Heliyon (Dec 2022)
Modelling of Lemna minor L. growth as influenced by nutrient supply, supplemental light, CO2 and harvest intervals for a continuous indoor cultivation
Abstract
Given the proper conditions, Lemna spp. rapidly produce a high amount of valuable biomass which is considered as an alternative source for feed and food. For a continuous and long-term indoor production under controlled conditions, environmental and harvest parameters have to be optimized to suppress algal growth and constantly yield a high-quality product. Experimentally assessing the effect of a larger number of parameters on the growth rate ri is impossible due to the theoretically high number of parameter combinations. Thus, a SIMILE® - based model has been developed. This enables production parameters to be assessed individually for its effect on the growth rate ri by a differential equation. Start values for numerical integration were taken from measured data and analytical solutions of the differential growth equation. At 400 ppm CO2, the regrowth rate ri in an optimized laboratory set-up amounted to 216 g FM·m−2d−1, harvesting one third of the biomass at intervals of 5 days. In up-scaled set-ups, lower regrowth rates ri of about 173 g FM·m−2d−1 (Kalkar) and 190 g FM·m−2d−1 (Berlin) were obtained, because temperature and light conditions were below optimum. At 3,500 ppm CO2, the regrowth rate ri in laboratory set-up increased to 323 g FM·m−2d−1 by shortening the harvest interval to three days. Maximum growth rates ri were obtained with an NH4+/NO3- ratio of 1/9 at 1.14 mM total N concentration. The results indicate how to optimize culture conditions and harvest intervals. Model runs closely match the experimental data taken from the three different approaches and thus confirm the validity of the model.
