Irrigation With Reclaimed Municipal Wastewater - A Guidance Manual

G.Stuart Pettygrove

• Publisher: CRC Press
• Year: 2018
• Print ISBN:
  9781315894805
• eBook ISBN:
  9781351090803
• Topic: Technology & Engineering
• Subtopic: Environmental Management
• Index: Technology & Engineering

Irrigation with Reclaimed Municipal Wastewater - A Guidance Manual is for use in the planning, design, and operation of agricultural and landscape irrigation systems using reclaimed municipal wastewater. It is written for civil and sanitary engineers, agricultural engineers, and agricultural extension workers and consultants. The manual is also useful as a reference for public works officials, municipal wastewater treatment plant operators, and students at colleges and universities. The text emphasizes irrigation for the purpose of optimizing crop production; therefore, it includes detailed instruction in the calculation of crop water requirements. Furthermore, the benefits and limitations of using reclaimed municipal wastewater for agricultural and landscape irrigation are discussed, as are other topics of special interest, including water management for salinity and sodicity control, and economic and legal aspects of reclaimed wastewater irrigation.

CHAPTER 1
INTRODUCTION: CALIFORNIA’S RECLAIMED MUNICIPAL WASTEWATER RESOURCE

G. Stuart Pettygrove, David C. Davenport and Takashi Asano

Much of California is semiarid. It not only has a poor geographic and seasonal distribution of water, but also faces increasing competitive demands for that water. Ironically, although the state's fresh water resources are abundant, not all of them are available to meet agricultural, municipal, industrial, environmental, and instream demands. Furthermore, much of the water demand occurs in areas where rainfall and local supplies are insufficient, thereby requiring importation of fresh water and wastewater reuse.

Some of the water that is reused includes treated municipal wastewater which must be applied in accordance with increasingly stringent regulations. Efforts should be continued to gainfully use this resource by irrigating selected agricultural and landscape vegetation and by supplementing freshwater supplies through return flows to streams and groundwater.

Wastewater Reuse As Part Of California's Water Balance

California's annual water balance depends on the difference between annual water inflow (mainly precipitation) and annual water outflow (irrecoverable losses, roughly two-thirds to the atmosphere and one-third to the ocean). Any water conservation action that reduces these irrecoverable losses will improve the temporal and spatial availability of water for additional beneficial uses during the year. Water is conserved within the state when potentially recoverable waters, such as return flows from agricultural and urban areas, are indeed recovered and reused. Such reuse supplements local fresh water supplies which are subject to increasing competitive demands. However, unless the wastewater would otherwise be irrecoverably lost (e.g., outflow to the ocean from coastal cities or unproductive evapotranspiration from inland areas), wastewater reel amation and reuse does not increase the state's net quantity of water available for additional uses. Substitution of reclaimed wastewater for pumped fresh water does, however, result in local water savings. In addition, wastewater reclamation has many other potential benefits including: (1) reduced costs of wastewater treatment and disposal, (2) reduction of pollutants in receiving water by diverting treated wastewater to land, and (3) delay, reduction, or elimination of fresh water facilities, thus reducing impacts on natura 1 water courses and reducing water supply costs.

The total annual quantity of water applied for agricultural, urban, and other uses in California is about 42.2 million acre-feet (MAF), most of which (35.6 MAF) is for agriculture [1]. Approximately 5.8 MAF is applied annually for urban use, of which 2.4 MAF goes to evapotranspiration and deep percolation, leaving 3.4 MAF as the average amount of urban wastewater generated annually.

Table 1-1 shows the disposition of California's 3.40 MAF of municipal wastewater.About 2. 54 MAF is irrecoverably lost from the state because it is discharged to saline waters, mainly the ocean (2.44 MAF),or evaporates (0.10 MAF), leaving only 0.86 MAF of municipal wastewaters actually reused. Of this 0.86 MAF, 0.25 is classifiedasintentional or planned,and 0.61 as incidental, reclamation (see footnotes to Table 1-1).Thus, although 18% of the 3.4 MAF of generated municipal wastewater is treated and returns to the state's freshwater system for subsequent incidental use, only 7% is put to “intentional” use.

Current Use Of Treated Municipal Wastewater

Land application of municipal wastewater is a well-established practice in California. According to a California State Department of Health Services (DOHS) survey [2], in 1977 wastewater was reclaimed at over 200 treatment plants and was applied to more than 360 locations (Table 1-2). Much of the reclaimed municipal wastewater (57%) was used for i rri gat ion of fodder, fiber, and seed crops (a use not requiring a high degree of treatment), and only 7% was used for irrigation of orchard, vine, and other food crops. An important use ( about 14%) was i rri gat ion of golf courses, other turf grass, and landscaped areas.Apart from i rri gat ion use, the survey showed that 14% of reclaimed municipal wastewater was applied for groundwater recharge, 5% for i ndustri al use, and smaller amounts were used for other purposes.

Table 1-1. Disposition of treated municipal wastewater in California, 1980 data [1].

Table 1-2. Use of reclaimed municipal wastewater in California, 1977 data [2].

Potential For Additional Irrigation With Reclaimed Municipal Wastewater

The greatest potential for reclaimed municipal wastewater contributing to water supplies, i.e., to gaining “new” water for California, is in coastal regions or elsewhere where wastewater is currently lost from the fresh water system by discharge to the ocean or other saline bodies. The potential for increased intentional reclamation and reuse is also significant in the San Joaquin and Sacramento Valleys and adjacent foothills, but in those locations, new reclamation and reuse will not contribute significantly to the state's water balance.

So far, direct potable use of reclaimed wastewater, and to some extent groundwater recharge with reclaimed wastewater, have been discouraged by public health agencies. This reflects the concern that not enough is known about some reclaimed wastewater constituents — chiefly stable trace-organic substances and viruses — to al low such use on a large scale. Crop irrigation with reclaimed wastewater at proper application rates is viewed as a more conservative and acceptable approach.

Projected use of reclaimed wastewater to the year 2010 in California for all purposes is presented in Table 1-3. The potential reuse for irrigation in three parts of the state is described in the following sections.

Southern California Coastal Areas

Data in Table 1-3 indicate that 70% of the projected statewide increase in use of reclaimed municipal and industrial wastewater between 1980 and 2010 will take place in Southern California coastal areas. Turfgrass and other landscaping are the major users of irrigation water in those regions. Turfgrass and landscape are appropriate uses of reclaimed wastewater not only because of the large potential acreage, but because of the less-stringent treatment requirements for use on some categories of landscaping compared to requirements for use on food crops. Furthermore, many of the agricultural crops grown in the area are sensitive to salts found in some Southern California wastewaters. Since a high salt content in irrigation water reduces growth and yield, turfgrasses and woody landscape plant species (which are grown for ornamental purposes rather than yield) are appropriate species to irrigate with saline municipal wastewater effluents. Furthermore, many salt-tolerant species of landscaping plants and turfgrasses are available.

Table 1-3. Present and projected annual use of reclaimed wastewater in California in 1,000's of acre-ft [1].

San Joaquin Valley Agricultural and Landscaped Areas

Overdraft of groundwater supplies, increasing energy costs for pumping, constraints on developing and transferring water from Northern California, and continued urban growth all point to a likely increase in the use of reclaimed wastewater in this area. For reasons explained above, wastewater reclamation and reuse in inland areas will not contribute “new” water to the state's water supply, but reclamation has many other potential benefits. Among these are energy savings, reduced cost of wastewater disposal, utilization of nutrients by crop and landscape pl an.ts, and delay, reduction, or el i mi nation of construction of fresh water facilities. Wastewater supplies in the San Joaquin Valley are often geographically close to large acreages of fodder, fiber, and seed crops which do not require highly treated wastewater.

Sierra Foothill Agricultural and Landscaped Areas

Foothi 11 areas draining into the Sacramento, San Joaquin, and Tulare Lake basins do not appear as separate areas in Table 1-3, but present a special opportunity for wastewater reclamation and reuse. An increase in the number of small-scale and part-time farmers and persons seeking a rural lifestyle in foothill areas is putting heavy pressure on limited water supplies. Wastewater reclamation and reuse in this environment may be less costly than treating to the degree necessary to eliminate pollution of surface waters. As in the San Joaquin Vall ey, i rri gation with reclaimed wastewater will not usually represent new water to the state but may result in cost savings and environmental benefits.

Use of The Guidance Manual

The main purpose of this manual is to assist planners and practicing engineers in understanding several aspects of the “field end” of reclaimed wastewater irrigation. Another objective is to encourage practices resulting in the economic maximum amount of harvested product (or in the case of landscaping, esthetic value) per unit of treated wastewater applied. The goal of maximum production is in contrast to the goal of wastewater disposal , but it does not conflict with the concept of slow-rate land treatment of wastewater as defined by the U.S. Environmental Protection Agency [3].

To meet these objectives, the manual presents a detailed treatment of special topics related to irrigation with reclaimed municipal wastewater rather than a “broad-brush” treatment of the entire field of irrigation system planning and design. The topics of special importance and the related chapters are summarized in the following sections.

Municipal Wastewater Characteristics and Suitability for Irrigation

One of the attractive features of irrigation with reclaimed wastewater, compared to several other non-potable and potable reuses, is that in many instances there is a less-stringent water quality requirement for irrigation, and hence a simpler and less costly treatment is required [4]. The quality of reclaimed water depends on several factors: Composition of the domestic water supply, presence of industrial waste, amount of infiltration into the sewage collection system, seasonal variations due to entry of storm water, use of water softeners, and wastewater treatment system characteristics. The impact of treatment system on water characteristics is discussed in Chapter 2 (Municipal Wastewater: Treatment and Reclaimed Water Characteristics) of this manual.

Water quality criteria for agricultural and landscape irrigation are well-established. These criteria can be used to evaluate both fresh water and reclaimed wastewater. Chapter 3 (Water Quality Criteria) and Chapter 7 (Water Management for Salinity and Sodi city Control) discuss this topic in depth.

Health and Environmental Aspects

The main goal of any wastewater treatment facility is to reduce health risks and prevent water pollution. When the wastewater effluent (reclaimed wastewater) from the facility is used for irrigation, consideration must also be given to potential hazards to farmers, farm workers, livestock, and consumers. Irrigation with reclaimed municipal wastewater has not resulted in any confirmed disease outbreaks in California, even though wastewater has been applied to land for many decades. Documented disease outbreaks in other parts of the world have always been associated with raw sewage or i rrigation with undisinfected wastewater effluent. Because treatment cannot remove all pathogens, and because wastewater may contain other constituents of health concern, a conservative approach is promoted by public agencies involved in approval of land application of wastewater.

Health concerns are related to the degree of human contact, effluent quality, and the reliability of the treatment system. For example, regulations and criteria established by the California Department of Health Services recognize higher treatment requirements for irrigation of parks, playgrounds, and food crops, than for cemeteries, golf courses, and forage crops (see Chapter 10, Health and Regulatory Considerations).

Regarding movement of pathogens into groundwater following irrigation with reclaimed wastewater, there is general agreement that soil is an effective filter of pathogens, including viruses. Prudence is recommended in the handling of treated wastewater because bacteria, viruses, and helminth (worm) eggs may remain viable in soil for periods of several months or longer ( see Chapter 14, Fate of Wastewater Constituents in Soil and Groundwater: Pathogens).

The concentration of trace elements in treated municipal wastewater is not high enough to result in short-term harmful effects, but metallic trace elements (for example, zinc, cadmium, nickel, lead, and copper) tend to accumulate in the soil. This subject is discussed in detail in Chapter 13 (Fate of Wastewater Constituents in Soil and Groundwater: Trace Elements) and Chapter 3 (Water Quality Criteria).

Recently, many potentially hazardous organic chemicals have been reported in wastewater, fresh water, and even in drinking water. However, they are usually at very low concentrations, and the environmental risks from trace organic substances associated with the use of reclaimed mun...

Table of contents

• Cover
• Title Page
• Copyright Page
• Preface
• Contents
• List of Tables and Figures
• Acknowledgments
• Contributors
• Chapter 1. Introduction: California’s Reclaimed Municipal Wastewater Resource
• Chapter 2. Municipal Wastewater: Treatment and Reclaimed Water Characteristics
• Chapter 3. Irrigation Water Quality Criteria
• Chapter 4. Site Characteristics
• Chapter 5. Crop Water Use
• Chapter 6. Crop Selection And Management
• Chapter 7. Water Management for Salinity and Sodicity Control
• Chapter 8. Irrigation System Design
• Chapter 9. On-Farm Economics of Reclaimed Wastewater Irrigation
• Chapter 10. Health and Regulatory Considerations
• Chapter 11. Legal Aspects of Irrigation With Reclaimed Wastewater in California
• Chapter 12. Fate of Wastewater Constituents in Soil And Groundwater: Nitrogen Nitrogen and Phosphorus
• Chapter 13. Fate of Wastewater Constituents in Soil and Groundwater: Trace Elements
• Chapter 14. Fate of Wastewater Constituents in Soil and Groundwater: Pathogens
• Chapter 15. Fate of Wastewater Constituents in Soil and Groundwater: Trace Organics
• Appendix A. Selected Municipal Wastewater Irrigation Projects in California
• Appendix B. California State Water Resources Control Board Division of Water Rights Petition for Change
• Appendix C. Application to Appropriate Water
• Appendix D. Memorandum of Understanding Between the Walnut Valley Water District (Walnut) and the Rowland Area County Water District (Rowland) Relating to the Terms and Conditions of Reclaimed Water Service for Existing and Future Customers Within the Rowland Service Area
• Appendix E. Sample Clauses Limiting and Indemnifying Supplier Liability
• Appendix F. Wastewater Reclamation Criteria
• Appendix G. Conversion Table
• Appendix H. Glossary
• Appendix I. Heavy Metal Contents of Selected California Soils