Sonochemical Degradation Studies of Isoniazid in Aqueous Medium

Pharmaceutical compounds, released into the aquatic system through normal human usage and industrial activities, are generally biologically active and persistent in the environment. This study investigated the active degradation of a pharmaceutical compound, isoniazid (INH), in an aqueous medium using sonochemical method. Sonochemical degradation was carried out by varying parameters such as frequency, power, pH, and the presence of co-existing surfactants, sodium dodecyl sulfate (SDS). An optimum frequency and power for the degradation were found to be 620 kHz and 80 W, respectively. Nearly complete degradation of INH was attained within 1 h of sonication with a pseudo first-order rate constant of 0.0543 min−1 under this experimental condition. Moreover, an appreciable COD reduction of 75% was achieved after 2.30 h of continuous irradiation even if a complete degradation of the INH was observed. The pH effect revealed that the protonation and deprotonation of INH played a significant role on the degradation of INH. In this case, an acidic pH was more favorable for the degradation compared to the other selected pHs such as 5 and 9. The surfactant, SDS, interfered the degradation and decreased the degradation efficiency primarily due to their scavenging effect. Formation of a number of aromatic intermediates, such as monohydroxlated compounds, is observed by LC-Q-ToF/MS analysis, and a possible mechanism for the degradation is proposed. Furthermore, the degradation efficiency was compared in a real contaminated river water to check the feasibility of the process in the real water treatment applications and was found that 70% of the initial INH was degraded under similar conditions.