## 3 Results and Discussion
### Duration of Filtration Cycles  
In preliminary tests, the pressure on the pristine membrane reached its limit (81 kPa--set by the software) in less than four hours of filtration, whereas with HAOPs surface loading of 20 and 17 g/m\({}^{2}\), no pressure increase was recorded. For HAOPs surface loading of 10 g/m\({}^{2}\), the increase was only 2.5 kPa within the same period of time (Figure 9). Figure 8: Data variability in ultraviolet absorption spectra in permeates for pristine membrane (H-0), adsorbent surface loading of 10 g/m\({}^{2}\) (H-10), 17 g/m\({}^{2}\) (H-17) and for 20 g/m\({}^{2}\) (H-20). Figure 9: Membrane fouling during filtration of feed water with varying amounts of pre-deposited HAOPs. Constant flux: 150 L/(m\({}^{2}\) h), the abscissa indicates the filtration time versus TMP. NOM concentration in terms of UV-VIS254 nm was 0.2525 1/cm on average. Pressure Loss  
Figure 9 presents the changes of TMP as a function of time. When HAOPs were applied, TMP was built up much slower than when the feed water was applied directly to the membrane (a control run). It has been observed that the higher the surface loading of HAOPs applied, the slower the TMP is built up. However, in the case of surface loading of 17 g/m\({}^{2}\) and 20 g/m\({}^{2}\), the difference was relatively small, unlike for 10 g/m\({}^{2}\) dose. Observed TMP build-up is in agreement with experimental results presented elsewhere [19; 22; 28]. With the flux used in these experiments (150 LMH), TMP increased exponentially during the control run, contrary to the filtration unit where HAOPs were pre-deposited. Additionally, the influence of the HAOPs surface loading on the effectiveness of NOM removal was assessed. Consistent with the results from previous reports, HAOPs efficiency in NOM removal reached up to 75% removal of aromatic parts of NOM on average [3; 4; 5; 6; 7; 8; 9; 10]. The tested surface loading (20, 17 and 10 g/m\({}^{2}\) as Al) did not significantly affect the removal of that fraction. However, there is a clear decrease in HAOPs effectiveness in NOM fraction removal at 220 nm, which is associated with carboxylic and aromatic chromophores. In the case of NOM removal, at the beginning of the filtration cycle, it was 77.73% and then, after 7 h of filtration, it decreased to 57.49%. During this filtration that lasted for 7 h permeate samples were taken for analysis every hour (Figure 10). The drop in removal efficiency may be due to DM depletion and the need of backwashing it, following pre-depositing a new HAOPs layer. The short operating time of DM adsorber may be caused by the lack of use of any kind of pre-filtration. In addition to the absorbance, and in order to assess NOM removal surrogates, such as COD-KMnO4, the turbidity and color test was executed. According to the results of the study, HAOPs perfectly removed the part of NOM which is responsible for the color of water. Regardless of surface loading, in the composite permeate, the removal was over 80%, turbidity was reduced by more than 90%, whereas, in the case of COD-KMnO4, the rate of removal was much lower and remained just below 60% on average. Figure 10: Removal efficiency (for the HAOPs surface loading of 17 g/m\({}^{2}\) as Al) during feed water filtration, NOM concentration in terms of UV-VIS254 nm was 0.2525 L/cm on average. This study is a confirmation that a layer of HAOPs can be effectively deposited on a membrane and create a permeable layer of DM that can protect the downstream membrane and be utilized for phosphorus removal from surface water. This particularly applies to highly contaminated surface water. However, this process requires optimization, because many parameters need to be considered before applying the studied technology. Factors such as adsorbent dose, temperature, and contact time need to be evaluated for a proper design of the setup as an operating system.