## 3 Results
### Membrane Performance
The negative effect of fouling on membrane permeability is related to three mechanisms: (i) pore constriction caused by adsorption of filtered species within the membrane pores, (ii) pore blocking at the membrane surface, and (iii) cake formation due to the species rejected by the membrane [49]. These effects are less evident in M8 and M15 membranes due to the repulsive forces involving the PAA embodied in the membrane and the HA in the feed solution, resulting in the mitigation of the solute deposition on the membrane surface. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Membrane**} & **Pressure** & **Permeate Flux** & **HA Rejection** & **FRR** & **Reference** \\  & **(bar)** & **(L/m\({}^{2}\cdot\)h)** & **(\%)** & **(\%)** & **Reference** \\ \hline PAN/CS/Fe\({}_{3}\)O\({}_{4}\) & 5.5 & 25.5 & 96.5 & - & [49] \\ \hline PES/PVP/TiO\({}_{2}\) & 1 & 21.927 & 92.96 & 99.03 & [50] \\ \hline CA/OMTT & 3 & 160 & 95.4 & - & [51] \\ \hline RC/SA & 1 & - & 91 & 67 & [52] \\ \hline M0 & 4 & 61.12 & 95.7 & 88.16 & This work \\ \hline M15 & 4 & 76.29 & 99.9 & 97.65 & This work \\ \hline \hline \end{tabular}  
* PAN: Polyacrylonitrile, CS: chitosan; PES: polyethylinesulfone, PVP: polyvinyl pyrrolidone, CA: Cellulose acetate, OMTT: Organically modified montmorillonite, RC: regenerated cellulose, SA: sulfonic acid.  
\end{table} 
Table 5: Comparison of permeate flux, HA rejection, and FRR reported by literatures with prepared membranes in this study. Figure 7: Time versus fluxes during three cycles of the HA UF experiment of the prepared membranes. To thoroughly investigate the antifouling properties of the membranes, Figure 8 depicts the recovery ratio (FRR) observed during the first two cycles. The results clearly show the advantage of blending since the FRR improved by increasing the PAA concentration in the membrane. For the first cycle, the FRR was 88.16% for M0 made of bare CA, which increased to 94.86% for M8 and reached the remarkable value of 97.65% for M15 because of the positive effect of the PAA. The same trend was observed during the second cycle: the water flux recovery ratio was 85.98% for M0, 86.41% for M8, and 95.93% for M15. The reversible fouling ratio (Rr) and irreversible fouling ratio (Rir), as well as their sum--total fouling ratio (Rt), were calculated and depicted in Figure 9. The neat CA membrane showed a total fouling ratio of 31.5% decreasing to 26.7% for M8 and to 22% for M15. However, this decline was mainly due to the reduction of the reversible fouling ratio (Rr), probably related to cake formation, minimized from 23.7% for M0 to 21.8% for M8 and to 16.5% for M15, whereas no relevant effects were observed on the Rir mostly due to HA absorption into the pores and onto the membrane surface. Definitively, the blending of CA with PAA mitigated the fouling largely reversible and facilitated the recovery of the membrane permeability by hydraulic cleaning, but irreversible fouling during long-term operation is still inevitable [50]. A comparison between the present results with some previous studies evidenced the interesting achievements obtained by blending CA with PAA (Table 5). Figure 8: FRR percentages results of the prepared membranes during the first two cycles. Experimental error below than 5%. Figure 9: Summary of percentage of total fouling ratio (Rt), reversible fouling ratio (Rr), and irreversible fouling ratio (Rir) of the prepared membranes during the humic acid ultrafiltration. * Cadmium Removal  
The performances of the membranes in Cadmium (Cd) removal were investigated by treating solutions containing \(10^{-3}\) mol L\({}^{-1}\) of Cd\({}^{2+}\) at various pH values as shown in Figure 10.  
Experiments were performed at values of pH below 6.5 in order to avoid the precipitation reactions between OH- anion and Cd\({}^{2+}\) cation in form Cd(OH)\({}^{2}\). Results confirmed the inefficacy of CA in Cd removal (% removal \(<10\%\)) with a minimal ion binding capacity related to the presence of hydroxyl and carboxyl functional groups.