## 3 Results and Discussion
### Nematodes  
The number and species of nematodes in the fouling layer on the membranes were characterized using a bright-field microscope and 165 rRNA sequencing, and the results are shown in Table 3 and Figure 7. Data were obtained from operation cycles 74, 78, 85, and 93 for PES-UF and cycles 89, 93, 100, and 108 for PVDF-UF and PTFE-MF. Table 3 summarizes the species of nematode observed in the membrane fouling layer. Six nematode species were identified, which were _Prismatolaimus intermedius_, _Rhabdolaimus rlerstris_, _Rhabdolaimus_ cf. _terrestris_, _Eumonlystera_ cf. _vurgaris_ and _Eumonlystera_ cf. _hungarica_. The _Rhabdolaimus_ and _Eumonlystera_ genera were dominant within the fouling layer (69% and 23%, respectively). The length of the nematodes ranged from 200 to 500 \(\upmu\)m.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**PES-UF/PVDF-UF and** & **Parameter** & **Feed Water** & **PES-UF** & **PVDF-UF** & **PTFE-MF** \\
**PTFE-MF Cycles (Days)** & **Parameter** & **Feed Water** & **Permeate** & **Permeate** & **Permeate** \\ \hline
16/31 (56/115) & & 2.8 & 2.5 & 2.5 & 2.5 \\
62/77 (216/275) & DOC (mg/L) & 2.7 & 2.7 & 2.7 & 2.7 \\
73/88 (247/306) & & 3.2 & 3.2 & 3.1 & 3.1 \\
81/96 (285/344) & & 3.6 & 3.6 & 3.6 & 3.6 \\ \hline
16/31 (56/115) & & 0.8 & 0.03 & 0.1 & 0.2 \\
62/77 (216/275) & Biopolymer & 0.4 & 0.02 & 0.1 & 0.1 \\
73/88 (247/306) & (mg/L) & 0.5 & 0.04 & 0.05 & 0.1 \\
81/96 (285/344) & & 0.7 & 0.3 & 0.2 & 0.1 \\ \hline
16/31 (56/115) & & 0.9 & 1.1 & 1.2 & 1.1 \\
62/77 (216/275) & Humic acids & 1.1 & 1.2 & 1.2 & 1.2 \\
73/88 (247/306) & (mg/L) & 1.3 & 1.0 & 1.5 & 1.4 \\
81/96 (285/344) & & 1.7 & 1.8 & 1.6 & 1.3 \\ \hline
16/31 (56/115) & & 0.3 & 0.4 & 0.4 & 0.4 \\
62/77 (216/275) & Building & 0.3 & 0.4 & 0.4 & 0.4 \\
73/88 (247/306) & blocks (mg/L) & 0.4 & 0.4 & 0.5 & 0.5 \\
81/96 (285/344) & & 0.4 & 0.4 & 0.5 & 0.4 \\ \hline
16/31 (56/115) & LMW & 0.4 & 0.5 & 0.5 & 0.4 \\
62/77 (216/275) & neutrals & 0.4 & 0.5 & 0.5 & 0.5 \\
73/88 (247/306) & (mg/L) & 0.4 & 0.5 & 0.5 & 0.5 \\
81/96 (285/344) & & 0.5 & 0.5 & 0.7 & 0.5 \\ \hline
16/31 (56/115) & & 0.4 & 0.5 & 0.4 & 0.4 \\
62/77 (216/275) & LMW acids & 0.4 & 0.7 & 0.5 & 0.5 \\
73/88 (247/306) & (mg/L) & 0.6 & 1.2 & 0.6 & 0.6 \\
81/96 (285/344) & & 0.3 & 0.6 & 0.7 & 1.2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Dissolved organic matter (DOM) characteristics of feed and permeate water during GDM filtration.  
Figure 7: Microscopic images of nematodes on the PTFE-MF membrane surface during GDM filtration.  
Figure 7 shows some representative images of nematodes observed on the PTFE-MF membrane. Based on the direct microscopic observations, higher numbers of nematodes were found in the fouling layers of PVDF-UF (31 \(\pm\) 14 count/cm\({}^{2}\)) and PTFE-MF (22 \(\pm\) 6 count/cm\({}^{2}\)), while nematodes were not observed on the surface of PES-UF. Many nematodes were observed on the rougher surface of PVDF-UF and PTFE-MF, with higher biomass concentrations compared to PES-UF. The activity of nematodes loosens the fouling layer and leads to a higher permeability with large fluctuations (Figure 3). Less biomass was accumulated onto the PES-UF, which has a smoother surface that nematodes preferred not to inhabit. The absence of nematodes in the fouling layer of PES-UF led to a gradual decrease in permeability without flux recovery.