Chlorella is a genus of single-celled green algae popular as a dietary supplement due to its dense nutritional profile. It is a photosynthetic microorganism, converting light energy into biomass, making it sustainable to cultivate. Unlike complex plants, Chlorella grows suspended in a liquid medium. With a controlled environment, it can be grown successfully at home.
Essential Setup and Materials
A successful Chlorella culture requires selecting the correct physical components to create a photobioreactor. A transparent vessel, such as clear glass or food-grade plastic, is necessary to allow light penetration into the liquid medium. The size of the vessel determines the culture volume, so starting with a smaller container, like a one-gallon jar, is advisable for beginners.
A consistent light source is the primary energy input, provided by natural sunlight or artificial grow lights. While intense sunlight can overheat the culture, a bright, indirect window location is often adequate for small-scale growth. For controlled, year-round production, a full-spectrum LED or fluorescent grow light is preferred, typically running on a 16-hour light and 8-hour dark cycle.
Continuous air movement is mandatory, requiring an aquarium air pump, tubing, and an air stone to bubble air into the medium. This aeration provides carbon dioxide for growth and keeps the microscopic cells suspended uniformly, preventing settling. Finally, the project requires a viable starter culture—a small, concentrated volume of living Chlorella cells—often purchased online from algae suppliers.
Preparing the Growth Medium
The liquid environment, or growth medium, must supply all the necessary nutrients for the algae to multiply. The process begins with clean water, such as filtered or distilled water. Tap water can be used if it is left exposed to the air for 24 hours to allow chlorine to dissipate. Chlorella requires a balanced diet of macronutrients: Nitrogen (N), Phosphorus (P), and Potassium (K), along with trace elements like manganese, zinc, and copper.
Many home growers use specialized commercial algae nutrient mixes, such as modified Bold’s Basal Medium, which provide a precise balance of these elements. Alternatively, a diluted, water-soluble commercial NPK fertilizer can be adapted, provided it is carefully measured to avoid nutrient burn or contamination. The medium’s acidity and alkalinity (pH) must also be regulated for optimal growth. Chlorella thrives in a slightly acidic to neutral range, typically between 6.5 and 7.5, which can be monitored with simple aquarium pH test kits.
Starting and Maintaining the Culture
Once the medium is prepared, inoculation involves carefully introducing the starter culture into the nutrient solution. This initial culture should be added at a concentration that allows for rapid exponential growth. Temperature is a major determinant of the growth rate, with the ideal range for many common strains of Chlorella falling between 25°C and 30°C (77°F and 86°F).
The continuous operation of the air pump is essential because the constant stream of bubbles prevents the algae from clumping and ensures every cell has access to light and nutrients. This agitation also facilitates gas exchange, supplying the necessary CO2 and removing excess oxygen. A healthy, rapidly multiplying culture will show a distinct change in color over a few days, transitioning from a translucent, pale green to a deep, opaque emerald green as the cell density increases.
Monitoring the culture involves regularly checking the density and looking for signs of potential contamination. Contamination may appear as a change in color, such as a brownish hue, or the presence of fuzzy molds or competing microorganisms. When the culture reaches its peak density—appearing very dark green—it is time for partial harvesting. Harvesting prevents the algae from consuming all the nutrients and entering a stationary phase. By removing 25 to 50 percent of the dense culture and replacing it with fresh, nutrient-rich medium, the remaining cells are re-fed and stimulated to continue growing in a semi-continuous cycle.
Harvesting and Processing
Harvesting is the process of separating the dense Chlorella biomass from the growth medium. Because Chlorella cells are exceptionally small, standard paper or cloth filters are ineffective for separation. The simplest home method is sedimentation: the air pump is turned off and the container is left undisturbed for several hours, allowing the dense algae cells to sink to the bottom.
Once the cells have settled, the clear, nutrient-depleted water on top can be carefully siphoned or poured off, leaving behind a concentrated, thick green paste. This paste is the harvested biomass, which should be washed with clean water to remove any residual growth medium. For consumption, the cell wall of Chlorella must be broken to make its nutrients digestible, a step often achieved commercially through mechanical disruption. At home, the wet paste can be spread thinly on a tray and dried using a food dehydrator set to a low temperature or a low-heat oven to produce a stable, dark green powder for storage.