Extracellular polymeric substances (EPS)-involved photodegradation of sodium dodecyl benzene sulfonate (SDBS) via photo-generated reactive intermediates (RIs)

Extracellular polymeric substances (EPS) produced by microorganisms are ubiquitous in natural and engineered aquatic systems, but limited research has been conducted on the photosensitivity of EPS for degrading organic pollutants. The degradation of sodium dodecylbenzene sulfonate (SDBS), a typical organic pollutant in natural aquatic environments, is closely associated with biofilms; however, the indirect photodegradation of SDBS by photosensitized reactive intermediates (RIs) of EPS remains unclear. Here, we extracted three types of EPS (soluble state-SEPS, loosely bound-LB-EPS, and tightly bound-TB-EPS) from biofilms from cultured biofilms to evaluate their photoactivities in generating RIs under irradiation and photodegradation mechanism of SDBS. We found that TB-EPS exhibited higher aromaticity, molecular weight and nitrogenous compound concentration, whereas SEPS and LB-EPS had higher proportion of CHO-like substances than TB-EPS did. The steady-state concentrations of 3DOM*, ·OH, and 1O2 for EPS solutions varied depending on the degree of attachment to the biofilm; specifically, looser attachment resulted in higher efficiency in generating RIs. EPS effectively facilitated the degradation of SDBS through RIs, with 1O2 contributing significantly. Products analysis demonstrated that RIs attacked the sulfonic acid groups within SDBS − possessing strong electron-donating ability − leading to benzene ring opening as well as oxidation-induced breakdown into low-molecular-weight substances. This study elucidates the intricate structure and photochemical properties of EPS, while also delving into the mechanistic role of RIs in the degradation of SDBS. These findings hold significant implications for enhancing the efficiency of organic pollutant photodegradation and broadening the application scope of photocatalytic technology.