1990-04-18_REVISION - M1977493 (4)

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BLACK & VEATO • Colorado Department of Health B&V Project 6913.007 Mr. Phil Hegeman 4 April 16, 1990 noted above, assuming the soil is at 50 percent solids, only 3.0 dry tons of soil are required per ton of dry sludge. As a point of reference, there are 1,200 dry tons of topsoil per acre assuming a 12-inch depth, 110 wet pounds per cubic foot, and a dry solids content of 50 percent. At a 3: 1 soil/sludge ratio, up to 400 dry tons of sludge can per applied per acre without the release of liquid sludge to the ground water. At a more reasonable reclamation loading rate of 25 dry tons of sludge per acre, a 48:1 soil/sludge mixing ratio would be available. This is 16 times the minimum required ratio. Therefore, uniform surface application of the sludge followed by soil/sludge mixing can prevent the seepage of sludge liquid to the groundwater table. In reality, Climax engineers report that the soil is at 90 percent solids. Therefore, the 50 percent solids example given above represents a very conservative evaluation. TABLE 1 MINIMUM SOIL/SLUDGE MIXING RATIOS TO ACHIEVE A 20 PERCENT SOLIDS MIXTURE --------Minimum Soil/Sludge Mixing Ratios------- (DryWeight of Soil) (Cubic Yards of Soil) In-Situ Solids Content per per of the Soil (Dry Weight of Sludge) (Dry Ton of Sludge)* 40% 3.7:1 6.2: 1 50% 3.0:1 4.0: 1 60% 2.6:1 3.0:1 90% 2.4:1 1.8:1 * Based on the in-situ soil at 110 pounds per cubic foot. Phosphorous Control. The phosphorous content of the sludge varies from three to five percent on a dry weight basis. Virtually all of this phosphorous is comprised of biological and chemical solids and the liquid portion of the sludge would have phosphorous concentrations on the same order of magnitude as the final effluent, i.e. about 0.02 mg-P/l. Therefore, based on a 7 percent solids sludge that contains a total dry weight phosphorous content of 4 percent, the breakdown among phosphorous species is estimated as follows: • 15 percent is aluminum phosphate precipitate. This is about 0.6 percent of the total dry weight solids content, or 420 mg-P/1 out of a total of 2,800 mg-P/1 on a wet basis. • 85 percent is biological phosphorous solids. This is about 3.4 percent of the total dry weight solids content, or 2,380 mg-P/1 out of a total of 2,800 mg-P/1 on a wet basis. • 0 percent is soluble phosphorous contained in the liquid portion of the sludge. This is based on 0.02 mg-P/1 out of a total of 2,800 mg/1 on a wet basis.