Nutrients from anaerobic digestion effluents for cultivation of the microalga Nannochloropsis sp. — Impact on growth, biochemical composition and the potential for cost and environmental impact savings

Abstract

Microalgal biotechnology has yielded a range of products for different consumer markets, but large scale production for bulk commodities is limited by the cost and environmental impact of production. Nutrient requirements for large-scale production contribute significantly to the cost and environmental impact of microalgal biomass production and should subsequently be addressed by more careful sourcing of nutrients. This study assessed the use of nitrogen and phosphorus contained in effluents from anaerobic digestion of food waste to cultivate the marine microalga Nannochloropsis sp.. With suitable dilution, effluent could replace 100% of nitrogen demands and 16% of required phosphorus, without significant impacts on growth or biomass productivity. Additional phosphorus requirements could be decreased by increasing the N:P molar ratio of the media from 16:1 to 32:1. Nannochloropsis sp. accumulated lipid up to 50% of dry weight under N-stress, with significant increases in the content of saturated and mono-unsaturated fatty acids. Using empirical data generated in this study, the cost and environmental impact of nitrogen and phosphorus supply was assessed versus the use of fertilizers for biomass and biodiesel production. Nutrient requirements predicted by the Redfield Ratio overestimating impacts by as much as 140% compared to empirical data. By utilising residual nutrients and optimising nutrient supply, the cost and environmental impact of nitrogen and phosphorus were decreased by 90% versus the use of artificial fertilizers.

Liquid Anaerobic Digestate as a Source of Nutrients for Lipid and Fatty Acid Accumulation by Auxenochlorella Protothecoides

“…Liquid digestate from methane fermentation of maize silage can be used as a substitute growth medium for A. protothcoides. In the study conducted by Mayers et al [20], effluents of anaerobically digested food waste were estimated as a potential nitrogen and a phosphorus source. The results of the studies demonstrate that a suitable dilution of this effluent could meet the nitrogen demands and, partially, the phosphorus demands of Nannochloropsis sp.…”

“…Nitrogen can account for 10% or more of the dry weight of algae, depending on the species and N availability for microalgal cells. Its availability is an important determinant of the lipid accumulation process in cells [20]. Liquid digestate fractions are primarily a source of inorganic N (mainly NH 4 ) and P-PO 4 [20].…”

Quantitative mapping of triacylglycerol chain length and saturation using broadband CARS microscopy

“…Nannochloropsis sp. (CCAP211/78) was cultivated according the methods used for strain maintenance and flask cultivation detailed in Mayers et al (45). Cultures were allowed to deplete media nitrogen for the purposes of this analysis to generate cells with higher lipid content.…”

“…Although lipid droplets in microalgae are to date not well understood (54), it has been found that the cellular lipid storages in Nannochloropsis increase, in size and number, under nitrogen depletion (55). It has also been shown that the same strain of microalgae grown under nitrogen starvation contains around 15.0±1.3% saturated fatty acids and 21.2±1.7 % unsaturated fatty acids (45). This results in an average chain length of 16.9 with 1.4 double bonds.…”

Testing the Waste Based Biorefinery Concept: Pilot Scale Cultivation of Microalgal Species on Spent Anaerobic Digestate Fluids

“…Therefore, this work reports on a pilot scale waste based biorefinery approach, utilising formulated digested agricultural streams as growth media, suitable for mass cultivation of industrially significant microorganisms, associated with chemicals and fuels production. Within this concept and to test its usefulness, two well known [20,21] autotrophic microalgae namely Nannochloropsis oceanica and Scenedesmus quadricuada were grown on treated digested agricultural wastewater of specific N:P ratio on a 800 L photobioreactor (PBR). The effluents were physico-chemically characterised and treated through membrane filtration to produce a balanced composition of nitrogen and phosphate effluent suitable for autotrophic algal cultivation.…”