chemical oxygen demand vials manufacturer USA Chemical Oxygen Demand (COD) TNTplus Vial Test, HR (20-1,500 Hach's USEPA-approved dichromate COD Method is the most widely used chemical oxygen demand (COD) method for NPDES reporting in the Chemical Oxygen Demand (COD) TNTplus Vial Test, HR (20-1,500 mg/L COD), 25 Tests | Hach USA - Overview