Apparent weight loss and surface modification of household waste-derived mixed PE/PP microplastics by Bacillus pumilus and fungal isolates

Microplastics are persistent contaminants of terrestrial and aquatic environments, creating a need for carefully validated remediation approaches. This laboratory study examined apparent weight loss and surface modification of household waste-derived mixed polyethylene/polypropylene (PE/PP) microplastics by Bacillus pumilus, Aspergillus niger, and Trichoderma harzianum. The isolates were incubated separately in carbon-deficient mineral salt medium containing microplastics as the only added carbon source. Apparent gravimetric weight loss, microbial growth, and pH were assessed, and Bacillus pumilus-treated particles were further examined by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Bacillus pumilus produced the numerically greatest apparent weight loss (40.0% ± 1.1%), followed by Aspergillus niger (30.0% ± 1.0%) and Trichoderma harzianum (20.0% ± 1.0%); however, the overall comparison was not statistically significant (one-way ANOVA, p = 0.243). SEM demonstrated surface roughening, pits, and cracks, while XRD showed lower relative crystallinity in treated particles (48% ± 3%) than in the untreated control (65% ± 2%). FTIR demonstrated spectral changes consistent with oxidative surface modification. The bacterial isolate was placed within the Bacillus pumilus group by 16S rRNA analysis, and preliminary liquid and calcium-alginate formulations were prepared. Because the substrate was a mixed PE/PP fraction and the analytical endpoints did not directly measure mineralization or molecular-weight reduction, the findings are interpreted as laboratory-scale apparent weight loss and polymer-associated surface and structural modification rather than complete biodegradation.