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GUIDE DE L’UTILISATEUR
CODE 80158.02
REV 0 02/10/09
(Sous réserve de modification)
Pag.: 26
Introduction
The most common methods in or-
der to estimate the organic con-
tamination are based on the global
determination of oxidizable mate-
ria existing in the water and that
are liable to oxide from the oxygen
of the medium, since the methods
that determine each of organic sub-
stances are complicated. The
methods of global test of organic
materia contaminated used cur-
rently are as follows:
- The chemical request of oxygen
(C.O.D.). Measure of the oxidizable
m ateria
by
the
potassic
dychromatic in an acid medium.
- The biological request of oxygen
(DBO). Measure of the organic ma-
teria biodegradable.
Some times, the limit of contami-
nation is determinated through the
expression: (DBO+C.O.D.) /2.
Overview:
The chemical request of oxygen,
C.O.D., can be considerated like a
measure approximativ e of the
theorical request of oxygen, that is
the quantity of oxygen consumed
by the whole oxidation of the
organical constituents to inorganic
products. The C.O.D.. is defined
like the quantity of oxygen that is
equivalent to the dychromat con-
sumed by the dissolved materia
and in suspension, when the sam-
ple is treated by the above oxidant
in the defined conditions.
Target and field of application:
Determination of the C.O.D. for
residual waters with value higher
than 30 mg/l and less than
700mg/l (without dissolution )
This method can be applied to
waters that after being dissolved
contain more than 2000 mg/l of
chlorure ions, like the water of sea
and brackish waters.
Description of the method:
Most of the organical materia is
oxidizable by the effect of a hot
mixture of dychromat and sulfure.
Take the mixture and put back flow
together with the acid solution with
an overrun of the chrome salt
.
After making the digestion, tritate
the overrun with an iron amonium
sulphate (FAS), that allows to know
the oxidizable organical materia,
calculated in terms of oxygen
equivalent (mg O /l).
This relation is of 1.5 mol of oxygen
by each one of dychromat.
Reagents:
Sulphuric acid 4 mol/l: to add to 500
ml. of water, 220 of sulphuric acid .
Let cool down and dilute until 1000
ml.
Sulphuric acid - silver acid: Add 10
g of silver sulphate to 35 ml of
water. Add 965 ml. of sulphuric acid.
Let lie 1 or 2 days in order to be
dissolv ed. You can help the
dissolution shaking it.
Iron sulphate (II ) and of amonium
(FAS),
titrated
solution,
(NH
4
)
2
Fe(SO
4
)
2
.6H
2
O 0.12 mol/l
Dissolve 47 g of FAS in water. Add
20 ml. of sulphuric acid (r= 1.84 g/
ml), Let cool down and dissolve with
water until 1000 ml.
This solution has to be contrasted
each day as follows:
- Dilue 10 ml of patron solution of
potasic dichromat until 100 ml. with
sulfuric acid 4 mol/l.
DQO-01 DETERMINATION OF CHEMICAL REQUEST OF OXYGEN (C.O.D.)
The solution of iron sulphate (II) and
amonium is titred, at the presence
of 2 or 3 drops of ferroine as
indicator.
The concentration c, expressed in
moles by liter of the iron sulphate
solution (II) and of amonium, is
obtained by the follow formule:
4. Potasic dichromat, standard
solution K
2
Cr
2
O
7
0.040 mol/l that
contains a mercury salt (II): to
dissolve 80 g. of mercury sulphate
(II) (HgSO
4
) into 800 ml of water.
Carefully add 100 ml. of sulphuric
acid (r=1.84 g/ml). Let cool down
and dissolve into the solution
11.768 g of potasic dichromat,
previously let dry at 105ºC during 2
hours. Transfer the solution to a
gauged balloon flask and dilute until
1000 ml.
The solution is stable during at
least 1 month.
Potassium Hydrogen Phthalate,
standard patron. Dilute 0.4251 g
previously dried at 105ºC, in the
water and fill until 1000 ml with
water.
The solution has a theorical value
of COD of 500 mg/l. This solution
remains stable at least one week if
it is conserved at 4ºC.
Ferroine, indicated solution: 0.7 g
of iron sulphate are dissolved (II)
heptahydratated FeSO
4
. 7H
2
O on
water. Add 1.5 g. of fenantroine -
1,10 monohydratated and it is
shaked until its dissolution. Then
dilute until 100 ml.
Balloons regulaters of ebullition Ø
3 mm.
C
FAS
=
0.04 M x 6 x 10 ml
=
2.4
V
FAS
x 1 V
FAS
CET ESSAI DEMANDE LA MANIPULATION DE SUBSTANCES DANGEREUSES
MANIPULATION OF CORROSIVE PRODUCTS IS REQUIRED
