Effects of nitrogen and phosphorus concentrations on the growth of microalgae Scenedesmus. LX1 in suspended-solid phase photobioreactors (ssPBR)

Attached microalgae cultivation is an effective way to decrease the high harvesting cost in microalgae biomass production. Nitrogen and phosphorus, as the two main nutrients, are hypothesized to influence the attachment efficiency and growth of microalgae. The attached growth of Scenedesmus. LX1 in the suspended-solid phase photobioreactor (ssPBR)1 with feed composed of different total nitrogen (TN) and total phosphorus (TP) concentrations was studied in this paper. The productivity of attached microalgae on Day 3 (3 × 106 cells·cm−3) at the nutrient levels of TN = 15 g m−3 and TP = 5 or 3 g m−3 was approximately 70% higher than that at relatively high-nutrient levels (i.e. TN = 150 g m−3 and TP = 10 or 15 g m−3). Under the nutrient levels of TN = 15 g m−3 and TP = 5, 3, 1.5, 0.5 g m−3, the average TN and TP concentrations in the microenvironment around microalgae biofilm were about 2.1 and 15.5 times higher than those of the bulk media, respectively. The higher nutrient concentration in the surrounding microenvironment of microalgae biofilm improved protein synthesis of attached microalgae compared to the suspended ones within the same reactor, especially at the late stage of batch cultivation.