Solar-induced generation of singlet oxygen and hydroxyl radical in sewage wastewaters

Abstract

Singlet oxygen (O-1(2)) and hydroxyl radical (center dot OH) play an important role in the degradation of pollutants in surface waters. However, the mechanism underlying the photochemical generation of O-1(2) and center dot OH in wastewaters is poorly known. Here we studied the photo-induced generation of O-1(2) and center dot OH in different sewage treatment plant units. The correlation between the generation of O-1(2) and center dot OH and the water constituents was discussed. Our results show that in sewage units the O-1(2) formation rate ranges from 2.19 x 10(-8) to 6.74 x 10(-8) mol L-1 s(-1), and the center dot OH formation rate ranges from 1.7 x 10(-11) to 3.06 x 10(-10) mol L-1 s(-1). The average O-1(2) formation rates in the various sewage units are similar to those in wetland and estuarine waters containing rich dissolved organic matter and 2-4 times higher than those in lake and seawater samples. The average center dot OH formation rates of the sewage units are 5-50 times higher than for other water samples reported. The center dot OH generation rate increased with the iron content with a correlation coefficient of 0.85, which indicates that the photo-Fenton reaction plays a dominant role in center dot OH generation in sewage wastewater