Kinetic model of Chlorella vulgaris growth with and without extremely low frequency-electromagnetic fields (EM-ELF)

• Extremely low frequency-electromagnetic fields are tested on Chlorella vulgaris.
• Chlorella vulgaris tends to form cell aggregates during growth.
• Custer formation is enhanced by the application of electromagnetic field.
• The effects of electromagnetic field on cell growth and clusterization are modeled.

Chlorella vulgaris was grown in two bench-scale photobioreactors with and without the application of a low intensity, low frequency electromagnetic field (EM-ELF) of about 3 mT. Cell concentration and tendency of cells to form aggregates inside the reactor were recorded over a 30 days-time period at 0.5 L-constant medium volume in the temperature range 289–304 K. At 304 K, after a cultivation period of 15 days, the rate of cell death became predominant over that of growth. In the temperature range 289–299 K, a two step-kinetic model based on the mitotic division and the clusterization processes was developed and critically discussed. The best-fitted curves turned out to have a sigmoid shape, and the competition between mitosis and clusterization was investigated. Without EM-ELF, the temperature dependence of the specific rate constant of the mitotic step yielded an apparent total enthalpy of 15 ± 6 kJ mol−1, whose value was not influenced by the EM-ELF application. The electromagnetic field was shown to exert a significant effect on the exothermic clusterization step. The heat exchange due to binding between cells and liquid medium turned out to be −44 ± 5 kJ mol−1 in the absence of EM-ELF and −68 ± 8 kJ mol−1 when it was active. Optical microscopy observations were in agreement with the model predictions and confirmed that EM-ELF was able to enhance cell clusterization.