An Algae Water Purification and Decontamination System That Removes Microplastics, Nitrogen and Phosphorus

Abstract

Microplastic pollution and excessive discharge of aquaculture tailwater have become important global issues. The use of filamentous algae to remove nitrogen, phosphorus, and microplastics in the same system has not been reported. In this study, we constructed an algal water purification and removal system and investigated its ability to remove microplastics, nitrogen, and phosphorus from the water column. Three kinds of filamentous algae were used, Spirogyra, Enteromorpha, and Cladophora, in microplastic removal experiments in the system; the three species of filamentous algae were the most effective in removing fibrous microplastics (88.50%, 79.50%, 75.50%) and the least effective in removing granular microplastics (67.50%, 53.00%, 55.00%), respectively. Spirogyra removed microplastics better than the other two algae; therefore, it was used for nitrogen and phosphorus removal experiments in the water column. The density of algae per unit area was set to 0 (control), 2, 4, and 6 g/dm2. Spirogyra showed a Total Nitrogen removal rate of 91.88% (4 g/dm2), a Total Phosphorus removal rate of 90.33% (6 g/dm2), and a PO43–-P removal rate of 90.38% (6 g/dm2) after 15 d. The density of 4 g/dm2 showed the highest removal rate, 90.38%. There were no significant differences between the experimental results of the 4 and 6 g/dm2 groups (P > 0.05). The results showed that the system effectively removed fibrous microplastics and absorbed nitrogen and phosphorus from the water body and that an algal density per unit area of 4 g/dm2 was the most suitable for removing nitrogen and phosphorus in this system.

Keywords

• microplastics
• aquaculture tailwater
• filamentous algae
• water purification and decontamination system