Issue 3

The removal of heavy metals from wastewaters is a matter of paramount importance due to the
fact that their high toxicity causes major environmental pollution problems. One of the most
efficient, applicable and low cost methods for the removal of toxic metals from aqueous
solutions is that of their adsorption on an inorganic adsorbent. In order to achieve high
efficiency, it is important to understand the influence of the solution parameters on the extent of
the adsorption, as well as the kinetics of the adsorption. In the present work, the adsorption of
Cu(II) species onto TiO2 surface was studied. It was found that the adsorption is a rapid process
and it is not affected by the value of ionic strength. In addition, it was found that by increasing
the pH, the adsorbed amount of Cu2+ ions and the value of the adsorption constant increase,
whereas the value of the lateral interaction energy decreases.

The important advantage of zeolite applied to water treatment is its high porosity when comparing to
other minerals. The porosity results in good hydrodynamic properties (the increase in the pressure
loss on the zeolite filters is 1.5-2.0 times smaller than in the case of sand filters) and adsorption
roperties, and in turn high capacity which allows for adsorption of contaminants (a clinoptilolite filter
allows for removal of phytoplankton and bacteria).
The increase in the application of artificial fertilizers and gradual contamination of water resulted
from discharging industrial wastewater into the environment led to the contamination of the
environment by nitric compounds. Wastewater contains about 15-50 mg dm-3 of nitric compounds
(based on nitrogen) – ammonia salts constitute about 55-60% whereas organic forms of proteins,
pesticides and aminoacids about 40-50%.
Natural clinoptilolite could be applied to remove ammonium ions from water and wastewater. The
ammonium ion uptake behaviour of clinoptilolite is connected to the processes of ion exchange. The
main aim of this investigation is to evaluate the adsorption capacity of clinoptilolite towards
ammonium ions. According to the obtained results the adsorption capacity of clinoptilolite for the
removal of ammonium ions demonstrates its potential application in the treatment of water,
wastewater and sanitary landfill leachate contaminated with ammonia. The highest adsorption
capacity of clinoptilolite towards ammonium ions of 3.79 mg g-1 was found for the initial
concentration of 300 mg L-1. The highest removal level reached by clinoptilolite for ammonium was
of 99.74% for the initial concentration of ammonia of 50 mg L-1. The effect of exposure time on
maximum uptake of ammonia was found to be insignificant.

The adsorption of polyacrylic acid (PAA) on hydroxyapatite (HAP) from HAP saturated solutions was
studied in this work as a function of PAA concentration, temperature, pH and ionic strength. In all
experiments, the adsorption was studied under conditions of negatively charged adsorbent and
adsorbate, respectively. These conditions ensured that adsorption was not electrostatically favored.
The solution composition was found to influence significantly the maximum of the adsorbed amount.
In fact, the adsorption of PAA, was found to increase with ionic strength, due to the decrease of
double layer thickness of HAP particles. The effect of temperature and ionic strength on the kinetics
of adsorption are also reported. Adsorption isotherms obtained at 30oC were found to be Langmuirtype,
while at higher temperatures they were of the Brunauer-Emmett-Teller (BET) type. The
absorbed amount of PAA was found to decrease with temperature, while it increased with ionic
strength. For pH values lower than 6.5, the adsorption increased while for pH between 6.5 and 9 the
adsorbed amount remained almost constant.

The dependence of Cd(II) and Cu(II) uptake by yeast cells on the age and temperature of cell culture
was studied. Saccharomyces cerevisiae, Kluyveromyces marxianus and Debaromyces Hansenii
were chosen as typical yeasts, while Cd(II) and Cu(II) as typical metal pollutants. Our results
revealed that higher metal uptake was obtained by cells grown at the optimum temperature (30 oC)
of cell culture. It was also found that the exponential phase cells resulted in a higher metal uptake
than the stationary ones. A first interpretation of relevant bibliographic data concerning the effect of
growth phase on metal uptake is proposed, assuming that limited qualitative changes in the cell wall
structure take place as the cells pass from exponential to stationary phase, in addition to quantitative
modifications, which have been reported in the literature. According to our interpretation the relative
abundance among quantitative and qualitative alterations of cell wall, determines if stationary or
exponential cells attain the higher metal binding capacity. An indication supporting our approach
may be the fact that our hypothesis implies a decrease of pKa values of cell wall carboxyl groups
with the age of cells, which is consistent with data reported by other authors.