Abstract
The simultaneous use of crude glycerol and effluent from anaerobic digestate, both wastes derived from the biofuel industry, were tested in the frame of circular economy concept, as potential low-cost nutrient sources for the cultivation of rich in docosahexaenoic acid (DHA) oil microalgae strain Schizochytrium limacinum SR21. Initially, the optimal carbon and nitrogen concentration levels for high S. limacinum biomass and lipids production were determined, in a culture media containing conventional, high cost, organic nitrogen sources (yeast extract and peptone), micronutrients and crude glycerol at varying concentrations. Then, the effect of a culture media composed of crude glycerol (as carbon source) and effluent digestate at varying proportions on biomass productivity, lipid accumulation, proximate composition, carbon assimilation and fatty acid content were determined. It was shown that the biomass and total lipid content increased considerably with varying effluent concentrations reaching 49.2 g L−1 at 48% (v/v) of effluent concentration, while the lipid yield at the same effluent concentration reached 10.15 g L−1, compared to 17.0 g L−1 dry biomass and 10.2 g L−1 lipid yield when yeast extract and peptone medium with micronutrients was used. Compared to the control treatment, the above production was obtained with 48% less inorganic salts, which are needed for the preparation of the artificial sea water. It was shown that Schizochytrium limacinum SR21 was able to remediate 40% of the total organic carbon content of the biofuel wastes, while DHA productivity remained at low levels with saturated fatty acids comprising the main fraction of total fatty acid content. The results of the present study suggest that the simultaneous use of two waste streams from the biofuel industry can serve as potential nutrient sources for the growth of Schizochytrium limacinum SR21, replacing the high cost organic nutrients and up to one half the required artificial sea water salts, but upregulation of DHA productivity through optimization of the abiotic environment is necessary for industrial application, including aqua feed production.
Highlights
The concept of circular economy (CE) is an exploitative industrial model, characterized as a regenerative system with a circular flow of materials and use of raw materials and energy through multiple phases [1]
It was evidenced that crude glycerol and effluent from anaerobic digestate, which are waste products derived from the biofuel industry, can serve as alternative nutrient source inputs in S. limacinum cultivation
The use of S. limacinum can be an effective tool for the waste stream processing of the biofuel industry, since this species can efficiently utilize crude glycerol as a carbon source for growth and development
Summary
The concept of circular economy (CE) is an exploitative industrial model, characterized as a regenerative system with a circular flow of materials and use of raw materials and energy through multiple phases [1]. The circular model is an alternative to the linear developmental model of the. Sci. 2020, 10, 4398 coupled with generation of waste without proper recycling [2], which led to heavy industrialization. Based on the CE concept, environmental friendly policies have been influenced and shaped worldwide, due to the rising global concerns and ecological awareness [3]. In the frame of a circular economy, converting wastes into value added products can increase their valorization, providing alternative routes of exploitation and environmental benefits from their management
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