Methods and systems for lactic acid production and polylactic acid recycling

A method for producing an 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 a metal oxide or a hydroxide to obtain a PLA hydrolysis slurry comprising L-lactate monomers and a first counterion;
• (b) fermenting organic waste with a lactic acid-producing microorganism in a fermenter in the presence of an alkaline compound to obtain a fermentation broth comprising L-lactate monomers and a second counterion, wherein the first and second counterions are the same;
• or wherein at least one of the first and second counterions is subjected to ion exchange thereby obtaining a first and second counterions which are the same;
• (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 an L-lactate salt,
• wherein the mixture comprising the PLA hydrolysis slurry of step (a) and the fermentation broth of step (b) is obtained by adding the PLA hydrolysis slurry to the lactic acid fermenter during fermentation.