Potential accelerated biotransformation of petrochemical plastic surfaces by anaerobic digester sludge microorganisms

This study investigated the biotransformation of three different plastic surfaces, polypropylene (PP), polyvinyl chloride (PVC) and polyethylene (PE), by anaerobic digestion (AD) system microorganisms under mesophilic conditions. For that, a laboratory-scale AD system was established and plastics were immersed in the sludge for a 50-day incubation period, measured for any significant mass loss. Statistical analysis showed a significant mass loss (p < 0.05) in PVC pieces with a 1.1 ± 0.16 mg average reduction, while PP and PE didn't show any significant mass loss. Raman spectroscopy analysis revealed temporally increasing novel peaks in PVC at 1729 cm^-1 corresponding to C = O stretching vibrations. This was considered significant and compared against an unchanged marker of PVC, revealing a newly identified peak that has not been documented in prior studies of this material. PP also indicated a temporal increase of novel peaks in the spectral range of C = C stretching vibrations in the region of 1512 cm^-1. Atomic force microscopy (AFM) analysis of PVC showed a reduction in average roughness amplitude from 100 to 90 nm in 30 days and 65 nm to 50 days revealing surface biotransformation. Phase-contrast microscopy further confirmed surface embrittlement across all plastics. Several bacterial species that were associated with plastic biotransformation were isolated and characterized using 16 s rRNA molecular marker gene-based identifications. In conclusion, this study suggests that, the changes to overall surface of the plastics and newly observed surface transformation of PVC leading to biodeterioration, by AD system microorganisms.