The COD is 348 mg/L.
The chemical oxygen demand (COD) is number of milligrams of oxygen needed to completely oxidize the solutes in a litre of water.
Step 1. Write the balanced equation for the combustion of formic acid.
2HCOOH + O₂ → 2CO₂ + 2H₂O
Step 2. Calculate the mass of HCOOH in 1 L of water.
Step 3. Calculate the mass of O₂.
The COD of this solution is 348 mg/L.