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Module 5: An imal Manure and Process -Generated
W astew ater Treatment
By Saqib Mukhtar, Texas A&M University
Intended Outcomes
The participants will
 Learn about treatment technologies available and under development, and their working
principles.
 Better understand the efficacy of using different treatment systems for liquid and solid manure
management.
 Learn to incorporate treatment technologies into a total manure management system for
environmental protection.
Contents
1. Introduction
2. Principles Used in Manure Treatment
A. Solids Removal
B. Aeration
C. Anaerobic Processes
D. Natural Systems
3. Manure Utilization and Treatment Technologies
A. Land Application
B. Anaerobic Processes
C. Composting
D. Vermicomposting
E. Mortality Composting
F. By-product Recovery
G. Energy Production
H. Constructed Wetland Systems
I. Emerging Technology Overview
4. Questions
Reviewers
The author wishes to thank Don Jones, Purdue University, and Jeff Lorimor, Iowa State University,
for their review of this module.
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Introduction
Livestock and poultry manure may be comprised of excreta, hair or feathers, spilled water and feed,
process-generated wastewater (water used for flushing gutters, etc.), bedding (sand, sawdust, wood
shavings, peanut hulls, composted manure, and other substances.), and mortality. Animals do not flush
toilets, take baths, or wash dishes or clothes. Therefore, animal manure may not have the same
characteristics and behavior as water or municipal wastewater. In general animal manure is much more
concentrated than municipal wastewater. Treatment of animal manure and wastewater is carried out, by
biological, chemical, and physical processes, to reduce potential degradation of natural resources prior to
a designated end use of the treated product and byproducts.
Animal manure treatment systems have historically been selected to recover or use valuable fertilizer
constituents or feed ingredients and to protect soil, air, and water quality. Over time, however, the
protection of soil, air, and water quality has evolved to include such considerations as the management of
potentially toxic materials such as copper, zinc, and antibiotics; concerns about proper nutrient
management; and increased emphasis on air quality. Odor; ammonia volatilization (the release of
nitrogen, in the form of ammonia, during decomposition to air); the release of hydrogen sulfide, methane,
and other gases; and the potential of dust to transport odors and produce biosolids (nutrient-rich organic
matter) have become major public concerns.
There has also been increased emphasis on the utilization of valuable constituents in manure and
mortalities through more effective constituent conservation and processing to value-added byproducts.
Manure treatment systems or alternative technologies are evaluated or selected for their ability to provide
the required protection of soil, water, and air resources. Some manure treatment systems or alternative
technologies can address several requirements, while some are so specialized that only individual manure
constituents are addressed. The following material discusses environmental quality concerns and the
manure treatment systems or alternative technologies required to protect resources or address particular
manure constituents or manure management needs or goals.
Principles Used in Manure Treatment
Many of the alternative and advanced manure treatment technologies being recommended and tested
for livestock and poultry manure are already being used for municipal and industrial waste. Often, these
technologies use basic principles to reduce solids, odor, and ammonia volatilization. In fact, several of
these technologies can reduce odor and ammonia volatilization and can provide increased nutrient
removal for either existing or new systems. It is important to understand the basic principles of manure
treatment and to determine the system that best meets a given need.
Solids Removal
Liquid-solid separation is one of the most common manure treatment practices to reduce organic and
inert materials from animal manure. Separated solids are used as fertilizer as well as composted and used
as livestock bedding. The remaining liquid with reduced solids content and less odor potential is easier to
manage in storage and treatment structures and during irrigation; it may be recycled for flushing manure.
Solids removal can be achieved using the following biological, chemical, and physical methods.
 Gravity/sedimentation
 Mechanical
 Flocculation
 Aeration
 Anaerobic processes
 Natural systems
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Gravity/sedimentation
One of the first processes in municipal wastewater treatment is removal of solids by gravity. Mineral
particles, biosolids, or generated biomass from biological treatment can be removed by reducing flow
velocity so it is not sufficient to keep a certain size or weight of solid in suspension. This process of
sedimentation can be advantageous because it helps prevent overloading of biological treatment systems
with solids and organic matter. Sedimentation also reduces clogging problems in pumps and pipes
carrying liquid manure.
While municipal wastewater treatment systems typically use a grit chamber, similar basins have been
used for solids removal from feedlot runoff or before lagoons. Settling basins (Figures 5-1 and 5-2) are
required below most open feedlots in humid areas. Sometimes, two parallel basins are built so that while
one is in use the other one can be draining, enabling workers to remove solids with a front-end loader by
using a sloped access area. Smaller solids can be removed in a sedimentation tank, which is a larger,
deeper version of a sedimentation basin that holds the manure longer before further treatment processes.
The longer holding time (also known as hydraulic retention time) and larger size greatly reduces the flow
velocity, allowing significant settling of solids in the tank.
Figure 5-1. Concrete settling basin to remove solids.
Figure 5-2. Earthen settling basin to remove solids.
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Gravity removal of solids can be beneficial; however, the advantages of sedimentation tanks must be
weighed against their potentially large size and management requirements, which result in high
construction and operational costs. Biosolids or sludge (the term for semi-solid residue left after a manure
treatment process) from a sedimentation tank or clarifier must be handled similarly to solids removed by
other processes.
Mechanical
A number of mechanical technologies have been developed to reduce the solids content of livestock
and poultry manure streams. These removal technologies include simple inclined screens (Figure 5-3),
self-cleaning screens, presses, centrifuge-type processes, and rapid sand filters. These types of separators
reduce carbon (C), nitrogen (N), and phosphorus (P) loads to subsequent treatment units. Separated solids
are typically collected to allow for easy removal and disposal.
Figure 5-3. Inclined screen liquid-solid separator.
Flocculation
The removal of solids, P, and other suspended or dissolved constituents can be improved by adding
chemicals to the influent of solids removal processes. The chemicals or flocculation (the attachment of
suspended solids to each other to form clumps) agents commonly used for municipal wastewater
treatment include alum and lime as well as a range of polymers (large molecules that can trap other
substances). It is especially important to add the minimum amount of chemicals possible and to obtain
good contact with all of the wastewater to maximize efficiency and minimize the amount of sludge.
Because polymers are expensive and results in large amounts of sludge that must be managed, new
equipment is being developed that effectively adds the minimum amount of polymer. If lime is used, the
resulting sludge has enhanced agronomic value.
Aeration
Aeration can be used to remove organic material or oxygen demand, which is often referred to as
biological oxygen demand (BOD) or chemical oxygen demand (COD). BOD and COD describe the
amount of organic material in water that removes oxygen during decomposition. High oxygen demand
can affect fish and wildlife populations by reducing available oxygen and accelerating the eutrophication
(natural aging of lakes and streams caused by nutrient enrichment) of a water body. Aerobic (in the
presence of oxygen) treatment also can remove a portion of the N and P by biological uptake. The
composition of microorganisms, which is about 50% C, 10% N, and less than 1% P, limits N and P
removal. Therefore, in aerobic treatment, about 50% of the C is converted to sludge or biomass and
removed in a sedimentation tank following aerobic treatment.
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Many different types of bubble or surface aerators (Figure 5-4) are available to provide aeration. The
aerators can be used in existing or new lagoons to reduce odor and ammonia release to the air. By selecting appropriate surface aeration equipment or by placing air defusers above the bottom sludge zone,
Figure 5-4. Floating surface-aeration system.
aeration can be designed to mix the total lagoon or to treat only the upper portion. When aeration is
limited to the lagoon surface liquid, the bottom, or sludge zone, remains anaerobic (a term used to
describe the absence of oxygen). Thus, the benefits of anaerobic decomposition of solids can be obtained,
and the upper portion may be aerated to reduce odor and ammonia volatilization at a reduced energy
input.
Anaerobic processes
Anaerobic processes take place naturally at ambient temperatures under oxygen deficient conditions
such as those that occur in landfills or animal manure storage and treatment lagoons. Bacteria that
function without oxygen degrade organic matter inherent in livestock and poultry manure. These
microorganisms are both temperature and oxygen sensitive, and thus design criteria for systems utilizing
anaerobic processes will vary regionally.
The major benefits of anaerobic process systems are the (1) reduction of COD or BOD and solids and
(2) production of methane gas, which has energy value. Sludge production is also reduced under these
conditions. Anaerobic digestion does not reduce manure’s P content, and thus the liquid and sludge
effluent must be managed in a manner that handles or uses these nutrients. To prevent failure, anaerobic
process systems must be operated under proper conditions and monitored and maintained regularly.
Natural systems
Many treatment or runoff control systems are being developed that follow the basic principles of
natural systems such as wetlands or riparian areas (the strip of land that runs along the banks of streams
and rivers). These treatment options utilize the general components of natural ecological systems (soil,
microbial activity, vegetation, and other elements) that can reduce nutrient, BOD, and suspended solid
loads. A combination of physical, chemical, and biological processes inherent to natural environments
transforms or deactivates these contaminants. A number of types of treatment systems using natural
processes are considered suitable, and some of these can be constructed and optimized for individual
production facilities. Constructed wetland systems that can remove high levels of N have been developed
for municipal waste and animal manure. Vegetative filter strips and riparian areas as well as overland
flow plots or wetlands are being used to reduce the pollution potential of runoff.
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Manure Utilization and Treatment Tech nologies
A variety of traditional and innovative technologies use the principles listed in the previous section to
reduce solids, odor, and ammonia volatilization. Each has associated advantages and disadvantages that
must be weighed to make the appropriate choice, one optimizing treatment efficiency, space
requirements, and costs for individual livestock and poultry operations. The following material is a brief
overview of both established and emerging techniques that producers can consider in developing a
manure management strategy.
Land Application
Land application, which is used as a terminal system for treated and untreated manure, is discussed in
detail in other resources such as the Livestock and Poultry Environmental Stewardship (LPES)
Curriculum lessons. While not discussed in full detail in this publication, it should be noted at this point
that land application presents an effective disposal option for most livestock and poultry producers when
adequate land is available.
Good land application strategies yield agronomic benefits when applied to crops or pasture. The
nutrient content of manure can substantially reduce fertilizer costs. Furthermore, the organic nature of
livestock and poultry manure can increase soil organic matter and improve soil tilth and aeration.
Proper application practices must be used to optimize nutrient benefits and reduce odor generation.
Increasingly, more stringent regulations may limit application rates based on nutrient content. These new
application guidelines may require greater land areas for application. Because P is often the primary
nutrient of concern, reducing P excretion to improve options for fertilizer use may prove to be a valuable
practice in relation to land disposal. This technique can help maximize agronomic rates while
simultaneously helping to meet P regulations. Animal dietary strategies that decrease P intake or improve
P digestibility in animal feed are one example of reducing P excretion.
Advantages and disadvantages of land application
Advantages
Reduced fertilizer costs
Increased soil quality
Low cost
Disadvantages
Potential odor problems
Large land area needed
Nutrient regulations may limit application
Anaerobic Processes
The two major methods of treating manure anaerobically are anaerobic lagoons and anerobic
digesters.
Anaerobic lagoons
Using anaerobic lagoons (Figure 5-5) is a well-established practice in animal manure management
and treatment. Lagoons consist of an excavated pit, levee, or similar structure that impounds manure for
the purpose of treatment and stabilization through biological activity. This dependence on biological
activity requires lagoon designers to consider the regional location of the facility to account for climatic
conditions. These environmental conditions reflect both temperature variations and precipitation patterns.
Methods for determining total lagoon volume are presented by the American Society of Agricultural
Engineers. The total volume consists of a minimum volume based on geographic location (relating
average monthly temperature and corresponding biological activity) plus volumes designed to manage
livestock and poultry manure, runoff, and sludge accumulation.
Lagoon systems are advantageous when appropriately managed, because the lagoons provide storage
of waste streams in addition to treatment. This allows for field application of the liquid portions, which
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Figure 5-5. Anaerobic lagoon.
are a source of both water and nutrients for crops and pastures. A portion of the liquid can also be
recycled to remove manure from buildings. While the manure remains stored, large losses of N to the
atmosphere can reduce the nutrient concentration.
The primary disadvantage of anaerobic lagoons is the large land area needed for the lagoon itself. As
with many manure management systems, proper maintenance, monitoring, and operation are required.
Lagoon systems should be fenced to keep people and animals away from the impounded water.
Advantages and disadvantages of anaerobic lagoons
Advantages
Provides storage of manure
Effluent can be recycled for flush water
Removes large amounts of N
Disadvantages
Large land area required
Potential odor problems
Safety concerns
Anaerobic digesters
Anaerobic digesters present a smaller alternative to lagoons but use the same process. Typically
consisting of small, covered lagoons or tanks made of concrete or steel, these systems are often
constructed partially underground to allow for gravity feed of manure and to help retain heat in colder
climates.
The most commonly used anaerobic digestion units operate at about 95ºF. Decomposition of organic
solids produces a gas with about 60% methane and 40% carbon dioxide. Although these systems can be
costly, this gas can be used as an alternative fuel source for gas combustion engines that drive generators,
producing electricity and hot water. Using this gas as an alternative fuel source is discussed more fully in
the Energy Production section of this document. Safety procedures need to be installed to reduce the risk
of methane explosions, because methane forms a highly explosive mixture with air in concentrations as
low as 5%. An added benefit of anaerobic digesters includes odor control; however, it should be noted
that nutrient levels (N, P, and potassium) are not reduced in these systems.
More heat intensive digesters operate at about 165ºF, which significantly increases the rate of gas
production and offsets increased heating requirements. However, the operation of these hotter digesters is
more demanding because the optimum temperature range is very small and biological upsets occur more
frequently.
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Advantages and disadvantages of anaerobic digesters
Advantages
Provide alternative fuel source
Increase solid decomposition
Require little land area
Reduce odors
Disadvantages
Require careful management
Do not reduce nutrients (N, P, & potassium)
Pose safety concerns–methane explosive
Have high costs
Composting
Composting is a natural aerobic process that stabilizes a variety of organic matter ranging from yard
waste to horse and cattle manure. It is one of the major recycling processes by which materials return to
the soil in the form of nutrients available for future use. When animal manure is properly composted, the
available organic matter is stabilized to the extent that it is no longer readily decomposable and no longer
subject to further anaerobic decomposition with its associated odors. Well-composted animal manure has
the odor of humus and is acceptable for land application in locations such as vegetable and flower gardens
or nursery plantations where fresh manure would be objectionable. Volume reduction during composting
ranges from 25% to 50%, depending upon the initial material. Because of the heat produced during
composting, well-controlled composting results in the destruction of most pathogens and weed seeds.
Recently, engineered in-vessel composting systems (Figure 5-6) using closed bins that rotate and
aerate manure during its conversion into compost have become popular. Some of this popularity has been
based on the concept of converting manure from a financial liability into a value-added marketable
product. Examples abound in which compost is being produced from manure and other waste materials at
a profit, but other examples can be cited in which compost production and marketing have not been
successful enough to justify costs.
Figure 5-6. In-vessel composting system.
The extent to which N is conserved in the composting process depends largely on the carbon-tonitrogen (C:N) ratio in the feed material. If the feed has a C:N ratio of 30 or above, little N loss occurs. If
the ratio is 20:1, N losses can be as high as 40%. Carbon-to-nitrogen ratios above 30:1 generally result in
nearly complete N conservation that may require a longer time to reach completion because the N is a
limiting nutrient.
Aerobic fermentation releases a considerable amount of heat during the composting process. The
composting material retains this heat, and elevated temperatures result. However, high temperatures are
essential for the destruction of pathogenic organisms and weed seeds. Decomposition also proceeds more
rapidly in the upper temperature ranges than at lower temperatures; the optimum temperature is around
60ºC (140ºF).
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Moisture is necessary for microorganism growth, but excessive moisture displaces the air that is
necessary for microorganism growth. The ideal moisture content for composting is between 40% and
60%; the upper limit somewhat depends upon the material being composted. If the material contains
straw, it may be possible to operate successfully well above 60% moisture, because straw retains its
strength at higher moisture contents and still allows air to move freely through the pile. Waste paper, in
contrast, becomes very soggy at 60% moisture and is packed with sufficient density to exclude air. Thus,
a compost pile containing waste newsprint needs to have a moisture content at the lower end of the range.
Aeration is necessary during aerobic digestion to produce high-quality compost and to avoid nuisance
conditions (e.g., odors, etc) during composting. Aeration also can be used to overcome excessive initial
moisture content. If a compost pile becomes anaerobic as indicated by odors or by a temperature drop
during the first 7 to 10 days, then turning (Figure 5-7) is required.
Figure 5-7. Tractor-driven windrow turner to aerate compost piles.
Throughout the history of engineered composting processes, the development and marketing of
additives to aid the composting process have steadily increased. Since initial waste materials are not
sterile, these additives are not essential during composting, including composting of animal manures.
Livestock and poultry producers who have a market for the finished product will more likely adopt
composting. That market may be nearby garden or nursery supply outlets, landscaping services, or
contractors establishing lawns or landscaping after a construction project has been completed. Cities
frequently use compost to establish and maintain parks and other recreational areas. The advantages of
compost over fresh manure are reductions in odor, fly attraction, pathogens, and weed seed concentration,
and according to many horticultural studies, a better plant response due to the addition of organic material
that builds better soil tilth. The disadvantages are the additional processing cost, additional space, and the
need to remove and manage a large amount of solids in the manure management system. Thus,
composting is not compatible with all livestock and poultry operations.
Advantages and disadvantages of composting
Advantages
Reduces odors
Controls pests, pathogens, and weed seeds
Increases soil quality
Provides marketable byproducts
Disadvantages
Requires careful management
Creates additional costs
Requires extra space
Vermicomposting
Vermicomposting is a process in which earthworms and microorganisms convert organic materials
into nutrient-rich humus called vermicompost. The resulting vermicompost can be used as a soil
amendment similar to conventional compost.
Removing the solids from a waste stream before a lagoon for vermicomposting or composting
reduces lagoon loading and thus the potential of odor, excessive sludge and P accumulation, and ammonia
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volatilization. It also reduces the amount of land required to apply the lagoon liquid. The
vermicomposting process stabilizes the nutrients and organic material diverted from the lagoon, making it
easier to find off-farm product uses.
Methods for growing earthworms range from extremely simple techniques such as using boxes and
outdoor windrows to complex automatic systems. In all of these systems, fresh organic manure is
frequently applied to the surface of the worm beds where the worms concentrate. The fresh manure must
be carefully added to maintain aerobic conditions and avoid excessive moisture. Following the
vermicomposting process, the worms are separated from the castings or compost product. The worms
needed for the vermicomposting process also have high value for animal and aquaculture feed.
Vermicomposting of dewatered swine manure is currently being conducted on a farm in North
Carolina that uses the manure solids recovered from a solid separator. The manure solids are applied to
worm beds that are maintained in an enclosed greenhouse facility. After a period of processing, the final
product is odor free and has excellent physical properties for use as a plant growth medium. The
vermicompost product is quite consistent throughout the year because the composition of the manure does
not change during the year, and greenhouse use eliminates extreme environmental fluctuations.
Advantages and disadvantages of vermicomposting
Advantages
Reduces lagoon loading/ excessive sludge
Controls odor
Provides nutrient reduction
Provides marketable byproducts
Disadvantages
Requires careful management
Requires extra space
Creates additional costs
Mortality Composting
Composting also can be used to dispose of dead livestock (Figure 5-8) and poultry. This process
presents an inexpensive method of processing mortality and biologically transforming it into a product
that can be land applied. Some materials, such as feathers, teeth, and bone fragments, that resist
decomposition, may be removed by mechanical screening if necessary.
Figure 5-8. Large livestock carcass composting bins.
The process of mortality composting differs from manure composting since the dead animal is not a
consistent mix of materials. Typically, animal mortality has a low C:N ratio, high moisture content, and a
compacted nature that reduces aeration. In practice, the mortality is surrounded by a C amendment, such
as sawdust or wood-shavings, with a high C:N ratio, moderate moisture, and good porosity.
The Ohio State University Extension staff describes mortality composting as “above ground burial in
a bio-mass filter with pathogen kill by high temperature.” A number of different facility types include
using bins and windrows. The decision-making process is based on the type of production, economics,
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regulations, access and land area for final application, and meeting environmental concerns (water
quality, disease, nuisances, and air quality).
Advantages and disadvantages of mortality composting
Advantages
Disposes of dead animals
Controls odor
Kills pathogens
Provides a marketable byproduct
Disadvantages
Requires careful management
Raises regulatory concerns
May have expensive initial setup
By-product Recovery
Many systems are being developed to process the manure nutrients derived from separated solids and
biomass or sludge into value-added byproducts. Raw and composted manure and mortalities have been
processed to such value-added byproducts as fertilizer, animal feed, and crab bait.
Animal manure and mortalities can be mixed with other organic materials or waste products and
processed by drying and pelletizing prior to dry storage as a feed or fertilizer. For example, fermentation
and preservation systems for converting poultry mortality mixed with sweet potato waste into valueadded products are also being studied. Turkey litter is being processed to produce a cattle feed ingredient,
and deep-stacked poultry litter is being processed to enhance its value as a cattle feed ingredient. Deepstacked poultry litter is also being evaluated as a protein supplement for animal feed.
Studies indicate that treated animal manure can serve as a beneficial addition to nursery potting soil
and can be used to grow ornamental crops. These components can substitute for nutritional additives such
as dolomitic limestone and minor element supplements. In addition, animal manure components tend to
increase P tissue levels in crops that are frequently deficient when grown in standard nursery potting soils.
Animal manure can provide nutrients early in the growth stage and serve the role of starter fertilizers
that growers frequently apply. On the other hand, use of these components requires careful management
of both nutrient application and irrigation management. Overall, nursery managers who have successfully
produced a wide variety of nursery crops with varied soil types also can successfully grow nursery crops
using treated animal manure (Figure 5-9) and benefit considerably from its use.
Figure 5-9. Nursery crops grown in a greenhouse using treated animal manure.
Advantages and disadvantages of by-product recovery
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Advantages
Provides a marketable byproduct
Creates feed supplements
Improves soil quality
Disadvantages
Requires careful management
Has time and space constraints
Energy Production
Alternative or advanced techniques for converting manure to energy result in the conservation of
valuable manure constituents and reduction of odor and ammonia volatilization. The energy retrieved
from animal manure can be used to supplement the fuel requirements of agricultural operations.
The direct combustion of dry manure or a mixture of manure and coal as a fuel source for a small
electric generator is one alternative being considered. Coal burning by U.S. electrical power utilities
consumes the majority of coal production and has been targeted as a significant air pollutant source. New
techniques are thus being developed to reduce production costs and gaseous emissions. Livestock and
poultry manure can be used as a supplemental fuel source. Since manure releases a range of gaseous
pollutants during storage and associated decomposition, overall emissions of greenhouse gases can be
reduced when blended with coal.
Anaerobic digestion has been used with beef, dairy, swine, and poultry manures to produce methane
gas, which farm owners may use to produce electricity for on-farm use or sale to an electric utility. The
biological breakdown of animal manure under oxygen-free conditions generates this biogas naturally. The
flammable gas is suitable for lighting and fueling combustion engines. Interest has recently increased in
collecting this byproduct, which can be gathered using covered lagoons or anaerobic digesters, for energy
generation. As mentioned previously, anaerobic digestion must be properly managed to reduce the risk of
explosive conditions.
Advantages and disadvantages of energy production
Advantages
Creates a marketable byproduct
Provides an on-farm fuel supplement
Can be used in conjunction with other manure
treatment facilities
Disadvantages
Requires careful management
Has safety risks
Constructed Wetland Systems
Constructed wetland systems provide a low-maintenance, cost-effective option for further treating
pretreated waste streams. These man-made wetlands (Figure 5-10) replicate the same general components
of natural wetlands (soil, microbial activity, vegetation, etc.) and can reduce nutrient, BOD, and
suspended solid loads. These contaminants are transformed or inactivated by a combination of physical,
chemical, and biological processes inherent to wetland systems.
Use of constructed wetlands typically requires pretreatment, because high organic loads may overload
the system with oxygen-demanding pollutants, reduce plant vitality, increase odors, and decrease
treatment effectiveness. Elevated solids content may lead to sediment accumulation at the wastewater
inlet and adversely affect treatment. Furthermore, excessive nutrient concentrations may overload the
system, potentially affecting the biology of the system and reducing discharged water quality.
Due to these problems, an appropriate strategy should be used to reduce contaminant levels to
promote wetland processes and remove settleable, floating, and non-degradable materials prior to a waste
stream entering a constructed wetland. Pretreatment can be accomplished using lagoons, dilution with
water, settling basins, and mechanical separators either singly or in combination. The USDA Natural
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Figure 5-10. Constructed wetland.
Resources Conservation Service (NRCS) recommends wastewater pretreatment achieving target
concentrations of approximately 1,500 mg/L total solids and 100 mg/L ammonia for water entering a
constructed wetland.
A number of constructed wetland types may be used for treating animal waste streams and feedlot
runoff. Surface-flow constructed wetlands are the most commonly used wetlands for treating animal
manure and the type that the USDA NRCS currently recommends in the technical requirements of the
Constructed Wetlands for Agriculture for Wastewater Treatment document. The advantages of surfaceflow wetlands include the ability to efficiently treat manure associated with the discharge from animal
lagoons and other pretreatment facilities, relatively low construction costs compared with subsurface
systems, relative ease of management, and ease of repair and maintenance if problems occur. Information
on other wetland types not discussed here can be obtained from the USDA.
Typical agricultural wastewater treated using wetlands includes milkhouse wastewater, manure
treatment lagoon effluent, and lot runoff pretreated with settling basins. Management of direct feedlot and
barnyard runoff poses some technical difficulties, because these sources provide an irregular supply of
water that will not solely support a wetland system in some climates.
Incorporation of a constructed wetland into an overall agricultural manure management system can
provide a number of benefits and advantages to a livestock or poultry operator. These systems typically
are an inexpensive method to reduce pollutants prior to discharge from the site. Producers may further
reduce costs by constructing their own wetlands (following proper guidance and regulatory statutes).
Maintenance requirements are low: although a monitoring regime should be employed to ensure effective
treatment. Additional benefits include aesthetically pleasing surroundings that may attract desirable
wildlife.
Disadvantages of treatment wetlands primarily depend on land constraints of a production facility.
Although constructed wetlands are not typically large, limited land area may prevent appropriate sizing.
In addition, the pretreatment requirements may be prohibited when considering highly concentrated waste
streams.
Advantages and disadvantages of constructed wetlands
Advantages
Inexpensive
Low maintenance
Aesthetically pleasing
Disadvantages
Only polish a waste stream
Require a large land area
Have high monitoring requirements
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Emerging Technology Overview
A number of innovative manure treatment technologies exist that currently remain in the
developmental and testing stages. This section provides a brief overview of some technologies that may
provide alternatives for treating animal manure in the future.
Polymer-enhanced solids separation utilizes the binding ability of polymers to remove solids from a
liquid stream and associated nutrients to increase separation efficiency. A study at North Carolina State
University is investigating the use of mechanical separators equipped with screens made of these
compounds. Other studies have investigated the use of adding these chemicals into a waste stream as an
additive to flocculate solid particles.
Use of aerated treatment basins may provide an alternative to anaerobic lagoons. Aerated basins,
termed bioreactors, can stimulate microbial activity to accelerate the breakdown of odorous compounds.
Decomposition of organic material also can be increased using such systems.
Artificial floating layers have been evaluated to control odors from livestock and poultry operations.
Although this technique lends itself to liquid manure systems, information may be inferred from this
research that could be applicable to covers for broiler litter and mortality compost piles. Scum materials
used included chopped cornstalks, sawdust, wood shavings, rice hulls, ground corncobs, and grass
clippings, all as separate amendments and as a mixture with oil (both waste oil and vegetable oil).
Use of duckweed as a lagoon cover also has received attention; it converts nutrients to plant biomass,
reducing the nutrient levels needed to be land applied. When harvested, the duckweed can be dried and
used as animal feed supplement. Systems are being tested to separate solids from liquids immediately
upon excretion. Belts and sloping floors are being tested in North Carolina and Michigan for their abilities
to keep urine and feces separate, thus eliminating the need to separate solids later.
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Questions
True or False
1. Constructed wetlands have proven effective enough to act as a primary manure treatment mechanism.
True
False
Answer: False
2. Manure can be mixed with coal to provide a fuel source.
True
False
Answer: True
3. When using an anaerobic lagoon system, most phosphorus in manure will be lost to the atmosphere.
True
False
Answer: False
4. Aerobic treatment takes place in the presence of oxygen.
True
False
Answer: True
5. Dead animals can be effectively disposed of using composting methods.
True
False
Answer: True
Multiple Choice
6. Anaerobic digestion will produce __________, which can be collected and used as a fuel source.
a. Ammonia
b. Carbon dioxide
c. Methane
d. Oxygen
Answer: c
7. Composting can help reduce all of the following except __________.
a. Pathogens
b. Odor
c. Weed seeds
d. Phosphorus
Answer: d
8. Vermicomposting uses __________ to help convert manure to humus.
a. Worms
b. Lagoons
c. Mites
d. Anaerobic digesters
Answer: a
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9. Land application of animal manure provides all of the following advantages except that it does not
__________.
a. Reduce fertilizer costs
b. Improve soil quality
c. Reduce odor problems
d. Provide essential plant nutrients
Answer: c
10. Disadvantages to constructed wetlands typically involve __________.
a. High costs
b. Large land area requirements
c. High maintenance
d. Incompatibility with other treatment systems.
Answer: b
Fill in the Blank
11. __________ is the process that describes the attachment of suspended solids to each other to form
clumps.
Answer: Flocculation
12. BOD and COD are ways to describe the amount of __________ in water that removes oxygen during
decomposition.
Answer: Organic matter
13. Particles can be removed by __________, which reduces flow velocity so it is not sufficient to keep a
certain size or weight of solid in suspension.
Answer: Sedimentation
14. Obtaining value-added products such as animal feed is known as __________.
Answer: By-product recovery
15. Sizing of anaerobic lagoons is based on the environmental factors of temperature and __________.
Answer: Precipitation
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