Agricultural wastewater is primarily the excess water that runs off the field at the low end of furrows, border strips, basins, and flooded areas during surface irrigation. This wastewater is also referred to as irrigation tailwater. A certain amount of tailwater runoff is necessary to ensure adequate penetration of water along the length of the furrow or border strip being irrigated and to achieve a modicum of irrigation efficiency.
Another source of agricultural wastewater is effluent from plants processing crops harvested from the field and those preparing processed food, operated by and for farmers, usually in centralized facilities. These facilities generate considerable amounts of agricultural/industrial wastewater, typically containing high concentrations of organic matter. Often, effluent from these plants is sent to a nearby municipal wastewater treatment plant. Because of the absence of sanitary wastes in the agricultural processing plants, it would be best if their effluent were handled separately and made suitable for reuse.
Both of these sources of wastewater can be reclaimed and beneficially used—usually on the farms close to the location where the wastewater is generated. Runoff from the low end of furrows can be utilized for irrigation of fields at lower elevations without treatment and without pumping. In many cases, the runoff can be captured and stored in ponds for later reuse with a pump. This water should not be allowed to infiltrate into the groundwater aquifer, because of its chemical content. The ponds should be lined with impermeable clay or a membrane liner and the water should be reused as soon as possible.
In very large agricultural regions—such as the Central Valley of California—the cumulative flow of tailwater from many farms has historically posed significant environmental problems as it was discharged to surface waters—wetlands, streams, rivers, the San Francisco Bay Delta, and the Sacramento River, culminating in San Francisco Bay and the Pacific Ocean. These discharges are now prohibited. The discharge contains salts, nutrients, pesticides, herbicides, and other agricultural chemicals from the fields where they are used for crop protection and yield maximization. The collection of tailwater from these farms and its treatment and reuse is a win-win solution for the farmers and for the environment. The costs involved are well worthwhile, when compared to the benefits to the farmers and to society as a whole. However, short-term profit and lack of vision often prevent this solution from being implemented, unless mandated by law and supported with public monies.
Agricultural wastewater from food processing plants is generally laden with organic matter (high biological oxygen demand—BOD), making treatment expensive and energy-intensive. Us of these wastewaters for soil conditioning and irrigation—at agronomic rates—can avoid the need for treatment while helping to improve soil organic content, soil tilth, soil cation exchange capacity, soil moisture holding capacity, and soil nutrient content and productivity. However, application of these wastewaters to the fields must be done with great care to avoid over-application, runoff, and groundwater contamination.
Where the most efficient irrigation methods (drip, tape, subsurface application, well-designed center-pivot, etc.) are already in use, there is no tailwater to reuse. Already, great savings have been realized over whatever practices were replaced. Where surface methods are in use, the savings in irrigation water volume can range from a few to over 50% depending on field slope, uniformity of topography, design of the fields, and manual and mechanical control mechanisms used on the farm.
In some cases, tailwater contains too much salt and nutrients to be used safely for irrigation of fields at lower elevation. Blending with lower-salinity source water can solve, or reduce this problem. In rare cases, desalination of tailwater may be an economic solution. The nutrient content of tailwater can be an asset if it is taken into account in application of commercial fertilizers where tailwater is used. Otherwise, it can lead to over-fertilization and groundwater contamination—especially with excess nitrogen.
Today’s farmers are sophisticated, much better educated than their grandparents, and tend to run their farms as businesses with a great deal of planning and agricultural engineering. For them, to put tailwater and food processing wastewater to beneficial use can be a profitable farm venture, if the long-term benefits of these practices are taken into account. They can look for opportunities to minimize or eliminate wastage of water and account for the resultant profits.
Collecting and reusing tailwater benefits the environment by avoiding discharge of salts, nutrients, and all kinds of agricultural chemicals into surface waters. The dissolved nutrients in tailwater can reduce the need for fertilization in the downstream fields where the water is reused. Tailwater reuse improves overall irrigation efficiency for surface irrigated farms. Another benefit is prevention of ponding at the low end of irrigated fields and the consequent loss of a portion of the crop.
Tailwater Return Systems
The University of California Division of Agricultural and Natural Resources published this excellent technical publication (8225), in 2007.
US Department of Agriculture Natural Resources Conservation Service’s Tailwater Recovery Standard 447-1 is a good technical resource for detailed design and construction of a farm tailwater recovery and reuse system.
A Landowner’s Manual – Managing Agricultural Irrigation Drainage Water
A guide for developing Integrated On-Farm Drainage Management systems
Developed for the State Water Resources Control Board by the Westside Resource Conservation District in conjunction with the Center for Irrigation Technology,
California State University, Fresno.
NRCS Technical Guide: NRCS provides a set of key technical resources to guide on-farm water (and other resource) management practices. These include information and recommendations about specific practices related to reuse of agricultural wastewater as they pertain to local areas. Visit the online Field Office Technical Guide (eFOTG) and click through to the map to your county for details. Once there, you can search through practices listed in Section IV of the pull-down menu in the left-hand column of the page. Here, you may also find information about financial support that may be available for implementing these practices. In addition to practice-specific assistance, the eFOTG provides key data to help growers in resource management decision-making, including natural resource information (Section II in the pull-down menu) about local soil (e.g. web soil survey), water, air, plant and animal resources; planning tools for developing resource management systems (Section III); and other useful tools and information.
Suncrest Nurseries is a California Institute for Rural Studies case study of a nursery utilizing tailwater ponds to clean and recycle water in the Watsonville area. Access the full report, California Water Stewards or download just the Suncrest case study.
A concise description of John Diener’s Integrated On-Farm Drainage Management system, the crops he grows, and by-products produced. John Diener’s integrated on-farm drainage management system has allowed him to reduce his irrigation water needs by 20%. This case study is one in a series produced by the California Institute for Rural Studies. A description of Diener’s solar evaporator can be found here.
Benziger Family Winery in Glen Ellen, California, employs several different practices to make efficient use of their irrigation water, including a constructed wetland to clean tailwater for re-use. This case study is one in a series produced by the California Institute for Rural Studies.
An example of dairy wastewater recycling through custom water reclamation systems at the Straus Family Creamery in Tomales, California. This video is part of the Water Stewardship video series produced by the Ecological Farming Association. The video describes Straus Family Creamery’s energy production system of methane digestion, which utilizes recycled water, and methane captured from cow manure. Correction to the case study: Straus Family Creamery is actually 500 acres, not 660 acres as stated. The 160 additional acres is Straus Home Ranch and is own by Michael Staus and his sisters.
This article describes innovative methods of addressing both drainage problems and irrigation needs on the west side of the San Joaquin Valley.
This video is part of the Water Stewardship video series produced by the Ecological Farming Association. Harley Farms Goat Dairy captures and recycles rainwater as well as water from the dairy and creamery. These efforts save 40,000 gallons of water per year and allow for the development of specialty crop production for on-farm dinners.
Content for the reuse of agricultural wastewater page was originally developed by Dr. Bahman Sheikh, a Water Recycling Consultant. Various others have since contributed content.