Livestock facilities are typically located to use natural surface-drainage. However, runoff—from open areas, such as feedlots, aprons adjacent to livestock confinement barns, and manure load out areas—transports pollutants including manure, waste feed, soil, chemicals, and dust from confinement buildings. These conditions require facilities for pollution control and drainage to intercept and store or treat surface runoff so contaminated waters do not enter surface or ground waters. A typical open-lot runoff control system is shown in Figure 23.
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| Figure 23. Runoff control system. (Source: Ohio State University Extension Bulletin 604, 1992 Edition.) |
Proper assessment of the pollution potential depends on the size and other physical characteristics of the lot and on rainfall intensity, duration, and frequency. An open lot may be any outdoor animal area, such as a beef feedlot, outdoor dairy feeding and resting area, or sow feeding pens, and may include an unpaved dirt lot, completely paved, or partially paved areas around feed bunks and waterers.
Where livestock spend only part of their time outdoors, a proportion of total manure production exposed to lot runoff is estimated. With a manure pack bedded area and lot feeding, the proportion of manure on the lot is typically about 50 to 70% for cattle. If sows are fed outdoors at least daily, a large proportion of the manure, up to 90%, is exposed to lot runoff.
Figure 24 illustrates the major components of a runoff control system.
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| Figure 24. Components of a runoff control system. (Source: Ohio State University Extension Bulletin 604, 1992 Edition.) |
All clean roof and surface water should be diverted away from the feedlot to a clean-water drainage system independent of the waste-handling system. This reduces the amount of waste to be handled, reduces the amount of solids eroded from the lot, and maintains the settling facility’s efficiency. All roofs that would contribute to runoff from the feedlot should have gutters, downspouts, and outlets that discharge water away from the feedlot. A 25-year, 24-hour storm should be used when designing the diversion system.
Lot runoff, whether from rainfall or snowmelt, may contain manure, soil, chemicals, and debris, and must be handled as part of the manure management system. Runoff can be collected and transferred to a settling basin or holding pond by diversions, curbs, gutters, lot paving, and, in some cases, by pumping.
A settling basin retains runoff and reduces the flow rate to allow settling out and recovery of solids. The liquids are drained off to a holding pond, constructed wetland, or vegetative treatment area, and the solids remain in the basin for drying and later removal and spreading.
The settling basin slows the runoff flow to allow solids to settle. Typically, runoff solids that will settle out will do so in about 30 minutes. To settle most solids, the basin should provide a large, shallow settling area (<3 feet deep) and retain runoff for at least 30 minutes. Although the most conservative approach would allow for a 25-year, 24-hour rainfall, experience shows that rainfall during a 10-year, one-hour storm can be used to size the settling basin, provided larger flows can bypass the settling basin without carrying manure solids, and be routed through a vegetative treatment area.
The required surface area for settling should be equal to at least 5% of the open-lot area plus any other areas that contribute runoff. To prevent scouring of the settled solids from the settling basin, the liquid cross-sectional area should be about 5% of the ponded surface area. The settling basin should be concrete or at least have a concrete bottom for solids removal and should provide at least one vertical wall to buck against for solids removal (Figure 25).
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| Figure 25. Concrete settling basin with screened perforated pipe. (Source: Ohio Natural Resources Conservation Service (NRCS) Design Staff. Used by permission.) |
Several types of basin outlets are available to drain liquids from the full depth of the basin and dewater the solids. The perforated pipe, slotted pipe, and porous-plank dam are common examples. The outlet design should take into account manure and other debris that can plug outlet holes. For perforated or slotted pipe outlets, an additional screen, such as an expanded-metal screen (3/4 inch, No. 9) around the outlet, will increase the screening area and protect the drain from larger debris. For a porous dam outlet, a material that can be easily cleaned by scraping the surface should be selected. Spaced boards, welded-wire fabric, or expanded-metal mesh can be cleaned easily.
Frequent maintenance and clean-out increases the efficiency of the settling basin. Cleaning the basin after every major runoff event will improve its treatment efficiency, reduce odors, and restore the basin capacity. A properly managed open lot and settling basin can retain up to 85% of the solids from the lot. If solids are not cleaned out after each runoff event, additional storage capacity must be included in the settling basin volume.
The solids storage volume required depends on the solids removal rate from the lot, lot size, and time between clean-outs. Rainfall runoff from an unpaved lot has up to about 1.5% solids, which is about 6 cubic feet of solids per 1,000 cubic feet of runoff. Longer and steeper slopes may result in more solids accumulating in the basin.
For a paved lot, the maximum amount of manure likely to be washed off between scrapings is 1 inch of solids over the lot area which would require 20 inches of storage depth assuming the settling area is 5% of the lot area. For dirt lots, a maximum of one-half inch of solids erode from the lot, requiring a minimum of 10 inches of depth for solids in the settling basin.
To ease scraping of the basin, liquid and solid depths can be reduced by proportionately increasing the surface area above the 5% basis. It is often practical to provide the settling basin as part of the feedlot by providing a curb along the low part of the lot to control lot runoff and trap solids, which can be removed after draining the water. It is important that the settling basin or channel is shaped and located so that it can be easily managed and maintained.
A holding pond, basin, or tank temporarily stores runoff water from a lot until it can be applied to the land. If manure solids are to be recovered, lot runoff must pass through a settling facility before going to the holding pond. The holding pond is not intended to receive roof water, cropland drainage, or other unpolluted waters and does not treat manure as in a lagoon.
Holding ponds must be sealed to prevent seepage into ground water. Although holding-pond bottoms tend to seal naturally, if the pond is located in sandy or gravelly soils or near fractured bedrock, the pond must be sealed with a synthetic liner or compacted clay. The Natural Resources Conservation Service, a geologist, or a professional engineer should be consulted during project planning for assistance to determine site feasibility.
The required storage volume should consider desired length of storage, source of liquids and runoff water, rainfall duration and frequency, and the balance between rainfall and evaporation. The holding pond should provide capacity for a 25-year, 24-hour rainfall with 25% added storage to the design volume for emergency situations. If a settling basin is not included or becomes short-circuited, capacity for manure solids must also be included in the storage volume.
To ensure maximum capacity, the holding pond should be emptied regularly, by pumping and land application using some type of irrigation. Because of the dilute nature of runoff, it may be feasible for direct irrigation onto growing crops. However, accumulated manure solids can affect the ability to irrigate unless they are separated. The pond should be emptied before it is full as specified in a nutrient-management plan.
A constructed wetland provides an opportunity to store and treat contaminated runoff by reducing nutrients, especially nitrogen and phosphorus. Before entering the constructed wetlands, solids must be removed in a settling basin. The wetlands should be designed in accordance with Natural Resources Conservation Service standards, which take into consideration nutrient and hydraulic loading rates. In addition to average runoff, constructed wetlands should provide storage for a 25-year, 24-hour rainfall.
A series of three or more wetland cells allow optimum treatment. Adjustable risers between the cells permit flexibility in controlling water depth, which should be uniform across each cell. Wetlands are not designed to discharge directly into waters of the state unless specifically permitted. Overflows from wetlands should outlet into vegetative infiltration areas or can be irrigated onto cropland.
The constructed wetland consists of an impervious subbase covered with a minimum six-inch layer of hydric soil, which will usually contain wetland plant seeds. If a hydric soil is not available, topsoil may be used. Plantings in each cell should be limited to two species that may include cattails, softstem bulrush, river bulrush, arrowhead, and pickerel weed. Following planting, the soil should be saturated to permit germination, then raised to the design depth at a rate that does not flood the plant but allows for optimum plant growth. Polluted runoff should not enter the constructed wetland until plants are well established. Livestock should not be permitted in the wetland, and muskrats must be controlled to prevent damage to earthen dikes.
Generally, runoff from open lots is applied to agricultural land for utilization of the manure nutrients. For holding ponds, it is usually economical to use irrigation equipment to transport the liquid to the application site. If the manure is handled as a liquid, it may be feasible to use the same disposal equipment for the contained runoff. The emptying schedule specified in the system’s waste management plan should be followed.
A vegetative treatment area is an alternative to holding ponds for runoff detention. Runoff flows through a settling facility to settle out most of the solids, then to a vegetated area where it is treated. It is essential that solids be settled out before runoff enters the treatment area. To be effective, a vegetative treatment area must be designed, constructed, vegetated, and adequately maintained.
The vegetative treatment area is designed either for overland flow or slow-rate infiltration. The vegetated area may be designed either as a long, grassed, gently sloping channel or a broad, flat area sloped away from the inlet. Divert all outside surface water so that only lot runoff and direct precipitation enter the infiltration area.
Overland flow treatment refers to a specific microbial remediation technique that has minimal infiltration of wastewater. Treatment by overland flow consists of the application of wastewater along the upper portion of a uniformly sloped strip of herbaceous-vegetation, allowing it to flow over the vegetated surface for aerobic treatment. Overland flow design consists of dosing the flow every two to four days over the treatment area. The size of the filter is based upon a loading rate for the soil and a minimum flow contact time.
The slow-rate infiltration process refers to a specific remediation technique involving the application of wastewater to a vegetated surface for treatment as it flows down through the plant-soil matrix.
The design hydraulic loading is based on the more restrictive of two limiting conditions—the capacity of the soil profile to transmit water (soil permeability) or the nitrogen concentration in the water percolating below the root zone. The anticipated nutrient loading should not exceed the vegetation’s agronomic nutrient requirement. To maintain soil infiltration, the treatment area should not be constructed or later traveled when the soil is wet. Other surface water should be diverted from the filter area. Livestock need to be excluded from the vegetative treatment area.
The success of the treatment depends largely on the establishment and maintenance of a good stand of vegetation. In planning the facility, provisions must be made to have an established stand of vegetation before allowing lot runoff on the filter. Fescue and reed canary grass have proven acceptable. Although the natural habitat for reed canary grass is a poorly drained, wet area, it is also one of the more drought-tolerant grasses and can utilize high fertility. The vegetation should be harvested and removed when conditions allow.
Water ponding and the buildup of solids at the beginning of the filter may be minimized by using a slope of 2% or more for the first 50 feet. Slopes can be decreased to 0.5% for the remainder of the filter area and the channel can be straight or can take on a switchback shape, depending on the area where the filter is located. On steep topography, the filter area should be a graded terrace with a slope that will not allow erosion.
The required infiltration area depends on the soil-infiltration capacity, soil water-holding capacity, and runoff volume and should be designed to control a 25-year, 24-hour rainfall event. Typically, the channel has a minimum bottom width of eight feet and can be up to about 24-feet wide. If wider channels are needed, meandering and channeling can be controlled with low dividing ridges. The length of the channel can be reduced by decreasing the lot area, diverting lot and roof water, decreasing the amount of manure exposed to rain, or by increasing the width of the grass filter. The bottom of the channel should be flat in cross-section.
The final design of the grass filter should take into consideration the topography and area available, number and size of animals, lot size, and lot management practices. The success of a vegetative filter is dependent upon a shallow flow depth uniformly spread over the entire filter width being in contact with dense vegetation.
Several management considerations need to be evaluated in the planning , design, and operation of a vegetative treatment area.
Silage drainage into streams can kill fish and other aquatic life. The sugars, proteins, and acids in the leachate have a high oxygen demand and are highly polluting to streams. Their loss also significantly reduces feed value. Typical silage leachate constituents are shown in Table 10.
| Table 10. Typical Silage Leachate Constituents. | ||
| Constituents | Silage Seepage (typical) | Dairy Manure Liquid (typical) |
|---|---|---|
| Dry Matter | 5% (2-10%) | 5% |
| Total Nitrogen | 1,500-4,400 mg/liter | 2,600 mg/liter |
| Phosphorus | 300-600 mg/liter | 1,100 mg/liter |
| Potassium | 3,400-5,200 mg/liter | 2,500 mg/liter |
| pH | 4.0 (3.6-5.5) | 7.4 |
| Biochemical Oxygen Demand (BOD5) | 12,000-90,000 mg/liter | 5,000-10,000 mg/liter |
| Source: American Society of Agricultural Engineers, Paper No. 94-25 60 by P. E. Wright and P. L. Vanderstappen, 1994, and Ontario Ministry of Agriculture Food and Rural Affairs, Agdex No. 723. | ||
Place forage in upright and horizontal bunker silos at the proper moisture content so as to avoid drainage from the silo. The amount of silage effluent varies throughout the year. Ideally, when a bunk silo is loaded, effluent flow starts. It peaks from five to 10 days later and then dwindles to a minimum by three months. Silage leachate production increases as the silage moisture content increases. Leachate production estimates are shown in Table 11.
| Table 11. Leachate Production Estimates. | |
| Dry Matter % | Leachate gal/ton |
|---|---|
| <15 | 100 to 50 |
| 15 to 20 | 50 to 30 |
| 20 to 25 | 30 to 5 |
| >25 | <5 |
| Source: American Society of Agricultural Engineers, Paper No. 94-25 60 by P. E. Wright and P. L. Vanderstappen, 1994. | |
Collect and divert the leachate so it does not enter field tile, drainage ditches, or streams. Collect the drainage in a holding tank or add to a liquid manure storage facility, and land-apply when conditions are appropriate.
As a rule of thumb one cubic foot of leachate storage should be provided for each ton of silage. (Animal Waste Management Field Handbook. Page 4-23, Natural Resources Conservation Service (NRCS), AWMFH).
Both the daily volume and the strength of milking-center wastewater must be considered when designing milking facilities. Table 12 provides estimated daily quantities of wastewater. As herd sizes increase, less water is used per cow because the milking equipment washwater does not increase proportionately. The values given are for facilities with parlors. It is assumed that holding areas are scraped and not washed down. Milking in stanchions produces less wastewater per day, and the quantity of wastewater from milk rooms will be one-third to one-half of the values given in Table 12.
| Table 12. Estimated Quantities of Wastewater Discharged from Milking Centers. | |
| Cows Milked | Quantity |
|---|---|
| Up to 50 | 7 to 10 gal/cow/day |
| 50 to 150 | 4 to 6 gal/cow/day |
| More than 150 | 2 to 4 gal/cow/day |
| Source: Ohio State University Extension Bulletin 604, 1992 Edition. | |
The design of the wastewater collection system in the milking center is very important. Poor drain locations, improper floor slopes, or inadequate piping can lead to continual frustration for the operator. Floor slopes should be a minimum of 2% (1/4 inch per foot). Drains should be recessed below floor level so that water and solids will easily enter the drain without ponding. Drains should be located in corners or at ends of gutters so that solids can be easily washed (hosed) into them. A water-seal trap must be located in the drainpipe between the water-disposal unit and the milking center to prevent gases from entering.
The use of the conventional septic tank and leach bed for modern milking-center wastewaters is not satisfactory, for three reasons:
Failure of a leach bed can result in discharge of untreated wastewater into waters of the state.
A very acceptable and easy method of handling milking-center wastewater is to put it into a liquid-manure system. Dairy manure requires addition of some water to ease agitation and pumping. Including milking-center wastewater in liquid manure storage structures will provide the necessary dilution and solve the wastewater disposal challenge. When designing liquid-manure-storage structures, extra volume must be provided for the wastewater.
When a dairy facility utilizes dry manure storage, milkhouse washwater must be handled independently of the manure. Alternatives include:
Whatever the disposal method used, proper management is needed to prevent pollution and nuisances.
Sanitary facilities from livestock enterprises are not to be directly mixed with livestock manure and need to be permitted by the District Office of the Ohio EPA. A septic tank/leach bed system is normally used.
Karen Mancl
Professor, Food, Agricultural, and Biological Engineering, The Ohio State University
Olli Tuovinen
Professor, Microbiology, The Ohio State University
The Department of Food, Agricultural, and Biological Engineering at The Ohio State University has an ongoing research program on the treatment of food processing wastewater. Wastewaters from meat and milk processing plants, restaurants, and even dairy farm milking facilities are significantly different from domestic and municipal sewage. Food processing wastewater has four to 10 times higher COD and BOD5 levels because of the presence of fats, oils, and grease.
These wastewaters are difficult to treat using conventional wastewater-treatment systems or soil-absorption systems.
The Ohio State University research program is studying the treatment of cheese- and turkey-processing wastewaters through gravel/sand bioreactors. Properly designed and intermittently loaded, these laboratory-scale bioreactors remove over 99% of the COD, BOD5, suspended solids and fats, producing effluent suitable for permitted stream discharge.
Some of the initial research findings include:
ASAE Paper No. 94-25 60, American Society of Agricultural Engineers. Peter E. Wright, Senior Extension Associate, Cornell University, Ithaca, NY 14853, and Peter L Vanderstappen, Civil Engineer, Natural Resources Conservation Service, Lebanon, PA 17042. wmc.ar.nrcs.usda.gov/partnerships/AWMIT/baseflow.html
USDA Natural Resources Conservation Service, Agricultural Waste Management Field Handbook. www.wcc.nrcs.usda.gov/awm/awmfh.html