Degradation of 4-chlorophenol, 3,4-dichloroaniline, and 2,4,6-trinitrotoluene in an electrohydraulic discharge reactor

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(1)C(i) - k(0), where dC/dN is the change in concentration per discharge; Ci is the initial substrate concentration; k(D) is the zero-order term that accounts for direct photolysis; and k(1) 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 mu M discharge(-1) and k(1) = (9.4 +/- 1.4) x 10(-4) discharge(-1). For a 200 mu M 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 x 10(-3). Ozone increases the rate and extent of degradation of the substrates in the EHD reactor. Combined EHD/ozone treatment of a 160 mu M 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.