Ecophysiological modeling of the impact of light intensity and quality on microalgal growth in outdoor high-density open ponds

Towards a consensus-based biokinetic model for green microalgae – The ASM-A

Some artificial light sources able to emit photons at specific wavelengths, such as LEDs, are useful for studying the effects of light quality on microalgal growth and production of fatty acids; however, they should not be used for outdoor cultivation of microalgae to produce bioenergy. Instead, various light filters capable of selectively transmitting red, blue, and red+blue light regions in solar radiation were used to cover 0.4 L bubble column photobioreactors to cultivate Tetraselmis sp. KCTC12236BP and investigate the influence of light quality on microalgal growth and fatty acid production. Biomass and fatty acid productivities in red light (0.10 ± 0.05 g/L/day and 11.8 ± 0.5 mg/L/day, respectively) were 7 ~ 53% and 9 ~ 61% higher than other colored lights based on the same number of supplied photons, respectively. The composition of fatty acids did not change significantly in response to transmitted light qualities of the filter. The ratio of saturated to unsaturated fatty acids was 3:7, and their contents were 12% in all groups, which corresponds with the results of LEDs. Plotting biomass and fatty acid productivity over the red photon fraction in supplied light revealed that increased productivities were closely correlated with red photon fraction in the filtered light. Overall, the results presented herein indicate that enhanced production of algal fatty acid could be achieved by application of light filters in outdoor settings without artificial lights.

Optimization of the growth of microalgae is essential due to demand for high biomass yields. In addition, the methods to estimate the growth (as cell density or biomass) of microalgae are tedious. The normal methods include cell counts, optical density, chlorophyll a and ash free dry weight. However, at least two of these methods were done together for every growth experiment to get a better result. Therefore, this study investigates the effect of mixing as one of the many factors that determines the growth of microalgae, Botryococcus sp. In addition, three different methods to estimate the growth (in terms of cell density or biomass) will be utilized. Three different treatments on the effect of mixing were employed (T1 using aeration; T2 manual hand shake two times daily; T3 no aeration and shaking) for these experiments. The experiment was carried out under outdoor conditions with temperature ranging from 25.8°C to 35.5°C, light intensity from from 200 Lux to 18000 Lux and pH of 7 to 8 units for 24 days using Bold basal medium (BBM) as growth media. Microalgae biomass was estimated by optical density, chlorophyll a and cell count using haemocytometer. The highest density of Botryococcus sp. was achieved (10.74 x 106 cell ml-1day-1; OD of 3.246 at 680nm; 0.7843 mg L-1day-1 chlorophyll a) with aeration. Whereas, the lowest (2.78 x 106 cell ml-1day-1; od 1.007 (680nm); chlorophyll a 0.1586 mg L-1day-1) and (3.07 x 106 cell ml-1day-1; od 0.999 (680nm); chlorophyll a 0.1545 mg L-1day-1) with shaking and no aeration, respectively. There exist a positive linear relationship between cell counting and optical density (R2=0.96); cell count and chlorophyll a (R2=0.95); and optical density and chlorophyll a (R2= 0.98) were observed. The result of this study suggested that constant aeration is required by the microalgae, Botryococcus sp. for growth in terms of cell density and biomass.

A validated model to predict microalgae growth in outdoor pond cultures subjected to fluctuating light intensities and water temperatures

The established microalgae growth models are semi-empirical or considerable fitting coefficients exist currently. Therefore, the ability of the model prediction is reduced by the numerous fitting coefficients. Furthermore, the predicted results of the established models are dependent on the size of the photobioreactor (PBR), light intensity, flow and concentration field. The growth mechanism of microalgae has not clearly understood in PBR cultivation. It is difficult to predict the microalgae growth by theoretical methods, owing to the aforementioned factors. We developed an exploratory bridging microalgae growth model to predict the microalgae growth rate in PBRs by using the nondimensional method which is effectively in fluid dynamics and heat transfer. The analytical solution of the growth rate was obtained for the parallel flow. The nondimensional growth rate expressed as function of Reynolds number and Schmidt number, which can be used for arbitrary parallel flow due to the solution was expressed as nondimensional quantities. The theoretically predicted growth rate is compared with the experimentally measured microalgae growth rate on the order of magnitude. The nondimensional method successfully applied to the microalgae growth problem for the first time. The general nondimensional solution can unify the numerous experimental data for different laboratory conditions, and give a direction for the disorder of the microalgae growth problem. The nondimensional solution may be useful to explain the growth mechanism of microalgae and design large-scale PBRs for microalgae biofuel production. The significance of the work is to give a theoretical foundation and methodology of biological theory of microalgae growth.

Light quality was a key factor for controlling the growth and polysaccharide production of microalgae. Growth and extracellular polysaccharide production by Porphyridium cruentum cultured in flat plate bioreactors were measured as a function of light wavelength and intensity. The growth rate and polysaccharide production of Porphyridium cruentum increased with enhanced of light intensity, however a light level beyond the saturation point inhibited the growth of microalgae. Here, Photon flux density of 80 mu E m-2 s-1 was the optimal light level for maximum biomass and polysaccharide production by Porphyridium cruentum. Continuous light radiation enhanced the growth rate, but the maximum polysaccharide production was obtained at the light-dark cycle of 18:6. It was found no significant difference in cell growth between different spectrums. Green light, natural light and yellow light were found more suitable for increasing polysaccharide production than blue light and red light.

A study on growth, fermentation and thermochemical conversion of two microalgae species

A comparative life cycle assessment of microalgae production by CO2 sequestration from flue gas in outdoor raceway ponds under batch and semi-continuous regime

Microalgal-based wastewater treatment and CO2 sequestration from flue gases with subsequent biomass production represent a low-cost, eco-friendly, and effective procedure of removing nutrients and other pollutants from wastewater and assists in the decrease of greenhouse gas emissions. Thus, it supports a circular economy model. This is based on the ability of microalgae to utilise inorganic nutrients, mainly nitrogen and phosphorous, as well as organic and inorganic carbon, for their growth, and simultaneously reduce these substances in the water. However, the production of microalgae biomass under outdoor cultivation is dependent on several abiotic and biotic factors, which impact its profitability and sustainability. Thus, this study’s goal was to evaluate the factors affecting the production of microalgae biomass on pilot-scale open raceway ponds under Northern Sweden’s summer conditions with the help of a mathematical model. For this purpose, a microalgae consortium and a monoculture of Chlorella vulgaris were used to inoculate outdoor open raceway ponds. In line with the literature, higher biomass concentrations and nutrient removals were observed in ponds inoculated with the microalgae consortium. Our model, based on Droop’s concept of macronutrient quotas inside the cell, corresponded well to the experimental data and, thus, can successfully be applied to predict biomass production, nitrogen uptake and storage, and dissolved oxygen production in microalgae consortia.

The influence of different light spectra and intensities was evaluated in an in vitro culture of Achillea millefolium L. (yarrow). The treatments were: use of light emitting diode (LED) lamps in the blue, red, green and white wavelengths, and the intensities of 13; 27; 35; 47 and 69 µmol m−2 s−1, obtained with a cool fluorescent lamp. At 45 days of culture in hormone-free MS medium, the production of dry matter, survival, rooting, length of shoots and roots, numbers of roots, pigments, as well as volatile constituents, were evaluated. The quality and intensity of light significantly influenced the in vitro growth of yarrow. In the experiment with LEDs, the blue spectrum provided the highest dry matter accumulation, number of roots, percentage of rooting and survival. In different light intensities, 27 µmol m−2 s−1 showed the highest values for the variables analyzed. Thus, blue LED spectrum or cool fluorescent lamp with 27 µmol m−2 s−1 benefits the in vitro growth of yarrow. A variation in number, content and profile of volatile constituents under the influence of quality and light intensity was also observed. The major constituents identified were sabinene, 1,8 cineole, borneol, β-caryophyllene and β-cubebene, independent of the light treatments. The amount and composition of the volatile compounds ranged with the intensity and quality of light. Thus, it is possible to adjust the ambient light in order to yield the compounds of interest.

The accumulation and inhibition mechanism of extracellular polymeric substances of Chlorella vulgaris during cycling cultivation under different light qualities

Light is an important factor that influences the growth and photosynthetic efficiency of microalgae; however, little is known about how light intensity together with the wavelength affect the photosynthetic capacity and growth of marine microalgae. In the present study, the growth of the marine green microalga Dunaliella parva was studied and optimized under different light intensities (25 ~ 70 μmol m-2 s-1) and qualities (blue, green, and red) in comparison with white light at 40 μmol m-2 s-1 as a control. The growth was monitored by counting the cell number, pigment content, Chl a, Chl b, and carotenoids concentrations. The optimal growth and highest photosynthetic efficiency (Fv/Fm) were recorded at a light intensity of 40 μ mol m-2 s-1, white light, and 1.25 M NaCl (1.47 and 0.678×106 cell mL-1, respectively). The activity of antioxidant enzymes, including catalase and peroxidase, as well as ascorbate content, showed the highest values of 0.190 µM/min.mg Chl, 0.434 and 13.3 mg/g f.wt. respectively, under the green light, which confirmed the presence of environmental stresses.

LED light stress induced biomass and fatty acid production in microalgal biosystem, Acutodesmus obliquus

Modeling the Effect of Temperature on Microalgal Growth under Outdoor Conditions

Light-dependent induction of strongly increased microalgal growth by methanol