UV/H 2 O 2 Treatment of Methyl tert-Butyl Ether in Contaminated Waters STEPHEN R. CATER,* ,‡ MIHAELA I. STEFAN, #,§ JAMES R. BOLTON, ‡,#,§ AND ALI SAFARZADEH-AMIRI ‡,† Calgon Carbon Corporation, 130 Royal Crest Court, Markham, Ontario, Canada, L3R 0A1, and The University of Western Ontario, 1400 Western Road, London, Ontario, Canada N6G 2V4 Methyl tert -butyl ether (MTBE) is a pollutant often found in groundwaters contaminated by gasoline spills or from leaking underground storage tanks. The common techniques often used for the remediation of contaminated water are not very effective for MTBE. This study examines the UV/ H 2 O 2 advanced oxidation technology to determine its effectiveness in the treatment of MTBE. The degradation of MTBEwas found to follow pseudo- first-order kinetics, and hence the figure-of-merit electrical energy per order (E EO ) is appropriate for estimating the electrical energy efficiency. The E EO values were found to depend on the concentrations of MTBE, H 2 O 2 , and other components, such as benzene, toluene, and xylenes (BTX). This study shows that MTBE can be treated easily and effectively with the UV/H 2 O 2 process with E EO values between 0.2 and 7.5 kWh/m 3 /order, depending on the initial concentrations of MTBE and H 2 O 2 . The treatment efficiency of 10 mg L -1 MTBE is not adversely affected by the presence of low concentrations of BTX (<2 mg L -1 ). However, the degradation efficiency is significantly decreased at BTX levels greater than 2 mg L -1 . A kinetic model, based on the initial rates of degradation, provides good predictions of the E EO values for a variety of conditions. Introduction The addition ofMTBEto gasoline poses a significant problem for the remediation of wastewater and water contaminated with gasoline because of the accidental spill and leakage from underground storage tanks and transfer pipelines. MTBE has low odor (45 μgL -1 ) and taste (39 μgL -1 ) detection thresholds (1)and a high solubilityin water [about 50 g L -1 (2)]. In the case of reformulated-gasoline soil contamination,MTBEpenetratesreadilyinto the aquiferand also increases the solubility of other petroleum derivatives, such as BTEX, by a cosolvent effect (1, 3). MTBE biodegrades very slowly in soils and groundwater (4-6). Recent laboratory research (7, 8) has demonstrated that pure bacterialstrains or naturalisolates can be effective in the oxidative biotreatment of MTBE, but the aquifers generally do not contain the nutrients needed for biodeg- radation (2). Consequently, bioremediation appears to be difficult to apply to large volumes of MTBE-contaminated water at μgL -1 to mg L -1 MTBE levels. Air-stripping is a traditional and reliable technology for the removal of VOCs from groundwater but is not easily applicable to the treatment ofMTBE,which has a low Henry’s Law constant [H/ RT ) 0.0216 at 25 °C(9)] and partitions substantially into water. By this process, up to 99% of the MTBEcan be stripped from contaminated groundwater,but large air-to-water ratios (100:1 and higher) and multiple air strippers in series are required.Water heatingcombined with aeration improves the removal yield of any volatile organic strongly partitioned into water. Both high airflow and water heatingsignificantlyincrease the capitaland operatingcosts of this technology. Moreover, the process achieves only a mass transfer from one phase to another, without solving the remediation problem. MTBE has a moderate affinity for granulated activated carbon (GAC), and for concentrations in the range of 10- 100 μg/L, GAC is an effective remediation technology. For concentrations above 100 μg/L, MTBEcan be treated at best with only moderate effectiveness by conventional remediation processes. Therefore, there is a need for an alternative process for the remediation of MTBE-contami- nated groundwater and wastewater in relatively high con- centrations between 0.1 and 80 mg/L. Advanced oxidation technologies (AOTs) provide a promising treatment option for MTBE in these ranges. As is well-known, the UV-driven AOTs combine the use of UVlight in conjunction with an oxidizer, such as H2O2 and/or ozone, to generate hydroxyl radicals ( • OH), which attack almost non-selectively any organic compound with very high reaction rate constants (k ∼ 10 6 -10 9 M -1 s -1 ). Th e UV/ H 2O2 processinvolvesthe photolysisofhydrogen peroxide to generate hydroxyl radicals ( • OH), which are very effective in the oxidation and mineralization ofmost organic pollutants (10, 11). This process has been used routinely worldwide for groundwater and drinkingwater remediation. Its main advantage over ozone-based processes is that it does not form bromate ion (a suspected carcinogen) from bromide (12, 13). Also with ozone-based treatments, there maybe a need to treat the off-gas and VOCs maybe stripped. Very few UV/ H2O2 studies have been directed specifically toward the destruction of MTBE in gasoline-contaminated wastewater and groundwater.Wagler and Malley(14)studied the UV/H2O2 treatment of MTBE in a model groundwater using a low-pressure mercury lamp. They observed only a minor pH effect in the low-alkalinity water and increasing rates ofdestruction as the hydrogen peroxide concentration was increased. The present investigation was undertaken to obtain an understandingofthe treatment efficiencyofthe degradation of MTBE in groundwater by the UV/H2O2 process as a function of the concentrations of various components. The companion paper by Stefan et al. (15) presents a thorough study of the intermediates and mechanism of the UV/H2O2 degradation of MTBE. Experimental Section and Methods Materials. MTBE was obtained from Aldrich (97%), and hydrogen peroxide (35%)was purchased from Canada Colors (Toronto, ON, Canada) and used as received. GeneralProcedure. Allexperimentswere conducted using Toronto municipaldrinkingwater.The contaminated water was treated in a standard Rayox1 kWbatch reactor.The unit *Correspondingauthorphone: (905)477-9242,ext.331;fax: (905)- 477-4511; e-mail: cater@calgcarb.com. ‡ Calgon Carbon Corporation. # The University of Western Ontario. § Current address: Bolton Photosciences Inc., Siebens Drake Re- search Institute, Room 230, 1400 Western Rd., London, ON N6G 2V4. † Current address: Hydroxyl Systems Inc., 9800 McDonald Park Rd., P.O. Box 2278, Sidney, BC, Canada V8L 3S8. Environ. Sci. Technol. 2000, 34, 659-662 10.1021/es9905750 CCC: $19.00  2000 American Chemical Society VOL. 34, NO. 4, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 659 Published on Web 01/06/2000