Effects Of Aeration And Fertilizer On Sedimentation Of Fine Sediment

The water,fertilizer and gas integrated drip irrigation technology uniformly mixes micro and nano bubbles with water and fertilizer,realizes the integration of water,fertilizer and gas,and synchronously inputs them into the soil of crop root zone,solves the contradiction between root water and oxygen,improves root activity and fertilizer utilization efficiency,and increases economic and social benefits.In recent years,the research and application of water,fertilizer and gas integrated drip irrigation technology are more and more.The filtration of fine sediment in irrigation water is difficult and the filtration cost is high.The fine sediment is very easy to enter the drip irrigation system and flocculate and settle in the emitter channel,increasing the risk of emitter clogging.Aeration in water can change the density and viscosity of water,which may affect the drag and transport of water to sediment,affect the process of sediment flocculation and sedimentation,and then affect the occurrence of emitter clogging.The study of the influence of aeration and fertilizer on the sediment settlement law is of great significance to clarify the emitter clogging mechanism of water,fertilizer and gas integrated drip irrigation system and put forward the technical scheme to alleviate the emitter clogging.Therefore,taking the Yellow River water with more fine sediment as the research object,this paper tested the effects of aeration and fertilizer on the flocculation and settlement of fine sediment under the conditions of static water and turbulent flow.The influence process of aeration and fertilizer on the flocculation and sedimentation of fine sediment is preliminarily explored.The research results provide a certain reference for taking reasonable measures to reduce sediment deposition in drip irrigation pipe network system.The main conclusions are as follows:（1）Aeration significantly promoted sedimentation of cohesive finesediment（P<0.05）and the promotion increases with the increase of initial sediment concentration（Initial sediment concentration was 3～10 g/L）.The median sedimentation velocity of sediment after aerated treatment in winter and summer increased by 48.67%～70.98%and 33.04%～57.52%compared with the non-aerated treatment and the median particle size of settling sediment increased by 7.62%～13.95%and 6.83%～13.24%.Aeration significantly increased the sedimentation velocity of sediment with median particle size less than 53μm（P<0.05）,which was 30.48%～68.69%higher than that without aeration.The effect of aeration on the sedimentation of fine sediment increases with the decrease of median particle size.（2）The type and concentration of fertilizer affect the sedimentation process of fine sediment.Under a hydrostatic condition,with the gradual increase of the mass concentration of potassium sulfate fertilizer or compound fertilizer,the median sedimentation velocity of sediment increases gradually.Potassium sulfate fertilizer with mass fraction of 0.5%～1.0%significantly accelerated sediment deposition（P<0.05）,and the median sedimentation velocity increased by 31.80%～43.68%compared with the non-fertilization treatment.Compound fertilizer with mass fraction of 0.2%or urea with mass fraction of 0.2%～1.0%significantly slowed down the sediment deposition（P<0.05）and the median sedimentation velocity decreased by 52.11%and 26.05%～47.13%respectively compared with the non-fertilization treatment.The high-speed flow(flow shear strength is 13.20 s^-1)hinders the sedimentation of sediment.The application of potassium sulfate fertilizer or high concentration compound fertilizer can reduce the obstruction of high-speed flow to sediment sedimentation to a certain extent,and aggravate sediment sedimentation compared with no fertilization treatment.The application of urea can enhance the blocking effect of high-speed water flow on sediment settlement to a certain extent,and slow down sediment settlement compared with no fertilization treatment.（3）The effect of aeration on the sedimentation of fine sediment is affected by the type and concentration of fertilizer.With the gradual increase of fertilizer concentration,the effect of aeration on sediment sedimentation decreases gradually.When the mass fraction of fertilizer is 0.2～1.0%,after aeration,the median sedimentation velocity of potassium sulfate muddy cement sand is the largest,which is 0.399～0.450 mm/s,and the median sedimentation velocity of compound fertilizer muddy cement sand is the smallest,which is0.288～0.330 mm/s.When the mass fraction of fertilizer is 1.0%,the increase of median sedimentation velocity of sediment after aerating muddy water with urea is the largest,followed by muddy water with potassium sulfate fertilizer,and the minimum with compound fertilizer,which is 89.27%,52.74%and 45.63%higher than that without aerating treatment,respectively.Aeration,fertilizer type and fertilizer concentration significantly affected sediment deposition alone or interactively（P<0.01）.There is a complex interaction among effects of aeration,fertilizer type and fertilizer concentration on sediment deposition.（4）The effect of aeration on accelerating fine sediment settlement decreases with the increase of flow shear strength.When the flow shear strength is less than 4.67 s^-1,aeration significantly accelerates sediment settlement（P<0.05）.The promoting effect of aeration on sediment deposition is related to the type of fertilizer.When the flow shear strength is 0～4.67s^-1,compared with the water fertilizer mixture without aeration,the median sedimentation velocity of potassium sulfate,compound fertilizer and urea water fertilizer gas mixture increases by 15.85%～52.74%,9.38%～45.63%and 19.30%～89.27%respectively.（5）Aerating significantly aggravates the sediment deposition in the front section of the lateral of integrated drip irrigation with water and fertilizer（P<0.05）.When potassium sulfate,compound fertilizer and urea are applied,the sediment quality in the front section of the lateral treated by aerating is increased by 30.33%,17.10%and 106.21%respectively compared with that without aerating.Channel sedimentation sediment quality in the front section of the lateral increased by 26.43%,20.14%and 31.06%respectively compared with that without aerating.When using high sediment concentration water source for integrated drip irrigation of water,fertilizer and gas,it is suggested to appropriately strengthen the flushing of sediment deposited in the lateral,so as to slow down the sediment deposition in the irrigation pipe network system and reduce the risk of emitter clogging.