Date of Award
Master of Science (MS)
Environmental Engineering and Science
Lee , Cindy M
Ladner , David A
N-nitrosodimethylamine (NDMA) has been used commercially in several applications, including the production of liquid rocket fuel, and a variety of foods, but gained more relevance when it was discovered as a drinking water disinfection by-product (DBP) in 1989. NDMA is a probable human carcinogen with 10-6 lifetime cancer risk associated with a drinking water concentration of 0.7 ng/L, and is listed as a priority pollutant in the Code of Federal Regulations; no federal maximum contaminant level has been established for drinking water yet. However, the United States Environmental Protection Agency is planning to make a preliminary regulatory determination in 2013 on regulating NDMA in drinking water.
The use of one or a combination of disinfectants is not likely to eliminate the formation of disinfection byproducts (DBPs), thus there is a need to apply treatment technologies to maximize the removal of DBP precursors from water before oxidant addition. Powdered activated carbon (PAC) is commonly added in water treatment plants (WTPs) at different locations for taste and odor control and/or removal of synthetic organic chemicals (SOCs) such as pesticides. Since PAC can adsorb different types of organic compounds, it might also be a promising option for removal of NDMA precursors.
The objectives of this project were (i) to examine the removal of NDMA FP by PACs in different waters and (ii) to examine the roles of PAC characteristics (e.g., raw material, surface chemistry, pore size distribution, and surface area) on the removal of NDMA precursors. Due to regulatory and practical significance, the removal of THM precursors was also simultaneously investigated.
To address the objectives I collected wastewater-impacted and surface water sources to conduct adsorption experiments using powdered activated carbon and activated carbon fibers, showing a wide range of physicochemical characteristics. Also, I ran additional experiments with wastewater effluents to further understand the impact of changes in concentration and reactivity of NDMA precursors on their adsorption by PAC.
The results showed that the removal efficiency of NDMA formation potential (FP) precursors by PAC is significantly higher in samples from wastewater effluents and close proximity of wastewater influence than surface waters. The removal of NDMA FP by PAC was affected by the initial concentration of NDMA FP, and increased with increasing NDMA FP in water. The removal of THM FP was not greatly affected by the water source, due to the presence of large natural organic matter (NOM) molecules and short contact time during the adsorption experiments.
The adsorbability of NDMA precursors and effectiveness of PAC adsorption decreased with increasing distance from the wastewater discharges due to their natural attenuation through a combination of processes (biodegradation, photolysis and adsorption). Adsorbable NDMA precursors showed a size distribution in the waters tested, and the adsorbable fraction included more precursors in the size region of 10-20 Å than < 10 Å, and THM precursors were found to be much larger than the NDMA precursors (> 20 Å).
Basic carbons showed higher removal of NDMA FP and THM FP than acidic carbons. However, the overall removal on a mass basis will depend on the surface area, pore size distribution and pHPZC. PACs with a basic surface and pores > 10 Å are likely to be more effective for NDMA precursor control.
Beita sandi, Wilson, "REMOVAL OF N-NITROSODIMETHYLAMINE AND TRIHALOMETHANE PRECURSORS WITH POWDERED ACTIVATED CARBON" (2013). All Theses. 1749.