Modifying filamentous algae nutrient scrubbers for improved wastewater treatment and harvestability - comparison with...

Algae have been well studied for their abilities to treat wastewater, and several types of treatment systems have been demonstrated at a range of scales. High Rate Algae Ponds (HRAP) are a microalgae-based system and Filamentous Algae Nutrient Scrubbers (FANS) a filamentous algae-based system. For FANS, nutrient removal rates are typically lower and more variable than HRAPs, while HRAPs have lower productivity and poor harvestability. This study investigated if modifying a FANS to mimic HRAPs (using high rate algae mesocosms HRAM), with respect to hydraulic retention time (HRT) and smaller footprint, overcomes FANS limitations, while increasing wastewater treatment and resource recovery compared to HRAPs. Biomass productivity on the FANS (10.5 ± 2.9 g m^-2 d^-1) and FANS with CO₂ addition (19.0 ± 4.8 g m^-2 d^-1) were significantly higher (p < 0.01) compared to the HRAMs (6.7 ± 1.4 g m^-2 d^-1) and HRAMs with CO₂ addition (8.1 ± 1.2 g m^-2 d^-1). Under phosphorus replete conditions, biomass production was significantly higher on FANS (44.8 ± 14.4 g m^-2 d^-1) than HRAMs (5.0 ± 0.6 g m^-2 d^-1). Effluent quality (nutrient removal) was significantly higher (p < 0.05) for FANS compared to HRAMS, regardless of treatment. For harvesting, FANS (2.9-41%) yielded significantly higher (p < 0.01) percentage solids with, and, without dewatering/gravity harvesting compared to the HRAM (0.04-0.11%). Modifying the operation of the FANS to mimic longer HRT of HRAMs resulted in higher areal biomass productivity and nutrient removal in the FANS than the HRAM, regardless of treatment. The use of filamentous algae on FANS greatly improved the percentage solids yield in the harvested biomass without the need for energy intensive harvesting techniques. Further investigations need to be undertaken to determine if benefits will be realised at fullscale.