Nutrient uptake and biomass productivity performance comparison among freshwater filamentous algae species on mesocosm-scale FANS under ambient summer and winter conditions

Abstract

Filamentous algae nutrient scrubbers (FANS) have demonstrated potential for cost-effective and sustainable nutrient bioremediation of a wide range of polluted waters. Their performance depends on the rate at which the algae can assimilate nutrients from the water and produce biomass. This study investigated the growth rates and nutrient uptake rates of four locally isolated filamentous algae species (Cladophora sp., Oedogonium sp., Rhizoclonium sp., and Spirogyra sp.) cultivated with nutrient enriched freshwater with a concentration of 2 mg L−1 of nitrate and 0.2 mg L−1 of phosphate under ambient summer and winter conditions to identify target species for use on FANS. Variation in environmental conditions had a large effect on the performance of each species. Biomass productivity of the four species ranged from 1.2 to 4.5 g DW m−2.d in summer and 0.7 to 1.6 g DW m−2.d in winter. Nutrient removal rates ranged from 0.39 to 0.51 g NO3 m−2.d and 0.16 to 0.18 g PO4 m−2.d in summer and 0.32 to 0.51 g NO3 m−2.d and 0.08 to 0.09 g PO4 m−2.d in winter. Overall, Oedogonium sp. was the best performer of the four species tested, with the highest biomass productivity (mean 4.5 g DW m−2.d in summer; 1.6 g DW m−2.d in winter) and the highest nitrate removal rates under summer (mean 0.51 g NO3 m−2.d) and winter (mean 0.51 g NO3 m−2.d) conditions. Furthermore, Oedogonium sp. FANS had the lowest contamination in terms of percentage cover of non-target species compared to the other three species under both summer and winter conditions. These results demonstrate that Oedogonium sp. has higher tolerance than the other three species to summer and winter ambient temperature and light variation, allowing Oedogonium sp. to maintain dominance on the floway for a longer period. For these reasons, Oedogonium sp. is identified as a promising target for year-round cultivation on FANS.