强化混凝和改性活性炭对二级出水DON的作用机制

探讨强化混凝和改性活性炭对城市污水厂二级出水中溶解性有机氮（DON）作用机制，分析相对分子量以及亲疏水组分变化，并考察氯化消毒副产物生成势变化特征，结合三维荧光（3DEEM）光谱分析手段，对强化混凝和活性炭吸附前后DON组成，化学结构特征进行研究.结果表明：强化混凝可以明显提高DON的去除效果，DON去除率通过pH值强化混凝提高到1.45倍，臭氧强化混凝提高到2.06倍，PAC强化混凝提高到2.09倍，PAM强化混凝提高到1.96倍.活性炭对DON吸附过程更符合准二级动力学模型.DON吸附过程中，酸改性活性炭表面主要是π-π色散力作用机理，而碱改性活性炭表面主要是给电子-受电子复合物形成机制.在强化混凝和活性炭吸附作用下，DON的相对分子量和组分发生较大变化，而消毒副产物的生成势大幅下降.经3DEEM和光谱区域体积积分法（FRI）分析，在强化混凝和活性炭吸附过程中DON及消毒副产物生成潜势与荧光区域Ⅱ和区域Ⅳ所代表物质有关.

Mechanism of enhanced coagulation and modified activated carbon on DON in the secondary effluent

In order to explore the mechanism on dissolved organic nitrogen (DON) removal in the secondary effluent of wastewater treatment plant by enhanced coagulation and modified activated carbon adsorption, the molecular weight distribution and hydrophobicity/hydrophilicity of DON were analyzed. Besides, chlorinated disinfection by-product (DBP) formation potential was investigated. Combined with three dimensional (3DEEM), DON compositions and their chemical structures before and after coagulation and adsorption were also studied. The results showed that (1) enhanced coagulation could significantly improve DON removal efficiency, with an increase in DON removal rate of 1.45-fold, 2.06-fold, 2.09-fold and 1.96-fold by pH enhanced coagulation, pre-ozonation enhanced coagulation, PAC enhanced coagulation and PAM enhanced coagulation, respectively; (2) the adsorption process of DON by the activated carbon was better correlated with the quasi-second-order kinetic model. During DON adsorption process, π-π dispersion mechanism mainly exists on the surface of acid-modified activated carbon, and electron donor-acceptor formation mechanism is present on the surface of alkali modified activated carbon; (3) after the enhanced coagulation and activated carbon adsorption, the molecular weight and composition of DON changed greatly, and DBP formation potential decreased significantly; (4) finally, the 3DEEM and fluorescence spectral region volume integral analysis suggested DON concentration and DBP formation potential were related with the fluorescent regions Ⅱ and IV in enhanced coagulation and activated carbon adsorption process.