Downscaling the chemical oxygen demand test.

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Green Chemistry

Background:

• The standard chemical oxygen demand (COD) test is crucial for water characterization but uses toxic reagents (Cr, Ag, Hg) and requires lengthy heating (2-3 hours).
• These drawbacks increase costs, environmental impact, and labor time, particularly for laboratories with high analytical throughput.

Purpose of the Study:

• To develop and validate a downscaled, greener method for COD analysis.
• To significantly reduce the use of toxic materials and the time required for COD testing.

Main Methods:

• A small-scale version of the standard COD test was developed.
• The downscaled method's performance was evaluated using potassium hydrogen phthalate (KHP) standards, municipal wastewater, and industrial wastewater samples.
• Accuracy and precision were compared against the standard COD method.

Main Results:

• The downscaled method achieved reductions of up to 80% in toxic residue generation and 67% in analysis time.
• Accuracy, measured by relative error, was comparable or improved for the small-scale method across different sample types (KHP, municipal, industrial wastewater).
• Chloride ions did not interfere at concentrations below 2000 mg NaCl/L.

Conclusions:

• The downscaled COD test offers a greener, more efficient alternative to the standard method.
• This approach provides significant savings in reagents, energy, and labor time.
• The method demonstrates potential for widespread adoption in analytical laboratories, especially those with heavy COD testing loads.