Co-cultivation of microalgae-cyanobacterium under various nitrogen and phosphorus regimes to concurrently improve biomass, lipid accumulation and easy harvesting

Abstract

Due to due to high-cost harvesting method, low biomass productivity (BP), and lipid yield (LY), commercialization of microalgae biomass is still impeded. Some researchers discovered that the combined effects of low nitrogen (N) and high phosphorus (P) resulted to an increase in biomass and lipid production. However, the choice of a balanced N:P ratio is still ambiguous between microalgal species and is up for debate. Here, we set various ranges of N:P ratios from 2:1–44.11:1 with the addition of glucose in the BG 11 medium to examine its influence on the growth of microalgae. The investigation was performed by subjecting a novel strain, Scenedesmus sp. DDVG I to these various mediums under heterotrophic and mixotrophic modes. The N:P of 100:50 or N-deficient P-over excessive (Ndef Poexcs) condition under mixotrophic mode had the highest growth rate of 0.15 d−1 ± 0.01, with a maximum BP and LY of 41.1 ± 0.5 mg/L. d and 39.1 ± 1.2 % dry cell weight (DCW), respectively. Further, in attempting to facilitate the harvesting step, we co-cultured Scenedesmus sp. with Limnothrix sp. DDVG II mixotrophically under inoculum ratio of 1:1, 1:2, 2:1 in the Ndef Poexcs condition. The co-culture 1:1 system achieved the maximum biomass harvesting efficiency of 99.9± 0.5 % with an increase in BP and LY up to 42.0 ± 0.9 mg/L. d and 40.2 ± 1.0 % DCW, respectively. The fatty acid methyl ester compositions of co-culture 1:1 was rich in C18:2 (36.05 %), C16:0 (32.25 %), C18:1 (16.86 %), and C18:0 (7.68 %). The biodiesel derived from the co-culture 1:1 also complied with standard specifications, making it appropriate for the production of biodiesel. The overall findings demonstrated a unique co-culture approach toward easy harvesting while concurrently maximizing biomass and lipid yield when grown in a balanced N:P ratio of 100:50. The techno-economic analysis of the system, biodiesel cost, and its implementation toward biorefinery approach can be envisaged in the future study.