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Digestate color and light intensity affect nutrient removal and competition phenomena in a microalgal-bacterial ecosystem
During anaerobic digestion, nutrients are mineralized and may require post-treatment for optimum valorization. The cultivation of autotrophic microalgae using the digestate supernatant is a promising solution; however the dark color of the influent poses a serious problem. First, the color of the di...
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Published in: | Water research (Oxford) 2014-11, Vol.64, p.278-287 |
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Main Authors: | , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | During anaerobic digestion, nutrients are mineralized and may require post-treatment for optimum valorization. The cultivation of autotrophic microalgae using the digestate supernatant is a promising solution; however the dark color of the influent poses a serious problem. First, the color of the digestates was studied and the results obtained using three different digestates demonstrated a strong heterogeneity although their color remained rather constant over time. The digestates absorbed light over the whole visible spectrum and remained colored even after a ten-fold dilution. Secondly, the impact of light and of substrate color on the growth of Scenedesmus sp. and on nitrogen removal were assessed. These experiments led to the construction of a model for predicting the impact of influent color and light intensity on N removal. Maximum N removal (8.5 mgN-NH4+ L−1 d−1) was observed with an initial optical density of 0.221 and 244 μmolE m−² s−1 light and the model allows to determine N removal between 15.9 and 22.7 mgN-NH4+ L−1 d−1 in real conditions according to the dilution level of the influent and related color. Changes in the microalgae community were monitored and revealed the advantage of Chlorella over Scenedesmus under light-limitation. Additionally microalgae outcompeted nitrifying bacteria and experiments showed how microalgae become better competitors for nutrients when phosphorus is limiting. Furthermore, nitrification was limited by microalgae growth, even when P was not limiting.
•O.D. of diluted (1/10) supernatant digestate ranged between 0.19 and 2.35 at 680 nm.•Digestates absorb throughout the visible spectrum.•Nitrogen removal up to 8.5 mgN-NH4+ L−1 d−1 in colored media.•Growth of microalgae limits growth of ammonia-oxidizing bacteria.•Chlorella is a better competitor for light than Scenedesmus. |
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ISSN: | 0043-1354 1879-2448 |
DOI: | 10.1016/j.watres.2014.07.012 |