脱硫石膏对土壤磷流失的阻控效应及机制试验

研究脱硫石膏(flue-gas desulfurization gypsum,FGDG)对土壤磷流失的阻控效果,既有利于开拓FGDG资源化利用新途径,又有助于丰富农业面源磷流失控制工程技术。借助土柱淋溶试验和人工边坡降雨侵蚀模拟试验,针对上海某火电厂的FGDG,系统研究不同质量配比(0、1%、2.5%和5%)的FGDG对农田土壤的固磷效果及机理。结果表明:1)FGDG的Ca2+将溶解态P转化成难溶态P,并将土壤无机磷中的Ca2-P、Al-P转化成Ca8-P和Ca10-P,有效控制溶解态磷(total dissolved phosphorus,TDP)直接流失,与对照组相比,施加FGDG对淋洗土柱TDP流失的阻控率达到92.8%~94.8%,而添加FGDG的各处理间无显著差异(P0.05);2)添加FGDG后,土壤的渗透性能和抗侵蚀能力极显著提高(P0.05),1%~5%的FGDG可使土柱渗透性能提升近10倍,添加FGDG的各处理组间无显著差异(P0.05),1%FGDG对坡面径流量的最大削减率为37.5%,对土壤侵蚀(泥沙流失)的最大削减率为59.5%,有利于控制泥沙结合态磷的流失;3)各FGDG处理对土柱中总磷(total phosphorus,TP)流失的阻控率为23.6%~79.5%,且随着配比增加而上升,与对照组相比,1%FGDG对人工边坡土壤TP流失的阻控率为61.5%。土壤流失的TDP量占流失TP的比例只有0.6%~6.1%,反映出改善土壤渗透性能、削减地表径流冲刷是FGDG控制P流失的主要机制,而Ca与P之间的沉淀反应属于从属机制。

Inhibiting effects and mechanism experiment of flue-gas desulfurization gypsum on soil phosphorus loss

Abstract: Increased phosphorus (P) losses from land to waterbody via runoff and drainage are one of the important factors causing eutrophication of surface waterbody. Flue gas desulfurization gypsum (FGDG) is a synthetic by-product generated from the flue gas desulfurization process in coal power plants. Due to the high Ca2+ content of FGDG it can potentially be used to immobilize P in soils. To study the effects of FGDG on soil P losses, not only to open up a new way of FGDG resource utilization, but also to enrich engineering technologies for controlling agricultural non-point source P load. In this study, soil column leaching experiment and artificial soil slope & rainfall simulation experiment were conducted to examine the impact of FGDG which came from one of Shanghai coal-fired power plant, on the leaching and runoff P losses from coastal plains soil of Chongming East Headland, Shanghai. Four mass rates of FGDG (0, 1%, 2.5% and 5%) were applied to soil column and two mass rates of FGDG (0 and 1%) applied to artificial soil slope. The results indicated that: 1) Ca2+ dissolved from FGDG transformed water-soluble P to insoluble P in soil, and turned Ca2-P, Al-P into Ca8-P and Ca10-P which were more inclined to fix in soil. Compared with the control group, the reduction rate of total dissolved phosphorus (TDP) loss of the soil columns applied with FGDG reached 92.8%-94.8% and there was no significant difference among three FGDG treatments (P>0.05). 2) FGDG significantly improved soil permeability and anti-erosion ability (P<0.05), 1%-5% FGDG made the saturated permeability of soil columns increase nearly 10 times, there was no significant difference among three FGDG treatments (P>0.05). Compared with the non-FGDG slopes, 1% FGDG addition achieved the maximum runoff reduction rate of 37.5%, the maximum reduction rate of sediment loss of 59.5%. It was indicated that much adsorbed P on suspended sediment was prevented from migrating along with surface runoff. 3) The reduction rate of TP loss of soil columns with FGDG addition was 23.6%-79.5% and ascended as the adding amount of FGDG increased. Up to 61.5% more TP was held in slope soil with 1% FGDG addition than the non-FGDG treatment. The ratio of TDP loss accounted for TP loss was only 0.6%-6.1%, reflecting enhancement of soil permeability and reduction of surface runoff and sediment loss were the primary mechanisms of FGDG to control P loss from soil, and the deposition reaction of calcium and phosphoric acid belonged to subordinate P-fixing mechanism. When the mass ratio of FGDG was more than 1%, the effect of FGDG on reducing the loss of soil P was not significant (P>0.05), which indicated that the effect of FGDG on soil P loss was also influenced by Ca2+ dissolution efficiency of FGDG, the TDP content and soil particle physical characteristics and other factors together. On the whole, using FGDG to control phosphorous losses from soil can achieve both resource utilization of desulfurization solid waste and reduction of water eutrophication risk due to P transportation.