Effects Of Reclaimed Water Irrigation On The Adsorption Characteristics Of Cadmium In Soils

Wastewater recycling is an important initiative to alleviate the contradiction between the supply and demand in water-scarce areas of China.However,reclaimed water resources have high salt,heavy metals and organic pollutants,its application may pose potential risk to the health of farmland ecological environment.Nowadays,there are few studies about the influence of different reclaimed water irrigation on soil adsorption capacity of heavy metals.Thus,in this study,we use the treated livestock wastewater and reclaimed water as irrigation resources,the Cd as tested heavy metal,through antecedently irrigated with livestock wastewater and reclaimed water,and later has verified the influence of short-term and long-term irrigation with these treated wastewater resources on the adsorption characteristics of Cd.The results could provide a reference for the safe utilization of unconventional water resources and prevent Cd pollution of soils.These main results were outlined as follows:（1）Livestock wastewater and reclaimed water can significantly influence soil physical and chemical properties like soil p H,clay and salt content etc.,and consequently,alter the soil adsorption capacity of Cd.Compared with the Langmuir model,the Freundlich model can better fit the Cd adsorption by soils with livestock wastewater and reclaimed water irrigation.（2）The results of the pot experiment for Cd adsorption by fluvo-aquic soil with short-term livestock wastewater and reclaimed water irrigation showed that,compared with the deionized water,when the Cd initial concentration was 5 mg/L during 120 h adsorption stage,both livestock wastewater and reclaimed water irrigation increased the Cd adsorption.and the desorption amount was also significantly lower than the control as well.When the Cd initial concentration was 10～50 mg/L,both livestock wastewater and reclaimed water irrigation reduced the Cd adsorption,and the desorption amount was also significantly higher than that of the control.（3）The results of the laboratory culture experiment for Cd adsorption by soil under short-term livestock wastewater and reclaimed water irrigation showed that,compared with deionized water,livestock wastewater irrigation reduced Cd adsorption of acid soil（red soil）at lower Cd concentrations（5～10 mg/L）but increased Cd adsorption at higher Cd concentrations（25～50 mg/L）.However,irrigation with reclaimed water reduced Cd adsorption of acid soil（red soil）.As for Alkaline soils（fluvo-aquic soil,lou soil black soil and dark loessial soil）,livestock wastewater irrigation reduced Cd adsorption.The Cd adsorption results of the fluvo-aquic soil with long-term livestock wastewater and reclaimed water are consistent with the Cd adsorption results of the fluvo-aquic soil after short-term irrigation.（4）The complexed form of cadmium is the main adsorption form in soils after irrigation with treated wastewater.After livestock wastewater and reclaimed water irrigation,the increase of soil p H,clay content,SO₄^2-and HCO₃^-,etc.can increase Cd adsorption while the increase of salinity can reduce Cd adsorption.Therefore,the influence of livestock wastewater and reclaimed water irrigation on the Cd adsorption ability is the result of the combined effect mentioned above.