# Removal of Crotamiton from Reverse Osmosis Concentrate by a TiO\({}_{2}\)/Zeolite Composite Sheet
## 1 Introduction  
Reverse osmosis (RO) is a well-established technology for water desalination, the production of potable water, and more recently, tertiary wastewater treatment [1; 2]. With increasing global water demand, it is predicted that the global market value of RO system components will reach 8.1 billion USD by 2018 [3]. Along with the purification of wastewater, the RO process produces a concentrate containing high levels of rejected pollutants (about 15-20% of the influent volume) [4]. Some of the emerging pollutants, such as pharmaceuticals and personal care products, are very persistent in sewage effluent, resulting in raised awareness of the environmental risk of RO concentrates [1; 5; 6]. Genotoxicity evaluation using the _SOS/umu_ test has provided direct evidence that RO concentrates have much higher toxicological risk than RO influents [7]. Therefore, suitable technology needs to bedeveloped for treating RO concentrates before discharging them into receiving water or recycling for other purposes. This requirement is especially important for large-scale RO treatment systems [8]. In a number of recent studies, TiO\({}_{2}\) photocatalysis has been used to treat pharmaceuticals in wastewater [9]. The nonselective oxidation ability of hydroxyl radicals enables effective degradation of various organic pollutants. However, the photocatalysis of target compounds can be inhibited by coexisting materials, such as inorganic ions and organic matter, in the wastewater [10; 11; 12]. In addition, toxic intermediates may be produced during photocatalysis, and the effects of pharmaceutical degradation products in the environment are of concern. Furthermore, when TiO\({}_{2}\) or nano-TiO\({}_{2}\) powder in water is exposed to ultraviolet (UV) radiation, radicals that are harmful to aquatic organisms are produced [13]. Therefore, the effective recovery of catalyst powder after wastewater treatment should be taken into consideration. Wastewater treatment frequently involves adsorption processes, and various types of adsorbents have been developed to remove different pollutants [14; 15; 16; 17; 18; 19]. The high-silica Y-type zeolite HSZ-385, which is a hydrophobic zeolite, has been used to remove sulfonamide antibiotics from wastewater and selectively removes sulfonamides even in the presence of high concentrations of coexisting materials [20]. However, after adsorption, the contaminants are permanently transferred to the sorbent and not destroyed, which can lead to problems with saturation of the adsorbent. Attempts have been made to synthesize TiO\({}_{2}\)-adsorbent composites that perform both photocatalysis and adsorption to remove pharmaceuticals from wastewater [21; 22; 23]. This synergistic effect has been confirmed for TiO\({}_{2}\) and zeolite in a TiO\({}_{2}\)/zeolite composite powder that was used to remove sulfonamide antibiotics [23]. [PERSON] et al. condensed nano-TiO\({}_{2}\) on the surfaces of carbon spheres through hydrothermal treatment to generate core-shell structures, and found that visible light absorption was enhanced compared with pure TiO\({}_{2}\) because of the interface formed between the two materials [21]. The activated carbon fiber felt (ACFF) in the TiO\({}_{2}\)/ACFF porous composites significantly enhances the photocatalytic property of toluene by hindering the recombination of electron-hole pairs, reducing the TiO\({}_{2}\) band gap energy, and accelerating toluene adsorption [24]. Using a papermaking technique, [PERSON] et al., prepared a paper-like composite sheet from TiO\({}_{2}\) and zeolite powder [25]. Under UV irradiation, bisphenol A was effectively degraded through the synergistic effect of the TiO\({}_{2}\) photocatalyst and zeolite adsorbent in these sheets [25]. In addition, the degradation intermediates of bisphenol A, which may be harmful to the environment, were temporarily captured by zeolite in the composite sheet and eventually decomposed through photocatalysis [26].