|M.Sc Student||Shalev Adva|
|Subject||Removal of Triclosan from Graywater by Innovative V-UV-UV-C|
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Eran Friedler|
|Professor Yael Dubowski|
|Full Thesis text|
Greywater (GW) reuse can increase the potential of potable water savings. In GW, micropollutants (MPs) mainly emerge from the use of personal care products. Triclosan (TC) a hydrophobic biocide, which is commonly found in antibacterial soaps and in toothpastes, falls within this category. Indeed, TC was detected in GW with concentrations ranging from ng L-1 to µg L-1. TC is not sufficiently removed by common biological treatment and thus advanced treatment is required for its removal. In this research TC removal efficiency was studied in an on-site small system comprising of advance oxidation process (AOP) of Vacuum UV. The system was constructed with a UV reactor emitting energy at 254-185 (V-UV/UV-C reactor).
AOPs produce highly reactive hydroxyl radicals that can oxidize most organic compounds. These radicals can be generated directly via water photolysis under UV light irradiation with wavelength below 200 nm without chemical additives as in this experimental system.
In order to investigate the system ability to degrade TC a set of experiments were performed in the combined V-UV/UV-C reactor. The process kinetics and sensitivity to pH, UV dose and wavelength were examined and quantified.
High removal was found for TC under UV-C and V-UV/UV-C irradiation. The degradation kinetics of TC was faster with the combined V-UV/UV-C irradiation than with UV-C irradiation alone, both in distilled water and treated GW. The reaction rate constants in distilled water were [s-1] and [s-1] (at pH 8) for the UV-V/C and UV-C lamps, respectively. When considering these rate constants, one should take into account that the radiation intensity of the V-UV lamp was only 4% of the one of the UV-C lamp. The reaction rate constant for treated GW spiked with 50 µg L-1 TC was [s‑1] under UV-V/C irradiation. The constant was lower in treated GW than in distilled water, suggesting that organic matter absorbs UV irradiation and hence competes with TC degradation. The concentrations in the UV-treated effluent were below the detection limit, under all conditions, at a UV dose of 3,500 mW s cm-2 (residence time of 165 s).
Following the degradation of TC a hazardous degradation product 2,7/2,8-dichlorodibenzo-p-dioxin (DCDD) was detected. The degradation of this metabolite was found to be faster under the combined V-UV/UV-C irradiation than under UV-C irradiation alone. The pH effected TC degradation and the reaction was faster at basic pH. The system was very efficient in degrading both TC and its identified degradation product.