Algae are a diverse group of photosynthetic organisms, ranging from microscopic phytoplankton to large seaweeds. They are not classified as true plants because they lack complex structures like roots and leaves. Algae produce much of the Earth’s atmospheric oxygen and form the base of aquatic food chains. They have wide-ranging applications, including use as nutritional supplements, sources for biofuel production, and ingredients in industrial products like cosmetics and pharmaceuticals.
Identifying the Algae You Need
The selection of an algae species depends on the desired application, generally falling into microalgae and macroalgae categories. Microalgae are single-celled organisms often cultivated for their high nutritional value. Species like Chlorella and Spirulina are popular for human consumption due to their protein and essential amino acid content. Spirulina (a cyanobacterium) thrives in warm, alkaline freshwater, while Chlorella is a spherical microalgae used as a dietary supplement.
Macroalgae, such as kelp and nori seaweed, are multicellular organisms typically farmed in open sea systems for food or hydrocolloids. For beginners, obtaining a starter culture from a scientific supplier or reputable online source is the most reliable method to ensure a pure, non-contaminated strain. Collecting from natural sources carries a high risk of contamination by unwanted organisms or non-nutritious species, which can compromise the culture. Buying a monoculture guarantees the specific characteristics and growth rates needed for a successful project.
Essential Environmental Requirements for Growth
Successful algae cultivation requires precisely managing several biological and chemical inputs, as optimal ranges are species-specific. Light is the primary energy source for photosynthesis, and its intensity, spectrum, and duration must be controlled. Most microalgae require light intensities between 2,500 and 5,000 lux. This intensity must be increased in deeper or denser cultures to prevent light limitation and self-shading. A common photoperiod is a 16-hour light followed by 8-hour dark cycle, although some cultivated species can grow normally under constant illumination.
Temperature is another factor, with most cultured microalgae tolerating 16 to 27 degrees Celsius. Optimal growth often occurs between 18 and 24 degrees Celsius. Temperatures below 16 degrees significantly slow growth, and exceeding 35 degrees Celsius can be lethal for many strains. The culture medium must be enriched with macronutrients, primarily nitrogen and phosphorus, typically supplied in an approximate ratio of 6:1.
Trace elements like iron and various vitamins, such as thiamin (B1) and cyanocobalamin (B12), are necessary for autotrophic growth. The pH level is usually maintained in a slightly alkaline range, typically between 7 and 9. The optimal range for most species falls between 8.2 and 8.7. Precise pH control is necessary because it directly impacts the availability of dissolved inorganic carbon used by the algae for growth.
Methods for Cultivating Algae
Once environmental parameters are established, the physical setup for cultivation, often called a photobioreactor (PBR), must be selected. Small-scale cultivation can be performed in sterile flasks or glass containers. Larger operations use either open pond systems or closed photobioreactors. Open pond systems, such as raceway ponds with paddle wheels, are simpler and cheaper but are susceptible to contamination and environmental fluctuations.
Closed photobioreactors, including tubular, flat-panel, or airlift designs, offer superior control over light, temperature, and contamination, leading to higher biomass productivity. The process begins with sterilization of the vessel and nutrient medium to prevent microbial growth. The pure starter culture is then carefully introduced, a process known as inoculation.
Maintaining culture health requires continuous aeration and mixing. This prevents the algae from settling and supplies carbon dioxide for photosynthesis. In closed systems, CO2 is often bubbled directly into the medium. When the culture reaches maximum density, a portion of the biomass must be harvested. Harvesting is typically done through simple filtering or straining for larger microalgae, or using flocculation or centrifugation for smaller, single-celled species.