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Oxygen-balanced mixotrophy (OBM) is a particular type of microalgae mixotrophic cultivation, where the supply of an organic carbon substrate is adjusted to match heterotrophic oxygen consumption with photosynthetic production. In this way, the need for aeration is eliminated due to intracellular gas recycling during daytime. After implementing this...
Commercial production of eicosapentaenoic acid (EPA) from photoautotrophic microalgae like Nannochloropsis oceanica requires higher productivity and larger scales to reduce costs. Improving productivity can be achieved by increasing biomass concentrations, which creates light gradients in the reactor depending on the culture’s acclimation and the r...
Microalgae are a promising renewable feedstock that can be produced on non-arable land using seawater. Their biomass contains proteins, lipids, carbohydrates, and pigments, and can be used for various biobased products, such as food, feed, biochemicals, and biofuels. For such applications, the production costs need to be reduced, for example, by im...
Photogranules are spherical aggregates formed of complex phototrophic ecosystems with potential for “aeration-free” wastewater treatment. Photogranules from a sequencing batch reactor were investigated by fluorescence microscopy, 16S/18S rRNA gene amplicon sequencing, microsensors, and stable- and radioisotope incubations to determine the granules’...
Oxygen‐balanced mixotrophy (OBM) is a novel type of microalgal cultivation that improves autotrophic productivity while reducing aeration costs and achieving high biomass yields on substrate. The scale‐up of this process is not straightforward, as nonideal mixing in large photobioreactors might have unwanted effects in cell physiology. We simulated...
Wastewater characteristics can vary significantly, and in some municipal wastewaters the N:P ratio is as low as 5 resulting in nitrogen‐limiting conditions. In this study, the microbial community, function, and morphology of photogranules under nitrogen‐replete (N+) and limiting (N−) conditions was assessed in sequencing batch reactors. Photogranul...
After light, temperature is the most relevant environmental parameter in outdoors cultivation of microalgae. Suboptimal and supraoptimal temperatures negatively impact growth and photosynthetic performance with a subsequent effect on lipid accumulation. It is generally recognised that lower temperatures trigger an increase in fatty acid desaturatio...
Photogranules are a novel wastewater treatment technology that can utilize the sun's energy to treat water with lower energy input and have great potential for nutrient recovery applications. They have been proven to efficiently remove nitrogen and carbon but show lower conversion rates for phosphorus compared to established treatment systems, such...
The urge for food security and sustainability has advanced the field of microalgal biotechnology. Microalgae are microorganisms able to grow using (sun)light, fertilizers, sugars, CO2, and seawater. They have high potential as a feedstock for food, feed, energy, and chemicals. Microalgae grow faster and have higher areal productivity than plant cro...
Carbon dioxide (CO2) and light are essential for high photosynthetic rates of microalgal cultures. Microalgal photosynthetic behavior at low CO2 concentrations has not been revealed yet at the same level of detail as leaf photosynthesis. In the present study, we investigated the short-term photosynthetic response of suspended Chlorella sorokiniana...
Microalgae are a promising renewable feedstock for a wide range of biobased products, such as food, feed, chemicals, and biofuels. To commercialize bulk products from microalgae, the production costs need to be reduced, for example, by improving biomass productivities in outdoor photobioreactors. Geographical locations near the equator are consider...
Microalgae express high protein levels and can be produced in contained cultivation systems with low water requirements and complete fertilizer use. The production potential is 22–44 tons of protein per hectare per year although the current production scale is small. Techno economic analyses have shown good potential for scale-up and cost reduction...
Multiple models have been developed in the field to simulate growth and product accumulation of microalgal cultures. These models heavily depend on the accurate estimation of growth parameters. In this paper growth parameters are presented for three industrially relevant microalgae species: Nannochloropsis sp., Neochloris oleoabundans, and Picochlo...
Despite their large number and diversity, microalgae from only four genera are currently cultivated at large-scale. Three of those share common characteristics: they are cultivated mainly autotrophically and are extremophiles or tolerate “extreme conditions.” Extreme growth conditions aid in preventing contamination and predation of microalgae, the...
G. sulphuraria is a polyextremophilic microalga that can tolerate low pH, high temperature and high osmotic pressure. We cultivated G. sulphuraria ACUF 064 in chemostat at a biomass concentration of 134 to 243 g·m⁻² aiming for maximal pigment content without compromising biomass productivity. Autotrophy was compared to ‘oxygen balanced’ mixotrophy...
Galdieria sulphuraria is an acidophilic microalga isolated in proximity of sulfuric ponds where pH is below 3 and most organisms cannot grow. We cultivated G. sulphuraria ACUF 64 free of contamination for over 2 months in a medium containing organic carbon at pH 1.7 with continuous, high intensity, lighting. We compared biomass productivity of chem...
Several technologies have aimed to recover nitrogen directly from urine. Nitrogen
recovery in these technologies was limited by the mismatch of the nitrogen-phosphorus molar ratio (N:P) of urine, being 30–46:1, and that of the final product, e.g., 1:1 in struvite and 16–22:1 in microalgae biomass. Additionally, the high nitrogen concentrations fou...
Industrial production of phototrophic microorganisms is often hindered by low productivity due to limited lightavailability and therefore requires large land areas. This letter demonstrates that supply of hydrogen gas (H2) increases inphototrophic biomass productivity compared to a culture growing on light only. Experiments were performed growingSy...
Using sunlight to fuel photosynthesis exposes microalgae to day-night cycles. Under day-night cycles microalgae tend to synchronize their metabolism by optimizing light utilization during daytime. During night storage compounds are consumed, leading to biomass losses and demand of O2. We investigated ‘oxygen balanced’ mixotrophy under14:10 day: nig...
Photogranules are dense, spherical agglomerates of cyanobacteria, microalgae and non-phototrophic microorganisms that have considerable advantages in terms of harvesting and nutrient removal rates for light driven wastewater treatment processes. This ecosystem is poorly understood in terms of the microbial community structure and the response of th...
Microalgae productivity was doubled by designing an innovative mixotrophic cultivation strategy that does not require gas-liquid transfer of oxygen or carbon dioxide. Chlorella sorokiniana SAG 211/8K was cultivated under continuous operation in a 2 L stirred-tank-photobioreactor re-designed such that respiratory oxygen consumption was controlled by...
Urine is a potential source of nutrients to grow microalgal biomass to be re-used as fertilizer and soil conditioner. In this study the impact of photobioreactor dilution rate on microalgae productivity and photosynthetic efficiency was assessed and used to determine operating conditions to reach both full nitrogen removal from urine and high bioma...
p>The liquid foam-bed photobioreactor is a novel photobioreactor for microalgae cultivation. A mathematical model was developed to evaluate its potential, and to optimize the design and operation of a large-scale unit. This model describes light limited microalgal growth in a rising foam column in a foam-bed photobioreactor, which is continuously o...
This poster presents the results of my master thesis, which served as a preliminary study of integrating a microalgal biofilm unit within a recirculation aquaculture system. This poster was presented on Wageningen Indonesian Network Scientific Exposure 2018 on July 5th, 2018, at Cibinong Science Center, Indonesia.
The liquid foam-bed photobioreactor is a recently developed photobioreactor concept that allows for cost reduction in microalgae cultivation. Long term operation was not yet achieved, due to degradation of the surfactant. In this study, Pluronic F68 was applied for foam stabilization. In order to compensate for the low algae partitioning to Pluroni...
In recent years bioprocessing has increased in popularity and importance, however, bioprocessing still poses various important techno-economic and environmental challenges, such as product yields, excessive energy consumption for separations in highly watery systems, batch operation or the downstream processing bottlenecks in the production of biop...
A novel liquid foam-bed photobioreactor has been shown to hold potential as an innovative technology for microalgae production. In this study a foam stabilizing agent has been selected which fits the requirements of use in a liquid foam-bed photobioreactor. Four criteria were used for an optimal surfactant: the surfactant should have good foaming p...
Microalgal biofilms of Chlorella sorokiniana were cultivated under simulated day-night cycles at high productivity and high photosynthetic efficiency. Comparing day-night to continuous illumination did not demonstrate differences in the light utilization efficiency. This indicates that biomass consumed overnight represents sugar consumption for syn...
A novel concept of cultivating microalgae in liquid foam was developed with the intention of reducing biomass production costs. This cost reduction is based on reduced harvesting costs due to high biomass densities, and reduced energy requirements due to improved mass transfer and lower pressure drop in the foam-bed photobioreactor. Foam generation...
Under high light conditions, microalgae are oversaturated with light which significantly reduces the light use efficiency. Microalgae with a reduced pigment content, antenna size mutants, have been proposed as a potential solution to increase the light use efficiency. The goal of this study was to investigate the competition between antenna size mu...
The loss of carbon dioxide (CO2) to the environment during microalgae cultivation is undesirable for both environmental and economic reasons. In this study, a phototrophic biofilm growth model was developed and validated with the objective to maximize both CO2 utilization efficiency and production of microalgae in biofilms. The model was validated...
The effect of biomass concentration on areal productivity and photosynthetic efficiency of Nannochloropsis sp. CCAP211/78 was studied in three outdoor pilot-scale photobioreactors: an open raceway pond (OPR), a horizontal tubular (HT) photobioreactor and a vertically stacked horizontal tubular (VT) photobioreactor. The reactors were operated contin...
Microalgae perform photosynthesis at a high efficiency under low light conditions. However, under bright sunlight, it is difficult to achieve a high photosynthetic efficiency, because cells absorb more light energy than can be converted to biochemical energy. Consequently microalgae dissipate part of the absorbed light energy as heat. The objective...
A generally applicable kineticmodel is presented to predict light limitedmicroalgal growth. Thismodel combines a mathematical description for photoautotrophic sugar productionwith a description for aerobic chemoheterotrophic biomass growth. The model is based on five parameters which are directly measurable but were obtained from literature for the...
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...
Background:
Microalgae are a potential source of sustainable commodities of fuels, chemicals and food and feed additives. The current high production costs, as a result of the low areal productivities, limit the application of microalgae in industry. A first step is determining how the different production system designs relate to each other under...
A key element to maximize photobioreactor (PBR) efficiency is the ability to predict microalgal growth and productivity depending on environmental conditions, out of which light availability is the most important one. As a result of mixing and light attenuation in a PBR, microalgae experience light–dark cycles that could enhance, or reduce, PBR pro...
A major limitation in achieving high photosynthetic efficiency in microalgae mass cultures is the fact that the intensity of direct sunlight greatly exceeds the photosynthetic capacity of the cells. Due to the high pigment content of algal cells, the light absorption rate surpasses the much slower conversion rate to biochemical energy. The excess o...
Microalgae are often considered as a promising alternative source of vegetable oils. These oils can be used for food and biofuel applications. Productivities that are projected for large-scale microalgal oil production are, however, often poorly supported by scientific evidence and based on too optimistic assumptions. To facilitate the inclusion of...
Microalgae biofilms could be used as a production platform for microalgae biomass. In this study, a photobioreactor design based on a rotating biological contactor (RBC) was used as a production platform for microalgae biomass cultivated in biofilm. In the photobioreactor, referred to as Algadisk, microalgae grow in biofilm on vertical rotating dis...
An economically feasible microalgal lipid industry
heavily relies on the selection of suitable strains. Because
microalgae lipid content increases under a range of adverse
conditions (e.g. nutrient deprivation, high light intensity),
photosynthetic activity is usually strongly reduced. As a consequence,
lipid productivity rapidly declines overtime,...
The ALGADISK project aims to develop a biofilm reactor for algae biomass production which could compete with current algae cultivation technologies (e.g. open-pond and tubular photo-bioreactors), meanwhile focusing on the need of SMEs. Due to its innovative design, the ALGADISK reactor is going to be scalable, automatic, and it can be used to captu...
In case of phototrophic cultures, photobioreactor costs contribute significantly to the total operating costs. Therefore one of the most important parameters to be determined is the maximum biomass production rate, if biomass or a biomass associated product is the desired product. This is traditionally determined in time consuming series of chemost...
Symbiotic microalgal–bacterial biofilms can be very attractive for municipal wastewater treatment. Microalgae remove nitrogen and phosphorus and simultaneously produce the oxygen that is required for the aerobic, heterotrophic degradation of organic pollutants. For the application of these biofilms in new wastewater treatment systems, the engineeri...
Due to the high nitrogen and phosphorus content, source-separated urine can serve as a major nutrient source for microalgae production. The aim of this study was to evaluate the nutrient removal rate and the biomass production rate of Chlorella sorokiniana being grown continuously in urine employing a short light-path photobioreactor. The results d...
In this study, for the first time, a microalga was grown on non-diluted human urine. The essential growth requirements for the species Chlorella sorokiniana were determined for different types of human urine (fresh, hydrolysed, male and female). Batch experimental results using microtiter plates showed that both fresh and synthetic urine supported...
An innovative pilot-scale phototrophic biofilm reactor was evaluated over a 5-month period to determine its capacity to remove nitrogen and phosphorus from Dutch municipal wastewater effluents. The areal biomass production rate ranged between 2.7 and 4.5 g dry weight/m(2)/day. The areal nitrogen and phosphorus removal rates averaged 0.13 g N/m(2)/d...
We explored the effect of pH and nitrogen supply on the biomass and fatty acid productivities of the microalga Neochloris oleoabundans cultivated in saline medium under continuous light. During light-limited and nitrogen-replete conditions, the maximal volumetric biomass productivity was 0.98 gDW L− 1 d− 1 at pH 8.2 and 0.47 gDW L− 1 d− 1 at pH 10....
An increasing number of wastewater treatment plants require post-treatment to remove residual nitrogen and phosphorus. This study investigated various harvesting regimes that would achieve consistent low effluent concentrations of nitrogen and phosphorus in a phototrophic biofilm reactor. Experiments were performed in a vertical biofilm reactor und...
The present invention relates to a method for obtaining algal biomass, a system for obtaining algal biomass and a cultivation medium for cultivating algae. The method comprises the step of culturing algae in a culturing medium having a pH above 8 such that lipid accumulation and/or carbohydrate accumulation is increased, wherein the medium is a sal...
Microalgae can be used for the treatment of municipal wastewater. The application of microalgal biofilms in wastewater treatment systems seems attractive, being able to remove nitrogen, phosphorus and COD from wastewater at a short hydraulic retention time. This study therefore investigates the area requirement, achieved effluent concentrations and...
As a result of mixing and light attenuation, algae in a photobioreactor (PBR) alternate between light and dark zones and, therefore, experience variations in photon flux density (PFD). These variations in PFD are called light/dark (L/D) cycles. The objective of this study was to determine how these L/D cycles affect biomass yield on light energy in...
As a result of mixing and light attenuation in a photobioreactor (PBR), microalgae experience light/dark (L/D) cycles that can enhance PBR efficiency. One parameter which characterizes L/D cycles is the duty cycle; it determines the time fraction algae spend in the light. The objective of this study was to determine the influence of different duty...
High annual microalgae productivities can only be achieved if solar light is efficiently used through the different seasons. During winter the productivity is low because of the light and temperature conditions. The productivity and photosynthetic efficiency of Chlorella sorokiniana were assessed under the worst-case scenario found during winter ti...
Nitrogen availability and light intensity affect β-carotene overproduction in the green alga Dunaliella salina. Following a previous study on high-light stress, we here report on the effect of nitrogen depletion on the growth characteristics and β-carotene as well as fatty acid metabolism of D. salina under a constant light regime in a turbidostat....
In this study, a metabolic network describing the primary metabolism of Chlamydomonas reinhardtii was constructed. By performing chemostat experiments at different growth rates, energy parameters for maintenance and biomass formation were determined. The chemostats were run at low irradiances resulting in a high biomass yield on light of 1.25 g mol...
The effect of elevated pH and salt concentration on the growth of the freshwater microalga Neochloris oleoabundans was investigated. A study was conducted in 24-well plates on the design of a growth medium and subsequently applied in a photobioreactor. An artificial seawater medium with reduced Ca(2+) and PO(4)(3-) could prevent mineral precipitati...
Nitrogen availability and light intensity affect β-carotene overproduction in the green alga Dunaliella salina. Following a previous study on high-light stress, we here report on the effect of nitrogen depletion on the growth characteristics and β-carotene as well as fatty acid metabolism of D. salina under a constant light regime in a turbidostat....
Efficient light to biomass conversion in photobioreactors is crucial for economically feasible microalgae production processes. It has been suggested that photosynthesis is enhanced in short light path photobioreactors by mixing-induced flashing light regimes. In this study, photosynthetic efficiency and growth of the green microalga Chlamydomonas...
Respiration and photosynthesis are two important processes in microalgal growth that occur simultaneously in the light. To know the rates of both processes, at least one of them has to be measured. To be able to measure the rate of light respiration of Chlorella sorokiniana, the measurement of oxygen uptake must be fast, preferably in the order of...
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...
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 efficiency winst. Wel vergt de algenkweek veel ruimte. Zelfs als de huidige auto’s vier keer zo efficiënt wor...
The effect of partial oxygen pressure on growth of Neochloris oleoabundans was studied at sub-saturating light intensity in a fully-controlled stirred tank photobioreactor. At the three partial oxygen pressures tested (P(O)₂= 0.24; 0.63; 0.84 bar), the specific growth rate was 1.38; 1.36 and 1.06 day(-1), respectively. An increase of the P(CO)₂from...
High oxygen: carbon dioxide ratios may have a negative effect on growth and productivity of microalgae. To investigate the effect of O(2) and CO(2) concentrations and the ratio between these on the metabolism of Chlamydomonas reinhardtii we performed turbidostat experiments at different O(2) : CO(2) ratios. These experiments showed that elevated O(...
Microalgal biofilms have so far received little attention as post-treatment for municipal wastewater treatment plants, with the result that the removal capacity of microalgal biofilms in post-treatment systems is unknown. This study investigates the capacity of microalgal biofilms as a post-treatment step for the effluent of municipal wastewater tr...
Algae are currently used for production of niche products and are becoming increasingly interesting for the production of bulk commodities, such as biodiesel. For the production of these goods to become economically feasible, production costs will have to be lowered by one order of magnitude. The application of two-phase systems could be used to lo...
A simple stoichiometric model is proposed linking the biomass yield to the enthalpy and Gibbs energy changes in chemo-heterotrophic, mixotrophic, and photo-autotrophic microbial growth. A comparison with calorimetric experiments on the algae Chlorella vulgaris and Chlorella sorokiniana confirmed the trends but revealed large calorimetric measuremen...
During the in situ extraction of β-carotene from Dunaliella salina, the causal relationship between carotenoid extraction and cell death indicated that cell growth and cell death should be at equilibrium for a continuous in situ extraction process. In a flat-panel photobioreactor that was operated as a turbidostat cell numbers of stressed cells wer...
In this feature, leading researchers in the field of microbial biotechnology speculate on the technical and conceptual developments that will drive innovative research and open new vistas over the next few years
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...
Dunaliella salina is a halotolerant green alga that is well known for its carotenoid producing capacity. The produced carotenoids are mainly stored in lipid globules. For various research purposes, such as production and extraction kinetics, we would like to determine and/or localise the carotenoid globules in vivo. In this study, we show that the...
beta-Carotene is overproduced in the alga Dunaliella salina in response to high light intensities. We have studied the effects of a sudden light increase on carotenoid and fatty acid metabolism using a flat panel photobioreactor that was run in turbidostat mode to ensure a constant light regime throughout the experiments. Upon the shift to an incre...
To be able to study the effect of mixing as well as any other parameter on productivity of algal cultures, we designed a lab-scale photobioreactor in which a short light path (SLP) of (12 mm) is combined with controlled mixing and aeration. Mixing is provided by rotating an inner tube in the cylindrical cultivation vessel creating Taylor vortex flo...
The biomass yield on light energy of Dunaliella tertiolecta and Chlorella sorokiniana was investigated in a 1.25- and 2.15-cm light path panel photobioreactor at constant ingoing photon flux density (930 µmol photons m⁻² s⁻¹). At the optimal combination of biomass density and dilution rate, equal biomass yields on light energy were observed for bot...
Maximal productivity of a 14 mm light-path panel photobioreactor under high irradiance was determined. Under continuous illumination of 2,100 micromol photons m(-2) s(-1) with red light emitting diodes (LEDs) the effect of dilution rate on photobioreactor productivity was studied. The light intensity used in this work is similar to the maximal irra...
In this work, the dependency of the volumetric hydrogen production rate of ammonium-limited Rhodobacter capsulatus chemostat cultures on their imposed biomass concentration and dilution rate was investigated. A deceleration-stat experiment was performed by lowering the dilution rate from 1.0 d(-1) to zero aimed at a constant biomass concentration o...
The process of the simultaneous production and extraction of carotenoids, milking, of Dunaliella salina was studied. We would like to know the selectivity of this process. Could all the carotenoids produced be extracted? And would it be possible to vary the profile of the produced carotenoids and, consequently, influence the type of carotenoids ext...
The relation between irradiance, skeletal growth and net photosynthesis was studied for the scleractinian coral Galaxea fascicularis to provide experimental evidence for mediation of light-enhanced calcification through photosynthesis. The hypothesis was tested that skeletal growth and photosynthesis are linearly correlated.A long-term experiment w...
The Green Solar Collector (GSC), a photobioreactor designed for area efficient outdoor cultivation of microalgae uses Fresnel lenses and light guides to focus, transport and distribute direct light into the algae suspension. Calculating the path of rays of light, so-called ray tracing, is used to determine local light intensities inside the photobi...
The unicellular alga Dunaliella salina is the most interesting cell factory for the commercial production of beta-carotene because this species accumulates carotenoids to high concentrations. Nevertheless, little is known about the underlying mechanisms of carotenoid accumulation. Here, we review the regulatory mechanisms involved in beta-carotene...
This article describes the design process of the Green Solar Collector (GSC), an area-efficient photobioreactor for the outdoor cultivation of microalgae. The overall goal has been to design a system in which all incident sunlight on the area covered by the reactor is delivered to the algae at such intensities that the light energy can be efficient...
Light is important as a source of energy for zooxanthellate corals. A short overview is presented of the current scientific insights in the physiology of light utilisation by the coral holobiont. This information is translated into practical considerations with respect to artificial lighting in coral reef aquaria.
