## 3 Results and Discussion
On the other hand, bacterial communities in POME final discharge were mostly from the Beta-, Delta- and Gamma-proteobacteria classes, which are dominated by the MWH-UniP1 (1.9%), Syntrophaceae (6.1%) and Chromatiaceae (9.6%) families, respectively. Observations from the first part of the system where the POME final discharge was introduced from day 2 to day 7 show that the unique bacterial community found in the rainwater was compromised. For instance, Legionellaceae (0.5%) that were originally detected in the rainwater were not detected once the POME final discharge was introduced into the system. Legionellaceae were reportedly found in the rainwater reservoir [52] due to their capability to thrive in poor-environment habitats and their inability to survive in a complex nutrient-rich environment [53]. Legionellaceae were able to thrive in drinking water systems by forming biofilm and parasitizing other bacteria with this ability [54]. Despite the fact that Legionellaceae has the potential to cause pneumococcal disease in humans, the composition of Legionellaceae was not identified after the groundwater treatment for drinking purposes due to their inability to tolerate the changes in their surroundings [55]. Figure 6: Heatmap of the relative abundance of bacterial orders and families within the Proteobacteria phylum at the relative abundance cut-of of 0.5%. Rainwater was first introduced as a control on day 1, followed by the addition of POME final discharge from day 2 until day 7. The addition of POME final discharge was stopped and the rainwater was reintroduced into the system from day 8 until day 15 to mimic the zero-emission concept. Notes: FD—final discharge: RW—rainwater: D—day. Other than that, it was suggested that the _Hyphomonadaceae_ (0.7%), _Alcaligenaceae_ (0.7%), MWH-UniP1 (1.9%), _Nitrosomonadaceae_ (0.7%), _Spiroblackllates_ (2.6%), _Chromatiaceae_ (9.6%), _Halomonadaceae_ (0.7%) and _Pseudomonadaceae_ (1.7%) families were introduced into the system due to the addition of POME final discharge into the receiving water since they were not detected in the rainwater sample. The compositions of _Spiroblackllates_ and _Halomonadaceae_ were reduced after the implementation of zero-emission of POME final discharge, and they were not detected after day 14 and day 11 onwards, respectively. _Spiroblackllates_ were found to be associated with the degradation of complex organic matters [56], while _Halomonadaceae_ were mainly correlated with the biodegradation of nitrate content in wastewater, and they were found to be among the dominant bacterial family in wastewater contaminated with high nitrate content [57]. This result suggests that the reduction in the complex organic matter and nitrates (Figure 4c) in the receiving water following the implementation of zero-emission of POME final discharge reduced the compositions of some of the bacterial communities in the sample. Hence, it is clear thus far that the implementation of zero-emission of POME final discharge could reduce the carried over bacterial population introduced by this effluent in the receiving water. It is worth discussing the presence of both bacterial indicators, _Chromatiaceae_ and _Alcaligenaceae_, in the receiving water but not in the rainwater, where they were suggested to be carried over from the POME final discharge into the artificial river water system. The composition of the _Chromatiaceae_ in the system introduced with POME final discharge increased starting from day 2 (2.2%) to day 7 (5.1%), then reduced after the implementation of zero-emission of POME final discharge on day 8 (2.2%) and became undetectable on day 15. This can be explained by the association of Chromatiaceae composition with the degradation of dissolved organic carbon (DOC) present in the POME [58]. On the other hand, the composition of _Alcaligenaceae_ showed a small reduction from 1.2% on day 8 to 0.9% on day 15. _Alcaligenaceae_ are known as the phenolic and aromatic compounds degraders [59].