A comparative study on biodegradation of low density polyethylene bags by a Rhizopus arrhizus SLNEA1 strain in batch and continuous cultures

Abstract

Biodegradation poses a challenge for environmentalists and scientific community, offering a potential solution to the plastic waste problem. This study aims to investigate the biological degradation of low-density polyethylene (LDPE) bags by a fungus in both batch and continuous cultures, with the goal of identifying an eco-friendly and cost-effective waste management strategy. The fungal strain Rhizopus arrhizus SLNEA1, isolated from a landfill located in northeastern Algeria, was tested for its capability to degrade LDPE films and utilize them as a sole carbon source in batch (α-LDPE) and continuous (γ-LDPE) cultures. The results indicated a higher rate of weight loss for γ-LDPE (29.74%) compared to α-LDPE (23.77%). The biodegradation effect was examined using scanning electron microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) to evaluate morphological and chemical changes in LDPE samples, highlighting alterations of LDPE films through cracks, veins and holes under SEM and chemical transformation and appearance of new functional groups in the FTIR data. Rhizopus arrhizus SLNEA1 demonstrated the ability to break down and utilize LDPE films as a carbon source. This isolate shows promise for LDPE biodegradation applications, which may be leveraged for the development of future plastic degradation systems involving fungi.

Keywords: Rhizopus arrhizus; . Biodegradation; Batch culture; Continuous culture; LDPE films.

Fig. 1

Experimental setup for continuous culture of Rhizopus arrhizus SLNEA1 in LDPE-enriched condition [24]

Fig. 2

Macroscopic appearance of Rhizopus arrhizus SLNEA1 on PDA after 7 days of incubation at 27 °C

Fig. 3

Microscopic appearance of Rhizopus arrhizus SLNEA1 strain under optical microscopy (10x and 40x magnifications) after 7 days of incubation

Fig. 4

Phylogenetic tree generated by maximum likelihood analysis of combined ITS- LSU sequence data of Rhizopus and Phycomyces species. The tree was rooted using Phycomyces blakesleeanus CBS 284.35. ML bootstrap support values greater than 50% are shown near the nodes. The isolate of interest SLNEA1 is indicated in bold

Fig. 5

Evolution of the weight of LDPE film after 30, 60 and 90 days of exposure to Rhizopus arrhizus SLNEA1 in a batch culture compared to the control

Fig. 6

Evolution of the weight of LDPE films (F1 to F6) after 30, 60 and 90 days of exposure to Rhizopus arrhizus SLNEA1 in a continuous culture compared to the control

Fig. 7

Control LDPE film under Scanning Electron Microscopy at 1000x (a), 1500x (b) and 2000x (c) magnification

Fig. 8

LDPE film exposed to Rhizopus arrhizus SLNEA1 in batch culture after 30 days of incubation under Scanning Electron Microscopy at 1000x (a), 1500x (b) and 2000x (c) magnification

Fig. 9

LDPE film (F5) exposed to Rhizopus arrhizus SLNEA1 in continuous culture after 30 days of incubation under Scanning Electron Microscopy at 1000x (a), 1500x (b) and 2000x (c) magnification

Fig. 10

LDPE film (F5) exposed to Rhizopus arrhizus SLNEA1 in continuous culture after 90 days of incubation under Scanning Electron Microscopy at 1000x (a), 1500x (b) and 2000x (c) magnification

Fig. 11

Energy dispersive X-ray spectroscopy analysis of control LDPE film

Fig. 12

Energy dispersive X-ray spectroscopy analysis of LDPE film exposed to Rhizopus arrhizus SLNEA1 in batch culture

Fig. 13

Energy dispersive X-ray spectroscopy analysis of LDPE film (F5) exposed to Rhizopus arrhizus SLNEA1 in continuous culture

Fig. 14

FTIR spectra of LDPE films exposed to Rhizopus arrhizus SLNEA1 in batch and continuous cultures compared to the control

Fig. 15

FTIR insights into chemical changes in LDPE films exposed to Rhizopus arrhizus SLNEA1 in batch (b) and continuous culture after 30 and 90 days of incubation (c and d respectively) compared to the control (a). (i) represents the intensity of the peaks