Water quality in drip irrigation附翻译.docx

1、Water quality in drip irrigation附翻译附录 英文翻译Water quality in drip/trickle irrigation:A review E S. Nakayama1 and D. A. Bucks2 1US Water Conservation Laboratory, 4331 East Broadway, Phoenix, AZ 85040, USA 2US Department of Agriculture, Agricultural Research Service, National Program Staff, Beltsville,

2、MD 20705, USASummary.：The intensive treatment of irrigation water re-quired for the proper operation of drip irrigation systems is presently an accepted practice. To control emitter clog-ging, we need to know the basic causes of clogging.The major clogging factors have been identified and control me

3、asures developed to prevent emitter malfunction. All emitter clogging problems, however, have not been solved primarily because of cost. The main approach to control clogging is proper water treatment. The type of treatment is based on the quality of the irrigation water, which can be classified in

4、terms of its physical, chemical and biological composition. The causes of emitter clogging and possible water treatment and preventive measures to maintain reliable operation are reviewed。Water quality and emitter clogging Drip irrigation in the mid-1960s through mid-1970s was considered an emerging

5、 technology with its application limited only to high-priced, specialty crops. Today it is used on a wide variety of crops, even those that were initially considered unprofitable for management under drip irrigation. Through careful nurturing, drip irrigation has grown into a stable and economically

6、 significant part of the farming community which has also had great impact on the irrigation and associated industries. In its infancy some difficult and seemingly unsolvable problems were encountered in operating drip/trickle systems particularly those related to the clogging of emitters. Also duri

7、ng this period, numerous inventors and entrepreneurs sold various types of non-clogging or self-cleaning emitters which were promised to solve the most serious problem of emitter plugging, but unfortunately did not adequately do so. The clogging problem, if not properly solved, would have resulted i

8、n the complete rejection or severe restriction of a promising, efficient method of irrigation and water conservation. Work on improving drip system operations went along two different directions, independent, but closely in touch with one another. One group concentrated on improving the hydraulic op

9、eration of the emitters; the other focused on studying the clogging process and from such knowledge developing procedures for alleviating the clogging problem. The main conclusion drawn from the latter type of studies is that clogging is closely related to the quality of water used in the drip syste

10、m, e.g. Bucks et al. (1977), Ford and Tucker (1975), Gilbert et al. (1981), McElhoe and Hilton (1974), Nakayama et al. (1977), Pelleg et al. (1974). Research continues to be reported on irrigation water quality, treatment, and uniformity of application (Hill et al. 1989; Kinoshita and Bui 1988; Pad-

11、 makumari and Sivanappan 1985). Water diverted from other traditional irrigation usage is presently the major source for drip irrigation, but this situation is beginning to change toward use of wastewater from cities and industries. These types of water have different water quality, and consequently

12、, different clogging parameters are involved so that different water treatment procedures must be used (Adin 1987; Adin and Elimelech 1989; Chandra- kanth et al. 1988; Gamble 1986).Causes of emitter clogging For surface-placed drip systems, inspection of the flow behavior can readily determine when

13、an emitter is operating properly. However, external examination alone can not give an accurate evaluation of the cause or causes of emitter clogging. Most clogging starts inside the emitter and it may start very slowly and progress slowly or occur almost overnight. Partial clogging is just as bad as

14、 a complete clogging because they both reduce application uniformity and alter the hydraulics of the entire system. To determine the exact nature of the clogging process, careful physical, chemical, and biological examination of the emitters and supply lines must be made. In addition, The compositio

15、n of the water used in the system must be determined. Because of the variety of factors involved, a multidisiplinary approach must be taken. To focus further on the multiple causes of emitter clogging, a table was developed, which incorporates all the information available at that time on the factor

16、s contributing to clogging (Table 1). Table 1. Physical, chemical and biological factors involved in emitter clogging (Bucks et al. 1979) The residues for a large number of emitters and tubing were examined chemically and microscopically to ascertain the components of the clogging material. Informat

17、ion on the compositions for various water sources and the related clogging problems at the respective sites were evaluated. The causes of clogging varied from location to location so that each site would require a different type of water treatment to prevent emitter clogging. Carbonate type material

18、s were prominent in samples from the south- western United States, whereas the microbial iron clog- ging substances were abundant in the samples taken in the southeastern region. The preceding factors, however, are not isolated to a specific region; instead, they have been observed within the same a

19、rea and, of course, worldwide. Suspended particles have been blamed for most emitter malfunction, but they may participate only indirectly in the clogging process. Frequently, the small, suspended particles are caught by the filament and slime by-products of bacteria and increase in size to cause em

20、itter plugging. Thus, the control of microorganisms would help greatly in alleviating emitter plugging. A surprising observation during our investigations on determining the causes of emitter clogging was the presence of large quantities of microscopic to sand-size plastic materials obstruction emit

21、ter openings. The plastic cuttings originate from the sawing of the pipes during the installation, modification or repair of the drip system. This problem can be readily corrected by cutting the pipe or tubing with specially designed cutters that do not form plastic particles. When sawing is necessa

22、ry, cleaning and flushing of the repaired sections before they are reconnected into the conveyance system can reduce plugging. Other unusual obstructions were the presence of oil and grease particles from leakage of bearing seals of well and booster pumps that are connected directly into the drip sy

23、stem. The obvious solution in this case is the proper maintenance of the lubricant seals. Also, the steel casing of wells was observed to be the source of dissolved iron, which is formed by iron-reducing bacteria. Emitter clogging prevention in such instance involves the control of the bacterial con

24、tamination or the use of plastic instead of steel casing. A brief comment should be made on the presence of snails in the drip lines. The adult snails can be readily removed from the water by simple filtration. However, their eggs or larvae can pass through filters and eventually mature to the adult

25、 form in the irrigation line and cause restricted water flow in the emitters and larger-sized tubing. Other organisms that can pass the filters and undergo similar metamorphism or increase in population or size would also create clogging problems. Root intrusion into emitter openings and tubing that

26、 restrict water flow has been observed for some types of buried tubing (Bui 1988; Kinoshita and Bui 1988). Emitter plugging in this case is not caused by irrigation water quality. Water quality evaluation and classification Based on the findings on emitter clogging and experience gained in controlli

27、ng it, investigators have derived a classification scheme that included the major factors involved in emitter clogging. This is related to irrigation water composition (Table 2). Such a classification can be used as a guide for identifying potential clogging hazard as well as for selecting and desig

28、ning water treatment systems. Little change in the classification scheme has been made since its proposal in the early 1980s. Except possibly for microbial population analysis, measurements of suspended load and chemical composition can be made by the operator or most agricultural service laboratori

29、es. The effect of fertilizer or other chemicals on the irrigation water that may create clogging problems can be tested by the operator by treating the water with the additive (Gilbert and Ford 1986). Tests can be performed in the laboratory or office, independent of the drip system, so that the sys

30、tem will not be adversely affected if any negative results are obtained. Any fertilizer or chemical additive that increases the pH (alkalinity) of the water to the point where carbonate, phosphate or hydroxide can precipitate should be avoided. Table 2. Water quality classification relative to its p

31、otential for drip emitter clogging (Bucks et al. 1979) Rolston et al. (1986) developed criteria for fertilizer application in drip systems. In their presentation, they consider the solubility of the fertilizer and the interactions of the fertilizer with the dissolve components in the irrigation wate

32、r. Since then, acidified forms of nitrogen and phosphorus have become available (urea-sulfate and urea-phosphate), which have less tendency to cause precipitation problems than earlier fertilizer formulations(Mikkelsen and Jarrell 1987). Waters with high concentrations of sulfide anions can cause ir

33、on precipitation. Iron and manganese sulfides are very insoluble even in acid solutions. The dissolved sulfide anion can also react with active chlorine when the water is chlorinated so that the effectiveness of the chlorination is reduced. Thus, the chlorination requirement of such water is higher than that of the typical non-sulfide irri