Adsorption of organic matter on ceramic membrane can lead to hydraulic-irreversible
fouling, which decreases the permeate
flux and the cost-efficiency of membrane devices.
In order to optimize the filtration process, detailed information is necessary
about the organic fouling mechanisms on ceramic membranes. In this study, dead-end
filtration experiments of both synthetic water and secondary effluent from a wastewater
treatment plant (WWTP) were conducted on a ZrO2 ceramic membrane.
The experiment results of synthetic water showed that humic acid (HA) was able
to be adsorbed by the ZrO2 membrane and cause permeate
flux decline; and that
HA-tryptophan mixture, at the same DOC level, promoted the filtration flux decline;
DOC removal in the case of HA-tryptophan was lower than that of HA alone. It
seems that hydrophilic organic matter with low molecular weight have some specific
contribution to the organic fouling of the ZrO2 membrane. The results also suggest
that tryptophan molecules were preferentially adsorbed on the membrane at the beginning,
exposing their hydrophobic sides which might further adsorb HA from the feed water. During the filtration of WWTP effluent, protein-like substances (mainly
tryptophan-like) were also preferentially adsorbed on the membrane compared with
humic-like ones in the initial few cycles of filtration. More humic-like substances were
adsorbed in the following filtration cycles due to the increase of membrane hydrophobicity.
A significant rise in hydraulic-irreversible
flux decline was obtained by decreasing
pH from near pHpzc to below pHpzc of the membrane. It suggests that a positively
charged surface is preferred for HA adsorption. Ionic strength increase did not affect
the filtration of HA, but it lessened the hydraulic-irreversible
flux decline of HA-tryptophan filtration. The adsorption of HA-tryptophan can be attributed to outersphere interaction while HA adsorption is mainly caused by inner-sphere interaction.
The results of pre-ozonated HA filtration showed that pre-ozonation lowered the
proportion of potential hydraulic-reversible foulants in HA. Filtration of pre-ozonated
WWTP effluent was also performed. Flux decline phenomenon similar to that of pre-ozonated HA was observed, and it is confirmed that smaller molecules have a stronger
affinity to ZrO2 membrane and tend to form hydraulic-irreversible fouling.
|Date of Award||Jul 2011|
- Biological, Environmental Science and Engineering
|Supervisor||Jean-Philippe Croue (Supervisor)|