Abstract
Anaerobic digestate supernatant can be used as a nutrient source for microalgae cultivation, thus integrating phytoremediation processes with high value products storage in microalgae biomass. Microalgae are able to use nitrogen and phosphorous from digestate, but high nutrient concentration can cause growth inhibition. In this study, two microalgae strains (C. vulgaris and S. obliquus) were cultivated on the anaerobic co-digestion supernatant (obtained from the organic fraction of municipal solid waste (OFMSW) and waste activated sludge (WAS)) in a preliminary Petri plate screening at different dilutions (1:10 and 1:5) using a synthetic medium (ISO) and tap water (TW). Direct Nile red screening was applied on colonies to preliminarily identify hydrophobic compound storage and then a batch test was performed (without air insufflation). Results show that C. vulgaris was able to grow on digestate supernatant 1:5 diluted, while Nile red screening allowed the preliminary detection of hydrophobic compound storage in colonies. The analysis carried out at the end of the test on ammonia, phosphate, nitrate and sulphate showed a removal percentage of 47.5 ± 0.8%, 65.0 ± 6.0%, 95.0 ± 3.0% and 99.5 ± 0.1%, respectively.
Highlights
The disposal of anaerobic supernatants can lead to several environmental problems, mainly due to their high nitrogen content
C. vulgaris and S. obliquus have been widely studied on several kinds of digestate and stand as the most promising microalgae strains with phytoremediation effects linked with secondary high value storage
Petri plate screening pointed C. vulgaris as a potential strain that could grow on digestate with hydrophobic compound storage
Summary
The disposal of anaerobic supernatants can lead to several environmental problems, mainly due to their high nitrogen content. C. vulgaris and S. obliquus have been widely studied on several kinds of digestate and stand as the most promising microalgae strains with phytoremediation effects linked with secondary high value storage (i.e., lipids, chlorophylls and carotenoids). They have different abiotic stresses, such as nutrient starvation, light intensity and salinity [9,19,26,29,30]. This study analyzed the effect of digestate dilution (both with synthetic medium (ISO 8692) and tap water (TW)) on biomass growth, chlorophyll production and nutrient removal efficiency
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