M.Sc Thesis


M.Sc StudentBarki Debra
SubjectRemoval of Chlorinated Organic Pollutants from Groundwater
using V-UV based Advanced Oxidation Process
DepartmentDepartment of Civil and Environmental Engineering
Supervisor ASSOCIATE PROF. Yael Dubowski
Full Thesis textFull thesis text - English Version


Abstract

The presence of chlorinated organic pollutants in water sources requires particular attention due to their slow decomposition, carcinogenicity, and toxicity. Advanced oxidation processes (AOP) are considered a promising technology for treating organic pollutants, commonly using UV-C radiation (254nm) with addition of different chemicals. Although previous AOPs were proved effective, chemical dosing complicates the treatment and increases its costs. This study examines removal kinetics of chlorinated organic pollutants using AOP based on V-UV radiation. V-UV irradiation generates hydroxyl radicals in-situ via photo-induced homolysis of water without chemicals addition. The proposed treatment was tested with two different sources of V-UV light: a low-pressure mercury lamp (LP-Hg) with combined UV-C/V-UV emission bands (95% at 254nm and 5% at 185nm) and a microplasma (MCP) lamp (prototype provided by UIUC) that emits solely in the V-UV range 187-200nm. Experiments were performed in different matrices (distilled-water, synthetic solutions, and groundwater). In the first stage, the effect of V-UV radiation (185nm) on degradation of Trichloroethylene and Tetrachloroethylene was tested, using a flowthrough reactor equipped with LP-Hg lamp. Faster degradation of both pollutants was observed in the presence of V-UV, even though it accounted for only 5% of the radiation. The maximal effect was observed in distilled-water solutions. DOC and byproducts analyses indicate that under combined radiation, high mineralization was obtained, while direct photolysis under 254nm resulted in build-up of byproducts with minimal mineralization. In more realistic matrices pollutants removal still occurred, but at lower efficiency due to the presence of interfering compounds. Various organic/inorganic species naturally present in groundwater may interfere with the AOP by competing for V-UV radiation and/or for the photogenerated OH radicals. Investigation of the effect of such substances enabled to identify the main interfering compounds and to develop a pre-treatment for their removal. Exact pH reduction prior irradiation yielded clear improvement in the process efficiency, by shifting the carbonates system to carbonic acid (less reactive toward OH) without enhancing the chloride OH-scavenging potential. In the second stage of this research the MCP lamp was tested as V-UV source, using a batch reactor and Atrazine as model compound. The MCP lamp removed Atrazine both in DIW and in synthetic GW solutions, though at slower degradation rate in the latter due to the presence of OH-scavengers. Comparison of Atrazine degradation under the three lamps (combined LP-Hg, 254nm LP-Hg and MP), indicated that the 254nm lamp was the least effective while the combined LP-Hg lamp was more efficient than the MCP lamp. The reason for the lower efficiency of the MCP lamp is still not fully clear but seems to reflect lower overlap between lamp output and water absorption spectra. Nevertheless, MCP lamp seems to have high potential for such treatment as it has low energy demand and physical design that enables to apply it in arrays. This study provides new information regarding the potential of using VUV-based AOP for treatment of persistent organic pollutants in real water matrices, especially for decentralized and small water treatment facilities.