Photochemical alteration of biogenic particles in wastewater effluents

Biogenic particles discharged by wastewater treatment plants play important roles in receiving water because of the large specific surface area and good mobility of the particles. In this study, the changes induced in biogenic particles by natural sunlight were investigated to understand the phototransformation of the particles in the receiving waters. The results showed that photoexposure resulted in significant decreases in the sizes of the biogenic particles but that photoexposure did not impact the zeta potentials. In addition, the photodissolution of biogenic particulate organic matter (POM) led to the generation of biogenic dissolved organic matter (DOM). Characterization using excitation–emission matrix (EEM) spectroscopy showed that photoexposure changed both the shapes and the intensities of the EEM spectra of the biogenic POM; the regions of the T1 and T2 peaks were susceptible to photoexposure. Modeling by parallel factor analysis (PARAFAC) decomposed the EEMs of the biogenic POM into four valid components, i.e., terrestrial or microbial humic-like substances, tryptophan-like proteins, tyrosine-like proteins and hydrophobic proteins. The humic-like substances in the biogenic POM from the effluents were subject to lower decreases (17.0 % and 11.6 %). Throughout the entire incubation time, the PARAFAC components in the biogenic DOM were dominated by elimination mechanisms rather than by production through photodissolution of the biogenic POM.