Toward production of microalgae in photobioreactors under temperate climate

The issue of presented paper is the cultivation of microalgae in temperate climate where the problems are: too low temperature and short vegetation season. The solution is to increase the efficiency of utilization of nutrients under unfavorable climate conditions. The cultivation could be performed in the closed systems, with the application of better source of light to lengthen the growing season and greenhouse to keep high temperature even during the night. The aim of the work was to choose the best method for growth, as well as harvesting the biomass to obtain microalage that can be used in the human diet, animal feed or for industrial applications. The description of available photobioreactors was provided. Different aspects of photobioreactors engineering were discussed: construction, mixing, separation, as well as the overall technology of microalgal biomass cultivation. Two novel photobioreactors were also proposed: column in large-laboratory scale with the capacity of 0.5 m3 and stirred tank in semi-technical scale with the capacity of 10 m3 located under the glasshouse. The strain of Spirulinamaxima was cultivated in the new photobioreactors, because of the simplicity of separation as well as the possibility to maintain the monoculture conditions. A higher growth rate was obtained in pilot-scale reactor (0.430 1/day) at a rate comparing to a column reactor (0.299 1/day), although the ratio A/V of 10 m3 reactor was 22 times smaller than the capacity of the reactor with the capacity 0.5 m3. After 45 days of culture in the column photobioreactor, about 0.3 kg of dry mass, and in the reactor with the capacity 10 m3 about 3 kg dry mass, was obtained.