Land treatment method of municipal
and industrial wastewaters for utilization
of nutrients in the wastes for raising
useful crops and tertiary(or advanced)
treatment of the water for improving
stream quality or to recharge
falling water tables is increasing in
some parts of the world, particulary
in the arid area. As emphasis in this
type of treatment method and prevention
of surface and underground waters from
contamination, it becomes necessary to
estimate efficiency of land treatment
in removing other types of contaminan~
ts including heavy metals.
In this paper, the results of adsorption
and desorption tests of mercury,
arsenic, and cadmium by various soil
and se4iment constituents, instabilit¥
coefficients, and isothermal adsorption
and desorption data have utilized for
evaluation of the land tratment efficiency
in removing heavy metals.
Inorganic mercury had a high affinity
for sulfur containing soils, clays
and synthetic scavengers such as silicon
alloys, anionicion exchange resins
and activated carbon. The desorption
of inorganic mercury was found to be
of the following order: 10% for sandi>
1% for Clay Organi CS (not observed).
Methylmercury had a high affinity for
sulfhydryl containing minerals and three
dimensional clays such as montmorillonite
and illite. Desorption of methylmercury
was simila~ to inorganic mercury.
Inorganic cadmium was found to have
a high affinity for oxide minerals,sulfhydryl
containing organics and threedimensional
clays such as illite and
clinoptilotite. Generally, the oxides
exhibited a very low desorption rate
except at severe levels of calcium,
chloride and PH
.a low binding capacity of cadmium with
a 80 percent desorption rate.
Inorganic arsenic, especially the
oxides, displayed high affinity for
soils. In general, arsenite had a better
affinity for sails than arsenate
and both exhibited a higher affinity
for oxide minerals and three dimentional
clays. Arsenite had an affinity for
sulfhydryl organic groups and arsenate
had an affinity for organic amine groups.
Monosodium methanearsonate (MSMA)
had the lowest affinity to soils, but
similar to arsenate in all cases. The
arsenic compounds generally desorbed
at the following increang order : Arsenite
Meanwhile, in investigating the pos
heavy metals such as mercury, arsenic
and cadmium can cause a hazardous release
by changing the form of the heavy
metal compound,thereby, totally changing
its chemical, physical and biological
properties.
This study represents a first step
in predicting the effectiveness of land
treatment for the removal of three
selected metals from waste water effluents.
Results underline the necessity
of proper characterization of both wastewater,
effluent quality and soil constituents.
Results also indicated that
site selection criteria must be specifi
for each proposed application
sible transport mechanisms for arsenic,
cadmium, and mercury, it was noted that
these metals could be affected by the
formation of complexes, fluctuations
in PH, changes in dissolved oxygen content
and/or oxidation-reduction Potential,
and biotic conversion. The degree
of complexation decreased respectively
from mercury, cadmium and arsenic. The
fluctuation of PH resulted in solubilization
and/or volatilization of adsorbed
metals. Oxidation reduction Potential
fluctuation have greatly affected
the release of mercury, cadmium and arsenic.
The biological conversion of
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