WASTE WATER ANALYSIS 1:CHEMICAL OXYGEN DEMAND (COD) & SUSPENDED SOLID (SS) -

Test	Parameter	Duration	Method
Wastewater analysis 1	COD	3 hours	Hach 8000
	pH	15 minutes
	Temperature	15 minutes
	SS	15 minutes	Hach 8006
Wastewater analysis 2	Manganese	15 minutes	Hach 8149
	Zinc	15 minutes	Hach 8009
	Sulfide	15 minutes	Hach 8131

1. EXP 1 : CHEMICAL OXYGEN DEMAND (COD)

OBJECTIVE

1. To determine chemical oxygen demand (COD) concentration in wastewater sample

INTRODUCTION

The mg/L COD results are defined as the mg of O2 consumed per liter of sample under conditions of this procedure. In this procedure, the sample is heated for two hours with a strong oxidizing agent, potassium dichromate. Oxidizable organic compounds react, reducing the dichromate ion (Cr2O7 2–) to green chromic ion (Cr3+). When the 0.7–40.0 or the 3–150 mg/L colorimetric method is used, the amount of Cr6+ remaining is determined. When the 20–1500 mg/L or 200–15,000 mg/L colorimetric method is used, the amount of Cr3+ produced is determined. The COD reagent also contains silver and mercury ions. Silver is a catalyst, and mercury is used to complex chloride interferences. Test results for the 0.7 to 40.0 mg/L range are measured at 350 nm. Test results for the 3 to 150 mg/L range are measured at 420 nm. Test results for the 20 to 1500 and the 2000 to 15,000 mg/L COD range are measured at 620 nm.

EQUIPMENT/APPARATUS

Beaker, 250-mL 1

Blender 1

COD Digestion Reagent vials varies

DRB200 Reactor 1

Light Shield 1

Magnetic stirrer and stir bar 1

Opaque shipping container for storage of unused, light-sensitive reagent vials varies

Pipet, TenSette®, 0.1 to 1.0 mL, with tips (for 200–15,000 mg/L range) 1

Pipet, volumetric, 2.00 mL 2

Pipet Filler, safety bulb 1

Test Tube Rack 2

PROCEDURES

1. Homogenize 100 mL of sample for 30 seconds in a blender. For samples containing large amounts of solids, increase the homogenization time. If the sample does not contain suspended solids, omit steps 1 and 2.

2. For the 200–15,000 mg/L range or to improve accuracy and reproducibility of the other

ranges, pour the homogenized sample into a 250-mL beaker and gently stir with a magnetic stir plate.

3. Turn on the DRB200 Reactor. Preheat to 150 °C. See the DRB200 User Manual for selecting pre-programmed temperature applications.

4. Remove the caps from two COD Digestion Reagent Vials. (Be sure to use vials for the

appropriate range.)

5. Prepared Sample: Hold one vial at a 45-degree angle. Use a clean volumetric pipet to add 2.00 mL of sample to the vial. Use a TenSette® Pipet to add 0.20 mL for the 200–15,000 mg/L range.

6. Blank Preparation: Hold a second vial at a 45-degree angle. Use a clean volumetric pipet to add 2.00 mL of deionized water to the vial. Use a TenSette Pipet to add 0.20 mL for the 200–15,000 mg/L range.

7. Cap the vials tightly. Rinse them with water and wipe with a clean paper towel.

8. Hold the vials by the cap over a sink. Invert gently several times to mix. Insert the vials in the preheated DRB200 Reactor. Close the protective lid. The sample vials will become very hot during mixing.

9. Heat the vials for two hours.

10. Turn the reactor off. Wait about 20 minutes for the vials to cool to 120 °C or less.

11. Invert each vial several times while still warm. Place the vials into a rack and cool to room temperature. Proceed to Colorimetric Determination Method 8000.

Colorimetric Determination

TNT thod 8000

1. Select the ultra-low range, low range, or high range test. Install the Light Shield in Cell Compartment #2.

2. Clean the outside of the vials with a damp towel followed by a dry one.

3. Insert the blank into the 16-mm cell holder.

4. Press ZERO. The display will show: 0.0 mg/L COD

5. Insert the sample vial into the 16-mm cell holder.

6. Press READ. Results are in mg/L COD.

7. If using High Range Plus COD Digestion Reagent Vials, multiply the result by 10. For most accurate results with samples near 1500 or 15,000 mg/L COD, repeat the analysis with a diluted sample.

DISCUSSION

Compare the COD concentration with Environmental Quality Act 1974

2. EXP 2 : SUSPENDED SOLID

OBJECTIVE

To determine suspended solid concentration in wastewater sample

INTRODUCTION

This method of determining suspended solids is a simple, direct measurement which does not require the filtration or ignition/weighing steps that gravimetric procedures do. The USEPA specifies the gravimetric method for solids determinations, while this method is often used for checking in-plant processes. Test results as mg/L total suspended solids (TSS) are measured at 810 nm.

EQUIPMENT/APPARATUS

Beaker, 600-mL, polypropylene 1

Blender 1

Cylinder, 500-mL polypropylene, graduated 1

Pipet, serological, 25-mL 1

Pipet Filler, safety bulb 1

Sample Cells, 1-inch square, 10 mL 2

PROCEDURES

1. Press STORED PROGRAMS.

2. Select the test.

3. Blend 500 mL of sample in a blender at high speed for exactly two minutes.

4. Pour the blended sample into a 600-mL beaker.

5. Prepared Sample: Stir the sample and immediately pour 10 mL of the blended sample into a sample cell.

6. Blank Preparation: Fill a second sample cell with 10 mL of tap water or deionized water. Remove gas bubbles in the water by swirling or tapping the bottom of the cell on a

table.

7. Insert the blank into the cell holder with the fill line facing right.

8. Press ZERO. The display will show: 0 mg/L TSS

9. Swirl the prepared sample to remove any gas bubbles and uniformly suspend any residue.

10. Insert the prepared sample into the cell holder with the fill line facing right.

11. Press READ. Results are in mg/L TSS.

DISCUSSION

Compare the suspended solid concentration with Environmental Quality Act 1974

REFERENCE

DR 2800 Spectrophotometer Procedures Manual November 2005 Edition 1