## 3 Results and Discussion
### Filtration Experiments
#### 3.3.1 Phosphorous Removal in Filtration Experiments  
The HAOPs technology was developed to mitigate fouling by removing NOM compounds responsible for it. The primary purpose of the application is to protect the downstream membrane and to ensure that the membrane is as effective as possible in removing contaminants. In this layout, DM made of HAOPs has the potential to remove other contaminants.  
In the presented studies, the pristine membrane removed up to 74 \(\pm\) 5% of phosphorus from the feed water. At the same time, in the case of phosphorus (P\({}_{\text{tot}}\)), the variations were greater (Figure 7). For the highest HAOPs dose, the degree of phosphorus removal ranged up to 93 \(\pm\) 5%. The same removal efficiency was observed for the lowest dose while for 17 g/m\({}^{2}\) of HAOPs the fluctuations were larger and varied from 64.7% to 92%. Such low removal efficiency for that dose may be due to the poor sealing in the first filtration which was fixed in all subsequent tests. An example of a typical variation in the removal of phosphorus over a period of time, corresponding to the duration of the control run, is shown in Figure 7. The HAOPs removal capacity was proportional to the thickness of the layer (of 5 um), which is consistent with the previous findings [19; 21; 22; 23; 24]. In the range of  
Figure 6: Effects of humic acid presence on phosphorus removal (adsorbent dose = 1 g/L, agitation speed = 200 rpm, temperature = 20 \({}^{\circ}\)C, contact time = 60 min).  
analyzed HAOPs doses, and thus the HAOPs layer thickness, no significant increase in pressure or decrease in the membrane flux was observed when DI was filtered through the system.  
In this study, a DM based on HAOPs reduced phosphorus from the Olesnica river by 77%, which is likely connected with its low initial concentration in feed water. [PERSON] et al. [52] outlined the impact of higher phosphorus concentrations on its removal. According to their study, the higher the concentration of reactants the greater the chemical potential for ligand exchange. The retention time, along with the initial phosphorus concentration in feed water, allowed for greater phosphorus removal [22]. Presented results confirmed the impact of initial concentration on removal efficiency. For the initial concentration between 0.32 to 1.3 mg/L the removal efficiency was up to 77% but when the concentration in the synthetic feed water increased, the removal efficiency also increased, and it was 99.9% for 18.2 mg/L. Therefore, the adsorption capacity of HAOPs is very likely dependent on phosphorus concentration in the feed water.  
Moreover, [PERSON] et al. (2019) reported 99.5% phosphorus removal when the MBR effluent was applied, in the concentration range from 4 to 9 mg/L [24].  
This study, although considering surface water, showed a significant difference in the removal of phosphorus. It may be connected with a relatively low concentration of phosphorus in the feed water within the analyzed period of time. The highest recorded concentration in the Olesnica river was 1.53 mg/L. The results show that the initial phosphorus concentration correlates with increasing phosphorous removal, which is in agreement with earlier studies [7; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61].