Composites of synthesized reduced graphene oxide (rGO) and titanium dioxide nanotubes (TNTs) were examined and combined at different mass proportions (3:1, 1:1, and 1:3) to develop an electrochemical double layer capacitor (EDLC) nanocomposite. Three different combination methods of synthesis—(1) TNT introduction during GO reduction, (2) rGO introduction during TNT formation, and (3) TNT introduction in rGO sheets using a microwave reactor—were used to produce nanocomposites. Among the three methods, method 3 yielded an EDLC nanomaterial with a highly rectangular cyclic voltammogram and steep electrochemical impedance spectroscopy plot. The specific capacitance for method 3 nanocomposites ranged from 47.26–165.22 F/g while that for methods 1 and 2 nanocomposites only ranged from 14.03–73.62 F/g and 41.93–84.36 F/g, respectively. Furthermore, in all combinations used, the 3:1 graphene/titanium dioxide-based samples consistently yielded the highest specific capacitance. The highest among these nanocomposites is 3:1 rGO/TNT. Characterization of this highly capacitive 3:1 rGO/TNT EDLC composite revealed the dominant presence of partially amorphous rGO as seen in its XRD and SEM with branching crystalline anatase TNTs as seen in its XRD and TEM. Such property showed great potential that is desirable for applications to capacitive deionization and energy storage.

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The capability of novel 3:1 reduced graphene oxide/titanium dioxide nanotubes (rGO/TiONTs) composite to desalinate using capacitive deionization (CDI) employing highly concentrated NaCl solutions was tested in this study. Parameters such as material wettability, electrosorption capacity, charge efficiency, energy consumption, and charge-discharge retention were tested at different NaCl initial concentrations—100 ppm, 2000 ppm, 15,000 ppm, and 30,000 ppm. The rGO/TiONTs composite showed good material wettability before and after CDI runs with its contact angles equal to 52.11° and 56.07°, respectively. Its two-hour electrosorption capacity during CDI at 30,000 ppm NaCl influent increased 1.34-fold compared to 100 ppm initial NaCl influent with energy consumption constant at 1.11 kWh per kg with NaCl removed. However, the percentage discharge (concentration-independent) at zero-voltage ranged from 4.9–7.27% only after 30 min of desorption. Repeated charge/discharge at different amperes showed that the slowest charging rate of 0.1 A·g−1 had the highest charging time retention at 60% after 100 cycles. Increased concentration likewise increases charging time retention. With this consistent performance of a CDI system utilizing rGO/TiONTs composite, even at 30,000 ppm and 100 cycles, it can be a sustainable alternative desalination technology, especially if a low charging current with reverse voltage discharge is set for a longer operation.

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Batch experiments were done to assess the removal of 17α-Ethinylestradiol (EE2) using sludge acclimated from a lab-scale submerged membrane bioreactor (SMBR). Though activated sludge (AS) was found to effectively remove EE2 from wastewater, membrane bioreactor showed a faster rate of removal. Results obtained revealed that EE2 was removed completely within 18 h in SMBR while it took 96 h in AS. The removal of EE2 fits first-order rate reactions with a kinetic rate constant, k, of 0.96 d-1 and 6.96 d-1 for AS and SMBR, respectively. This showed that EE2 rate of removal using SMBR sludge is 7X faster than using AS. The role of nitrification in enhancing the removal of EE2 was investigated in terms of the effect of different initial ammonium concentration on both sorption and biodegradation. As the initial ammonium concentration is increased, biodegradation of EE2 is enhanced whereas sorption of EE2 onto the SMBR biomass is decreased. Sorption studies revealed that competition for sorption sites happened between ammonium ions and EE2. The partitioning coefficients, K D were 0.31 L (g MLSS)-1 and 0.09 L (g MLSS)-1 for SMBR and AS, respectively. These results showed that EE2 adsorbed more to SMBR sludge than to AS. Results of this study suggest that MBR improves the biological removal of EE2.