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1.1 Experimental Objectives

1.1.1 Biochemical Oxygen Demand (BOD)

The aim of the experiment in this practicum is to determine the levels of Dissolved Oxygen (DO) and Biochemical Oxygen Demand (BOD) in water samples.

1.1.2 Chemical Oxygen Demand (COD)

The aim of this experiment is to calculate the COD levels contained in the sample.

1.2 Experimental Method

The method used in this practicum is the titrimetric method with Winkler titration.

The method used in this experiment was titration using a Ferro Ammonium Sulfate (FAS) solution using a Ferroin indicator.

1.3 Experimental Principles

Oxygen will oxidize Mn²⁺ in alkaline conditions to form MnO2 precipitates, adding alkali iodide in acidic conditions will liberate iodine.

Reaction that occurs:

Mn²⁺ + 2OH^- + 1⁄2O2 → MnO2 + H2O MnO2 + 2I^- + 4H⁺ → Mn²⁺ + I2 + H2O I2 + S2O32- → S4O62- + 2I^-

BOD measurements consist of measuring the sample, incubation for 5 days at 20°C and measuring dissolved oxygen during incubation to show the amount of oxygen needed in the water sample.

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MINISTRY OF HIGHER EDUCATION, SCIENCE AND TECHNOLOGY

FACULTY OF ENGINEERING, UNIVERSITAS ANDALAS

DEPARTMENT OF ENVIRONMENTAL ENGINEERING

WATER LABORATORY

Campus Unand Limau Manis Padang 25163 Phone. (0751) 7862901, Fax. (0751) 72566

AGUSTI NURUL RAHMI 2310943006 1.3.2 Chemical Oxygen Demand (COD)

Organic compounds in water are oxidized by a solution of Potassium Dichromate in an acidic environment at a temperature of 150^oC for 2 hours. Excess Potassium Dichromate is titrated by FAS solution with Ferroin indicator.

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The tools used in the BOD practicum are:

1. Measuring glass 100 mL;

2. volumetric flask 1000 mL;

3. erlenmeyer 500 mL;

4. funnel;

5. buret 25 mL;

6. measuring pipette 25 mL;

7. suction ball;

8. winkler bottles 300 mL;

9. statip and clamp;

10. drop pipette;

11. aerator;

12. incubator.

3.1.2 Chemical Oxygen Demand (COD) The tools used in the COD practicum are:

1. COD reactor;

2. test tubes;

3. test tube rack;

4. erlenmeyer 100 mL;

5. buret 25 mL;

6. measuring pipette 10 mL;

7. drop pipette;

8. funnel;

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WATER LABORATORY

AGUSTI NURUL RAHMI 2310943006 3.2 Materials

The materials used in this BOD and COD practicum are:

3.2.1 Biochemical Oxygen Demand (BOD) The materials used in the DO-BOD practicum are:

1. 0.025 N sodium thiosulfate solution;

2. alkaline iodide (NaI) solution;

3. starch Indicator solution;

4. concentrated sulfuric acid solution (H2SO4);

5. manganese sulfate solution (MnSO4);

6. magnesium sulfate solution (MgSO4);

7. CaCl2 solution;

8. FeCl3 solution;

9. phosphate buffer;

10. aquadest;

11. sample.

3.2.2 Chemical Oxygen Demand (COD) The materials used in the COD practicum are:

1. K2Cr2O7 0.25 N digestion solution;

2. sulfuric acid-silver sulfate reagent;

3. ferroin indicator;

4. solution Ferro Ammonium Sulfate (FAS);

5. aquadest;

6. sample.

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3.3 Work Procedure

The work procedure that will be carried out in this practicum are:

The work procedure that will be carried out in BOD experiment are:

1. Aerate the distilled water in the reactor for 1 hour;

2. 100 mL of the sample was taken using a measuring cup, then the sample was put into a 1000 mL measuring flask and diluted with distilled water to a volume of 1000 mL;

3. distilled water is put into a measuring flask containing samples up to a volume of 1000 mL for blank;

4. FeCl3 solution, CaCl2 solution, MgSO4 solution, and Phosphate Buffer solution were added 1 ml each to the sample and blank, then homogenized;

5. samples were put into 4 BOD bottles (Winkler bottles), of which 2 bottles were for determining DO5 and 2 bottles were for determining DO0;

6. step 4 is carried out on the blank;

7. to the BOD-DO0 bottle, 1 mL of MnSO4 solution and 1 mL of alkali iodide solution were added, then kept in the incubator for 10 minutes;

8. after 10 minutes, the BOD-DO0 bottle was taken, poured into a 500 ml Erlenmeyer flask and added 1 mL of concentrated sulfuric acid. Then titrated with Sodium Thiosulfate solution until light yellow;

9. starch indicator is added and titrated again with Sodium Thiosulfate solution until the color is clear. The volume of the bottle sample and the volume of 0.025 N Sodium Thiosulfate used were then recorded;

10. do the same thing (procedure 6-7) on BOD-DO5 bottles after 5 days of storage in the incubator.

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WATER LABORATORY

AGUSTI NURUL RAHMI 2310943006 3.3.2 Chemical Oxygen Demand (COD)

How the COD practicum works are:

1. 2.5 mL of sample is put into a test tube;

2. 1.5 mL of digestion solution was added;

3. 3.5 mL of Ag2SO4 was added to the solution. The solution was stirred until homogeneous;

4. the tube containing the solution was placed into the COD reactor. Then heated at 150^oC for 2 hours;

5. after cooling, add 3 drops of ferroin indicator;

6. titrated with 0.05 N FAS solution until the color changes from green to red- brown;

7. a blank experiment is required using the method above.

3.4 Calculation Formula

1. Thiosulfate solution standardization formula (Na2S2O3):

Normality Na₂S₂O₃ = (Volume K₂Cr₂O₇) × Normality K₂Cr₂O₇ Volume Na₂S₂O₃

2. DO and BOD calculation formula:

DO (mg/L) = (Volume Na₂S₂O₃) × Normality Na₂S₂O₃ × 8 × 1000 Sample Volume

BOD5 days, 20˚C= (DO₀- DO₅) - (B₀- B₅) (1- p) p

Information:

B0 = DO 0 blank days (mg/L) B5 = DO 5 days blank (mg/L) DO0 = DO 0 day sample (mg/L)

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DO5 = DO 5 day sample (mg/L) P = dilution number

COD as O2 =(A-B) × N × 8000 mL Sample

Information:

A = mLFAS for blank B = mL FAS for sample N = FAS normality