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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Bibliographic Details
Published in:Water research (Oxford) 2014-11, Vol.64, p.278-287
Main Authors: Marcilhac, Cyril, Sialve, Bruno, Pourcher, Anne-Marie, Ziebal, Christine, Bernet, Nicolas, Béline, Fabrice
Format: Article
Language:English
Subjects:
Agriculture, rearing and food industries wastes
AOB community evolution
Applied sciences
Bacteria
Bacteria - chemistry
Bacteria - growth & development
Bacteria - metabolism
Biological and medical sciences
Biological treatment of sewage sludges and wastes
Biotechnology
Chlorella
Chlorella - chemistry
Chlorella - growth & development
Chlorella - metabolism
Color
Constraining
Digestate
Dilution
Environment and pollution
Environmental Sciences
Exact sciences and technology
Fundamental and applied biological sciences. Psychology
Industrial applications and implications. Economical aspects
Influents
Light
Mathematical models
Microalgae
Microalgae - chemistry
Microalgae - growth & development
Microalgae - metabolism
Nitrogen - metabolism
Nutrients
Phosphorus - metabolism
Pollution
Scenedesmus
Scenedesmus - chemistry
Scenedesmus - growth & development
Scenedesmus - metabolism
Waste Disposal, Fluid - methods
Waste Water - chemistry
Wastes
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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.
ISSN:0043-1354
1879-2448
DOI:10.1016/j.watres.2014.07.012