## 3 Findings and Discussion
### The Removal of Tetracycline in the CW Treatment System
For example, a recent study reported that _Phragmites australis_, a large perennial grass from tropical and temperate regions, could successfully remediate several antibiotics, including TC, from an aqueous system [53]. Not only this, but [PERSON] [54] found that _Vetiver_ grass has the ability to remediate TC from a water source by taking up TC into its roots and translocating it to the shoots, and by metabolizing or transforming TC. From the literature, it can be concluded that TC can be taken up by plant roots and translocated to shoots. Interestingly, during operation time, no visible symptoms (such as yellow spots and stripes) were observed on the _Coperus involucratus_ leaves, which means that _Coperus involucratus_ growth was not significantly affected by the initial TC concentration of the tests, 1-10 mg/L, and perhaps _Coperus involucratus_ is a TC-tolerant plant. In this study, other TC removal mechanisms could occur in the  
Figure 7: The effects of the initial TC concentrations on treatment efficiency of CW. CW based on volatilization, hydrolysis [10; 41] and cation exchange, with different processes often occurring simultaneously [40]. It can be seen that when the initial TC concentrations in the CW were 0.980, 4.819, and 10.481 mg/L, the TC concentrations in the effluent were 0.097, 0.598, and 0.474 mg/L, respectively. This suggests that the initial TC concentration affected the removal of TC. A lower TC concentration is probably associated with a higher removal efficiency. As mentioned above, TC was adsorbed onto biofilm, soil, and gravel with little biodegradation and there would be an adsorption coefficient that indicates the substrates adsorbed TC at a certain concentration. When the TC concentration in the influent is high enough to exceed the adsorption capacity, the media would no longer adsorb TC and this would lead to lower removal efficiency [55]. However, this phenomenon was not observed in our test at 0.980 and 4.819 mg/L of TC concentration in the influent. Even in the high TC initial concentration at 10.481 mg/L, the decrease in the TC level was significant, reaching 0.474 mg/L, which was lower than that in case where the initial TC concentration of 4.819 mg/L. This may due to mechanisms other than adsorption which help to reduce TC concentration in water. According to the results shown in Figure 8, TC removal in the CW system was characterized by an initial phase (0-2 h) of rapid TC removal, followed by a slower removal rate period. It was respectively found that about 81.3%, 80.6% and 95.1% of the initial TC concentrations of 0.840, 4.728, and 12.113 mg/L was removed from influent water during the first two hours for three tests. It can be assumed that the initial removal of TC was mainly due to adsorption and photodegradation, followed by other abovesuggested processes. After the initial period, maybe adsorption fully reached equilibrium and thus reduces the removal rate during the later time of operation in the CW considerably [42]. In fact, according to the study of [PERSON] et al. [56], the adsorption kinetics of TC on soils exhibits two distinct stages: a very rapid adsorption (\(<\) 1 h) during the initial stage, followed by a relatively slow adsorption. [PERSON] et al. [57], and [PERSON] and [PERSON] [58] also observed similar results for oxytetracycline adsorption on clay and for TC adsorption on sediments, respectively. Performance of the Combination of Constructed Wetland and TiO\({}_{2}\) Photocatalysis in Treating Water  
In general, using a CW in conjunction with PCR produces better effluent water quality than that obtained by using CW alone [17; 59; 60]. In fact, one of the drawbacks of only using CW is that the disinfection obtained in many cases is not high enough to meet the standards for the reuse of the treated water [59]. In addition, in this study, the CW effluent may consist of microbiological organisms, bacteria and OM. Effluent from the CW, therefore, has to be disinfected before being used for drinking.