Modeling the efficacy of Algae at removing microplastics in wastewater treatment plants

Microplastics have emerged as a significant environmental contaminant in aquatic ecosystems and drinking water supplies, with growing evidence linking prolonged exposure to adverse human health outcomes. In accordance with the United Nations Sustainable Development Goal 6 of “clean water and sanitation”, current research investigates proposed mechanisms of reducing this plastic contamination in our water systems. One proposed mechanism is to improve upon the photobioreactors in wastewater treatment plants (WWTPs). Algae, like the ones used in WWTP photobioreactors, have shown promise in removing microplastics from water through heteroaggregation. However, mathematical models of this process remain limited. In this paper, we develop a system of coupled ordinary differential equations for algae growth, consumption of nutrients, and removal of microplastics, using literature-drawn parameters. Numerical solutions to this model predict plastic removal levels of 35% relative to influent concentrations at equilibrium. Sobol sensitivity analyses identified solid retention time (SRT) and hydraulic retention time (HRT) as sensitive parameters for plastic removal. Equilibrium analyses identified the necessary conditions for algae to be appropriately seeded and highlighted the positive effect of increasing SRT and HRT on plastic removal. Overall, this study provides a quantitative framework for understanding algae-mediated microplastic removal and offers insights for optimizing wastewater treatment processes to improve water quality.