Effects of Water Quality on Destruction of Methyl tert-Butyl Ether (MTBE) by the Pulsed-UV/H_2O_2 Process

摘要

A series of bench-scale tests were carried out to investigate the performance of the pulsed-ultraviolet (UV) and pulsed-UV/hydrogen peroxide (H_2O_2) processes for removing methyl tert-butyl ether (MTBE) with varying levels of the radical scavengers or the UV absorbing species in the background water matrix. The waters tested include groundwater from the City of Santa Monica, California; the Suffolk County Water Authority, New York; the City of Long Beach, California; and effluent from the Miami Dade Wastewater Treatment Plant in Florida. These four waters were chosen based on the level of total organic carbon (TOC) and alkalinity to investigate the effects of these constituents on removal of MTBE during the pulsed-UV process. Some waters also contained other variables such as NO_3~-, which affect the pulsed-UV/H_2O_2 process by filtering out some of the available UV light. For all four types of water tested, excellent removal of MTBE was observed. With irradiation time of 12 min at the UV pulse rate of 3 flashes per second (Hz), less than 5-6 μg/L of MTBE was measured in the effluent (greater than 99 percent removal of MTBE) for all waters spiked with initial MTBE concentrations of 1,000 to 2,000 μg/L and H_2O_2 concentration of 7 to 20 mg/L.The typical MTBE removal efficiency with 6-min irradiation time at 3 Hz was greater than 94 percent, which is indicative of the efficiency of the process for removing MTBE. The presence of NO_3~- at the levels of 10 to 20 mg/L inhibited the rate of the removal of MTBE. In fact, the rate of reduction (k) was 4.3 × 10~(-3) s~(-1) for Santa Monica water, with background NO_3~- of 20 mg/L compared with 8.6 × 10~(-3) s~(-1) for Long Beach water and Miami Dade water, where the NO_3~- levels are low. With the addition of H_2O_2, however, more consistent removal of MTBE was achieved regardless of the water quality characteristics. For Santa Monica water, the rate of MTBE reduction increased to 7.8 × 10~(-3) s~(-1) with the addition of 20 mg/L of H_2O_2. The effects of background water characteristics were much more evident in the rate of formation and the fate of the MTBE degradation by-products. For example, the water with high level of NO_3~- yielded higher levels of tert-butyl formate and tert-butyl alcohol, two primary degradation products of MTBE during the advanced oxidation process.