Mass balances, denitrifying treatment plants
hydraulic load:
0 11,4 m/h
3
(g/m3) 112 c112
~ 14,4 . .
g/(m . h) rv
6
e 17,2
240
• 23,2
• 27,3
180
4
3 1/2 ·1
k 112 v = 51 (g/m )
h
120
2
60
s
.___ ___ ..._ __ __,...,__....,. e
h
0.1
0.2
5
10
15
20 25 g/m 3
0
Fig7.3
Example of a lullforder reaction. The filter consists of3-5 mm gravel covered by biomass
which reduces nitrate to atmospheric nitrogen. Temperature 1 ?"C. /5/.
hence a parabola with its top point at the zero point.
The figure to the left shows the measured profiles down through the filter which
gives a straight line for the square root of the concentration plotted as a function of
the retention time derived from Expressions (5.37) and (5.42):
It clearly appears from the figure that it is a half order reaction.
The points fall on the same line for different hydraulic loads. This proves that it is
not hydraulic film diffusion; that is, the diffusion to the biofilm is not limiting for the
process in comparison with the diffusion in the biofilm. More detailed information
about the experiment is found in I 41 and I 5 I.
236
Example 7.2
In the biofilter, from which the data shown in Fig 7.3 are derived, the thickness of the
biofilm is estimated at L = 200 j..lm. The specific surface has been found to be w =
1000 m 2 /m 3 • The diffusion coefficient for nitrate is set at 0.7 · 1o-4m 2 /d. How big
should the nitrate concentration be to obtain full penetration?
31,/.
k%V,N03 = 51 (g/m ) 2 /h
1.2 · 10 3 g N03-N%m-%d- 1