Aerial Pollutants in Swine Buildings - American Chemical Society

Critical Review pubs.acs.org/est

Aerial Pollutants in Swine Buildings: A Review of Their Characterization and Methods to Reduce Them Lomig Hamon,* Yves Andrès, and Eric Dumont Laboratoire de GEnie des Procédés - Environnement - Agroalimentaire (GEPEA), UMR CNRS 6144, Ecole des Mines de Nantes, 4 rue Alfred Kastler BP 20722, 44307 Nantes Cedex 3, France S Supporting Information *

ABSTRACT: The swine industry follows a large increase of meat production since the 1950s causing the development of bigger swine buildings which involves a raise of pollutants emissions. Due to recent anthropological pressures concerning the animal welfare, the limitation of neighborhood disturbances and atmospheric pollutions limitations, the livestock farming has to adapt their management methods to reduce or treat the aerial pollutants emissions. Through the diversity of livestock barns configurations, their climatic location, their size, and their management, we thus propose hereafter a critical review of the characterizations of these aerial pollutants. This is realized by distinguishing both solids and gaseous emissions and by referencing the measurements methods mainly used to analyze and quantify airborne particles, odorants, and gaseous compounds in the atmosphere of swine buildings. The origins of these pollutants are focused and the sturdiest techniques for concentration measurements are highlighted. Finally, we discuss pollutants abatement techniques criticizing their implementation in swine buildings and emphasizing the use of biological ways such as biofiltration for gases and odors treatment.

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INTRODUCTION

geographical location of swine buildings. The latter results in climate and weather variations leading to different configurations of livestock management and different ways of controlling effluents and pollutants. Consequently, a number of countries are involved in the treatment or abatement of nuisances related to pork meat production, especially the treatment of manure and gaseous emissions. Girard et al.2 recently published a review on the environmental problems of managing manure to limit its impact. More generally, Figure 3 summarizes the network involved to treat the liquid and solid pollutants from pigs and piggeries but does not consider gas pollutant emissions. Our aim here, therefore, is not to follow the same approach but to focus on the problems linked to the emissions of gases and airborne dust particles. Usually, different livestock management methods induce different treatments of gaseous and airborne pollutants. The emissions of gases, odorants, and dust are strongly dependent on the configuration of the swine building, that is, on the layout of the livestock. Three main categories can be described in swine farming (Figure 4): (i) outdoor, (ii) indoor on litter, and (iii) indoor on a slatted floor. Outdoor farming generally occurs in fields where the swine are protected from bad weather by huts. Compared to the other two configurations, outdoor

In 2009, the world production of pork meat represented 106 million tons and the stocks were 942 million heads.1 For the last 50 years, this production has increased by a factor of 4, especially under the influence of China which is currently the main producer (Figure 1). The production of pork meat is linked to its consumption which is mainly located in North America, Western Europe, Russia, and Eastern Asia (Figure 2). However, problems linked to swine production differ from one country to another because of the swine density, the number of heads of live animals per inhabitant and the

Received: Revised: Accepted: Published:

Figure 1. World swine production as a function of time.1. © 2012 American Chemical Society

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Environmental Science & Technology

Critical Review

Figure 2. World distribution of swine production in 2009 (largest circle for China corresponding to a production of 49.9 million tons; countries with a production of less than 10 000 tons are not shown).1.

Figure 3. General overview of the treatment network of liquid and solid pollutants from piggeries, adapted from FSA Environmental.3.

Figure 4. Examples of the three main types of livestock management: (a) outdoor livestock farming; (b) indoor farming on litter; (c) indoor farming on a slatted floor.4. 12288

dx.doi.org/10.1021/es3025758 | Environ. Sci. Technol. 2012, 46, 12287−12301


Critical Review

Table 1. Main Techniques for Gas Concentration Measurements in Swine Buildings method

analyzed gases

range of concentrations

olfactometry

odorants

electronic noses

odorants

reactant containing tubes

all compounds

colorimetry

all compounds soluble in aqueous solutions

gas chromatography photoacoustic detection

depends on detectors all compounds

FTIR spectroscopy

NH3, CH4, CO2, N2O

proton transfer reaction-mass spectroscopy (PTRMS) chemiluminescence NO analyzer

molecules with affinity to protons greater than those of water NOx and NH3

accuracy

from ppbv up to several thousands of ppmv from ppbv up to several thousands of ppmv from ppbv up to several thousands of ppmv from ppbv up to several thousands of ppmv from ppbv up to 100% from ppbv up to several thousands of ppmv from 3 ppbv up to several tens of ppmv from 1 ppbv up to 10 ppmv

depends on analyzed compounds and panelists depends on analyzed compounds

from 0.2 ppmv up to several hundreds of ppmv

0.2 ppmv

depends on analyzed compounds depends on analyzed compounds depends on detectors used ∼1 ppbv, ∼0.1 ppmv for commercial apparatus ∼10 ppbv ∼1 ppbv

its concentration, and (iii) the exposure time, and is thus highly dangerous especially for farm workers and pigs. Moreover, it should be noted that odorants and gases can be fixed in or onto dust. In order to address the main problem of removing these pollutants from the atmosphere of swine buildings (only indoor farming is studied here), this review reports the main origins of pollutants such as gases, odorants, and dust. To establish their typical concentrations, measurement techniques and methods are discussed. These elements are of major importance to establish an overview of pollutant concentrations and finally to determine the optimal methods for pollutant removal.

farming is not common in North America and Europe. Farming on litter is used more because it allows a greater swine density; it generally takes place in a barn with a floor covered with straw or sawdust. Finally, farming on a slatted floor is the most used method especially in intensive livestock management. The slats in the floor allow the waste to fall directly into a pit. These three configurations present advantages and disadvantages so their use depends on constraints linked to the swine farmer (savoir-faire) and the geographical location of the piggery (climate). Some combinations of these three configurations also exist, for example, births in the open air, weaning on a fully slatted floor, and fattening on a partially slatted floor combined with litter. A major advantage of farming on a fully slatted floor is the reduced workload for farmers because the waste falls directly into the pit and the litter is not handled. Nevertheless, this configuration greatly reduces the activity of swine, whereas farming on litter keeps swine active as they play with the litter, which contributes to their welfare. Gaseous pollutants from swine buildings can be divided into two classes: (i) odor pollution and (ii) environmental pollution.5,6 These two aspects are necessarily linked but we chose to distinguish them by considering odor pollution only a human disturbance and health problem whereas environmental pollution has an impact on nature. This discrimination into two parts is very useful to separate the different compounds found in swine-building air because their abundances do not necessarily influence odors or pollutants in the same way: for example, whereas ammonia is very concentrated in the air and is thus a strong environmental pollutant, the presence of low concentrations of sulfur compounds could hide the ammonia smell.7 Thus, human perception is not necessarily the best measurement method for the evaluation of environmental pollutant concentrations. For instance, several pollutant compounds, such as carbon dioxide (CO2) and methane (CH4), are odorless but have a marked impact on the environment. For this reason, in addition to human measurements, the “mapping” of all the compounds present and the measurement of those at the highest concentrations must be carried out in order to choose or develop the best way to remove these odorous and pollutant compounds. Odorants and gases are often just considered nuisances in spite of their potential hazard at high concentrations. The presence of dust in piggeries must also be taken into account. Dust can cause lung diseases depending on (i) the dust size, (ii)

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CHARACTERIZATION OF AERIAL POLLUTANTS IN SWINE BUILDINGS Odors and Gases. The distinction between gases and odors can be blurred. In fact, odors can be defined as emanations detected by human olfactory perception which are present in the vapor state or dust-borne, while gases can be defined as free molecules in the atmosphere. However, gases such as ammonia and hydrogen sulfide are odorant. Compared to odorants, gases represent the greatest abundance in terms of molar (or mass) concentrations. Gases such as ammonia (NH3), CO2, CH4, and sulfur compounds (e.g. hydrogen sulfide and mercaptans) are the most abundant gaseous compounds in the air of swine buildings but the measurement of their concentration is not simple. Gas Concentration Measurements. Gas concentration measurements are not straightforward because of inconsistencies between the methods used. In fact, the measuring equipment is not adapted to the specific conditions of swine buildings (temperature, relative humidity, swine activity, dust). The main methods used for gas concentration measurements are summarized in Table 1 and subsequently explained in detail. Olfactometry. The main aim of olfactometry is to establish correlations between human sensory thresholds and concentration (and intensity) levels of odorant products. The characterization of odor based on human measurements gives information on intensity, character, hedonics, detectability, and adaptability.8 Thus, physiological parameters have to be considered in such studies; the odor detection thresholds for individuals, their variability and their changes over time are generally processed via statistics. The introduction of standards, recommendations and guidelines for measurements began in 12289



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Table 2. Characteristics of the Main Gas Detectors in the Literature detector thermal conductivity detector (TCD) flame photometric detector (FPD) flame ionization detector (FID) electron capture detector (ECD) mass spectrometry (MS) ion chromatography (IC) a

principle

analyzed gases, limitations

authors using the detectorsa

differential measurement of resistive variation of two filaments induced by thermal variation

all gases, simple and sturdy

19

a blue ray for sulfur compounds or a green ray for phosphorus compounds is emitted when gas passes through a hydrogen flame; the intensity of the ray is measured via an interferential filter and photomultiplier a hydrogen flame ionizes molecules; an electric field allows ions to be collected

specific for sulfur and phosphorus compounds

19−23

organic compounds, not for permanent gas electronegative molecules such as halogenated compounds or N2O all compounds

19,20,24−27

vector gas is ionized by β-particles; electronegative molecules lead to a fall in polarization current which is amplified gas molecules are ionized and then separated according to their m/z ratio; a detector converts ion current into electric signals separation of ions and polar molecules based on their charges 30

27 19,21,24,26,28,29 31

The cited studies used these detectors for swine-building air analysis. The list is not exhaustive.

Colorimetry. Colorimetric measurements are used for occasional measurements to measure a specific compound concentration quantitatively. This method is based on the solubilization of the gaseous compound in an aqueous solution (e.g., the solubilization of NH3 in an acidic solution such as hydrochloric acid): the bubbling of a known volume of air containing the pollutant allows the absorption of the pollutant. The pollutant is fixed in aqueous solution by adjusting the pH. By measuring the volume of air passed through the bubbling system, a titration with a coloring agent can determine the compound concentration using a spectrophotometer. The coloring agents are commercially available. The accuracy of such a method depends on the calibration of the spectrophotometer with reference solutions. The accuracy of colorimetry is estimated at around 0.5 mg m−3 for either NH3 or hydrogen sulfide (H2S) concentration measurements. Gas Chromatography. Gas chromatography (GC) is one of the most popular and precise methods for both quantification detection and quantitative analysis. The literature associated with this measurement technique is thus very abundant (for example, see Baugh,16 Karasek,17 or Grob and Barry18). Whereas the human nose can detect and discriminate odors at concentrations even lower than those detected by gas chromatography,6 without matching chemical concentration measurements with olfactometric measurements, gas chromatography appears to be one of the most popular techniques to separate and identify gaseous odorant compounds. These systems allow pseudocontinuous assessments, but the choice of the detectors is the main problem to be solved, particularly if the gas mixture to be analyzed is totally unknown. Note that some of the detectors described below (Table 2) can be used without gas chromatography to enable continuous measurements. Photoacoustic Detection. Photoacoustic detectors, also called infrared photoacoustic detectors, enable continuous measurement and are currently one of the main techniques used to measure the major gas concentrations in swine buildings.32−38 This technique is based on the absorption by gas molecules of electromagnetic energy coming from an infrared source. The absorption of energy induces a thermal expansion of molecules leading to pressure waves that can be detected via an acoustic detector. Filters enable the infrared frequency to be adapted to obtain the highest harmonic absorption wavelength depending on the analyzed molecules.

the 1980s and has continued to develop, for example, a European olfactometry standard in 1996.9,10 Developments and interlaboratory comparisons have been reviewed by van Harreveld et al.11 The unit used is the Odor Unit (OU) which is based on the detectability of thresholds in dynamic dilution olfactometry. Electronic Nose. The development of electronic noses is based on a biomimetic approach consisting of combining chemical receptors for the detection of volatile chemical compounds. Electronic noses contain an array of sensors: organic semiconductors, sintered metal-oxides, catalytic metals, conducting polymers.12,13 These sensors respond to a range of chemical compounds by changing their resistance in the presence of chemical vapors. In the presence of a volatile compound, the change in resistance of one sensor from its initial resistance produces a pattern of resistance changes across the array of sensors; an electronic computing processor then identifies and quantifies the volatile compounds. The output signal is generated as a change in resistance at the sensory surface, which is fast and temporary. Data are computed to recognize the pattern of the compound mixture and to discriminate it. Statistical analysis and a database are used to reveal the composition and concentration of the volatile compounds. Reactant Containing Tubes. Colorimetric tubes are very useful to evaluate gas and odorant concentrations approximately. Historically, they were developed to replace canaries used as sensors in coal mining.14,15 These tubes are vials containing chemical mixtures which react with chemical agents contained in air by changing color (e.g., bromophenol blue sodium salt reacts with NH3 changing color from yellow to blue). A known volume of air containing the compounds to be measured is injected into the tube; the change of color and a printed scale enable the concentration in air of the studied compound to be assessed giving a “semi-quantitative” indication. Because the line of color is partially diffused, the reading cannot be precise. Moreover, the reactants contained in the tube are sensitive to the humidity of air so the measurement is not very accurate (in comparison with measurement techniques such as gas chromatography). In general, the use of tubes is practical for occasional measurements or the fast and low-cost evaluation of the presence of compounds in air but these concentration measurements do not appear to be very accurate compared to other methods. 12290



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suitable for phenolic compound sampling.49 A discussion of the sampling methods is provided by Koziel et al.53 The measurement techniques referred to here present advantages and disadvantages, especially for the analysis of swine-building air. For example, although gas chromatography is very accurate and enables almost all the compounds present to be detected, the analysis is difficult to carry out in terms of gas chromatograph parameter optimization and these apparatus are generally nontransportable so sampling bags must be used. To the best of our knowledge, for the quantification of the most abundant compounds (such as NH3, CO2, and CH4), photoacoustic detection, FTIR spectroscopy, and colorimetry are the most suitable methods. Although calibrations are needed, these methods appear to be robust in terms of accuracy and stability. Colorimetry is very suitable for occasional measurements while photoacoustic detection and FTIR are more appropriate for continuous measurements. Moreover, these systems are portable and thus can be used in the field for swine buildings. Origins of Odors and Gases. The sources of gaseous and odorous compounds are similar and arise mainly from bacterial activities. In the case of ammonia, the two main sources of formation are urine puddles and slurry. Ammonia from urine puddles comes from the hydrolysis of urea to ammonia catalyzed by the enzyme urease, and carbamic acid which is hydrolyzed to form carbonic acid and ammonia.54 In this ammonia production, nitrates and amino acid deamination are involved55 while the decarboxylation of amino acids also causes the emission of NH3 implicating Streptococcus, Peptostreptococcus, and Bacteroides.56 The formation of ammonia in a slurry pit could be linked to the degradation of fresh urine at the surface or in the top layers of slurry along with anaerobic digestion in the bottom layers of the slurry. This degradation of urea begins as soon as it is in contact with feces containing urease: all the urea is hydrolyzed in one day.57 Note that, because dietary crude proteins are the primary sources of nitrogen, their level influences ammonia emissions.27 A reduction in dietary crude protein decreases the concentration of nitrogen contents in fecal excretion, and especially in urine excretion, thus limiting NH3 emissions.58 From the degradation of manure, many other gases are produced (CH4, CO2, CO, or H2S) by bacterial action on animal wastes stored in manure pits under the building where they undergo anaerobic decomposition.59,60 H2S can soar to acute toxic levels when the manure is agitated to facilitate emptying of manure pits.61 Note that emission sources of NH3 depend on pig inventory, pig mass and phase of production, house type and management, manure storage and treatment, land application, feed nitrogen content, nitrogen excretion rates per pig, and environmental conditions.62,63 The feed nitrogen content, which is one of the primary sources of nitrogen, is one of the main parameters influencing NH3 and odor emissions.64,65 Although NH3 and H2S are abundant odorants in terms of concentrations in the air of piggeries, approximately 400 different odorous compounds can be listed from the literature (see Supporting Information (SI) for a complete list of the referenced compounds).19,21,24−26,28,29,40,43,46−50,66−71 In addition, among the most abundant are the odorless greenhouse gases (GHG) CH4 and CO2. The emission rates of gases such as GHG or NH3 and H2S depend on the seasonal conditions, the local climate and the housing system. Consequently, the evaluation of the range of emissions rates is difficult. For instance, NH3 emissions range from 146 mg of NH3 h−1 pig−1

The accuracy level of such apparatus is approximately 95% with a detection limit of around 0.1 ppm for the most common gases in swine buildings. FTIR Spectroscopy. Unlike infrared spectroscopy, which is based on the absorption of a monochromatic light beam by molecules, Fourier transform infrared spectroscopy involves the absorption of a polychromatic light beam. The absorbance signal is then deconvoluted to calculate the original absorbance spectrum as a function of the absorbance wavelength. Because of the fast data acquisition of spectra, FTIR can be coupled with GC. In swine buildings, FTIR spectroscopy is used to measure concentrations of simple molecules such as NH3, CH4, CO2, or nitrous oxide (N2O).39,40 Note that Open-Path FTIR is adapted to measure gas concentrations over relatively long paths for atmospheric analyses.40 Proton Transfer Reaction-Mass Spectrometry. Proton transfer reaction-mass spectrometry (PTR-MS) is based on the protonation of gas molecules and their counting with a mass spectrometer. H3O+ ions are formed by ionizing water and by ion−molecule reactions in a drift tube.41,42 The reaction between gas molecules and H3O+ ions gives a proton transfer thus charging the gas molecules to be analyzed by an MS. This system allows a continuous measurement of gases with a proton affinity higher than that of water. Whereas the detection limit of such an apparatus is smaller than ppb, the maximum concentrations cannot exceed 10 ppm because the formation of protonated molecules supposes that the decrease in primary ions is negligible. Note that not all the molecules are detectable: the proton affinity with gas molecules has to be higher than water. This system appears to be suitable for continuous and real-time gas concentration measurements in swine buildings.43 Chemiluminescence NO Analyzer. This technique, used to analyze NOx-containing gas, is based on a reduction of all the NOx compounds into nitric oxide (NO) over a heated catalyst. Then, the reaction of NO with added ozone gives nitrogen dioxide (NO2); this ozone reaction produces a photon which is counted by a photomultiplier. NH3 analysis is also possible by a primary thermal conversion of NH3 into NO by oxidation with O2. The accuracy of such commercially available apparatus is around 0.2 ppm of NOx in air. Gas and Odor Sampling. Odor sampling has to be carried out carefully because of the potential influence of the sampling system on the composition of the gas sample.44,45 Several techniques for gas concentration measurements can be used directly in swine buildings without sampling systems. For nonmobile analyzers or for analytical techniques needing measurements in the laboratory, various sampling methods are available. Condensable gases and odorants can be liquefied and stored in cold trap collectors46 or absorbed in aqueous solution depending on their pH.47,48 Sorption in polymers is also commonly used: for example, activated carbon (desorption by heating),25,49 Chromosorb (expanded form of styrenedivinylbenzene copolymer),50 Poropak or Tenax,21,26 and Tedlar bags especially for olfactometry analysis.21 However, Tedlar bags can bias air samples for olfactory analysis because of parasite sorption causing a variation in the concentrations of some compounds.51 After collection on a porous polymer, samples can be concentrated by eluting with dimethyl ether or solvent mixtures containing ether.52 The sampling method depends not only on the technique used to measure gas and odor concentrations but also on the chemical class of the analyzed compounds: for example, Tenax GC appears to be 12291



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for swine on litter up to 381 mg of NH3 h−1 pig−1 for swine on a fully slatted floor.72,73 Typical Odor and Gas Concentrations. A literature review of the odorous compound emissions has been carried out by O’Neill and Phillips7 and a review of the models of ammonia emissions is provided by Ni.74 Table 3 shows the concentration

to describe airborne particles. This term is especially used in the fields of air quality and atmospheric sciences (PM is thus equivalent to aerosol). In this literature review, the generic term of dust describes both PM (or aerosol) and sedimentary dust. We thus assume a global analysis by minimizing the complexity of the aerosol and dust studies but, by adopting the generic term of dust, our action comes within the context of a complete characterization of dust and its removal from the atmosphere of swine buildings. Dust Characterization. Reviews of the sampling equipment used for analyzing agricultural dust have already been provided by Donham,59 Ashman80 and Carpenter.81 These have recently been updated by Cambra-López et al.79 The types of equipment mainly used in swine buildings for dust characterization are shown in Table 4.

Table 3. Concentrations of the Main Pollutant Compounds in Swine Buildings compounds

concentrations

common name

formula

CAS number

ammonia carbon dioxide methane hydrogen sulfide nitrous oxide

NH3 CO2 CH4 H2S N2 O

7664−41−7 124−38−9 74−82−8 7783−06−4 10024−97−2

(mg m−3) 0−18 629−5220 1.3−24.4 0.004−2.4 0.5−0.6

(ppm) 0−40 350−2900 2.0−37.3 0.003−1.7 0.28−0.33

Table 4. Main Equipment for the Analysis of Dust (by Donham 1986).59

ranges of the main gaseous compounds found in the atmosphere of swine buildings. The table is not organized as a function of the different swine-building configurations because some referenced studies do not give concentration data. They give emission rates determined by using ventilation rates, often not indicated. Moreover, it could be difficult to determine the gas concentrations for outdoor farming because of the choice of the sampling point. The range of concentrations varies from one study to another or, more precisely, from one barn configuration to another. Moreover, the age of swine and the climatic conditions both influence the concentrations and the emission rates. Thus it appears that the rationalization of such concentration data is impossible. Nevertheless, some trends are apparent: • The emission rates of ammonia and greenhouse gases (GHG) are linked to the configuration of the barn: for example, whereas farming on litter is appreciated as a good image for swine welfare, the emissions of ammonia and GHG are higher than those from farming on a fully slatted floor (5.0 ± 0.8 g pig−1 day−1 on a slatted floor, from 12.1 ± 0.6 to 13.3 ± 3.5 g pig−1 day−1 on straw litter)35,36 but the emissions of odors are lower (olfactory analysis: odorant intensity of 7.2 ± 1.2 for fattening pigs on a slatted floor and 4.6 ± 1.6 for fattening pigs on straw or sawdust litter);75 • The emission rates of gases and odorants are strongly dependent on the external conditions, that is, the emission rates depend on the seasonal and climatic parameters (ammonia emissions 56% higher during the summer period than in other seasons, from Aarnink et al.);76 • Pig activity modifies the concentrations of pollutants: there is an emission peak in the morning for young swine, whereas for fattening pigs a peak is observed during the afternoon, these peaks corresponding to activity periods.76 However, a large area allowing activity does not increase the emission rates per swine.77 Dust. Like other pollutants in and from swine buildings, dust represents the solid part of aerial emissions but its definition is sometimes confused. For several authors,78,79 dust comes from solid particles resulting from the mechanical fracture of primary solids so, from this point of view, dust settles under the action of gravity. However, the term particulate matter (PM), which refers to solids or liquids in suspension in air, is generally used

mass sampling

all dusts separation by size

use of paper fiber or glass fiber filters cyclone cascade impactor vertical elutrior

particle counting

light scattering beta attenuation laser light microscopy scanning electron microscopy Electrostatic Precipitation chemical analysis endotoxin protease aflatoxin protein analysis Antigenic Analysis microbial analysis andersen sampling nucleopore filter analysis slit sampling

This table summarizes the various techniques used to characterize dust. Details and references are presented in the paper by Donham.59 The concentration ranges and the accuracy of each type of equipment are reported by Kulkarni et al.82 Other discussions on dust measurement methods can be found in Phillips et al.39 and Razote et al.83 Let us note that mass sampling, which involves weighing a filter, can be largely marred by uncertainties due to the small mass variation.39 Moreover, sampling operations, that is, suction flow and velocity, strongly affect the theoretical upper size limit of the collected particles:66 respecting the isokinetic conditions appears to be a key factor in dust sampling. Origins of Dust. The origins of dust are varied and their quantity as well as their size distribution is linked to the nature of the local environment. The size of dust is generally less than 50 μm with D50 less than 18 μm. The major part of dust is organic,84 comprised of skin, hair, dried feces, urine, dandler, serum, skin squames, bacteria, yeasts, fungi, and bedding particles.64 It also includes components from feed59,81,85 and from mold, pollen, grain mites, insect parts and mineral ash. It is generally admitted that dust levels are linked to feed.59,64,79,85−92 According to Donham,59 dust particles contain 25% protein coming from feed. Swine also emit dust, especially bacteria.93 Although the composition of dust certainly depends on the barn configuration and many other parameters, Aarnink et al.84 analyzed its chemical composition, 12292



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Table 5. Chemical Composition of Dust from Different Sources.84 dry matter

ash

N

P

K

Cl

Na

sources

(mg g−1)

(mg g−1)

(mg g−1)

(mg g−1)

(mg g−1)

(mg g−1)

(mg g−1)

airborne dust settled dust feed dust feces dust skin particle dust

921 910 903 915 922

150 120 26 149 114

67.0 59.0 21.8 40.8 67.8

14.7 11.4 3.4 20.5 10.7

27.8 24.4 10.2 12.7 33.2

7.83 7.32 7.12 1.10 15.50

8.18 6.60 3.58 3.83 13.00

Maghirang et al.104 showed that the size distribution function follows a log-normal distribution with a median diameter of 13 μm. Particles with a diameter between 0.1 and 10 μm do not contain many microorganisms105 but smaller ones present higher concentrations of endotoxins than larger particles suggesting that the smallest contain a large amount of fecal matter.103 Between 28% and 31% of the particles allowing the formation of bacterial colonies have a size less than 4.7 μm.106 Impact of Pollutants on Human and Swine Health. Finally, the impact on human health is one of the first preoccupations of pig farmers. Odor nuisance can be defined as the FIDO:107 frequency, intensity, duration, and offensiveness.5,7 Threshold regulations are now discussed.11,108−110 Table 6 shows the exposure limits of the most abundant

as summarized in Table 5, and showed it to be similar for both airborne and settled dusts. Generally, dust concentrations can also be linked to swine activity.94 Hence, they are higher in nurseries because the temperature there is higher than in finishing barns and because young swine activity leads to high levels of dust.66 Some models95,96 have been developed to characterize the dust emission rates taking into account parameters such as livestock configuration, and seasonal and diurnal variations. These models show that the presence or absence of swine does not seem to influence significantly the distribution of concentrations, which appears to contradict the experimental results. To sum up, dust emission rates mainly depend on swine activity and barn management tasks (weighing, cleaning) as well as feed, which is largely made up of organic matter (Dawson cited by Robertson).64,86 The dust emission from buildings (building materials) is negligible. Let us note that a part of or all gases and odorants may be fixed onto dust.46,59,90,97,98 Hammond et al.67 also claimed that odorants are adsorbed onto dust as opposed to existing in the gas phase: 2% in weight of the dust mass is attributed to odorants and dust is odorless after methanol extraction. Dust Concentrations. Mass concentrations of dust listed in the literature range between 2 and 20 mg m−3. However, like for odorant compounds, they mainly depend (ascending order of importance) on swine activity, inside and outside temperatures, relative humidity, feeding quantities, feeding method, swine mass, and ventilation rate.88 Swine activity is generally linked to swine density in the barn, that is, to the lack of space, the combination of different groups of animals, and the techniques of manipulation used by the farmer.64 After a period of high activity, a reduction in dust concentration can be achieved by ventilation.86 Feeding also affects the dust concentrations99 because, for example, feeding directly onto the floor twice a day is less emitting than self-feeding but the sedimentary dust emissions are higher for feeding on the floor.88 The concentration of dust returns to its normal level in 100 min after a feeding operation.86 Measurements of dust emission rates show that they are greater during the day than at night.100 Several authors have reported that there is no correlation between the age of swine and dust concentrations.101 The results vary: some authors suggest that the dust concentrations are lower in fattening rooms than in birth rooms or nurseries102 while others claim that concentrations could be higher in fattening rooms than in nurseries.103 Nevertheless, the literature mainly reports that dust concentrations are lower in barns with a fully slatted floor than in those with a nonslatted floor. The analysis of the dust size distribution is of major importance to evaluate the impact on farmer and animal health, and to design dust abatement systems. Particles with a diameter less than 5 μm are thus estimated at 70% in number,88 whereas those with a diameter less than 2.6 μm make up 50%.87

Table 6. Main Gases in the Atmosphere of Swine Buildings and Exposure Limits USA ACGIH

b

France

Germany

c

NIOSH

25 ppm TWA 35 ppm STEL 5000 ppm TWA 30 000 ppm STEL 1000 ppm TWA 10 ppm TWA 15 ppm STEL 50 ppm TWA

25 ppm TWA 35 ppm STEL

10 ppm TWA 20 ppm TWA 20 ppm STEL 5000 ppm TWA 5000 ppm TWA 30 000 ppm STEL

10 ppm ceiling (10 min)

5 ppm TWA 10 ppm STEL 25 ppm TWA 50 ppm TWA compounds

5 ppm TWA 100 ppm TWA

common name

formula

CAS number

OSHAa

ammonia carbon dioxide methane hydrogen sulfide nitrous oxide

NH3 CO2 CH4 H2S N2O

7664−41−7 124−38−9 74−82−8 7783−06−4 10024−97−2

50 ppm TWA 5000 ppm TWA 20 ppm ceiling

a OSHA: Occupational Safety and Health Administration. bACGIH: American Conference of Governmental Industrial Hygienists. c NIOSH: National Institute for Occupational Safety and Health.

gaseous compounds in the U.S., France, and Germany. Major significant differences are observed for NH3, H2S, and N2O thresholds between these countries. These limits are strongly dependent on the local legislation, when it exists. Two limits are highlighted: (i) the short-term exposure limit (STEL) corresponds to a maximum of 15 min exposure, (ii) the timeweighted average (TWA) corresponds to an exposure of 8 h. Beyond these exposure times, the worker’s health could be affected. These values are sometimes exceeded in intensive livestock farming. 12293



Critical Review

Dust Abatement. Dust emissions can be limited by the prevention of their formation.93 The use of additives, the cleaning of surfaces, oil or water spraying and the control of ventilation rates by ventilation case cleaning can all restrict dust emissions.122 Some recommendations that have been given64,86 include • using feed additives such as animal fat or vegetable oil (e.g., soybean oil 123) • changing the shape of the feed and its mode of issue124 • paying attention to the feed delivery method as this strongly generates dust • studying the kind of feed, which is generally dried granules; • having smooth rather than rough internal surfaces in barns; • spraying oil and soap mixtures into the air for short periods, several times a day. Oil or water spraying is also an abatement technique which is widely used in swine buildings but, whereas water spraying seems to be inefficient, the spraying of oil and water mixtures combined with a feed enhanced by fat significantly decreases dust concentrations.125−131 Although oil spraying is effective for several hours,132 this technique can affect human respiratory capacities.133 It is thus recommended to use vegetable oils, not mineral ones.134 The animal production performances are not modified after spraying an oil and water mixture;135 • sucking up dust is tedious work and its efficiency for decreasing dust concentration has not been proven. The use of fiber filters, wet scrubbers, and electrostatic impactors also decreases dust concentrations.122 Filtration appears to be the best way to achieve dust concentration reduction in terms of cost and removal efficiency (up to 99% efficiency).136,137 It is a good compromise between the cost of the operation and the fall in concentrations.81 Nevertheless, when filtering using glass or paper fiber filters, cleaning has to be regular and consistent, whereas for electrostatic impactors or wet scrubbers the frequency of maintenance is less important. Electrostatic impactors, which are relatively simple systems to design,138 can halve the respirable amounts of dust in birth barns and reduce them by 33% in nurseries. The wet scrubbing method is currently being rapidly developed. It is described by Lemay et al.139 and Guingand.140 Odor and Gas Treatments. Like dust emission limitation, gas and odorant emission can be restricted at source or using palliative methods. Modification of Feed. The main origins of odors and gases are fecal material and urine thus modifying feed can affect the emanations. Even though a decrease in proteins does not change the emission of GHG such as CO2 or CH4, the amount of NH3 emitted is greatly reduced. Hence, for each percent reduction of crude protein in feed, the emission rate of NH3 decreases by 9.5%.27 Feed additives include clay minerals, zeolites, algae, bacteria, enzymes, or chemical products such as acids. Slurry Additives. Additives can be added to slurry or manure.141,142 H2S emissions are decreased by adding nitrites or molybdates involving a mechanism of inhibition of sulfatereducing bacteria and a mechanism of oxidation of sulfide.22 Peroxides decrease the generation of odorant compounds143 such as phenolics by a mechanism of oxidation by peroxidase and peroxide used as an electron acceptor.144 However, the

Considering dust, the main proportion of respirable particles has a diameter less than 5 μm.91 Indeed, particles can be classified according to where they are deposited:81 - >10 μm: nasal passage; - 5−10 μm: upper respiratory tract; -

Aerial Pollutants in Swine Buildings - American Chemical Society

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