Browsing by Author "Liyanaarachchi, VC"

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    Astaxanthin accumulation in the green microalga Haematococcus pluvialis: Effect of initial phosphate concentration and stepwise/continuous light stress
    (2020) Liyanaarachchi, VC; Nishshanka, GKH; Premaratne, RGMM; Ariyadasa, TU; Nimarshana, PHV; Malik, A
    Nutrient composition and light stress significantly affect the productivity of astaxanthin in Haemotococcus pluvialis. Hence, the present study aimed to investigate the effect of initial phosphate concentration and two distinct light regimes on astaxanthin accumulation in H. pluvialis. In the green stage, microalgae were cultivated in different initial phosphate concentrations under 2000 lx and a 12:12 h photoperiod. To initiate astaxanthin accumulation, an increased light intensity of 5000 lx was provided using two methods; (i) stepwise light stress, where a 12:12 h photoperiod was provided for 14 days, followed by 14 days of continuous illumination, and (ii) continuous illumination for 28 days. Phosphate limitation and continuous light stress were favourable to enhance cellular astaxanthin accumulation, which reached 7% by weight. The highest astaxanthin concentration of 27.0 ± 1.9 mg/L and lowest specific light energy consumption of 32.9 ± 2.3 kW h/g astaxanthin were reported in cultures grown in 41 mg/L phosphate under continuous light stress.
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    Investigation of the effect of solar irradiation and temperature on h. pluvialis production in photobioreactors under outdoor cultivation in Sri Lanka
    (IEEE, 2021-07) Perera, M; Muthunayaka, K; Madushanka, D; Liyanaarachchi, VC; Premaratne, M; Ariyadasa, TU; Adhikariwatte, W; Rathnayake, M; Hemachandra, K
    The complicated and varying weather conditions and contamination from fungi, protozoa, and bacteria are major problems associated with outdoor microalgae cultivation. In this study, outdoor microalgae cultivation was investigated in a 3.2 L vertical tubular photobioreactor in Moratuwa, Sri Lanka. During December, when both the solar irradiation and temperature were high, the water spray system in combination with two agro shading nets (each with a shading rate of 40-50%) could effectively reduce the temperature to 2±2 0C and control solar irradiation below 13500 lux. Under an initial biomass density of 0.2875 g/L and an atmospheric air flow rate of 1 vvm, Haematococcus pluvialis showcased a maximum biomass accumulation of 0.45 g/L and the maximum productivity of 20 mg/L/day. In addition, the reactor system and its design exhibited good performance, implying a potential scale-up opportunity. However, operation under outdoor conditions showed slightly poorer performance due to the light inhibition effect.
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    Nitrogen-limited cultivation of locally isolated desmodesmus sp. For sequestration of CO2from simulated cement flue gas and generation of feedstock for biofuel production
    (Elsevier, 2021) Premaratne, M; Liyanaarachchi, VC; Nishshanka, GKSH; Nimarshana, PHV; Ariyadasa, TU
    Biological CO2 sequestration from flue gas using microalgae has emerged as a promising alternative to conventional carbon capture technologies, since it concurrently generates valuable biomass which can be utilized to produce biofuels. In the current study, the locally isolated microalga Desmodesmus sp. was utilized for sequestration of CO2 from gas mixtures simulating undiluted cement flue gas (1x), and cement flue gas diluted by two-fold (1/2x), four-fold (1/4x) and eight-fold (1/8x). The current study aimed to assess the feasibility of maintaining high CO2 sequestration rates in nitrogen-limited culture media while simultaneously producing biomass rich in target metabolites for biofuel production. Accordingly, Bold’s Basal Medium (BBM) and BBM with three times the standard nitrate concentration (3N-BBM) were employed as culture media for nitrogen limited and nitrogen replete experiments respectively. The highest CO2 fixation rates were demonstrated in undiluted flue gas containing 15.50% CO2. Moreover, the average CO2 fixation rate of Desmodesmus sp. over the 8-day cultivation period (0.21 ± 0.02 g/L/d) was not significantly reduced in nitrate limited media (BBM). Nitrate limited cultivation in undiluted flue gas enhanced the accumulation of carbohydrates in microalgae (32.44 ± 0.45% and 327.65 ± 23.39 mg/L), although the increment in lipid content was not as significant as expected (41.54 ± 1.13% and 419.57 ± 31.52 mg/L). Biodiesel properties of microalgal lipids were within the limits of the ASTM D6751–12 standard. Higher heating values of microalgae biomass were in the range of 21.97–23.17 MJ/kg. Nonetheless, pilot scale studies using actual flue gas are essential prior to microalgal biofuel production and simultaneous CO2 sequestration.
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    Sustainable cultivation of haematococcus pluvialis for the production of natural astaxanthin
    (IEEE, 2021-07) Nishshanka, SH; Liyanaarachchi, VC; Premaratne, M; Ariyadasa, TU; Nimarshana, V; Adhikariwatte, W; Rathnayake, M; Hemachandra, K
    Haematococcus pluvialis is a microalga with the ability to accumulate high quantities of astaxanthin. However, the large freshwater footprint and the requirement of external nutrient supply are issues in its commercial-scale cultivation. In the present study, synthetic dairy wastewater was employed as an alternative culture media for H. pluvialis under varying light intensities to determine the best lighting conditions for biomass and astaxanthin accumulation. The highest biomass concentration ( 1.359±0.013 g/L ) and astaxanthin concentration ( 20.783±0.105 mg/L ) was achieved in the culture supplied with 3250 lux light intensity during the growth stage. Nevertheless, the highest specific growth rate ( 0.0625±0.000 /day) and cellular astaxanthin content (1.696±0.007%) were observed in the culture supplied with 4000 lux during the growth phase. It was also observed that the total lipid content of cultures did not vary significantly with light intensity. Moreover, it was observed that total lipid content of residual H. pluvialis decreased significantly after astaxanthin extraction. Nonetheless, H. pluvialis showcased considerable potential of nutrient removal efficiency, achieving over 90% reduction of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP). Thus, it could be speculated that cultivation of H. pluvialis under moderate light intensities could yield astaxanthin and lipid-rich biomass simultaneous to phycoremediation.