The effect of LEDs on Galdieria sulphuraria cultivation at indoor and outdoor condition.

Abstract

Conventional methods for recovering heavy metals from industrial waste stream often involve significant energy consumption and chemical use. Hence, using microalga as a biosorbent material can be a low-cost and eco-friendly solution. Galdieria sulphuraria is a red microalga which is known to be capable of recovering heavy metals. This algal species is resistant to extreme temperatures and acidic environment. It is also well-established that light emitting diodes (LED) is effective at promoting algal growth. Our research objectives were to study the effects of LED lightings (red, blue, green, and white) on the growth of G. sulphuraria and to compare the growth in indoor and outdoor cultivations. In this work, the culture medium was the modified 2x Allen’s with pH 2.5. To promote the rapid growth of G. sulphuraria, the culture medium was supplemented with 2% CO2. Algal growth was determined by measuring the optical density at 750nm (OD750) using UV-vis spectrophotometer. Results have shown that in indoor cultivation, the growth rate of G. sulphuraria was highest under red light (μ= 0.06 day−1) and lowest under blue light (μ= 0.02 day−1). For outdoor cultivation, algal growth rate increased by 2 to 6-fold higher compared to that in indoor cultivation. Algal cultivation in outdoors was best with white light (OD = 2.46 ± 0.09; μ = 0.13 day−1). Although the use of LEDs enhanced algal growth, we found it did not make a significant difference statistically when compared to the set without LEDs. This may be attributed to the Malaysia’s environment (photoperiods, temperatures, etc.). This paper will serve as a foundation for future research on cultivating G. sulphuraria indoors and outdoors using various LED lights.