Degradation of 4-Chlorophenol, 3,4-Dichloroaniline, and 2,4,6-Trinitrotoluene in an Electrohydraulic Discharge Reactor

Abstract

An electrohydraulic discharge (EHD) process for the treatment of hazardous chemical wastes in water has been developed. The liquid waste in a 4-L EHD reactor is directly exposed to high-energy pulsed electrical discharges between two submerged electrodes. The high-temperature (>14 000 K) plasma channel created by an EHD emits ultraviolet radiation and produces an intense shockwave as it expands against the surrounding water. The oxidative degradation of 4-chlorophenol (4-CP), 3,4-dichloroaniline (3,4-DCA), and 2,4,6-trinitrotoluene (TNT) in an EHD reactor was explored. The initial rates of degradation for the three substrates are described by dC/dN = −k_1C_i − k_0, where dC/dN is the change in concentration per discharge; Ci is the initial substrate concentration; k_0 is the zero-order term that accounts for direct photolysis; and k1 is the first-order term that accounts for oxidation in the plasma channel region. For 4-CP in the 4-L reactor, the values of these two rate constants are k_0 = 0.73 ± 0.08 μM discharge^(-1) and k_1 = (9.4 ± 1.4) × 10^(-4) discharge^(-1). For a 200 μM 4-CP solution, this corresponds to an overall intrinsic zero-order rate constant of 0.022 M s^(-1) and a G value of 4.45 × 10^(-3). Ozone increases the rate and extent of degradation of the substrates in the EHD reactor. Combined EHD/ozone treatment of a 160 μM TNT solution resulted in the complete degradation of TNT and a 34% reduction of the total organic carbon (TOC). The intrinsic initial rate constant of TNT degradation was 0.024 M s^(-1). The results of these experiments demonstrate the potential application of the EHD process for the treatment of hazardous wastes.