A Comparative Study of Biodegradation of Virgin and Weathered Low-density Polyethylene by Proteus andLactobacillus spp.

The environmental and public health burdens arising from plastic wastes, and the need to develop an eco-friendlystrategy to manage the wastes prompted this research work. In this study, the role of microorganisms in virgin andweathered low-density polyethylene degradation was investigated. Two (2) bacterial species, Lactobacillus andProteus were isolated from a waste dumpsite in Avu, Owerri West LGA, Imo State, Nigeria. Incubation of thepolyethylene sachets with the test isolates was for 60 days, and their ability to degrade polyethylene was evaluated bymicrobial growth measurement (OD600), changes in the functional groups of the polyethylene (FTIR) and weight lossanalysis. Results revealed the presence of gas bubbles and turbidity of the microbial inoculated culture media. Optical density measurement showed progressive and gradual increase in absorbance, with Lactobacillus sp. recording higher concentrations in both virgin (0.115 – 0.550) and weathered (0.116 – 0.790) polyethylene cultures than Proteus sp. (0.122 – 0.451) and (0.114 – 0.710). Fourier transform infrared spectroscopy (FTIR) revealed the presence of additional carbonyl, hydroxyl and methylene functional groups in the polyethylene sachets treated with the test isolates (Lactobacillus sp: virgin PE – 10 peaks, weathered PE – 13 peaks; Proteus sp: virgin PE- 7 peaks, weatheredPE – 10 peaks) as against the control (virgin PE – 8 peaks and weathered – 7 peaks). Similarly, weight loss analysesalso revealed higher percentage weight loss in weathered PE than virgin PE, with Lactobacillus sp also recording greater percentages (44% and 32%) than Proteus sp (28% and 22%). These observations were indications of microbial metabolic activities, and the degradation and utilization of the polyethylene by the test organisms as solesource of carbon and energy. It was concluded that Lactobacillus sp. and Proteus sp. have the ability to degradepolyethylene, with Lactobacillus sp. displaying a higher capability, and that weathered polyethylene is moresusceptible to microbial attack than virgin. Keywords: polyethylene, Lactobacillus sp., Proteus sp. biodegradation, microbial isolates