Erica Marti

Effects of molecular ozone and hydroxyl radical on formation of N-nitrosamines and perfluoroalkyl acids during ozonation of treated wastewaters

N-Nitrosamines—toxic disinfection byproducts commonly associated with chloramination—have recently been shown to increase after ozonation of some surface waters and treated wastewaters. In addition to five nitrosamines, two perfluoroalkyl acids (PFAAs) are included in the most recent U.S. EPA Contaminant Candidate List due to potential public health risks. In this manuscript, the potential roles of molecular ozone (O3) and hydroxyl radical (˙OH) were investigated in the formation of N-nitrosamines and PFAAs in treated wastewaters. The results herein are based on controlled bench-scale experiments designed to isolate the effects of O3 with the use of t-butanol as a ˙OH scavenger. Nitrous oxide gas saturated samples were exposed to gamma radiation to isolate the effects of ˙OH, and para-chlorobenzoic acid was used to assess ˙OH exposure. This study found that the presence of molecular ozone versus the hydroxyl radical promoted N-nitrosodimethylamine (NDMA) formation. Six other N-nitrosamines showed very little or no formation upon the ozonation of six treated wastewaters up to an O3 : TOC ratio of 1.0. For PFAAs, perfluorohexanoic acid (PFHxA) formed the highest and most consistently upon ozonation (up to an O3 : TOC ratio of 2.0) of the same six treated wastewaters. Presence of molecular ozone (more so than hydroxyl radical), appears to promote the formation of PFHxA and perfluorobutane sulfonic acid (PFBS). The effect of pH in the range of 6–8 upon the formation of NDMA and PFAAs was found to be minimal. These findings provide new understanding of the formation of oxidation byproducts during ozonation of reclaimed wastewaters. Depending on future regulatory determinations, NDMA and a few PFAAs could be of concern for potable reuse treatment systems that employ ozone.

Impact of secondary treatment types and sludge handling processes on estrogen concentration in wastewater sludge

Endocrine-disrupting compounds (EDCs), such as estrogen, are known to be present in the aquatic environment at concentrations that negatively affect fish and other wildlife. Wastewater treatment plants (WWTPs) are major contributors of EDCs into the environment. EDCs are released via effluent discharge and land application of biosolids. Estrogen removal in WWTPs has been studied in the aqueous phase; however, few researchers have determined estrogen concentration in sludge. This study focuses on estrogen concentration in wastewater sludge as a result of secondary treatment types and sludge handling processes. Grab samples were collected before and after multiple treatment steps at two WWTPs receiving wastewater from the same city. The samples were centrifuged into aqueous and solid phases and then processed using solid phase extraction. Combined natural estrogens (estrone, estradiol and estriol) were measured using an enzyme-linked immunosorbent assay (ELISA) purchased from a manufacturer. Results confirmed that activated sludge treatments demonstrate greater estrogen removal compared to trickling filters and mass concentration of estrogen was measured for the first time on trickling filter solids. Physical and mechanical sludge treatment processes, such as gravity thickeners and centrifuges, did not significantly affect estrogen removal based on mass balance calculations. Dissolved air flotation thickening demonstrated a slight decrease in estrogen concentration, while anaerobic digestion resulted in increased mass concentration of estrogen on the sludge and a high estrogen concentration in the supernatant. Although there are no state or federally mandated discharge effluent standards or sludge application standards for estrogen, implications from this study are that trickling filters would need to be exchanged for activated sludge treatment or followed by an aeration basin in order to improve estrogen removal. Also, anaerobic digestion may need to be replaced with aerobic digestion for sludge that is intended for land application.