| Author | Bajracharya, Kiran |
| Call Number | AIT Diss. no. EV-89-04 |
| Subject(s) | Soils--Cadmium content
|
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering |
| Publisher | Asian Institute of Technology |
| Abstract | Groundwater and top soil contaminations are the major adverse
environmental risks resulting from the impacts of land disposal of wastes . Due
to the high toxicity of Cadmium (Cd) and the relatively high concentrations of
zinc and NH4, these three components were chosen for detailed study so as to
evaluate the transport phenomena of these components from uncontrolled land
disposal sites. To design an efficient sanitary landfill, basic information on
the behaviour of pollutants in the soil- water environment is required.
The kinetic studies on Cd adsorption unto sand, sandy soil (SoilA) and
silty soil (SoilB) revealed that adsorption was a fast process usually taking
a few minutes to adsorb about 70 to 80% of the total amount adsorbed. The
observed kinetics of Cd adsorption in soil was adequately explained by Static
Physical Non- equilibrium Model (SPNAM). Partitioning of Cd (concentration
range 100 - 1000 μg / L) into solid and liquid phases was studied at pH 2, 6, and
12. Freundlich isotherm described the solid and liquid phase equilibria of the
solute very well in all the soils. SoilA which contained maximum clay and
organic matter, adsorbed the highest amount of Cd; at pH 2, adsorption was not
observed and at pH 12, precipitation was the major governing process.
The capacity of the soils to adsorb Cd reduced by 10 to 50% in the
presence of Zn and NH4. Competitive Freundlich Adsorption Model (CFAM),
Modified Competitive Freundlich Model (MCFAM), and Ideal Adsorbed Solution
Theory (IAST) adequately predicted the observed liquid phase Cd concentration
in the bi- solute system. The adsorption of Cd and Zn from zinc wastewater was
found to be less than that in the bi- solute system of Cd and Zn.
From the column experiments conducted with Cd and Zn for two different
kinds of soils viz. sand and SoilA (at a pH of 6 and under different
velocities), it was found that the amount of solutes Cd and Zn adsorbed in
dynamic system was more than that in the static system and were different for
different velocities. Equilibrium Adsorption Model (EAM), Dynamic Physical
Non-equilibrium Adsorption Model (DPNAM), and Two Site Adsorption Model (TSAM)
were tested for their applicability. In most of the cases, EAM with adsorption
coefficients evaluated from column experiments predicted the concentration
history curves satisfactorily.
In the experiments conducted with solutions containing Cd and Zn, and Cd
and NH4 in sand and SoilA , an earlier breakthrough of solutes were observed in
the bi-solute system than in the single solute system. Column experiments were
also conducted with zinc wastewater in SoilA where the breakthrough of Cd and
Zn were also observed to be quite early. The Competitive Dynamic Adsorption
Model (CDAM) predicted the observed data reasonably well. It was found that a
fitting parameter had to be incorporated with Freundlich isotherm constant K
to improve the prediction. The variation of the fitting parameter followed a
uniform trend with the increase in Cd concentration.
In the unsaturated experiments conducted at pH 6 in sand, Cd was retained
in the first few millimeters of the sand. The Unsaturated Unsteady Equilibrium
Adsorption Model (UUEAM) predictions of water profiles were in good agreement
with the observed data and the solute front predictions were also reasonably
good.
Practically speaking, the phenomena occurring in the land application of
wastes can be described as a dynamic system. The adsorption isotherm constants
derived from batch laboratory experiments do not adequately predict the
transport phenomena. But the adsorption coefficients evaluated from column
experiments (although time-consuming) give the best predictions of the
adsorption phenomena. Thus simple mathematical models with isotherm constants
evaluated from column experiments are found adequate in the predictions of Cd
profiles both temporally and spatially. |
| Year | 1989 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering (EV) |
| Chairperson(s) | Vigneswaran, S.;Gupta, Ashim Das; |
| Examination Committee(s) | Chongrak Polprasert;Yamamoto, K.;Paudyal, Guna N.;Kobus, H.E.; |
| Scholarship Donor(s) | Japan; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1989 |