Methods and systems for lactic acid production and polylactic acid recycling

A method for producing magnesium L-lactate salt from a combined recycling of polylactic acid (PLA) and organic waste, the method comprising the steps of:

• (a) hydrolyzing PLA waste with magnesium oxide or magnesium hydroxide to obtain a PLA hydrolysis slurry comprising L-lactate monomers and magnesium counterions;
• (b) fermenting organic waste with a lactic acid-producing microorganism in a fermenter in the presence of magnesium oxide, magnesium carbonate, or magnesium hydroxide to obtain a fermentation broth comprising L-lactate monomers and magnesium counterions;
• (c) optionally contacting the PLA hydrolysis slurry of step (a), the fermentation broth of step (b), or a mixture comprising the PLA hydrolysis slurry of step (a) and the fermentation broth of step (b) with a D-lactic acid degrading enzyme or a D-lactic acid-utilizing microorganism to eliminate D-lactate monomers thereby obtaining L-lactate monomers;
• and
• (d) purifying a mixture comprising the PLA hydrolysis slurry of step (a) and the fermentation broth of step (b) or the L-lactate monomers of step (c) thereby obtaining magnesium L-lactate salt.