Transformation of nutrients and heavy metals during vermicomposting of the invasive green weed Salvinia natans using Eisenia fetida

Purpose Effective vermicomposting of Salvinia natans is agood alternative for protecting wetlands damaged by theweed due to the vast potential for use of the product vermicompostin agriculture, but the presence of toxic metalsin the weeds may deter the usage.Methods Research was carried out on the physico-chemicaland biological characteristics as well as bioavailabilityand leachability of nutrients and heavy metals (Zn, Cu, Mn,Fe, Ni, Pb, Cd and Cr) during vermicomposting of S.natans mixed with cattle manure and sawdust in five differentcombinations [trial 1 (eight S. natans: one cattlemanure: one sawdust), trial 2 (seven S. natans: two cattlemanure: one sawdust), trial 3 (six S. natans: three cattlemanure: one sawdust), trial 4 (five S. natans: four cattlemanure: one sawdust) and trial 5 (ten S. natans: 0 cattlemanure: 0 sawdust)] for 45 days with Eisenia fetidaearthworm.Results The highest growth of earthworms was in trial 4,having the highest (40 %) cattle manure. Trial 4 alsoindicated the highest reduction of volatile solids (38.6 %)and soluble BOD (82.3 %). The water-soluble forms of allnutrients were increased significantly. The highlybioavailable water-soluble and DTPA-extractable forms ofheavy metals were reduced favourably after the process.The toxicity characteristic leaching procedure (TCLP) testindicated that leachable heavy metals of the vermicompostswere also reduced and were within the threshold limits foragricultural applications.Conclusions Eisenia fetida was very effective for reductionof bioavailable and leachable forms of selected heavymetals, and the TCLP test confirmed that the vermicompostwas not hazardous for soil applications. The potential ofthe earthworms to increase the available nutrients, butmitigate the metal toxicity during vermicomposting of S.natans will be useful for sustainable land renovationpractices.