Microalgae for phosphorus removal and biomass production: a six species screen for dual-purpose organisms

Microalgae biofuel production can be feasible when a second function is added, such as wastewater treatment. Microalgae differ in uptake of phosphorus (P) and growth, making top performer identification fundamental. The objective of this screen was to identify dual-purpose candidates capable of high rates of P removal and growth. Three freshwater Chlorella sp., Monoraphidium minutum sp., and Scenedesmus sp. and three marine Nannochloropsis sp., N. limnetica sp., and Tetraselmis suecica sp. species were batch cultured in 250 mL flasks over 16 days to quantitate total phosphorus (TP) removal and growth as a function of P loads (control, and 5, 10, and 15 mg L-1 enrichment of control). Experimental design used 100 mu mol m-2 s-1 of light, a light/dark cycle of 14/10 h, and no CO2 enrichment. Phosphorus uptake was dependent on species, duration of exposure, and treatment, with significant interaction effects. Growth was dependant on species and treatment. Not all species showed increased P removal with increasing P addition, and no species demonstrated higher growth. Nannochloropsis sp and N. limnetica sp. performed poorly across all treatments. Two dual-purpose candidates were identified. At the 10 mg L-1 treatment Monoraphidium minutum sp. removed 67.1% (6.66 mg L-1 +/- 0.60 SE) of TP at day 8, 79.3% (7.86 mg L-1 +/- 0.28 SE) at day 16, and biomass accumulation of 0.63 g L-1 +/- 0.06 SE at day 16. At the same treatment Tetraselmis suecica sp. removed 79.4% (6.98 mg L-1 +/- 0.24 SE) TP at day 8, 83.0% (7.30 mg L-1 +/- 0.60 SE) at day 16, and biomass of 0.55 g L-1 +/- 0.02 SE at day 16. These species merit further study using high-density wastewater cultures and lipid profiling to assess suitability for a nutrient removal and biomass/biofuel production scheme.