Characteristics, Evaluation And Mechanism Of Bio-clogging Process In Drip Irrigation Emitters

Drip irrigation emitter clogging shows direct impact on irrigation uniformity, service life and operating benefits of the system, and has become one of the most significant restrictions in the application and promotion of the drip irrigation technology. Especially in nowadays, water pollution is as serious as water shortage, and their complicated water quality characteristics lead to higher risk of emitter clogging and more complicated clogging mechanism, and thus emitter clogging commonly represents as the typical bio-clogging type. The emitter clogging issue is a worldwide puzzle in drip irrigation studying area till now, and it mainly because of lacking knowledge in emitter clogging mechanism.In this paper, the reclaimed water was selected and imported to the drip irrigation system, due to its most complicated water quality characteristics and most typically bio-clogging type. In 5 years, the on-site drip irrigation emitter clogging experiments were carried out in the wastewater treatment plant and the indoor simulation experiments were also performed along with refined tests, to study the drip irrigation emitter bio-clogging process and characteristics, and then proposed a rapid evaluation method of emitter anti-clogging ability. Based on the formation and growth process of bio-clogging substances, their impacts on bio-clogging process and the inducing mechanism were studied. The results in this paper could provide theoretical support to anti-clogging design of drip irrigation emitters, and the safe and high-efficiency operation of the drip irrigation system. The main results and conclusions were as following:The emitter clogging parameters were confirmed to vary in order as fluctuation balancing period-initial linear decreasing period-accelerated linear decreasing period in the two-year operation, through the long-term and high-frequency measurements in drip irrigation emitter outflows. Thus the emitter bio-clogging process was described quantitatively, and the effects of reclaimed water quality, emitter type and structural parameter, and irrigation frequency on emitter bio-clogging process were also studied.A brand new evaluation method of emitter anti-clogging ability was proposed, based on the emitter bio-clogging characteristics. The new anti-clogging ability evaluation index (Ia) was mainly affected by flow path length, the ratio of flow path width to depth, and the internal average water shear force. Using dimensional analysis theory, the estimated calculating method of Ia was established according to emitter rated outflow and flow path geometrical parameters. Ia was then verified in the accuracy and feasibility to evaluate emitter anti-clogging ability rapidly.With the help of modern environmental microbiology testing methods, the clogging substances components were tested systematically, and their S-shape patterns with emitter clogging degrees were characterized quantitatively (R2>0.92**,p<0.01). Emitter clogging degrees showed "sensitive-micro sensitive-extreme sensitive" trend with the increasing clogging substances components. Furthermore, the influential paths of clogging substances components in emitter clogging were acquired.Considering the nutrition transportation and water shear force distribution within drip irrigation system, the effects of emitter type and flow path geometrical parameters, drip irrigation later positions, and fertilizer types used in drip irrigation system on the formation and growth of clogging substances were systematically studied. The reasonable controlling threshold values were proposed.After the comprehensive consideration of emitter types, flow path geometrical parameters and lateral positions etc., and based on the original Logistic growth model, the growth kinetic model of clogging substances components was established in this paper and it could well describe the "growing adaptive period-rapid growing period-dynamic stable period" growing trend (R2>0.85**,p<0.01). Meanwihle, the evolvement features of microbial community, which played important role in bio-clogging substances, were described quantitatively, and the key bacterial strain affecting emitter clogging process was also confirmed. Based on these mentioned above, the emitter bio-clogging mechanism was revealed and a reasonable emitter clogging controlling strategy was proposed.