Eight emitters clogging characteristics and its suitability under on-site reclaimed water drip irrigation

Drip irrigation is the most effective and reliable method for reclaimed water irrigation. The water usually contains a lot of suspended particles, metal salt ions, organisms and microbial communities, which will enhance the possibility of emitter clogging or more complex clogging mechanism. Emitter clogging has become one of  the key problems to the application and popularization of the drip irrigation technology. In this paper, we selected four kinds of pressure-compensating emitters and four kinds of non-pressure-compensating emitters, and executed the experiment of drip irrigation with on-site reclaimed water treated with cyclic activated sludge system (CASS). The emitter discharge ratio variation (Dra), coefficient of uniformity (CU) and clogging rate distribution were analyzed to evaluate the emitter clogging characteristics after eliminating the effect of temperature and pressure on the emitter outflow by data correction. The results showed that Dra and CU varied in three periods as system operation. The beginning of experiment was the fluctuated balance period, Dra and CU recurrent fluctuated in 5 %, and the emitters clogged at some spots after the system run 36–48 h. Then the two parameters varied linearly in 60–108 h, tuning into the initiate linear period, as the non-pressure-compensating emitters got an obvious linear change than the pressure-compensating ones with the gradient changed from ?0.094 to 0.042 and ?0.073 to 0.047, respectively. Some of the emitters have a significant difference on these two parameters at this stage. After the restarting in the second year, Dra and CU decreased sharply. The maximum decrement was, respectively, 9.6 and 10.7 %. Then they varied in line with a greater slope degree as all emitters reached the significant level, the gradient ranges were ?0.176 to 0.115 and ?0.216 to 0.117, respectively. This stage was called the accelerated linear period. Seriously clogged and completely clogged emitters appeared, and both Dra and CU dropped down to 38.7 and 41.5 %. Various degrees of clogged emitters often emerged in the end part of lateral at first then propelled to the head gradually, the completely clogged emitters in the end accounted for more than 73.0 % when the system run 540 h. Comprehensively considered, the pressure-compensating emitters and cusp-shaped saw-tooth non-pressure-compensating emitters with short flow path are recommended in reclaimed water drip irrigation. These researches are aimed to provide references explaining the emitter clogging mechanism of reclaimed water drip irrigation as well as its technological application and popularization.     

Laboratory experiment on drip emitter clogging with fresh water and treated sewage effluent

A laboratory experiment was carried out to study the emitter performance of three commonly used emitter types with the application of freshwater and treated sewage effluent (TSE). The three emitter types are the inline-labyrinth types of emitters with a turbulent flow (E1) and a laminar flow (E2) and the online pressure-compensation type of emitters (E3). The qualities of freshwater and TSE were measured, and the emitter performance was evaluated, using the relative emitter discharge, the reduction of emitter discharge (q_reduction), the coefficient of variation of emitter discharge (CV), the emission uniformity (EU), Christiansen uniformity coefficient (CU), and the percentage of emitter clogging (P_clog). Results showed that all indices were affected by water quality, emitter type and time of operation. The values of q_reduction, CV and P_clog for the TSE treatments were greater than those for the freshwater treatments. The values of EU and CU for the TSE treatment were lower than those for the freshwater treatments. The q_reduction, CV and P_clog increased and the EU and CU decreased as operational time increasing for the TSE treatment. For both freshwater and TSE treatments, the emitter clogging was more severe, the CV was greater, and the EU and CU were smaller for emitter type E2 than those for emitter types E1 and E3. Thus a more severe clogging was found for emitter type E2 due to its smaller flow-path dimension and higher manufacturing coefficient of variation in addition to the high pH values and relatively high total dissolved solids (TDS) values of the used water. Analyses of water quality and the precipitation components inside and at the outlet of emitters revealed that chemical precipitation was the main reason for emitter clogging due to high pH and ions’ concentration, especially in the TSE. Flushing emitters and drip pipes did not efficiently alleviate emitter clogging caused by chemical precipitation. In a conclusion, emitter type E3 showed a better anti-clogging function than emitter types E1 and E2 and was recommended for irrigation with TSE in the Beijing area of China.     

Assessment of emitter discharge in microirrigation system as affected by polluted water

A drip irrigation system has the advantage of maintaining high water content near the plant root. However, its performance depends on water quality as it may induce the emitter clogging. In the Tohaku National Irrigation Project, in western Japan, mist spray emitters are widely used for irrigation in the field and greenhouses for vegetable and orchard crops. Seven emitters of different types were evaluated for the variation in their discharge rate without filter. The statistical analysis of mean discharge ratio and the coefficient of variation of the performance of emitters along a lateral line in the field indicated that the mist spray emitters had the best performance for irrigation in Tohaku area, particularly the new emitters or 1-year old emitters. The results suggest that after using the emitter line for two irrigation seasons it should either be replaced in the third season or washed carefully if further used.     

浑水特性与水温对滴头抗堵塞性能的影响

为探明迷宫流道滴头发生物理堵塞的成因及过程,采用分段粒径浑水周期间歇滴灌的试验方法,分别对含沙量、泥沙颗粒粒径和水温对滴头堵塞发生过程的影响进行研究。结果表明:对于泥沙颗粒粒径小于0.1 mm的浑水滴灌而言,粒径越小越易造成滴头堵塞,且其堵塞程度随浑水含沙量的升高而急剧升高;存在造成滴头堵塞的敏感粒径范围,在夏季灌溉时小于0.031 mm的粒径为易堵塞粒径;水温是影响滴头堵塞的重要因素,水温越高滴头的抗物理堵塞性能越好。     

Surface topographic characteristics of suspended particulates in reclaimed wastewater and effects on clogging in labyrinth drip irrigation emitters

Drip irrigation is the most effective and reliable method for reclaimed wastewater irrigation. Emitter clogging is the major problem for extending the drip irrigation technology. The existence of suspended particulates in irrigation water is the main reason for the emitter clogging. However, the reclaimed wastewater quality is extremely complex, and there is a series of physical, chemical, and biological reactions between suspended particulates and other materials contained such as microorganisms, which make the characteristics of suspended particulates in reclaimed wastewater complicated. In this paper, two types of widely used wastewaters treated with fluidized-bed reactor (FBR) and biological aerated filter (BAF) processes respectively were selected. The scanning electron microscope (SEM) technology and fractal theory were used to quantitatively describe the characteristics of the surface topography of suspended particulates. The results showed that the suspended particulates in two reclaimed wastewater were flocculent and porous. The pore system mainly consisted of solid suspended particulates, and most areas between the particulates were filled with microbes and extracellular polymers (EPS). The complex structure of biofilms was formed. That the biofilms grew and detached in irrigation system and deposited continuously at the inlet and outlet of labyrinth path was the major reason for the emitter clogging. The surface topography of suspended particulates in both reclaimed wastewaters showed fractal and multifractal characteristics, and the fractal dimension could not characterize the local and microsingularity of particulates but multifractal dimension could. The uniformity of the distribution of sediment pores increased with the size. Comparatively, the uniformity of suspended particulates in reclaimed wastewater treated by FBR was lower. With operation of reclaimed wastewater irrigation system, the average discharge of emitters decreased continuously with obvious fluctuations. The clogging degree of emitters was low during the first 256 h, and the clogging degree of the two types of reclaimed water was similar. But then, the degree of clogging increased greatly, and the FBR treatment on the emitters discharge were more obvious than BAF. It was closely related to the growth, detachments and sediment of biofilms in the irrigation system. Hence, using the reclaimed wastewater treated by BAF for drip irrigation is more suitable.     

Influence of fine particle size and concentration on the clogging of labyrinth emitters

The evolution of drip emitter clogging with labyrinth channel was investigated experimentally to study the fine particle size and concentration effects in the irrigation water. Short-term clogging tests were performed using muddy water containing particles with 8 different sizes (all less than 0.1 mm). The particles used in this study were composed of fine sands, slit and clay. Afterwards, verification tests were conducted to prove the results obtained from short-term clogging tests. The impacts of particle size and particle concentration in muddy water on emitter clogging were analyzed by means of calculating the mean discharge and the Christiansen uniformity coefficient. The results showed that for particles that were smaller than 0.1 mm in diameter, sediment concentration significantly affected clogging. The clogging level of emitters increased with raising the concentration. Especially when the sediment concentration was higher than 1.25 g/L, the impacts became remarkable. On the other hand, the sensitive sediment particle range that could get emitters clogged easily was found. In this study, the sensitive particle range were D6 (0.038–0.034 mm) and D7 (0.034–0.031 mm) The results aim to help in improving drip irrigation methods using water with high sediment concentration and providing experimental data for optimization design of emitter channel.     

化学离子对再生水滴灌灌水器堵塞的影响

为探究不同化学离子(Fe2+、Ca2+)对滴灌灌水器堵塞发生过程的影响及堵塞机制,以二级处理再生水和地下水为水源,选取标称流量为1.1~1.8L/h的4种灌水器进行灌水器堵塞试验。试验中每天灌水12h,定期测定灌水器流量,试验结束后测定灌水器生物膜干重及胞外多聚物EPS重量。结果表明:化学离子改变生物膜的形成过程和结构稳定性,增加了堵塞物质的形成和生长速度;向地下水加入Fe2+增大灌水器发生生物化学堵塞的风险,地下水同时加入Fe2+、Ca2+,灌水器以化学堵塞为主;再生水加入Ca2+提高了灌水器化学堵塞风险,加入Fe2+或同时加入Fe2+、Ca2+增加了发生生物化学堵塞的风险。     

含沙水滴灌条件下灌水器抗堵塞试验研究

对4种不同滴灌管(带)在含沙水滴灌条件下灌水器的出流量变化及淤积堵塞情况进行了田间试验研究。经过多次灌水试验,结果表明,4种滴灌管(带)灌水器出流量均随灌水次数的增加和距离毛管进水口长度的增加呈减小趋势,最后完全堵塞的灌水器均发生在毛管的末端;在相同水质和灌水压力下,大流量灌水器抗堵塞性能较好,即大流道灌水器的抗堵塞性能优于小流道灌水器;随着灌水次数的增加在滴灌管(带)的管腔内有细小泥沙淤积,小流量滴灌管(带)在70～80 m处泥沙淤积量骤然增加,大流量滴灌管(带)在80～90 m处骤然增加,管内泥沙的沉积大大增加了灌水器的堵塞几率,因此定期对滴灌带进行冲洗可以有效减小堵塞。     

Trickle irrigation: Emitter clogging and other flow problems

Trickle irrigation experiments with Colorado River water on citrus trees in southwestern Arizona were conducted to develop water treatment methods for preventing emitter clogging and maintaining long-term operation of the system under actual field conditions. Eight trickle emitter systems in combination with six water treatments were evaluated during a comprehensive 4-year study. Emitter clogging was related to emitter design and to degree of filtration treatments of Colorado River water. If not positioned upright, emitters designed with moving parts were more susceptible to malfunctioning and clogging. Emitters with flexible membranes either failed after a few months of use with chemically conditioned water or showed serious deterioration and decomposition after 4 years. Five of the eight emitter systems required sand and screen (200 mesh) filtration plus chemically conditioned water to keep suspended materials from physically clogging the emitter. However, two emitter systems with the same design but different flow rates have continued to operate with only screen (50 mesh) filtration. For emitters unaffected by material deterioration, the water conditioned continuously with acid alone was just as effective as a combination of continuous or intermittent chlorine and acid treatments in reducing emitter clogging. The dominant causes of emitter clogging and flow reduction were physical particles; next, and minor in comparison, was the combined development of biological and chemical deposits.     

Effect of filter, emitter and location on clogging when using effluents

The effect on emitter clogging of four filtration systems (sand, screen, disc and a combination of screen and disc filters) and six emitter types placed in laterals 87 m long, using two different effluents with low suspended solid levels from a wastewater treatment plant, was studied for 1000 h. Four of the emitters were molded and welded into dripline wall, two of them being pressure-compensated and the other two non-pressure-compensated. The other two emitters, both pressure-compensated, were inserted into thick wall. Emitter clogging was affected mainly by emitter type, location along the lateral and the interaction between these two factors. Differences among emitters with larger clogging were only observed at the end of dripline. Two molded and welded emitters showed the worst performance: one non-pressure-compensated with the lowest passage section, and the other pressure-compensated that, after 800 h working at higher dripline flow and particle load, experienced an important decrease in flow rate. Only with the effluent that had a higher number of particles, did the filter and the interaction of filter and emitter location have a significant effect. Emitters placed after screen and sand filters showed the largest flow rates at the lateral ending, even though only sand filtration significantly reduced turbidity and suspended solids. Emitters protected by a disc filter experienced the largest flow rate reductions.     

滴灌毛管泥沙分布与灌水器堵塞试验研究

为探明滴灌毛管泥沙分布及灌水器堵塞规律,通过对8种粒径的泥沙进行短周期浑水试验和堵塞试验,研究了泥沙在不同毛管分布和灌水器堵塞规律。结果表明:泥沙在不同毛管中淤积量的不均匀程度可以通过毛管淤积分布系数来衡量;泥沙在支管中的运动状态对进入毛管中的泥沙量影响很大,通过计算支管泥沙悬浮指数,可确定泥沙在不同毛管中的淤积状况,悬浮指数越大,泥沙在各毛管淤积量越不均匀,突变发生在悬浮指数等于0.325处;大颗粒泥沙在毛管底部以推移质形式运动,是造成灌水器突然堵塞的直接原因,且主要出现在第1、2条毛管中,而细小颗粒的絮凝作用是造成灌水器逐渐堵塞的主要原因。     

新型微压滴灌灌水器水力性能试验研究

在试验室内,对研制的微压灌水器进行了水力性能试验。试验结果表明:在微压(2~5 m)工作时,新型微压滴灌灌水器在自由出流状态下的出流规律符合设计要求;在工作压力范围内,微压灌水器的流量稳定,变化小;新型微压滴灌灌水器在连续工作1周后流量略有变化,出流更加均匀;微压滴灌灌水器抗堵塞能力强,性能可靠。     

滴灌系统灌水器堵塞及防堵措施研究进展

滴灌系统灌水器堵塞一直是制约滴灌技术应用推广的关键问题,为探索预防、解决该问题的方法,首先,从灌溉水源、灌水器流道结构、滴灌系统运行方式等方面总结了灌水器堵塞类型,论述了该领域的研究成果;其次,通过控制水源处理、配置合适过滤设备、改进灌水器流道、选用较优系统运行方案等方式提高灌水器抗堵塞性能,提出进一步研究发展灌水器堵塞防治新技术;最后,讨论了目前研究中存在的问题及下一步研究建议,为更好地防治灌水器堵塞问题提供新思路。      

温室水肥滴灌系统迷宫式灌水器堵塞试验

为探明温室滴灌灌水器堵塞的影响因素及机理,研究了灌水量和施肥量对灌水器堵塞的影响,并利用场发射扫描电镜分析了灌水器内的堵塞物质。结果表明,灌水器平均流量随着灌水量和施肥量的增加呈下降趋势,下降幅度在1.51%~14.16%之间。方差分析表明施肥量对灌水器平均流量的影响达到极显著水平(P0.01)。解剖灌水器后发现堵塞物质多沉积在流道前部。堵塞物质主要由生料带残渣、微小沙粒和白色粉末状化学沉淀物组成,其中白色粉末主要由钙、镁、碳、氧、磷元素等组成。说明本试验中灌水器堵塞主要是由物理堵塞和化学堵塞共同作用引起的。     

常压灌水器在低压条件下水力性能试验研究

鉴于目前国内低压滴灌系统中的滴灌带(管)基本沿用常压滴灌下使用的滴灌带(管),对常压滴灌系统中使用较多的国内6种单翼迷宫和内镶片式滴灌带在低压下的水力性能进行了试验研究,试验结果表明,在2~8 m和6~14 m水头压力范围拟合的流量与压力关系式不相同,在2~8 m水头压力范围的流态指数明显高于在6~14 m水头压力范围的流态指数。在较低压力下测定灌水器的制造偏差时,相比额定压力下所测定的结果表现出增大的趋势,即由于灌水器制造工艺和材料配方引起的制造偏差,在工作压力较低时表现的更为明显。     

Effects of average velocity on the growth and surface topography of biofilms attached to the reclaimed wastewater drip irrigation system laterals

Emitter clogging, a phenomenon commonly seen in reclaimed wastewater drip irrigation systems, is a severe obstacle to the wide applications and popularization of the irrigation technology. Some experiments showed that the emitter clogging was tightly related to biofilms formation attached to the irrigation system. In this paper, two types of wastewaters reclaimed respectively by fluidized-bed reactor (FBR) process and biological aerated filter (BAF) process were chosen as the experiment objects and then the effects of the average velocity on the growth and topography of biofilms attached to the irrigation laterals were studied. The parameters of biofilms reached their maximal values at a critical velocity of 0.45 m/s. The formation of biofilms was primarily controlled by the transport of the nutrients and suspended particles within the laterals when the average velocity is below the critical velocity, whereas it was primarily controlled by the hydraulic shear force when above the critical velocity. The main mechanism for emitter clogging was that the biofilms detached from laterals accumulated and grew at the inlets and outlets of emitters. A similar variation pattern was observed for both reclaimed wastewaters. However, the growth of biofilms for BAF process was more affected by the shear force than that for FBR process, since the nutrients and suspended particles for BAF were larger than those for FBR.     

浑水泥沙粒径与含沙量对迷宫流道堵塞的影响

为客观评价浑水中泥沙特性对滴头流道堵塞的影响以及合理选择滴灌水质处理方法,采用L9（34）的正交试验设计方法,进行了浑水间歇灌水测试,并提出了以滴头平均相对流量和灌水均匀度系数作为基本参数的滴头堵塞程度综合评价方法,比较分析了压力、含沙量以及泥沙粒径等变化对滴头堵塞比例和堵塞程度的影响规律.研究结果表明：对于粒径小于0.1 mm的泥沙颗粒,工作压力对流道堵塞的影响非常显著,其次为泥沙粒径;滴头堵塞程度的大小是由粒径、含沙量、工作压力三者相互耦合作用引起的,且相互之间不存在单调相关关系.在实际灌水过程中,当灌溉水中含有较多小于0.1 mm的泥沙颗粒时,应尽量滤除粒径小于0.048 mm的颗粒,并可加入分散剂,阻止细小黏粒的团聚絮凝作用,以提高滴头抗堵塞能力.     

Biofilm development in micro-irrigation emitters for wastewater reuse

Laboratory experiments were carried out to investigate bioclogging on three types of online emitters using synthetic wastewater filtered at 10 μm (COD = 200 mg L^?1). The three types of emitters were as follows: non-pressure-compensating emitters delivering 2 L h^?1 (NPC2), non-pressure-compensating emitters delivering 4 L h^?1 (NPC4) and pressure-compensating emitters delivering 2.2 L h^?1 (PC). They were plugged on two parallel pipe diameters (16 and 20 mm). Emitter performance was followed by flow rate measurements. The results showed that PC emitters seemed to be more sensitive to clogging than NPC emitters. Biofilm was observed mainly on NPC flow paths and PC membranes; its presence was also confirmed by the assessment of different water quality parameters such as total organic carbon and pH. Experimental results compared with a model designed with computational fluid dynamics Software (ANSYS Fluent^®) showed relations between biofilm development and velocity distribution on NPC flow paths. Finally, pipe diameter also appeared to be a parameter inducing emitter clogging.     

Preliminary surface topographical characteristics of biofilms attached on drip irrigation emitters using reclaimed water

Drip irrigation is the most effective and reliable method for reclaimed water irrigation. Emitter clogging is the bottleneck to restrain the application and popularization of reclaimed water drip irrigation technology, and some researchers have reported that this was tightly related to the formation of biofilms in the irrigation system. We selected reclaimed water treated with cyclic activated sludge system (CASS) and four kinds of labyrinth emitters in cusp-shaped saw-tooth, rectangular straight-tooth, arc-shaped saw-tooth and arc-angular straight-tooth and studied the surface topographical characteristics of biofilms in different positions of reclaimed water drip irrigation emitters with the 3D white-light scanning interferometer (WLSI). The results showed that biofilms in different positions of units were different with each emitter while showing the largest thickness in water-side tooth-tip zone (>20 μm); the biofilm thickness in the same monitoring sites inside one unit segment gradually decreased along the flow direction, while the flow at the inlets was much larger than that at the outlets; comparing the head, middle and tail parts, the biofilm thickness at the inlet and outlet showed the largest in the tail part, followed by the middle and the head parts. This can be explained by the equilibrium relation between hydrodynamic behavior and the transportation of nutrient and particles inside the emitters. The water-side tooth-tip zone of the first unit in the last emitter was selected to monitor surface topographical characteristics of biofilms, and its biofilm thickness also could be used as the indicator for evaluating the characteristics of surface topography. These results were aimed to provide references to explain the emitter clogging mechanism of reclaimed water drip irrigation as well as its technological application and popularization.