## 1 Introduction  
Massive anthropogenic activities generate 359.4 \(\times\) 10\({}^{9}\) m\({}^{3}\) of wastewater annually, and only 52% is treated before its discharge into natural water bodies [1]. The existing treatment methods in urban wastewater treatment plants (UWWTPs) are not effective either because [2; 3; 4; 5; 6]: (i) the conventional secondary treatments are ineffective in the reduction of contaminants of emerging concern, such as heavy metals, pharmaceuticals, and antibiotic-resistant bacteria and their genetic determinants (ARB&Gs); (ii) the implementation of tertiary treatments require high energy demands and thus are cost-effective; or (iii) some of the existent disinfection processes (such as chlorination or ozonation) imply the use of additional chemicals or the generation of other harmful by-products, some of them classified as carcinogenic compounds [7; 8; 9]. Hence, the continuous disposal of wastewater containing high concentrations of chemical pollutants, pathogens, and ARGs, can severely put freshwater quality at risk and jeopardize public health [10; 11; 12; 13]. Reutilizing treated wastewater is seen as an alternative to reducing water demand, particularly in world regions that are affected by water scarcity. Treated UWW reutilization almost always implies a storage period for transportation or temporal need. Reports show that treated water storage may induce the regrowth of bacteria, namely ARB&Gs [14]. Therefore, the great challenge has been the development of reliable, effective, low-cost, and environmental-friendly strategies for pollutant removal and reduction of ARB&Gsproliferation in UWWTP effluents that allows a safe reutilization of treated water. Biological final treatments, namely with microalgae technology, appear as a more environmentally friendly alternative, particularly due to their high metabolic flexibility and the non-generation of toxic by-products. Additionally, the biomass obtained at the end of the process can be converted to commercially valued products, such as biofuels or biofilizers, paying off the photobioreactor implementation's costs [15, 16]. Moreover, the operational conditions inherent to microalgal production (such as pH, dissolved oxygen and carbon dioxide concentrations, light exposure, and hydraulic retention time), were described to create hostile conditions for some potentially harmful bacteria, such as faecal coliforms [4, 17, 18, 19, 20]. Particularly, light exposure above 115 umol m\({}^{-2}\) s\({}^{-1}\) has a crucial role in _E. coli_ removal, in combination with DO values between 1.2-8.18 mg L\({}^{-1}\) and alkaline pH (above 8.5) [21, 22]. Besides, some physiological characteristics of microalgae may have a role in the reduction of pathogens' proliferation, including [18, 20, 23]: (i) the production of toxins and antimicrobial compounds; (ii) the content in extracellular polymeric substances (EPS), from which humic substances are part of the composition, and (iii) the capacity of co-sedimentation with bacteria. The possibility of forming a consortium between microalgae and bacteria has several reported benefits related to cooperative interactions in nutrient uptake, microalgal growth, environmental resistance, and pathogens reduction. Pieces of evidence show that _Chlorella vulgaris_ in consortium with bacteria from activated sludge improved the reduction of the abundance of _Pseudomonas aeruginosa_, _Escherichia coli_, and _Enterococcus faecalis_ in 59, 56, and 55% when compared to the single-use of activated sludge. Moreover, a recent study highlighted the potential of _C. vulgaris_ and a _C. vulgaris_ -_Bacillus licheniformis_ consortium to remove exogenous plasmids carrying ARGs, such as _su1_, while keeping an efficient uptake of phosphate-phosphorus (PO4-P) [24]. Even though several studies report the effective use of _C. vulgaris_ for conventional pollutants removals, such as nitrogen and phosphorus [25, 26], few are related to disinfection and ARGs reduction of abundance [4, 20, 24].