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.