Reclaimed water irrigation management – 1/14

Chapter 1. Introduction In order to design and manage reclaimed water systems, one must understand fundamental topics such as soils, economics, wastewater characteristics, and spatial variability of soil properties. After covering these topics, the course continues with the design approaches for reclaimed water irrigation systems. Finally, fundamental and design principles are used to evaluate reclaimed water case studies. History and definition of terms In regions where water is in short supply, wastewater reuse is becoming an important component of the water balance. Wastewater reuse accomplishes two objectives: it prevents wastewater from entering natural water bodies and it serves as a water resource for a beneficial purpose. Asano (2001) stated that it will be the greatest challenge of the 21st century. Wastewater reclamation is the treatment or processing of wastewater to make it reusable (Asano, 2001). In some regions, untreated wastewater is used as a water and fertilizer source for crops; however, the environmental and health costs are too great to allow this process to continue (Asano, 2001) Wastewater or water reuse is the beneficial use of treated water for purposes such as agricultural irrigation (Asano, 2001). Wastewater or water recycling is the redirection of effluent into the water use scheme by a single user (Asano, 2001). Direct reuse requires a direct link from the treatment system to the reuse application. This requires a piping system from the water reclamation facility to the user (Asano, 2001). Indirect reuse is discharge of water into a receiving water body but this does not constitute planned direct reuse (Asano, 2001). Potable reuse is the use of highly treated reclaimed water to augment drinking water supplies. Non-potable reuse includes all other applications other than drinking water supplies (Gerba, 2004) The history of water reclamation began with sewage farms in Europe in the mid 1800’s. Although there were sewage farms in Germany as early as 1550, large-scale sewage farms (disposal of wastewater on agricultural farms) did not become widespread until the 1800’s with the advent of flush toilets and running sewers. The stench from open sewage disposal was a huge problem in London in the 1850’s and John Snow associated a cholera outbreak with the London sewage discharge in the Thames River. Sir Edwin Chadwick came up with the saying, “the rain to the river, and the sewage to the soil,” and sewage farms were established outside London. A brief history of wastewater reclamation is given below (Gerba, 2004).

1550 Sewage farms in Germany. • 1850 Broadstreet Cholera outbreak John Snow – waterborne transmission – beginning of sewage farms in Eng. •1890 Water pollution demonstrated by Pasteur •1892 Sodium hypochlorite disinfection of water •1914 Activated sludge process demonstrated •First regulations for sewage irrigation in CA

Reclaimed water irrigation management – 2/14

Recycling and reuse of water began in Namibia, the most water stressed country in the world approximately 40 years ago and was followed by criteria and guidelines for wastewater reuse published by WHO and USEPA in the following decades (Gerba, 2004).

1965 Research on direct potable reuse, Windhoek, Namibia • 1972 Clean Water Act – U.S.A. – “fishable and swimmable” surface waters •1970 Pomona Virus Study •1977 “Title 22” California Wastewater Reclamation Criteria •1987 WHO Guidelines For Agricultural Reuse •1993 – USEPA Guidelines for Water Reuse issued Contaminants (Waller) There are three major categories of contaminants in reclaimed wastewater: biological , physical and chemical. Biological organisms and organic matter are removed by microbiological and oxidation (chlorine) processes. Physical contaminants are removed settling and filtration, and chemical contaminants may be removed by air stripping, ion exchange, activated carbon and others (table 1-1). Table 1-1. Wastewater reclamation treatment processes (Gerba, 2004). Primary treatment Solid/liquid separation

Sedimentation Gravity sedimentation of particulate matter Filtration Particle removal by passing water through sand or other

porous medium Secondary, biological Treatment Aerobic biological treatment Biological metabolism of organic matter Oxidation pond Ponds 2-3 ft. in water depth Biological nutrient removal Combination of aerobic, anoxic, anaerobic processes for

nitrogen reduction. Inactivation of pathogenic microorganisms

Advanced treatment Activated carbon Contaminants absorbed onto the surface of activated

carbon Air stripping Transfer of ammonia and other volatile constituents from

water to air Ion exchange Exchange of ions onto exchange resin Chemical coagulation and precipitation

Use of aluminum or iron salts, polyelectrolytes to promote precipitation of phosphorous

Lime treatment Use of lime to precipitate cations and metals Membrane filtration Microfiltration, nanofiltration, and ultrafiltration Reverse osmosis Membrane system to separate ions from solution

Reclaimed water irrigation management – 3/14

Permits for wastewater use are dependent on the level of treatment and the number of fecal coliform per 100 ml of a water sample (USEPA) Table 1-2. Categories of wastewater reuse. Category Process/criteria Allowed use Urban use Unrestricted Secondary, filtration, disinfection

Turbidity: ≤2 NTU, Fecal coliform: Nondetect/100 mL

Landscape irrigation; ornamental fountains; toilet flushing

Restricted access irrigation Secondary and disinfection. Fecal coliform: ≤200/100 mL

Golf courses

Agricultural irrigation Food crops Secondary, filtration, disinfection Crops consumed uncooked

Non-food crops and food crops consumed after processing

Secondary, disinfection, Fecal coliform: ≤200/100 mL

Fodder, fiber, pastures, nurseries, sod farms

Recreational use Unrestricted Secondary, filtration, disinfection,

Fecal coliform: Nondetect/100 mL

Swimming

Restricted Fecal coliform: ≤200/100 mL

Fishing, boating

Other Environmental enhancement Unrestricted urban use

requirements

Artificial wetlands, natural wetlands

Groundwater recharge

Site specific Groundwater replenishment; salt water intrusion control

Industrial reuse

Secondary and disinfection Fecal Coliform: ≤ 200/100 mL

Cooling-system make-up water, boiler feed water

Potable reuse Safe drinking water requirements Pipe to pipe supply One of the major concerns with reclaimed wastewater is the transmission of disease by the fecal-oral route. However, the allowable risk varies between countries and between uses. A comparison of microbiological quality regulations for different organizations and different uses is shown in table 1-3.

Reclaimed water irrigation management – 4/14

Table 1-3. Microbiogical quality regulations. Category Reuse Conditions Intestinal

NematodesFecal or Total Coliforms

Wastewater treatment requirements

WHO Crops likely to be eaten uncooked, sports fields, public parks

< 1/L 1,000/100 mL A series of stabilization ponds or equivalent treatment

WHO Landscape irrigation where there is public access, such as hotels

< 1/L 200/100 mL Secondary treatment followed by disinfection

Calif. Spray and surface irrigation of food crops, parks

No standard

< 2.2/100 mL Secondary treatment followed by filtraton and disinfection

WHO Irrigation of cereal crops, fodder, pasture, and trees

< 1/L No standard Stabilization ponds with 8-10 day retention or equivalent removal

Calif. Irrigation of pasture No standard

23/100 mL Secondary treatment followed by disinfection

Soils (Waller) In order to understand irrigation design, a fundamental knowledge of soils is required. One of the most important parameters is the volume of water that the soil can hold, which is available to the plant between irrigation events. This volume is defined by the field capacity (figure 1-1) and permanent wilting point of the soil. Other important topics include hydraulic conductivity, infiltration rate, and soil texture.

Figure 1-1. Field capacity. Salinity (Waller) Even if disease-causing contaminants are removed from wastewater, and public health is not threatened, the soil can still be ruined by excess sodium and salinity in the water. Managing salinity by regular leaching of the soil is an important part of reclaimed water irrigation management. In addition, crop yield can be adversely affected by high salinity. Reclaimed water systems often have excess sodium, which can lead to a decrease in soil hydraulic conductivity. Excess nutrients in reclaimed water, nitrogen and phosphorous can lead to groundwater pollution. Figure 1-2. Decrease in crop yield due to salinity.

Reclaimed water irrigation management – 5/14

Vertical salinity and nutrient models (Waller) Soil salinization can easily happen within one growing season. However, it may not be convenient for farmers to leach salts below the root zone by applying excess water during the growing season, if water is in limited supply. A salt balance can be constructed in which it is possible to calculate the expected salinity over time. A simple mass balance is presented with which water, nutrients, and salinity are modeled in the vertical direction. This model is given to the students in an Excel/VBA program (figure 1-3).

Figure 1-3. Excel/VBA model of water and salinity in soil. Horizontal spatial variation, salinity and yield (Waller). Soil has spatially varying properties such as hydraulic conductivity and porosity in the horizontal plane. This leads to a nonuniform distrbution of salinity and yield in the field (figure 1-4). In this section, fundamentals of spatial variation statistics are presented, and then students are instructed how to use a spatially variable model in Excel/VBA (figure 1-5). This model is used by the students to estimate the salinity and yield variation in a field for different irrigation systems.

Reclaimed water irrigation management – 6/14

Figure 1-4. ECe and leached depth for AW = 50 and CV = 0.2. ECe is the upper line.

Figure 1-5. Excel/VBA model of spatially varying yield and salinity.

0.00

2.00

4.00

6.00

8.00

10.00

12.0014.00

16.0018.00

0 10 20 30 40

Distance (m)

ECe

(dS/

m) a

nd L

each

ed (c

m)

Reclaimed water irrigation management – 7/14

Irrigation economics (Waller) Although irrigation systems are not generally designed according to economic criteria other than minimizing the cost of the parts, irrigation designs should consider all costs and benefits,

including water cost, power cost, labor, and expected yield. In this section, fundamentals of engineering economics are used to evaluate irrigation systems design. A second question, with respect to economics is the optimal depth of water to apply to the field. This is a function of the value of the yield and cost of the water. The relationship between yield and depth applied is quantified with crop water production functions (figure 1-6).

Figure 1-6. Yield vs. applied water for cotton (Grimes and El-Zik). Overview of reclaimed water use in Jordan (Al-Ghazawi) Jordan emphasizes development of reclaimed water with new reclaimed water treatment plants in most major cities and reclaimed water use in nearly all cities. Reclaimed water is one part of the total water balance in Jordan, which also includes rainwater and groundwater. A summary of volumes and areas irrigated by different water sources is given in this lecture. Reclaimed wastewater treatment (Yitayew)

The steps required for producing reclaimed water are reviewed, especially as they pertain to the suitability of reclaimed water for irrigation. Tertiary treatment is normally required before use of reclaimed water for irrigation of urban landscapes. However, alternative treatment methods that are increasing in popularity, such as wetlands (figure 1-7) and soil aquifer treatment systems, may, in fact, provide better water treatment. Figure 1-7. Cattail and bulrush (shallow) and open water zones. Courtesy of Elizabeth Willott.

0

200

400

600

800

1000

1200

1400

0 20 40 60 80 100 120

Applied water and ET (cm)

Lin

t yie

ld (k

g/ha

)

ET Applied water

Reclaimed water irrigation management – 8/14

Crop water requirement (Yitayew) Concepts such as reference evapotranspiration (figure 1-8), crop coefficients and expected evapotranspiration throughout the growing season are reviewed. Probably the most important measurement for irrigation systems design is the crop water evapotranspiration requirement. This determines the size of the pump and the flow rate of water delivered to the farm. If these are undersized, then the farmer is disappointed, to say the least. Rules of thumb can be used in an area in order to quickly estimatewater and power requirements. In addition, models of evapotranspiration that are used in agricultural weather stations are briefly reviewed.

Figure 1-8. Transpiration and evapotranspiration. Courtesy of Don Slack. Water source and site evaluation (Yitayew) Procedures must be established for monitoring and maintaining reclaimed water irrigation systems. Sampling schemes and wastewater analysis procedures have been established by governments and organizations that are intended to ensure acceptable water quality. High salinity water leads to the need for greater leaching and selection of salt tolerant crops may be necessary. Tables are presented that list the salt tolerance of a range of crops to aid in selection and that list acceptable ranges of salinity and sodicity in reclaimed water. The criteria for use of reclaimed water can be different than for other water sources. The quality of the water will determine the permissible level of human contact. Soils that may be susceptible to sodicity problems, regions where groundwater pollution is likely, or fields in which surface water pollution may occur are likely to be unacceptable, if the water treatment level is not high. The loading rate of the reclaimed water should be designed such that nutrients in the reclaimed water match that of the crop requirement. The infiltration rate of the soil should be quantified

Soil Surface

Evapotranspiration Transpiration

Reclaimed water irrigation management – 9/14

with a series of infiltration tests in order to select and design the irrigation system. A series of pits and soil cores should be excavated in order to assess the soil water holding capacity and soil chemical characteristics throughout the farm. The water supply must be balanced with the water requirements of the land. Students are given problems that ask them to assess the required area of land for given reclaimed water sources in Jordan. Management of salinity and sodicity (Yitayew) Criteria have been developed for the leaching requirement, based on the irrigation water salinity and the crop tolerance to salinity. Tables, figures, and equations for calculating the leaching requirement are presented. Equations and measurement techniques that are used to quantify the salinity and sodicity hazard are presented. Finally, tables and figures are presented, which quantify the salinity tolerance of various crops. Irrigation system design for reclaimed water (Yitayew) There is no such thing as a “best” irrigation system. The selection of the best type of irrigation system depends on many factors: soils, crops, water cost, water source, water quality, and the farmer’s ability to manage the system. This class reviews design procedures for some of the more popular irrigation systems, with a major focus on salinity management and water quality aspects of reclaimed water systems. This section begins with a brief review of pipe hydraulics, pumps, and canal flow, and irrigation scheduling (depth of water applied during each irrigation event and number of days between irrigation events). Next, design procedures for surface irrigation of agricultural crops (figure 1-9), urban sprinkler irrigation of turf (figure 1-10), subsurface drip irrigation applications for agricultural crops and effluent disposal (figure 1-11), and low head gravity bubbler systems for agriculture are reviewed. Specific water quality problems associated with wastewater use in drip irrigation systems are reviewed. Expected distribution of salts for each of these systems (figure 1-12) and the advantages and disadvantages of each system for application of high salinity water are reviewed. Finally, design and management criteria to minimize leaching of nutrients and other contaminants to the ground water are reviewed. Basin wide evaluation of salinity with recycled water systems (Al-Ghazawi /Waller) A continuous process of recycling water with no flushing of water out of the basin can lead to the eventual buildup of salts in the basin, most likely in the groundwater. Principles for assessing the basin-wide salinity hazard associated with recycling water are reviewed.

Reclaimed water irrigation management – 10/14

Figure 1-9. Furrow irrigation system. Courtesy of Bert Clemmens. USDA-ARS

Figure 1-10. Sprinkler handlines. Courtesy of NRCS.

Reclaimed water irrigation management – 11/14

Figure 1-11. Drip irrigation system with polyethylene turbing on soil surface. Courtesy of NRCS.

Figure 1-12. Salinity profiles with different irrigation systems. Courtesy of Glenn Hoffman.

Reclaimed water irrigation management – 12/14

Case studies (Al-Ghazawi/Waller) The decision making process in selecting reclaimed water irrigation applications must incorporate all of the topics covered in the first part of this course. Sometimes, unexpected constraints, such as politics, ultimately determine the final use of reclaimed water. Several case studies will be used to demonstrate the decision-making and design process for reclaimed water allocation as well as the costs and benefits of reclaimed water use. Urban systems

1. Use of reclaimed water in Tucson, Arizona, USA (figure 1-13) for irrigation of sweet sorghum as a biofuel crop or irrigation of golf courses – which is a better use? (Waller). Includes discussion of criteria for reclaimed water systems design in urban areas.

2. Use of reclaimed water for landscape irrigation or industry in Aqaba, Jordan. (Waller). Includes discussion of criteria for reclaimed water systems design in urban areas.

Agricultural systems 3. Reclaimed water demonstration project in at JUST (Al-Ghazawi). 4. Minimally treated wastewater application to fields in Jordan (Al-Ghazawi). 5. Al-Samra wastewater treatment plant and allocation of reclaimed water (Al-Ghazawi). 6. Reclaimed water project in Wadi Musa (Al-Ghazawi). 7. Use of alternate year cropping strategies to take advantage of leaching by rainwater in

alternate years. (Al-Ghazawi)

Figure 1-13. The Tucson reclaimed water irrigation pipe network supply system.

Reclaimed water irrigation management – 13/14

Why worry about salinity? In saline soils, osmotic potential becomes very negative and holds the water in the soil, resisting the movement of water toward plant roots (figure 1-14).

Figure 1-14. Water held by salts resists plant uptake. Courtesy of Glenn Hoffman. Unless irrigation depth is increased beyond the evapotranspiration so that water leaches below the root zone, salinity builds up in the soil. Without adequate drainage, even excess irrigation cannot leach salts from the root zone. Adequate drainage occurs if the water table is at least 1 to 2 m below the ground surface. If the water table is near the soil surface, then it can be lowered by the installation of subsurface drains. These drains allow leaching and remove water and salt from the root zone (figure 1-15).

Figure 1-15. Salinity removal by subsurface drains. Courtesy of Glenn Hoffman.

Salt attracts water by osmotic potential

Reclaimed water irrigation management – 14/14

Many regions of the Western United States have salt-affected soils (figure 1-16). The Natural Resource Conservation Service encouraged the installation of subsurface drains in irrigated areas by cost sharing with farmers (the Federal Government paid for a significant portion of the cost of drainage). However, in many parts of the world, irrigation systems were installed in areas with high water tables, and no subsurface drains were installed. One example of the importance of salinity management is the drained Imperial Valley in the United States contrasted with the same valley in Mexico just south of the border (figure 1-33) which is undrained and has become salinized and unproductive. (figure 1-17).

Figure 1-16. Salt-affected soils in the United States. Courtesy of Glenn Hoffman.

Figure 1-17. The Imperial Valley in California and Mexico (the line in the white sand is the Imperial Canal). Courtesy of Glenn Hoffman.

Most of the large irrigation projects in world history have failed due to soil salinization, the exception being the Nile River Valley which has operated for the last several thousand years. In fact, it is quite alarming that in this time of growing population and urbanization of fertile alluvial land, many of the world’s agricultural soils are becoming salinized and unproductive. According to the FAO, approximately 3 ha per minute are lost to salinization in the world, and 80 million ha (the area of Pakistan) have already been lost to soil salinization.