Fate and transport of microplastics at water recycling plants

Microplastic pollution is a growing global concern for environmental and public health. Water Recycling Plants (WRPs) are a significant pathway for microplastics (MP) to enter the environment. However, existing WRPs are not specifically designed to manage microplastic pollution. Water utilities generally have limited or no experience in sampling and analysing MPs. There was also no knowledge about the efficiency of lagoon-based WRPs in removing MPs. In Australia, 60% of more than 1,200 WRPs use pond/lagoon as the primary treatment step, while 77% use ponds as one of the treatment steps. Additionally, there is very limited understanding of seasonal variation of MPs in WRPs influent. As the first long-term MP study at WRPs, this research investigated the fate and transport of MPs in three Australian WRPs via a 2-year study, covering different treatment scenarios used by the water industry. Our study allowed water utilities to gain a first experience in sampling and characterising MPs. It identified that different treatment systems can all achieve promising removal of MPs (>97%). A seasonal variation of MPs concentration was also found, which was most likely related to stormwater events in the catchment. A multimedia model was established to help water utilities to predict MPs behaviours and enhance their removal. The results highlighted the potential of low-cost/low-energy lagoon-based WRPs for MP control. The new knowledge addresses water industry key knowledge gaps, helps water utilities to successfully manage MPs in WRPs, mitigates microplastic pollution risks in the environment, and addresses community’s concerns.