Determination of Chemical Oxygen Demand (COD)-A Complete Procedure (Dichromate Mercury Free Method)

Summary

This video provides a comprehensive guide to measuring Chemical Oxygen Demand (COD), a crucial indicator of water and wastewater quality. It outlines the three main steps: sample and blank preparation, digestion, and absorbance measurement. Viewers are introduced to the necessary materials, including COD reagent vials and a spectrophotometer, while receiving essential safety tips. The video also highlights the significance of the COD test in assessing organic water contaminants, concluding with a practical demonstration that showcases the ease of obtaining accurate COD values.

Takeaways

• 🔬 The Chemical Oxygen Demand (COD) test measures the quality of water and wastewater, essential for monitoring treatment efficiency.
• 🧪 The COD test consists of three main steps: sample preparation, sample digestion, and absorbance measurement.
• 📏 Different COD reagent vials are available: medium-range for 0-1500 mg/kg and high-range for 0-15,000 mg/kg, depending on the expected COD levels.
• 📝 Proper labeling of vials is crucial: label the sample vial with a sample ID and the blank vial as 'blank'.
• 🔄 When preparing the sample, ensure thorough mixing by shaking and rotating the container before transferring it to the vial.
• 🌡️ During the digestion phase, both sample and blank vials must be heated to 150°C for two hours in a COD reactor.
• ❄️ After digestion, allow vials to cool to room temperature without shaking to avoid turbidity, which can affect results.
• 📊 The spectrophotometer must be calibrated and set to the appropriate method for the COD analysis based on the chosen reagent range.
• ⚖️ The absorbance reading from the spectrophotometer provides the COD value directly, eliminating the need for further calculations.
• 🚨 Handle hot vials with care during the mixing process, and ensure proper technique to avoid contamination or inaccuracies.

Q & A

What is the Chemical Oxygen Demand (COD) test used for?

The COD test measures the amount of oxygen required to chemically oxidize organic contaminants in water and wastewater, helping to assess water quality.

Why is the COD test important for water treatment plants?

It is used to monitor the efficiency of water treatment plants by evaluating how effectively they remove organic pollutants from wastewater.

What are the three main steps involved in conducting a COD test?

The three main steps are sample and blank preparation, sample digestion, and measuring absorbance with a spectrophotometer.

What equipment is necessary to perform the COD test?

You will need a COD reactor heater, a spectrophotometer, a micropipette, and COD reagent vials (medium-range or high-range).

How do you prepare the sample for the COD test?

Shake and mix the sample thoroughly, then transfer 2 milliliters into a labeled reagent vial, and invert the vial to mix with the reagent.

What is the purpose of preparing a blank vial in the COD test?

The blank vial is used as a control to calibrate the spectrophotometer and to ensure accurate measurement by comparing the sample against a baseline of deionized water.

What temperature and duration are required for the digestion phase in the COD test?

The vials must be digested at 150 degrees Celsius for two hours.

What should you do after the digestion process is complete?

Allow the vials to cool to 120 degrees Celsius, mix them again, and then cool them to room temperature without shaking.

How do you set up the spectrophotometer for reading the COD sample?

Turn on the spectrophotometer, calibrate it using the blank vial, and then insert the sample vial to take the measurement.

What does the spectrophotometer display after reading the sample vial?

It displays the COD value directly, indicating the amount of oxygen demand in the water sample, such as a value of 263 mg/kg.