A facile and efficient approach for the removal of high concentrations of ammonia nitrogen in wastewater: Liquid-phase plasma treatment

We report the facile and effective liquid-phase plasma treatment (LPPT) approach for removing high concentrations of ammonia nitrogen from wastewater. The effects of the operating parameters, including the pH and temperature, the pulse repetition frequency, the pulse duration, and the reaction time, were investigated to obtain the optimal removal conditions using a simulated wastewater sample. It was found that a higher pulse repetition, a longer pulse duration, and alkaline conditions were favorable for the removal of ammonia nitrogen. Thus, at pH 12, a pulse repetition frequency of 30 kHz, and a pulse duration of 3.0 μs, the removal efficiency of ammonia nitrogen reached 100% in 25 min during the LPPT. In addition, when isopropanol (IPA) and 1, 4-diazabicyclooctane triethylenediamine (DABCO) were used as scavengers for ∙OH and 1O2, respectively, the removal efficiency of ammonia nitrogen after 25 min decreased from 71.7% to 68.1% in the presence of DABCO and from 71.7% to 62.8% in the presence of IPA. Based on these results, the mechanism of ammonia nitrogen removal was proposed to constitute the collision of accelerated electrons and the oxidation reaction of ∙OH. Moreover, it was confirmed that the LPPT approach was feasible for the removal of ammonia nitrogen from wastewater.