Influence of light intensity on microalgal growth, nutrients removal and capture of carbon in the wastewater under intermittent supply of CO₂

Abstract

BACKGROUND: The role of light intensity in microalgal cultivation supplied with CO 2 is still required to be fully investigated. This study researched the growth of Chlorella vulgaris (C. vulgaris), nutrient removal and carbon capture in the wastewater for various light intensities under the intermittent injection of CO 2 . RESULTS: The biomass for 80 mol m −2 s −1 reached maximum value within 6 days. The chlorophyll content of C. vulgaris exhibited an ascending trend when increasing the light intensity from 20 to 60 mol m −2 s −1 . Cultural pH for 80 mol m −2 s −1 showed the largest level of increase in the first 4 days, then began to decline. The light intensity of 80 mol m −2 s −1 had the quickest TN and TP reduction trend in the wastewater. The difference in consumed N versus P ratio was caused by the different specific growth rates and demands for nutrients at each growth stage of C. vulgaris. The degradation of tryptophan-like substances and the increase of other substances were likely due to the release of extracellular polymeric substance of C. vulgaris. CONCLUSION: The light intensity of 80 mol m −2 s −1 resulted in the highest biomass, the quickest TN and TP reduction trend in the wastewater. Light intensity exhibited no significant influence on removal of organic carbon, but affected the transformation of organic compounds in the wastewater under intermittent supply of 10% CO 2 . RESULTS AND DISCUSSION BiomassThe biomass of C. vulgaris presented an ascending trend when increasing the light intensity from 20 to 60 μmol m −2 s −1 , as described in Fig. 1(a). However, no significant differences in biomass were observed between 60 and 80 μmol m −2 s −1 . The biomass for 80 μmol m −2 s −1 reached a plateau within 6 days, being 1.04 g L −1 , whereas the plateaus (0.65, 0.95, 1.03 and 0.95 g L −1 ) were reached within 6.5 days for 20, 40, 60 μmol m −2 s −1 and gradual increase treatments. Thus, C. vulgaris attained the maximum biomass for various light intensities at 6 or 6.5 days. Higher light intensity resulted in an increase in maximum biomass concentration achievable, but when the light intensity was above a certain threshold value, the highest biomass achievable become lower. The result was in agreement with the finding J Chem Technol Biotechnol 2018; 93: [3582][3583][3584][3585][3586][3587][3588][3589]

Evaluation of microalgae growth in a mixed‐type photobioreactor system for the phycoremediation of wastewater

“…in effluent medium and that CO 2 addition is an important variable. In addition, the use of intermittent CO 2 is an option for a high yield in biomass . These results also showed the importance of the mixing effect (homogenization of the culture medium) and their cooling provided for certain level of turbulence caused by the diffusion of air at the base of the vertical tubes and by flow through the turf scrubber which prevents the accumulation of biomass and allows gas exchange.…”

“…In addition, the use of intermittent CO 2 is an option for a high yield in biomass. 50 These results also showed the importance of the mixing effect (homogenization of the culture medium) and their cooling provided for certain level of turbulence caused by the diffusion of air at the base of the vertical tubes and by flow through the turf scrubber which prevents the accumulation of biomass and allows gas exchange. This could be achieved due to the mixed design of the system that allowed the advantages of open forms (reservoir with turf scrubber) and closed (tubular photobioreactors) to microalgae cultivation.…”

Light intensity-dependent changes in the photochemistry of photosystem II, cell constituents, and lipid accumulation in the Wild-type (WT) and DCMU-tolerant mutant of green alga Scenedesmus vacuolatus

“…Further, an increase in the light intensities (80-100 µmol m − 2 s − 1 ) beyond their respective tolerance limits caused a drastic decrease in the growth and cell constituents of both the strains except the lipid. Liu et al (2018) found that the maximum growth of C. vulgaris under a light intensity of 60 and 80 µmol m − 2 s − 1 . They also suggested that the light intensities beyond the growth saturating limit caused a drastic decrease in the light use e ciency of the microalgal cells.…”

“…Earlier workers have reported that photosynthetic microalgae have developed many strategies to handle the excess light energy such as down-regulation of the photosynthetic process by photoinhibition (Murata et al, 2007), anti-oxidative defense system (Yilancioglu et al, 2014;Snoeijs et al, 2012) and storage of excess light energy into high energy compounds like lipid (He et al, 2015). The metabolic strategy of the algal cells to divert the photosynthetic carbon ux towards fatty acid synthesis can be useful for biofuel production technology (Liu et al, 2018).…”

Microalgal biorefinery: Challenge and strategy in bioprocessing of microalgae carbohydrate for fine chemicals and biofuel

“…Apart from that, the effect of light intensity and surrounding temperature was also reported that could influence the carbohydrate content in microalgal biomass [46]. It is worth mentioning that, during microalgal photosynthesis, carbohydrates are produced as the final product to be used as an energy source during respiration.…”