Saturday, 15 July 2006

Reducing Sludge-P Phytoavailability as a Means to Maximize Soil Capacity for Sludge Disposal.

Xiao-Lan Huang1, Moshe Shenker2, and Yona Chen2. (1) Miami Univ, CIMAS, Rosenstiel School of Marine and Atmospheric Sciences, 4600 Rickenbacker Causeway, Miami, FL 33149, (2) The Hebrew Univ of Jerusalem, Faculty of Agricultural, Food and Environmental Quality Sciences, Dept of Soil and Water Sciences, Rehovot, 76-100, Israel

Three chemicals: aluminum sulfate (alum), ferrous sulfate (FeSul) and calcium oxide (CaO), were used to stabilize the phosphorus (P) in fresh dewatered anaerobically digested sewage sludge (FSS) to produce alum-SS, FeSul-SS, and CaO-SS, respectively. Two incubation experiments were set up to test the efficiency of P stabilization in the sludge as a means of maximizing the land's capacity to safely receive this waste material. Olsen-P, water-soluble P (WSP) and water-soluble Ca, Fe, Al, Mg, K, and S were monitored during the incubation period. Phosphorus phytoavailability in these sandy soil amended with different sludge materials or KH2PO4, at rates of 50 to 250 mg P kg-1, were probed by a newly developed rapid bioassay which corresponded to the inorganic P(Pi) content of tested plant. Increased P application rates resulted in increased WSP and Olsen-P values after a 110-day incubation period, but the increase was dependent on the sludge pretreatments: at the same amount of applied P, the Olsen-P and WSP values in the sludge materials were ranked as follows: FSS >> CaO-SS > alum-SS > FeSul-SS. At the end of incubation, WSP in the soil amended with Fe-Sul-SS did not increase over the control even at the highest P rates. At the same time, water-soluble Al and Fe decreased and water-soluble Ca, S and K increased in the soil amended with FeSul-SS and alum-SS. The order of P phytoavailability with the same rate of P application was KH2PO4 >> alum-SS ≥ BSC ≥ CaO-SS > FSS >> FeSul-SS. Phosphorus phytoavailability was positively related to P rates and WSP content for each soil, but the corresponding dependency coefficients differed considerably. Overall, these results indicate that P solubility and phytoavailability can be either enhanced or reduced by sludge pretreatments, and the soil capacity to safely receive high loads of sludge can be increased significantly by sludge pre-stabilization with FeSul. This approach is expected to benefit the practice of land disposal of sewage sludge, providing a long-term outlet for this troublesome waste stream.


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