Overview | Water Savings | Applications | Additional Benefits | Resources | Case Studies
Celery using recycled water in Castroville, CA
Overview
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.
Water Savings
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.
Applications
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.
Additional Benefits
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.
Resources
Tailwater Return Systems
The University of California Division of Agricultural and Natural Resources published this excellent technical publication (8225), in 2007.
State Water Resources Control Board recommendations
The State of California entered its third year of drought in 2009. As a result, the State Water Resources Control Board, which controls water rights for agriculture and other uses, issued a notice of surface water shortage for 2009 in February. Farmers and other water rights holders were alerted that their deliveries may well be curtailed significantly. To enable farmers to reduce their need for water in a drought situation, the SWRCB provided 15 specific recommendations—along with the warning of potential curtailment of water deliveries. Second from the top of the list of 15 recommendations is improvement of water use efficiency on the farm—including reuse of tailwater.
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.
Tailwater Recovery as a Best Management Practice for Phosphorus. By Dennis Carman, P.E.
USDA-NRCS, Little Rock, Arkansas.
Case Studies
Suncrest Nurseries
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” here.
Red Rock Ranch
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
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.
Straus Family Creamery
An example of dairy wastewater recycling through custom water reclamation systems at the Straus Family Creamery in Tomales, California.
Cow Creek Watershed
The Central Valley Regional Water Quality Control Board collaborated with other watershed-based stakeholders and studied water quality improvements in a watershed as a result of control, storage, and reuse of irrigation tailwater. The highly positive results are shown dramatically in a PowerPoint presentation available at this link: Cow Creek Watershed Williamson Tailwater Pond: A Working Model For Improved Water Quality by Mike Harris, West Side Resource Conservation District.
