## 3 Results and Discussion  
### Stage 1--LF-DSS Treatment and M-BGS Production  
#### 3.1.1 Biomass Growth  
For the first two cycles of H-PBR operation, the biomass grew along the typical pattern for microalgae. The initial 3 days marked the adaptation (lag) phase, (Figure 6a). During this time, microalgae concentration grew from 500\(\pm\) mgTS/dm\({}^{3}\) to 760 \(\pm\) 83 mgTS/dm\({}^{3}\). The biomass then proceeded to grow exponentially until day 12, when it reached 3050 \(\pm\) 94 mgTS/dm\({}^{3}\). Days 13 to 15 were when the growth rate decelerated and reached the stationary phase, with the final biomass concentration being 3210 \(\pm\) 140 mgTS/dm\({}^{3}\) (Figure 6a). The growth rate throughout the exponential phase was 268 \(\pm\) 12 mgTS/dm\({}^{3}\)-d. At the outset of the second cycle (days 16 to 30), the lag phase lasted 3 days, just as before. The growth rate for the nascent M-BGS ranged from 610 \(\pm\) 139 mgTS/dm\({}^{3}\) to 930 \(\pm\) 77 mgTS/dm\({}^{3}\), only to accelerate in the subsequent days (Figure 6b). Exponential growth was maintained for the next 8 days, reaching 3260 \(\pm\) 199 mgTS/dm\({}^{3}\) by day 26. The microbial growth rate then leveled off, reaching the stationary phase at 3610 \(\pm\) 242 mgTS/dm\({}^{3}\) (Figure 6b). During the exponential phase, the growth rate was significantly higher than before, reaching 296 \(\pm\) 17 mgTS/dm\({}^{3}\)-d.  
M-BGS growth was significantly higher in the next experimental cycle. The large abundance of bacteria caused the growth curve to diverge from the normal pattern for  
Figure 6: M-BGS biomass production in phases: (**a**) phase 1 (days 1–15) and (**b**) phase 2 (days 16–30) of the H-PBR operation. microalgae, as the microbial population grew at an exponential rate from the very beginning (Figure 7). Through days 31 to 43, the microalgae + AS microbes biomass grew from 540 \(\pm\) 103 mgTS/dm\({}^{3}\) to 3990 \(\pm\) 422 mgTS/dm\({}^{3}\), which translates to a growth rate of 317 \(\pm\) 29 mgTS/dm\({}^{3}\)-d. The growth rate subsequently tapered off, with no further significant increases. The final concentration at the end of the phase was 4250 \(\pm\) 432 mgTS/dm\({}^{3}\) (Figure 7a). Throughout days 46 to 60, the microbial community entered its final stage of structure and population, and saw no further changes over the remaining period of operation. The mature M-BGS biomass grew at its highest rate--423 \(\pm\) 39 mgTS/dm\({}^{3}\)-d. No lag phase was observed. In the end, the population grew to a concentration of 4800 \(\pm\) 503 mgTS/dm\({}^{3}\), significantly higher than in previous phases (Figure 7b). The available literature lacks reports from studies into the use of real wastewater. It is certainly a gap that needs to be filled. More extensive research is available regarding laboratory analyses of synthetic wastewater [17]. However, it needs to be emphasized that such results require large-scale validation during the treatment of real wastewater and leachate. A study conducted by [PERSON] et al. (2020) [31] demonstrated that the M-BGS population grew exponentially during the treatment of synthetic domestic wastewater, leading to the ultimate biomass concentration in reactors at 5.77 \(\pm\) 0.08 gTS/dm\({}^{3}\)[31]. In the work by [PERSON] et al. (2021) [32], the authors proved that the biomass of microalgal-bacterial consortia might reach the concentration of 7.89 \(\pm\) 0.03 gTS/dm\({}^{3}\) during synthetic wastewater treatment. In turn, [PERSON] et al. (2021) [33] achieved M-BGS concentration at 4.42 \(\pm\) 0.16 gTS/dm\({}^{3}\) in days 1 to 21 as well as 4.34 \(\pm\) 0.09 gTS/dm\({}^{3}\) in days 22 to 23 of synthetic saline wastewater treatment. Subsequent days of the treatment process brought successive decrease in biomass concentration in the reactor, i.e., to 3.20 \(\pm\) 0.11 gTS/dm\({}^{3}\) in days from 33 to 60 and to 1.23 \(\pm\) 0.08 gTS/dm\({}^{3}\) in days from 61 to 110.