Assessment of the performance of an anoxic-aerobic microalgal-bacterial system treating digestate Andr  es F. Torres-Franco a, b, c , Maribel Zuluaga a, b, d , Diana Hern  andez-Rold  an a, b, d , Deborah Leroy-Freitas a, b, c , Cristian A. Sepúlveda-Mu ~ noz a, b , Saúl Blanco e, f , C  esar R. Mota c , Raúl Mu ~ noz a, b, * a Department of Chemical Engineering and Environmental Technology, Valladolid University, Dr. Mergelina, s/n., 47011, Valladolid, Spain b Institute of Sustainable Processes, Dr. Mergelina, s/n, 47011, Valladolid, Spain c Department of Sanitary and Environmental Engineering, Federal University of Minas Gerais, Belo Horizonte, 31270-010, Brazil d Faculty of Environmental Engineering UPAEP University, Puebla, 21 Sur 1103, Barrio de Santiago, 72410, Puebla, Mexico e University of Le on, Campus de Vegazana, 24071, Le on, Spain f Laboratory of Diatomology, Institute of Environment, Natural Resources and Biodiversity, La Serna 58, 24007, Le on, Spain highlights graphical abstract  4 and 2-fold diluted digestate was efficiently treated in an anoxic- aerobic system.  Undiluted digestate treatment inhibited nitrification and favored NH 3 stripping.  Chlorella vulgaris and Proteobacteria dominated the microalgal-bacterial community.  Nutrients recovery as microalgal- bacterial biomass was quantified via mass balances. article info Article history: Received 17 August 2020 Received in revised form 15 December 2020 Accepted 21 December 2020 Available online 29 December 2020 Handling Editor: Derek Muir Keywords: Microalgal-bacterial symbiosis Digestate Nitrification-denitrification Microalgae Photobioreactor abstract The performance of an anoxic-aerobic microalgal-bacterial system treating synthetic food waste diges- tate at 10 days of hydraulic retention time via nitrification-denitrification under increasing digestate concentrations of 25%, 50%, and 100% (v/v) was assessed during Stages I, II and III, respectively. The system supported adequate treatment without external CO 2 supplementation since sufficient inorganic carbon in the digestate was available for autotrophic growth. High steady-state Total Organic Carbon (TOC) and Total Nitrogen (TN) removal efficiencies of 85e96% and 73e84% were achieved in Stages I and II. Similarly, PO 3 4 -P removals of 81 ± 15% and 58 ± 4% were recorded during these stages. During Stage III, the average influent concentrations of 815 ± 35 mg TOC$L 1 , 610 ± 23 mg TN$L 1 , and 46 ± 11 mg PO 3 4 -P$L 1 induced O 2 limiting conditions, resulting in TOC, TN and PO 3 4 -P removals of 85 ± 3%, 73 ± 3%, and 28 ± 16%, respectively. Digestate concentrations of 25% and 50% favored nitrification- denitrification mechanisms, whereas the treatment of undiluted digestate resulted in higher ammonia volatilization and hampered nitrification-denitrification. In Stages I and II, the microalgal community was dominated by Chlorella vulgaris and Cryptomonas sp., whereas Pseudoanabaena sp. was more abundant during Stage III. Illumina sequencing revealed the presence of carbon and nitrogen transforming bacteria, with dominances of the genera Gemmata, Azospirillum, and Psychrobacter during Stage I, II, and III, respectively. Finally, the high settleability of the biomass (98% of suspended solids removal in the settler) * Corresponding author. Department of Chemical Engineering and Environmental Technology, Valladolid University, Dr. Mergelina, s/n., 47011, Valladolid, Spain. E-mail address: mutora@iq.uva.es (R. Mu~ noz). Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere https://doi.org/10.1016/j.chemosphere.2020.129437 0045-6535/© 2020 Elsevier Ltd. All rights reserved. Chemosphere 270 (2021) 129437 Chemosphere & it sga ELSEVIER Check for updates ■ * tn>6c An»c ■ , - > CO , L Assimilation NH , * - ►Org - N Amorifiartlon s I Anacrotic Treated c Illicit dRCStOI Extcrial rccircilMioa AgrkiMture PDF Compressor Pro