15. Greywater Treatment in Continuous Flow Solar Photocatalytic Reactor Using Graphite Supported Nitrogen-Doped TiO₂

The increasing water demand has been one of the major global issues for the past decades. An enormous amount of potable water is required for household, industrial and agricultural activities, which led the water authorities to look-out for suitable alternatives. Treated greywater reuse and recycling is an economically viable and attractive option for meeting a portion of future water demand. The feasibility of a continuous mode solar photocatalytic system in greywater treatment was explored in this study. The solar photocatalytic tests were employed with graphite-supported nitrogen-doped titanium dioxide (N-TiO₂). The effect of flow rate (20–70 mL/min) was investigated under pH-3, H₂O₂ dosage-1 g/L, catalyst dosage-5 g/L in a continuous reactor. These tests revealed that the maximum removal efficiency in terms of COD, TOC and NH₄-N was accomplished at 20 mL/min, while the lowest removal efficiencies were found at 70 mL/min. The removal efficiencies of COD, TOC, and NH₄-N were progressively reduced from a flow rate of 20 to 50 mL/min, followed by a sharp drop at a flow rate of 70 mL/min. The reactor operation at the lowest flowrate i.e. 20 mL/min showed the removal efficiencies of 71.8, 65.1 and 63.7% for COD, TOC and NH₄-N, respectively. The result showed that a solar photocatalytic system with GT-NTiO₂ could be effectively used for greywater treatment under continuous mode operation.