Islamic Azad University (IAU)

Compost' leachate recycling through land treatment and application of natural Zeolite


Background: The entrance of untreated wastewater or disposal leachate to water resources such as surface water,
groundwater or irrigation water increases the risk of contaminant accumulation. Removal or deduction of water
contaminant concentration is then crucial before entering water to the natural resources or its transfusion directly
to the soil as irrigation water. Four studies were carried out in a pilot plant to evaluate the effect of natural zeolite
to decrease chemical and biological index of compost factory leachate. Land treatment was considered as the main
strategy; however, some pounding and column experiment was implemented as well. Wastewater chemical and
biological indexes were analyzed. These indexes consisted of Na, K, Mg, Ca, Co3, HCO3, Ni, Cd, Pb, Cr, chemical
oxygen demand (COD), fecal coliform and total coliform (TC). In addition, soil was analyzed for EC, pH, cation and
Results: In the first study, three types of zeolite derived from Semnan, Mashhad and Miyaneh mines were tested
with four sizes (70, 140, 270 and 840 μm) at 25°C in summer 2007. It was concluded that high value of the cation
concentration in the leachate causes neither adsorption of remaining cation nor heavy metals. There was no
statistically significant difference between the zeolite sizes and the heavy metal adsorption. The results also showed
that the adsorption ratios were 52%, 23% and 40% for Na, Ca and Mg, respectively. In the second study, a loamy
sand soil was enriched by adding 5% and 10% of the zeolite. The result uncovered that adding 10% of the zeolite
to the soil brings about more elements' absorption in comparison to application of the 5% zeolite. Irrigation with
the leachate reduced soil specific yield significantly. In the third study, a complete randomized design experiment
was used with six treatments (two kinds of soil, loamy sand and clay loam, and three levels of zeolite, 0%, 5% and
10%) and three replications performed in the lysimeter size. The results revealed that irrigation with the leachate
reduces soil bulk density, infiltration rate and saturated hydraulic conductivity. Heavy metals could not be absorbed
by loamy sand soil, whereas clay loam soil had a high ability to absorb heavy metals and reduce the salinity. In
loamy sand and clay loam soil, 10% zeolite had a significant effect on heavy metals' absorption. The result of
subsequent study (the same setup as the third study) exhibited the fact that the COD was significantly decreased
by application of 5% zeolite, whilethis reduction occurred via applying 10% of zeolite in TC.
Conclusions: In short, this research indicated that the wastewater can be treated in a simple, economically process
of land treatment through application of a clay loam soil texture with a cation pre-treatment.
Keywords: Zeolite, Heavy metal, Soil, Leachate, Wastewater, Compost

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