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Mechanisms of Physically Irreversible Fouling during Surface Water Microfiltration and Mitigation by Aluminum Electroflotation Pretreatment
journal contribution
posted on 2014-01-21, 00:00 authored by Neranga
P. Gamage, Shankararaman ChellamA modified poly(vinylidene
fluoride) membrane was used to directly
microfilter untreated Lake Houston water, which was then regenerated
by surface washing and hydraulic backwashing, a process that was cycled
five times. The source water was also electrochemically precoagulated
using aluminum and microfiltered, and the membrane was physically
regenerated for five cycles. Attenuated total reflectance-Fourier
transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron
spectroscopy (XPS) were used to characterize foulants on membrane
surfaces and rigorously deduce their contributions to physically irreversible
fouling after cycles 1 and 5. Hydrophobic molecules primarily appeared
to initiate fouling during microfiltration of untreated raw water
because O–H/N–H bands were attenuated while C–H
bands remained relatively unchanged in FTIR-spectra of membrane surfaces
after only one cycle. However, O–H/N–H and symmetric
and asymmetric C(O)O– stretching bands significantly
intensified with continued filtration/regeneration of untreated water,
showing the importance of hydrophilic molecules and the role of complexation,
respectively, to longer term irreversible fouling. Distinct C–H
bands were detected in floated flocs after electrolysis, suggesting
the sorption and subsequent removal of a substantial portion of the
hydrophobic moieties present in Lake Houston water during pretreatment.
Consequently, hydrophilic compounds appeared to contribute more to
irreversible fouling in pretreated waters throughout the course of
filtration as evidenced by significantly more intense O–H bands
(compared with C–H bands) on the membrane surface after cycles
1 and 5. Therefore, electroflotation pretreatment reduced accumulation
of hydrophobic foulants but simultaneously increased complexation
of hydrophilic foulant molecules along with any carried-over aluminum
hydroxide precipitates evidenced by increasing Al and O concentrations
via XPS and intense C(O)O– stretching bands
in IR spectra.