Study of PFOA-contained wastewater treated by electro-membrane filtration
Date Issued
2010
Date
2010
Author(s)
Hsu, Tzu-Cheng
Abstract
Recently, it has been concerned by every field that PFCs have the characteristics of persistence and bioaccumulation. Because semiconductor industry cannot find the substitute of PFCs, it is still one of the major pollution sources in our environment. Compared to other PFCs, PFOA has more toxicity and is hard to decompose. Therefore, PFOA is the most representative material of PFCs. Because of the complexity of wastewater, this study used 0%, 0.05%, 0.1% SiO2 and 0 mg/L, 20 mg/L, 40 mg/L humic acid (HA) as the representatives of inorganic and organic matters of wastewater to dispense nine various background matrix samples. In addition, the study investigated the strength of electric field that affects the quantity and quality of filtrate.
For the flux part, both of SiO2 and humic acid cause the fouling of membrane surface. Under 95 V/cm electric field, normalized flux ratio (J/J0) raised from 4.2% to 75% (SiO2=0.05%) and 56% to 100% (HA=20 mg/L, E=142.5 V/cm), respectively. In resistance analysis, it was observed that total resistance (Rf) would decrease along with the strength of electric field. However, resistance would increase due to irreversible resistance (Ri) when electric field was above the critical electric field strength.
For the rejection part, membrane process could not separate PFOA via screening mechanism without electric field. The rejection of PFOA elevated to 31% when background matrix contained 0.1% SiO2, because membrane surface charge is changed due to SiO2 fouling. However, PFOA rejection would not change when membrane fouling by humic acid. PFOA can be directly separated by electrophoretic force, and its rejection would increase with application of electric field strength. Under background matrix contained 0.1% SiO2, PFOA rejection increased from 41% (0% SiO2) to 79% (0.1% SiO2) with 95 V/cm of critical electric field strength, which also revealed the effect of electrostatic repulsion. On the other hand, under background matrix contained HA, PFOA rejection had no significant change with electric field application. Moreover, PFOA rejection would decrease with the increase of humic acid concentration when background matrix contained SiO2 (47.5 V/cm). This result could attribute to the humic acid fouling which decreased membrane surface charge. In conclusion, the above outcomes showed that the optimal operating electric field is close to the critical electric field.
According to the comparison between wastewater and simulation sample, the data demonstrated that PFOA rejection could be improved by application of electric field. However, wastewater treatment plants with the coagulation/flocculation process that could greatly increase conductivity, the flux and rejection would be reduced. As the result, if electro-membrane filtration could be applied in front of coagulation/flocculation process, it would improve its rejection efficiency.
Subjects
Electro-membrane filtration
PFOA
SiO2
Humic acid
Electrophoretic
Electroosmosis
SDGs
Type
thesis
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