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Influences of natural zeolite on speciation of heavy metals during rotary drum composting of green waste

Posted on 9. May, 2014.

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The water hyacinth (Eichhornia crassipes) is a free floating aquatic weed originating in the Amazon in South America and has been considered as the most noxious plant species in the world.

It has become the world’s worst invasive aquatic plant due to its extremely rapid propagation and density of growth. However, water hyacinth has been used in phytoremediation for the removal of pollutants such as heavy metals from water. Composting is one of the most cost-effective and easy techniques for the handling and final disposal of water hyacinth after phytoremediation as it combines material recycling and biomass disposal. 

The major drawback of water hyacinth composting is the high content of heavy metals in the mature compost. Metal uptake by plants and its accumulation in the food chain is a potential hazard to animals and human health if the compost contaminated with heavy metals is used as a soil conditioner.

Application of natural zeolites (clinoptilolite) during water hyacinth composting may be helpful to immobilise heavy metals. The present study was carried out on the speciation of heavy metals (Zn, Cu, Mn, Fe, Pb, Ni, Cd and Cr) during rotary drum composting of water hyacinth mixed with cattle manure, sawdust and natural zeolite. The Tessier sequential extraction method was used for heavy metal speciation determination. The water hyacinth, cattle manure and sawdust at a ratio of 6:3:1 ratio was mixed with 5, 10 and 15% natural zeolite by weight. Influences of physicochemical parameters such as temperature, pH and organic matter degradation on speciation of heavy metals were studied during the process. A rotary drum composter has been shown to be highly efficient for organic matter degradation. 

The most bioavailable fractions (exchangeable and carbonate fractions) were reduced significantly due to the combined 
effects of zeolite addition and metal complexing with stabilised organic matter as a result of the high degradation of organic matter in a rotary drum. Ni, Pb and Cd were not found in the reducible and oxidisable fractions. Overall, the addition of an optimum quantity of natural zeolite significantly reduced the bioavailability fractions of heavy metals during rotary drum composting of the water hyacinth.

Read the full article in Chemical Speciation and Bioavailability, Volume 26, No.2, April 2014, pp. 65-75(11)

DOI:10.3184/095422914X13953177945668

Image: Clinoptilolite-Na. Courtesy of Christian Rewitzer/CC-BT_SA-3.0