Metro - ECCV Zero Liquid Discharge Pilot Study_Application

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water applied to the crops. Adding to increased TDS concentrations are the land disturbance, fertilizer, herbicide and pesticide applications plus the leaching of salts in the soil as excess irrigation water percolates through the soil to the water table and returns to the stream system as return flows. As an example, Figure 3.1 depicts the water and salt balance for a sprinkler irrigation system typically found in the South Platte. The alluvial groundwater pumped for crop irrigation has an assumed TDS concentration of 900 mg/1. The irrigation efficiency of the agricultural sprinkler system is 85%, meaning that 85% of the water pumped is consumed through evaporation and crop consumption (evapo-transpiration or E-T) and 15% of the water returns to the water table and stream system as groundwater and surface water return flows. The crop uptake of salts is very limited and since the salts are a conservative substance and not consumed in the irrigation process, these salts are concentrated in the 15% return flow not consumed by the crops. This results in a return flow concentration of 5,900 mg/l TDS before accounting for additional TDS loading from agricultural practices and soil leaching. 15% Return Flow TDS = 5,900 mg/L plus TDS added by I fertilizers, pesticides, etc. Current Water Balance: TDS Load with Agricultural I Irrigation /) TDS - 900 mg/L I - - - Sp...inkle... I......igation Figure 3.1. Schematic of Agricultural Spri nkler Irrigation Effects on TDS Concentration. 4.0 Membrane Treatment Overview The treatment of drinking water by membrane technology is rapidly becoming more prevalent in the United States. In addition to removing TDS from brackish water supplies, membranes are being widely used to control both organic and inorganic contaminants, remove pathogens, reduce turbidity and lower concentrations of disinfection by-products. An important advantage of membrane treatment is its ability to remove several contaminants at once, allowing multiple treatment objectives to be met 7