## 1 Introduction  
In light of the increasingly stringent standards regarding treated effluent, new and efficient waste treatment processes need to be identified. Research and deployment efforts target solutions that can efficiently remove organics and neutralize substances that promote microbial growth [1; 2; 3]. Environmental benefits and reduced investment/operational costs are prioritized [4]. The main deciding factors in choosing a wastewater treatment process include its compatibility with the frameworks and strategies, as well as the energy and environmental policies currently in place [5]. The deployed technologies should be in line with the principles of circular economy, zero waste policy, and energy/material recycling [6; 7]. Also of importance is managing energy consumption by improving system efficiency, energy recovery, and harvesting of value-added products [8; 9]. This can support environmental protection efforts aimed at promoting alternative energy sources and sustainability [10; 11]. Microbial granules can serve as an alternative to conventional technologies [12]. There has been fast-growing interest in methods harnessing aerobic granular sludge (AGS) and anaerobic granular sludge (AnGS), as well as microbial-bacterialgranules (M-BGS), as evidenced by the fast-growing number of studies on the subject, and by the number commercial installations developed [13; 14]. AGS and AnGS sewage treatment systems have already gone beyond the stage of research and experimental work [15; 16]. Their technological readiness level is sufficient for commercial-scale design and deployment. There is, however, a new and underexplored direction in biotechnological microbial granulation--systems that harness microalgae-bacteria symbiosis [17]. Results obtained and published so far on M-BGS have earned them a reputation as a very promising and versatile new technology, which can serve as an alternative to current wastewater treatment processes [18; 19]. Research on generating and successfully harnessing M-BGS is still in its early stage. So far, experiments tend to be small-scale (mostly laboratory-scale) [18; 19; 20]. The current focus is mostly on selecting optimal conditions and process parameters. However, of equal importance is the screening of the right operational data and environmental parameters for reproducible and efficient M-BGS granulation [21]. Adding microalgal biomass to the M-BGS boosts nitrogen and phosphorus removal rates compared with conventional AGS [22]. It has also been demonstrated that granules formed through microalgae-bacteria symbiosis store more fatty substances, directly adding to their calorific value [23]. This lipid content makes M-BGS biomass a more universal and valuable substrate for energy production. M-BGS can also accumulate other value-added substances, whose recovery from the surplus sludge may be technologically and commercially viable [24]. This is part of the reason why M-BGSs are emerging as a promising and sustainable method for biotechnological wastewater treatment. Commonly cited advantages of this type of biomass include: easy separation, excellent settleability, high pollutant removal rates, lower running (aeration) costs, and production of high-value-added biomass [25]. There is a dearth of semi-industrial and pilot-scale experiments that would explore M-BGS granule formation mechanisms. The majority of the studies have been conducted in laboratory scale [18; 19; 20]. Scaled-up experiments are needed to identify real-world constraints and technological/operational hurdles. The resultant findings could be used to obtain a realistic balance of investment and operating costs, as well as an assessment of environmental performance [17]. These experiments would also provide a basis and sufficient data for a life cycle assessment (LCA) [26]. So far, little focus has been devoted to exploring how taxonomic classifications and chemical profile of M-BGS affect the anaerobic digestion process and its products.