Nitrogen sparger for spent caustic treatment

Hello, Our company received MR for spent caustic treatment system. Of many specification, i don't understand specificaiton for nitrogen sparger as below red text. The second neutralization tank shall include a nitrogen sparger, and the appropriate controls to activate the sparger when the treated spent caustic is off spec with respect to either pH or COD.  Why nitrogen sparger is needed according to above red text condition (when the treated spent caustic is off spec with respect to either pH or COD) ?   Thanks