Influence Of Flue Gas Desulfurization Gypsum On Phosphorus Loss Of Agricultural Non-point Source Pollution In Plain River Network Area

Agricultural non-point source and farm runoff are the main sources of nutrition and driving force of polluted water bodies.In particular,excess nitrogen and phosphorus in agricultural soil gradually migrate to rivers and lakes through surface runoff,soil erosion and leaching to cause problems such as algal blooms and eutrophication.The Yangtze River Delta region in China has a high degree of agricultural concentration,and the wide application of chemical fertilizers has significantly increased soil phosphorus content in many areas and a low utilization efficiency of phosphorus have caused serious agricultural non-point source pollution in those regions and growing risk of water loss by farmland runoff to the water environment.In order to continue agricultural production activities on those sites,it is necessary to implement technology to control agricultural non-point source and study the means to reduce and stop runoff in order to reduce the loss of phosphorus in the soil.Flue gas desulfurization gypsum,a byproduct of the desulfurization of flue gas discharged by coal-fired power plant,is mainly used in industrial production,which has gradually been adopted in agricultural production and environmental remediation in foreign countries.The application of the gypsum can increase the permeability and phosphorus absorption capacity of soil and reduce the possibility of soil phosphorus loss.Applying flue gas desulphurization gypsum will not only develop a new application field to control agricultural non-point source pollution in China's plain water network area,but also form a set of economical and large-scale agricultural surface source pollution prevention and control technology.Meanwhile,the gypsum can provide an economical and reliable technical means to cut agricultural non-point pollution source and reduce the pollution of rivers and lakes.In this study,Visual MINTEQ software simulation and X-ray diffraction were used to analyze the morphological changes of calcium in soil after flue gas desulfurization gypsum was applied,Combining with Visual MINTEQ software simulation and X-ray diffraction the effects of FGD Gypsum on phosphorus loss and soil phosphorus composition in soil of the Yangtze River Delta were studied through laboratory and outdoor experiments.The purposes of this study are 1)to confirm the optimizing effects of FGD Gypsum on the physical and chemical properties of soil,especially the soil permeability;2)to explore the fixing effect of FGD Gypsum on soil phosphorus,especially the morphological characteristics of soil inorganic phosphorus;3)to confirm FGD Gypsum's ability to control the phosphorus loss in the plain water network area and its effect on the growth of plants;4)to explore the role of FGD Gypsum to control the ecological safety of soil phosphorus loss in farmland soils,in particular,the change of the heavy metal content in soil,and the effect of FGD Gypsum in controlling soil phosphorus variety.The main research contents and conclusions are as follows:1)The results of the model Visual MINTEQ further verified the results of field experiments.With the progressive application of FGD Gypsum,Ca2+and PO43-in the soil formed a series of water-soluble calcium phosphate compounds.The dissolved phosphorus was gradually fixed into a poorly soluble calcium phosphate salt,which in some extent reduced the possibility of soil phosphorus loss.The results of X-ray diffraction analysis also showed that the Ca₈-P and Ca₁₀-P in soil calcium phosphate increased with the increase of FGD gypsum dosage.2)Flue gas desulfurization gypsum significantly improved the soil permeability and erosion resistance.The FGD Gypsum improved soil permeability about 10 times,and it reduced the artificial slope runoff rate with the maximum 37.5%,and it decreased the rate of slope sediment loss with the maximum 59.5%.The FGD Gypsum significantly increased the permeability of Chongming Dongtan's soil after2a test,and the soil infiltration capacity increased 4.8 times with FGD Gypsum at 60t/ha.The FGD Gypsum not only reduced farmland runoff but also diminished the possibility of phosphorus in soil with surface runoff erosion.3)The exchangeable Ca²⁺in FGD Gypsum reacted with the phosphate ions in the soil,and the active P form in the soil transformed to more stable and insoluble inorganic phosphorus forms(Ca₈-P,Ca₁₀-P),which effectively controlled the direct loss of the P in dissolvable form.The resistance rate of FGD Gypsum to dissolve state P of soil column was 92.8%⁹4.8%.The inorganic phosphorus content in soil gradually increased with the increased FGD Gypsum.The insoluble calcium phosphate was the dominated one in all increased various calcium phosphate salt contents.Among soil salt components,Ca₁₀-P was the highest,accounting for more than 60%of the total calcium phosphate salt,and Ca₈-P content was the second highest;however,Ca₂-P only increased marginally.4)The available phosphorus in soil and the soluble phosphorus in soil leachate showed a decreasing trend with the increased FGD Gypsum.The FGD Gypsum obviously reduced soil soluble phosphorus loss and adding 1%FGD Gypsum reduced 90%loss of soil P.The decreased available phosphorus and soluble phosphorus content reduced soil excess phosphorus through surface runoff and leaching to water.FGD Gypsum had no significant effect on soil total phosphorus.5)The abundance of available phosphorus in soil and calcium phosphate in inorganic phosphorus component did not affect the absorption of P in a certain range.The biomass of Echinacea in seedling and flowering stage was higher than the control.FGD Gypsum generally increased the biomass,maturity,total root length,and plant height of early season rice.But excessive FGD Gypsum inhibited the growth of plants.Thus,the appropriate addition of FGD Gypsum is the key to control soil phosphorus,and 30⁴5 t/ha was the most appropriate amount of FGD Gypsum.6)FGD Gypsum significantly reduced ESP and pH in alkaline soil.The FGD Gypsum did not increase the heavy metal content in soil,and soil heavy metal content in all treatments was less than the grade two standard?agricultural background?of"soil environmental quality standard"?GB15618-1995?.FGD gypsum even at 60 t/ha did not cause heavy metal pollution in soil.This study first used the traditionally-defined solid waste,FGD Gypsum,onto the phosphorus-rich soil in the plain river network area in China to fix the excess phosphorus.The gypsum can effectively fix the high phosphorus content by transforming the easily dissolvable phosphorus into precipitable and stable inorganic phosphorus to reduce the soil phosphorus pollution to the environment and the occurrence of eutrophication.The results of this study can provide technical reference for use of FGD Gypsum in the control of agricultural non-point source pollution.