Polyvinylidene fluoride (PVDF) membranes with polyethylene glycol (PEG) as porogen additives have been prepared with phase inversion methods and precipitation immersion techniques. In particular, adding 30% NaCl to the coagulation bath produces an asymmetrical membrane. The presence of NaCl in the coagulation bath causes liquid-liquid demixing which minimizes the formation of macrovoid. Increasing the potential for fouling is a real consequence of this action. In particular, this study aims to evaluate the fouling potential of PVDF membranes filled with NaCl on the separation of humic acid.

 

To trigger fouling, PVDF membrane is used in the separation humic acid solution as much as 4 times using a dead-end reactor. To evaluate the effectiveness and efficiency of regeneration of humic acid fouled membranes, cleaning is done using the chemical cleaning methods. In this procedure, the membrane is washed using NaOCl in a number of different conditions. The operational conditions applied to this process refer to commonly used conditions. In this study, the concentration of NaOCl used was 0.01 M; 0.05 M; 0.1 M with an exposure time of 10 min; 30 min; 60 min. The effectiveness and efficiency of chemical cleaning using NaOCl were analyzed from the flux recovery value.

 

The results show that higher concentration and exposure times can eliminate more humic acid in the PVDF membrane. However, regenerated membranes using NaOCl have decreased mechanical strength and thermal resistance. The nature of NaOCl as a strong oxidizer is predicted to be closely related to the damage of the PVDF membrane polymer chain. PVDF membrane with the highest recovery flux (85.04%) resulted from chemical cleaning using NaOCl with a concentration of 0.1 M and 60 minutes exposure time.

 

 

Figure 1. PVDF membrane flux value after four times humic acid filtering

 

Table 1. The flux recovery value of PVDF membrane

Membrane

Flux Recovery Value (%)

O₁

13.49

O₂

37.51

O₃

55.44

O₄

17.85

O₅

39.05

O₆

77.34

O₇

19.13

O₈

52.11

O₉

85.04

 

Mechanical strength and termal resistance become the next important parameter that can be used to identify the effects of fouling and regeneration using chemical cleaning on the PVDF membranes characteristics. The autographs and Thermo Gravimetric Analysis (TGA) results showed that all PVDF membranes through chemical cleaning procedures experienced a reduction in mechanical strength and thermal resistance. This condition is triggered by damage to the PVDF polymer chain on the membrane due to the strong oxidizing properties of NaOCl.