Date of Award
Doctor of Philosophy (PhD)
Dr. Andrew Benedek
Activated carbon adsorption is the most widely considered process for the removal from drinking water of low level toxic chemicals as well as many other organic substances. The adsorption of these compounds involves complex competitive interactions which are not well understood, however, they are crucial to the design of safe and cost effective adsorbers. To obtain a better understanding of competitive adsorption as observed in water treatment adsorber, at the time of a toxic spill, a three part study was conducted with a representative bisolute mixture. The mixture consisted of a toxic chemical (1,1,2-trichloroethane (TCEA)) and the naturally occurring organic substance from a northern river considered as a single compound and measured as TotaI Organic Carbon.
The first part of this study consisted of single solute adsorption and desorption experiments as well as blsolute equiIibrium experiment. The adsorption of TCEA was found to be completely reversible, while that of the background organics was virtually irreversible. The bIsolute experiments showed that the background organics substantIally decreased the adsorption capacIty of TCEA, while the adsorption capacity of the background organics was only marginally reduced by the presence of TCEA. The predictive multisolute Isotherm models in the literature could not describe the experimental data. Two other models, which assume that a fraction of the adsorption does not involve competition, were found to describe the data successfully.
The second part of this study investigated the rates of adsorption from one-adsorbate and two-adsorbate soIutions. The data of both single adsorbate kinetic experIments were described very well by the homogeneous surface diffusion model. The adsorption of the background organic was very slow, yet it was not necessary to utilize separate terms for the slow and rapid adsorption mechanisms. All of the adsorption occurred by the slow mechanism. The slow adsorption phenomenon, which is suspected to occur in very small pores, appears to be related to the irreversible adsorption observed during equilibrium studies. The background organics that adsorbed by the slow mechanism were virtually not desorbable, while TCEA which adsorbed completely reversibly, did not show any slow adsorption during the kinetics. As expected from the large difference in the values of the diffusion coefficients, to properly model the bisolute batch kinetic experimental data, diffusional interactions such as cross diffusion terms had to be included.
The third part of this investigation was a column study involving six different phases, each with a different feed solution. The results were consistent with the equilibrium predictions. Phase IV showed that an expected and potentially dangerous large scale desorption of previously adsorbed toxic organics, caused by a substantial increase in the feed background organics, did not occur. The elution of TCEA actually decreased, probably due to cross diffusional interactions. The column experiment also confirmed that due to competitive interactions and to the increasing loading of background organics on the carbon with time, the adsorbers became substantially less effective at treating toxic spills as the operation cycle proceeded.
Narbaitz, Roberto Martin, "Modelling the Competitive Adsorption of 1,1,2-Trichloroethane with Naturally Occurring Background Organics onto Activated Carbon" (1985). Open Access Dissertations and Theses. Paper 1095.