No abstract

Photobioreactors are used to produce microalgae biomass for many purposes in industries and agriculture. This research was aimed at investigating alternative source of nutrients with lower cost to produce a sustainable microalgae biomass production in a photobioreactor system other than using F2 nutrient medium, the most commonly microalga nutrient compositions used in laboratories. Firstly, two nutrient sources were used to cultivate Chlorella sp. in the laboratory, i.e., a commercial fertilizer (GrowMore™) and a common fertilizer (NPK) having nitrogen equals to 12.3 mg/L. Chlorella sp. biomass grown in the medium containing the commercial fertilizer or NPK was not significantly different to that of F2 medium, as well as when the dose of the commercial fertilizer was doubled. The commercial fertilizer was then selected as a source of nutrients in the cultivation of microalgae in 135 litre photobioreactors. Chlorella sp. biomass grown in the photobioreactors for 14 days using F2 medium was 0.80 mg/L, while using the commercial fertilizer was 0.75 g/L. Cost analyses of microalga production using these commercial fertilizers showed that it was 80% less than the cost of using F2 nutrient composition. These results showed that the commercial fertilizer could be used as alternative nutrient source for microalgae cultivation in photobioreactors.

Microalgae cultivation is considered fit to the concept of green economy, in which greenhouse gases (GHG’s) mitigation and production of valuable substances is performed simultaneously. Carbon dioxide consumption by the algal cells reduces GHG’s emission to the atmosphere, while biomass conversion to biofuel feedstock supports the concept of circular economy of microalgae cultivation process. In this study, Chlorella sp. was cultivated in a Multi Tubular Airlift Photobioreactor (MTAP) system with a total volume of about 600 L. The result of a thirteen days batch culture showed the ability of the system to fix 1.57 g CO2 L-1 day-1. At the last day of experiment, 600 L MTAP showed biomass production of 0.35 g L-1 and 18% oil from cell dry weight was observed. This research showed the ability of 600 L MTAP to absorb 942 g CO2 and produce 37.8 g oil as biofuel feedstock. Compared to other experiments, percentage of oil in this experiment (18% from cell dry weight) was in the average range from other experiments (of about 10 – 40% from cell dry weight). However, this MTAP showed higher performance than other systems (mostly below 1 g CO2 L-1 day-1) in CO2 fixation rate.