Design of anaerobic plants
The sludge age, 9x,M. is estimated at 20 d by means of Fig 9.3. The sludge concentration is estimated at 8 kg COD/m 3 by means of Table 9.4. From Expression (9.1 0) we
find the sludge production:
Fsp = 01 · X1.1 + 01 · (C1- 8s,3) · Yobs
Here 0 1 = 1.200 m 3 /d
X1 ,1 = 0.2 kg COD/m 3
C1 = 2.7 kg COD/m 3
(9.10)
The effluent concentration of biodegradable organic matter, 8s.3, can be found from
the expression:
8roT,3 = 8s,3 + 81.3
of which 8s,3 = 8ror,3 - 81,3 = 0.3- 0.1 = 0.2 kg COD/m 3 as 81.3 is assumed
to be- 81.1·
The yield constant, Y obs. is in the interval 0.05-0.10 kg COD/kg COD. It is here estimated at 0.08 kg COD/kg COD.
By substituting the now known/estimated values in Expression (9.1 0) we find the sludge production:
Fsp = 1,200 m 3 /d · 0.2 kg COD/m 3 + 1 ,200 m 3 /d (2.7 kg COD/m 3 0.2 kg COD/m 3 ) ·
0.08 kg COD/kg COD = 480 kg COD/d
9x,M. Fsp and Xs.M,2 are substituted in (9.4) after which the necessary tank volume, V2,
can be found:
V2 = (20 d · 480 kg COD/d)/(8 kg COD/m 3 ) = 1 ,200m 3
(that is, the hydraulic retention time, e, is 1 d)
If the whole sludge production leaves the plant together with the treated water, the
concentration of suspended COD, Xcoo,3 , is as follows:
Xcoo,3 = Fsp /01 = (480 kg COD/d) /(1 ,200m 3 /d) = 0.4 kg COD/m 3
The total effluent concentration, Ccoo.3 , is:
CcoD,3 = 8coD,3 + XcoD,3 = 0.3 + 0.4 = 0.7 kg COD/m 3
9.3.2 Design of anaerobic filter plants
The basis for the design of anaerobic filter plants is more uncertain than the design
basis for the plants with suspended sludge. The filter plants can be designed on the
basis of:
- volumetric load (Expression (9.8))
-sludge load (Expression (9.9))
- sludge specific removal rate, rv,x
300