Agricultural wastewater mainly consists of excess water that runs off fields during surface irrigation, like furrows, border strips, basins, and flooded areas. We call this runoff “irrigation tailwater.” It’s necessary to have some tailwater runoff to ensure proper water penetration along the furrows or border strips and achieve decent irrigation efficiency.

Another source of agricultural wastewater comes from plants that process crops harvested from the fields and prepare processed food. These facilities, operated by farmers, generate a significant amount of agricultural/industrial wastewater with high concentrations of organic matter. Typically, they send this wastewater to nearby municipal treatment plants, but it’d be better if they treated it separately for reuse.

Both of these wastewater sources can be reclaimed and put to good use, usually on the farms near where the wastewater is produced. We can use the runoff from the lower end of furrows to irrigate fields at lower elevations without needing treatment or pumping. Sometimes, we collect and store this runoff in ponds for later reuse, with the help of a pump. To prevent groundwater contamination, it’s crucial to line the ponds with impermeable clay or a membrane liner. The stored water should be reused as soon as possible.

In regions with extensive agriculture like California’s Central Valley, the combined tailwater flow from numerous farms has caused significant environmental problems when discharged into surface waters, like wetlands, streams, rivers, the San Francisco Bay-Delta, and ultimately the Pacific Ocean. Now, discharging such wastewater is prohibited due to the presence of salts, nutrients, pesticides, herbicides, and other agricultural chemicals used in the fields for crop protection and yield enhancement. Collecting and treating tail water from these farms for reuse is a win-win solution for both farmers and the environment, despite the associated costs. But sometimes, short-term profit motives and lack of foresight hinder the implementation of this solution unless it’s mandated by law and supported with public funds.

The agricultural wastewater from food processing plants has a high biological oxygen demand (BOD) due to its organic content, making treatment expensive and energy-intensive. Instead of treating it, farmers can use this wastewater for soil conditioning and irrigation at appropriate agronomic rates. This application helps improve soil organic content, tilth, cation exchange capacity, moisture holding capacity, nutrient content, and productivity. However, careful application to the fields is necessary to prevent over-application, runoff, and groundwater contamination.

By Vaughn H.