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 nonpressure-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.
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 lm); 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.
The depth of the flow path of a drip irrigation emitter can affect the anti-clogging ability of a drip irrigation system by changing the flow velocity distribution and material transportation process. In order to evaluate these effects, in this paper a drip irrigation experiment using reclaimed water was performed, and four types of emitters with four flow path depths were chosen for the experiment. The dynamic outflow changes of the emitters were tested with constant intervals and the surface topographical characteristics of biofilms at the inlets and outlets of emitters and the inner lateral walls were tested with the 3D-WLSI (3D white-light scanning interferometer). Thus, the effect of flow path depth on emitter clogging was analysed. The results showed that emitter clogging with different degrees in the 204 hrs was observed. The discharge ratio variation (Dra) and coefficient of uniformity (CU) of emitters all slightly decreased with fluctuant changes. Moreover, clogged emitters were more likely to occur at the end part of the lateral, which revealed obvious difference among emitters with different flow path depths. The average thickness (S d ) and relative average thickness (RS d ) of biofilms increased with deeper flow path, while surface topographical characteristics of biofilms varied from smooth to rough. On the other hand, the average thickness and relative thickness of the biofilms at different positions of the lateral represented the order as:This was because the flow velocity decreased from the head to the end part of the lateral. Higher flow velocity resulted in limited nutrient supply and slower microbial metabolism, as well as higher turbulence intensity and hydraulic shear stress, which led to the easier detachment of biofilms. In contrast, the lower flow velocity and turbulence could result in the accumulation of biofilms and more serious clogging in the end part. Moreover, the average biofilm thickness at the emitter inlet closest to the end part of the lateral could be selected as a suitable site for monitoring emitter clogging and biofilm growth characteristics. On the other hand, the appropriate range of flow path depths for drip irrigation emitters using reclaimed water was 0.70-0.75 mm, which will provide the reference for exploring the emitter clogging mechanism of reclaimed water drip irrigation and developing efficient clogging control strategies.
As electricity plays a paramount role in modern life, the electric power outage is always considered to be a serious problem. For this purpose, our research focuses on improving the efficiency of water turbine. By studying the effects of the number and curvature of turbine blades and stimulating water faucet, the water turbine is expected to effectively boost the rotation under non-immersive condition. The goal of the study is to improve the blade design for higher efficiency of the turbine. This project presents the research of performance on drag based water turbine. The water turbine, whose whole structure is exposed in the air, in the research is an alternative for conventional immersed water turbine. The size of the water turbine is relatively small compared with industry size. Incoming water can be from any direction. The water turbine displays certain advantageous perspectives. Following the past experiments about this device, a myriad of developments has made over years. The blades of drag based water turbine have been tested with numerous combinations and permutations; thus, the effective choices of blade curvature decided in the research are one-quarter of a circle, one-third of a circle and half a circle, with the arc lengths and thicknesses to be the same. Besides, the number of blades in different experiments are 2, 3, 4 respectively. The incoming flow rate is expected to be constant, even though it fluctuates between 5.45 LPM and 5.95 LPM because of limited experiment equipment. Effects of blade number and curvature are examined, and corresponding conclusions are made.
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