by Ted Funk, Georgios Bartzis, and Jonathan Treagust
University of Illinois at Urbana-Champaign
Cooperative Extension Service
Pit systems store manure until it is returned to the land. However, where land is scarce and leaching levels are high, these systems may present a pollution problem. Composting and the use of additives for decomposition are only convenient in small-scale intensive systems. Livestock waste lagoons, however, not only handle manure in the liquid form for convenience and low labor, they treat and stabilize livestock manure while meeting the requirements of state and federal law.
Waste lagoon systems treat and store livestock manure for disposal onto land. They also store waste water for irrigation and flushing. Systems can be compatible with irrigation equipment, and they have reasonable construction costs and minimal fly problems. Livestock waste lagoons do require periodic sludge removal and careful management to prevent the pollution of groundwater and the emission of powerful odors
To avoid problems with odor and sludge, lagoons must be large enough for sludge to decompose biologically. Lagoons must also be loaded gradually and consistently at the start, taking care to avoid overloading.
Once in full operation, a lagoon must never be pumped below the minimum design volume. The minimum design volume is the volume the lagoon requires to ensure efficient bacterial action for continuous decomposition of livestock waste manure. Waste treatment efficiency can be improved by weekly agitation, though this can increase odor problems. This agitation can be performed by a tractor-powered lagoon pump. The sides of the lagoon should also be maintained by planting grass and mowing regularly.
Aerobic, anaerobic, and facultative lagoons A livestock lagoon treats manure as a liquid, the manure having been diluted by wash water and runoff. The lagoon acts as a biological tank, decomposing the waste before it is utilized as a resource in the form of irrigation liquid. The biological reaction is achieved by either anaerobic bacteria (these bacteria are inhibited by oxygen), aerobic bacteria (these bacteria require oxygen), or facultative bacteria (these bacteria decompose the waste, with or without oxygen).
To operate successfully, aerobic lagoons require shallow depths and large surface areas because the aerobic process requires huge amounts of oxygen and sunlight. This system is impractical for many farms because large areas of flat land have to be sacrificed to accommodate it. Aerobic lagoons do control sludge and odors better than anaerobic ponds, but they may need mechanical aerators to do so.
Anaerobic lagoons are most commonly used for livestock waste treatment. They can store, dilute, and treat high loading rates of livestock waste rather inexpensively with minimal labor and maintenance. The land area needed to construct such a lagoon is also relatively small, making the anaerobic lagoon practical for many operations.
Facultative lagoons combine the benefits of anaerobic and aerobic decomposition. In the anaerobic process, some offensive gases may be emitted, leading to odor problems. An aerator can be used to make the top of the lagoon aerobic, reducing odors.
Anaerobic single-stage versus anaerobic multiplestage lagoons Anaerobic livestock waste lagoons are divided into two categories: single-stage lagoons and multiple- stage lagoons (Figures I and 2). In multiple-stage lagoons, the effluent produced in the first stage or cell is transferred to the secondary cells where further treatment occurs through bacterial action and oxidation. In single-stage lagoons, there is no secondary treatment. The advantage of the secondary treatment is that it reduces undesirable odors, and it reduces the possibility that disease may be transmitted when the lagoon water is used for flushing gutters.
The design volume required to construct a multiple- stage lagoon is approximately twice that of a single- stage lagoon. Construction costs can be cut by siting the two lagoons side by side so that they share a common wall. Operators often overlook the option of building a secondary cell, but the advantages may far exceed the costs, especially in areas that are close to residential buildings.
Operators of single-stage lagoons who wish to benefit from the advantages of multiple-stage lagoons may add a second stage at least 50 percent of the size of the first lagoon. If the water in the second stage is going to be used for flushing, this size may be increased to 75 percent. This will leave the first stage at the minimum design volume and allow water to be taken only out of the second stage (Figure 2).
Figure 1. Single cell anaerobic lagoon
Federal, state, and local regulations
Illinois law does not require a permit for a nodischarge system such as a livestock waste lagoon. Federal law does regulate agricultural pollution; certain laws prevent wastes from entering public waters and others prevent the emission of strong odors. Essentially, the law states that no effluent may be discharged unless the discharge is a result of a specified storm; and to accomplish this, the technology used must comply with the no-discharge limitations where it is economically and technically possible. if the system is built to discharge, a National Pollutant Discharge Elimination System (NPDES) permit is required.
Current Illinois laws require that lagoons must be protected against excessive water from floods and storms. The standard used is a one-in-ten-year flood and a 25-year, 24-hour storm. Lagoons must have a "freeboard" or excess capacity adequate for such a storm. The law also prohibits building a lagoon within a ten-year flood plain. A lagoon cannot be sited within one-half mile of a populated area or within one-fourth mile of a nonfarm residence, although there are exceptions to this law. Lagoons must also be built on soil of low permeability, or they must be sealed against contamination of groundwater.
Loading and sludge accumulation rates
To load a lagoon, fill it with water from one-third to one- half of its total volume. Then add manure consistently and in increasing amounts until the total volume level is reached. While loading the lagoon, never allow the volume to drop below the minimum design volume. Use a highly visible post gauge marked at minimum design volume and safety volume levels so that these stages can easily be recognized (Figure 1).
It is best to start a lagoon in the spring because warmer weather increases bacterial action; this activity helps to ensure correct operation of the lagoon and minimizes odors. Regular loading of the lagoon-daily or weeklyalso protects against undesirable odors. In winter, when temperatures are low and waste decomposes more slowly, it is best to store or land-apply as much manure as possible to reduce the load on the lagoon.
Lagoon loading rates depend on the size, number, and species of animal kept and the latitude of the location. For example, a swine farm located in southern Illinois can load a lagoon with more waste than a farm in northern Illinois with a lagoon that is the same size. Because of this difference, Tables 1, 2, and 3 are provided to help determine the correct volume for central, northern, and southern Illinois.
The sludge accumulation rate of a lagoon varies with loading rates and is difficult to predict. Cattle lagoons accumulate sludge more rapidly than swine lagoons. If the manure contains bedding (bedding has a slow decomposition rate), the sludge accumulation rate will be higher.
Measure the sludge accumulation rate at least once a year to assess the lagoon's efficiency. If sludge accumulates rapidly, pump it out and apply it to the land, either by incorporating or injecting it into the soil. Then refill the lagoon with fresh water to its minimum design volume.
Frequency of dewatering
The volume of water in a lagoon increases constantly due to surface runoff, water added from the livestock operation, and direct precipitation. When the lagoon's water line approaches the safety level, pump the lagoon down (dewater it). Some lagoons may need to be dewatered every six months to return them to the minimum design volume. Dewatering controls mineral buildup, prevents overflow, and reduces the amount of sludge. It also provides nutrients to crops.
Various types of irrigation equipment can be used for dewatering. This process can cause odor problems, so try to dewater when the wind is blowing away from neighbors.
Other factors that influence how often dewatering should occur are salt concentration and soil type. To a certain extent, the soil type of the area where the water is to be pumped affects dewatering. It may not be possible to dewater every six months if the land area is small or if the area is already high in certain salts or nutrients. Soil tests are advisable.
Water supply and drainage
When starting up a lagoon, allow clean surface water such as roof drainage and rainwater to fill the lagoon to the desired level. After the lagoon is filled to about one-third capacity, there may be a need to divert runoff water to reduce the filling rate.
In an anaerobic lagoon, use enough water to maintain the minimum design volume depth. If less water is entering the lagoon because of low rainfall, the lagoon may need to be diluted with clean water to reduce salt concentrations. It is very important that the lagoon does not overflow, so gutter any extra water from roofs of buildings to channel it away from the lagoon. All water added to a lagoon before dewatering is the dilution volume, and for a specific length of time, this volume should be approximately equal to the livestock waste volume (Figure 1). Where surface runoff is inadequate, find a viable source of dilution water, such as water from ponds and wells.
Species and expected values of manure production
The design of a livestock waste lagoon is influenced by the quantity and composition of the manure entering it, which depends on animal species, age, stage of production, and the environment.
Published manure production values include not only feces and urine but also average amounts of waste water and other materials that find their way into the waste collection system. For example, a livestock waste facility for a swine nursery unit may have to handle three to four times as much waste as the actual feces and urine produced due to the large amounts of wash and waste water entering the system.
Soil and location
Lagoons should be positioned over nearly impermeable soil that can seal the bottom and side walls. Soil Conservation Service and Cooperative Extension Service personnel can help determine a soil's suitability for lagoon siting. Remove and seal field tile lines that cross the site to prevent the lagoon from becoming a pollution hazard. Avoid sandy sites and sites close to limestone unless the lagoon is lined with clay or soil cement. Liners can be used, but they are initially expensive and difficult to install. Over time, the lagoon seals naturally due to the buildup of animal waste in the form of sludge.
When siting a lagoon, remember these important criteria. A lagoon cannot be within 200 feet of a water well unless the well is owned by the lagoon's owner. In this case, the lagoon can be as close as 75 feet to the well, but this situation is not recommended. For convenience, a lagoon should be downhill from the source of manure, and it should be far enough away from streams to prevent pollution.
Minimum design volume
The minimum design volume is the volume the lagoon requires to ensure efficient bacterial action for continuous decomposition of livestock waste manure. The liquid level of waste in the lagoon should never drop below the minimum design volume. if this happens, decomposition will be poor and odor problems will occur.
Livestock waste volume
The livestock waste storage volume equals the total amount of waste produced by the livestock operation for a specific period of time. This volume will depend on whether the lagoon is dewatered once or twice a year. If a lagoon is dewatered once a year, the livestock waste volume will be double that of a lagoon dewatered twice a year. If coarse solids are removed from the liquid manure before it enters the lagoon, the total lagoon design volume can be reduced by up to 25 percent. Either a settling tank or a mechanical separator can remove solids from the liquid manure stream; solids are then available for land application or perhaps composting.
The dilution volume for any type of livestock waste lagoon in Illinois should be approximately equal to the livestock waste volume. The dilution volume includes all extra water such as building wash water, spillage from livestock watering devices, feedlot runoff, direct precipitation, and water pumped from a well or stream.
Determining the volume
Tables 1, 2, and 3 recommend total and minimum design volume for both single- and multiple-stage, one- or two- dewatering lagoons. Use the appropriate table for your particular location, and consult the left-hand column of that table for the type and weight of animal kept. Across from this column, find the minimum design volume and total volume values for single- or multiple-stage lagoons that are dewatered once or twice a year.
Now find the total volume line, labeled "total," and look for the column that applies to your particular situation. There are two main choices: one or two dewaterings per year and single- or multiple-stage lagoons. The figures give total volume for single-stage lagoons and total volumes for each lagoon in a two-stage system. The number represents the volume of the lagoon in cubic feet; this figure must be multiplied by the number of animals at that given size. For different animals and different weights, all the volumes must be found and added together to give the grand total volume. The minimum design volume is also given as a guide for initial filling of the lagoon and for its pumping down. This figure is found in the row above the total volume labeled "mdv." The total volume does not include the safety volume; this is taken into account in the dimension given in Table 4.
[TABLE 1] - [TABLE 2] - [TABLE 3] - [TABLE 4]
Permissible depth varies widely according to site and location. Table 4 gives four different depths for each volume; build the lagoon as deep as possible without getting closer than 4 feet to the highest expected water table level. A deep lagoon provides reduced surface area, better mixing qualities, reduced odor emission, and a smaller shoreline for better mosquito control. The depths given include the 2 feet of freeboard needed for the safety volume.
After determining the volume of the lagoon and deciding on the appropriate depth, use Table 4 to determine the length-to-width ratio of the inside of the lagoon. For example, if a 350,000-cubic-foot lagoon is to be built 20 feet deep, the dimensions 175 feet by 200 feet can be derived byusing Table 4. These dimensions were chosen to give a roughly square lagoon. Single-stage lagoons are usually square or circular, while multiplestage lagoons may be more rectangular (Figure 3).
The amount of space available will limit the lagoon's shape; it is important to allow for an 8-foot top width for the berm and space for the outside dry slope in addition to the dimensions derived from the table. Plan well ahead and think about possible extension in the future or adding a second stage if constructing a single-stage lagoon.
Table 4 assumes inside slopes of 2.5 to 1. Slopes that are steeper than this may require gravel riprap to stop erosion. If a dash appears in Table 4, the lagoon design is not possible because the slopes collide in the middle.
Figure 3. Barn, feedlot, and multiple-stage lagoon
Designing the earth embankment
The top width of the berm around the lagoon should be at least 8 feet. When constructing the berm, allow an extra 10 percent for settling. If possible, the berm should be capped with topsoil and seeded to grass. The outside slope of the lagoon berm should be at least 3 feet of run to I foot of rise if animals will be grazing on the land and 5 to 1 if the area is to be mowed by a tractor.
A safety volume or freeboard of 2 feet has been calculated into the dimensions in Table 4 to allow for unusually heavy rainfalls such as a 25-year, 24-hour storm. This precaution will usually prevent the lagoon from overflowing. A gravelled slope with a ratio of no more than 15 to I should also be included somewhere in the embankment design so that tractors will have access to the lagoon for dewatering, agitating, or mowing.
Designing the inlet and outlet
Open channel versus pipe. When a lagoon is sited below the source of waste, it is possible to use gravity to feed the lagoon and deliver the waste in either open channels or pipes. Open channels provide easy access for cleaning and have greater liquid-carrying capacity. They do, however, freeze in winter and may add to odor problems. Pipes can be used for a system that collects animal waste in a sump and pumps it to the lagoon. Eight- to 10-inch pipes with cleanouts and rigid joints are ideal to transport the waste.
The inlet to the lagoon can be either above or below the water surface. Any inlet should project at least 20 feet into the lagoon and should be supported every 8 feet. It should discharge into at least 3 to 5 feet of liquid depth. If the inlet is above the surface, it may freeze during winter. When it is below the surface, the system requires pressure to work properly and it may require daily cleaning with fresh water in isolated cases to control blockages.
Outlet to next lagoon. in a multiple-stage system, the outlet or overflow to the next lagoon should be able to handle one-and-a-half times the peak daily inflow of waste. A typical overflow device is a 6- inch pipe (trickle tube) through the first lagoon's berm. The pipe is tilted I foot on an uphill slope so that the liquid enters the pipe 1 foot below the surface of the first lagoon. The pipe's submerged inlet keeps floating solids out of the second lagoon stage. Locate the trickle tube or outlet pipe as far away from the inlet pipe as possible. A T-tube may also be used to hold floating solids back.
Designing the pumping system
Placement. In many cases, it is necessary to use a sump pump to either pump the waste to a lagoon that is higher than the source or to pump waste to a site where it can easily be screened. A sump pit is used to collect the waste at a low point common to all the animal confinement areas. A sump pump is placed in this pit to lift the waste to the screen or the lagoon. The sump pit must be large enough for a person to work in, and it should contain a device to close the inlet pipe while work is being done. The sump pit must never be entered until adequate ventilation has removed potentially lethal gases.
Selecting equipment. Use a commercial-grade sewer pump with either an automatic or a manual switch. Automatic switches include flotation, mercury, or pressure switches that are automatically activated when the sump pit is full. To minimize salt and crystal buildup problems around the pump and sump pit, a secondary pipe circuit may be included to flush a 30-percent hydrochloric acid solution around the pump to dissolve the salt. Also, use smooth-walled plastic pipes and as few joints and elbows as possible to help reduce salt buildup. Ground pumps correctly to ensure that a voltage differential does not encourage crystalline buildup.
Start up new anaerobic lagoons in spring or summer to ensure maximum bacterial reproduction, waste digestion, and stabilization before cold weather. The first stage of the start-up procedure is filling the lagoon with clean water to at least one-third of its total volume. Sources of clean water may be nearby streams, lakes, wells, or directed surface runoff and roof drainage.
The second stage of the start-up procedure is to gradually increase manure loading. Start by adding waste at one-fourth of the normal recommended loading rate during the first two months. Over the next two months, add half the normal amount; and over the fifth and sixth months, add three-fourths of the normal loading rate. After six months, the lagoon should be ready to receive the full loading rate of manure. Until the lagoon is ready, store the manure or apply it to the land.
Odors may occur during start-up. if they become severe, decrease the loading rates or begin the start-up procedure again.
Breaking a crust
Sometimes solids float on the surface of the lagoon, forming a crust. This crust helps to maintain anaerobic conditions, keep temperature constant, and minimize offensive odors. Odors may be released when the crust is broken during pump-down. The crust should be broken and removed when it becomes more than 1 foot deep. To do this, pump liquid on top of it during agitation with a chopper-type pump.
Inspecting the lagoon
Inspect lagoons regularly to ensure odor control, overflow control, fly control, and proper lagoon operation. Mow grass and weeds around the lagoon's embankment to simplify inspection, decrease the organic loading rate, and discourage flies and mosquitoes. Keep trees from growing on the embankments; their roots may destroy the berm or leave root channels that seep. Use a permanent post gauge in the lagoon to determine volumes and dewatering times.
Remove sludge when the buildup occupies about one- third of the lagoon's total design volume. Sludge can be removed by using agitation, sludge pumps, a hydraulic dredge, or a dragline. It can then be disposed of with surface or large-bore sprinkler irrigation systems if enough dilution water is used. Semisolid sludge can be hauled with manure spreaders; diluted sludge can be irrigated directly onto land if there is no danger of damaging the leaves of a growing crop.
Animal waste is high in nitrogen, potassium, and phosphorus. During lagoon operation, nitrogen is converted to ammonia, leaving a small amount of nitrogen in the sludge. Phosphorus accumulates in the sludge so little is lost; and most of the potassium remains in solution in the lagoon. Take representative lagoon samples regularly and analyze them before pumping the lagoon.
Odor is one of the greatest problems associated with livestock waste lagoons. It usually seems stronger in the spring because the organic matter has not been completely digested during the winter. To prevent odor problems, use the correct start-up procedure, add the right amount of dilution water, and decrease the loading rates during winter and early spring.
Lime and nitrates can be added, but they are an expensive and temporary solution. Several enzyme products, available as deodorants and disinfectants, can be used to treat lagoon odor. These products can be very costly; test them first by using the recommended dosage in a 5-gallon container of lagoon liquid. Then prepare an untreated sample of the same size. After a few days, compare the smell of the two samples to assess the product's effectiveness.
When the problem is severe, plastic coverings over the lagoon can be an expensive but efficient method of odor control. Aeration equipment-for example, mechanical aerators-are effective, but they are initially expensive, have high operating costs, and require maintenance. Odor problems may be intense during the first two weeks after installation, but they should become less intense after a few months of operation.
Dewatering the lagoon
Pump the lagoon down to its minimum design volume when the water level reaches or is near the bottom of the freeboard. The type and size of the dewatering irrigation equipment depends on the size of the lagoon and the solids content of the liquid manure. it will also depend on the solids content of the waste water. Thus, the irrigation equipment can vary from 2-horsepower gasoline pumps with 1-1/4-inch black plastic pipe and lawn-type sprinklers to the "big-gun" sprinklers with large nozzles. The big-gun sprinklers require pressures up to 100 pounds per square inch and pumping rates up to 800 gallons per minute. An alternative for medium- sized systems is gated pipe laid on a contour.
Tank wagons can transport fluids in capacities ranging from 400 to about 3,000 gallons, but they are more expensive and time-consuming than irrigation systems unless the lagoon's volume is less than about 75,000 cubic feet. Tank wagons are commonly loaded with either centrifugal, vacuum, or helical rotor high- capacity pumps; and they can spread the manure evenly on both sides or one side of the wagon.
Lagoons are potentially dangerous places. Install fences around lagoons to prevent easy access and place warning signs at intervals around the fence. It is important to ventilate sump pits properly to prevent buildup of lethal concentrations of gases such as hydrogen sulfide, ammonia, carbon dioxide, and methane. Enter a manure pit only after it has been well ventilated. Make sure that anyone entering the pit has a breathing apparatus and that two people are on hand to pull out anyone who collapses. Keep open flames away from sump pits because methane is highly explosive.
The total volume for the second stage would be 24,500 cubic feet + 59,325 cubic feet = 83,825 cubic feet.
The producer requires lagoons that are approximately 12 feet and 15 feet deep respectively, due to the presence of limestone in the area. Both lagoons should also be roughly square to make maximum use of available space.