Nanomembranes - Nanotechnologies for Water Environment Applications - page 380

2007) showed that the lower the solution pH value, the higher the amount of HA
adsorbed on DL membrane and the greater the increment in adsorption of estrone on
membrane by addition of HA. More importantly, it was found that, the presence of HA
could enhance the rejection of estrone under all the pH conditions investigated in this
study, with the greatest “enhancement effect” on estrone rejection at pH 4. It was also
noted that, with the elevation of the Ca 2+ ion concentration in feed solution, the
influence of HA on the fate and transport of estrone during filtration process was less
and less noticeable as the addition of Ca 2+ ions led to a compacted HA conformation,
which might restrict the association of estrone with HA. In addition, ionic strength in
feed solution played a critical role in HA effect on the fate and transport of estrone
during filtration process. Less noticeable “enhancement effect” of HA on estrone
adsorption and rejection was observed at a higher ionic strength.

Table 12.4 Summary of HA effects on estrone adsorption and rejection.

pH 4 pH 7 pH 10.4

Adsorbed HA on Membrane (mg) 103.45 18.16 7.58

Increment in Estrone Adsorption on
Membrane (%)

61.5 32.0 11.4

Increment in Estrone Adsorption/
Adsorbed HA (%/mg)

0.59 1.76 1.51

Increment in Estrone Rejection (%) 19.7 3.8 4.6

In another study (Tan, 2004), the effects of competition among EDCs on their
rejection, pH, ionic strength, adsorption, and 24-hour operation were investigated using
two types of membrane materials (cellulous acetate and polyamide). A synthetic feed
water was used to evaluate factors influencing EDC rejection by RO and NF membranes.
Rejection of EDCs was investigated at a permeate flux of 0.007 m 3 / (h·m 2 ) in a bench
scale study. RO membranes (AG and ST-28) were found to be more effective at the
EDC rejection after 24-hour operation with rejections ranging from 73 - 85 %.
Adsorption and physical sieving could be attributed to the early stages of the 24-hour
operation while physical sieving would have been the dominant mechanism over the 24-
hour operation. Membrane adsorption of EDCs was affected by competition among the
EDCs in a mixture. This resulted in a decreased rejection of any one EDC in the mixture.
Acidic and neutral pH were more suitable for estrone rejection than the basic pH. The
unexpected drop in estrone rejection at high pH could be due to membrane surface
modification at high pH.

Since steroid estrogens are hydrophobic compounds of low volatility, adsorption
plays an important role in their removal. Therefore, hydrophobic polymer membranes
and strong adsorbent such as fullerene could be effective in removal of estrogens from
aqueous phase. In one study (Jin et al., 2007b), new polymer membranes based on
hydrophobic polymer - poly (2, 6-dimethyl-1, 4-phenylene oxide) (PPO) modified by