Effect of algal organic matter (AOM) extracted from Microcystis aeruginosa on photo-degradation of Diuron

The presence of algal organic matter (AOM) and emerging organic contaminants in surface drinking water sources has received increasing attention recently. Nevertheless, interactions between these two harmful co-existing compounds in water sources have rarely been reported. This study investigated the influence of AOM, including intracellular organic matter (IOM) and extracellular organic matter (EOM), on the photo-degradation of Diuron, under UV and visible light (VL) irradiation. Kinetics analyses indicated that both the direct and indirect photolysis of Diuron followed a pseudo-first-order reaction (R2 > 0.98). Diuron was rapidly removed under UV irradiation accompanied by minor impacts from AOM. Under VL irradiation, the photo-excited phycocyanin in the IOM was capable of accelerating Diuron degradation, whereas the coexistence of other organic compounds in the IOM inhibited the reaction due to a screening effect, resulting in a slower overall rate of Diuron degradation. By comparison, EOM promoted the reactions when pH exceeded 5.0. The AOM-mediated generation of triplet DOM (3DOM∗) accounted for 82% and 64% of the Diuron removal in the presence of IOM and EOM, respectively. Spectral excitation-emission matrices produced by AOM in solutions demonstrated the primary mechanisms of the co-existing AOM on Diuron degradation.