Removal of sugars in wastewater from food production through heterotrophic growth of Galdieria sulphuraria

The unicellular extremophilic red alga Galdieria sulphuraria is capable of chemoheterotrophy and its growth has been investigated on some defined and undefined substrates. In this study, the removal of sugars in wastewater from fruit‐salad production with G. sulphuraria strain SAG 21.92 was analyzed. Growth and sugar consumption were determined under variation of temperature, pH‐value and concentration of a model substrate, containing sucrose, glucose and fructose. In shake flask cultivation maximum specific growth rate and specific substrate consumption rate of 1.53±0.09 day(−1) and 2.41±0.14 g(Sub)·g(DW) (−1)·day(−1) were measured at pH 2 and 42°C. A scale‐up of this process was conducted in a 3 L stirred tank reactor (STR). Wastewater from fruit‐salad production was diluted to 15 g·L(−1) total sugar concentration, supplemented with micronutrients and ammonia and pH was set to 3. Determined growth rate and substrate consumption were 1.21 day(−1) and 1.88 g(Sub)·g(DW) (−1)·day(−1), respectively. It was demonstrated, that high sugar concentrations in wastewater streams from food production processes can be significantly reduced with G. sulphuraria SAG 21.92. This strain could achieve substrate consumption rates in wastewater, equal to the more common strain 074G, but at higher pH values. Generated biomass can be used for production of phycocyanin, a valuable nutraceutical.