There numeous factors affecting on clogging of emmitters as follow:

Effect of Water Quality on the Emitter Clogging of Drip Irrigation- A. Review

Ismael O. Ismael

M.Sc. Student

Article Review supervised by Prof. Dr. Akram O. Esmail

Soil & Water Department, College of Agriculture, Salahaddin University-Erbil, Kurdistan Region, Iraq.

Email: [email protected]

Abstract

The intensive treatment of irrigation water required for the proper operation of drip irrigation systems is presently an accepted practice. To control emitter clogging, we need to know the basic causes of clogging. The major clogging factors have been identified and control measures 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 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. The results of the studied indicated to the effect of chemical properties of irrigation water or clogging of emitters especially the type of ions in water or salt composition of water. The decrease in solubility of salts cause increase of clogging and the versus is true, for example in the dominate salt in CaCO3 or calcite CO3 they cause to the highest emitter clogging but if the salt in KNO3 the clogging will minimize.

Keywords: Water quality, Clogging, Drip irrigation, Salt composition.

1. Introduction

Although drip irrigation systems are based on a long working experience and have reached a high technological level, these systems are most not able to deliver all of their nominal benefit. Plugging of emitters is considered to be the largest maintenance problem with drip/trickle systems. In reality, half or complete clogging reduces emission uniformity and, as a consequence, decreases irrigation efficiency and increases the water volumes needed for crop growing. In many cases, to assure irrigated plants of the necessary water volume, it is necessary to put up with a water loss due to over irrigation(Capra and Scicolone, 1998).(1)

Over irrigation causes deep percolation and consequent disadvantages due to water and energy costs, fertilizer leaching and drainage needs(Capra and Scicolone, 1998) (1). In an analysis of papers on clogging and mitigation procedures,Nakayama and Bucks (1991) (2) established that these processes are closely related to the quality of water used; the authors also pointed out that the water quality problem will increase on account of the use of urban and industrial wastewater. The plugging of emitters can be caused by physical, chemical or biological contaminants. Physical clogging is caused by suspended inorganic particles (such as sand, silt, clay, plastics), organic materials (animal residues, snails, etc.), and microbiological debris (algae, etc.); physical materials can be combined with bacterial slimes (Bucks et al., 1979)(3).

Chemical problems are due to dissolved solids when they interact with each other to form precipitates and to the precipitation of calcium carbonate in waters rich in calcium and bicarbonates. Biological clogging is due to algae, iron slimes and sulphur slimes. The causes of clogging are different from location to location: suspended particles, and high contents of iron and hydrogen sulfide cause clogging problems in Southern Italy. Water analysis prior to system design, a preventive maintenance program and field evaluation of clogging and uniformity are strongly recommended (Nakayama and Bucks, 1991) (2).An examination of the research papers on the above mentioned topics showed that a number of problems still remain. No water quality evaluation method capable of representing potential emitter clogging has yet been developed; the causes of clogging vary from location to location and, for the same water, clogging depends on other local conditions, such as water temperature, and on emitter features. In the early 1980s,(Nakayama and Bucks, 1991) (2).

2. Water Quality

Capra and Scicolone (1998) (1) indicated to number of parameters must be con­sidered in dealing with recycled water quality. Although the nutrient content of applied water has been listed as an advan­tage of using recycled water, many of the nutrients may be salts that will influence total soluble salts (TSS), TDS, or salinity. The most desirable situation is for recycled water to have as little residual dissolved or suspended material as possible.

Recycled water dis advantages:Water quality varies greatly depending on the source of the water and the efficiency of the treatment system. Water quality can range from good to poor, depending upon its composition, and additional inputs to the management program may be re­quired to compensate for this impact.

Water quality analysis should evalu­ate the following characteristics: concen­trations of suspended solids, specific ions and pH, total soluble salts and calcula­tion of a leaching requirement, SAR, bio­logical oxygen demand (BOD), chemical oxygen demand (COD), toxic materials (particularly volatile organic compounds [VOCs]), and total or fecal coliforms (Ta­ble 4). Local regulations may also dictate additional analysis. Problems associated with each of these characteristics and their potential effects on turf manage­ment are described below by Peacock et al.,(1970) (4) as follow:

a- Suspended solids. These can accu­mulate on the surface and cause sealing of the soil. This is especially critical if the ac­cumulation includes a substantial mineral component. If the solids are organic, they may be decomposed by soil microorgan­isms if soil temperatures favor microor­ganism activity. Accumulations of materi­als in surface zones during cooler weather with subsequent decomposition during warmer weather may lead to periods of extreme oxygen depletion in the soil if (as is the usual situation) decomposition occurs at very shallow depths where the root system may be concentrated.

Another consideration is the effect of suspended solids on highly modified soils.

b- Nitrogen loading. All inorganic nitrogen is immediately available for turf uptake. If it is not taken in by the plant or used by the microbial population, it may leach. The management program will be affected if the plants are over stimulated and become soft and succulent. With organic nitrogen, as little as 20% or as much as 50% may be mineralized in the first year. This means a significant amount of nitrogen could build up and then be released during the warmest time of the year, when soil temperatures allow for unlimited microorganism activity. This makes it very difficult to control turf fertil­ity, especially after a few years of organic nitrogen accumulation.

c- Phosphorus and potassium. These nutrients do not normally pose a problem unless the recycled water is being held in a retention lake for an extended length of time. If so, phosphorus and nitrogen favor algal blooms that become a significant lake management problem. The amount of phosphorus and potassium added sel­dom exceed what the soil can assimilate and the turf requires; in fact, it is rare that the effluent can add, and that the soil can retain, adequate potassium for the annual requirement.

d- Calcium, magnesium, sodium. The major concern with calcium and magnesium is not the total amounts of these elements but their relationship to sodium content and the resultant SAR. Excess sodium displaces calcium on the soil exchange sites, causing DE flocculation of the soil structure, or soil dispersal. This can result in increased compaction, thereby limiting oxygen exchange and affecting rooting and turf vigor. When the SAR exceeds 10, a recommendation normally is made to apply calcium, usu­ally as gypsum, and to apply excess irri­gation to displace and leach the sodium. However, there are costs involved. For example, gypsum requirements and costs may be high, and there will be a require­ment for excess irrigation to leach. All of this requires labor, electricity for pump operation, and increased wear on the ir­rigation system.

e- pH and total carbonates. Bicarbon­ates and carbonates both affect the pH of the recycled water and potentially the chemical properties of the soil. These are measured in mille equivalents per liter and are a source of alkalinity that may affect the water and soil. Water quality analysis commonly reports total carbonates (bicar­bonates and carbonates) because both car­bonates affect pH levels. If the amount is significant — greater than 2.5 meq/l (150 ppm) — the pH of the soil may be affected by long-term use of recycled water. This in turn affects nutrient availability. To offset this effect, one may use acid-forming ni­trogen fertilizers, inject acid into the irri­gation water, or apply sulfur to the soil.

f- Biological oxygen demand/chemical oxygen demand (BOD/COD). These measurements are functions of the organic and mi­crobiological load in the effluent. They represent the amount of oxygen requiredfor decomposition to occur. The most accurate analysis is the COD because it represents the maximum potential oxygen requirement once the organic materi­als are deposited in the soil. Because the microorganism population in the soil is so diverse, organic materials added in the recycled water stream become an energy source for microorganisms and therefore possess an oxygen requirement for their metabolism. This can result in subtle but measurable reductions in growth under low BOD/COD concentrations. If organic loading creates a situation where the mi­croorganisms use oxygen at a greater rate than the exchange capacity of the soil, oxygen depletion and an interruption in root function may result.

g- Electrical Conductivity (EC). Salinity problems primarily manifest in three ways: osmotic effects, accumula­tions of specific ions, and their effect on soil physical conditions. The relative salinity tolerance of grasses and plants used in the landscape may cause a shift in the components as saline irrigation favors one species over another. Leaching of salts from the root zone is critical to maintaining turf under saline irrigation. The conductivity of soils can be two to ten times higher than that of the irriga­tion water. Saline irrigation requires con­stant attention to ensure that adequate leaching occurs. On sandy soils, leaching of salts is easily accomplished with ex­cess irrigation. On more heavily textured soils, larger volumes and longer irriga­tion times are required, making leaching more difficult. Also, many of these salts may become attached to the colloidal complex of the soil, making their leach­ing potential is lower and requiring more intensive irrigation.

Table(1): Recycled Water Quality Parameters That May Affect Turf Management

Parameter Analyzed

Potential Impact

Effect on Turf Management

Suspended solids

Soil sealing

Increase coring

Total-N, NH4+-N, NO-3-N, organic-N

Buildup of nitrogen; untimely availability

Control nitrogen fertility

P and K

Contaminated runoff to lakes

Control runoff; monitor soil levels

Ca, Mg, Na

High SAR; soil sealing

Increase calcium applications

pH, carbonates, bicarbonates

Increased soil pH; effect on nutrient availability

Acidify water or nitrogen sources

BOD/COD

Organic loading; depletion of soil oxygen

Increase coring; improve root growth

Conductivity (TSS, TDS)

Accumulation of salts in root zone

Leach with irrigation

B, Cl-, SO42-

Potential specific ion toxicity

Monitor and offset with fertilization

Heavy metals

Toxicity to plant roots

Monitor and precipitate with P

Toxic materials

Toxicity to plant

Monitor and leach or treat with charcoal

Total/fecal coliforms

Human exposure

Monitor and isolate

h- Heavy metals. These include cop­per, nickel, zinc, lead, chromium, mercu­ry, and arsenic. The exact levels at which these become a problem (either separately or collectively) are unknown. However, levels of heavy metals should be moni­tored periodically both in the water and in the soil. Many of these metals complex with phosphorous and other elements to make them biologically unavailable. As soil levels build, it may be necessary to increase phosphorus applications to com­plex these ions and keep them unavailable.

i- Toxic organics. Many of these are also known as volatile organic compounds (VOCs), such as toluene and xylene. They may create direct toxicity problems if present in high concentrations.

Table (2)reports the analyzed water quality factors affecting occlusion: pH, suspended solids (Ss), electrical conductivity (Ec) at 25¡C, total iron (Fe), hydrogensulphide (H2S), manganese (Mn), magnesium (Mg), calcium (Ca), bicarbonates (Bc), dissolved oxygen (DO) and the corresponding classification of hazard rating according to (Bucks et al., 1979) (3) .The tested irrigation waters can be classified, in general, as a moderate hazard for pH, severe for suspended solids, moderate for electrical conductivity and for total iron, from moderate to minor for hydrogen sulphide and manganese.The classification proposed for total iron, hydrogen sulphide and manganese is more cautious than that proposed.According to the hazard rating is, in general, severe for total iron, and severe or minor for hydrogen sulphide and manganese.(Capra and Scicolone, 1998) (1).

Bucks et al., (1979) classified the water quality depended on their effect of clogging for example in the pH (7 – 7.7). Chemical of the water medium if the manganese Mn(mg/L) water (0.04 to 1.5). While Boswell, (1909) (5) classified them to (0.02 to 0.7), It mean there is not a same classification because it affects by climatically condition, other properties of water like physical or biological.

📷

3. Measuring Salinity

Because soluble salts in a water solution will conduct an electric current, changes in electrical conductivity (EC) can be used to measure the water’s salt content in electrical resistance units (d S m-1). This EC measurement can be converted to parts per million (ppm) or milligrams per liter (mg L-1) relationships (Peacock et al 1970).

Water salinity, reported as total dissolved solids (TDS), is approximated as follows:

ECw [dSm-1] × 640 = TDS [ppm or mg L-1]

This is an approximation because the exact relationship is determined by the composition of the salt. The ions of individual elements conduct electrical current at slightly different rates.

Based on salt concentration and EC conductance, water can be classified for irrigation use as follows:

< .25 dSm-1 Low hazard

.25 – .75 dSm-1 Usable with moderate leaching

.75 – 2.25 dSm-1 Avoid use on poorly drained soils and salt-sensitive plants

> 2.25 dSm-1Not suitable for irrigation.

Sodium can com­pete with potassium for absorption by the plant, and reduced potassium uptake creates a less stress-tolerant plant because sodium does not play the same role as potassium in metabolism. The relative concentrations of sodium (Na), calcium (Ca), and magnesium (Mg) in ir­rigation water are used to calculate the sodium absorp­tion ratio (SAR), as follows:

📷

Where the values are given in mill equivalents per liter (meq L-1). A high water SAR can reduce permeability when applied to more finely textured soils, such as silts or clays, over an extended period of time. The SAR interacts with the EC to determine the suitability of ir­rigation water.

4. Water quality and emitter clogging

Nakayama and Bucks(1991) refereed to drip irrigation in the mid-1960's through mid-1970's was considered an emerging 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 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 during 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 in the complete rejection or severe restriction of a promising, efficient method of irrigation and water conservation(Nakayama and Bucks, 1991).

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 operation 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 system, (Nakayama et al. (1977) and Pelleget al. (1974). Research continues to be reported on irrigation water quality, treatment, and uniformity of application. 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, different clogging parameters are involved so that different water treatment procedures must be used(Nakayama and Bucks, 1991).

5. Effect of water quality on emitter clogging

Nakayama and Bucks (1991),refereed that for surface-placed drip systems, inspection of the flow behavior can readily determine when 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 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.

5.1. Chemical composition or chemical proportion of water.

Chemical denotes mineral precipitation, which may form when minerals solubility is low enough. Solubility of a given mineral is dependent on the water temperature, its pH, redox potential and the concentration of the mineral elements present in the water. The common elements that may clog drip emitters by precipitation and sedimentation are calcium, magnesium, iron and manganese, where calcium carbonate being the most common precipitate. Water that contain high levels of these elements, and have a pH above 7.0, might potentially cause clogging of drip emitters ( Buckset al. 1979).

Adding fertilizers to source water (fertigation) can potentially cause clogging of drip emitters due to chemical interactions and high mineral concentrations, exceeding their solubility limit. Therefore, it is advised to perform a jar test, or use an appropriate software, to determine if a specific combination of fertilizers may result in precipitation. Acid injection, to reduce irrigation water pH, can prevent chemical clogging of drip emitters.

Generally speaking, surface water carry more biological and physical clogging agents, while ground water are usually characterized by higher mineral concentration, posing a chemical clogging hazard ( Buckset al. 1979). .

5.1.1. Saturation Index Value

Analysis and water of DeMartini (1938) explained that saturation index used to predict the calcium carbonate stability of water. It indicates whether the water will precipitate, dissolve, or be in equilibrium with calcium carbonate. In 1936, Wilfred Langelier developed a method for predicting the pH at which water is saturated in calcium carbonate (called pHs). The LSI is expressed as the difference between the actual system pH and the saturation pH:

LSI = pH (measured) − pHs

For LSI > 0, water is super saturated and tends to precipitate a scale layer of CaCO3.

For LSI = 0, water is saturated (in equilibrium) with CaCO3. A scale layer of

For LSI < 0, water is under saturated and tends to dissolve solid CaCO3.

If the SI have + value it may cause to emitter clogging due to precipitation of CaCO3, then also depends on the environmental factors especially temperature.

The Langelier saturation index(LSI) is temperature sensitive. The LSI becomes more positive as the water temperature increases. This has particular implications in situations where well water is used. The temperature of the water when it first exits the well is often significantly lower than the temperature inside the building served by the well or at the laboratory where the LSI measurement is made. This increase in temperature can cause scaling, especially in cases such as hot water heaters. Conversely, systems that reduce water temperature will have less scaling. The LSI value for surface and ground water Kurdistan Region is positive (+ve), it means the management is necessary for reducing emitter clogging.

Table (3):Chemical, physical and biological factors involved in emitter clogging

(Bucks et al. 1979).

Chemical

Physical

Biological

Alkaline earth

heavy metal

cations

magnesium

iron

manganese

Inorganic materials

Sand (50-250 µm)

Silt (2-50 µm)

Clay ( 2.25 dSm-1Not suitable for irrigation.

Sodium can com­pete with potassium for absorption by the plant, and reduced potassium uptake creates a less stress-tolerant plant because sodium does not play the same role as potassium in metabolism. The relative concentrations of sodium (Na), calcium (Ca), and magnesium (Mg) in ir­rigation water are used to calculate the sodium absorp­tion ratio (SAR), as follows:

📷

Where the values are given in mill equivalents per liter (meq L-1). A high water SAR can reduce permeability when applied to more finely textured soils, such as silts or clays, over an extended period of time. The SAR interacts with the EC to determine the suitability of ir­rigation water.

4. Water quality and emitter clogging

Nakayama and Bucks(1991) refereed to drip irrigation in the mid-1960's through mid-1970's was considered an emerging 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 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 during 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 in the complete rejection or severe restriction of a promising, efficient method of irrigation and water conservation(Nakayama and Bucks, 1991).

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 operation 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 system, (Nakayama et al. (1977) and Pelleget al. (1974). Research continues to be reported on irrigation water quality, treatment, and uniformity of application. 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, different clogging parameters are involved so that different water treatment procedures must be used(Nakayama and Bucks, 1991).

5. Effect of water quality on emitter clogging

Nakayama and Bucks (1991),refereed that for surface-placed drip systems, inspection of the flow behavior can readily determine when 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 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.

5.1. Chemical composition or chemical proportion of water.

Chemical denotes mineral precipitation, which may form when minerals solubility is low enough. Solubility of a given mineral is dependent on the water temperature, its pH, redox potential and the concentration of the mineral elements present in the water. The common elements that may clog drip emitters by precipitation and sedimentation are calcium, magnesium, iron and manganese, where calcium carbonate being the most common precipitate. Water that contain high levels of these elements, and have a pH above 7.0, might potentially cause clogging of drip emitters ( Buckset al. 1979).

Adding fertilizers to source water (fertigation) can potentially cause clogging of drip emitters due to chemical interactions and high mineral concentrations, exceeding their solubility limit. Therefore, it is advised to perform a jar test, or use an appropriate software, to determine if a specific combination of fertilizers may result in precipitation. Acid injection, to reduce irrigation water pH, can prevent chemical clogging of drip emitters.

Generally speaking, surface water carry more biological and physical clogging agents, while ground water are usually characterized by higher mineral concentration, posing a chemical clogging hazard ( Buckset al. 1979). .

5.1.1. Saturation Index Value

Analysis and water of DeMartini (1938) explained that saturation index used to predict the calcium carbonate stability of water. It indicates whether the water will precipitate, dissolve, or be in equilibrium with calcium carbonate. In 1936, Wilfred Langelier developed a method for predicting the pH at which water is saturated in calcium carbonate (called pHs). The LSI is expressed as the difference between the actual system pH and the saturation pH:

LSI = pH (measured) − pHs

For LSI > 0, water is super saturated and tends to precipitate a scale layer of CaCO3.

For LSI = 0, water is saturated (in equilibrium) with CaCO3. A scale layer of

For LSI < 0, water is under saturated and tends to dissolve solid CaCO3.

If the SI have + value it may cause to emitter clogging due to precipitation of CaCO3, then also depends on the environmental factors especially temperature.

The Langelier saturation index(LSI) is temperature sensitive. The LSI becomes more positive as the water temperature increases. This has particular implications in situations where well water is used. The temperature of the water when it first exits the well is often significantly lower than the temperature inside the building served by the well or at the laboratory where the LSI measurement is made. This increase in temperature can cause scaling, especially in cases such as hot water heaters. Conversely, systems that reduce water temperature will have less scaling. The LSI value for surface and ground water Kurdistan Region is positive (+ve), it means the management is necessary for reducing emitter clogging.

Table (3):Chemical, physical and biological factors involved in emitter clogging

(Bucks et al. 1979).

Chemical

Physical

Biological

Alkaline earth

heavy metal

cations

magnesium

iron

manganese

Inorganic materials

Sand (50-250 µm)

Silt (2-50 µm)

Clay (

Hi Abdrabbo,

Ozonation followed by filtration (of precipitates) is a common technological solution for dealing with both iron and manganese. Much of the work is on drinking water, but in theory it would be effective for irrigation water as well. Cost of any treatment system can be a barrier, and ozone is no different. Just curious, what are 'severe' levels of Fe & Mn in your case?

Best,

Thomas

The methods are :

1- Pricipitation them in the form of carbonate or hydroxyl by addig chemical compounds.

2- Ozonation and infiltration.