Recycling Nannochloropsis oceanica culture media and growth inhibitors characterization

Cross-study analysis of factors affecting algae cultivation in recycled medium for biofuel production

“…Growth inhibition (or lack of inhibition) may be more strongly influenced by other factors (such as those presented in Section 3.4), and not some universal inhibitor that accumulates with each reuse. Even so, several studies observed declining growth performance with increasing medium reuses and/or organic matter accumulation [23,37,103], though these results are outweighed by other experiments in the regression. A limitation of this analysis, however, is that the experimental duration of each medium reuse is different across studies.…”

“…Of the studies that did measure organic compounds in recycled medium (including [15,17,22,23,25,26,37,38,52,61,69,86,89,97,103]), most measured polysaccharides, the most abundant algal exudate, and observed an accumulation [15,22,25,37]. Depraetere, et al [37] confirmed that although polysaccharides in recycled medium inhibited Arthrospira growth to some degree, there were other factors intensifying the inhibition.…”

“…Searches were performed up until November 12, 2016. A total of 86 sources were included in the meta-analysis from both ecological and biotechnological sources (Table S1 and Figure 1) [15,17,[22][23][24][25][26]]. An additional 67 sources deemed potentially relevant were excluded because they did not meet the inclusion criteria or the full text in English was unavailable (Table S2).…”

“…Rijstenbil [81] found that activated carbon did not remove inhibitory compounds from the filtrate of marine diatom cultures. Zhang, et al [23] showed that activated carbon removed organic matter and could improve specific growth rate of Nannochloropsis in recycled medium, but biomass concentration was still below that in fresh medium.…”

“…These compounds can be photosynthetic waste products, signaling molecules, allelochemicals, colony formation and motility aids, or metal chelators, among others [15][16][17][18]. Released organic compounds could be directly inhibitory, such as fatty acids [19,20] released from lysed cells, or may alter physical and chemical aspects of the water (e.g., viscosity [21]) that could influence nutrient availability and uptake, motility, gas exchange, cell aggregation, and shading [22,23].…”