Study On Stabilization Of Heavy Metals In Sewage Sludge And Its Adsorption Behaviour In Some Ornamentals When Used In Mixed Soils

How to treat the Sewage sludge, which has a lot of different contents including nutritional elements for plants and heavy metals, is one of the most important environmental problems we have to face. Resource reuse of sewage sludge is believed as one of the best and promising disposing ways, but the heavy metals in sewage sludge is the main obstacle for this purpose.In our paper, Taopu sewage sludge from Shanghai Taopu Wastewater Treatment Plant has been applied for the study. The analysis results of Taopu sewage sludge showed that It contained high concentrations of heavy metal including Cd , Cr , Cu, Ni, Pb ,Zn and so on. Standard toxicity characteristic leaching procedure (TCLP) was used to analyze the composition distribution and concentrations of different heavy metals. It was indicated that Taopu sewage sludge must be treated by stabilization or other ways to ensure the safety for environment before being used in agriculture.Six kinds of chemical reagents including Na₃PO₄, Na₂HPO₄, NaH₂PO₄, CaO, CaSO₄ and Na₂SO₄ were choosed for investigation of the stabilization of heavy metals in the sewage sludge. By different sequential extraction procedures and standard toxicity characteristic leaching procedure (TCLP), the chemical state distribution and leaching behavior of heavy metals in the sewage sludge were studied before and after the stabilization stage. The reasult showed that the effect of phosphate was the best among the selected reagents. The possible mechanism of the stabilization process was also briefly discussed.In this thesis, the adsorption behaviour of heavy metals from composted sewage sludge in some ornamentals was also studied. The experiment soil was the mixed soil produced by Quyang composted sludge and blank soil from Shanghai Baoshan District. The plants for experiments included Buxus Microphylla Sieb et Zucc, Pittosporum Tobira, Rhododendron Simsii Planch, Tagetes Patula and Salvia Splendens. The results showed that all these five plants growed well in the mixed soils, and the concentration of Zn in every plant rised with the rising of Quyang composted sewage sludge quantity in the mixed soil.