Impact of mechanical and thermo-chemical pretreatments to enhance anaerobic digestion of poly(lactic acid)

To date, the introduction of biodegradable plastics such as PLA in anaerobic digestion systems has been limited by a very low rate of biodegradation. To overcome these limitations, pretreatment technologies can be applied. In this study, the impact of pretreatments (mechanical, thermal, thermo-acid, and thermo-alkaline) was investigated. Mechanical pretreatment of PLA improved its biodegradation rate but did not affect the ultimate methane potential (430-461 NL CH4 kg(-1) VS). In parallel, thermal and thermo-acid pretreatments exhibited a similar trend for PLA solubilization. Both of these pretreatments only achieved substantial solubilization (>60%) at higher temperatures (120 and 150 degrees C). At lower temperatures (70 and 90 degrees C), negligible solubilization (between 1 and 6%) occurred after 48 h. By contrast, coupling of thermal and alkaline pretreatment significantly increased solubilization at the lower temperatures (70 and 90 degrees C). In terms of biodegradation, thermo-alkaline pretreatment (with 5% w/v Ca(OH)(2)) of PLA resulted in a similar methane potential (from 325 to 390 NL CH4 kg(-1) VS) for 1 h at 150 degrees C, 6 h at 120 degrees C, 24 h at 90 degrees C, and 48 h at 70 degrees C. Reduction of the Ca(OH)(2) concentration (from 5% to 0.5% w/v) highlighted that a concentration of 2.5% w/v was sufficient to achieve a substantial level of biodegradation. Pretreatment at 70 and 90 degrees C using 2.5% w/v Ca(OH)(2) for 48 h resulted in biodegradation yields of 73% and 68%, respectively. Finally, a good correlation (R-2 = 0.90) was found between the PLA solubilization and its biodegradation.

Automated summary

This study investigates the impact of pretreatments on the biodegradation of biodegradable plastic, polylactic acid (PLA), in anaerobic digestion systems. The results show that mechanical pretreatment improves the degradation rate of PLA, while thermal and acid pretreatments have similar effects on PLA solubilization. Thermo-alkaline pretreatment significantly increases solubilization and biodegradation of PLA at lower temperatures.