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

Chlorella vulgaris was grown in a two specially-designed 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 (k1) yielded to 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. Microscopic optical Optical microscopy observations were in agreement with the model predictions and confirmed that EM-ELF is was able to enhance cell clusterization.