Regulating Generation of Radical and Non-Radical in Plasma Systems for Selective Degradation of Persistent Organic Pollutants in Water: Regulatory Method and Selective Mechanism

Abstract

Selective degradation of persistent organic pollutants (POPs) and salinity resistance of practical wastewater pose great challenges to non-thermal plasma (NTP). This paper proposes for the first time to solve the above problems by regulating radicals and non-radicals. The band structure and active site of CN were modified by doping of B and Cu elements. The addition of CN allows NTP to activate persulfate efficiently. These adjustments made the regulation of radical and non-radical possible. Sulfamethoxazole (SMX), bisphenol A (BPA) and methyl orange (MO) were selected as typical POPs. Based on experiments and theoretical calculations, the degradation effects, catalysis mechanism, water matrix, intermediate product toxicity and influencing factors were investigated. Research shows that the radical system has higher selectivity for hydroxyl and amine groups, while the non-radical system has higher selectivity for benzene ring. For the same pollutant, the radical system (99.3%) often exhibits a better degradation effect versus non-radical system (78.2%). However, non-radical systems show phenomenal adaptability to real wastewater and complex water matrix environments. For the actual wastewater with high salinity disturbance, the non-radical system can increase the removal rate by nearly 40.1%. It can be also found that the disinfection byproducts of non-radical system have significantly lower toxicity. This paper provides an important reference for regulating radicals and non-radicals to improve pollutant selectivity and salinity adaptability.

Keywords: non-thermal plasma, Radical and non-radical, complex water matrix, CN catalyst, toxicity of disinfection byproducts