Treatment Plants for Denitrification
1-lmax,H
rv;s = -y-- · Tlg · Xs,H
max,H
(7.4)
Example 7.1
The wastewater from a German chemical company has a high content of nitrate and a
high content of organic matter which can be utilized for a direct (separate) denitrification.
The following is known about influent and effluent:
Element
In
COD
600
N03-N
50
The wastewater flow is
0 1 = 2,700 m 3 /d
The tank volume for denitrification is
V2 =400m 3
Out
Unit
140
gCOD/m 3
2
g N03-Nim 3
Find the nitrate removal rate, rv,s. when it is assumed to be constant throughout the
plant.
Expression (7.2) is used:
SN03, 1 - SN03,3
rv.s =
e2
The hydraulic retention time, ~. is
e2 = V2/01 = (400 m 3 )/(2,700 m 3 /d) = 0.15 d
substituted together with SNo3, 1 and SNoo.3 we have
(50- 2) g N03 -N/m 3
_
3
rv,s =
0 _ 15 d
= 320 g N03 -N/(m . d)
Biofilters
A nitrate balance for the plant in Fig 7.1b looks as follows:
(7.5)
where rA,N03 is the nitrate removal rate of the biofilm per unit area as carrier
material.
For a denitrifying biofilter, either the organic matter or the nitrate is potentially
limiting for the removal. What is limiting is determined by the ratio between the
concentrations and the diffusion coefficient for the materials in the biofilm, see
Expression (5.32). If the organic matter is easily degradable (that is, if it can diffuse
into the biofilm) and the process in the biofilm is a zero order, the following applies:
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