Effect Of Fertilizer On Flocculation And Settlement Of Fine Sediment

The Yellow River is a highly sediment-laden river,and the viscous fine sediment is abundant.After strict filtration,a large amount of sediment with particle size less than 0.01 mm still enters the irrigation system in the drip irrigation project of the Yellow River.Because of its special electrochemical Because of its special electrochemical properties,fine sediment is easy to flocculate in water and form flocculants,which make it easier to settle down.Sediment flocculation is a common phenomenon in estuaries or coastal areas,and there are many studies in this area.At present,many scholars have studied the effect of electrolytes such as NaCl and MgCl2 in seawater on the flocculation and sedimentation of fine sediment in estuaries of the Yangtze River and the Yellow River by various methods,and the electrolytes contained in fertilizers commonly used in irrigation are fine in the irrigation area of the Yellow River Basin.At present,there are relatively few studies on the effect of flocculation settling of granular sediment,but previous studies have shown that fine sediment in freshwater can also produce flocculation phenomenon.The Yellow River is a highly sediment-laden river,and the viscous fine sediment is abundant.After strict filtration,a large amount of sediment with particle size less than 0.01 mm still enters the irrigation system in the drip irrigation project of the Yellow River.With the application and popularization of water-fertilizer integration technology,the application of water-soluble fertilizer and liquid fertilizer in irrigation water will affect the flocculation and sedimentation of fine sediment in the Yellow River water,thus affecting the transport and deposition of sediment in irrigation pipeline network,dripper blockage,operation of irrigation system,increasing the cost of filtering equipment and investment cost of drip irrigation belt.Therefore,it is urgent to find out the effect of water-soluble fertilizer on flocculation and sedimentation of cement sand in the process of integrated drip irrigation with water and fertilizer,to provide theoretical explanation and theoretical basis for further study on the mechanism of dripper blockage,and to provide technical basis for formulating reasonable management scheme of drip irrigation system.In this study,through hydrostatic and hydrodynamic tests,sediment with different potassium sulfate concentration,four initial particle size ranges(<100,50-100,34-50,<34 um),different urea concentration and different settling cylinder speed were set up.The effects of different fertilizer types and fertilizer concentration on sediment settling process,median particle size after sediment settling and sediment settling process in turbulent flow were studied to guide the Yellow River diversion.The integrated technology of water and fertilizer for drip irrigation with high sediment content water source in irrigation area provides theoretical reference.The main conclusions are as follows:(1)Potassium sulfate promotes flocculation and sedimentation of fine sediment.Potassium sulfate significantly promotes the decrease of sediment concentration,and with the increase of potassium sulfate concentration,the decrease range of relative sediment concentration,median settling velocity of sediment and median size of sediment after settling also increase;but when the concentration of potassium sulfate exceeds a certain range,with the increase of potassium sulfate concentration,the decrease range of relative sediment concentration,median settling velocity of sediment and median size of sediment after flocculation increase.The increase is no longer a significant trend.(2)The finer the initial sediment particles,the greater the influence of potassium sulfate on the change of sediment particle size after sedimentation.Potassium sulfate has the greatest influence on the flocculation settling of sediment with particle size < 34 micron,the smallest effect on the particle size of 50-100 micron,and the middle effect on the particle size of 34-50 micron.Potassium sulfate can reduce the relative content of small sediment particles and increase the relative content of large or coarse sediment particles.(3)When the sediment concentration is 10 g/L,the sediment settling process and the median size of sediment after flocculation do not show obvious regularity with the change of urea concentration,that is,urea concentration has no significant influence on the sediment settling process and the median size of sediment after settling.(4)For fine sediment,low-speed flow has a weak promoting effect on flocculation and sedimentation of sediment particles at the initial stage of sedimentation,but after a certain period of time,the promoting effect of low-speed flow becomes weaker and weaker,even has a restraining effect,while high-speed flow always hinders sediment sedimentation.The hindrance effect of potassium sulfate on water flow is also partially reduced.The degree of reduction varies with the concentration of potassium sulfate and the relative velocity of water flow.