Determination of microplastic pollution in marine ecosystems and its effective removal using an advanced nanobubble flotation technique

Microplastics (MPs), defined as plastic debris with a diameter <5 mm, have become a significant global hazard, posing risks to human health and the marine ecosystem. Assessing and efficiently removing MPs from marine water is crucial in preventing harm to marine life, human health, and the environment. This study aims to investigate the occurrence, abundance, and composition of MPs in marine waters in Hong Kong and propose the use of nanobubble flotation technology for their effective removal. The findings indicate that seawater samples collected from three locations within the study area exhibited high levels of MPs (82–137 particles/m³), with fragments and fibers being the most common shapes. The predominant size of MPs fell within the 0.1–0.5 mm range, with transparent being the dominant observed color. Given the prevalent environmental challenge posed by small-sized MPs, we investigated the implementation of nanobubble flotation (NB) technology as a novel approach to remove MPs <100 μm in size. Our results showed a significant improvement in removal efficiency, particularly for small-sized MPs (<50 μm) when using NB flotation compared to conventional dissolved air flotation (DAF). The superior removal efficiency of MPs through NB flotation is attributed to the small size and high concentration of NBs, which enhance particle-bubble collisions and adhesion, along with improved hydrophobic interactions.