/m 3
(9.14)
The sludge specific removal rate is estimated at 0.5 kg COD/(kg COD · d) from Table
9.7, and the sludge concentration, X2, is estimated at 10 kg COD/m 3 from Table 9.4.
By substitution into Expression (9.14) we find:
V2 = (1 ,200m 3 /d) · ((2.7- 0.2) kg COD/m 3 ) /(0.5 kg COD/(kg COD· d) · 10 kg COD/m 3 )
V2 =600m 3
The specific filter area is estimated at 100 m 2 /m 3 from Table 9.4. Hence the total area
is:
A2· = V2 · oo =600m 3 · 100 m 2 /m 3 = 60,000 m 2
(which, as previously mentioned, (only) has an academic interest for the time being,
but as this book is written for scientifically oriented persons, it is of course of interest to
the reader).
9.3.3 Gas production, anaerobic processes
In connection with the anaerobic removal, gases are produced, including:
-methane
- carbon dioxide
-hydrogen
- hydrogen sulphide
- free nitrogen
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