Investigation of degradation potential of polyethylene microplastics in anaerobic digestion process using cosmetics industry wastewater

Abstract

In this study, the effect of polyethylene (PE) microplastics (MPs) with different sizes (150 mu m and 50 mu m) and abundances (1 g/L, 2 g/L, and 4 g/L) on the anaerobic digestion (AD) of the cosmetic industry wastewater (CoIW) was investigated. The results showed that 50 mu m PE-MPs did not significantly affect the cumulative biogas production compared to the control. On the other hand, three different scenarios were observed considering the different abundances of 150 mu m PE-MPs. The 150 mu m of PE-MPs at 4 g/L showed the most adverse effect on AD and cumulative biogas production was significantly inhibited and decreased by approxi-mately 7 % compared to the control group, while cumulative biogas production increased by approximately 12 % at 1 g/L MP abundance. Removal of sCOD averaged 52-53 % for all abundances of 50 mu m MPs. For 150 mu m MPs, the sCOD removals for 1 g/L, 2 g/L, and 4 g/L were determined as 52 %, 58 %, and 56 %, respectively. Model -based analysis indicated that 50 mu m PE-MPs at all MP abundances decreased the control's hydrolysis coefficient (k). The inhibition of biogas production potential could be attributed to smaller-sized MPs having larger surface areas, so they adsorb more inhibitors in the medium and thus limit the activity of anaerobic microorganisms. In support of this, SEM results indicated that 150 mu m PE-MPs surfaces possessed more erosions and grooves.