Increased concern is being paid to the health and environmental risk caused by trace natural and synthetic hormones discharged from sewage treatment plants. This study, which is part of a larger project on the investigation of hybrid membrane processes for trace hormones removal in water recycling, focuses on binding of hormones to microfiltration membranes in filtration of solutions containing trace hormones. The adsorption capacity of the membrane, kinetics of adsorption and desorption of to/from microfiltration hollow fibre membranes, and the factors affecting adsorption to the membranes have been studied using estrone as model solute. The experiments showed that the adsorption of estrone to the microfiltration membranes could result in high retention of estrone molecules. However, since the mechanism of retention is adsorption rather than sieving, the retention decreases with increase in the amount of estrone accumulated on the membrane, and breakthrough occurs when the accumulated estrone on the membrane reaches an equilibrium concentration corresponding to the feed concentration. For long-term operation, although membranes could be saturated by hormone molecules, the membrane processes could still have a function of buffer for instantaneous high hormone concentration because the saturation surface concentration increases with the increase in the feed concentration. In addition, the experiments also indicated that the adsorption capacity of the membranes for hormones could be affected by membrane types, pH, affinity of hormones to water, as well as the presence of other organics. These results are of relevance to the potential release of trace hormones from water treatment systems where microfiltration membranes are used as a process barrier.

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