Organic wastes/by-products as alternative to CO 2 for producing mixotrophic microalgae enhancing lipid production
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RESEARCH PAPER
Organic wastes/by‑products as alternative to CO2 for producing mixotrophic microalgae enhancing lipid production Davide Veronesi1 · Giuliana D’Imporzano1 · Barbara Menin2 · Silvia Salati1 · Fabrizio Adani1 Received: 8 October 2019 / Accepted: 15 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this work, white wine lees (WWL), cheese whey (CW), and glycerol (GLY) were used as carbon (C) sources to mixotrophically support the production of the microalga Nannochloropsis salina, replacing CO2 supply. In doing so, the alga was allowed to grow on C sources dosed at 2 g L−1, 3 g L−1, and 4 g L−1 of C, in the presence and absence of C O2 supply. WWL and CW were not able to support the algal growth due to a fungal contamination that was genomically identified, while GLY gave interesting results in particular with 3 g L−1 of C. GLY-C was able to replace CO2-C completely when the latter was omitted, showing an algal biomass production similar to those obtained in autotrophy. If C O2-C was provided jointly with GLY-C, biomass production and lipid contents increased more than 30% and 23%, respectively, compared to autotrophy. Keywords Algae production · Carbon dioxide · Mixotrophy · Organic wastes · Organic by-products
Introduction Nowadays, the importance that microalgae could play in several sectors, such as agriculture, animal feeding, green chemistry, nutraceutics, pharmaceutics, and bioenergy production, is increasingly recognized [1]. To grow and reproduce, these microorganisms require an energy source (light), a carbon source ( CO2 for autotrophic microalgae), and a growth medium (water plus nutrients) [2]. This is the common modality of algal cultivation, i.e. photoautotrophy, in which algal cells use light energy to extract protons and electrons from water, reducing C O2 to organic molecules. Photoautotrophic cultivation is limited by high production costs; in particular, nutrients and CO2 supplies are the major production costs in a full-scale microalgal production plant [3]. To reduce these costs, several authors suggested the use of wastewaters as culture medium [4, 5]. Some other studies suggested, as a feasible alternative to the photoautotrophic cultivation, the exploitation of the ability of some algae strains to grow under mixotrophic conditions using raw
* Fabrizio Adani [email protected] 1
Gruppo Ricicla-DiSAA, Università Degli Studi Di Milano, Via Celoria 2, 20133 Milan, Italy
CNR, Milan, Italy
2
materials rich in carbon (C) and nutrients [6, 7]. Mixotrophic cultivation is the mode by which microalgae can drive both photoautotrophy and heterotrophy and can utilize both inorganic and organic carbon sources [8]. Inorganic carbon is fixed through photosynthesis which is influenced by illumination conditions, while organic compounds are assimilated through aerobic respiration, which is affected by the availability of organic carbon [9]. Some scientists suggested that the specific growth rate of microalgae under mixotrophic cultivati
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