CIR871 Some Devices for Flushing Animal Wastes 1 R.A. Nordstedt and L.B. Baldwin 2 Flushing of animal wastes offers several advantages for the livestock producer including labor efficiency and a more pleasant if not actually more healthy environment in animal housing areas. This report describes flushing facilities the authors designed or observed to remove wastes from flush alleys under slatted floors in swine houses, floors in dairy shade barns, and outdoor holding slabs for dairy cows. Tilt Tanks Flush gutters up to about 3 feet (1 meter) wide can be flushed successfully with small tanks made from 55 gallon (208 liter) drums hung to swing on a longitudinal axle (see Figure 1). The dump opening is made by cutting out one quarter of the cylinder wall and replacing it with a straight lip running at a tangent to the lower edge of the opening. Steel scrap or lead counterweights are attached to hold the tank with the opening spanning 12 to 3, or 9 to 12 o'clock, as viewed from the ends. The tank can be filled with a hose bib mounted over the tank opening. Upon dumping, the lip of the tank can strike the concrete floor to stop rotation and discharge directly down the gutter. To flush a 6 foot (2 meter) wide alley, two drums welded end to end and swung on a common axle may be used. The volume of flush water is usually about 80 percent of the nominal size of the tanks, about 15 gal/ft (55 liters/meter) of gutter width. The striking force between tank lip and concrete floor is acceptable for both single and double tanks. No shock control linkage or swing stops other than the floor are needed. The drum tanks have been effective for calf and swine wastes on troweled concrete up to about 80 feet (24 meters) in length at 1 percent slope. Lengths greater than this require repeated, rather than once or twice daily flushing, to clean the floor. Greater volume per foot of alley width and increased floor slope will improve the flush on longer gutters. The use of long tilt tanks constructed from more than two 55 gallon (208 liter) drums placed end to end is impractical due to the light construction of the drums compared to the necessary axles and supporting bearings needed to handle the weight involved. In order to flush wider floors such as in feeding or loafing shade barns for dairy cows, larger tanks may be selected. Multiple large tanks have been used for a floor which was 30 feet (9 meters) wide, 80 feet (24 meters) long, at a 2 percent slope. The finish was broomed for better footing. Three standard 287 gallon (1086 liter) cylindrical tanks were used. The openings and lip were in the same proportion as the 1. This document is CIR871, Agricultural Engineering Extension Report 85-5, one of a series of the Agricultural and Biological Engineering Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date December, 1989. Reviewed July, 2002. Visit the EDIS Web Site at http://edis.ifas.ufl.edu. 2. R.A. Nordstedt, associate professor; L.B. Baldwin, associate professor emeritus, Agricultural Engineering Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville FL 32611. The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service/Institute of Food and Agricultural Sciences/University of Florida/Larry R. Arrington, Interim Dean.
Some Devices for Flushing Animal Wastes 2 percent of the nominal size of the tanks, providing 20 gal/ft (250 liters/meter) across the floor. Initially, the tanks were allowed to dump every few hours to keep the loafing barn floor quite clean. This practice resulted in sore hooves from continually wet conditions on the hard floor. The tanks are presently operated daily for two or three dumps as rapidly as the tanks refill. Although accurate costs were not obtained for the large, three tank installation, it is apparent that the device is costly. For most applications, it appears that tilt tanks' practicability extends to the 100 to 150 gallon (380 to 570 liter) volume, but diminishes above that range due to the necessity of supporting the greater weights and providing shock absorber systems or curved backwalls--all of which are expensive. Piped Gravity Discharge Figure 1. Gator Gusher: Self-Dumping Tank for Flushing Wastes smaller drum tanks. Counterweights to hold the tanks in position while filling were provided by pouring about 2 inches (5 centimeters) of concrete in the tanks after mounting on the swing axle. A 4-inch (10 cm) steel pipe was used as a common axle for the three tanks, with adequate spacing between tanks for pillow block bearings to support the apparatus. Uniform filling of the tanks was accomplished by perforating the axle inside each tank and supplying water through a connection at one end of the axle. Large pipes or other conduits which deliver water by gravity are sometimes called "siphons" even though they do not depend on atmospheric pressure to function, as a true siphon does. This misnomer is most frequently used when some sort of air trap is used as a pressure controlled valve. The devices discussed in this report are not true siphons, in that the discharge pipe does not run above the stored water level (see Figure 2). Large tanks tend to self-destruct when floor-lip contact is used as a tilt stop during the dump. Shock absorbers may be used, or the tanks may be mounted high enough to swing freely. The latter has the advantage of simplicity of mounting. The major disadvantage of a free swing dump is the tendency to drop the water vertically, with resultant initial flow in all directions and a lower wave traveling down slope. The dump can be given down-slope direction by forming a curved concrete wall behind the tanks and dumping against it. The large tanks operated satisfactorily as described. The flush water amounted to about 70 Figure 2. Typical arrangement of Air-Trap-Valveto initiate discharge from elevated storage tank.
Some Devices for Flushing Animal Wastes 3 Flushing from elevated tanks by means of large pipes offers the advantage of discharging large volumes of water with minimal involvement of moving parts. It is necessary to support the weight of the water for each flush which is usually an amount exceeding the capability of standard building roofs. Discharge pipes can theoretically be sized or multiple-mounted to deliver any needed quantity of water rapidly enough to develop a flushing wave. The materials and equipment selected should be commercially available and reasonable in price. A large swine building for farrowing and a nursery with flush alleys under slatted floors was equipped to demonstrate multiple-pipe discharge from elevated tanks. There were two alleys 135 feet (41 meters) long and 7.7 feet (2.3 meters) wide, and two alleys 90 feet (27 meters) long and 10 feet (3 meters) wide. All alleys were sloped 2 percent with troweled finish, and a concrete sealer was applied to reduce sticking. Concrete tanks were built on the roof of a concrete block section of the housing facility. Additional reinforcement was needed. The air-trap valve arrangement shown in Figure 2 was used to automate flushing. The 7.7 foot wide alleys were each equipped with two 4 inch (10 cm) pipes with pipe traps formed from standard PVC plastic pipe and fittings. Simultaneous discharge was achieved by mounting the pipe inlets under a common air-trap bell fabricated from sheet aluminum. Trap charging holes, and notches along the lower edge of the bell were provided for complete aspiration following discharge. The 10 foot wide alleys were each equipped with three 4 inch pipes, also under a common bell. Each of the four sets of discharge pipes drained a concrete tank containing approximately 600 gallons (2300 liters). Discharge time was between 15 and 20 seconds, delivering approximately 80 gallons/foot (990 liters/meter) and 60 gallons/foot (760 liters/meter) to the 7.7 and 10 foot wide alleys, respectively. The pipe outlets were set behind a 6 inch (15 cm) high curb which extended across the upper end of each alley. The purpose of the curb was to evenly spread the water entering the alley. The discharge and alley dimensions appeared to be well-matched. Measured flow depth at the lower end of the alleys was about 3 inches (7.5 cm). Wastes were removed satisfactorily with a single flushing, twice daily. Expanding on experience with the facility just described, a dual tank facility was designed with four 4-inch pipes under a common bell in each tank with a 2-inch (5 cm) air line connecting the bells for simultaneous discharge. The floor to be flushed was 24 feet (7.3 meters) wide and 150 feet (46 meters) long, sloped at 3 percent. The floor surface was grooved irregularly for better footing. The building was designed to house beef brood cows for feeding and loafing. Several innovations were used in this flushing facility. It was constructed using a pole supported platform, 10 feet (3 meters) high, outside the building, for two standard 660 gallon (2500 liters) stock watering tanks. These tanks were 2 feet (.6 meter) deep. Air-trap bells were made from smaller, shallower sheep watering tanks, placed in an inverted position over pipe intakes. Trap charging and bell aspirator holes were provided. The air line connecting the bells was equipped with a manually operated valve to vent the bells to the atmosphere and initiate the flush. One discharge pipe trap was selected to be the trigger for automated discharge. This is often necessary with large, multipipe devices because the water fill rate is not adequate to overcome initial spillover in all the tubes and continue to increase the tank level to cause air escape and discharge. A piece of plastic tubing was installed across the top loop of the trap to reduce the length of the water column resisting discharge by about 1 inch (2.5 centimeters). This method can be used to correct a trap that is too long for the available tank head without cutting and reassembling the trap. Automatic discharge (when the increasing water level in the tanks causes the bells to vent air down the pipes) has not been entirely satisfactory with this two-tank, two-bell facility. The air purge by this means results in about 30 seconds of low flow down all eight pipes before air flow finishes and the main surge of water occurs. This diminishes the flushing wave. When the discharge was triggered by opening the air valve above the bells, full water flow was
Some Devices for Flushing Animal Wastes 4 quickly started and discharge of the approximately 1000 gallons (3800 liters) occurred in about 20 seconds, providing about 42 gallons/foot (520 liters/meter) of floor width. Like large tilt tanks, multiple pipes for large volume flushing can become tricky to design and expensive to construct, particularly the support of elevated water tanks. The air bell for single or multiple discharge tubes can be operated as a quick discharge valve by venting the bell manually, as described above. This would require controlling the fill level to prevent overflow. The relative cost of air-trap valves, either automatic or manually operated, in place of one or more large, quick opening mechanical valves should be considered. Gated Discharge Floor Level Tanks Tanks built at floor level or on a slightly elevated floor can be sized to contain large volumes of water at low cost. Several gates are commercially available to empty large tanks rapidly enough to create a flush wave. Also, homemade gates can be devised. Gates can be automated, but most producers prefer manual operation which avoids the hazard of unexpected operation and reduces cost. Floor level tanks with low sides can sometimes function as watering tanks. They are usually constructed of reinforced concrete block with cement plaster or other lining that will provide waterproofing. Examination of several floor level tank flush systems for feedlots and wide dairy feed and loafing lanes reveals a wide range in the volume of water used for each flush and in the number of flushes per day. Manufacturers of flush gates usually recommend flush volume based on floor width, slope, and length. The more common volumes recommended are up to 120 gallons per foot of floor width (1000 to 1500 liters/meter) for floors at 2 percent slope and up to 150 feet (46 meters) long. Greater floor length requires proportionally more water. Animal density and the time animals remain on the flush floor determine flushing frequency. Twice-a-day flushing is often employed at dairies to correspond with the milking and feeding cycle. Enclosed buildings may be flushed more frequently for better odor control. High Volume Pumping Another method of flushing is the use of high volume pumping to produce sustained flow for periods of several minutes up to an hour. This method is used to flush gutters under layer cages by introducing flow of 80 to 100 gallons per minute per foot of pit width (1000 to 1500 liters/min/meter) on slopes of around 0.5 percent. Flows of the magnitude required are obtained at reasonable costs with low-head pumps using the waste lagoon as a water source. This system is less attractive if potable water from a well is to be used. Large, irregularly shaped floors which are sloped can be flushed by introducing a flow of water along the upper end of the slope. Such a system was constructed at the IFAS dairy research farm. The floor was a holding area about 200 feet (60 meters) long and 32 feet (10 meters) wide. Slope was about 3 percent, running across the floor. The flush system utilized a high-pressure irrigation pump and barn waste water collected in a pit. Flush water was discharged along the 200 foot (60 meter) top of slope by means of 4 inch (10 cm) steel pipe, perforated with 3/8 inch (.95 cm) holes at 18 inch (46 cm) intervals. Discharge was estimated at about 4.5 gpm per foot (57 pm/meter). The system was operated daily for an hour or more, with some supplemental hosing. General Guidelines The capability to flush animal wastes reduces labor requirements and generally improves the appearance and the environment of animal housing and holding areas. Where daily or more frequent cleaning is required, flushing devices generally do not increase total water requirements. Waste water can often be reused for flushing. Disadvantages of flushing can be waste volume increase in some cases, plant nutrient losses, and higher capital costs for waste management. Capital costs and maintenance of flushing devices can be minimized by the use of simple principles and economical, long lasting materials. The key to successful flush cleaning is proper layout and construction of the floors and gutters to be flushed. Surge or wave flushers are particularly
Some Devices for Flushing Animal Wastes 5 dependent upon uniform slopes and floor finishes. Experience indicates that the frequency and number of flushes can be altered to compensate for changes in manure accumulation, drying manure, or other variables. On the other hand, it is difficult to design a flush system to operate satisfactorily on irregularly sloped or flat floors. Pits or gutters under slatted floors or cages should have a smooth surface. Wide areas can be flushed more efficiently if they are divided into 4 to 6 foot (1.2 to 1.8 m) alleys with curbs. Flush surfaces occupied by animals may be grooved either transversely or with a diamond pattern. Grooves which would lead flowing water to one side of the flush alley should be avoided. All flush systems require storage or outflow capacity at the foot of the flush area to prevent ponding on the area. Reduced water velocity will result in settlement of waste solids and poor cleaning. Deep cross gutters can be used to achieve this, but they must be drained and perhaps independently flushed to prevent filling with sediment. The corrosive atmosphere near manure accumulation, particularly when waste water is being used for flushing, make the use of intricate steel linkages and structures undesirable. Some manual operation may be preferred to long term dependence on float valves and switches which may corrode, fail, and result in power and water waste. Low maintenance design is critical to the continued proper functioning of waste management facilities. Safety is an ever present factor when heavy loads and quick moving devices, such as tilt tanks and drop gates, are involved. Initial design and construction to assure adequate support, and enclosures to block entry to danger areas should be of primary concern in planning flush systems.