Effect of microplastics on sulfate reduction in landfill leachate-saturated zone

The sulfate reduction behavior in the leachate-saturated zone of landfills is significantly influenced by the type of microplastics (MPs) and temperature. This study established different temperature conditions based on the leachate-saturated zone of landfills to investigate the sulfate reduction behavior influenced by different types of MPs at different temperatures. The results showed that H₂S release was more intense under the influence of polylactic acid (PLA). Additionally, the cumulative H₂S release increased with rising temperature. In the PLA group, the cumulative H₂S release at 55 °C was 33.2, 2.3, and 1.4 times higher than at 25 °C, 35 °C, and 45 °C, respectively. The sulfate reduction behavior in the PS, PE, and PVC groups is relatively weak, with the cumulative H₂S release at 55 °C being only 0.004-0.01 times that of the PLA group. Compared to the influence of temperature, the type of MPs was the main factor contributing to significant differences in the dissimilatory sulfate reduction (DSR) process. The DSR functional genes were more easily enriched in PLA, leading to the release of large amounts of H₂S. However, for the assimilatory sulfate reduction (ASR) process, the overall consumption of SO₄^2- for microbial synthesis of cell components was not significantly influenced by the type of MPs. Furthermore, temperature was the main factor contributing to significant differences in the ASR process, with the enrichment ability of MPs for ASR functional genes decreasing as the temperature increased. Additionally, compared to the PS, PE, and PVC, PLA was more conducive to the growth and enrichment of dissimilatory sulfate-reducing bacteria , but the dominant genus responsible for H₂S release was determined by temperature. The dominant genus changed from Desulfonatronum and Thermodesulfomicrobium at mid-to-low temperatures (25 °C and 35 °C) to Candidatus_Desulforudis at high temperatures (45 °C and 55 °C) in the PLA group. This study reveals the sulfate reduction behavior under the influence of MPs in the leachate-saturated zone of landfills, providing new insights for landfill management and pollution control, such as controlling the entry of microplastics at the source to reduce the risk of significant H₂S release.