Effects of natural zeolite on speciation of heavy metals during agitated pile composting of water hyacinth

Background Water hyacinth (Eichhornia crassipes) isone of the worst weeds in the world. Composting is one ofthe most economical ways for the treatment and final disposalof water hyacinth, because it combines materialrecycling and biomass disposal. A major restriction of landapplication of water hyacinth compost is the possible highheavy metal concentration in the final product. Zeolitesmay be useful as metal scavengers in metal-rich waterhyacinth compost. The speciation of heavy metals (Zn, Cu,Mn, Fe, Pb, Ni, Cd and Cr) was done according to Tessier’ssequential extraction method during water hyacinth compostingmixed with cattle manure, sawdust and naturalzeolite. The water hyacinth, cattle manure and sawdustwere taken in the 6:3:1 ratio with 5, 10 and 15 % naturalzeolite, respectively.Results The temperature was measured in the range of48.6–56.2 C in control and zeolite treatments. Higherreduction of exchangeable (F1) and oxidizable (F4) fractionsof Zn was observed about 72.8 and 79.6 %, respectively,in zeolite 1 treatment but higher reduction ofcarbonate (F2) and reducible (F3) fractions was observedabout 70 and 37 %, respectively, in zeolite 2 treatment.The F1, F2, F3 and F4 fractions of Cu and Fe were reducedin the control and all zeolite treatments. The F1, F2, F3 andF4 fractions of Mn were reduced significantly in the allzeolite treatments in comparison to control. The bioavailabilityfactor (BF) of Zn, Cu, Mn, Fe, Ni, Cd and Cr wasreduced significantly in zeolite treatments in comparison tocontrol. There was no significant change observed with BFof Pb in zeolite treatments. The total concentration of Pbwas higher than Zn, Cu, Mn, Ni and Cr but its BF waslowest among the all these metals.Conclusion Addition of optimum percentage of naturalzeolite was successful for enhancing degradation oforganic matter and reducing bioavailability of heavy metalsduring water hyacinth composting mixed with cattle manureand sawdust. The bioavailable fractions of heavymetals were effectively correlated with pH and TOC incontrol and zeolite 1 treatment as compared to zeolite 2 and3 treatments.