Effect of rhamnolipid biosurfactant on biodegradation of untreated and UV-pretreated non-degradable thermoplastics: Part 2

Abstract

The capabilities of a microbial consortium, composed of Penicillium raperi, Aspergillus flavus, Penicillium glaucoroseum and Pseudomonas spp, for biodegrading of ultraviolet (UV)-pretreated and un-pretreated mixed plastics (polyethylene (PE), polystyrene foam (PS) and polyethylene terephthalate (PET)) in the presence of biosurfactant (rhamnolipid) was examined. The “UV-pretreated & bio-treated + biosurfactant” was found the most effective condition for PS samples with the highest physical weight loss (7.47%), surface degradation, wettability (< 5˚). The highest biofilm formation was observed on PS for “UV-pretreated & bio-treated + biosurfactant” and “UV-pretreated & bio-treated” with OD 595 nm of 1.53 and 1.31 conditions, respectively. Atomic force (AFM) and scanning electron microscopy (SEM) showed considerable surface degradation (cracks and holes) for the PS sample incubated at “UV-pretreated & bio-treated + biosurfactant” condition compared to PE and PET in the same condition. In contrast, PE and PET had a higher biodegradation efficiency only in “UV-pretreated & bio-treated” condition. The utilisation of biosurfactant had negative effects on biodegradation and wettability of PE and PET, due to the consumption of rhamnolipid as food source rather than the plastic itself. Chemical transformation indicated a new peak (C-O) in PS at both “UV-pretreated & bio-treated” and UV-pretreated & bio-treated + biosurfactant) conditions. However, the chemical transformation of PE and PET remained unchanged in all conditions except “UV-pretreated & bio-treated”. Thermogravimetric analysis showed 20 ˚C lower thermal stability of PS incubated at “UV-pretreated & bio-treated + biosurfactant” than other conditions.