I am trying to develop dynamic model for algae cultivation and found a relevent paper. There were few assumptions mentioned inorder to develop the model but the explanations for the considered assumptions was not provided. the Following are the assumptions
The assumptions considered in developing the models in this study are:
(i) the pond is modelled as completely stirred tank reactors (CSTR); (ii) algal specific growth rate is a function of light intensity, total dissolved CO2 and total inorganic nitrogen;
(iii) exchange of O2 and CO2 between the pond and the atmosphere is not included;
(iv) evaporative losses are not considered due to lower water loss.
The model is for developing a high rate algal pond.
1. Complete mixing is required to aid sufficient mixing of algae, nutrients, CO2 and O2.
2. Light energy or photo-energy is the most critical factor in algal cultivation, for algal growth and assimilation of nutrients and CO2. This phenomenon is similar to plants but not similar to many bacterial species without chlorophyll which rely on chemical energy rather than photo-energy. As you can see, during the time light energy is available, CO2 is essential as a C source for algae to synthesise organic compounds to grow and reproduce.
3. Assuming growth rate is a function of only inorganic-N could result in erroneous results. Of the two inorganic-N available for growth, NO3-N is least preferred in algal trials because it demands more energy to synthesise into protein form than the ammoniacal-N counterpart. Moreover, algae can also successfully utilise dissolved organic-N as a source of N to derive its protein.
4. I presume exchange of O2 and CO2 between the pond and the atmosphere is not included to keep the model simplistic.
5. Substantial pond water evaporation can result in water loss and apparent algal and nutrient level changes (generally increases).
Kind regards
Selva
Hello Vuppaladadiyam,
In short, assumptions (i) and (ii) will make the simulated pond more productive while assumption (iii) and (iv) will make the model setup simpler. Without stirring, you would have extensive growth in the top few centimeters of the pond (assuming light is provided only on the pond surface). This stratified growth would prevent algal productivity by two mechanisms: blocking light penetration deep into the water column (with consequent effect on temperature, depending on the depth of the pond) and consuming the carbon source in the growth stratum (i.e., C becomes a limiting factor for growth). By stirring the pond, there would be a redistribution of algae and nutrients, favoring light penetration and nutrient availability. The last two assumptions keep the boundary conditions constant, which simplifies the model setup and reduces changes of model instability, especially if the model solves differential equations.
I hope this helps,
Marcos
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