Limiting Lateral Biofilm Formation For Controlling Emitter Clogging Of Drip Irrigation System

Presently,issues of water pollution and water shortage are serious and complex water quality characteristics may undoubtedly cause emitter clogging more easily in the drip irrigation system.Studies have shown that the bio-clogging of emitters in drip irrigation system is closely related to the formation and growth of the internal clogged material(biofilm).However,the configuration of filtration equipment or system flushing is a temporary measure to the total solution avert the problem of emitter clogging.Hence the control of biofilm formation attached on the flow path of emitter imperative if emitter's clogging is to be completely solved.Therefore,limiting the formation of biofilm has become the most important pointBased on the above,the study focused on limiting biofilm formation.In order to achieve this,first,the formation characteristics of biofilm of the inner wall of the capillary tube and the inner epiphytic biofilm in the drip irrigation system were studied,then,the internal hydraulic conditions of the irrigation channel and the microbial community in the biofilm were analyzed by designing and processing of the experimental unit and the test platform.Finally,the formation of biofilm is controlled by four aspects:microbial antagonistic technique,electrochemical technique,inferior water mixing technology,and optimizing the threshold of hydraulic shear force at the boundary of the flow path.The purpose of the paper is to provide the theoretical and practical basis for solving the problem of emitter's clogging completely,which is of great significance to the application and popularization of drip irrigation technology in China and helpful for the efficient and safe operation of drip irrigation system.The main research contents and conclusions include:(1)According to the Logistic growth model,the growth kinetics model of the key components of the biofilm under the influence of the water source type,flow path geometric parameters and wall shear force changes,was established.We obtained that the similarity of the growth process of the epiphytic biofilm on the inner wall of the drip irrigation system and the epiphyte biofilm on the inner wall of the emitter flow path.,the growth process of biofilm and its components showed a "S" growth trend,which could provide reference information for the time of monitoring the biological clogging process(R2>0.90,F>96 significant level a=0.01).(2)Using high throughput sequencing technology to analyze the microbial community in the internal biofilm of the irrigator,29 phylum,68 classes,128 orders,243 families,418 genus,641 species were detected in the microbial community of biofilm attached on the surface of emitter's flow path,and it was found that the ?-proteobacteria class being the dominant bacteria.The Bacillus Subtilis and Bacillus Amyloliquefaciens were selected as antagonism.And we confirmed that two kinds of antagonists could not only effectively control the formation of biofilm,delay the process of emitter clogging,but also restore the flow of the already clogged emitter.When the microbial antagonist is selected as Bacillus Subtilis,the optimized application is 126h(application time)+ after 10%(degree of clogging of emitter),but after the use of 42h,it needs to be washed in time.(3)When the electrochemical device is connected to the drip irrigation system,the optimized application is 7 V(applied voltage)+0?126h(application time)+ before 10%(degree of clogging of emitter),and the formation of the 67.59%biofilm on the inner wall of the emitter can be suppressed,the electrochemical technique was applied not only to delay the process of emitter's clogging(delay 150%emitter's clogging time)but also restore the flow of the clogged emitter(recover 7.24%?39.16%).Which confirms the feasibility of electrochemical technology in inhibiting biofilm formation and relieving the clogging of emitter.(4)Through the fine analysis of the particulates characteristics of the epiphytic biofilms on the inner wall of the emitter flow path,it is clear that the most important material in the internal biofilm of the YR(Yellow River water)emitter is silicon precipitation.The main material in the inner biofilm of the BW(brackish water)emitter is calcium and magnesium precipitation,and the surface of biofilm in condition of mix-water was smoother,and the thickness,Sq and Sdr of biofilm in condition of mix-water were smaller.The result of this study has proved that mixing Yellow river water and brackish water can relieve emitter's clogging effectively.(5)We have studied the effect and mechanism of the physical,chemical and biological components of the biofilm inside the drip irrigation system under the indoor controlled condition.It is clear that the influence mechanism of the hydraulic shear force on the biofilm is duality:under the condition of high shear force,it is easy to form biofilm with small thickness,and the low shear force will limit the migration speed of microbes and nutrients,reduce the ability of microbes to secrete polysaccharides,and cause the biofilm structure loose,unstable and easy to fall.We put forward the optimum control threshold of suitable hydraulic shearing force is[0,0.2]U[0.4,+?]Pa under the condition of drip irrigation with poor quality water.It is of guiding significance.