Nutrients in wastewater from a phosphate fertilizer manufacturing plant stored for irrigation

Summary Wastewater from a fertilizer manufacturing plant in southern Idaho was pumped into a storage impoundment during the winter months and stored for irrigating and fertilizing agricultural crops the next summer. Analyses of water samples from the impoundment taken monthly showed the following mean annual nutrient concentrations: Total Kjeldahl Nitrogen (TKN) 94, NH ₄ ⁺ -N 61, NO ₃ ^– -N 8, total P 17, ortho P 15, and K 17 mg/L. The impoundment surface area averaged 10.5 ha with a maximum pond volume during the year of 362,000 m³. Accumulated nutrients in the impounded wastewater available for irrigating and fertilizing agricultural crops at the beginning of the growing season was TKN 30.2, NH ₄ ⁺ -N 23.2, NO₃-N 4.3, total P 9.7, and K 6.2 metric tons. Nitrification in the pond was minimal. Redox potentials were between 480 and 500 mv at all depths and locations measured in the pond in the summer and denitrification was minimal. The redox potential indicated that the water was near oxygen saturation.