Practical Approaches to Odour Control

Larry D. Jacobson

Biosystems and Agricultural Engineering, University of Minnesota, 1390 Eckles Avenue, St. Paul, MN, USA 55108

Introduction

Odours from pig facilities are an issue for many communities and pork producers. People seem to have less tolerance of nuisances than in the past, especially when it comes to pig manure. Continuing urban sprawl and the economic importance of animal agriculture make it essential for communities to find adequate solutions to the odour problem. A prerequisite to good solutions is a thorough understanding of the problem.

Odour and Gas Emissions

Odours and gases are emitted from all pig production enterprises. The odours and gases emitted are a by-product of the microbial decomposition of manure and other organic matter. The amount and type of emissions is dependent on the amount and type of microbial activity. Microbes are sensitive to moisture content, temperature, pH, oxygen concentration, and other environmental parameters. Any changes in these parameters will alter odour and gas emissions. For example, as temperature decreases, microbial activity slows down; consequently, during the winter months few odours are generated.

There is a difference between the odours and gases found in and outside pig production systems. Gases are individual compounds, such as ammonia and hydrogen sulfide, which may or may not have an odour. These compounds are measurable and their concentration in the air is usually expressed as parts per million (ppm). Odour consists of many gases which have an offensive smell. Odour is not directly measurable. However, methods are being used to determine the dilution to threshold value using an olfactometer and odour panel. Odour intensity units may be expressed as the amount of dilution air needed for odorous air to reach this threshold level.

Source of Odours

The emission of odours from a pig production enterprise may originate from three primary sources--the buildings, manure storage, and during land application of the manure. An estimate of the percentage of odours from these three sources for pig farms (Table 1) was made in the United Kingdom by Hardwick (1985) from odour complaints received during a complete year. Spreading of manure onto cropland accounted for roughly 50% of the odour as measured by odour complaints in this study. Even though application methods may be different in North America, land application will probably account for around half of the odours. Manure storage and buildings sources made up most of the remaining odour complaints. Storage units are perceived to be a more frequent odour source than what is shown in the study and what really occurs.

Table 1. Source and percent of odour complaints from pig farms in the United Kingdom during 1982 (Hardwick, 1985).
Odour Source Number of complaints Percentage
Buildings 224 22
Storage 169 17
Spreading 526 52
Other 94 9
TOTAL 1013 100


The frequency of these odours also varies by source. Odours released from buildings are relatively constant over the year while odours from manure storage units and spreading of manure onto the land is seasonal to quite sporadic, maybe occurring only once a year. It would seem logical to assume that there exists a baseline of odour (primarily from the buildings) emitted by a pig production system which is significantly increased on certain days of the year from the other two sources--spreading and storage. Those are the days when odour complaints occur for an individual farm since the odour emissions from the farm reaches and/or exceeds a "threshold" level. What the threshold odour level is and when it is reached are very difficult to predict for any given farmstead.

Odour Reduction Methods

Land Application

The largest percentage of odour from a pig production system is released during land spreading of manure onto cropland. A considerable amount of research has been done in land application of manure to (1) conserve valuable nutrients for plant use, (2) to reduce potential of surface water pollution, and (3) to reduce odours. Phillips et al. (1990) measured both odour and ammonia emissions for five different types of application procedures (Table 2). The application methods tested included the following: conventional tanker with splash plate (broadcast), a shallow injector, a deep injector, surface application with trailing or hanging hoses, and a travelling gun irrigator.

Table 2. Odour and ammonia emissions (mean and standard deviations) from five separate application methods during land spreading of pig slurry per volume of manure spread (Phillips et al., 1990).
Spreading Method Odour Emissions

(thousands of OU)

 Ammonia Emissions

(g NH3)

Shallow injector 133 ± 97 0.21 ± 0.08
Trailing /Hanging hoses 35 ± 27 0.16 ± 0.17
Deep injector 182 ± 100 0.09 ± 0.09
Travelling gun irrigator 6,520 ± 5,690 22.48 ± 7.50
Conventional tanker

with splash plate

 349 ± 130 1.68 ± 0.54


Table 2 shows very clearly that large amounts of odours are produced whenever slurry is sprayed into the air, either by a splash plate on a vacuum tank or with an irrigator gun. Considerable reductions in odour result when manure is either surface applied with hanging hoses or injected into the soil. It is interesting to note that the surface applied methods using trailing hoses actually produced slightly less odours than injectors although there was no statistical difference because of the large standard deviations. Thus, from this study and from numerous other findings both here and overseas, to reduce odour during the spreading of pig manure, it should be injected or thinly applied to the surface.

Manure Storage

Another source of odours emitted from pig farms is the manure storage units. This source is presently in the spotlight in the United States because of the number of relatively large pig production facilities that have been recently constructed with outside manure storage, especially earthen storage basins. Less is known about techniques to reduce the odours emitted from this source than from land spreading of manure. The primary methods of reducing odours from manure storage are covers, aeration, and additives.

Covers can be a very effective way to reduce the odours from manure storage units. There are a variety of covers that have been evaluated for pig manure storage. De Bode (1990), from the Netherlands, compared both odour and ammonia emissions from storages with the following types of covers: tent, corrugated metal sheets, floating foil, and expanded polystyrene. Table 3 shows the odour and ammonia reduction percentages for the four type of covers indicated above, compared to a control without any cover. The odour concentration for the non-cover storage with pig manure was 200 odour units per cubic meter (o.u./m3) in the summer and 120 o.u./m3 in the winter.

Table 3. Reduction in odour and ammonia emissions from coverings on pig manure storage (De Bode, 1990).
Type of Cover Odour reduction, % NH3 reduction, %
summer winter summer winter
Tent 35 15 94 84
Corrugated sheet 50 28 84 54
Floating film 28 0 94 73
Expanded polystyrene 40 10 85 78


All covers did not give as high a reduction for odours (all less than 50% in the summer) as they did for ammonia emissions. De Bode indicated that this may partially be explained by the fact that the cover material itself may emit some odours and may bias the odour measurements. These measurements were taken during the first year after installation and improvements in odour reduction may result after this initial year. Other researchers (Mannebeck, 1985) have found greater odour reduction percentages for covers such as floating foils and tarpaulins (> 60%) and permanent roofs constructed of wood or concrete (>95%). He also found natural floating covers (i.e., from cattle manure) to be an acceptable odour reducer (between 60 and 85%), but artificial floating covers like straw to be less effective (between 40 and 50%).

How long these covers will last and the cost and labour to install and maintain them are also very important issues. Mannebeck estimated the useful life of the covers they evaluated, varying from a half­year for straw and up to 20 years for a concrete cover. Others have indicated that a two or three inch layer of straw will only last for several weeks. Mannebeck estimated that straw would cost as little as $.05 per ft2 of storage area while a floating tarpaulin would be $2.50 per ft2. Not only is the initial cost of concern, but also the installation and maintenance costs, which are the major drawbacks to using covers on storages in North America at the present time.

Aeration of manure storage is the other main method of controlling odours from manure storage units. Very effective control of odours have been reported when storages have been "totally" aerated with mechanical aerators, but the process is very energy intensive and estimated costs have been as high as $5.00 per pig marketed. Several more efficient oxygen transfer processes are being investigated using either very small bubbles of air and/or bubbleless (membrane fibers) systems to aerate the upper surface (6 to 12 inches) of the manure storage.

Natural aeration as occurring in an "aerobic" lagoon is not feasible for pig production because of the surface area requirements, but a properly sized "anaerobic" lagoon will minimize odour levels during normal weather conditions. Some odour from an anaerobic lagoon is inevitable during the spring "turnover" if loading of the manure is intermittent or not at a constant level.

The control of odours from manure storage units by chemical and biological additives has been a highly controversial subject. Very little independent research has been done on these products, primarily because no standard testing procedure has been established. Several universities and at least one independent ad hoc group are developing protocols for testing additives either in the laboratory or on farms. Recent research in Europe (Navarotto et al., 1991) using several chemical and biological additives, suggest that these products are rarely effective in reducing odours from pig manure storage.

Buildings and Facilities

Odour emitted from the buildings themselves should also be of concern to producers, even though little information is available on techniques to reduce odours exhausted through ventilation fans or by buoyancy or wind forces in naturally ventilated barns. Methods to reduce odours from pig buildings can be classified into the following categories:

Pig diets which allow the animal to more efficiently utilize protein will result in lower excretion of urea and uric acid. Assuming the volume of manure remains the same, this will lower ammonia emission. Nutrition also affects the odorous compounds like phenol, cresol, and toluene, but probably not proportionally to ammonia, so odour may not be reduced as much as ammonia using nutrition methods.

Biofilters can be used to absorb odours and gases from polluted air, but must be routinely maintained. Odorous compounds are converted to CO2 and H2O while ammonia is oxidized to NO2 or NO3. Air scrubbers with an acid solution are more efficient in removing ammonia than odours, thus, they may not be as valuable to United States' producers who are primarily concerned with odour control (O'Neil and Phillips, 1991).

Floors in pig housing units should be sloped or slatted to reduce the amount of manure (primarily urine) remaining on the surface. Alternatively, if manure is removed very quickly from the solid surface before the conversion of urea then ammonia emission will be lowered. Even though ammonia emissions are reduced when floors are drained or cleaned there is some evidence that odour emissions are only reduced slightly.

In many situations the manure storage in a barn is covered with a slatted floor and contributes to the odour emitted from that building. Estimates in a pig finishing barn have found that about 70% of the ammonia emissions from the building are coming from the manure pit. The ammonia is released at the manure surface. Even in a barn with slatted floors, the frequent removal of manure from the pit does not significantly reduce ammonia emission because the storage surfaces (floor and sides) are contaminated with manure residue. Frequent removal may reduce odour emissions, but no data has been generated for pigs to support the claim (Spoelstra, 1978).

Pig housing systems that use bedding, especially deep bedding, typically produce less odour compared to other systems. Groenestein et al. (1992) measured a reduction in ammonia emissions of 23 to 57% in a deep litter pig facility compared to fully slatted floor units. However, the N2O emission exceeded the ammonia emission so the total nitrogen emission for the deep litter system actually exceeded that of the slatted floor barn. Again, odour emissions are perceived to be less, but no hard numbers are available.

Summary and Conclusions

There are limited techniques or methods available to the pig producer who wants to reduce odours from his or her enterprise. More options exist for reducing odours during the land application of manure onto cropland than for cutting odours from manure storage units or the pig buildings themselves. The biggest concern at the present time in the United States is focussed on odours produced by manure storage. Research, both basic and applied, is being initiated to address this odour source. However, producers must implement the "proven" techniques of odour reduction during land application which are presently available, and also be ready to adopt methods that would lower odour produced from manure storage and buildings if they want to address all of the existing "odor" problems in the pork industry.

References

De Bode, M.J.C. (1990) Odour and ammonia emissions from manure storage. pp. 59-67. In: Odour and Ammonia Emissions from Livestock Farming. Eds.: V.C. Nielsen, J.H. Voorburg, and P. L'Hermite. Elsevier Applied Science Publishers, New York.

Groenestein, C.M., J. Oosthoek, H. Montsma and B. Reitsma. (1992) The emission of ammonia and other nitrogen compounds from deep-litter systems for fattening pigs: a field study. In: Proceedings workshop deep-litter systems for pig farming, 1992. Eds. J.A. Voermans. Research Institute for Pig Husbandry, Rosmalen, Netherlands.

Hardwick, D.C. (1985) Agricultural problems related to odour prevention and control. pp. 21-26. In: Odour Prevention and Control of Organic Sludge and Livestock Farming. Eds: V.C. Nielsen, J.H. Voorburg, and P. L'Hermite. Elsevier Applied Science Publishers, New York.

Mannebeck, H. (1985) Covering Manure Storing Tanks to Control Odour. pp. 188-193. In: Odour Prevention and Control of Organic Sludge and Livestock Farming. Eds: V.C. Nielsen, J.H. Voorburg, and P. L'Hermite. Elsevier Applied Science Publishers, New York.

Navarotto, P., S. Piccinini, G. Piva, S. Belladonna, L. Valli, and M.T. Scicluna (1991) Deodorising and Stabilising Efficiency of Chemical and Biological Agents in the Treatment of Swine Manure. Convegno CIGR-Udine. Sett.

O'Neil, D.H. and V.R. Philips. (1991) A review of the control of odour nuisance from livestock buildings. J. Agricultural Engineering Research. N. 50.

Phillips, V.R., B.F. Pain and J.V. Klarenbeek. (1990) Factors influencing the odour and ammonia emissions during and after the land spreading of animal slurries. pp. 98-106. In: Odour and Ammonia Emissions from Livestock Farming. Eds: V.C. Nielsen, J.H. Voorburg, and P. L'Hermite. Elsevier Applied Science Publishers, New York.

Spoelstra, S.F. (1978) Microbial aspects of the formation of malodorous compounds in anaerobically stored piggery waste. Ph.D. Thesis, 1978. Agricultural University, Wageningen, Netherlands.