The Roles of Different Fractions in Freshwater Biofilms in the Photodegradation of Methyl Orange and Bisphenol A in Aqueous Solutions

Abstract

Freshwater biofilms play an important role in the migration and transformation of organic pollutants, especially under illumination conditions. Nonetheless, the roles of variable fractions in freshwater biofilms, e.g., extracellular polymeric substances (EPS), microbial cells and original biofilms, in promoting the photodegradation of trace organic pollutants remain largely unclear. In this study, two contaminants, i.e., methyl orange (MO) and bisphenol A (BPA), were selected, and the roles of different fractions in freshwater biofilms in their photodegradation performances were investigated. After dosing 696 mg/L SS biofilm harvested from an effluent-receiving river, the direct photodegradation rate of MO and BPA was increased 8.7 times and 5.6 times, respectively. River biofilm EPS contained more aromatic fractions, chromogenic groups and conjugated structures than biofilm harvested from a less eutrophic pond, which might be responsible for the enhanced photodegradation process. The quenching experiments suggested that when EPS fractions derived from river biofilm were dosed, 3EPS* was the major reactive oxygen species during the photodegradation of MO and BPA. Meanwhile, for EPS derived from the pond biofilm, OH/1O2 was predominantly responsible for the enhanced photodegradation. Batch experimental results suggested that the cells and EPS in river biofilms could collaboratively interact with each other to enhance the preservation of reactive species and protection of microbes, thus facilitating the photoactivity of biofilms. Our results might suggest that biofilms generated from eutrophic waterbodies, such as effluent-receiving rivers, could play a more important role in the photodegradation processes of contaminants.

Experimental testing of two urban stressors on freshwater biofilms

“…This could be the result of photodegradation of the contaminant or of an increase in DDBAC retention by biofilms under ALAN conditions. A previous study showed that freshwater biofilms can improve the photodegradation of organic contaminants by being a source of reactive oxygen species (ROS) such as hydroxyl (OH•) or superoxide (O2•) radicals (Yin et al 2022).…”

Impacts of Urban Stressors on Freshwater Biofilms

“…This could be the result of photodegradation of the contaminant. A previous study showed that freshwater biofilms can improve the photodegradation of organic contaminants by being a source of reactive oxygen species (ROS) such as hydroxyl (OH•) or superoxide (O2•) radicals (Yin et al 2022). Contrary to the hypothesis of Pozo-Antonio and Sanmartin (2018), who suggested that artificial light could lead to an increase in internalization of the contaminant, we found no significant difference in BAC12 concentrations in biofilm between the different light conditions (Table 2).…”