Wig Sci (1986) 7:205-212 Irrigation Science .3 Springer-Verlag 1986 Nutrients in Wastewater from a Phosphate Fertilizer Manufacturing Plant Stored for Irrigation J. H. Smith J. A. Bondurant', W. A. Wolleson 2 . and J. F. Cochrane 2 Snake River Conservation Research Center, USDA-ARS, Kimberly, ID 2 J. R. Simplot Co., Minerals and Chemical Division, Pocatello, ID Received February 12, 1986 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. 61, NO3–N 8, total P 17, ortho P 15, and K 17 mg/L. The impound- ment 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, NH4–N 23.2, NO,--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 my 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. With the increased use of wastewater in the United States, storage facilities have been constructed for impounding wastewater for crop land irrigation in the summer. A computer search of all available data bases did not find any published literature citations relating to nutrients contained in impounded waters for irrigating and fertilizing agricultural crops. Several published articles were found on the subject of nutrients in wastewater impoundments and eutrophic lakes where the objective was to evaluate the influence of the nutrients and provide for their removal or reduction. Pipes (1980) suggested that the subjects of disinfection (particularly virus inactivation), nitrification and denitrification, and potential health hazards from land disposal of effluents, seem to be of interest to a number of investigators. Ashton (1979) reported on algal fixation of N in a eutrophic lake receiving municipal and industrial effluents in South Africa. He estimated N fixation to be 1.13 metric tons in the lake with an area of 492 km 2 during a two month period in 1975. Others researchers have reported on nitrification in wastewater impound- 206 J. H. Smith et al, ments [Prakasam et al. (1979); Reinhard (1979); Reddy (1983); Reddy and Graetz (1981); and Shade (1979)]. Their emphasis has been mostly on nitrification in wastewater impoundments where N is unwanted and is being removed. Argaman and Miller (1979) modeled recycling systems that were designed to provide nitrification and denitrification in systems where N was being removed in waste- water treatment. Stratton (1969) developed a mathematical relationship showing that NH, volatilization from wastewater impoundments obeyed a first order reac- tion proportional to the NH,–N concentration in solution. He reported that warm eutrophic impoundments are potentially able to liberate significant quantities of gaseous NH,–N to the atmosphere by natural degasification. The objectives of this research were to measure concentrations of fertilizer nutrients in wastewater impounded from a fertilizer manufacturing plant, to deter- mine changes in concentrations of nutrients with storage, to measure inflow into storage and outflow for irrigation, and to calculate seepage and nutrient losses, with a goal of determining how much water and nutrient would be available for use in irrigating and fertilizing agricultural crops. Materials and Methods A wastewater impoundment was constructed in a hillside east of Pocatello, Idaho. 1,414 m above mean sea level. The impoundment was designed to contain approximately 106 m3 of wastewater, and its impoundment dike, bottom, and side slopes were specified to be compacted to no less than 95% of maximum soil density as determined by ASTM D698 standard Proctor Method A. The impoundment liner, 10 cm thick after compaction, was installed on the bottom and side slopes. The bentonite-polymer mixture in the liner was specified to be no less than 3.4% of the dry soil blended mixture to give a design seepage rate of less than 6 mm/day. The walls of the impoundment were covered with rip rap of crushed stone to the elevation of the spillway. A concrete inlet structure almost 11 m high with its top at the same level as the dam was built to allow pumping water into and out of the impound- ment with the filling point at about the 1,414 m elevation. Water samples were taken from the surface of the water at the four corners of the im- poundment at monthly intervals from Nov. 20, 1981 to Oct. 27, 1982. Water pH and tem- perature measurements were made on site. The water samples were taken to the laboratory and analyzed immediately for Chemical Oxygen Demand (COD), NH,*–N, NO3–N, and total Kjeldahl N (11(N). The water was then subsampled and frozen for later analyses for total and ortho P and for K. COD, Nat, and TKN analyses were according to American Public Health Assn. Inc. (1971), NO3 was determined with a specific ion electrode, P by persuifate oxidation (USEPA 1974), and K by flame photometry. Redox measurements to determine oxygen saturation in the water were made in the reservoir on May 27 and June 29, 1982, using a portable millivolt meter and probe from a small row boat with reservoir profiles from the surface to the bottom of the water taken continuously across the reservoir. Because of the almost continuous windy conditions on the reservoir, water mixing was thorough as indicated by the similar redox measurements from the surface to the bottom of the impoundment. Average monthly wind and air temperature measurements recorded by a meteorological station located on the inlet structure are reported in Table 1. Water volume pumped into the impoundment, water level, and evaporation from an evaporation pan were measured regularly. Water volume pumped from the impoundment was measured part of the time and because of problems with the water meter in the pipeline leading from the impoundment and another water source used for irrigation mixed with the impounded wastewater calculation of a water balance were not possible. Seepage losses from Nutrients in Wastewater from a Phosphate Fertilizer Manufacturing Plant 207 Table 1. Wind speed and air temperature at a wastewater reservoir near Pocatello, Idaho from September 1981 to October 1982 Average wind Days of Air temperature, °C speed, km/h record Monthly average Maximum Minimum Mean Sept, 1981 10.8 16 24.3 12.8 18.6 Oct. 14.1 23 12.6 4.7 8.7 Noy. 14.5 28 7.1 1.9 4.5 Dec. 18.4 16 3.7 - 0.8 1.5 Jan. 1982' 0 - 1.9 11.2 - 6.6 Feb. 20.8 15 1.2 - 4.8 -1.8 Mar. 20.0 29 3.6 - 0.7 1.5 April 18.5 28 8.4 - 0.5 4.0 May 14.0 31 15.5 5.0 10.3 June 12.0, 30 21.1 9.8 15.5 July 11.5 31 24.4 14.2 19.3 Aug. 11.9 19 27.6 15.8 21.7 Sept. 12.0 27 21.1 11.3 16.2 Oct. 13.8 29 10.7 3.3 7.0 January data obtained from Pocatello airport Table 2. Constituents of impounded phosphate fertilizer manufacturing wastewater at Po- catello, Idaho Sampling TKN NOs-N COD P P K pH Temp Redox date Total Ortho °C potential my mg/L 11-20-81 82 56 8 146 11.0 9,6 17 7.9 3.0 12-19-81 88 62 8 80 24.9 20.8 18 8.5 1.0 1-29-82 101 70 10 58 25.8 25.2 19 - 0.5 2-26-82 56 49 8 39 14.7 14.3 10 - 3.5 3-30-82 100 64 12 108 26.7 20.5 17 7.5 6.0 4-29-82 94 66 12 78 23.9 22.4 18 8.4 10.5 5-27-82 82 57 11 50 24.2 19.2 18 8.1 15.5 500-480 6-29-82 107 89 6 95 13.5 11.8 19 7.7 22.0 500-480 7-29-82 78 52 4 90 6.8 6.6 16 7.2 25.0 8-26-82 102 50 3 126 6.6 6.4 19 8.1 20.2 .9-29-82 116 55 4 104 14.1 12.5 18 7.9 11.0 ' T0-27-82 116 57 6 102 11.1 10.2 16 8.1 7.0 Mean 94 61 8 90 16.9 15.1 17 the reservoir were calculated from measurements of pond level made at intervals of at least one month when water was not being pumped into or out of the reservoir. Evaporation and rainfall were accounted for in calculating seepage loss. Results and Discussion Concentrations of plant nutrients and COD as well as pH, temperature of water, and redox potentials are presented in Table 2. During February rapid thawing of a 208 3. H. Smith et al. heavy snowpack occurred and the ensuing runoff exceeded the runoff diversion canal capacity and ran into the reservoir on the uphill side, diluting the normal concentrations of nutrients. Therefore the average of the January and March nutrient concentrations were used in calculating the water and nutrients contained in the impoundment and the seepage losses of nutrients for February, rather than the measured February data.