Sonochemical oxidation of piroxicam drug: Effect of key operating parameters and degradation pathways

BACKGROUND Piroxicam (PRX) is a non-steroidal anti-inflammatory drug (NSAID) commonly used to relieve pain and swelling of conditions like arthritis. PRX has been extensively detected in seawater, surface, and sewage waters worldwide and therefore its efficient treatment is an issue of emerging concern. In this work, the sonochemical degradation of PRX was investigated. RESULTS All experiments were conducted at constant ultrasound frequency of 20 kHz while the following range of experimental conditions was investigated: initial PRX concentration 320–960 µg/L, ultrasound power density 20–60 W/L, temperature 20–60 °C, reaction time up to 60 min. The effect of different water matrices, namely surface water (SW), bottled water (BW), ultrapure water (UPW) and humic acid (HA) aqueous solution on process efficiency was also explored. It was found that PRX degradation reached 96% after only 10 min of treatment at the best conditions (i.e. [PRX]0 = 320 mg/L, 20 °C, 36 W/L) assayed. Power density could positively affect PRX degradation. Nevertheless, PRX degradation decreased when its initial concentration and the temperature of the bulk liquid was increased. PRX degradation was found to decrease, in different water matrices, in the order: UPW > 5 mg/L HA > BW > 10 mg/L HA >SW. High resolution mass spectrometry analysis revealed that fourteen transformation by-products (TBPs) were formed and subsequently degraded during treatment while the PRX degradation pathways were also elucidated. CONCLUSION At the optimal operating conditions assayed, PRX was efficiently degraded after about 10 min of sonochemical oxidation, thus rendering it a promising technology for the treatment of xenobiotics