Specific Growth Rate Of Microalgae Research Articles

Effects of different biomass ratios of light-tolerant microalgae-nitrifying bacteria consortia on ammonia removal

Research on microalgae-nitrifying bacteria has increased due to their ability to remove nitrogen without expensive mechanical aeration. However, due to photosensitivity of nitrifying bacteria, their outdoor application in certain environments can lead to poor treatment performance or process breakdown. Hence, we developed a light-shielding hydrogel encapsulating nitrifying bacteria to form a light-tolerant microalgae-nitrifying bacterial consortium. The established light-tolerant microalgae-nitrifying bacteria consortium can successfully remove ammonia even under bright light conditions. Batch experiments were conducted using light-tolerant microalgae-nitrifying bacteria consortia under 500 µmol photons m−2 s−1 to evaluate the effects of biomass ratios on the microalgal growth and ammonia removal. The maximum specific growth rate of microalgae, i.e. 1.3 d−1 was obtained for a biomass ratio (microalgae: nitrifying bacteria) of 1:9. Multiple regression analysis also revealed that the abundance of nitrifying bacteria was associated with a higher ammonia removal efficiency than microalgae. These findings can be used to design an effective treatment process for removing high concentrations of ammonia by microalgae-nitrifying bacteria consortia exposed to intense light.

Modeling Effect of Bubbles on Time-Dependent Radiation Transfer of Microalgae in a Photobioreactor for Carbon Dioxide Fixation

Microalgae are considered one of the most efficient and environmentally friendly ways for carbon dioxide fixation. The bubbles play an important role in analyzing the radiation transfer in photobioreactors during microalgae growth. Herein, Chlorella sp. and Scenedesmus obliquus were cultured in the airlift flat plate photobioreactor and evaluated for the temporal evolution of radiation characteristics. A one-dimensional model of bubbles on time-dependent radiation transfer in a photobioreactor was proposed, and it was well verified with the experimental result. The results indicated that with the increase of bubble volume fraction or the decrease of bubble radius, the local irradiance increased at the illuminated surface of the microalgal culture and was attenuated more rapidly along with the radiation transfer. The average specific growth rate of microalgae decreases as bubble volume fraction increases or bubble radius decreases. The volume fraction of 0.003 and a radius of 3.5 mm are the optimal operating conditions in this study for microalgae growth and carbon dioxide fixation. The presented analysis would facilitate the design and optimization of the optical and aeration configurations of photobioreactors for carbon dioxide fixation.

Control of Microalgae Growth in Artificially Lighted Photobioreactors Using Metaheuristic-Based Predictions

A metaheuristic algorithm can be a realistic solution when optimal control problems require a significant computational effort. The problem stated in this work concerns the optimal control of microalgae growth in an artificially lighted photobioreactor working in batch mode. The process and the dynamic model are very well known and have been validated in previous papers. The control solution is a closed-loop structure whose controller generates predicted control sequences. An efficient way to make optimal predictions is to use a metaheuristic algorithm, the particle swarm optimization algorithm. Even if this metaheuristic is efficient in treating predictions with a very large prediction horizon, the main objective of this paper is to find a tool to reduce the controller’s computational complexity. We propose a soft sensor that gives information used to reduce the interval where the control input’s values are placed in each sampling period. The sensor is based on measurement of the biomass concentration and numerical integration of the process model. The returned information concerns the specific growth rate of microalgae and the biomass yield on light energy. Algorithms, which can be used in real-time implementation, are proposed for all modules involved in the simulation series. Details concerning the implementation of the closed loop, controller, and soft sensor are presented. The simulation results prove that the soft sensor leads to a significant decrease in computational complexity.

Investigating the effect of several Palm Oil Mill Effluent (POME) dilutions on biomass and specific growth rate of C. sorokiniana

High amount of turbidity was identified as one of the important factor affecting the successful cultivation of microalgae in palm oil mill effluent (POME). In this study, Chlorella sorokiniana was cultivated in POME, under different dilutions of 80, 60, 40 and 20% (v/v) with distilled water. The aim of the study is to investigate the effect of POME turbidity and the dilutions on the specific growth rate of microalgae. The results found that, C. sorokiniana grew on both sterilized and unsterilized condition. The result of the batch experiment showed that, POME turbidity of 45 NTU produce the maximum specific growth rate by C. sorokiniana of 0.14 d-1, which correspond to biomass production of 4.06 g/L and 0.2 d-1, which correspond to biomass production of 5.94 g/L in sterilized and unsterilized POME respectively. The POME of high turbidity concentration of 98 NTU yield only 0.07 d-1 maximum specific growth rate of algae. Results of this study identified 80% dilution as the optimal medium that can enhance maximum biomass production in POME. This could be useful in reducing the cost of bioenergy generation

Optimization of culture conditions of <italic>Isochrysis galbana</italic> by response surface method

<italic>Isochrysis galbana</italic> has the advantages of small size and fast reproduction. It has become one of the main micro-algae with great potential for green sewage treatment technology under the new concept. Because of its high nutritional value, it is often used as bait in the artificial breeding of bivalve shellfish such as <italic>Meretrix meretrix</italic>, <italic>Solen grandis</italic>, <italic>Sinonovacula constricta</italic> and so on. Response surface method is a combination of statistics and mathematics. It not only has the interaction in the orthogonal experiment, but also can use the mathematical model to get the functional relationship between the response and each variable, so it is an effective method to further predict the combination of all variable factors and get the optimal response surface value to solve scientific and production problems. Specific growth rate refers to the increased biomass of single-celled organisms per unit mass per unit time, which is an important parameter reflecting the growth rate of single-celled organisms such as microalgae and bacteria. The specific growth rate can not only accurately reflect the specific growth rate of microalgae in a certain time period, but also can comprehensively reflect the dynamic changes of the balance between microalgae growth and mortality. In order to optimize the culture conditions of <italic>Isochrysis galbana</italic>, using the method of experimental ecology and response surface (Box-Behnken mode), different experimental groups with different temperatures, salinities and initial inoculation levels were set up. Single factor experiment and multifactor experiment (Box-Benhnken model) were constructed to obtain the specific growth rate of <italic>Isochrysis galbana</italic>. Results showed that: 1) In a certain range of temperature, salinity and initial inoculation level, the specific growth rate of <italic>Isochrysis galbana</italic> increased first and then decreased with the increase of various factors; 2) The optimization of culture conditions of <italic>Isochrysis galbana</italic> respectively were: temperature 26.38 ℃, salinity 26.61, and initial inoculation level 1.29×10⁶ cell·mL^-1,and the maximum specific growth rate of <italic>Isochrysis galbana</italic> was 0.44 d^-1. The model conclusion data is available and can be applied to the actual production process.Our results could provide scientific basis for laboratory culture and large-scale propagation of <italic>Isochrysis galbana</italic>.In this paper, taking the specific growth rate of <italic>Isochrysis galbana</italic> as an index, the optimum conditions of suitable temperature, salinity and initial inoculation level were optimized by response surface method to provide scientific basis for laboratory culture and large-scale breeding of <italic>Isochrysis galbana</italic>.

Расчёт удельной скорости роста микроводорослей

В работе рассматриваются методические приёмы количественной оценки удельной скорости роста микроводорослей в периодической и непрерывной культуре. Показано, что для доказательства постоянства удельной скорости роста достаточно неизменности либо соотношения двух химических характеристик биомассы, либо размерной структуры популяции клеток. Проведён критический анализ правомерности использования логарифмической формулы для оценки удельной скорости роста (µ) микроводорослей в экспоненциальной фазе роста накопительной культуры: µ = (lnB2 – lnB1) / (t2 – t1), где В1 и В2 ― плотности (концентрации) культуры в моменты времени t1 и t2 соответственно. Эта формула повсеместно используется большинством исследователей микроводорослей без доказательств экспоненциального характера роста. При наличии таких доказательств применение логарифмической формулы теряет смысл. Приведены примеры количественного описания экспериментальных данных для двух видов морских микроводорослей в экспоненциальной и линейной фазах роста культуры.

Influence of light on microalgae growth in continuous culture of low density

A mathematical model of the dependence of the specific growth rate of microalgae on the light intensity for a continuous culture of low optical density is proposed. In the basis of the mechanism of light-limited growth is the thesis on photosynthesis having light and dark phases. The product of the first phase is carbohydrates, which are used in the dark phase as a source of energy and carbon skeletons for the synthesis of all structural components of cells .Rates of the processes are described by linear splines. The equations describing the dependence of the specific growth rate on the intensity of the acting light are obtained.

Evaluation of Nutrient Removal and Biomass Production Through Mixotrophic, Heterotrophic, and Photoautotrophic Cultivation of Chlorella in Nitrate and Ammonium Wastewater

In this study, the effect of mixotrophic, heterotrophic, photoautotrophic (CO2 of air source), and photoautotrophic (bicarbonate source) cultivation of Chlorella vulgaris was investigated on microalgae growth rate and nutrient removal under different kinds of nitrogen sources. The highest N–NH3+, N–NO3−, P–PO43− (in ammonium source), and P–PO43− (in nitrate source) removal efficiency (87.28 ± 0.89, 70.00 ± 1.20, 87.00 ± 3.10, and 78.10 ± 1.95%, respectively) was reached in the mixotrophic culture. In all cultivations, when nitrate was used as the nitrogen source, specific growth rate, biomass productivity, and specific oxygen production rate (SOPR) were higher than the one with ammonium source due to decreased pH. However, in all cultures except for photoautotrophic cultivation (in the CO2 of the air), nitrogen removal rates improved in the ammonium source. In addition, in both ammonium and nitrate source, the respiration activity of mixotrophic microalgae was higher than the photosynthetic activity of the cells. When CO2 was used as inorganic carbon, the specific growth rate of microalgae was lower than with the bicarbonate source. Based on the obtained results, mixotrophic conditions would be the most useful cultivation for application in N-rich wastewater treatment systems.

Parameter sensitivity analysis of a mechanistic model to simulate microalgae growth

In this paper, sensitivity analysis is applied to a mechanistic model developed to simulate microalgae growth. The Morris method of Elementary Effects (EEs) is applied to evaluate the sensitivity of model outputs with respect to a subset of key input parameters. For an easier interpretation, results were plotted as distributions of elementary effects means and standard deviations for each input parameter. The model outputs were very sensitive with respect to the maximum specific growth rate of microalgae (μalg). Results of the sensitivity analysis indicate that the transfer of ammonia (Ka,NH3) and carbon dioxide (Ka,CO2) have a non-linear relation with nitrogen uptake and carbonate concentrations, respectively. This analysis helped identify the parameters with the greatest impact on simulation outputs. The results indicated that maximum specific growth rate of microalgae (μalg) was the most critical parameter to calibrate properly.

KEPADATAN DAN LAJU PERTUMBUHAN SPESIFIK Nannochloropsis sp. PADA KULTIVASI HETEROTROPIK MENGGUNAKAN MEDIA HIDROLISAT SINGKONG

Growth of Nannochloropsis sp. was observed in laboratory cultivation condition with enrichment of cassava hydrolysate into culture medium as follow : 25 ml microalgae strain, 75 ml seawater, without cassava hydrolysate (A); 25 ml microalgae strain, 25 ml cassava hydrolysate, 50 ml seawater (B), 25 ml microalgae strain, 50 ml cassava hydrolysate, 25 ml seawater (C). Cultivation condition was fixed as follow temperature 29°C, seawater pH 8, and salinity 30 ‰. Microalgae cultivation was performed at microalgae laboratory of Surfactant and Bioenergy Research Center using 100 ml Erlenmeyer covered by black plastic to prevent the influence of light. The specific growth rate of Nannochloropsis sp. was observed in 7 days for different cultivation medium composition. The highest density of microalgae was in the 4th days with 50ml cassava hydrolysate’s feeding (C treatment) about 172.661 cell/mL. The highest specific growth rate for Nannochloropsis sp. cultivation was observed in the 6th days without cassava hydrolysate’s feeding. Result of statistical analysis showed that different cassava hydrolysate’s feeding treatments (ml) in heterotrophically microalgae cultivation influenced the density of microalgae (cell/mL) but not influenced the specific growth rate of microalgae (per day).Keywords: Cassava hydrolysate, Density, Heterotrophic cultivation, Spesific growth rate, Nannochloropsis sp.

A cost analysis of microalgal biomass and biodiesel production in open raceways treating municipal wastewater and under optimum light wavelength.

Open raceway ponds are cost-efficient for mass cultivation of microalgae compared with photobioreactors. Although low-cost options like wastewater as nutrient source is studied to overcome the commercialization threshold for biodiesel production from microalgae, a cost analysis on the use of wastewater and other incremental increases in productivity has not been elucidated. We determined the effect of using wastewater and wavelength filters on microalgal productivity. Experimental results were then fitted into a model, and cost analysis was performed in comparison with control raceways. Three different microalgal strains, Chlorella vulgaris AG10032, Chlorella sp. JK2, and Scenedesmus sp. JK10, were tested for nutrient removal under different light wavelengths (blue, green, red, and white) using filters in batch cultivation. Blue wavelength showed an average of 27% higher nutrient removal and at least 42% higher chemical oxygen demand removal compared with white light. Naturally, the specific growth rate of microalgae cultivated under blue wavelength was on average 10.8% higher than white wavelength. Similarly, lipid productivity was highest in blue wavelength, at least 46.8% higher than white wavelength, whereas FAME composition revealed a mild increase in oleic and palmitic acid levels. Cost analysis reveals that raceways treating wastewater and using monochromatic wavelength would decrease costs from 2.71 to 0.73 $/kg biomass. We prove that increasing both biomass and lipid productivity is possible through cost-effective approaches, thereby accelerating the commercialization of low-value products from microalgae, like biodiesel.

Singular Perturbation Based Solution to Optimal Microalgal Growth Problem and Its Infinite Time Horizon Analysis

The problem of the optimal microalgal growth is considered here. The objective is to maximize the specific growth rate of microalgae by manipulating the irradiance. The model describing the growth of microalgae is based on the mechanistic description in the form of the so called photosynthetic factory (PSF) resulting into the second order bilinear system which is, nevertheless, known in biotechnological literature to comprise many important features of microalgal growth. To obtain the solution of optimal control problem, the singular perturbation approach is used here to reduce fast components of system dynamics leading to a less dimensional system with more complex performance index which allows a nice analytical solution. Its infinite horizon analysis shows that the optimal solution on large time intervals tends to the optimal steady state of PSF thereby supporting the hypothesis often mentioned in the biotechnological literature. Finally, the numerical algorithm to compute optimal control is applied to the original non-reduced system giving very similar results as the reduction based approach.

Optimal Feedback Control of Microalgal Growth Based on the Slow Reduction

A state feedback law is proposed for on-line optimization of microalgal growth in a photobioreactor in the presence of non-measurable disturbances. The objective is to maximize a photosynthetic production rate (specific growth rate of microalgae) by manipulating the irradiance. The model describing the growth of microalgae is based on the mechanistic description in the form of the so-called photosynthetic factory. The reduction to a slow dynamics is used to derive analytically the approximation of the optimal feedback control. The analysis of the obtained explicit formula shows that the optimal feedback control actually performs optimal transfer to a constant optimal irradiance developed earlier but does not achieve principally better performance than the optimal control within the class of constant irradiance. Therefore, by reducing fast dynamics one can not reveal possible more complex optimal solutions. At the same time, this contradicts to a common belief in biotechnological community that the fast phenomena may be neglected. Illustrative simulations are included.