Nutrient Rich Recycled Water For Sustainable Agricultural Use

About 4,220 m3/h (30,000 acre-feet per year (AF/year) or about 27-mgd) of potable water is currently used to irrigate large acreages of avocado, citrus and vineyards to the east and west of the City of Temecula, California. This is not sustainable, particularly in water-short Southern California, where recent cuts in fresh water supply from the Bay area and continued drought in the Colorado River catchment make the outlook for imported water supply that much bleaker. A recent evaluation confirmed that partially desalinated wastewater would be a cost effective means to replace potable water currently used for irrigation. The study determined that an initial desalination treatment train would produce around 1,410 m3/h (10,000 AF/year) and that this could be expanded to around 2,530 m3/h (18,000 AF/year) in the future, depending on the availability of wastewater in the region. Raw water from Metropolitan Water District of Southern California (MWD) would be used to supplement the difference needed to replace potable water use.Wastewater agencies spend considerable sums on removing nutrients (mainly nitrogen and phosphorus) from wastewater before it is returned to the environment. The agricultural sector, on the other hand, spends considerable sums on purchasing commercial fertilizers to provide most of the same nutrients for their crops. Providing a nutrient rich water source for agricultural use provides a perfect match that benefits both sectors. One potential treatment train evaluated to partially desalinate wastewater for irrigation incorporates a process arrangement that enhances the recycled water quality by allowing nutrients (nitrogen and phosphorus) from the wastewater streams to be directed to the recycled water effluent. This provides a double energy benefit for the region and reduces the carbon footprint; it reduces costs incurred by the wastewater treatment facility to remove nutrients, and reduces the need for highly energy intensive commercial fertilizers. It also provides a water source containing soluble nutrients, which could improve nutrient uptake by the plants and reduce nutrient runoff.