Novel Assay for Attached Filamentous Algae Productivity and Nutrient Removal

Abstract

Filamentous algae nutrient scrubbers (FANS) have demonstrated potential for cost-effective and sustainable nutrient bioremediation of a wide range of wastewaters. Typically, FANS are seeded with a mixed assemblage of algae species, however, growing a monoculture of one species on FANS could facilitate biomass use by providing a more consistent and high-quality substrate for end-product applications. To date, a standardised bioassay to assess the productivity and nutrient removal of filamentous algae attached to a bottom substrate (that could help identify promising species for FANS monoculture) has not been developed. Therefore, we developed a microscale filamentous algae nutrient scrubber (µFANS) and a protocol to establish monocultures of freshwater filamentous algae to compare performance in terms of attachment capability, nutrient removal and biomass production. Four common filamentous algae species ( Cladophora sp., Oedogonium sp., Rhizoclonium sp. and Spirogyra sp.) were seeded by evenly distributing and rubbing the biomass onto µFANS textured liner to “hook” algal filaments, providing initial physical attachment. Within 14 days, a “lawn” of the seeded algae had established and the “hooked” biomass had attached biologically. Depending on species, biological attachment resulted from either holdfast development from filaments that grew from settled zoospores, growth of rhizoids or adhesion of filament fragments to mucilage. Biomass productivity of each species ranged from 2.2 to 5.3 g DW m ⁻² day ⁻¹ while nutrient removal rates ranged from 8.8 to 28.4 mg NO ₃ g ⁻¹ DW day ⁻¹ and 2.2 to 8.1 mg PO ₄ g ⁻¹ DW day ⁻¹. Oedogonium sp. was the best performing species overall, with the strongest holdfast attachment, high biomass productivity (mean 4.2 g DW m ⁻² day ⁻¹) and high nutrient removal rates (mean 21.8 mg NO ₃ g ⁻¹ DW day ⁻¹; 5.6 mg PO ₄ g ⁻¹ DW day ⁻¹).