Cultivation of marine microalgae, Nannochloropsis sp. in macro-bubbles photobioreactor system

Abstract

Oil production from microalgae may be more effective, leaving a smaller environmental footprint and avoiding competition for arable land or biodiversity ecosystems. Present outdoor and open algae cultivation systems and lipid induction methods, on the other hand, need to be significantly improved and are vulnerable to being contaminated by other algae or algal grazers. The cultivation system for the current indoor bioreactor, however, is expensive due to its materials. Closed-culture systems (photobioreactor type) have high production but not cost-effective for maintenance, where else, opened-culture systems have contamination issues resulting in lower productivity. This study focuses on cultivating microalgae using a contemporary design of a closed system using an airlift loop photobioreactor with a draft tube placed in the middle of the reactor and using a cheaper material (autoclavable polycarbonate material). The cultivation optimisation of Nannochloropsis sp. was carried out at a different condition of photobioreactor system with a range of aeration rate, light intensity, and inoculum concentration. The best growth performance was in a macro-bubble column system with 0.211 g/mL and a 0.9 L/min aeration rate that produced a maximum cell dry weight of 0.288 g/mL of algal biomass. For the light intensity parameter, the best growth performance was at 3000 lux, with a dry cell weight of 0.211 g/mL followed by inoculum concentration at 15% v/v that produced the highest maximum dry cell weight of 0.213 g/mL of algal biomass. In this study, a low-cost indoor photobioreactor system using cheap autoclavable material has been tested and shown a promising result, thus has the potential to be commercialised in the future.