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Study of the biodegradability of polylactide fibers in wastewater treatment processes
Summary
Researchers exposed polylactide (PLA) fibers — a common biodegradable bioplastic — to activated sludge under both mesophilic and thermophilic wastewater treatment conditions, finding very limited degradation even under thermophilic conditions. The results show that PLA fibers are not effectively broken down during standard wastewater treatment and may persist in the environment similarly to conventional synthetic fibers.
The aim of this research was to study what happens to polylactide (PLA) fibers when they are released to wastewater systems. Samples of PLA fibers were immersed in activated sludge and subjected to typical activated sludge treatment in mesophilic (36 °C) and thermophilic (56 °C) conditions for up to 4 weeks. The characteristics of the surface and cross-sections of PLA fibers were analyzed by scanning electron microscopy (SEM), showing the settlement of the microorganisms on the surface of PLA fibers immersed in sludge and also the erosion of the material with time. Differential scanning calorimetry (DSC) analysis provided information on small changes in the crystalline structure of PLA fibers, and the results of tensile tests proved only partial degradation of PLA material treated in the activated sludge system during the processing time. The study confirmed that the standard processing of wastewater in the activated sludge system, in both mesophilic and thermophilic variants, is insufficient for the biodegradation of PLA. Therefore, PLA microplastics can be released from wastewater treatment plants.