Preliminary Investigation of Upcycling Polylactic Acid 3-D Printing Waste to Candidate Single-Cell Protein Feedstock

Polylactic acid (PLA) is the most common extrusion-based distributed 3-D printing material. Unfortunately, large amounts of PLA are wasted from failed prints, support materials, material changes for multi-color printing, and poorly designed iterative prototypes. To overcome this waste challenge, distributed recycling with recyclebot technology is used to convert 3-D printing waste back into filament. This process can only be repeated five times before serious mechanical degradation of the resulting materials is observed. To overcome these challenges at the end-of-life of PLA 3-D printing material, this preliminary study explores a new approach that uses hydrolysis of PLA to create a candidate single-cell protein (SCP) feedstock that can be converted to human-edible food after required safety validation. Three concentrations of sodium hydroxide (NaOH) are tested for their ability to perform hydrolysis on PLA at room temperature using readily accessible equipment and chemicals. The solution is then neutralized, and yeast is grown in an open-source bioreactor, dried, and quantified to determine the preliminary yield of SCP. The results show a clear positive correlation between PLA degradation efficiency with higher NaOH concentration and yeast biomass production. The average performance of the 0.33 g NaOH/g PLA treatment resulted in an 8.5-fold yeast biomass increase. In summary, the current bench-scale process has proven technically viable and may be an economically justified method of yeast production on the household scale using PLA waste as a starting material. The dominant cost is energy, not reagents, which also lends the positive early results to future safety investigation using a scaled-up bioreactor.