Characteristics And Mechanism Of Emitter Clogging In Drip Irrigation With Hard Water

Widespread drip irrigation systems with ground water are used in well-irrigation district of China.But drip irrigation emitter chemical clogging caused by high hardness of ground water seriously restricts the large-scale popularization and application of this technology.The key of solving clongging is to figure out the mechanism of emitter clogging and identify the factors.In this paper,experiments of drip irrigation with hard water were conducted.The basic laws were ascertained of emitter and drip irrigation system chemical clogging.The physicochemical characteristics and dynamic changing process were found out about clogging material.The dynamic process of clogging occurrence was described.The emitter chemical clogging mechanism was revealed and a reasonable opration mode of drip irrigation system with hard water was proposed.The main results and conclusions include:(1)The discharge ratio variation(Dra)of emitter average value and coefficient of uniformity(CU)both varied as a rule of first “plateau period” and then “declining period”.The discharge decline of independent emitter also conformed to the same change rule.The emitter chemical clogging classified as gradually clogging,suddenly clogging and fluctuation clogging.Clogging material analysis showed calcium carbonate was the main composition of emitter with hard water which was confected by tap water and chemical reagents.Silt-sized particle and teflon tape residue were also the main clogging material except chemical precipitation.(2)The experiment studied the effect of emitter characteristic parameters and water hardness on emitter clogging.The results indicate that the effect of the minimum size of flow passage section on the emitter chemical clogging was statistically significant(p<0.01).The bigger the min(W,H)value,the better the anti-clogging property of the emitter performance.For water hardness,the emitter clogging was more severe with the increase of water hardness.The hardness of drip irrigation water should control within 250mg/L for practical application.(3)The growth process of adhesion layer inside the emitter comprised two stages: a rapid growth stage and a gradual growth stage.The two growth stages correspond to the two changing phases of the discharge decline respectively.A dynamic model for growth described the growth process of adhesion layer under hard water.The process of emitter chemical clogging was described on the micro level.The random characteristics of the chemical clogging distribution on lateral were explained.The emitter chemical clogging mechanism was revealed.(4)Compared to continuous drip irrigation,the operation mode of intermittent drip irrigation effectively improved the discharge ratio variation(Dra)of emitter average value and coefficient of uniformity(CU)of drip irrigation system.It significantly inhibited the growth and thickening of the adhesive layer and alleviated the occurrence and aggravation of emitter chemical clogging.However,this measure has different effects on different emitters.Clogging materal inside emitter was easily washed away under single labyrinth channel structure or a larger cross-section channel,it could achieve a better anti-clogging effect.Intermittent drip irrigation was a safe and effective operation mode to prevent clogging for drip irrigation.In the test,the thickness of the adhesion layer can be up to 200?m.Considering adhesion layer characteristics on the inner walls,and the flow passage also needs certain space to allow flaking blocks passing,it was suggested that flow passage size of emitter(including depth and width)should be at least 0.8mm when using hard water of high clogging risk.