Intracellular organic matter from Chlorella vulgaris enhances the photodegradation of acetaminophen.

Algae is able to accelerate the photodegradation rate of contaminants under sunlight irradiation, and this process can be attributed to algal substances, namely, intracellular organic matter (IOM) and extracellular organic matter (EOM). This study aimed to investigate the efficiencies and mechanisms of the photodegradation of three pharmaceuticals - acetaminophen (ACE), codeine (COD) and cephradine (CFD) - in the presence of Chlorella vulgaris and its algal substances. The result shows that a much higher photodegradation rate of acetaminophen was obtained in the presence of IOM (kobs = 0.250 hr-1) than in the presence of EOM (kobs = 0.060 hr-1). The photodegradation mechanisms of acetaminophen were demonstrated and verified by scavenger experiments and probe tests. The major reactive species for acetaminophen photodegradation was triplet-state IOM (3IOM∗), which contributed 93.52% of the photodegradation, while ⋅OH was the secondary contributor (5.60%), with 1O2 contributing the least (0.88%). Chlorella vulgaris also effectively enhanced the photodegradation of codeine and cephradine. However, the photodegradation behaviors of codeine and cephradine in the presence of algal substances were different from those of acetaminophen, indicating that the photodegradation mechanisms might depend on the type of compound. This study not only demonstrates the effectiveness of algal substances in the photodegradation of acetaminophen, codeine and cephradine under sunlight irradiation but also provides a comprehensive study on the photodegradation mechanisms of acetaminophen in the presence of algal substances.