The Effort of Waste

Managing manure is not a one-size-fits-all procedure. Farm size, animal density, land characteristics, financial resources, available labor, storage facilities and equipment, and water resources are just some of the variables that impact manure management decisions. Making the best decisions to minimize manure hazards and maximize manure benefits begins with knowing your options.

Manure management is a part of the overall nutrient management plan for a livestock farm. Such a plan will identify the acreage available for spreading nutrient-laden manure, and help to determine whether your farm has enough acreage to handle the volume of manure produced, without negatively impacting the soil and water quality. Nutrient management calculations factor in your land characteristics and soil properties, grazing schedule and crop production, special environmental concerns, manure volume and other variables, which will impact how animal waste can safely be managed on the farm.

Manure management systems

Managing manure means ensuring that nutrients, most importantly nitrogen and phosphorus, are not being lost to the soil or water, that harmful air emissions from manure are minimized, and that any manure pathogens are not causing animal or human health issues. Manure is a natural fertilizer, containing N-P-K (nitrogen-phosphate-potassium), as well as micronutrients. It is also a source of organic manner. A manure management system is inclusive of the amount and type of livestock manure generated, whether it is fresh or composted, the manner in which it is collected, stored and transported, any treatment it undergoes, and how it is ultimately utilized.

Perhaps the simplest manure management system is the direct application of manure on pasture by grazing animals. Controlling the land that is grazed, the density of animal units, and the time spent in various pasture locations keeps the land fertile, without excessive fertility concerns.

But when manure accumulates, it must be managed more intensively. The first step to managing manure is deciding how to handle it. Removing manure from livestock areas and safely holding it until it can be judiciously used can be accomplished in a variety of ways, from simple to complex.

Runoff, odor and pathogen concerns need to be addressed with any storage solution. Manure can be handled and stored as a liquid, a solid, separated into both components, or handled as a slurry. Each type of handling and storage option has its pros and cons, and allows for certain treatment and use options.

Solid and liquids are separated on the farm after being flushed from the dairy barn with recycled waste water.
Solid and liquids are separated on the farm after being flushed from the dairy barn with recycled waste water. Liquid wastewater is collected in a 2.5 million-gallon lagoon, where waste is pumped out and used on the crop fields, and is used to feed the 680,000-gallon methane digester, installed in 2009. The digester provides electricity for one-third of the entire operation, heating 1,800 gallons of water for the on-farm processing plant, and leaving a by-product of manure residue, which is spread on the fields as fertilizer.Courtesy of the Maryland Department of Agriculture and Kilby Creamery.

Storage basics

Keeping water out of manure storage areas or livestock areas where manure accumulates is an important first step for any manure management system. Roofs, gutters and basins to direct water are essential to control runoff and contamination. Directing any liquid runoff into vegetative treatment strips and filters out excessive nutrients. Runoff needs to be evenly distributed, and vegetative areas should be regularly harvested to prevent nutrient buildup.

On a small farm, manure often was traditionally handled by collecting, hauling and spreading it onto fields daily. But frozen ground, rainy days and too much manure at the wrong time can cause runoff and other issues. One option is to collect the manure in a spreader, so there is more control over when field application occurs. With fresh manure, pathogens can pose problems, so careful timing before grazing and following all safety regulations for fresh manure on cropland is necessary.

Stockpiling manure, so it is available for use when conditions are optimal, is a more flexible and productive management option. Stockpiled manure can be removed from the farm for use elsewhere, or utilized on-farm. Either way, siting the storage on a gravel pad, covering the pile to control moisture and odor, and implementing a vegetative filter strip or berm to control any runoff are crucial. Upgrading from a stockpile to a dry stack facility – one with three walls to contain the manure, and a sloped concrete floor for drainage, is a step up. Either option involves collecting manure and bedding and handling it in a solid form.

Manure can also be handled in slurry form, where little bedding is added to the manure and urine, and the waste is collected in a form that is about 10 percent solids. Here, the manure is collected in a pit or tank under the barn via slotted floors, or is scraped or vacuumed from barn areas into tanks. Slurry manure can be pumped into a tankwagon, or pumped via pipeline, for field application.

Liquid manure handling – where solids are less than 5 percent – options are more expensive, and typically found on larger dairy farms or confined animal feeding operations, where water is added to livestock waste. The advantage is less ongoing daily labor in managing the manure. In a basic system, wash water flushes the manure into a storage pond or above-ground tank. These will be emptied and applied onto the field according to the nutrient management plan.

Manure treatments

While manure handling and storage are necessary parts of livestock farming, manure treatment options move one step beyond safe use, and change the manure by adding something, taking something away, or otherwise altering it into something more.

Some treatment systems help to remove excess nutrients from soils and waterways, such as denitrifying woodchip bioreactors, by lessening the impact of any nutrient runoff. Others work by turning livestock waste into on-farm energy, or even consumer products. Some make manure solids available for other farm uses such as bedding or compost, and still others treat liquid manure, making it available for irrigation purposes.

One common system is solid-liquid manure separation. This takes the liquid or slurry and mechanically separates it into solids and liquids. Solids can be composted or used as bedding, while liquid portions can be applied as fertilizer, or recycled for dairy flush water.

For solid manure, composting is a treatment option that kills pathogens, reduces odors, and reduces the volume of manure. It also decreases the nutrients load, so the risk of adding too much nitrogen or phosphorus, and leeching nutrients from the soil is minimized.

Composting manure isn’t the same as storing it. Composting is an active process, involving aerobic microbial activity, a balance of ingredients, attention to the amount of liquid, and a turning of the pile for aeration. A compost system can be achieved via windrows, on compacted soil, or a gravel or concrete bed, or can be accomplished with several dry stack bays, from which the manure and bedding, along with any other waste being composted, is turned and aerated as it is moved from bay to bay.

The resulting compost can then be utilized on the farm, or can be sold as a consumer product. Either way, composting helps to eliminate some nutrient management concerns by converting raw manure into a more useable product with less potential negative environmental impacts.

Aerobic digestion treatments can also be utilized in lagoon treatment systems. A treatment lagoon, where manure microbes act to degrade manure solids under large dilution volumes, works to reduce odor, as well as greenhouse gas emissions, with aerobic agitation systems offering better results than anaerobic treatment lagoons. Aeration equipment varies. A lagoon, unlike a storage pond or tank, is not designed to be emptied regularly of its separated solids, which are degraded by the microbes. Depending on the system, liquid from lagoons can be further treated and applied as irrigation water for crops.

No matter how manure is handled and treated, applying it to fields is a balancing act, and field runoff is a primary pollutant of many waterways. Reducing the amount of nutrients being introduced, without impacting crop yield or removing fields from production, may be as simple as a denitrifying woodchip bioreactor.

A bioreactor is placed underground in a ditch on the field edges, five or six feet deep, where it can be run over and mowed. The bioreactor design utilizes naturally-occurring microbes on a woodchip substrate. These microbes, under anaerobic conditions, consume carbon and oxidize nitrogen. Field nitrates are converted into harmless dinitrogen gas. Adding biochar has the potential to mitigate phosphorus levels, too.

The Conservation Fund
The Conservation Fund, Freshwater InstituteCourtesy of Laura Christianson, Ph.D.,

Beyond the basics

All livestock farms have to manage manure. It either must be hauled away, or used onsite as a part of a comprehensive management plan. But today, innovative ways not only to save money through efficient manure handling and usage, but to make money from manure, go beyond selling it as fertilizer or compost.

Anaerobic digestion of manure is being used primarily on dairy farms to process manure and generate energy. Here, microbes operate in an oxygen-free environment, biodegrading manure into solids, liquids and gas. Anaerobic digestion of manure reduces methane emissions, odors, pathogens and weed seeds and produces biogas, which can be captured for renewal energy productions. Manure solids can be recovered and utilized as bedding, made into compost, applied to fields, or further utilized in other consumer products.

Typically, anaerobic digestion systems work in conjunction with slurry or liquid manure handling systems. They can take the form of a covered lagoon digester, a plug flow digester – a covered, narrow concrete tank, or a complete mix digester in a enclosed, heated tank. Dry digesters, working with solids, are also available.

But digesters leave a good amount of excess heat behind, which can be captured and re-utilized. In one study, Cornell student researchers captured this heat, and used it to chill water, which was then piped through water beds to cool down dairy cows. The heat can be recaptured and used in a variety of other applications as well.

Associate professor Eric Coats, of the University of Idaho, has led graduate students in the design of a system that utilizes manure to create a 100 percent biodegradable plastic, which can be used in a variety of consumer products. Planter pots, weed barrier products, seed coatings and other single-use plastic applications are the intended end-result.

The process involves tank fermentation of manure, which converts some of the waste product into organic acids. These are then consumed by naturally-occurring bacteria, of which over 300 species are known. These bacteria can convert the organic acids into carbon, which they store in the form of polyhydroxyalkanoate (PHA), a biodegradable plastic. The carbon is then harvested for use. Coats and his team are working on a practical, cost-effective manure-to-plastics system that can be used economically on individual farms.

Thermal manure-to-energy systems utilize solid manures, which are combusted, pyrolized or gasified, depending on oxygen levels and temperature, and convert them into combustible gas. The gas is directed through a heat exchanger, and the heat is captured for use. Co-products include liquid bio-oils, diesel fuel, and combustible gases, as well as biochar and ash, both of which contain nutrients and can be utilized as soil enhancers.

One example of a manure management system that provides energy, reduces nutrient concerns and creates value-added by-products was designed by Bion Environmental Technologies. While designed for concentrated animal feeding operations, with a minimal size of about 1,800 head of dairy cattle, the potential also exists for this technology to be utilized off-farm as a regional processing site taking manure from smaller farms and processing it.

“Bion’s modular platform utilizes patented biological, mechanical, chemical and thermal processes to recover up to 95 percent of the nutrients in the effluent, reduce greenhouse gases by 90 percent, virtually eliminate ammonia emissions, and substantially reduce pathogens, antibiotics and hormones in the waste stream,” Craig Scott, Bion communications director, said. “In addition to reclaiming valuable nutrients and clean water, the technology platform also recovers renewable energy from the waste stream,” and will “separate and aggregate the various components of the waste stream to produce industry-standard value-added by-products such as organic fertilizer and soil amendment products.”

While a system such as Bion’s requires a large capital outlay and ongoing maintenance and operational costs, it creates financially-valuable by-products, generates energy, and is able to produce verified nutrient credits. While not scaled for small farm use, nutrients from large-scale CAFO farms contribute the majority of agricultural manure nutrients found in many watersheds, and controlling these can potentially allow small farms to operate under less regulatory pressure, Scott said.

“Smaller scale best management practices are much more effective than Bion’s technology at small and medium sized livestock operations,” Scott said. “Bion’s technology is definitely not a solution for all farms, but it can be effective on the largest farms which are generally the largest contributors of nutrient pollution.”

No matter your size, raising livestock means managing manure. Scaling manure management practices to farm size maximizes benefits, and minimizes costs. From simple manure storage to innovative ways of converting waste into energy, or even into consumer products, managing manure properly adds value to your farm, and limits any negative impact to the environment.