The Potential of Ozonation to Reduce Impact of Waste Sludge-Entrapped Microplastics to Biogas Production

Due to low degradability of plastic materials, high usage, and low cost, microplastics (MPs) is becoming ubiquitous environmental pollutant. Wastewater treatment plants (WWTP) are one of main sources, where most of the MPs from wastewaters ends in waste sludge. Anaerobic digestion is one of most promised techniques of waste sludge management. The aim of this paper was to evaluate the impact of polyethylene terephthalate (PET) and polypropylene (PP) microplastics in the waste sludge with and without ozonation as possible pretreatment, on biogas and methane production with OxiTop$^®$ method. In the first set of experiments, PET inhibited (up to 6% at 0.1 g $L^{−1}$) or promoted (up to 3% at 1 g $L^{−1}$) methane production but increased cumulative biogas production (up to 38% at 0.5 g $L^{−1}$). PP inhibited methane production (up to 5% at 0.5 g $L^{−1}$) but its impact on biogas production was dependent upon concentration of MPs added. In the second set of experiments, pretreatment of non-contaminated waste sludge by ozonation (3.54 $g_{ozone}$ $h^{−1}$) inhibited methane yield. Longer time of ozonation of PP-contaminated waste sludge reduced inhibition of methane yield, while in the case of PET-contaminated waste sludge, it was increased.