Integrated inactivation of Microcystis aeruginosa and degradation of microcystin-LR by direct current glow discharge plasma in liquid-phase: Mechanisms and cell deactivation process

Abstract

The frequent occurrence of blooms of Microcystis aeruginosa (M. aeruginosa) and the subsequent release of microcystin-LR (MC-LR) in eutrophic waters pose a serious threat to aquatic ecosystems. This study investigated the optimal conditions for inactivating M. aeruginosa and the degrading MC-LR using direct current glow discharge plasma in liquid phase (DC-LGDP), analyzed the potential inactivation mechanisms and the cell deactivation process of M. aeruginosa. The results showed that DC-LGDP generated reactive species (i.e., •OH, ¹O₂, and H₂O₂), active Cl and electroporation effect collectively contributed to inactivation of M. aeruginosa and degradation of MC-LR. The 97.07% inactivation efficiency of M. aeruginosa and 94.98% degradation rate of MC-LR were achieved with higher energy yield and without generating nitrogen oxides. Meanwhile, DC-LGDP destroyed the cell integrity, eliminated their antioxidant capacity and reduced the content of photosynthetic pigments. The transcriptome analysis indicated that the transcripts of genes related to photosynthesis, ribosome biosynthesis, ABC transporters, and nitrogen metabolism pathway in M. aeruginosa were altered by DC-LGDP. This study provides insights into the inactivation of M. aeruginosa by DC-LGDP, while elucidating the potential inactivation mechanisms and the cell deactivation process involved. It may be important for the eco-friendly inactivation of M. aeruginosa blooms in natural water bodies.

Environmental implications

The frequent occurrence of blooms of M. aeruginosa and the subsequent release of MC-LR in eutrophic waters are a global issue. Although glow discharge plasma technologies have been applied for the inactivation of M. aeruginosa, limitations such as low energy yield and additional nitrous oxide production remain. This study aims to explore the optimal conditions for inactivating M. aeruginosa and degrading MC-LR using direct current glow discharge plasma in liquid phase (DC-LGDP), as well as to analyze the inactivation mechanisms and the cell deactivation process of M. aeruginosa. Our results show that the 97.07% inactivation efficiency of M. aeruginosa by DC-LGDP is achieved at higher energy yield and without the generation of nitrogen oxides. The inactivation of M. aeruginosa and degradation of MC-LR are involved in the reactive species generated by DC-LGDP and electroporation effect. These factors induce oxidative stress damaging the cell integrity, impairing the photosynthesis and ribosome biosynthesis pathways of M. aeruginosa, ultimately leading to the cell deactivation of M. aeruginosa. Our findings provide insights into the effective inactivation of M. aeruginosa and the degradation of MC-LR by DC-LGDP with lower energy consumption and environmental friendliness. Thus, it may be important for the inactivation of M. aeruginosa blooms in natural water bodies.