Drinking water treatment residuals as an amendment to alkaline soils: Effects on bioaccumulation of heavy metals and aluminum in corn plants

An alum-based drinking water treatment residue (DWTR) is the by-product from the production of potable water. Land application of DWTR has received a considerable attention for its potential as a low-cost disposal alternative. A greenhouse experiment was conducted to quantify the effects of DWTR on bioaccumulation of some heavy metals in plant tissue and to determine the effects of the DWTR on soil aluminum and aluminum phytotoxicity for the corn plants in alkaline soils. The results indicated that land application of DWTR significantly decreased extractable heavy metals in all studied soils. Combined analyses of all soils and rates of DWTR application showed significant relationship between DTPA-extractable heavy metals and heavy metals uptake of corn plants. Addition of DWTR with different rates (10, 20, 30 and 40 g/kg) to different soil types did not cause aluminum phytotoxicity symptoms for corn plants grown in all studied alkaline agricultural soils because the application rates of DWTR did not increase extractable Al in amended soils > 8 mg Al/kg and the Al phytotoxicity may occur below pH 5.5. Extractable Al is associated with pH of the studied soils, combined analyses of all soils and rates of DWTR application showed a significant relationship between extractable Al and pH. Based on the results of current study, the DWTR is considered an ameliorating material for heavy metals removal from soils; however, additional studies are necessary to confirm these results under field conditions.