Growth of Microalgae-Bacteria Flocs for Nutrient Recycling from Digestate and Liquid Slurry and Methane Production by Anaerobic Digestion  
[PERSON]  
1 Laboratory of Reactions and Process Engineering, University of Lorraine, 54000 Nancy, France;  
[EMAIL_ADDRESS] (O.B. ); [EMAIL_ADDRESS] (S.P. ); [EMAIL_ADDRESS] (H.-Z.L.) 2  
[PERSON]  
1 Laboratory of Reactions and Process Engineering, University of Lorraine, 54000 Nancy, France;  
[EMAIL_ADDRESS] (O.B. ); [EMAIL_ADDRESS] (S.P. ); [EMAIL_ADDRESS] (H.-Z.L.) 2  
[PERSON]  
1 Laboratory of Reactions and Process Engineering, University of Lorraine, 54000 Nancy, France;  
[EMAIL_ADDRESS] (O.B. ); [EMAIL_ADDRESS] (S.P. ); [EMAIL_ADDRESS] (H.-Z.L.) 2  
[PERSON]  
1 Laboratory of Reactions and Process Engineering, University of Lorraine, 54000 Nancy, France;  
[EMAIL_ADDRESS] (O.B. ); [EMAIL_ADDRESS] (S.P. ); [EMAIL_ADDRESS] (H.-Z.L.) 2  
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and nutrients [4; 5]. As pointed out in several bibliographic references, it is also recognized that microalgae can play an important role in wastewater and effluent bioremediation to reduce the high amounts of organic matter represented by chemical oxygen demand (COD), ammonia nitrogen (NH\({}_{4}\)-N), and phosphorus (PO\({}_{4}\)-P), as well as the environmental impact of various contaminants and micropollutants [6; 7]. Indeed, wastewater pollutants will be recycled and used as nutrients for algal growth, which reduces the high costs of algal cultures while capturing atmospheric CO\({}_{2}\), depolluting wastewater, and in some cases, allowing compliance with discharge standards [8; 9; 10]. The algal mass produced can thus be used to produce biogas for electricity production or cogeneration [6; 11]. It, therefore, appears interesting to couple microalgae culture for wastewater treatment with anaerobic digestion. In addition, processes using a consortium of microalgae-bacteria (Ma-B), applied to the treatment of industrial and agricultural wastewater, are currently the subject of particular attention [12]. In these systems, symbiotic connections between photo-autotrophic algae and aerobic heterotrophic bacteria are maintained by a simultaneous exchange of gases (O\({}_{2}\) and CO\({}_{2}\)) and nutrients [13]. Thus, during wastewater treatment, this symbiosis avoids an external supply of O\({}_{2}\)/CO\({}_{2}\) and tends to eliminate nutrients as well as reduce CO\({}_{2}\) emissions to the atmosphere [12]. As for the production of biogas (and thus biomethane, CH\({}_{4}\)) by anaerobic digestion, it is strongly influenced by the choice of the substrate but also the inoculum, such as municipal sludge, sediments, industrial effluents, or agricultural wastes such as animal manure and slurry, which contain various bacterial populations [14]. Various studies have demonstrated the efficiency of CH\({}_{4}\) production by digesting microalgae with different substrates. Recently, several algal species such as _Chorella_ spp. and _Chroococcus_ spp. have been selected for their high methane production capacity, [12]. Agricultural effluents include liquid slurry but also the liquid digestate resulting from an anaerobic digester. Both still contain nutrients (organic matter, N, and P), which are essential for the cultivation of microalgae [15; 16; 17]. Reference [18] reports, for example, that plant liquid digestate has a high nutrient potential for the growth of various photosynthetic microorganisms such as cyanobacteria (_Arthrospina maxima_), freshwater microalgae (_Tetradesmus obliquus; Botryococcus braunii_), and marine diatom (_Phaeodactylum tricornutum_).