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Lecture II.01 Dissolved Oxygen

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ENVIRONMENTAL
CHEMISTRY
II
IMPORTANT REMINDERS
Grading:
g
Midterm exam 1
Midterm exam 2
Laboratory Experiments
Final exam
% in Total
20
20
20
40
Grade DC will be assigned to mark 40 (out of 100)
ATTENDANCE
At least 70 % attendance is mandatory
y to the class course.
At least 80% attendance is mandatory to the laboratory exercises
If you have an excuse, you should submit it IN ADVANCE
Any axcuse submitted at the end of the semester wil NOT be accepted
RESOURCES
Lecture Book
L
B k in
i English:
E li h
 Chemistry for Environmental Engineering and Science. 5th ed.
 C.N.
C N Sawyer
Sawyer, P.L:
P L: McCarty and G
G.F.
F Parkin,
Parkin McGraw Hill

Lecture Book in Turkish
 ÇEVRE MÜHENDİSLİĞİ ve BİLİMİ için KİMYA (E: İsmail Toröz)
 NOBEL AKADEMİK YAYINCILIK
(http://nobelyayin com/detay asp?u=3714)
(http://nobelyayin.com/detay.asp?u=3714)


Laboratory
y resource:
 Standard Methods for the Examination of Water and Wastewater,
American Public Health Association (APHA)
 Relevant
R l
t sections
ti
off this
thi book
b k will
ill be
b given
i
t you…
to

Course Outline
Week
Topic
1
Organic compounds,
compounds Dissolved Oxygen
2
Biochemical Oxygen Demand (BOD)
3
Chemical Oxygen Demand (COD)
4
Applications of BOD, COD, ThOD, TOC
5-6
5
6
Nitrogen Compounds
7
Phosphorus Compounds
8
Fats, Oil and Grease
9
Midterm Exam 1
10
Surface Active Substances +Phenols
11-13
Chemistry of aerobic and anaerobic degradation (VFA+Gas analyses)
13
Trace pollutants, Heavy metals, Cyanite
14
Midterm Exam 2
15
Chlorine Chemistry
Laboratory Experiments
Week
Experiment
1
No experimental work
2
Dissolved O2 + Biochemical Oxygen Demand (BOD)
3
Biochemical Oxygen Demand (BOD)
4
Chemical Oxygen Demand (COD)
5
NH3 + TKN
6
NO2 + NO3
7
Phosphorus Compounds
8
Fats, Oil and Grease
9
Midterm 1
10
April 23rd: Holiday
11
May 1st: Holiday
12
Surface Active Substances +Phenols
13
VFAs
14
Midterm 2
15
Gas analyses (or Heavy metals)
Organic
g
Contaminants
in the Environment
A

Supplementary Document is provided
for you on the website:
http://www.yarbis.yildiz.edu.tr/saral-Dersler-1853
 You
are supposed to study this document
and you will be responsible for this
document…
Di
Dissolved
l d Oxygen
O
(Aqueous
q
Oxygen
Oxygen)
yg )
O2(aq)
aq)
General

All living organisms are dependent upon oxygen in one
form or another to maintain the metabolic processes
th t produce
that
d
energy for
f growth
th and
d reproduction.
d ti

Aerobic processes are the subject of greatest interest
because of their need for free (dissolved) oxygen.

Humans are vitally
y concerned with the oxygen
yg content
of the air that they breathe, since they know from
experience that an appreciable reduction in oxygen
content will lead to discomfort and possibly death.
General
 Environmental
engineers and scientists
are,, of course,, interested in atmospheric
p
 conditions in relation to humans,
 but,
b t iin addition,
dditi
 tthey
ey are
a e vitally
ta y co
concerned
ce ed with
t
 the "atmospheric conditions" that exist
on/o er liquids,
on/over
liq ids water
ater being the liq
liquid
id in
greatest abundance and importance
General
All the gases of the atmosphere are soluble in water to
some degree.
 Both
B th nitrogen
it
and
d oxygen are classified
l
ifi d as poorly
l
soluble, and since they do not react with water
chemically their solubility is directly proportional to their
chemically,
partial pressures in the atmosphere.
 Hence,
e ce, Henry's
e y s law
a may
ay be used to
o ca
calculate
cu a e the
e
amounts present at saturation at any given temperature.
 The solubility
y of both nitrogen
g and oxygen
yg varies
greatly with the temperature over the range of interest
for natural waters.

General

Th solubility
The
l bilit iis lless iin saline
li waters.
t

Under the partial
partial-pressure
pressure conditions that exist in the
atmosphere, more nitrogen than oxygen dissolves in
water.

The solubility of atmospheric oxygen in fresh waters
ranges from
f
14.6
14 6 mg/L
/L at O°C to about
b
7 rng/L
/L at
35°C under 1 atm of pressure.

Since it is a poorly soluble gas, its solubility varies
directly with the atmospheric pressure at any given
temperature.
 Existence of Oxygen
 In Gas Phase:
in Nature
• F
Found
d att 20.95
20 95 % ((~21%)
21%) by
b volume
l
i the
in
th atmosphere.
t
h
Its partial pressure (sea level) :
PO2 = 0.21
0 21 atm.,
atm or
•
210.000 ppm by volume
• 21 %  210.000 ppm

IIn Liquid
Li id Phase
Ph
(Di
(Dissolved
l d Oxygen):
O
)
In all natural water bodies
It concentration
Its
t ti is
i variable
i bl (depending
(d
di on
conditions)
C diti
Conditions:
T
Temperature,
t
P
Pressure,
other
th conditions
diti
(dissolved matters, salinity etc),
Gas--Liquid Transfer of Oxygen
Gas
Gas--Liquid Reactions
Gas
 Notations
Notations::

Gas phase
: Tr : O2 (g)
Eng : O2 (g)

Liquid phase
: Tr : O2 (s)
Eng : O2 (l)

Liqid
q p
phase (dis
dis.. g
gas)) : Tr : O2 (ç)
gas
•
Solid phase
: Tr: O2 (k)

Eng
g : O2 ((aq
aq)
q)
aq:: aqueous
aq
Eng : O2 (s)
Gas--Liquid
Gas
q
Reactions

Solubility of Gases in Water:

All gases in the atmosphere are soluble in water to some
extent.

Saturation Concentration:


Concentration of a gas in water which is in equilibrium with
the concentration of that gas in the atmosphere
Solubility
S
l bilit in
i water
t depends
d
d on the
th conditions:
diti
 Purity of water (existance of other dissolvde matters)
 Temperature
 Pressure
 Partial prassure of dissolved gas.
Henry’s
Henry
s Law
Henry’s
Henry
s Constants for some gases
Saturation Concentrations
Saturation Concentrations
Temp
C
Dissolved Oxygen Concentration
Concentration,, mg/l
Salinity,, ‰ (~
Salinity
(~ g/L = ~1000mg/L )
0
5
10
15
20
0
14.60
14.11
13.64
13.18
12.74
5
12.76
12.34
11.94
11.56
11.18
10
11.28
10.92
10.58
10.25
9.93
15
10.07
9.77
9.47
9.19
8.91
20
9.08
8.81
8.56
8.31
8.07
25
8.24
8.01
7.79
7.57
7.36
30
7.54
7.33
7.14
6.94
6.75
Salinity concentration: 1 ‰ = ~1 g/L = ~1000 mg/L
Importance
po ta ce o
of Dissolved
sso ed O
Oxygen
yge

An indictor for aerobic or anaerobic conditions
in a water media

An indicator of the life in a water body

A crucial step of BOD test

A indicatro
An
i di t off the
th performnce
f
off aerobic
bi
treatment processes

Causes corrosion in wet media
Importance
po ta ce o
of Dissolved
sso ed O
Oxygen
yge
Need of dissolved oxygen of fishes
Trout (alabalık)
Min. Dis. Oxygen
Need (mg/L)
44-55
Sea bass (levrek)
3-4
Carp (sazan )
2-3
Yayın Balığı
12
1-2
Fish
Special Sampling Conditions and
Sample Preservation for D.O. Test

Sample water should be prevented from
contact with air
air. Sample water should be filled
in container with overflow,

Dissolved oxygen in sample should
immediately
y be fixed byy chemical agents.
g

Sample should be stored in cold and dark
place,
l

Sample should be analyzed in 6 hr after fixation
Çözünmüş
Çö
ü üş O
Oksijen
s je Tayini
ay
Kullanılan Yöntemler
-
Isıtarak toplanan gazdaki oksijenin gaz analiz
yöntemleri ile belirlenmesi
-
Hacimsel Metodlar
-
-
Winkler Metodu ((İyodometrik
İyodometrik
y
Yöntem))
-
Winkler Metodunun Azid Modifikasyonu
-
Winkler Yönteminin Rideal
Rideal--Stewart Modifikasyonu
Çözünmüş Oksijen Membran Elektrodlarının
Kullanımı
Hacimsel Metodlar
Çö ü ü Ok
Çözünmüş
Oksijen
ij T
Tayini
i i
Winkler Yöntemi ((İyodometrik
İyodometrik Yöntem)
veya
y Modifikasyonları
y
-
-
-
Alkali şartlarda Mn+2 iyonu ortamdaki oksijenle
daha yüksek değerliklere oksitlenir
oksitlenir.
Elde edilen yüksek değerlikli manganez, asit
şartlarda I- iyonunu serbest I2’a
a okside eder
eder.
Ortaya çıkan I2 oksijen eşdeğeri kadardır.
Açığa çıkan I2 standart sodyum tiyosülfat ile titre
edilerek çözünmüş oksijen eşdeğeri olarak
hesaplanır.
hesaplanır
Hacimsel Metodlar
Çö ü ü Ok
Çözünmüş
Oksijen
ij T
Tayini
i i
Modifiye Edilmemiş Winkler Yöntemi
-
-
-
Nitrit ve Fe+3 ile pozitif girişim (I-’yi I2’ye
okside ederler)
Fe+2, SO32-, S2- g
gibi iyonlarla
y
negatif
g
girişim (I2’yi I-’ye indirgerler)
Sadece temiz sularda kullanılması
uygundur.
yg
Hacimsel Metodlar
Çözünmüş Oksijen Tayini
Hacimsel Metodlar
Çözünmüş Oksijen Tayini
Modifiye
y Edilmemiş
ş Winkler Yöntemi
MnSO4 ve Alkali İyodür (NaOH + KI) ilave
edildiğinde Çözünmüş Oksijen Varsa
1
Mn 2  2OH   O2 
 MnO2   H 2O
2
veya
1
Mn (OH ) 2  O2 
 MnO2   H 2O
2
Çö ü ü Ok
Çözünmüş
Oksijen
ij Yoksa
Y k
Mn 2  2OH   0  O2 
M

 Mn
M (OH ) 2 
Hacimsel Metodlar
Çözünmüş Oksijen Tayini
Modifiye
y Edilmemiş
ş Winkler Yöntemi
Çökelme tamamlandıktan sonra Sülfirik asit ilavesi
MnO2 + 2I- + 4H+ → Mn2+ + I2 + 2H2O
Hacimsel Metodlar
Çözünmüş Oksijen Tayini
Modifiye
y Edilmemiş
ş Winkler Yöntemi
0,025 N Sodyum Tiyosülfat ile Titrasyon
2 Na
N 2 S2O3  5H 2O  I 2 

 Na
N 2 S4O6  2 NaI
N I  10 H 2O
 S4O62  2 I 
2 S2O32  I 2 
Hacimsel Metodlar
Çö ü ü Ok
Çözünmüş
Oksijen
ij T
Tayini
i i
Kullanılan Tiyosülfat Çözeltisinin Normalitesi
-
Oksijenin Ekivalent Ağırlığı = 8 gram
-
1 ml Tiyosülfat = 1 mg Oksijen eşdeğeri olmalı
-
-
-
Dolayısıyla Tiyosülfatın Normalitesi = N/8 (0,125 N)
olacaktır.
1 Litre numune için 1ml N/8’lik tiyosülfat kullanılırsa
numunenin 1 mg/L oksijene sahip olduğu söylenir.
200 mL numune için 5 kat seyreltilmiş Tiyosülfat
kullanılırsa (N/8 * 1/5) = N/40 (0,025N) olacak ve
hassasiyet de korunmuş olacaktır.
Hacimsel Metodlar
Çö ü ü Ok
Çözünmüş
Oksijen
ij T
Tayini
i i
Winkler Yönteminin Azid Modifikasyonu
2 NO2- + 2I- + 4H+ → I2 + N2O2 + 2H2O
N2O2 + 1/2O2 + H2O → 2 NO2- + 2H+
-
Girişimi önlemek için Sodyum Azodür (NaN3)
-
NaN3, Alkali-KI
Alkali KI çözeltisi ile birlikte
Asit ilave edildiğinde;
ğ
NaN3 + H+ → HN3 + Na+
HN3 + NO2- + H+ → N2 + N2O + H2O
Hacimsel Metodlar
Çö ü ü Ok
Çözünmüş
Oksijen
ij T
Tayini
i i
Winkler Yönteminin RidealRideal-Stewart Modifikasyonu
Asit ş
şartlarda Potasyum
y
Permanganat
g
((KMnO4) ilavesi ile
nitritleri de içeren bir çok indirgen maddenin girişiminin
önlenmesi
10 mg/L’den büyük Fe3+ konsantrasyonları için F- ilavesi
Aşırı KMnO4, Potasyum okzalat tuzu ile giderilir.
Membran Elektrotlar
Çözünmüş Oksijen Tayini
Biyokimyasal Oksijen İhtiyacı (BOİ)
Biyokimyasal Oksijen İhtiyacı (BOİ)
Tahmini BOİ (mg/l)
Seyreltme %
0–7
4 – 14
10 – 35
20 – 70
40 – 140
100 – 350
200 – 700
400 – 1 400
1 000 – 3 500
2 000 – 7 000
4 000 – 14 000
10 000 – 35 000
20 000 – 70 000
100
50
20
10
5
2
1
0.5
0.2
0.1
0.05
0 02
0.02
0.01
Biyokimyasal Oksijen İhtiyacı (BOİ)
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