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

Abstract

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 gSub·gDW−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 gSub·gDW−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.

Heterotrophic cultivation of Galdieria sulphuraria under non‐sterile conditions in digestate and hydrolyzed straw

“…In comparison, the doubling time calculated from the growth rates 1.2, 1.0 and 0.9 day − 1 obtained in this study were 18.5 h, 16.6 h and 13.9 h in cyanidium medium, 25 and 50% (v/v) as well as 100% (v/v) digestate, respectively, which lies in the range of doubling times reported earlier (Graziani et al, 2013). Scherhag and Ackermann measured growth rates as a function of substrate concentration and temperature (Scherhag & Ackermann, 2021). As substrate a mixture of sucrose, glucose, and fructose in the range from 6 to 60 g L -1 was tested.…”

“…The authors further used wastewater from fruit processing containing 15 g L -1 sugars and obtained at 42 • C a growth rate of 1.2 day − 1 . However, other than in the present study Scherhag and Ackermann supplemented the wastewater with micronutrients and ammonium (Scherhag & Ackermann, 2021). It should generally be admitted that different G. sulphuraria strains do grow differently under heterotrophic conditions and doubling times from 16 to 95 h have been shown (Graziani et al, 2013).…”

Acid Tolerant and Acidophilic Microalgae: An Underexplored World of Biotechnological Opportunities

“…Moreover, the low pH reduced the initial bacterial population by 98% and removed all the pathogens originally present in the waste water. Therefore, cultivation of microalgae at low pH might offer a means to bioremediate urban waste water (di Cicco et al, 2021) or valorize agro-industrial side streams (Scherhag and Ackermann, 2020), while minimizing the risk of contaminations by unwanted microorganisms.…”

Cell adaptation of the extremophilic red microalga Galdieria sulphuraria to the availability of carbon sources

“…Galdieria sulphuraria presents other interesting characteristics, such as the ability to grow up to 56°C (with an optimum at 42°C) and at very low pH (with an optimum at 2) ( Hirooka and Miyagishima, 2016 ) which is explained by the conditions of its natural environment consisting of hot and acidic sulfurous springs of volcanic regions ( Toplin et al, 2008 ; Ciniglia et al, 2014 ). These harsh growing conditions limit the presence of contaminating microorganisms, and even allow cultivation under non-sterile conditions ( Pleissner et al, 2021 ; Scherhag and Ackermann, 2021 ). These characteristics are even more appropriate when the culture medium contains organic substrates that can be easily metabolized by contaminants such as fungi or bacteria that grow faster than microalgae.…”

“…These characteristics are even more appropriate when the culture medium contains organic substrates that can be easily metabolized by contaminants such as fungi or bacteria that grow faster than microalgae. Moreover, G. sulphuraria has potential for biotechnological applications including bioremediation and biofuel production ( Cheng et al, 2019 ; Cui et al, 2020 ; Somers et al, 2021 ), the capacity to resist to high salt concentrations, to recover heavy metals and nutrients from wastewaters ( Ju et al, 2016 ; Delanka-Pedige et al, 2019 ; Scherhag and Ackermann, 2021 ; Sun et al, 2021 ), and to produce high added-value biocompounds such as phycocyanin and α-tocopherol ( Carfagna et al, 2015 ; Bottone et al, 2019 ) and for nutritional applications ( Graziani et al, 2013 ).…”