1. OXYGEN Dissolved Oxygen (DO) Chemical Oxygen Demand (COD)
Biochemical Oxygen Demand (BOD)

2. Objectives After this session, the students are expected to be able :
to explain the steps of determination of DO, COD and BOD
to explain the objectives of every step
to explain the function of reagents
to conduct the determination of DO, COD and BOD
to do the calculation in the determination of DO, COD and BOD
to arrange the report of the determination of DO, COD and BOD
Teknologi dan Rekayasa

3. Oxygen in water
Presence of Oxygen in water found from air and result of algae photosynthesis reaction
Benefits of oxygen in water are following :
- respiration process for variety of aquatic biota
- oxidizing agents for organic and inorganic compounds
 chemically or microbiological
High level of oxygen concentration in water is useful to aquatic biota and human, nevertheless caused damage to industrial activity

4. Dissolved Oxygen (DO)
DO defined as mg Oxygen dissolved in 1 liter of water
Solubility of Oxygen in water is 8-9 mg/L (T=20oC)
Solubility of Oxygen in water influenced by :
- Temperature
- Pressure
- Water turbulance
- Level of contamination
High level of DO  quality of water is good
Low level DO  quality of water is not good content of high contaminant

5. Determination of DO
Method of determination DO in water are following :
1. Electrochemical, by DO-meter, using membrane electrode  for field/ laboratory necessary
2. Titration, by Winkler manner  for routine laboratory work

6. Determination of DO by electrochemical method
Principle of Analysis :
Electrical measurement produced when electrode system ,which consist of cathode and anode were remain in electrolyte solution (salt solution)
On DO meter :
Electrode consist of, Ag as cathode and Pb or Au as anode  electrode system is protecting by plastic membrane semi-permeable toward O2  only O2 could pass
Reaction
Cathode : O H2O + 4e  4 OH-
Anode : Pb + 2OH-  PbO + H2O + 2e
 flow of current electricity depends on amount of O2 on cahtode

7. DO meter apparatus

8. Determination of DO by Winkler method
Principle of Analysis :
Oxygen in sample oxidizing Mn2+ which additionally under base condition, until precipitate formation of MnO2. By addition of H2SO4 and KI, then will be released I2 equal to dissolved O2. Released of I2 then titrated by standard Na2S2O3 solution
Reaction :
MnSO KOH  Mn(OH)2 + K2SO4
Mn(OH)2 + ½ O2  MnO2 + H2O
MnO I H+  Mn I H2O
I S2O32-  2I- + S4O62-

9. Step of Determination DO Winkler Method
Put sample into Winkler bottle (If there is not available, use measured stopper bottle)
Add 2 mL MnSO4 solution and 2 mL alkali-iodida-azida (addition started from bottom of bottle)
Close carefully the bottle, shake for 1 minute  let the precipitate decrease
Pour the clear solution  add 12 mL H2SO4 6N into the precipitate through partition of bottle
Titration by standard Na2S2O3 0,025 N solution until around end point add starch solution , end point reached when dissapearness of blue colour

10. Calculation 1000 1000 DO (mg/L) = x a x 0,2 mg/L (Vbottle – 4)
a : Volume of thio
1000
DO (mg/L) = x a x [Na2S2O3] x 8
(Vbottle – 4)

11. Chemical Oxygen Demand (COD)
Definition of COD : amount of mg Oxygen needful to oxidizing all organic compound chemically in 1 liter of water
COD, often being as parameter to determine of waste quality
Parameter of COD influenced by organic contamination level
High level of COD  high level of organic high growth of microorganism quality of water is not good
Influential through level of DO

12. Determination of COD Titrimetric and Spectrofotometric
1. Process of oxidizing organic compound by oxygen chemically take very slow (need a long time)
2. While in process function of oxygen replaced by
K2Cr2O7 or KMnO4
3. This replacement appear various ideas range from to : when determination of COD not only organic compound oxidizing but also inorganic to, so COD become indicator of contamination level caused by organic and inorganic compound - based on characteristic of K2Cr2O7 as strong oxidizing agents

13. Determination of COD Interruption to COD analysis :
Chloride( ≥ 2000 ppm) could annoyance the function of catalyst from Ag2SO4, under certain condition also oxidized by dichromate
 to be lost by addition of HgSO4
Nitrite, oxidized by dichromate to nitrate
 to be lost by addition of sulfamate acid
Sulfite, oxidized by dichromate sulfate
 to be lost by addition of sulfamate acide

14. Determination of COD by titrimetric method
Principle :
Organic compound in water sample oxidizing by excessive of K2Cr2O7 under acid and hot condition. Excess of K2Cr2O7 titrated by standard FAS solution to feroin as indicator .
End point : greenish-blue to brownish-red
Reaction :
CxHyOz + Cr2O72-(excessive)  CO2 + H2O + Cr3+
Cr2O72-(residue) + 6Fe H+  6Fe3+ + 2Cr3+ +7H2O
Ag2SO4

15. Step of determination COD by titrimetric method
Put 50 mL sample of water into Erlenmeyer flask + boiling chip
Add 1 g HgSO4 + 5 mL reactant of sulfuric acid (H2SO4+Ag2SO4), shake until HgSO4 is dissolved
Add 25 mL K2Cr2O7 solution , shake well (if COD<50 ppm [dichro] = 0,025 N, if >50 ppm [dichro]=0,250 N)
Reflux for 2 hours, then let it cool and rinse of the condensor with aquadest ± mL
Dillution of sample until the volume twice from beginning + feroin
Titrated by standard FAS solution until end point
Titration for blank with same preparation, change the sample by free organic compound

16. Calculation of COD (a-b) x N x 8000 COD = mL sampel Note. :
a = mL FAS for blank titration
b = mL FAS sample titration
N = Normality of FAS

17. Determination of COD by Spectrophotometric method
Principle :
Organic compound in sample of water oxidized by amount of K2Cr2O7 under acid and hot condition with Ag2SO4 as catalyst The colour formation then measured to absorbance at  420/600 nm. COD of sample determined by ditentukan dengan intrapolation of sample absorbance to standard curve
Reaction :
CxHyOz + Cr2O  CO2 + H2O + Cr3+
420nm = measure A from remain of K2Cr2O7 (yellow)
600nm = measure A from Cr3+ (green)
Ag2SO4

18. Step of Determination COD by spectrofotometric
Making of stock solution COD 500 ppm (KH-Ptalat 425 mg dissolved in 1 L of aquadest
Making of measurement soution ppm
Sample of water
Transfer by volumetric pippete 10 mL + 6 mL of (K2Cr2O7+H2SO4+HgSO4) + 14 mL reactant H2SO4 (H2SO4+Ag2SO4)
Reflux for 2 hours under 150oC
Let it cool, let the precipitate formed
Read the absorbance of standard and sample at  420/600 nm

19. Biological Oxygen Demand (BOD)
Definition of BOD: amount of mg Oxygen needful to oxidizing all organic compound biochemically in 1 liter of water
BOD, reputed as procedure of wet oxidizing, as microorganism in water used as oxidizing agents of organic compound to CO2, H2O and NH3
BOD, often being as parameter to determine quality of home/industrial wastes
BOD, indicates level of contamination organic compound which have biodegradable characteristic
Parameter of BOD influenced by : level of contamination, especially organic compound (high level of BOD  quality of water is not good)
Influenced to DO level

20. Determination of BOD by Titrimetric method
Principle of Analysis :
Measurement of amount dissolved oxygen in content of sample water before or after incubation at temperature 20oC for 5 days. Amount of dissolved oxygen (DO) determine by Winkler titration
Principle of Winkler : Oxygen in sample will oxidizing Mn2+ which additional under base condition, so MnO2 is formed. By additional of H2SO4 and KI, then will released I2 which equivalent with dissolved O2. Freed I2 titrated by standard Na2S2O3 solution

21. Reactions Oxidizing of organic compound :
CxHyOzNc + O  CO2 + H2O + NH3
Reaction of Winkler titration :
MnSO KOH  Mn(OH)2 + K2SO4
Mn(OH)2 + ½ O2  MnO2 + H2O
MnO I H+  Mn I H2O
I S2O32-  2I- + S4O62-
Microorganism

22. Step of Determination BOD by titrimetric method
Diluting of sample: Based on data of COD. For example COD for sample 1000 ppm. For BOD5, diluting = COD/5
diluting = 1000/5 = 200
Total volume of diluting, ex. 800 mL. 800/Vsample = 200 Volume of sample = 800/200 = 4 mL, dilute until 800 mL with diluting solution
Put sample which have been diluted into 2 bottles of BOD (capacity of 300 mL) Put 1’ st bottle into incubator at 20oC
2’ nd Bottle + 2 mL MnCl2 20% and 2 mL reactant of O2. Shake well and let the precipitate turn down
Put filtrate and precipitate is dissolved by additional of sentrat H2SO4 6 N shake and bundle with sentrate
Titrated by standard thio 0,025 N

23. BOD (mg/L) = [(D00-DO5) – (B0-B5)] x f
Calculation
BOD (mg/L) = [(D00-DO5) – (B0-B5)] x f
Note :
DO0 = DO day 0 B0 = Blank of day 0
DO5 = DO day 5 B5 = Blank of day 5
f = factor for diluting of sample
1000
DO (mg/L) = x a x [Na2S2O3] x 8
(Vbottle – 4)