Effects of municipal sewage sludge stabilized by fly ash on the growth of Manilagrass and transfer of heavy metals.

A greenhouse experiment was carried out to evaluate the feasibility of using an artificial soil for cultivation of Manilagrass. The transfer and transformation of heavy metals in the artificial soil-Manilagrass system were discussed at the same time. The results showed that fly ash-sludge indicated a positive effect on the growth of Manilagrass. The pots with 14% sludge and 6% fly ash mixture had the highest yield and nutrient concentrations of Manilagrass. With the increasing application of coal fly ash, the concentrations of Ni, Zn, Mn, Sb and Cu in Manilagrass decreased significantly, while Pb, V and Ti increased. Otherwise, the concentrations of Cd, As, Cr, Co, and Fe did not show a remarkable change. Except for Sb, the values of bio-concentration factor of heavy metals in Manilagrass were all below 1.0 after treated by the fly ash-sludge treatment, decreased as Sb>Ni>Zn>Cu>Pb>Mn>Co=Cr>Cd>Fe=V>Ti>As in an average for all treatments. Compared to the contrast check, the proportions of heavy metals in exchangeable, reducible and oxidizable fractions increased. Manilagrass could be used to reduce the eco-toxicity and bioavailability of Ti, V, Mn, Co, Cr and Cd in fly ash-sludge amended soil.