Is there a comparison of the different Chemical Oxygen Demand (COD) methods available?

Document ID

Document ID TE4099

Published Date

Published Date 05/21/2019
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Question
Is there a comparison of the different Chemical Oxygen Demand (COD) methods available?
Summary
Comparison of the COD methods.
Answer
Below is a comparison of the COD methods available:
 
Option 1: Method 8000 with Hg-COD vials and ezCOD recycling service
 
  • United States Environmental Protection Agency (USEPA) approved for wastewater for reporting COD when using Low Range (LR) or High Range (HR) vials.
  • An accurate and reliable method for determining COD with four different ranges to ensure best accuracy and ease of use, including bar-coded vials in TNTPlus™ product line.
  • The ez COD™ buckets offer a convenient low-cost mercury recycling program for the reagents.
  • Avoids interference from ammonia and chloride up to 2000 ppm Cl (or 20,000 ppm in the High Range Plus method)
 
Option 2: Method 8000 with COD2 Mercury-free vials
 
  • Not USEPA approved for reporting COD
  • Can be accurate with 3 concentration range options, but most samples require estimating the interference due to ammonia and chloride. See the article titled, " Does Hach have any literature on Chemical Oxygen Demand (COD) testing?"
  • Requires additional testing of ammonia and chloride, then using the interference chart to calculate the corrected COD result.
  • Additional cost per test for ammonia and chloride also must be considered.
  • The ez COD™ cannot be used for disposal of the COD2 reagents. Proper disposal must be considered since the COD2 vials still contain concentrated sulfuric acid, dichromate, and silver even though they are mercury-free.
  • Additional hazardous chemical waste might be generated by the ammonia and chloride tests, depending on which method is used. Most chloride tests require the use of mercury or silver.
 
Option 3: Method 10067 with MnIII COD vials
 
  • Not USEPA approved for reporting COD
  • Can be accurate, but most samples require chloride removal procedure as described in the test method.
  • The MnIII method only comes in 1 range, which is 30-1000 ppm, with precision of +/- 24 ppm.
  • The ezCOD™ cannot be used for disposal of the MnIII COD vials. Proper disposal must be considered since the MnIII COD vials contain permanganate and concentrated sulfuric acid. 
  • The Device, Vacuum Pretreatment (Product # 4900000) referenced in Method 10067 is obsolete with no replacement. This device was used to remove chloride from samples.

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