[Study on the degradation of phenol wastewater using hydroxyl radical produced by plasma and the course by UV spectra]

The phenol wastewater with high concentration was treated by hydroxyl radical produced by a strong ionization discharge plasma in the present article. Salicylic acid used as molecular probe to determine the concentration of hydroxyl radical. The phenol elimination efficiency of wastewater whose initial concentration was 1 21 5 mg x L(-1) could reach 99.11% when the concentration of hydroxyl radical was 1 037 mg x L(-1); while the initial concentration of 8 853 mg x L(-1) of phenol wastewater dropped to 6 250 mg x L(-1) under the same conditions, that is, 1 mg hydroxyl radicals could oxidize 2.5 mg of phenol. The smaller the initial phenol concentration, the higher the removal. However, the higher the initial concentration, the greater the absolute quantity of treatment. And the relation between the changes including pH value and the conductivity and the concentration of hydroxyl radical was stated and explained. With the concentration of hydroxyl radicals increasing, the pH value of wastewater changed from close to neutral to acidity gradually. The higher the concentration of hydroxyl radical, the stronger the acidity of wastewater. When continuing the increase in the concentration of hydroxyl radical, the change began to smooth. With the addition of hydroxyl radical, as is different from other phenomena, there was a tiny descending stage before ascending as shown on the conductivity curve, indicating that phenol had been oxidized and generated the organic acids continuously. Catechol, hydroquinone and benzoquinone are the important compounds of the intermediate products as shown by the analysis of UV spectra and chromatography. The final UV spectra curve indicated that there were little organic compounds containing conjugated structure in the treated wastewater.