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Vermicomposting of water hyacinth is a good alternative for the treatment of water hyacinth (Eichhornia crassipes) and subsequentially, beneficial for agriculture purposes. The bioavailability and leachability of heavy metals (Zn, Cu, Mn, Fe, Ni, Pb, Cd, and Cr) were evaluated during vermicomposting of E. crassipes employing Eisenia fetida earthworm. Five different proportions (trials 1, 2, 3, 4, and 5) of cattle manure, water hyacinth, and sawdust were prepared for the vermicomposting process. Results show that very poor biomass growth of earthworms was observed in the highest proportion of water hyacinth (trial 1). The water soluble, diethylenetriaminepentaacetic acid (DTPA) extractable, and leachable heavy metals concentration (percentage of total heavy metals) were reduced significantly in all trials except trial 1. The total concentration of some metals was low but its water soluble and DTPA extractable fractions were similar or more than other metals which were present in higher concentration. This study revealed that the toxicity of metals depends on bioavailable fraction rather than total metal concentration. Bioavailable fraction of metals may be toxic for plants and soil microorganisms. The vermicomposting of water hyacinth by E. fetida was very effective for reduction of bioavailability and leachability of selected heavy metals. Leachability test confirmed that prepared vermicompost is not hazardous for soil, plants, and human health. The feasibility of earthworms to mitigate the metal toxicity and to enhance the nutrient profile in water hyacinth vermicompost might be useful in sustainable land renovation practices at low-input basis.

The bioavailability and leachability of heavy metals is important role when considering their toxicity during composting following land application. Therefore, studies were carried out on Zn, Cu, Mn, Fe, Ni, Pb, Cd and Cr during 30 days agitatedpile composting of water hyacinth (Eichhornia crassipes). This study investigated the influence of parameters such as pH, temperature and organic matter content on the distribution of heavy metal bioavailability and leachability during composting of water hyacinth. Results showed that the contents of total metal concentration increased during the composting process. The bioavailability of heavy metals was investigated in the form of water soluble and diethylene triamine pentaacetic acid (DTPA) extractable. In the water soluble, DTPA and leachable Zn, Cu, Mn, Ni and Cr reduced but there was a gradual increase in the Fe concentration during the composting process. Furthermore, in water soluble and leachable Ni, Cd and Pb were not detected and in DTPA extractable Cd and Pb were also not detected during 30 days of composting.

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