Adsorption Kinetics of N-Nitrosodimethylamine (NDMA) Onto Activated Carbons

According to the U.S. Environmental Protection Agency, N-Nitrosodimethylamine (NDMA) is classified as a probable human carcinogen. A risk assessment indicated that a concentration of 0.7 ng/L (parts per trillion) of NDMA in drinking water represents a 1 x 10^–6 increased cancer risk level. NDMA is highly mobile in soil and can be an unintended byproduct of the chlorination of wastewater. The treatment standards for NDMA typically range from 1 to a few ng/L, which creates analytical challenges for monitoring and development of remediation methods.

The purpose of this research was to test the ability of biochars made from local biomass wastes to adsorb NDMA from water at treatment-relevant concentrations. The adsorption kinetics of biochars produced from pecan shells and local forestry residues were tested and compared with a commercially available coconut shell-derived activated carbon. Further testing of the commercially available carbon was conducted in a lab-scale column for adsorption of NDMA to be used as a basis for future work.

Calgon coconut shell carbon (CSC) provided the fastest and highest capacity for NDMA adsorption; synthesized pine bark char adsorbed more NDMA by the end of the kinetics study than the commercial pecan shell char; and synthesized pecan shell char was the worst performing char. Intraparticle diffusion was negligible for CSC but controlled a noticeable segment of adsorption for the other carbons. Column breakthrough trends did not follow expected patterns: breakthrough occurred much more rapidly than models indicated, and faster flowrates resulted in slower breakthrough and more apparent adsorption.