Source characterization and removal of N-nitrosamine precursors during activated sludge treatment

Abstract

Municipal wastewater discharges are a major potential source of N-nitrosamine precursors which may impact downstream source water quality. To elucidate the sources of N-nitrosamine precursors and their fate during biological wastewater treatment (i.e., the activated sludge (AS) process), the formation potentials (FPs) of seven N-nitrosamine species were monitored in blackwater (i.e., human urine and feces), greywater (i.e., from kitchen food and detergent, laundry, and showering), and the influent from four wastewater treatment plants (WWTPs) during batch AS treatment. N-Nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR) and N-nitrosopiperidine (NPIP) precursors originate mainly from biological waste materials (e.g., human urine, sweat in laundry greywater or shower greywater, food leachates), while detergents and personal care products (e.g., shampoo and body wash in shower greywater) could be the main sources of N-nitrosodiethylamine (NDEA), N-nitrosodi-n-butylamine (NDBA), and N-nitrosodi-n-propylamine (NDPA) precursors. AS from two domestic WWTPs (one urban and one rural) exhibited better removal of NDMA precursors from biological waste materials, while the textile AS more effectively removed most N-nitrosamine precursors from detergents or personal care products. The type of WWTP influent negligibly (i.e., <8% differences) affected the removal of NDMA precursors. Rather, AS sources and seasonal changes in AS activities may have an impact. Increasing the incubation time from 6 to 24 h enhanced the removal of N-nitrosamine precursors, especially for precursors from detergents and personal care products. These results suggest that there is no single source containing various precursors of N-nitrosamines. The AS types, sampling seasons and hydraulic retention time (or incubation time) may all impact the removal efficiencies for N-nitrosamine precursors.