Photochemical degradation of the algae-derived dissolved organic matter in Lake Taihu

Abstract

蓝藻水华暴发过程会产生大量的溶解性有机质——藻源溶解性有机质（A-DOM）；A-DOM的光化学降解影响其迁移转化和在湖泊中的功能.本研究从太湖藻华中提取A-DOM，利用三维荧光光谱平行因子分析法（EEMs-PARAFAC），研究A-DOM中各组分的光化学降解；再研究不同光照强度、溶解氧浓度、A-DOM浓度、波长对A-DOM的降解的影响.结果显示，A-DOM中含有4种EEMs-PARAFAC组分：C1（UVC类腐殖质）、C2（UVA类腐殖质）、C3（类色氨酸）和C4（类络氨酸），对总荧光强度的贡献比例分别为22.2%、8.6%、68.1%和1.1%.当DOC初始浓度为10 mg/L、反应温度为28℃、pH=8.0时，经500 W汞灯（391.7 W/m²）光照12 h，A-DOM的总光化学降解率（以a₃₅₅计）为70.4%；荧光组分C1、C2和C3的降解率分别为96.1%、85.4%和99.2%，三者的光反应性为C3 > C1 > C2.条件控制实验显示溶解氧的增加和光强的增强均有助于A-DOM的降解；A-DOM光化学降解主要发生在紫外区，可见光不能使C1和C2得到降解.结果表明A-DOM的光化学降解速度较快，且能通过控制光强、照射光波长和引入溶解氧等条件控制降解速度.实验结果可为湖泊蓝藻水华暴发时的应急处理和保障饮用水安全提供理论依据.;During the cyanobacteria bloom, a large amount of dissolved organic matter could be produced. The photochemical degradation is one important transformation way of algae-derived dissolved organic matter (A-DOM). In this study, the photodegradation of A-DOM, extracted from the blooming cyanobacteria in Lake Taihu, is investigated by UV-Vis spectrum and excitation emission matrix spectroscopy combined with parallel factor analysis (EEMs-PARAFAC). In addition, the effects of the light intensity, light wavelength, dissolved oxygen (DO) concentration and the initial A-DOM concentration on the photodegradation are studied. Four PARAFAC components are identified, including C1 (UVC humic-like substance), C2 (UVA humic-like substance), C3 (tryptophan-like substance) and C4 (tyrosine-like substance) with the relative abundances of 22.2%,8.6%, 68.1% and 1.1%, respectively. Under 12 h radiation by a 500 W mercury lamp, the removal percentages of a₃₅₅, C1, C2 and C3 are 70.4%, 96.1%, 85.4% and 99.2%, respectively (pH=8.0; T=28℃;[DOC]₀=10 mg/L). The photoreactivities of the three PARAFAC components follows C3 > C2 > C1. Increase in the light intensity and DO concentration is helpful for the photodegradation of A-DOM. The increase of UV light contributes most photodegradation of A-DOM. The results show that the photodegradation of A-DOM is quick and could be controlled by changing photoreaction operational parameters, which could shed light on the treatment of algae bloom and ensure the safety of drinking water.