Lab-scale comparison of PLA/PBAT disintegration in composting and vermicomposting: fertilizer quality, phytotoxicity, and day-120 bacterial community profiles

The widespread use of poly(lactic acid) and poly(butylene adipate-co-terephthalate) (PLA/PBAT) bioplastics presents disposal challenges, as their degradation in domestic environments is often incomplete. This study compared the efficiency of composting and vermicomposting (using Eudrilus eugeniae ) in degrading PLA/PBAT mixed with organic waste (cabbage and cow manure). A 120-day lab-scale mesophilic experiment was conducted to evaluate compost maturity, bioplastic fragmentation, and phytotoxicity (GI). Results indicated that both treatments achieved maturity, reducing the C/N ratio to below 20, and vermicomposting accumulated higher C/N ratio, TP, TK, Ca, and CEC. Heavy metal concentrations remained well below maximum allowable limits. Moreover, 120-day vermicompost demonstrated better overall, achieving a GI of 136% compared to 101% in compost. Pearson’s correlation coefficient was used to analyze the relation of GI and some physicochemical indicators. Regarding bioplastic degradation, FTIR and SEM confirmed polymer bond rupture and structural deterioration. The disintegration rate was slightly different, 59.91% in vermicomposting and 55.96% in composting. Lysinibacillus and Clostridium were found in 120-day mixture, may contribute to polymer degradation, secreting extracellular enzymes on the plastic surface. Nevertheless, complete degradation was hindered because the mesophilic conditions did not reach the T g (∼60 °C) although Litorilinea was found, as evidenced by the presence of heat-resistant bacteria. This clearly indicates that composting temperature can reach thermophilic levels. In conclusion, while the experiment cannot fully degrade PLA/PBAT within 120 days, vermicomposting represented a numerically higher value of performance under the investigated conditions for enhancing compost maturity, minimizing phytotoxicity, and accelerating polymer fragmentation.