For some background on the cultivation and use of biomass, see our Flora Basics page

Our cultivation model

In cultivating microalgae, productivity of each individual cell relies on its position in the liquid media it is growing in; this is because the light intensity is not uniform. In fact, it is reported that in open pond cultivation (growing in a shallow pool under the sun), the biomass density that can be reached does not surpass 0.5g/L, because at this point the light intensity sufficient for algal growth penetrates about 6cm deep into the media ¹ (Wang). This means in a typical cultivation pond with a depth of ~ 25cm, at high cell density less than 30% of cells are sufficiently illuminated at any given time. Meanwhile, cells near the surface receive far higher light intensity than required. These data may vary by circumstances of cultivation, but it remains that a major drawback among open pond systems is inefficient light utilization.

Below is presented a model demonstrating a solution to increase the time any given cell receives sufficient light in a day, by bringing each cell closer to the light-receiving surface, and by increasing the surface area receiving light, followed by some notes for operating it.

Notes to understand the model:

• Light intensity is presented as PPFD (photosynthetic photon flux density), which describes the amount of light which the organism can use in photosynthesis; this unit is μmol/m²/s

• This model presents increasing the surface area (SA) receiving light within a set ground area, so light receiving SA per ground SA can be thought of as m²ₗᵣ/m² where ₗᵣ indicates ‘light receiving’

• ‘Angle to surface’ in the model indicates the angle to ground surface which the surface of the media is positioned, which impacts the SA. The surface the angle is applied to is called the ‘adjusted surface’

• The model calculates the hours per day that the surface of media receives sufficient target light for growing, both for the ground surface and for the adjusted surface

• The cell multiplying the hours receiving target light x adjusted SA can be thought of as mₗᵣ*h/day

• The relative time * SA receiving target light is calculated, and can be thought of as (mₗᵣ*h)/(m*h), giving a value which compares the increased SA and accompanying reduction in light intensity to ground surface

For filling in the input cells (in pink), here are some notes:

• For latitude, enter the value excluding N or S. Ex.: Melbourne = 37.8, Salamanca = 41.0, Popayán = 2.4

• For day of year, enter the number of the day in the solar year. Ex: Apr. 11 in northern hemisphere = 101, in southern hemisphere (+180) = 283

• For target light intensity, enter your target value (in μmol/m²/s). Microalgal cultivation in labs vary, often using anywhere from 100-400μmol/m²/s for growth depending on the goal

Several assumptions are made in these calculations:

• All days are based on a sunny day with a maximum solar constant of 2000μmol/m²/s

• The structure increasing surface area permits 100% of light

• The model calculates time meeting the target light intensity with implications on biomass production, and does not account for if productivity is higher at higher light intensity

To discuss how AF’s R&D and patent pending system of aquaculture could help your production, reach us at accessflora.contact@gmail.com

Further information

For calculations and references, see below