Odour Control on Livestock and Poultry Farms

Agdex#:	700
Publication Date:	December 2003
Order#:	03-111
Last Reviewed:	December 2003
History:	Replaces OMAFRA Factsheet Odour Control on Livestock and Poultry Farms, Order No. 96-103
Written by:	Michael Toombs - Rural/Urban Interface Specialist/OMAF; OMAFRA Staff

Table of Contents

• Introduction
• Sources of Odours
• Spread of Odours
• Malodours - Unacceptable Odours
• Practical Ways to Help Minimize Odour Complaints
• Preventing the Production of Odour Through Management
• Preventing the Release and Transport of Odours
• Biofilters
• Windbreaks
• In-barn Conditions
• Treating Odours
• Additives

Introduction

In Ontario, more than half the complaints regarding agriculture concern odour. Nuisance odour complaints are exempt from the Environmental Protection Act. However, odours that create health problems are addressed in the Environmental Protection Act.

Complaints concerning odours from animal agricultural operations are increasing. The trend toward larger animal facilities with liquid manure systems only intensifies the problem. This Factsheet outlines practical methods to help control odours from barns and manure storages.

Many odour control techniques cost nothing more than operator time. These include good housekeeping, good manure management, careful siting of animal housing and manure storages through the use of Minimum Distance Separation (MDS) formulae, and communication between neighbours.

Table 1 below contains sample MDS requirements that are calculated as the product of 5 factors including type of farm operation, type of manure system and form of development present or being proposed.

If prevention measures fail to stop disputes over farm odours, technology-based approaches to odour control may be necessary. These may be expensive and their effectiveness may vary widely. Current odour control methods include preventing the production, release and transport of odours and odour treatment.

Sources Of Odours

Odours originating from livestock manure are a result of a broad range of over 168 odour-producing compounds. Commonly reported compounds associated with livestock waste include hydrogen sulphide (a rotten egg odour) and ammonia (a sharp pungent odour).

Most offensive odours are created by the anaerobic (without air) decay of wet organic matter such as manure, feed or silage. Warm temperatures (Figure 1) enhance anaerobic decay and foul odour production. Odours primarily originate from the animal housing facility, manure handling, silage storage, improperly handled deadstock and decaying organic matter. Odour is measured according to 3 parameters: quality, strength and occurrence. Odour quality is a comparison with a known odour such as rotten eggs or roses. Strength is the amount of fresh air needed to dilute odorous air to the threshold odour level where it can just be detected. Occurrence is the frequency and length of time the odour persists.

Figure 1. If the right combination of organic matter, water and warm temperatures exist, there is the potential for foul odours to be created.

Spread Of Odours

Odours can either be broadcast through air as a gas or be absorbed and transported by dust particles. Odours tend to linger in an area on humid, windless days. Odours will dissipate on dry, windy days.

Malodours – Unacceptable Odours

The main factors affecting the acceptability of farm-generated odours are frequency, duration, offensiveness and sensitivity. Neighbours may tolerate frequent or intense odours that are of short duration and do not linger in the air. Offensiveness and sensitivity to odours varies from person to person. Odours are context dependent — a person's experiences, memories, emotions and visual perceptions all combine in determining whether or not an odour is acceptable. A clean, orderly livestock farm with landscaping is effective in creating a non-offensive situation. Some people are more stressed by the thought of the odours than they are by any actual physical effects from the odours.

Practical Ways To Help Minimize Odour Complaints

Preventing the Production of Odour Through Management

• Clean up spilled feed, silage and manure. Even small leaks in feed augers can result in large accumulations of waste feed over time.
• Wash manure-caked spreading equipment shortly after use.
• Keep animals clean — their warm bodies accelerate anaerobic decay.
• Dispose of deadstock promptly and properly in accordance with the Dead Animal Disposal Act.
• Minimize dust levels to prevent odours attached to dust particles from escaping through the ventilation system.
• Keep organic matter such as feed or bedding dry. Anaerobic decay, the major process of odour generation, is inhibited if moisture content is kept below 40%.
• Grade the farmstead to avoid standing water. Direct clean water away from manure piles.
• Check regularly for leaks from drinking water supplies — especially in chicken and turkey broiler barns.
• Ensure the ventilation systems are in good working order. Good ventilation helps to keep barns dry.

Preventing the Release and Transport of Odours

Odour production cannot be completely prevented on a farm. Therefore, most odour control methods are designed to keep or dissipate odours within the farm boundary, thus minimizing odour complaints from surrounding neighbours.

Odours from solid manure, that is, manure below 75%–80% moisture content, generally do not generate complaints. However, excessive moisture in solid manure can cause odours because it creates anaerobic conditions. To prevent wet conditions:

• Divert clean water away from manure storages.
• Reduce water bowl spillage.
• Obtain drier manure by adding bedding to absorb water.
• Roof a solid manure storage to exclude precipitation.
• For liquid manure storages the intensity of odours generated increases in direct proportion with the amount of top surface area. A covered manure storage generates almost no odours. A circular concrete tank with the same storage capacity as a liquid earthen manure storage generates less odours than an earthen manure storage since it has less top surface area. For example, consider a barn that needs 1,071 m³ (37,800 ft.³) of manure storage capacity. The barn would require a circular concrete storage 3.7 m (12 ft.) deep by 21 m (69 ft.) diameter, which would have a surface area of 350 m² (3,740 ft.²). A rectangular earthen design for the same capacity with 2.5:1 inside slopes would be 3.7 m (12 ft.) deep by 24.4 m (80 ft.) wide by 42 m (138 ft.) long with a top surface area of 1025 m² (11,040 ft.²), almost 3 times the surface area of the circular concrete storage.

Crust formation limits the exposed liquid surface area and helps reduce odours as shown in Figure 2. As odorous air

passes through a crust or permeable cover, the moist aerobic environment within the crust helps to break down odours. Floating permeable covers that imitate crust formation effectively reduce odours. There are 2 types of floating permeable covers — natural and manmade. Natural covers usually consist of blown chopped straw or peat moss. The natural covers tend to sink after a while. There is some ongoing research into spraying straw with mineral oil to help keep it afloat longer. Manmade covers of geotextiles are available commercially.

Filling liquid manure storages from the bottom minimizes agitation and preserves the crust to help reduce odours. High fibre feeds also promote crusting. Many existing storages can easily be altered to be filled from the bottom.

Figure 2. Crust formation on a liquid manure storage.

Biofilters

Biofilters for barn ventilation systems work on a similar principle as a floating cover on a manure storage. The air ventilated from the barn is screened for dust and pressurized in a plenum under the biofilter. The air is then forced through a box usually containing a filter medium of woodchips, peat moss or compost, achieving odour reductions of 60%–80%. As the airflow tends to dry out the filter medium, it needs to be regularly sprayed with water. The filter medium also has to be changed every 2–5 years. Dust clogging can be a problem with some biofilters. While effective for controlling odour, biofilters are expensive to install and operate.

Windbreaks

Trees and other windbreaks around manure storages help reduce top surface agitation by the wind action and help promote vertical air mixing and dilution of the odours. This further reduces the transport of odours to neighbours. Visual screening provided by trees and other windbreaks also help reduce the number of odour complaints.

In-barn Conditions

For liquid manure, the lower the solids content of the manure the lower the odour generated. Reducing feed spillage keeps the solids content down. Solid/liquid separation can be very effective in reducing odours. The use of silica fume cements in the barn reduces odours and increases the durability of concrete. Silica fume cement is 100 times finer than Portland cement, and when combined with a low water cement ratio, the size of pores in the concrete is reduced to less than .01 micron. Since E. coli bacteria is typically 1 micron in diameter, it is unlikely to penetrate into the concrete. Concrete using silica fume cement should have better bacteria control, be easier to clean, and produce fewer odours.

For short-term in-barn manure storage systems, odours start to build up in 4 or 5 days, and reach a peak in approximately 20 days. If possible, it is recommended to transfer the manure to a longer term manure storage at least every 7 days and more frequently if possible for odour control.

Treating Odours

If methods for containing odours within the boundary of the farm are insufficient, odour treatment methods may be necessary.

Manure and other organic matter can be treated biologically or chemically to reduce odour potential. Biological treatments include aerobic (with air) systems such as aeration, and anaerobic (without air) systems such as anaerobic digesters. Other methods include using additives designed to chemically or biologically alter, reduce or mask odours.

In aeration, air is introduced into the liquid manure storage by mechanical agitation, or under pressure with compressors or blowers. The resulting aerobic breakdown of manure is much less odorous, however, the process requires a lot of electrical power.

Digestion under controlled anaerobic conditions (Figure 3) speeds up a natural biological decay process to create biogas and a low-odour, biologically stable manure. Under controlled conditions at elevated temperatures the anaerobic digestion is more complete, odorous compounds are created and are then converted to odourless biogas. While digesters are only beginning to become economically effective in gas production, they have been very effective in reducing odours.

Figure 3. This schematic cross-section shows the flow of liquid manure from storage, through the anaerobic digestion process, then finally to gas storage.

Additives

Odour control additives have been designed to mask, neutralize or alter, either chemically or biologically, odours or odour production. By strictly following the manufacturer's instructions, the correct additive under the proper conditions may reduce odour emissions. Research has generally been inconclusive on the effectiveness of additives. Cost and the duration of effective odour treatment are factors when considering the use of additives.

Fly ash has been tested as a stabilizing agent that can inhibit the production of odours. The ashes are rich in calcium which, when added to manure, will raise the pH to 12 where all microbial activity ceases and sulphur compounds are fixed. About 250 kg of fly ash per m³ (2.5 lbs./imp. gal) of manure is required. After an initial strong ammonia odour, the treatment lasts for approximately one month. Similar to fly ash, lime can also be used to raise the pH of manure to reduce odours.