Potential of Cyanobacterium Spirulina platensis for Eutrophic Water Restoration

Abstract

Around 70% of the world is covered with water but only 2.5% of it is freshwater and even less is available for the ecosystem and humanity. The limited available fresh water is facing increasing challenges from water pollutions and eutrophication is one of the major concerns worldwide. The reason of eutrophication is the presence of excessive amounts of phosphorus and nitrogen in water bodies, which may cause algal blooms and a variety of harms to aquatic ecosystem in association with algal blooms. Among these two components, phosphorus plays a major role in eutrophication control and recovery since atmospheric N2 can be fixed by biological nitrogen fixation (BNF) processes and is therefore of little meaning to control. In this study, we investigated for the first time the potential of using controlled growth of algae and, in particular, filamentous cyanobacterium Spirulina platensis, for eutrophic water restoration. This study investigated the algal cell growth, algal by-product production, and removal of phosphate by S. platensis at different phosphate levels in artificial wastewaters and eutrophic waters. Results indicate that S. platensis could remove 90.17% of phosphorus from artificial wastewaters containing 10 mg/L phosphate in a 16-day cultivation period. When tested for eutrophic water restoration, S. platensis was able to convert hypo-eutrophic, eutrophic, and meso-eutrophic waters to oligotrophic water. It was shown that by using 100- micron nylon mesh cloth we could keep biomass concentration to be lower than 0.30±0.02 g/L. In the meantime, light/dark tests indicate that the dissolved oxygen level would not go below the hypoxic level, i.e., 4 mg/L after a 12-hour dark period at biomass concentration up to 1 g/L. These results indicate that it is possible to use S. platensis for both control of point source discharge and eutrophic water restoration.