Design example 103Waste storage tank

Mr. Bill Walton of Middlesburg, Tennessee, has requested assistance on a waste management system. The selected alternative includes a below-ground, covered, slurry storage tank for his Holstein dairy herd. He has 150 milkers that average 1,400 pounds and 75 heifers that are about 1,000 pounds each. Bedding material is not used with these animals. Based on crop utilization of the nutrients, storage is needed for 75 days. The critical storage periods are January 1 to March 15 and July 1 to September 15. The wash water from the milkhouse and parlor is also stored. No runoff will be directed to the storage. Worksheet 10A-1 shows how to determine the necessary volume for the storage tank and several possible sets of tank dimensions. It also shows how to estimate the total solids content of the stored waste.

Manure production—The animal type, average weight, and number are entered on lines 1, 2, and 3. The equivalent 1,000 pound animal units (AU) for the animal type is calculated and entered on line 4. The daily volume of manure (DVM) production for each animal type is selected from table 4-5 and entered on line 5. The storage period (D) is entered on line 6. The total manure volume (VMD) is calculated for each animal type and entered on line 7. Add the VMD for each animal type and enter the sum (TVM) on line 8.

Wastewater volume—The daily wastewater volume per animal unit description (DWW) is selected from table 4-6 and entered on line 9. The wastewater volume for the animal type for the storage period (WWD) is calculated and entered on line 10. Add the wastewater volumes for each animal type and enter the sum (TWW) on line 11.

Bedding volume—Bedding is not used in this example. If bedding were used, however, its volume for the storage period would be determined using lines 12 through 15.

Waste volume—WV is the total volume of waste material that will be stored including total manure (TVM), total wastewater (TWW), and total bedding volume (TBV). Provisions are to be made to assure that outside runoff does not enter the tank. In addi-

Added water:

tion, if the tank is not covered, the depth of precipitation less evaporation on the tank surface expected during the most critical storage period must be added to the depth requirements.

|9,45Q ft3 + (q.3 ft x 33,58Q ft3)Jx 7.48 gal / ft3 = 78,72Q gal

Total depth available—The desired depth is the total planned depth based on such considerations as foundation condition, tank wall design, and standard drawing depth available.

Added water/ft3 manure:

78,2Q

Surface area—The surface area (line 21) dimen sions are calculated using the equation for SA.

Tank dimensions—Because tanks are rectangular or circular, various combinations of length and width can be used to provide the SA required. If the depth is held constant, only one solution for the diameter of a circular tank is possible. The dimensions of either shape can be rounded upward to match a standard detail drawing or for convenience.

Total solids content—The initial TS content of the manure is given in table 4-5 in chapter 4. Because there are two sources of manure, the solids content of the total manure must be weighted by the contribution from each animal type. The adjusted total solids content of the stored manure is determined from figure 10-40 using the added water from the milkhouse and parlor, the runoff (none in this example), and the net rainfall during the storage period. Because the total solids content of milking center wastewater is so low, it can be ignored.

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