Cultivation of Nannochloropsis sp. using narrow beam angle light emitting diode in an internally illuminated photobioreactor

Abstract

This paper reports on the growth condition of Nannochloropsis sp. in an annular column-type photobioreactor (PBR) using light-emitting diode as an internal illumination. The microalgae growth in the 20-L batch culture mode under mixed blue (450 nm) and red (660 nm) light-emitting diode (LED) in various conditions such as photoperiod and light intensity (controlled by supplied current) was monitored. Compact-type 5-W LED module with narrow beam angle (radiation pattern) was installed in the PBR so as to obtain higher intensity and deeper penetration to the culture. Based on the PBR dimension with optical path length 120 mm, the minimum light intensity required at the PBR tank inner surface at initial stage of cultivation was approximately 350–370 mol m−2s−1, while mean light intensity derived was 140–160 mol m−2s−1. Photoperiod ratio of light:dark at 18:6 h provided better results compared to 12:12 in terms of final cell density achieved. Efficiency of light utilization was calculated to be 9.0 × 109 cell/mol photon (0.49 g/mol photon), while biomass volumetric productivity was 0.04 g L−1day−1. The usage of narrow beam angle LED was feasible to be used but with further improvement is necessary.