A method for producing lactic acid comprises the steps of culturing in a culture medium comprising concentrated whey permeate or delactosed whey permeate as a substrate a bioconversion competent Bacillus bacterial strain capable of converting delactosed whey permeate into lactic acid for a period of time sufficient to allow the bacteria convert at least some of the lactose present in DLP or concentrated whey permeate into lactic acid, and then recovering the lactic acid from the culture medium.