Subarctic microalgal strains treat wastewater and produce biomass at low temperature and short photoperiod

In Northern countries, microalgal-based processes are challenging due to low light and temperature conditions during a significant part of the year. Three natural strains from Northern Sweden (Chlorella vulgaris, Scenedesmus sp., Desmodesmus sp.) and a collection strain (Scenedesmus obliques UTEX 417) were cultured in municipal wastewater, comparing their performances, biomass composition and nutrients removal under continuous light at standard (25 degrees C) and low temperature (5 degrees C), short photoperiod (3 h light, 25 degrees C), or moderate winter conditions (6 h light, 15 degrees C). Only the natural strains grew at low temperature, highly consuming total nitrogen and phosphate ( > 80% and > 70%, respectively) even during cold- and dark-stress. At reduced growth rates, C. vulgaris and Scenedesmus sp. produced similar amounts of biomass ( > 1 g/l) as in standard conditions. Scenedesmus sp. and Desmodesmus sp. showed phenotypic plasticity and increased carbohydrate content. Short photoperiod strongly reduced growth rates, biomass and storage compounds and induced flocculation in C. vulgaris.