Application of light-emitting diodes in bioreactors: Flashing light effects and energy economy in algal culture (Chlorella pyrenoidosa)

Abstract

Light‐emitting diodes (LEDs) were used as the sole light source in continuous culture of the green alga Chlorella pyrenoidosa. The LEDs applied show a peak emission at 659 nm with a half‐power bandwidth of 30 nm. Selection of this wavelength range, which is optimal for excitation of chlorophylls a and b in their “red” absorption bands makes all photons emitted potentially suitable for photosynthesis. No need for additional supply of blue light was found. A standardized panel with 2 LEDs cm−2 fully covered one side of the culture vessel. At standard voltage in continuous operation the light output of the diode panel appeared more than sufficient to reach maximal growth. Flash operation (5‐μs pulse duration) enables potential use of higher operating voltages which may render up to three times more light output. Flat airlift fermentor‐type continuous culture devices were used to estimate steady state growth rates of Chlorella pyrenoidosa as a function of the light flux (μmol photons · m−2 · s−1) and the flashing frequency of the light‐emitting diodes (which determines the duration of the dark “off” time between the 5‐μs “on” pulses). At the fixed voltage and turbidostat setting applied a 20‐kHz frequency, which equals dark periods of 45 μs, still permitted the maximum growth rate to become nearly reached. Lower frequencies fell short of sustaining the maximal growth rate. However, the light flux decrease resulting from lowering of the flash frequency appeared to reduce the observed growth rates less than in the case of a similar flux decrease with light originating from LEDs in continuous operation. Flash application also showed reduction of the quantum requirement for oxygen evolution at defined frequencies. The frequency domain of interest was between 2 and 14 kHz. LEDs may open interesting new perspectives for studies on optimization of mixing in mass algal culture via the possibility of separation of interests in the role of modulation on light energy conversion and saturation of nutrient supply. Use of flashing LEDs in indoor algal culture yielded a major gain in energy economy in comparison to luminescent light sources. © 1996 John Wiley & Sons, Inc.

Microalgal Biotechnology and Bioenergy in Dunaliella

“…The light requirement coupled with high extinction coefficient of chlorophyll in algae has necessitated the design and development of novel system for large scale growth. Experiments have also elucidated that algal biomass production can be boosted by the flashing light effect (Matthijs et al, 1996), namely by better matching photon input rate to the limiting steps of photosynthesis. Indeed, the best annual averaged productivity has been achieved in closed bioreactors.…”

Eco-Physiological Barriers and Technological Advances for Biodiesel Production from Microalgae

“…Flashing light from blue LEDs is also a promising illumination method for H. pluvialis growth and astaxanthin production (Katsuda et al 2006). The use of flashing LED as sources of intermittent light in indoor algal culture can yield a major gain in energy economy comparing to fluorescent light sources (Matthijs et al, 1996). The research results by Nedbal et al (1996) also suggest that algal growth rates in intermittent light can be higher than those in equivalent continuous light.…”

Estudo da produção de biomassa e lipídios no cultivo de Neochloris oleoabundans sob diferentes condições de estresse nutricional e físico

“…No caso das clorofilas a e b, as faixas de absorção estão presentes no azul e nas regiões espectrais vermelhas. Em termos de economia energética, os fótons vermelhos são menos energéticos e servem igualmente bem para a fotossíntese como os fótons azuis, com aproximadamente 40% mais energia; este excesso de energia não é adequadamente utilizado, sendo liberado em forma de calor para que a clorofila passe de um estado altamente excitado a um estado de menor excitação dentro do fotossistema (MATTHIJS et al, 1996).…”

“…(BALDISSEROTTO et al, 2012;BAND et al, 1992;SANTOS et al, 2012). pronunciada assimilação e desassimilação dos carboidratos, enquanto que e os valores de proteínas permanecem constantes (MATTHIJS et al, 1996).…”

“…Finalmente, o ensaio com luz LED vermelha duplicou o teor de lipídios quando comparado com o ensaio controle e aparentemente não tem um efeito regulatório no metabolismo de proteínas e carboidratos, como sugerido pelo grupo de Matthijs (1996). Do mesmo modo, foi calculada a concentração de lipídios totais produzidos nos ensaios, seguindo a formula:…”