Cultivation of microalgae: effect of light/dark cycles on biomass yield

In this thesis the efficiency of light utilization of microalgae was studied under light/dark cycles encountered in photobioreactors. Phototrophic microorganisms such as microalgae and cyanobacteria could provide valuable compounds. For many of these applications it is essential to use enclosed photobioreactors in which monocultures can be maintained for an extended time. Because light energy is the growth limiting substrate, light supply plays a key role in photobioreactor design.The light regime inside photobioreactors is complicated: algae are exposed to high-intensity sunlight in the so-called photic zone close to the reactor surface and complete darkness in the interior. As a result of mixing of the reactor liquid, algae are exposed to light-gradient/dark cycles and this fluctuating light regime could have a considerable influence on the efficiency of light utilization for biomass growth, also referred to as the photosynthetic efficiency.The present study therefore was limited to medium-frequency light/dark cycles. These have a duration of a few seconds to 100 s. The efficiency of light utilization was determined as the yield of biomass, measured as protein, on light energy, measured as 'photosynthetic active radiation' (PAR, 400 - 700 nm). In addition, the quantum yield of photochemistry was determined using pulse-amplitude-modulation (PAM) fluorometry. Both determinations showed that the efficiency of photosynthesis is lower during the light period of light/dark cycles in comparison to continuous illumination.In addition to this general conclusion, it was found that, in the situation the dark period comprises was less than 33 % of the full cycle duration (= dark fraction), the yield was about equal to the one determined under continuous illumination. The biomass yield was mainly affected by the light fraction (e), whereas cycle duration only had a small influence. Additional experiments showed that together with the biomass yield on light energy also the capacity of the photosynthetic apparatus decreased. Furthermore, evidence is presented photoacclimation occurs after a shift from continuous illumination to medium-frequency light-dark cycles. This could explain the decrease in efficiency in the light period. An efficiency increase was only observed under short light/dark cycles (0.19 s) in comparison to continuous illumination.As a summary, the state-of the-art of enclosed outdoor photobioreactors was analyzed. Characteristic examples were selected and studied with respect to the light regime and the photosynthetic efficiency. It is shown that high photosynthetic efficiencies only can be reached at high biomass concentration in short light-path bioreactors. It is demonstrated, however, that these and also the other types of photobioreactors are poorly scalable and/or not applicable for cultivation of monocultures. This is the reason new photobioreactor designs are proposed in which light capture is physically separated from photoautotrophic cultivation

Phase toxicity of dodecane on the microalga Dunaliella salina

In the so-called milking process of Dunaliella salina carotenoids are extracted and simultaneously produced by the culture, whilst the biomass concentration remains constant. Different theories exist about the extraction mechanisms although none have been proven yet. In this research, direct contact between dodecane and cells during the extraction process was studied microscopically and effects of direct contact were determined during in situ extraction experiments. Our results showed that water– solvent interphase contact resulted in cell death. This cell death and consequent cell rupture resulted in the release and concomitant extraction of the carotenoids. Furthermore, it has been suggested to add a small amount of dichloromethane to the biocompatible dodecane to create an organic phase with more extraction capacity. Our results showed that the addition of dichloromethane resulted in increased cell death and consequently the extraction rate increased. The improved solubility of carotenoids in an organic phase with dichloromethane did not significantly increase the extraction rate

Bio-methane & Bio-hydrogen. Status and perspectives of biological methane and hydrogen production

Eerst wordt het kader geschetst voor de potentiële rol van bio-methaan en bio-waterstof in de energiehuishouding en de invloeden daarop van de ontwikkeling van eindgebruikstechnologie en infrastructuur, en het energiebeleid. Daarna wordt uitvoerig ingegaan op de technieken voor bio-methaan en bio-waterstof productie. Achtereenvolgens worden belicht: methaanproductie via anaërobe vergisting, biologische waterstofproductie via (donker) fermentatie, en fotobiologische waterstofproductie

Microalgal Photosynthesis and Growth in Mass Culture : Chapter Four

The development of large-scale outdoor microalgae production requires a thorough understanding of microalgal growth which should be encompassed in a mathematical model. The model should be as simple as possible allowing use in outdoor practice by persons with varying backgrounds. This chapter provides a basis for such a model connecting microalgal growth and photobioreactor productivity to light exposure. Only light exposure is included as an environmental variable because sunlight irradiance will ultimately limit areal productivity and all other cultivation parameters must be balanced to that number. Within microalgal mass cultures inside photobioreactors a light gradient will develop determining microalgal growth. This light gradient depends on microalgal specific light absorption and biomass concentration. Based on the light gradient the local rates of photosynthesis are calculated and integrated over reactor volume. The model is connected to our current understanding of photosynthesis by adopting proven photosynthesis models developed by Blackman and Jassby & Platt, and employing efficiency parameters based on theoretical evaluations and practical experiments. The wavelength dependency of light absorption is included. Photosynthesis is then connected to microalgal growth adopting the model of Pirt and distinguishing between maintenance-related respiration and growth-related respiration. The model is used to analyze productivity of simple photobioreactor geometry (1-dimensional light path) and calculate the limits of light-use efficiency. At the end of the chapter the assumptions and simplifications made are discussed in the light of possible effects of photoacclimation, mixing along the light gradient, day/night cycles, and the complexity of accurately modeling the light field

Floating biofilm

The present invention relates to a system and method for cultivating and/or growing microorganisms capable of photosynthesis. The system comprises at least one body of water containing essential nutrients for the microorganisms; at least one sheet which floats, or is held afloat, on the at least one body of water; at least one layer of microorganisms capable of photosynthesis covering at least part of the upper surface of the at least one sheet; and a gas preferably comprising carbon dioxide above the at least one sheet. The system can be used in a method for cultivating and/or growing microorganisms capable of photosynthesis

Floating biofilm

The present invention relates to a system and method for cultivating and/or growing microorganisms capable of photosynthesis. The system comprises at least one body of water containing essential nutrients for the microorganisms; at least one sheet which floats, or is held afloat, on the at least one body of water; at least one layer of microorganisms capable of photosynthesis covering at least part of the upper surface of the at least one sheet; and a gas preferably comprising carbon dioxide above the at least one sheet. The system can be used in a method for cultivating and/or growing microorganisms capable of photosynthesis

Pro’s en contra’s van rijden op dieselolie uit algen

Het wegtransport slorpt bijna een kwart van al onze energie op. Om dit aandeel te verduurzamen is een keuze voor dieselolie uit algen uit energetisch oogpunt een zinnige optie. Vergeleken met elektrische auto's is er sprake van aanzienlijke efficiencywinst. Wel vergt de algenkweek veel ruimte. Zelfs als de huidige auto's vier keer zo efficiënt worden is hiervoor nog steeds een oppervlakte ter grootte van de Provincie Groningen nodig

A study of the growth for the microalga Chlorella vulgaris by photo-bio-calorimetry and other on-line and off-line techniques

Calorimetry and other on-line techniques are used for the first time as complement to the traditional off-line methods in order to follow the growth of the green Chlorella vulgaris microalgae. A 2-L photo-bio-reactor was adapted from a commercial calorimeter used previously to study heterotrophic microbial growth. An external source of light was added to favor the photosynthesis of the autotrophic cells. Heterotrophic growth was also tested with external glucose in the broth. A third mode, mixotrophic, allowed faster autotrophic plus heterotrophic growth. Calorimetric measurements were performed considering the corresponding calibrations in order to consider only the energy involved during the microalgal growth. The three different modes of Chlorella cultures were energetically characterized. Besides calorimetry, the weight of diluted nitric acid added to maintain the pH of the culture was correlated with the cellular growth and the nitrogen composition of the algae. Additionally, the on-line infrared spectroscopy proved to be an efficient technique to follow the composition of the broth in glucose, nitrates, and phosphates. These results were compared and complemented with some classic off-line techniques used to track this kind of cultures