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Review Articles |
School of Engineering, University of Guelph, 50 Stone Rd., Guelph, Ontario, Canada N1G 2W1
1 Corresponding author: bvanheys{at}uoguelph.ca
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SUMMARY |
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 TOP SUMMARY DESCRIPTION OF PROBLEMEMISSION FACTORSBEST MANAGEMENT PRACTICESCONCLUSIONS AND APPLICATIONSREFERENCES AND NOTES |
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Key Words: broiler • layer • turkey • ammonia • particulate matter • emission factor • best management practice
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DESCRIPTION OF PROBLEM |
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TOPSUMMARYDESCRIPTION OF PROBLEMEMISSION FACTORSBEST MANAGEMENT PRACTICESCONCLUSIONS AND APPLICATIONSREFERENCES AND NOTES |
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One type of animal housing that has relied heavily on extrapolated EF is the commercial poultry sector. In many North America jurisdictions, a single EF for a given pollutant has been used to describe the emissions from all types of poultry production. For this reason, several research groups have placed a higher priority on improving EF for poultry over other types of livestock housing.
The production of poultry results in the release of several pollutants to the atmosphere, although most research has focused on NH3 and particulate matter (PM) emissions because of their detrimental effects to human health and the environment. Each type of poultry operation generates different amounts of these contaminants, and their emission rates are further confounded by the different house management and operation practices. Information on the emissions of NH3 and PM from different types of poultry production is currently available, but the various findings need to be summarized by translating them into a comparable EF format using a consistent production unit.
This compilation of comparable EF will allow any knowledge gaps to be identified that may warrant additional measurement studies. A comprehensive set of emissions data will also enable individual poultry producers to select the most appropriate EF to estimate the target pollutant emissions from their specific facility. Government agencies can benefit from these data by developing more comprehensive inventories of NH3 and PM releases. However, for policy makers to truly benefit from these data, they must be educated with additional information on mitigation techniques aimed at lessening the effect on air quality.
Various research groups have been investigating several innovative best management practices (BMP) for poultry facilities to reduce their effects on both the indoor and outdoor environments. For these BMP to be useful for poultry producers and government agencies, their potential to reduce the emission of a target pollutant must be reported for each type of poultry operation and house design. This information would enable policy makers to begin coordinating with poultry producers to work toward feasible pollutant reduction programs. Although this summary only investigates the potential pollutant reductions of the BMP, additional considerations, such as capital costs, availability, and maintenance costs of the BMP, need to be assessed before wide-scale implementation.
The objectives of the paper are to report the NH3 and PM EF for various types of poultry operations and house configurations, which can be used to determine whether or not the variability in emissions has been fully characterized. The paper also describes several BMP along with their potential effectiveness at reducing NH3, PM, or both, emissions that will provide an indication of the current knowledge gaps in this area.
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EMISSION FACTORS |
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TOPSUMMARYDESCRIPTION OF PROBLEMEMISSION FACTORSBEST MANAGEMENT PRACTICESCONCLUSIONS AND APPLICATIONSREFERENCES AND NOTES |
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For studies that do not provide the necessary information to convert their reported emissions to an EF on an AU basis, the following information provided by the NFPC [2] for typical poultry production was assumed as default for the industry:
It should be noted that these statistics are most appropriate for the Canadian poultry industry and may not reflect common practices in other jurisdictions such as the United States. Studies requiring the default statistics for conversion to an AU basis EF have been identified in Tables 1
and 2.
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. Ammonia emissions from poultry houses vary significantly based on the type of poultry operation, their climatological region, and the management practices used by the house operators. For this reason, the geographical location, type of ventilation, and manure management system were identified with the NH3 EF summarized in Table 1. The NH3 EF for broiler production ranges, on an average basis, from 57 g/d per AU up to 391 g/d per AU, although most are consistently between 150 and 225 g/d per AU. This range of EF is only slightly higher than the 100 g/bird per year (equivalent to 118 g/d per AU using the NFPC [2] statistics) proposed by the US Environmental Protection Agency. The highest EF for this type of operation was developed by Wheeler et al. [3] and Lacey et al. [4] based on data from broiler houses in the United States (Kentucky and Pennsylvania and Texas, respectively). It is a common practice at commercial broiler facilities in most parts of the United States to reuse the floor litter for up to 3 or 4 bird-production cycles before replacing it with fresh bedding. In other regions, such as Canada and Europe, the litter is typically replaced after each production cycle. This manure management practice may explain the elevated NH3 emissions in the United States. Because some inconsistencies in emissions still exists among the EF developed from the European studies using similar manure management practices, the ventilation system of the poultry house may be a better indicator of the EF variability. Only a few studies provide information on the type of ventilation system used at the studied facility, which is insufficient to confirm its influence on the emission of NH3.
There is a large degree of spread in the developed EF for layer chickens, which range, on an average basis, from 64.8 g/d per AU up to 468 g/d per AU (or 724 g/d per AU if the variability in the Heber et al. [5] study is included). It is difficult to identify definitive reasons for some of the variability, because there is a variety of manure management systems used in egg production, and very little information is given on the type of ventilation system. Because NH3 emissions typically result from the decomposition of poultry manure, layer operations that use a battery cage system with manure removal belts frequently generate less NH3 emissions than those without a manure removal system (i.e., percheries and deep-pit systems). Once again, the United States studies consistently reported higher NH3 EF for layer hens than those conducted in Europe.
Three studies have quantified the NH3 emissions from turkey production, but 2 studies did not report the type of turkey operation. The NH3 emissions from the unspecified turkey production (126 and 113 g/d per AU) are comparable to the grow-out turkey facility studied by Gay et al. [6] (120.5 g/d per AU). In addition, these EF are similar to those for broiler chickens on an AU basis. The brooder facility studied by Gay et al. [6] emitted much less NH3 (7.2 g/d per AU). This EF may be misleading, because the emissions were measured for 2 d only with the turkeys being introduced to the facility shortly before the start of the measurement campaign. The turkeys may not have excreted enough fecal matter to generate representative EF.
Two studies reported NH3 EF but neglected to include the type of poultry operation the study was based on. Hence, Table 1 includes these studies under a generalized poultry category.
PM Emissions
Several characteristics of PM can be used to describe its toxicity, including its size (or aerodynamic diameter, AD), origin, formation mechanisms, chemical composition, and pathogenicity. Becasuse the AD of a particle will determine if it is capable of penetrating deep into the human respiratory-cardiopulmonary system, it is the most commonly used particle classification scheme. In the past, particles have been divided into 3 size classifications: total suspended particulates, those capable of entering the respiratory tract (or particles with an AD equal to or smaller than 10 µm, PM10), and respirable dust (RD; equivalent to 5 µm or less). More recently, 2 additional particle sizes have been introduced to better describe the toxic effects of PM, specifically particles with AD equal to or smaller than 2.5 and 1 µm (PM2.5 and PM1, respectively). Limited research has been conducted at poultry facilities to quantify the emissions of the latter 2 particle size classifications, and as such, the developed EF may not accurately represent the average PM emissions from typical poultry houses. The size-fractionated PM EF from several studies, given in Table 2, have been divided into the type of poultry operation and their location.
The amount of total suspended particulates emitted on an AU basis by broiler chickens (170.2 g/d per AU on average) is significantly greater than that released by layer chickens (42.8 g/d per AU on average). However, the PM10 emissions from both types of operations, as well as turkey production, are all within the range of 0.23 to 15.8 g/d per AU, which implies that a large portion of the total suspended particles are in the larger size fraction. Possible sources for the coarser particles are mechanical generation by the poultry, the manure management systems, and the feed delivery systems. Contrary to the fairly consistent PM10 EF reported for all types of poultry facilities, the RD EF are larger for broiler operations than all types of layer operations. In fact, the RD emissions, a smaller size fraction than PM10, from broiler houses are greater than the measured PM10 emissions from similar houses. Given that the studies reporting RD emissions were conducted 5 yr earlier than those reporting PM10 emissions, it is possible that the instrumentation used to quantify the PM emission rates have improved the EF estimates. Advancements in PM measurement technologies have enhanced the on-site and semicontinuous quantification capabilities of the instruments, which has eliminated the inherent errors associated with sample transport and laboratory analysis.
Since recognizing the importance of the 2 fine PM size classifications, only 2 studies have generated poultry house EF for PM2.5. The 2 studies, one at a layer facility [7] and the other at a broiler house [8], reported similar PM2.5 EF on a live weight basis. The mean PM2.5 release for both types of operations is slightly greater than 1 g/d per AU. The broiler house study is the only one to report a PM1 EF, which was estimated to be slightly less than 1 g/d per AU. The nearly equivalent PM2.5 and PM1 EF reported indicates that the fine fraction of PM emitted from poultry operations is mostly comprised of submicron particles. However, this conclusion is not definitive, because it is difficult to gauge variability within the poultry sector with only 1 PM1 EF.
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BEST MANAGEMENT PRACTICES |
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TOPSUMMARYDESCRIPTION OF PROBLEMEMISSION FACTORSBEST MANAGEMENT PRACTICESCONCLUSIONS AND APPLICATIONSREFERENCES AND NOTES |
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. Note that studies have not considered the different size fractionations of PM, and consequently, Table 3 reports all PM size classifications as a collective grouping. Also, in some instances, the focus of the research group was placed on reducing the indoor levels of a pollutant, so only the percentage of reduction in its concentration was reported rather than its emission. It was therefore necessary to assume that a decrease in concentration would translate to the same decrease in emissions to the atmosphere.
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In general, the oil solutions are not purely oil but a mixture consisting of a low percentage of oil in water. Researchers have tested different types of vegetable oil at various levels of dilution, which has resulted in inconsistent findings. Another possible reason for the inconsistencies in the reduction potential is the method of applying the oil solution. Oil can be applied by automated sprinkler systems, manual sprayers, ultrasonic sprayer, or foggers [9, 10]. Each method will produce a different mean diameter of the oil droplets, which will affect its efficacy to conglomerate fine particulates as well as the distribution of the oil on the litter. Patterson and Adrizal [9] recommend a mean droplet size of approximately 150 µm to obtain the most effective oil application.
Only 1 study has applied this type of BMP at a broiler house [10]. The oil solution consisted of 3% rapeseed oil in water, which caused a 12% decrease in PM concentrations. However, it should be noted that the control for this experiment was another broiler house using water spraying on the litter. The application of water to broiler litter may be able to reduce PM releases slightly, because it may cause some particles to conglomerate, just to a lesser extent than oil spraying. Two studies have tested different mixtures of vegetable oil (2% emulsified canola oil in water and 10% vegetable oil in water) at layer operations [11, 12]. Ikeguchi [11] utilized an ultrasonic sprayer to apply the 2% emulsified canola oil solution and was able to achieve an emission reduction for various size fractionations of PM between 42 and 49%. Von Wachenfelt [12] applied the 10% vegetable oil mixture and achieved a 50% reduction in PM. Although the 2 researched layer facilities demonstrated promising results, they are inconsistent with the studied broiler facility.
Ultimately, this BMP needs to be further investigated to generalize its overall effectiveness for size-fractionated PM and NH3 at different types of poultry facilities. A standardized oil, application rate, application method, and oil:water ratio is also necessary to better estimate its pollutant reduction efficiency.
Litter Amendment
A variety of litter amendments exist that target reductions in NH3 emissions from poultry litter rather than PM emissions. For all types of amendments, their intent is to lower the litter pH, which effectively inhibits the generation of NH3. In the United States, poultry litter treatment (PLT) is becoming the most commonly used litter amendment. It is a dry granular mixture of primarily sodium bisulfate and other compounds, which lower the litter pH [13]. Application rates of PLT ranging from 0.5 to 1.5 kg/m2 in layer facilities have demonstrated an NH3 reduction potential of 74 to 92% [13].
The addition of aluminum sulfate is the most commonly used means to acidify litter, and its effectiveness has been investigated at a few poultry operations as well as on litter in a controlled laboratory-scale study [14]. The reduction in NH3 can vary between 25 and 94% at commercial facilities, although the laboratory-scale study suggests that the volatilization of NH3 from litter can be nearly entirely eliminated with the addition of aluminum sulfate. Amon et al. [15] report the only findings for a litter amendment at a broiler house. This makes it difficult to assess whether its relative ineffectiveness (15 to 35% NH3 reduction) is a result of the chemical used or an undetermined distinctive factor in the broiler house environment.
Overall, these preliminary studies suggest that litter amendments can substantially lessen the NH3 emissions from various types of poultry operations and, in particular, layer facilities. Given the success of litter amendments, it would be of interest to examine whether litter amendments were capable of effectively lowering PM releases as well. Particulate matter reduction is a possibility with this BMP, because liquid applications will agglomerate some of the particulates within the litter matrix and thus prevent them from becoming entrained in the poultry house air.
Feed Additives
Feed additives are primarily intended to alter the diet of a bird to improve their uptake of N so the amount being excreted is reduced, which in turn, lowers the quantity capable of being converted to NH3 in the litter. Some other feed additives have been investigated that focus on a different aspect of NH3 release, and a few have been aimed at reducing PM emissions at the feed delivery stage. Ultimately, though, feed additives are relatively ineffective at reducing NH3, and no studies have reported on their ability to inhibit the release of PM.
Amon et al. [15] applied a 2% by weight clinoptilolite to the feed ration at a broiler facility. The NH3 emissions from the broiler house were reduced by 8% using this feed additive. McCubbin et al. [16] focused on altering the protein levels in poultry feed to reduce the amount of N excreted by the birds. These authors stressed the importance of lessening the overall protein content without disrupting typical bird growth and egg production. To achieve the desired protein levels, only the essential amino acids were added to the feed. With this feed formulation, McCubbin et al. [16] suggested that an overall decrease of 10 to 25% in NH3 concentration was achievable for poultry operations in general.
Feed additives are less effective at lowering NH3 emissions than other BMP but are becoming increasingly popular, because they are easy to incorporate into a poultry house with no additional labor. Although other BMP may only delay the NH3 emission to the time of field application of the manure, feed additives essentially remove a portion of N permanently from the waste stream and thus contribute to reducing the NH3 emissions from the whole farm system. There is, however, some uncertainty in the reduction potential of PM emissions of feed additives.
Electrostatic Precipitators
Unlike the previous management practices that inhibit the release of target pollutants, electrostatic precipitators are a control technology used to reduce already airborne particulates and gaseous NH3. These devices provide a negative charge to aerosols, which results in their precipitation onto grounded surfaces [9]. It is somewhat unclear as to how the electrostatic precipitators are able to efficiently reduce NH3 emissions, although it is possible that positively charged ammonium ions condense to surrounding particles and settle with the aerosol.
Different variations of electrostatic precipitators have generated high PM and NH3 reduction efficiencies. Electrostatic space charge systems consist of an enclosed space with several grounded trays. Particles exiting a poultry facility pass through the enclosed space and are given a strong negative charge, causing them to collect on the grounded trays [17]. In a broiler breeder facility, electrostatic precipitators were capable of reducing NH3 and PM emissions by 56 and 60%, respectively [17].
Gast et al. [18] installed negative air ionizers inside environmental isolation chambers to charge particles being exhausted from a layer house. Similar to the space charger, the charged particles precipitate onto grounded surfaces. Using this technology, PM emissions from a layer operation were decreased by 36.6 to 65.6%. Unfortunately, gaseous NH3 was not considered in this study. Overall, the performance of the electrostatic precipitators in these 2 studies suggests that this control technology is capable of effectively reducing both NH3 and PM emissions.
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CONCLUSIONS AND APPLICATIONS |
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TOPSUMMARYDESCRIPTION OF PROBLEMEMISSION FACTORSBEST MANAGEMENT PRACTICESCONCLUSIONS AND APPLICATIONSREFERENCES AND NOTES |
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REFERENCES AND NOTES |
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TOPSUMMARYDESCRIPTION OF PROBLEMEMISSION FACTORSBEST MANAGEMENT PRACTICESCONCLUSIONS AND APPLICATIONSREFERENCES AND NOTES |
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