Evaluating and modeling the activated carbon adsorption of wastewater-derived N-nitrosodimethylamine precursors

Abstract

N-Nitrosodimethylamine (NDMA) is a disinfection byproduct (DBP) of health concern with high precursor concentrations in wastewater effluents. Wastewater-derived NDMA precursor sorption was evaluated with both batch and column tests using a range of activated carbon (AC) types and operational conditions. NDMA and other DBP (trihalomethane, haloacetic acid, and haloacetonitrile) precursor removal, assessed using formation potential (FP) conditions, was evaluated relative to organic matter (OM) characteristics. In batch tests, lignite- and wood-based powdered ACs (PACs) achieved significantly better removal than bituminous- and coconut-based PACs. At a 5 mg L⁻¹ dose, lignite- and wood-based PAC removed >95% of NDMA FP, while bituminous- and coconut-based PACs removed 67% and 53%, respectively. Mesoporous ACs performed better than microporous ACs. Proportional diffusivity designed rapid small-scale column tests (RSSCTs) with the lignite-based GAC effectively removed NDMA precursors at both 10- and 20 minute empty-bed contact times, at levels significantly better than bulk OM and the other DBP precursors. NDMA precursors exhibited linear mass-balance behavior during column runs with wastewater blends. Overall, NDMA precursors adsorbed independently from other DBP precursors and standard OM measures (e.g., TOC, UVA) in batch and column tests, showing similarities to micropollutant adsorption. Fluorescence spectroscopy OM indicators, however, showed similar adsorption behavior as NDMA precursors in column tests. Correlations using overall fluorescence intensity were developed that may be used as predictive tools for wastewater-derived NDMA precursor removal. A model based on the RSSCT results effectively predicted NDMA precursor adsorption of pilot-scale results for the same wastewater effluent and three other external data sets.