Anaerobic Wastewater Treatment
The sludge age, Ox,M is found from Fig 9.3, the sludge concentration, XB,M,2t is a
plant parameter which can be chosen/estimated by using Table 9.4 within an
interval of 5-15 kg VSS/m 3 (7-20 kg COD/m~ whereas the sludge production, Fsp,
is to be calculated/ estimated, see below.
The sludge production can be calculated from the following expression:
Fsp = suspended inert organic matter in wastewater + sludge production from the
biological process
Using the symbols from Fig 9.2 we have:
Fsp = Ot ·Xu+ Ot · (Ct- Ss,3) · Yobs
where Ss,3 is dissolved biodegradable organic matter in the effluent,
Ct is biodegradable organic matter in the influent.
(9.10)
The overall yield constant, Yobs- varies in the interval 0.05-0.10 kg COD/kg COD,
see Chapter 3, Section 3.7.2.
Sludge separation technique
Hydraulic surface load
m 3 water/(m 2 tank· h)
Sludge surface load
kg SS/(m 2 tank· h)
Settling, traditional
0.5-1.0
2-4
Lamella sedimentation
1.0-2.0
3-6
Gas/sludge separator, sludge
0.5-1.0
-
blanket plant
Fluidized filter, top of tank
0.5-1.0
2-4
Hyper-filtration
0.005-0.040.
-
m 3 water/(m 2 membrane· h)
Table9.6
Typical data for sludge separation plants, among others based on /5/,/6/. The figures are based on the
average hourly flow rate, Qh,av·
Design of sludge separation
Sludge separation is designed on the basis of the hydraulic surface load and the
sludge surface load. Table 9.6lists the loads for a number of separation techniques
used in anaerobic plants.
Example 9.3
Design of anaerobic contact plants by using of the sludge age.
The wastewater from Example 9.2 is going to be treated in an anaerobic contact plant.
The effluent concentration of dissolved COD is assumed to be 0.3 kg/m 3 .
The necessary tank volume, V2, can be found by using Expression (9.4):
v2 = 9x,M. Fsp/Xs,M,2
(9.4)
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