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Changing the Paradigm for Manure Management

Bruce T. Bowman, Former Chair
CARC Expert Committee for Manure Management

last updated July 11, 2003

Ideas and opinions expressed in this document are those of the author and do not represent the official position or policies of any organization. This document is a work-in-progress and will be updated from time to time.

The purpose of this document is to stimulate discussion on this important issue. If you have any comments or suggestions,
please forward them to Bruce Bowman

Other related information

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Agriculture has been challenged in managing its livestock manures since farmers started housing livestock in barns many eons ago. However, problems associated with confined livestock operations have increased greatly in recent decades with the rapidly increasing scale of operations relative to the available land base for utilizing their manures.  Farmers often have limited options as to how, where and when they can spread the manure on their land base.

From a public perspective, the most common issue associated with manure management has been objectionable odours, and more recently, negative impacts on water quality by nutrients and pathogens, especially since the Walkerton water crisis of 2000. The odour issue, in particular, may have been accentuated because of the increasing popularity of labour-saving liquid manure handling systems which favour anaerobic storage conditions fostering the production of many odour-producing compounds.

Not only has the intensity of rural livestock operations increased. There has been a steady exodus of urban populations into rural areas of the country seeking a more quiet, pristine environment, away from urban noise, stress and pollution. In most cases these people have limited knowledge of how agriculture operates, and even less understanding or appreciation of how their food is produced or where it comes from. Consequently the clash of the two "cultures" has led to increased tension between neighbours, and resulted in increased involvement of municipal governments in agricultural operations. As the intensity of livestock operations has increased, so have the numbers and complexity of rules and regulations that try to bring some semblance of order to the entire livestock production system while providing an acceptable level of comfort to the general public.


The New Paradigm

In the past few years, a variety of forces, both from inside and outside the livestock industry have started to interact with and influence decisions on how farmers manage their operations.

These forces may well facilitate changing the entire paradigm for manure management from one driven by prescriptive regulations, to a more sustainable paradigm in which farmers can realize some economic benefits by processing and adding value their livestock manures while virtually eliminating environmental problems such as odour and pathogens. Thus, prescriptive regulations become a safety net, rather than being the principle driver for directing manure management practices.

Forces Impacting on the Livestock Industry

1. Impacts of the 2000 Walkerton water crisis. Canadians have become much more aware and interested in their drinking water sources since this tragic incident in 2000. While the main reasons why E. coli O157H:7 contaminated the drinking water system and compromised the health of many people were a consequence of failed municipal water treatment systems, the primary source of this pathogen was traced back to a nearby well-run beef operation that followed current best management practices, and in fact exceeded many of the regulatory requirements of the day. (Part 1 Report, Walkerton Commission, Jan. 2002). While the risk of repeating the same occurrence is quite low, nevertheless it is real. However, to keep this issue in perspective, it is important to also recognize that there are measurable risks associated with other contributing pathogen sources to surface water contamination, including wildlife and rural septic systems. One consequence of this crisis is increasing expectations by the public that livestock manures be processed in some fashion before being land-applied, especially when used in off-farm applications.

2. Nutrient Management Planning. The introduction of more rigorous nutrient management planning at both the national and provincial levels will bring a better accounting system for managing nutrients, and will ultimately assist the farmer in more efficient and economic utilization of nutrients. One likely consequence will be that many livestock farmers will discover that they have excess nutrients for their existing land base, and will be looking for innovative ways of exporting those nutrients.

3. Nutrient Excesses and Large-Scale Nutrient Re-distribution. For the past century, agriculture has increasingly relied upon mineral fertilizers for crop production. Over the past several decades, specialization in agriculture has uncoupled cereal crop production from livestock production. Consequently, there are now livestock production areas with nutrient excesses, and with no practical way of recycling those excesses back to crop production areas requiring annual nutrient inputs. Likewise, there are large nutrient excesses throughout the human food and waste chains that also need to be recycled back to the source crop production areas (25% of agriculturally-applied nitrogen leaves the farm as food - Barton and Atwater, 2002).

From:  Philip K. Barton and James W. Atwater. 2002.Nitrous Oxide Emissions and the Anthropogenic Nitrogen in Wastewater and Solid Waste.  
J. of Environ. Eng.128: 137 - 150.

"In the 20th century, human interference in the nitrogen cycle has caused a doubling of the global nitrogen fixation rate, thereby intensifying global nitrous oxide (N2O) production during microbial nitrification and denitrification. Nitrous oxide is a powerful greenhouse gas, important in climate change, and as well, is a stratospheric ozone-depleting substance. It is likely that much of the Earth’s population now relies on anthropogenic nitrogen in its food supplies, resulting in anthropogenic nitrogen contained in wastes requiring management."

4. Kyoto Protocol - Commitments to reduce greenhouse gas (ghg) emissions in agriculture. With the signing of the Kyoto Protocol, Canada has made commitments to reduce its ghg emissions to 1990 levels, including those in agriculture. Methane (21 x impact of CO2) and nitrous oxide (310 x impact of CO2) are the two largest ghg sources in agriculture, and manure management practices contribute significantly to the production of both of these sources. Over the next few years there will be increasing pressure for agriculture to develop manure management practices that minimize these emissions.

5. Privatization of Electrical Generating Utilities. The privatization of electrical generation utilities that started in California several years ago is now starting in several Canadian provinces. The immediate impacts are for more volatile end-user costs, which especially affect many livestock operations because of their heavy usage and dependence on electricity. Since the end-user cost is roughly twice that of the original generating cost, "energy independence" will become of increasing interest to livestock producers.

6. Development of Renewable Energy Sources. Because of the increasing difficulties in developing new environmentally-friendly sources of electrical energy, there is also a rapidly increasing interest in the development of "distributed, renewable energy" sources which decrease dependence on traditional fossil fuel sources, and which also reduce aerial emissions of GHGs and other pollutants. Livestock manures can be an excellent renewable energy source for providing continuous 7/24 operation, unlike some other renewable sources, such as wind or solar power.

7. Emission Trading Credits - Associated with renewable energy sources is the potential for emission trading credits for the avoidance of creating GHG emissions, which are just in the early stages of development in Canada, but which could provide an additional revenue stream for livestock operations.

Manure Processing- Options

In order to comprehensively address odour and pathogen issues, manure must be processed in some fashion, regardless of whether it is in liquid or solid form. Although there are numerous products on the market which claim to reduce odours and pathogens in liquid manure systems, these products at best can only reduce some odour emissions or pathogen levels, not treat the entire liquid volume. Other practices such as lagoon covers can suppress odour release, but do not treat the causes of odour production.

Composting and anaerobic digestion are two different technologies that process the entire manure volume and can greatly reduce or essentially eliminate both odour and pathogens from manure. Table 1 compares some of the features of composting with anaerobic digestion.

Table 1. Comparisons between composting and anaerobic digestion
  Elimination of Renewable
Energy Generation
Ammonia -Nitrogen
after Processing
Pathogens Odours



  Y/N 3

Y/N 4

N 5

Anaerobic Digestion 1

   Y 2




Y 6

Y = Yes; N = No;  Y/N - depends on operating conditions employed
1 - Assuming mesophilic operation (37°C)
2 - Complete destruction with post- or pre-thermophilic stage (65-70°C).
3 - Limited - possible to capture heat from large composting systems for heating nearby greenhouses
4 - Immature static compost piles can turn anaerobic, generating methane emissions
5 - Excessive turning of compost can result in substantial ammonia losses
6 - Anaerobic digestion conserves virtually all nutrients during processing

While composting is a relatively low tech, low cost approach, anaerobic digestion is a much more expensive and complex process to manage, but offers some important advantages:

1. Biogas (methane) generation for heat and electricity, which can be an important, continuous revenue stream for the operation, and one which can provide realistic payback opportunities. There is the additional benefit of avoidance of methane emissions.

2. Conservation of nutrients. Over 90% of all nutrients entering anaerobic digesters are present following processing. One key disadvantage of composting is that significant amounts of ammonia-N are frequently lost during the turning process. This becomes more of an issue as replacement N fertilizers increase in cost, in addition to greenhouse gas emissions and energy consumption associated with new N fertilizer production. Furthermore, ammonia can be considered a pre-cursor of nitrous oxide (the worst ghg gas) since it easily converts to NH4+ at neutral pHs, and through the nitrification process, can partially be transformed into nitrous oxide (Barton & Atwater, 2002, P.138). There is a relatively new rotary drum composting system that may be able to reduce ammonia-N losses during composting by controlling air flow through the system.

While manure can be processed in either the liquid or solid states (see above) for value-added processing and exporting from the farm, it is necessary that it be dried, since transporting water is not cost effective. There are several options for processing liquid or solid manures (Table 2).

Table 2. Options for Processing Livestock Manure
Physical State Options for Processing
Liquid 1 1. De-water + composting
2. Anaerobic digestion -----> direct land application
3. Anaerobic digestion -----> de-water (off-farm use)
Solid 2 1. Composting
2. Blend with liquid -----> anaerobic digestion -----> de-water (off-farm use)
1 - Solids content usually < 12% - must be pumpable
2 - Composting requires moisture content <65%, or de-water first

De-watering (solid-liquid separation) manure slurries usually produces a nutrient-rich liquid phase which must also be managed. The liquid phase can either be land-applied (if sufficient land base), or the nutrients scavenged from the liquid back into the solid phase, to add value. There are numerous technologies (some from the municipal waste management sector), such as coagulation, filtration, membrane separation, etc., that can increase the removal efficiencies of nutrients in the de-watering process. For anaerobic digestion systems, there is a vacuum cascade drying system that is basically a low-temperature water condensation process using excess heat from the digester to de-water the processed slurry under a partial vacuum, and which produces relatively clean (low nutrient content) water that can be discharged. This process also kills all pathogens since it operates near 70°C.

Option # 2 for solids processing - blending solid manure with liquids - at first glance does not make much sense, unless there are significant economic returns available from anaerobic digestion, such as co-generating biogas (methane) for heat and electrical power. This option becomes more attractive for livestock operations in which there is already nutrient-rich runoff and collection, such as from feedlots, which in itself adds value to the process.

Changing the Paradigm

Opportunities for economic benefit for the livestock producer could be the principle drivers for creating a new paradigm for manure management, in which producers solve most of the environmental problems associated with livestock manures for economic, rather than regulatory reasons.

These economic drivers include:

1. Combined Heat and Electrical Power (CHP) generation from co-generating anaerobic digestion systems, with sale of renewable energy back to the power grid or sale of excess heat to nearby businesses;

2. Sale of emission trading credits created by the avoidance of ghg emissions during the storage, handling and processing phases;

3. Off-Farm sale of value-added recycled livestock nutrients in the form of organic amendments that are bulk-blendable with existing mineral fertilizer products.

While anaerobic digestion systems can provide all three revenue streams, composting can benefit from only the third, off-farm sale of recycled nutrients. Thus the farmer must balance the advantages of a more complex high-tech approach vs the lower cost and simplicity of the low-tech approach.

There are currently several key barriers impeding the wide spread adoption of these processing technologies:

  1. Lack of premium buy-back rates for "green"/renewable forms of energy.
  2. Lack of access to power grids for renewable energy sources.
  3. Lack of a fully developed emissions trading credit system which includes agriculture.
  4. Lack of a viable private market for recycled livestock nutrients.
  5. Lack of environmental loan guarantees by governments to assist livestock producers in making large capital investments for environmental improvements.
Table 3. Current status of barriers to implementing new manure management paradigm
Barrier Status

Premium buy-back of green energy

Some recent interest by Federal Government.

Buy-back rates > $0.12/kwh will provide reasonable pay back periods, and will be a catalyst for adoption

Access to power grids for green energy suppliers

Attitudes of energy utilities changing quickly as governments promote distributed, renewable energy sources.

Emissions trading credits

System for trading is in early stages of development - by late 2004, may be operational - need for brokers to assemble "blocks of credits" from groups of farmers to trade with utilities, municipalities, governments.

Market for recycled livestock nutrients

Need for technical & economic assessments to determine barriers to becoming a successful private business - may require some incentives (tax concessions) to assist development of this industry.

Environmental loan guarantees

Immediate need for governments to underwrite some of risk for farmers to make large investments for environmental improvements - may be single greatest barrier to adoption of advanced manure processing technologies.


Concept of Shared Benefits - Who pays?

Farmers have traditionally been stuck with majority of the costs of implementing environmental improvements on their farms, because, unlike many other areas of private industry, they are unable to pass on those increased production costs to the consumer. Where farmers make investments strictly for their own economic gain, then that as their own business decision and risk. However, when farmers make substantial investments for which there are environmental benefits for the general public as well as for themselves, this is a shared benefit for which the public should contribute for the betterment of society.

Many of the positive outcomes from advanced manure processing technologies are shared benefits, including pathogen and odour reduction, avoidance of ghg emissions, generation of renewable (green) energy, and the recycling of livestock nutrients.


Given the present trends towards the development of distributed, renewable energy sources and the development of a emission trading credit system, there is a fairly high probability that the premiums for generating clean, green energy and avoiding ghg emissions will become significant catalysts for farmers to consider investing in advanced manure processing systems.

Although the payback period may be quite reasonable (< 7 - 10yr), the single greatest barrier may well be the need for environmental loan guarantees to assist the producer in managing the risks during the design, installation and initial testing phases of the processing system.

The economic viability for manure processing systems would be considerably enhanced by development of a market for value-added, treated manure products, that will be a key means for recycling excess livestock nutrients back to crop production areas. Granulated, treated manure products that can be bulk-blended with mineral fertilizers may be one viable approach.

One of the positive spin-offs for advanced manure processing systems should be an increased level of comfort by the general public for the safe management of livestock manures, and lessen the conflicts that are currently prevalent in rural communities across the country between livestock producers and their neighbours.


Related Reading

Challenges and Opportunities in Manure Management. W.G. Bickert, BioSystems Eng., Michigan State U., pp. 361-367 in Fifth Int. Dairy Housing Proc. 29-31 Jan. 2003 Conference, (Fort Worth, Texas, USA), ed. K. A. Janni., 29 Jan. 2003. ASAE Pub #701P0203  - The challenges in manure management today result directly from evolutions related to technology and economics. Animal manure, once viewed as an important soil conditioner and a source of crop nutrients is now viewed as a waste and potential pollutant. Anaerobic digestion, an important means to reduce manure odor, has not been attractive because the energy produced can often be obtained more cheaply elsewhere.

Interesting series of papers on Sustainable Farming by Dr. John Ikerd, Prof. Emeritus, U. of Missouri - Complete set of Papers   (approx. 65) [3572 KB pdf].




Bruce T. Bowman, Archivist
Last Updated: Tuesday, April 18, 2017 02:47:40 PM