An algae bioreactor is used for cultivating

micro Micro may refer to: Measurement * micro- (μ), a metric prefix denoting a factor of 10−6 Places * Micro, North Carolina, town in U.S. People * DJ Micro, (born Michael Marsicano) an American trance DJ and producer * Chii Tomiya (都宮 � ...

macroalgae Seaweed, or macroalgae, refers to thousands of species of Macroscopic scale, macroscopic, Multicellular organism, multicellular, ocean, marine algae. The term includes some types of ''Rhodophyta'' (red), ''Brown algae, Phaeophyta'' (brown) and ...

Algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

may be cultivated for the purposes of

biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...

production (as in a seaweed cultivator),

wastewater treatment Wastewater treatment is a process which removes and eliminates contaminants from wastewater. It thus converts it into an effluent that can be returned to the water cycle. Once back in the water cycle, the effluent creates an acceptable impact on ...

, CO₂ fixation, or aquarium/pond filtration in the form of an

algae scrubber An algae scrubber is a water filtering device which uses light to grow algae; in this process, undesirable chemicals are removed from the water. Algae scrubbers allow hobbyists to operate their saltwater or freshwater tanks or ponds using nat ...

. Algae bioreactors vary widely in design, falling broadly into two categories: open reactors and enclosed reactors. Open reactors are exposed to the atmosphere while enclosed reactors, also commonly called

photobioreactor Moss photobioreactor to cultivate mosses like ''Physcomitrella patens'' at the laboratory scale A photobioreactor (PBR) refers to any cultivation system designed for growing photoautotrophic organisms using artificial light sources or solar ligh ...

s, are isolated to varying extents from the atmosphere. Specifically, algae bioreactors can be used to produce fuels such as

biodiesel Biodiesel is a renewable biofuel, a form of diesel fuel, derived from biological sources like vegetable oils, animal fats, or recycled greases, and consisting of long-chain fatty acid esters. It is typically made from fats. The roots of bi ...

and

bioethanol Ethanol fuel is fuel containing ethyl alcohol, the same type of alcohol as found in alcoholic beverages. It is most often used as a motor fuel, mainly as a biofuel additive for gasoline. Several common ethanol fuel mixtures are in use a ...

, to generate animal feed, or to reduce pollutants such as NO_x and CO₂ in flue gases of power plants. Fundamentally, this kind of bioreactor is based on the

photosynthetic Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...

reaction, which is performed by the

chlorophyll Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...

-containing algae itself using dissolved carbon dioxide and sunlight. The carbon dioxide is dispersed into the reactor fluid to make it accessible to the algae. The bioreactor has to be made out of transparent material.

Historical background

The first microalgae cultivation was of the unicellular ''

Chlorella vulgaris ''Chlorella vulgaris'' is a species of green microalga in the division Chlorophyta. This unicellular alga was discovered in 1890 by Martinus Beijerinck, Martinus Willem Beijerinck as the first microalga with a well-defined nucleus. It is the typ ...

'' by Dutch microbiologist

Martinus Beijerinck Martinus Willem Beijerinck (, 16 March 1851 – 1 January 1931) was a Dutch microbiologist and botanist who was one of the founders of virology and environmental microbiology. He is credited with the co-discovery of viruses A virus i ...

in 1890. Later, during World War II, Germany used open ponds to increase algal cultivation for use as a protein supplement. Some of the first experiments with the aim of cultivating algae were conducted in 1957 by the

Carnegie Institution for Science The Carnegie Institution for Science, also known as Carnegie Science and the Carnegie Institution of Washington, is an organization established to fund and perform scientific research in the United States. This institution is headquartered in W ...

in Washington. In these experiments, monocellular ''

Chlorella ''Chlorella'' is a genus of about thirteen species of single- celled or colonial green algae of the division Chlorophyta. The cells are spherical in shape, about 2 to 10 μm in diameter, and are without flagella. Their chloroplasts contain t ...

'' were cultivated by adding and some minerals. The goal of this research was the cultivation of algae to produce a cheap animal feed.

Metabolism of microalgae

Algae are primarily

eukaryotic The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

photoautotrophic Photoautotrophs are organisms that can utilize light energy from sunlight, and elements (such as carbon) from inorganic compounds, to produce organic materials needed to sustain their own metabolism (i.e. autotrophy). Such biological activities ...

organisms which perform oxygenic photosynthesis. These types of algae are classified by their light-harvesting pigments which give them their color. The

green algae The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...

species, also known as Chlorophyta, are often used in bioreactors due to their high growth rate and ability to withstand a variety of environments. Blue-green algae, also known as

cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

, are classified as

prokaryotic A prokaryote (; less commonly spelled procaryote) is a single-celled organism whose cell lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Ancient Greek (), meaning 'before', and (), meaning 'nut' ...

photoautotrophs due to their lack of a nucleus. Light provides essential energy the cell needs to metabolize , nitrogen, phosphorus and other essential nutrients. The wavelengths and intensities of light are very important factors. Available is also an important factor for growth and due to the lower concentration in our atmosphere, supplementary can be added as seen with the bubble column PBR below. Microalgae also possess the ability to take up excess

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

and

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

under starvation conditions, which are essential for

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

and

amino acid synthesis Amino acid biosynthesis is the set of biochemical processes (metabolic pathways) by which the amino acids are produced. The substrates for these processes are various compounds in the organism's diet or growth media. Not all organisms are able to ...

. Higher temperatures and a pH above 7 and below 9 are also common factors. Each of these factors may vary from species to species so it is important to have the correct environmental conditions while designing bioreactors of any sort.

Types of bioreactors

Bioreactors can be divided into two broad categories, open systems and photobioreactors (PBR). The difference between these two reactors are their exposure to the surrounding environment. Open systems are fully exposed to the atmosphere, while PBRs have very limited exposure to the atmosphere.

Commonly used open systems

Simple ponds

The simplest system yields a low production and operation cost. Ponds need a rotating mixer to avoid settling of algal biomass. However, these systems are prone to contamination due to the lack of environmental control.

Raceway ponds

A modified version of a simple pond, the

raceway pond A raceway pond is a shallow artificial pond used in the cultivation of algae. The pond is divided into a rectangular grid, with each rectangle containing one channel in the shape of an oval, like an automotive raceway circuit. From above, many p ...

uses

paddle wheels A paddle is a handheld tool with an elongated handle and a flat, widened end (the ''blade'') used as a lever to apply force onto the bladed end. It most commonly describes a completely handheld tool used to propel a human-powered watercraft by ...

to drive the flow in a certain direction. The pond is continuously collecting biomass while providing carbon dioxide and other nutrients back into the pond. Typically, raceway ponds are very large due to their low water depth.

Other systems

Less common systems include an incline cascade system where flow is gravity-driven to a retention tank, from where it gets pumped back up to start again. This system can yield high biomass densities, but also entails higher operating costs.

Commonly used photobioreactors (PBRs)

Nowadays, 3 basic types of algae photobioreactors have to be differentiated, but the determining factor is the unifying parameter – the available intensity of sunlight energy. Photobioreactor PBR 500 P IGV Biotech

Flat plate PBR

A plate reactor simply consists of inclined or vertically arranged translucent rectangular boxes, which are often divided in two parts to affect an agitation of the reactor fluid. Generally, these boxes are arranged into a system by linking them. Those connections are also used for making the process of filling/emptying, introduction of gas and transport of nutritive substances. The introduction of the flue gas mostly occurs at the bottom of the box to ensure that the carbon dioxide has enough time to interact with algae in the reactor fluid. Typically, these plates are illuminated from both sides and have a high light penetration. Disadvantages of the flat plate design are the limited pressure tolerance and high space requirements. Photobioreactor PBR 4000 G IGV Biotech

Tubular PBR

A tubular reactor consists of vertically or horizontally arranged tubes, connected together, in which the algae-suspended fluid circulates. The tubes are generally made out of transparent plastics or

borosilicate glass Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (≈3 × 10−6 K−1 at 20 °C), ma ...

, and the constant circulation is kept up by a pump at the end of the system. The introduction of gas takes place at the end/beginning of the tube system. This way of introducing gas causes the problem of carbon dioxide deficiency and high concentration of oxygen at the end of the unit during the circulation, ultimately making the process inefficient. The growth of microalgae on the walls of the tubes can inhibit the penetration of the light as well.

Bubble column PBR

A bubble column photo reactor consists of vertically arranged cylindrical columns made out of transparent material. The introduction of gas takes place at the bottom of the column and causes a turbulent stream to enable an optimum gas exchange. The bubbling also acts as a natural agitator. Light is typically sourced from outside the column, however recent designs introduce lights inside the column to increase light distribution and penetration.

Industrial usage

The cultivation of algae in a photobioreactor creates a narrow range of industrial application possibilities. There are three common pathways for cultivated biomass. Algae may be used for environmental improvements, biofuel production and food/biofeed. Some power companies already established research facilities with algae photobioreactors to find out how efficient they could be in reducing CO₂ emissions, which are contained in flue gas, and how much biomass will be produced. Algae biomass has many uses and can be sold to generate additional income. The saved emission volume can bring an income too, by selling emission credits to other power companies. Recent studies around the world look at the algae usage for treating wastewater as a way to become more sustainable. The utilization of algae as food is very common in East Asian regions and is making an appearance around the world for uses in feedstock and even pharmaceuticals due to their high value products. Most of the species contain only a fraction of usable proteins and carbohydrates, and a lot of minerals and trace elements. Generally, the consumption of algae should be minimal because of the high

iodine Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...

content, particularly problematic for those with

hyperthyroidism Hyperthyroidism is a endocrine disease in which the thyroid gland produces excessive amounts of thyroid hormones. Thyrotoxicosis is a condition that occurs due to elevated levels of thyroid hormones of any cause and therefore includes hyperth ...

. Likewise, many species of diatomaceous algae produce compounds unsafe for humans. The algae, especially some species which contain over 50 percent oil and a lot of carbohydrates, can be used for producing biodiesel and bioethanol by extracting and refining the fractions. The algae biomass is generated 30 times faster than some agricultural biomass, which is commonly used for producing biodiesel.

Microgeneration

The built in 2013 in Germany is a showcase experimental bionic house using glass facade panels for the cultivation of micro algae. Once the panels heat up

thermal energy The term "thermal energy" is often used ambiguously in physics and engineering. It can denote several different physical concepts, including: * Internal energy: The energy contained within a body of matter or radiation, excluding the potential en ...

can also be extracted through a

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...

in order to supply warm water to the building. The technology is still in an early stage and not yet fit for a wider use. The Green Power House in Montana, United States used newly-developed Algae Aquaculture Technology within a system that uses sunlight and woody debris waste from a lumber mill for providing nutrients to eight algae ponds of the AACT that cover its floor. Identified challenges of algae façades include durability of microalgae panels, the need for maintenance, and construction and maintenance costs In 2022, news outlets reported about the development of algae biopanels by a company for sustainable energy generation with unclear viability.