title: Digestate color and light intensity affect nutrient removal and competition phenomena in a microalgal-bacterial ecosystem.
abstract: 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- [Formula: see text]  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- [Formula: see text]  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.
authors: Irstea, UR GERE, 17 av. de Cucillé, CS 64427, F-35044 Rennes, France; Université Européenne de Bretagne, F-35044 Rennes, France.
authors: Cyril
authors: C
authors: Marcilhac
authors: INRA, UR0050, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, F-11100 Narbonne, France.
authors: Bruno
authors: B
authors: Sialve
authors: Irstea, UR GERE, 17 av. de Cucillé, CS 64427, F-35044 Rennes, France; Université Européenne de Bretagne, F-35044 Rennes, France.
authors: Anne-Marie
authors: AM
authors: Pourcher
authors: Irstea, UR GERE, 17 av. de Cucillé, CS 64427, F-35044 Rennes, France.
authors: Christine
authors: C
authors: Ziebal
authors: INRA, UR0050, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, F-11100 Narbonne, France.
authors: Nicolas
authors: N
authors: Bernet
authors: Irstea, UR GERE, 17 av. de Cucillé, CS 64427, F-35044 Rennes, France; Université Européenne de Bretagne, F-35044 Rennes, France. Electronic address: fabrice.beline@irstea.fr.
authors: Fabrice
authors: F
authors: Béline
mesh_terms: D001419:Bacteria / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism*; D002708:Chlorella / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism; D003116:Color; D008027:Light; D058086:Microalgae / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism; D044444:Scenedesmus / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism; D014865:Waste Disposal, Fluid / Q000379:methods; D062065:Wastewater / Q000737:chemistry*
chemical_list: D009584:Nitrogen; D010758:Phosphorus; D062065:Wastewater
keywords: AOB community evolution; Color; Digestate; Light; Microalgae