Organic Matter (OM), whether in natural water bodies or wastewater treatment effluent, contains photosensitizers that generate photochemically reactive intermediates (RIs). Processes utilized in Wastewater Treatment Plants (WWTPs) alter the structure of effluent OM (EfOM), resulting in changes in RI kinetic mechanisms. Since RIs play a crucial role in the photodegradation of Contaminants of Emerging Concern (CECs), the fate of CECs may be affected as well. To investigate the effect of WWTP processes on CECs photodegradation, p-Cresol (pC) photodegradation experiments were carried out in different effluent samples. pC was chosen as a surrogate for other phenolic CECs, which are persistent in nature and toxic. Because pC's absorption spectrum does not overlap with sunlight, its degradation is not caused by direct photolysis, making it a good candidate for tracking indirect photolysis caused by RIs such as singlet oxygen. Wastewater effluent samples were obtained from four Michigan municipal WWPTs (Mt Pleasant, Muskegon, East Lansing, and Delhi) with different treatment trains. 300 mL reactors containing effluent samples spiked with 50 μM pC were exposed to light in a sunlight simulator. The concentration of pC was measured by HPLC/DAD every 30 minutes for four hours. Excitation Emission Matrices of EfOM were measured by fluorescence spectroscopy every 60 minutes. Optical parameters such as specific UV absorbance, humification index, fluorescence index, spectral slopes, spectral ratios, and E2:E3 ratio were determined as indicators of the EfOM’s concentration, molecular weight, aromaticity, and light absorbance. Results showed that pC photodegradation varies not only in different WWTPs but also in each step of the treatment process. Optical parameters indicated that a farming step before the final effluent discharge in the Muskegon WWTP changes the EfOM’s molecular weight and aromaticity, leading to almost 15% more pC photodegradation than photodegradation in samples before the farming step. This could be explained by the increase in the humic acid concentration and, therefore, in photosensitizers concentration. On the other hand, chlorine and UV disinfection in East Lansing and Mt Pleasant WWTPs did not alter the EfOM’s optical parameters neither the pC photodegradation. A better understanding of the transformations of OM in the treatment process could help elucidate photodegration mechanisms of CECs.

Wastewater treatment process influence in the structure of effluent organic matter and its effect on contaminants of emerging concern photodegradation

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.