Boost of algae growth by ultra short pulsed electric field treatment

Due to their ability to accumulate considerable amounts of triglycerides, microalgae are considered as the most promising future biomass feedstock for oil production. Nanosecond pulsed electric field (PEF) can induce growth stimulation on plants and fungi, as we have shown in previous work. In the frame of this study, we transposed such growth stimulation process on microalgae in suspension to increase the cultivation yields in order to reduce biomass production costs. Optical density measurement of cell culture growth revealed to be a very sensitive diagnostic tool for determination of the algae growth and algae lethality exposed to PEF treatments. At first approach, the lethal pulse parameters of PEF treatment of Chlamydomonas rheinhardtii and Chlorella vulgaris algae suspension were determined by monitoring the optical density over the entire cultivation time. As a first important result we found that a 30 min long PEF treatment at field strength of 40 kV/cm and pulse duration of 25 ns doesn't affect algae growth. In this case the specific energy dose was 1.4 kJ/kg. PEF treatments at specific treatment energies below this limit were considered to be non-lethal. We found that the average value of the growth rate (0.08±0,03 h-1) of nsPEF treated C. rheinhardtii suspension doesn't deviate significantly from the average growth rate of the sham cultivation (0.07±0,02 h-1) indicating no stimulation effect. In case of C. vulgaris the 30 min PEF treatment with a non-lethal dose during exponential growth phase led to an increase of biomass yield in the range of 10-20%. This increase was significant towards the end of cultivation after 5 days.