Preliminary Studies on Microbial Degradation of Plastics Used in Packaging Potable Water in Nigeria
A simple technique using proprietary solvents to solubilize and powderize Linear Low Density Polyethylene (LLDPE) used in packaging potable water in Nigeria was developed. The increased surface area created, promoted better exposure of the LLDPE to soil microbes. Using the culture enrichment techniques, eight microbial colonies were found capable of utilizing LLDPE as their sole carbon source. The most prolific organism, producing red pigment, was isolated and identified as Serratia marcescens marcescens. This organism was characterized as gram negative rod, reactivity with ß-gal, ß-glu, and urease was positive while indole production and H2S was negative. Fermentation test was positive for glucose, sucrose, glycerol, fructose, sorbitol alanine and citrate. The conditions for the pigmentation could not be ascertained. However, the pigment absorbed radiation within UV region and formed a precipitate with ferric chloride. The SEM micrographs of the plastic film surfaces after exposure to S. marcescens revealed some indentations that were attributed to the degrading ability of the organisms. Micrographs of films in medium without S. marcescens (control) presented smooth surfaces. The Tg of degraded and undegraded plastics determined by Differential Scanning Calorimetry (DSC) were 52.43oC and 63.33oC respectively, suggesting a higher degree of motility of the shorter chain length produced after degradation. DSC measurement further showed ÄH as 89.936 J/g before and 31.945 J/g after microbial degradation. A decrease was also observed in the crystallization temperature (118.980 to 112.25 °C) and the enthalpy of crystallization (-83.241 J/g to -34.776 J/g). The result of the DSC thermograph was an indication of reduced crystallinity associated with degradation processes.
Keywords: Polyethylene, biodegradation, prodigiosin, serratia marcescens marcescens, pigmentation.