Remediation of Dichloromethane (CH 2 Cl 2 ) Using Non-thermal, Atmospheric Pressure Plasma Generated in a Packed-Bed Reactor Zaenab Abd Allah, †,‡ J. Christopher Whitehead, § and Philip Martin* ,† † School of Chemical Engineering and Analytical Science, and § School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom ‡ Higher Institutes for Environmental Research, University of Tishreen, Lattakia, Syria * S Supporting Information ABSTRACT: This work describes the application of a non-thermal plasma generated in a dielectric barrier packed-bed plasma reactor for the remediation of dichloromethane (CH 2 Cl 2 , DCM). The overall aim of this investigation is to identify the role of key process parameters and chemical mechanisms on the removal efficiency of DCM in plasma. The influence of process parameters, such as oxygen concentration, concentration of initial volatile organic compounds (VOCs), energy density, plasma residence time, and background gas, on the removal efficiency of 500 ppm DCM was investigated. Results showed a maximum removal efficiency with the addition of 2-4% oxygen into a nitrogen plasma. It is thought that oxygen concentrations in excess of 4% decreased the decomposition of chlorinated VOCs as a result of ozone and nitrogen oxide formation. Increasing the residence time and the energy density resulted in increasing the removal efficiency of chlorinated VOCs in plasma. A chemical kinetic model has been developed on the basis of the proposed reaction scheme, and the calculation of end product concentrations are in general good agreement with the observed values. With the understanding of the effect of the key parameters, it has been possible to optimize the remediation process. 1. INTRODUCTION Volatile organic compounds (VOCs) are a class of air pollutants that affect both the environment and human health. 1,2 Some VOCs are produced from natural sources, including emissions from plants and natural forest fires. The VOCs that are harmful for both the environment and human health are primarily released by man-made activities, such as from oil refineries, petrol storage and distribution, vehicle exhausts, solvent usage and manufacturing, surface coating and painting, and many other industrial processes. 1,3-5 Reducing the use of VOCs is the ideal approach, but “end-of-pipe” technologies are still necessary to remove or remediate. This work investigates the remediation of dichloromethane (CH 2 Cl 2 , DCM) as an example chlorinated VOC, using a packed-bed plasma reactor. DCM causes several health problems, such as headache, nausea, dullness, dizziness, pulmonary irritation, and effects on the central nervous system. Excessive exposure can cause abortion, affect the birth weight, and potentially cause cancer. 2,6 There are several traditional ways to remove VOCs from waste gas streams, such as thermal oxidation, catalytic oxidation, and adsorption, but these techniques suffer from a variety of problems. Thermal oxidation has the problem of generating NO x and other harmful byproducts; catalytic oxidation suffers from catalyst deactivation and poisoning by lead, sulfur, and halogens as well as the disposal of contaminated used catalyst; and adsorption by materials, such as activated carbon and zeolites, requires a batch operation and disposal of the adsorbing material. However, non-thermal plasmas generated at atmospheric pressure and room temper- ature provide several advantages for air pollution control. No heating is required for the non-thermal plasma process; it is generated at room temperature. The energy input into the reactor can also be rapidly varied and controlled depending upon load for increased energy efficiency compared to traditional thermal techniques. For example, atmospheric pressure plasmas have been shown to reduce diesel exhaust pollutants as well as several VOCs. 7-15 Several studies have previously investigated the decom- position of DCM in plasma using different types of plasma reactors and operating conditions, for example, dielectric packed-bed, 16,17,19,21 pulsed corona, 22 electron beam, 22 and low-pressure radio-frequency (rf) plasma reactors 34 with differing background gases and oxygen levels. Fitzsimmons et al. 16 investigated the effect of the oxygen concentration on the removal efficiency of 500 ppm DCM in a non-thermal plasma generated in a packed-bed plasma reactor. They found a maximum DCM removal efficiency in nitrogen plasma with the addition of 2-3% oxygen. Despite these numerous studies, a Received: July 19, 2013 Revised: October 22, 2013 Accepted: November 25, 2013 Published: November 25, 2013 Article pubs.acs.org/est © 2013 American Chemical Society 558 dx.doi.org/10.1021/es402953z | Environ. Sci. Technol. 2014, 48, 558-565