Effect of a Metabolic Stimulant on Ammonia Volatilization from Broiler Litter1

©2007 Poultry Science Association, Inc.

Effect of a Metabolic Stimulant on Ammonia Volatilization from Broiler Litter1 S. B. Shah,2 C. L. Baird, and J. M. Rice Department of Biological and Agricultural Engineering, North Carolina State University, Raleigh 27695

SUMMARY High NH3 concentrations in broiler and turkey houses can adversely affect bird performance and the environment when exhausted into the atmosphere. Acidifying amendments have been used in poultry houses to reduce NH3 levels, but the acidifiers are caustic and may not be effective for the entire growout of 8 to 9 wk. In this 45-d study, the effect of a metabolic stimulant (biostimulant), Bio-Kat, on exhaust NH3 concentrations from chambers containing broiler litter (supplemented daily with layer manure slurry) was evaluated. Average NH3 concentration in the exhaust air from the chambers containing Bio-Kat-treated litter was reduced by 61% compared with untreated litter. Also, ammoniacal-N concentration in the Bio-Kat-treated litter was double that of untreated litter at the end of the study. The Bio-Kat amendment was most effective during the first 10 to 12 d, and its efficacy decreased over time. Additional work is required to evaluate the more concentrated formulation (for duration of effectiveness and application rate) and identify the proper method of application (i.e., incorporation vs. broadcasting on the surface). Key words: acidifier, amendment, Bio-Kat, biostimulant, chamber, poultry, concentration, emission 2007 J. Appl. Poult. Res. 16:240–247

DESCRIPTION OF PROBLEM Ammonia is produced in broiler and turkey houses when uric acid in the urine and organic N in the feces and spilled feed are converted to NH4+, a plant-available N form, by the microbes in the litter and feces. Depending on temperature, moisture content, and pH of the litter, a portion of NH4+ may be converted into NH3. Ammonia is a pungent gas that irritates the eyes and the respiratory system and can reduce resistance to infection in poultry. Because high NH3 levels adversely affect bird per1

formance [1] and worker health [2], productivity can be improved by maintaining low NH3 levels in poultry houses. Although in the past, it was recommended that NH3 concentrations in poultry houses be maintained at or below 25 ppm [3], more recent research [4] has indicated that even 10 ppm of NH3 can damage the respiratory system of a bird and increase the risk of infectious diseases. However, with old litter, reduced ventilation, and high moisture (condensation during cold weather and leaky drinkers), poultry houses can have very high NH3 concentrations (50 to 200 ppm) [3, 5].

The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service or the North Carolina Cooperative Extension Service of the products mentioned nor criticism of similar products not mentioned. 2 Corresponding author: [email protected]

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Primary Audience: Poultry Producers, Flock Supervisors, Production Managers, Researchers, Extension Agents

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NH3 and chemical O2 demand in the lagoon [15]. Based on the success of the biostimulant Bio-Kat in swine production (as well as other wastewater treatment systems), its manufacturer has modified the formulation into a solid form for use in poultry houses with litter systems to reduce NH3 levels. The manufacturer has reported that Bio-Kat increased the cellular metabolism of the bacterial microorganisms present in the wastewater by supplying the missing or deficient intercellular microenzymes and micronutrients that were lacking in the organic constituent of the wastewater. The material safety data sheet supplied by the manufacturer indicates that the liquid formulation of Bio-Kat is neutral in pH and requires no personal protective equipment during handling and application. Because acidifiers are corrosive and require precautions, ease in handling BioKat could be an advantage to poultry producers. Further, the manufacturer has reported that the solid Bio-Kat was formulated to act as a slowrelease amendment that could suppress NH3 volatilization over a longer period. Because producers are growing larger birds by increasing the growout duration (8 to 9 wk), an amendment that provides NH3 control for a longer period would definitely be advantageous. Hence, the objective of this study was to compare NH3 concentrations in exhaust air from Bio-Kat-treated litter vs. untreated litter.

MATERIALS AND METHODS This 45-d study was conducted at the Animal and Poultry Waste Management Center research facility at North Carolina State University (NCSU) from January 26 through March 10, 2006. Details on the experiment are provided below. Chamber, Manifold, and NH3 Scrubber Designs A total of 6 chambers were built. Each chamber consisted of a polyvinyl chloride (PVC) pipe of 8-in. nominal diameter with an inside diameter of 200 mm (8 in.) and a height of 457 mm (18 in.) capped permanently at the bottom with a PVC cap. Eight 6.4-mm (1/4 in.) air intake holes were drilled at equal spacing

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Many poultry producers control NH3 levels in poultry houses by increasing the ventilation rate. Excessive ventilation to manage in-house NH3 not only increases energy consumption and reduces N analysis of the litter but is also a source of environmental concern. Once emitted into the atmosphere, NH3 may be rapidly converted to NH4+ aerosol, which forms fine particulate matter [particles with aerodynamic diameters less than 2.5 ␮m (PM2.5)]; the PM2.5 has adverse health effects, because it can be deposited in the smallest airways in the lungs [6]. Additionally, NH4+ aerosols can contribute to haze [6]. Ammonia or NH4+ deposition (dry or with rainfall) may contribute to soil acidification and algal growth in water bodies [6]. Because NH3 is a precursor of PM2.5, the Environmental Protection Agency is considering regulation of its emission from animal feeding operations. Neighbors also complain about odor from animal facilities, and NH3 may contribute to this smell. Ammonia levels in poultry housing can be controlled by using amendments, mostly acidifiers. Common acidifiers in poultry houses include Al+Clear or alum [Al2(SO4)3ⴢ14H2O] [7], Poultry Litter Treatment (PLT; NaHSO4) [8], and Poultry Guard (clay soaked in 36% sulfuric acid) [9]. At application rates of 0.49 kg/m2 (100 lb/1,000 ft2) or higher, all 3 acidifiers have been effective in maintaining NH3 levels below 25 ppm and substantially lower than with no acidifier at least for a portion of the growout [10, 11, 12]. In the above studies, acidifiers reduced in-house NH3 concentrations, and this likely improved bird performance. Adsorbers (e.g., zeolite) [13] and urease enzyme inhibitors [14] have also been somewhat effective in reducing NH3 levels in broiler houses and tray studies, respectively. Beneficial microbes, enzymes, and metabolic stimulants (or biostimulant) have also been advertised by their manufacturers as being effective in reducing NH3 levels in poultry houses. A biostimulant, Bio-Kat (a commercial formulation), has been used to treat swine barn pits and swine anaerobic lagoons to reduce gaseous emissions and solids buildup [15]. Use of the biostimulant in the barns has reduced NH3 losses, mortality, and antibiotic use compared with an untreated barn. The Bio-Kat treatment also has reduced

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around the circumference of the pipe 114.3 mm (4.5 in.) above the bottom to allow the chamber to be filled with broiler litter to a depth of 101.6 mm (4 in.). The air intake holes were covered with C filter fabric to ensure NH3-free air supply to the chambers (Figure 1). The top of the chamber was capped with a PVC cap that could be removed. A 6.4-mm (1/4 in.) barbed hose tee connector was installed at the center of the PVC cap. One port of the tee connector was connected to a manifold (discussed below), whereas the other port was connected to a gas scrubber system. Based on the industry stocking rate of 0.065 m2/broiler (0.7 ft2/broiler), the chamber area equaled half the area required for 1 broiler. The manifold consisted of a 304.8-mm (12 in.) length of 8-in. PVC pipe capped at both ends with PVC caps; at midheight, the manifold had 6 holes (with 6.4-mm barbed hose connectors) on the circumference at equal intervals. A 6.4-mm barbed hose connector was installed at the center of the PVC cap at the top end of the manifold. Flexible PVC tubing with an inside diameter of 6.4 mm (1/4 in.) and a length of

1.52 m (5 ft) connected 1 port of the barbed hose tee on the chamber with 1 of the 6 ports on the side of the manifold. The barbed hose connector at the top of the manifold was connected to the suction side of a rotary vane oilless vacuum pump [16] with an airflow rate of 127.4 L/min (4.5 cfm). When the rotary vacuum pump was operated, it pulled equal volumes of air per unit time (21.2 L/min or 0.75 cfm) from each chamber. For reference, an airflow rate of 21.2 L/min represented the required ventilation rate for a 0.45-kg (1 lb) broiler at 16°C (60°F) [17]. A gas scrubber was used for sampling the NH3 concentration in the exhaust air from each chamber (Figure 1). Air drawn from the chamber through 1 port of the tee was conveyed through a 6.4-mm PVC tube to a polycarbonate volumetric flask containing 200 mL (or 250 mL during weekends) of 3% boric acid solution. Ammonia in the air was scrubbed by the boric acid and converted into NH4+ borate, and the scrubbed air was pulled out by a diaphragmtype vacuum pump [18] with a nominal airflow rate of 3.6 L/min. The outlet of the vacuum pump was attached to a flowmeter [19]; a needle

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Figure 1. Schematic of the test system.

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Table 1. Characteristics of broiler litter cake used in the study Characteristic

Value1

Analytical method

Total solids, %

46.0 (1.2)

Gravimetric, 70°C

Total Kjeldahl N, mg/kg

34,024 (1,310)

EPA 351.2 with slight modification including dialysis: persulfate digestion, NH3-salicylate method for automated analysis using colorimetry

Ammoniacal N, mg/kg

8,547 (1,181)

EPA 351.2: NH3-salicylate method for automated analysis using colorimetry

Nitrate N, mg/kg

102.2 (12.4)

EPA 353.2: cadmium reduction method for automated analysis using colorimetry

pH

8.98 (0.02)

EPA 350.1: electrometric

Mean (and SD) of 3 samples; sampled on January 23, 2006.

valve on the flowmeter was used to control the airflow rate through the scrubber (Figure 1) to a nominal value of 2.5 L/min. Preliminary data indicated that such a scrubber system, when evaluated downwind of an exhaust fan in a turkey house, had an NH3-trapping efficiency of 99.5%. In May 2006, we learned that installing the flowmeter downstream of the scrubber resulted in an overestimation of airflow rate [20]. Air bubbles emerging from the boric acid solution are at a pressure lower than atmospheric pressure and thus are less dense than air at atmospheric pressure. Hence, a laboratory study was performed to measure airflow rate with a flowmeter installed upstream while the needle valve on an identical flowmeter installed downstream of the scrubber (and the vacuum pump) was used to control airflow rates in the range of 1.5 to 2.5 L/min corresponding to flowmeter readings of 10 and 20 units, respectively. The plot of the flowmeter reading upstream (y) and downstream (x) of the scrubber yielded a linear equation (r2 = 1). Hence, the linear equation was

used, post hoc, to calculate flowmeter readings upstream of the scrubber based on flowmeter readings recorded downstream. Waste Characteristics In this study, both broiler litter and layer manure were used. Broiler litter cake that had been stockpiled under a shed at Lake Wheeler Field Laboratories Broiler Unit at NCSU was analyzed in triplicate for total solids, total Kjeldahl N (TKN), ammoniacal N, nitrate N, and pH (Table 1) at the Environmental Analysis Laboratory (EAL) at NCSU. Fresh layer manure obtained from the same source was diluted with an approximately equal volume of tap water (to improve handling and application) and then analyzed for the same constituents as the litter at the EAL (Table 2). Because small quantities of layer manure slurry were added to the chambers (daily during weekdays, as discussed below), layer manure slurry prepared at the beginning of the experiment was stored in a cooler at 4°C to minimize biochemical changes. At

Table 2. Characteristics of layer manure slurry used in the study Value1 Characteristic Total solids, % Total Kjeldahl N, mg/L Ammoniacal N, mg/L

Initial2 23.4 (0.1)

Final3 23.1 (0.7)

Analytical method Gravimetric, 70°C

15,528 (999)

15,805 (993)4

2,027 (119)

2,410 (292)D

Extraction with 1.25 N K2SO4 followed by EPA 351.2

EPA 351.2

Nitrate N, mg/L

0 (0)

0 (0)

Extraction with 1.25 N K2SO4 followed by EPA 353.2

pH

6.04 (0.04)

5.51 (0.03)

EPA 350.1: electrometric

1

Mean (and SD) of 3 samples except where indicated otherwise. Sampled on January 23, 2006. 3 Sampled on March 10, 2006. 4 Mean (and SD) of 2 samples; 1 sample with very high total Kjeldahl-N and ammoniacal-N concentrations was discarded. 2

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244 the end of study, the layer manure slurry was again analyzed in triplicate (Table 2). Operation

CG =

CL ⴢ V ⴢ (17/14) Q ⴢ ∆t ⴢ 0.001

[1]

Initially, it had been felt that addition of the water through the slurry would suffice to support microbial activity. However, decline in NH3 concentration over the course of study (discussed later) was attributed to low litter moisture content that inhibited organic N mineralization. Hence, on d 31 (Friday), the litter was stirred thoroughly, and 25 mL of water was sprinkled over the litter (or litter-amendment surface) in each chamber in addition to layer manure slurry. Thereafter, during d 34 to 37, ten milliliters of water was added to each chamber daily. Because the daily addition of 10 mL of water (25 mL on Friday, d 31) did not increase NH3 losses, on d 38 (Friday), 50 mL of water was added to each chamber to see if NH3 volatilization could be increased. During d 41 to 44, twenty-five milliliters of water was added to each chamber daily. The study was terminated on d 45. At the end of the study, the litter or litter-amendment mixture was thoroughly stirred, and 100-g samples were bagged and sent to the EAL for analysis of constituents. The constituents were analyzed using the same procedures used for analyzing the initial litter samples (Table 1). Data Analyses Ammonia-N concentrations in the exhaust air from the 2 treatments over the 45-d study were compared using repeated-measures ANOVA. Characteristics of the litter from the 2

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All 6 chambers, the manifold, and gas scrubbers were in a plywood enclosure equipped with a thermostat and heater to operate the chambers in a desirable temperature range. The average daily temperature in the enclosure during the study was 21.4°C (70.5°F) with a range of 19.4 to 25.6°C (66.9 to 78.1°F). The rotary vacuum pump was kept outside the enclosure to prevent NH3-laden air from being recirculated through the chambers. About 3.5 L of broiler litter was applied to each chamber and compacted to a height of about 100 mm. The 2 treatments (Bio-Kat and control) were randomly assigned to the 6 chambers with 3 replications per treatment. As per recommendation of the manufacturer, the BioKat material [21] was sprinkled on the surface of the litter at the rate of 400 g/chamber to an approximate depth of 13 mm (1/2 in.). This application rate was equivalent to 12.3 kg/m2 (2,527 lb/1,000 ft2). Although the Bio-Kat application rate in this study may seem high, higher amendment application rates have been reported for alum in a chamber study [22]. Thereafter, the chambers were capped, and the rotary vacuum pump and the scrubber vacuum pumps were turned on. The needle valves on the flowmeters connected to the scrubber vacuum pumps were adjusted such that all vacuum pumps pulled air at about 2.5 L/min. To prevent overheating, all pumps were set on a timer to allow them to stop for 1 h after 11 h of operation. Beginning the second day, about 5.1 g (1 level teaspoon) of layer manure slurry was sprinkled on the litter or amendment surface to simulate defecation. During the workweek, scrubber solutions were replaced every 24 h, whereas they were replaced after about 72 h on Monday. Airflow rate through each scrubber was determined in the beginning and at the end, and the average value of airflow rate was assigned for that period. The volume of the boric acid solution was determined, and for the first 10 batches, 1-mL aliquots from each scrubber were sent for NH4+-N analysis to the Analytical Services Laboratory in the Depart-

ment of Soil Science at NCSU using ion chromatography with a detection limit of 0.01 mg/ L. However, because the scrubber solutions had very high NH4+-N levels that required multiple dilutions, for the rest of the study, the scrubber solutions were analyzed at the EAL for NH4+ N using colorimetry (detection limit = 0.05 mg/L). Based on the NH4+-N concentration in the scrubber solution aliquot (CL, mg/L), scrubber solution volume (V, L), average airflow rate through the scrubber (Q, L of air/min), and duration of operation of the scrubber (∆t, min), NH3 concentration in the exhaust air (CG, mg/ m3 of air) from any chamber was calculated as follows.

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treatments were compared at the end of the study using the Student’s t-test. For all statistical analyses, the level of significance α was set equal to 0.05. The software package, SAS Version 9.1 [23] was used for all statistical analyses.

RESULTS AND DISCUSSION NH3 Concentrations in the Exhaust Air Ammonia-N concentrations were significantly higher in the control vs. the Bio-Kat treatment (repeated-measures ANOVA, P < 0.001). Difference in NH3-N concentrations between the control and Bio-Kat treatments were very high at the start of the study (Figure 2), particularly the first 10 d; thereafter, the difference between the treatments declined over time. Averaged over the entire study, NH3-N concentrations in the exhaust air from the Bio-Kat and control treatments were 1.94 and 5.00 mg/ m3, respectively. Although use of the Bio-Kat amendment reduced NH3 concentrations in the chamber compared with the control treatment, its mecha-

nism was unclear; the authors who used BioKat in the swine study [15] also reported that the reason for reduced NH3 in the Bio-Kat treatment was unclear. It could be argued that the thick layer of the amendment covering the litter physically prevented NH3 in the litter from volatilizing. However, when the litter in each chamber was thoroughly mixed and wetted on d 31, there was no upsurge in NH3 volatilization from the Bio-Kat treatment, indicating that NH3 in the litter had somehow been treated by the amendment. It seemed likely that during the early days of the study, a large fraction of the NH3 produced by the litter was immobilized by the microbes into organic N in the Bio-Kat treatment. Later in the study, the efficacy of the amendment was likely reduced as evidenced by similar NH3-N concentrations in the 2 treatments (Figure 2). This may have resulted in suboptimal conditions for the microbes in the Bio-Kat treatment (compared with conditions earlier in the study), resulting in increasing microbial dieoff. Increasing microbial dieoff in the Bio-Kat treatment over time probably resulted in increased N mineralization, as evi-

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Figure 2. Comparison of NH3-N concentrations in the exhaust air from the 2 treatments during the 45-d study. Because no data were collected during the weekends, the points corresponding to Monday and Friday are located further apart than between days during the workweek. All data points except those indicated below represent a mean of 3 replications. On d 9, 22, and 23, there were only 2 replications for the Bio-Kat treatment, whereas on d 24, there were 2 replications for both treatments; on d 31, all data for the control treatment were discarded. Volumes of water added and dates of addition are indicated.

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Table 3. Statistical comparison of litter characteristics in the Bio-Kat and control treatments at the end of the 45d study at α = 0.05 Adjusted for dilution1

Property

Control

Bio-Kat

Student’s t-test SignifiP-value cance — 0.084 <0.001 0.006 —

— No Yes Yes —

Bio-Kat 75.0 (2.4)2 24,834 (1,669) 3,318 (151) 59.8 (9.3) 8.17 (0.07)

Student’s t-test SignifiP-value cance 0.120 0.013 <0.001 <0.001 0.056

No Yes Yes Yes No

1

Assumed that 25% of total mass at the end was amendment. Mean (and SD) of 3 samples. 3 Oven-dry basis. 2

denced by higher ammoniacal-N concentrations in the Bio-Kat-treated litter (vs. control) at the end of the study (discussed later). Given the near-neutral pH values of the litter from the 2 treatments at the end of the study (discussed later), most of the ammoniacal N was likely in the nonvolatile NH4+ form; hence, despite addition of water toward the end of the study (Figure 2), NH3 volatilization did not increase in either treatment. It seemed unlikely that the Bio-Kat only facilitated the conversion of NH3 to NH4+, because this is purely a chemical process. Litter Characteristics at the End of the Study Because the masses of litter or litter plus Bio-Kat were not measured at the end of the study, comparison of litter constituents between the 2 treatments were based on both an assumed dilution (i.e., the amendment was 25% of the total mass) and no dilution. The actual concentration of litter constituents, corrected for the amendment mass remaining, was likely between the no dilution and assumed dilution values. It may also be noted that being an organic product, loss of some mass of the amendment as CO2 and water vapor could not be ruled out. When adjusted for dilution, the control and Bio-Kat treatments were not significantly different in TKN concentrations (Table 3); however, with no dilution, the control treatment had significantly higher TKN concentrations (Table 3). Regardless of whether the concentrations were adjusted for dilution or not, significantly greater ammoniacal-N concentration in the Bio-

Kat vs. the control treatment (Table 3) indicated that the Bio-Kat treatment immobilized NH3 and reduced its volatilization. Similarly, for both conditions, nitrate-N concentration in the Bio-Kat treatment was significantly lower than the control treatment (Table 3). The pH values in the 2 treatments were not significantly different (Table 3). Hence, based on the NH3 concentration and litter analysis results, the Bio-Kat treatment significantly reduced NH3 emissions compared with the control treatment during the 45-d study. The Bio-Kat treatment may be more effective in reducing NH3 concentrations in broiler and turkey houses at the application rate of 12.3 kg/m2 (2,527 lb/1,000 ft2) during the first 10 to 12 d. With passage of time, as the efficacy of the amendment is reduced, its ability to aid in the immobilization of NH3 into organic N will likely be reduced. Under the study conditions, the litter treated with Bio-Kat had more than double the ammoniacal-N concentration than the control litter at the end of the study. Even though the Bio-Kat formulation used in this study could help in NH3 management in broiler houses, it required application rates 50 to 100 times higher than acidifiers such as alum and PLT. However, the manufacturer of BioKat has indicated that the product could be concentrated >100 times vs. the current formulation [24]. Although they did not have a price for the formulation used in this study or a more concentrated product, the manufacturer has reported that the liquid formulation that is used in a concentration of 1 ppm (vol/vol) with waste water sold for $37 to $100/gal (depending on the size of the order) [24].

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Total solids, % 80.6 (4.2) — 33,112 (2,225) Total Kjeldahl N, mg/kg3 29,820 (1,110) Ammoniacal N, mg/kg3 1,661 (90) 4,424 (201) 118.7 (3.2) 79.3 (12.4) Nitrate N, mg/kg3 pH 7.90 (0.16) —

Not adjusted for dilution

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CONCLUSIONS AND APPLICATIONS

REFERENCES AND NOTES 1. Reece, F. N., B. D. Lott, and J. W. Deaton. 1981. Low concentrations of ammonia during brooding decrease broiler weight. Poult. Sci. 60:937–940. 2. Schiffman, S. S., B. W. Auvermann, and R. W. Bottcher. 2001. Health effects of aerial emissions from animal production waste management systems. Pages 103–113 of Proc. Int. Symp.: Addressing Animal Production and Environmental Issues. G. B. Havenstein, ed. North Carolina State Univ., Raleigh. 3. Carlile, F. S. 1984. Ammonia in poultry houses: A literature review. World’s Poult. Sci. J. 40:99–111. 4. Blake, J. P., and J. B. Hess. 2001. Sodium bisulfate as a litter treatment, ANR-1208. Alabama Coop. Ext. Syst., Auburn. 5. Wathes, C. M., M. R. Holden, R. W. Sneath, R. P. White, and V. R. Philips. 1997. Concentrations and emission rates of aerial ammonia, nitrous oxide, methane, carbon dioxide, dust, and endotoxin in UK broiler and layer houses. Br. Poult. Sci. 38:14–28. 6. NRC. 2003. Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs. Natl. Acad. Press, Washington, DC. 7. General Chemical Corp., Parsipanny, NJ. 8. Jones-Hamilton Co., Walbridge, OH. 9. Oil-Dri Corp., Vernon Hills, IL. 10. Moore, P. A., Jr., T. C. Daniel, and D. R. Edwards. 2000. Reducing phosphorus runoff and inhibiting ammonia loss from poultry manure with aluminum sulfate. J. Environ. Qual. 29:37–49. 11. Pope, M. J., and T. E. Cherry. 2000. An evaluation of the presence of pathogens on broilers raised on Poultry Litter Treatment-treated litter. Poult. Sci. 79:1351–1355. 12. McWard, G. W., and D. R. Taylor. 2000. Acidified clay litter amendment. J. Appl. Poult. Res. 9:518–529. 13. Nakaue, H. S., J. K. Koelliker, and M. L. Pierson. 1981. Studies with clinoptilolite in poultry. II. Effect of feeding broilers and the direct application of clinoptilolite (zeolite) on clean and reused broiler litter on broiler performance and house environment. Poult. Sci. 60:1221–1228.

14. Singh, A., K. D. Casey, A. J. Pescatore, and R. S. Gates. 2005. Efficacy of urease to reduce ammonia emissions from broiler litter. Pages 219–226 in Proc. 2005 Waste Manag. Symp., Research Triangle Park, NC. North Carolina State Univ., Raleigh. 15. Schneegurt, M. A., D. L. Weber, S. Ewing, and H. B. Schur. 2005. Evaluating biostimulant effects in swine production facility wastewater. Pages 1–6 in Proc. State Sci. Anim. Manure Waste Manag. Symp., San Antonio, TX. Natl. Cent. Manure Waste Manag., Raleigh, NC. 16. Model 0523, Gast Manufacturing, Benton Harbor, MI. 17. Weaver, W. D., Jr. 1990. Fundamentals of ventilation. Pages 113–128 in Commercial Chicken Meat and Egg Production. 5th ed. D. B. Bell and W. D. Weaver Jr., ed. Kluwer Acad. Publishers, Norwell, MA. 18. Model 7893B05, Thomas Scientific, Swedesboro, NJ. 19. Model GF-8321-1401, Gilmont Instruments, Barrington, IL. 20. Harper, L. 2006. Univ. Georgia, Athens. Personal communication. 21. Solid Bio-Kat formulation (grey, powdery) was supplied by Natural Resources Protection Inc., Ft. Lauderdale, FL. 22. Moore, P. A., Jr., T. C. Daniel, D. R. Edwards, and D. M. Miller. 1995. Effect of chemical amendments on ammonia volatilization from poultry litter. J. Environ. Qual. 24:293–300. 23. SAS OnlineDoc. Version 9.1. SAS Inst. Inc., Cary, NC. 24. Schur, H. B. 2006. Natural Resources Protection Inc., Ft. Lauderdale, FL. Personal communication.

Acknowledgments We gratefully acknowledge the funding and material support provided by Natural Resources Protection Inc. for this project. Frank Humenik (deceased) was instrumental in getting this study funded. North Carolina State University personnel Carl Whisenant, Mike Adcock, and L. T. Woodlief helped with fabrication and data collection. The Environmental Analysis Laboratory in the Department of Biological and Agricultural Engineering performed most of the analyses.

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1. Compared with the control treatment, the Bio-Kat treatment significantly reduced NH3 concentrations in the exhaust air during the first 10 d as well as total NH3 emissions. 2. The efficacy of the Bio-Kat treatment in reducing NH3 volatilization declined with time. 3. The litter treated with the Bio-Kat treatment had a significantly higher ammoniacal-N concentration at the end of the study than the untreated litter. 4. The Bio-Kat formulation used in this study required much heavier application than acidifying amendments such as alum or PLT; the sheer mass of amendment required will likely dissuade poultry producers from using this product. 5. As indicated by the manufacturer of Bio-Kat, its more concentrated formulation that requires application rates comparable to acidifying amendments should be evaluated for its ability to reduce NH3 emissions. 6. Efforts should also be made to evaluate the duration of effectiveness of the concentrated product. 7. The effect of incorporating the Bio-Kat amendment into the litter on NH3 volatilization should be considered.