Nanomembranes - Nanotechnologies for Water Environment Applications - page 379

The existence of the bulk organics in aquatic matrix can significantly affect the
fate and transport of micropollutants such as estrone by binding (Kulikova and
Perminova, 2002; Yamamoto et al., 2003). Therefore, it is predicted that NOM, which
co-present in feed solutions, would bind estrone molecules, and thus, improve the
rejection of trace estrone due to the interaction between NOM and membrane.
Alternatively, some portion of NOM can be adsorbed onto membrane. The presence of
other organic compounds on membrane may either lower estrone adsorption on
membrane by competing adsorption sites on membrane or encourage more estrone
partition from aquatic solution. These possible influences of NOM on the rejection of
estrone molecules during membrane separation processes are determined by the
characteristics of NOM as well as solution chemistry. Thus, in this part of the study (Hu
et al., 2007; Jin et al., 2007a), two types of NOMs (dextran and HA) with different
physicochemical characteristics were chosen to examine the effects of NOM on estrone
removal in the water matrix containing either dextran or humic acid by two kinds of NF
membranes (DL and CK).

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Figure 12.7 Estrone rejection in NOM-containing solution by DL (left) and CK (right).

It is noted that dextran presented negligible effects on the fate and transport of
estrone molecules, especially at the later filtration stage when the whole system reached
equilibrium. As a result, the addition of 3.5 mg C/L dextran did not lead to any
pronounced change in estrone removal compared with the electrolyte background case
for any of the NF membranes used. However, the presence of HA with great aromaticity
improved estrone adsorption on membrane significantly as well as estrone rejection, but
slightly, by 3.8% for DL membrane and by 5.1% for CK membrane (Figure 12.7). These
diverse impacts on membrane performance might be attributed to the difference in the
aromaticity of DOM for dextran and HA, which was related to the affinity of steroid
hormone to DOM (Yamamoto et al. , 2003) and the adsorption of DOM on membrane
polymers. In addition, the experimental results in Table 12.4 (extracted from Hu et al.,