The conventional process for tanning leather uses large amounts of calcium oxide and sodium sulfide  Tanning leather using biological catalysts costs about the same as using these conventional chemicals if the cost of waste disposal is left out of the comparison  However, nearly 20 percent less waste is produced with biological catalysts, and waste disposal is a substantial part of the overall cost of tanning
It is ttherefore less costly to tan leather if biological catalysts are used instead
Disposal of tanning waste produced with biological catalysts does not cost significantly more than disposal of the same amount of waste produced with the conventional process.