Modelling of Lemna minor L. growth as influenced by nutrient supply, supplemental light, CO2 and harvest intervals for a continuous indoor cultivation

Karl-Michael Schmidt; Heiner E Goldbach

doi:10.1016/j.heliyon.2022.e12194

Modelling of Lemna minor L. growth as influenced by nutrient supply, supplemental light, CO₂ and harvest intervals for a continuous indoor cultivation

Heliyon. 2022 Dec 8;8(12):e12194. doi: 10.1016/j.heliyon.2022.e12194. eCollection 2022 Dec.

Authors

Karl-Michael Schmidt¹, Heiner E Goldbach¹

Affiliation

¹ University of Bonn, INRES, Karlrobert-Kreiten-Str. 13, 53115 Bonn, Germany.

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 r_i 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 r _i 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.

Keywords: Biomass production; Carbon dioxide CO2; Lemnaceae; Liebig's law of the minimum; Lndoor-cultivation; Michaelis-Menten; Modelling; Nutrient medium; Specific PAR spectra; Yield.