Abstract
The ability of microalgae, such as the rich in docosahexaenoic acid (DHA) heterotrophic marine microalgae Schizochytrium limacinum SR21, to utilize nutrients in their culture media derived from low-cost nutrient sources makes them a promising low-cost alternative source for the production of useful substances used in aqua feeds. The assessment of culture parameters, one of which is the pH, for every different nutrient growth medium used for microalgae cultivation is important, as they affect the biomass and secondary metabolite microalgae production. This study assessed the effect of different growth medium pH levels (6, 7, 8 and 9), at laboratory and pilot scale systems, on S. limacinum biomass productivity, lipid accumulation, proximate composition, carbon assimilation and DHA. The microalgae were cultivated in growth media containing two different alternative low-cost nutrient sources: (a) crude glycerol derived from biofuel industry as carbon source and (b) effluent digestate from biogas production of livestock decomposition as a source of nutrients and trace elements. It was found that a neutral pH (7) was the optimum level, as it enhanced biomass productivity of the lab and pilot scale cultivation systems at 44.9 g L−1 and 11 g L−1 and DHA content at 7.5% and 19% of the total lipid content, respectively.
Highlights
Industrialization of agriculture food production led to an abundance of agri-waste streams derived from conventional agriculture practices, in order to withstand the increasing global population and food scarcity [1]
This study achieved to recover successfully nutrients contained in the effluent digestate and crude glycerol both waste streams derived from the biofuel industry in order to cultivate the marine microalgae S. limacinum SR21 in the frame of the circular economy concept, converting wastes into a potential value-added product
It was evidenced that the strain S. limacinum SR21 can successfully grow at a wide range of pH levels
Summary
Industrialization of agriculture food production led to an abundance of agri-waste streams derived from conventional agriculture practices, in order to withstand the increasing global population and food scarcity [1]. These include crop residues from arable farming, food waste and manure from livestock farming [2] with the latter posing a great impact on environmental pollution. Anaerobic digestion or co-digestion of livestock manure with agriculture crop residues is a process where microbial decomposition of organic matter produces biogas in order to generate electricity. Byproduct from this process is the decomposed organic matter or digestate which can be further utilized as crop fertilizers due to its high nutritional value, since it is rich in nitrogen [5], phosphorous [6], potassium [7], amino acids [8] and trace elements [9]
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