Factors affecting removal of NDMA in an ozone-biofiltration process for water reuse.

N-nitrosodimethylamine (NDMA) is a carcinogen and a disinfection byproduct that is formed by ozone and combined chlorine. Various factors affecting NDMA formation and removal were examined at pilot-scale for a treatment train consisting of ozone, biologically-active carbon (BAC) filtration, and granular activated carbon (GAC) adsorption applied to two distinct feed waters. High concentrations of ozone and monochloramine were added to the influent, demonstrating that ozone removed monochloramine precursors of NDMA. Further, longer empty bed contact times (EBCTs) of 10 min for BAC and 10 and 20 min for GAC removed NDMA to <10 ng/L for both feed waters. NDMA removal by the BAC process was most favorable >22 °C, presumably due to elevated microbial activity. A monochloramine residual of 3 mg/L-Cl2 in the BAC influent reduced NDMA removal in the 5 min EBCT BAC from 79% to 36% and in the 10 min EBCT BAC from 88.5% to 73.7%. The absence of ozone in the treatment process significantly reduced NDMA formed post ozone, but decreased NDMA removal in BAC, probably due to lower NDMA concentration in the BAC influent. Finally, adding 5 mg/L of allylthiourea, an inhibitor of ammonia-oxidizing bacteria, indicated that removal mechanisms for ammonia and NDMA are distinct. However, nitrification is still a good indicator for NDMA biodegradation potential, because nitrifying bacteria appear to flourish under similar EBCT, temperature. and monochloramine residual conditions during BAC filtration.

Mathematical modeling of biologically active filtration (BAF) for potable water production applications.

In this study, a modeling framework was developed to simulate biologically active filtration (BAF) headloss buildup in response to organic removal and nitrification. This model considered not only the biofilm growth on the BAF media but also the particle deposition in the BAF bed. In addition, the model also took temperature effect into consideration. It was calibrated and validated with data collected from a pilot-scale study used for potable water reuse and a full-scale facility used for potable water treatment. The model prediction provided insights that biofilm growth rather than particle deposition primarily contributes to the headloss buildup. Therefore, biofilm control is essential for managing headloss buildup and reducing the backwash frequency. Model simulation indicated that the BAF performance in terms of pollutant removal per unit headloss is insensitive to the BAF bed depth but can be effectively improved by increasing the media size. The partial biofilm coverage of the media is confirmed in this study and was mathematically verified to be a prerequisite for the model fitness.

Effect of High Strength Food Wastes on Anaerobic Codigestion of Sewage Sludge.

Anaerobic codigestion has been practiced at water resource recovery facilities to increase methane production, but the impact of many variables is still not well understood. In this study, the feasibility of codigesting fats, oils, and grease (FOG), and other high strength wastes (HSWs) with municipal sewage sludge was investigated. Four laboratory-scale digesters were operated at a working volume of 9.75 L, 15 days solids retention time (SRT), and at a temperature of 37 °C. Wastes including whey (cheese), juice, grease trap waste (GTW), and dissolved air flotation waste (DAF), along with municipal sewage sludge, were fed to the digesters in varying amounts. The addition of HSWs led to higher methane production at lower organic loadings. However, at higher organic loadings, the GTW appeared to be toxic to methanogens, leading to a decrease in digester pH and biogas production, and an accumulation of volatile fatty acids within the digester.