Biodegradation of low-density polyethylene (LDPE) using the mixed culture of Aspergillus carbonarius and A. fumigates

Abstract

Low-density polyethylene (LDPE) possesses various applications in several industries owing to its durability, low-cost, and many mechano-thermal properties. Unfortunately, LDPE waste creates an environmental threat. The level of biodegradation of black LDPE sheets with fungi isolated from different landfills sites in Sharqiyah Governorate, Egypt, was evaluated. LDPE sheets, the only source of carbon, along with minimal salt medium were incubated on a rotary shaker at 30 °C and 120 rpm for 16 weeks. Aspergillus carbonarius MH 856457.1 and A. fumigatus MF 276893 confirmed to be good candidates for LDPE biodegradation. A mixed culture of two strains showed the excellent weight loss% of sheets as compared to single isolate. Further efforts to improve the degrading capacity through physical and chemical treatments were performed. The biodegradation was significantly stimulated by 39.1% (thermal treatment), 17.76% (HNO3 treatment), and 5.79% (Gamma-irradiation treatment). Laccases and manganese peroxidases activities were assayed. LDPE biodegradation was analyzed by scanning electronic microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and gas chromatography–mass spectrometry (GC–MS). FTIR spectra showed the appearance of new functional groups assigned to hydrocarbon biodegradation and confirmed the role of manganese peroxidase in process. The changes in the FTIR spectra of the mixed culture biomass before and after the biodegradation (Δ73 cm−1) and the surface changes in the biodegraded LDPE (as indicated from SEM) confirmed the depolymerization of LDPE. From GC–MS analysis, the plasticizers bis(2-ethylhexyl) phthalate, Diisssctyl phthalate, 1,2-benzenedicarboxylic acid diisooctyl ester, and tributyl acetylcitrate completely biodegraded. Moreover, several antioxidants, antimicrobial, and anticancer compounds, and methyl esters of fatty acids were produced.