滴灌条件下水的硬度对滴头堵塞的影响

Effect of water hardness on emitter clogging of drip irrigation

为探明滴灌条件下水的硬度对滴头堵塞的影响规律及堵塞机理,该文选取不同硬度水源和2种滴头(内镶圆柱式、内镶贴片式)进行滴灌试验,研究滴头的流量变化和堵塞规律,并用场发射扫描电镜技术观测了滴头内堵塞物的结构及成分。结果显示:硬水滴灌条件下,2种滴头的平均相对流量随着滴灌运行时间的增加呈均匀下降趋势,且水质越硬下降越明显;硬水滴灌会造成滴头堵塞,且水质越硬堵塞程度越严重。但同一硬度水源处理下,2种滴头的平均相对流量和堵塞程度基本一致。堵塞的滴头在毛管的前1/3段、中1/3段、后1/3段都有分布。堵塞物质分析显示,Ca CO3沉淀导致的化学堵塞是滴头堵塞的主要原因。研究结果为滴灌技术在灌溉水质较硬地区的推广使用提供参考。

Hard water is used for drip irrigation in some areas of China due to precipitation and groundwater resource limitation. But it is proved that drip irrigation emitters can be clogged when using hard water for irrigation. In order to explore the influence of temporary hard water on emitter clogging and clogging mechanism in drip irrigation system, a laboratory experiment was conducted to investigate the variations of the emitter＇s average relative flow rate and the distribution of clogged emitters along the drip line and the clogging materials in the clogged emitters. The experiment started in April 2014 at the Irrigation Hydraulics Laboratory of Northwest AF University. Two kinds of emitters（internal cylindrical type and internal inserting type） were used and water hardness was set at 3 levels（0, 250 and 500 mg/L） in this experiment. Corresponding to 3 kinds of irrigation water, 3 independent and identical drip irrigation systems with cyclic water were built. Each system has 4 drip lines（2 drip tubes with internal cylindrical emitter and 2 drip tapes with internal inserting emitter）. And there were 18 emitters on each drip line. The total duration of irrigation was 35 d, with a daily application of 4 h（from 8：00 to 12：00） under working pressure of 100 kP a. Flow rates of all the emitters were measured once every 7 days using the weighting method. The clogging in the labyrinth passage was analyzed by the field emission scanning electron microscope（FESEM） after all irrigation events. The results indicated that the water hardness had a very significant influence on the level of emitter clogging. For the 2 kinds of emitters, the average relative flow rates were maintained at more than 95% of the original flow rate during whole experiment with 0 hardness water, and none of emitters was clogged; the average relative flow rates were 51.1% and 59.4% respectively for internal cylindrical emitter and internal inserting emitter with 250 mg/L hardness water, and the percentages of clogging emitter were 50% and 41.7% respectively; with 500 mg/L hardness water, the average relative flow rates were 15.4% and 19.1% and the percentages of clogging emitter were 100% and 97.2% respectively. Therefore, hard water can cause emitter clogging in drip irrigation, which manifests as the decrease of emitter flow rate. And the harder the water, the less the flow rate. But in the experiment, the average relative flow rates and the clogging percentages were nearly the same for the 2 kinds of emitters with the same water hardness. The clogged emitters were distributed along the drip line uniformly including upper 1/3, middle 1/3 and lower 1/3 segments. There was no obvious clogging distribution pattern for each part of the drip line. FESEM analysis showed that there was an adhesion layer formed by white sediment attaching on the surface of emitter flow path. The sediment was formed by crystal particles. And the crystal particles were connected very closely. Energy spectrum analysis showed that the white sediment was composed by elements O（oxygen）, Ca（calcium）, C（carbon） and very small amounts of Fe（iron）. It could be concluded that white sediment was a mixture of CaC O3 and a very small amount of other chemical precipitations. So, the main reason for emitter clogging is chemical clogging caused by CaC O3 precipitation. To maintain a high system performance, the water temporary hardness should be less than 250 mg/L at least. The results will provide a reasonable proposal and a theoretical reference to understand emitter clogging mechanism for hard water drip irrigation.