Liquid plasma discharge with low pulse voltage for efficient and ultra rapid removal of tetracycline hydrochloride and evaluation of its degradation pathway

Abstract

Cathode liquid plasma discharge (LPD) is an efficient and ultra rapid method to degrade organic pollutants, mainly because it can produce a large number of strong oxidizing radical species during the process of plasma discharge. In this paper, the LPD process was firstly used to degrade the tetracycline hydrochloride (TCH) in water. The effects of the cathodic materials, pulse voltages, and anode-cathode distances on the degradation efficiency of the TCH were investigated, and the antibacterial activity and cytotoxicity of the degradation products were also evaluated. The results show that the degradation efficiency of the TCH can reach 98.13 % within only 1 min by the LPD process for initial concentration of 100 mg/L, and the TOC removal rate is maintained at over 81 % in 5 min. The Ti electrode performs the lowest ionic dissolution concentration and the solution near the cathode produces a plasma region for the degradation of the TCH, which contains a number of strong oxidizing radical species (such as ∙OH). The primary intermediate products (m/z = 445, 279, 149, and 123) and secondary intermediate products (m/z = 90.5, 81, and 59) are captured, and a possible degradation pathway of the TCH is also proposed. The cytotoxicity results show that the LPD degraded solutions are non-toxic effect on the NIH3T3 cells. The LPD process is a promising method to efficiently eliminate the TCH in wastewater. This work also provides a new experimental basis and reference for the ultra rapid degradation of organic pollutants in wastewater without using catalysts.