Journal of Environmental Protection, 2011, 2, 867-872
doi:10.4236/jep.2011.27098 Published Online September 2011 (
Copyright © 2011 SciRes. JEP
Treatment of Swine Slurry by an Ozone Treatment
System to Reduce Odor
A. R. Omer, Paul M. Walker
Department of Agriculture, Illinois State University, Normal, USA.
Received May 12th, 2011; revised June 17th, 2011; accepted July 21th, 2011.
Development of a technology that can reduce the odor of liquid swine manure during agitation and land application
could prove beneficial to the swine industry. The purpose of this study was to evaluate a commercial ozone treatment
system for swine slurry under production scale cond itions. The facility used for this study was a curtain sided finishing
building housing 500 grow–fi nis h m arket ho gs loc at ed ove r a man ure pi t measuring 12.2 m wide × 25.9 m long × 2.4 m
deep with a total pit capacity of 770,142 l, containing 577,607 l. The system evaluated exposes air to ultra-violet light
creating O3. The O3 is then injected into slurry at a rate of 851.6 l/min. treating 51,097 l/h. In this study the entire pit
contents were treated every 11.3 h. At 0, 24, 48, and 96 h two slurry samples were collected with a 3.05 m probe and six
air sample bags were collected via a vacuum pump. No significant differences were detected in slurry samples between
time periods. Mean slurry values were 13.6 ± 4.6% solids dry wt., 850 ± 70 mg/l settable solids, 54,200 ± 4384 mg/l
total suspended so lids, 61,050 ± 12,657 mg/l chemical oxygen demand, 0.86 ± 0.14%N, 0.49 ± 0.27%P, 0.45 ± 0.01%K
and dissolved oxygen below detection limits. Ammonia concentrations decreased (P = 0.004) from 0 to 96 h. Odor pan-
elists analyzed air samples for intensity at recognition (IR), offensiveness at recognitio n (OR), intensity at full strength
(IFS) and offensiveness at full strength (OFS). Panelists fou nd OR, IFS and OFS were reduced (P < 0.01) at 48 h and
96 h compared to 0 h and IR was reduced (P < 0.04) at 24 h and 48 h and not at 96 h but trended lower (P = 0.12) at
96 h. The system evaluated significantly improved air quality within the building suggesting that odor emanating from
swine buildings and odo r generated during land application of slurry shou ld be reduced.
Keywords: Swine Slurry, Odor, Treatment, Ozone
1. Introduction
Concentrated manure odors within the swine industry can
be partially attributed to the replacement of bedding with
the slatted floor-pit system. Swine slurry collected by the
slatted floor system is subject to anaerobic conditions
producing anaerobic bacteria, a common source of odors
[1]. Fermentation by anaerobic microbes leads to the
production of volatile fatty acids, ammonia, amines, in-
doles, phenolics, and volatile sulfur compounds [2]. Out
of the 168 compounds found in livestock waste, 30
compounds are most likely to cause odors [3]. Of those
30 compounds: volatile fatty acids, p-cresol, indole, ska-
tole, diacetyl and ammonia are found in high concentra-
tions and have low detection thresholds (> 0.001mg·m³).
Options for reducing swine slurry odor are limited.
Chemical odor control can be expensive and most cost
effectively used as an additive to other methods [1].
Ozone combined with ultra-violet (UV) light can form a
powerful oxidant [4] that can be used to destroy the cell
walls and cytoplasmic membranes of odor causing bacte-
ria [5]. A 1 g/l dosage of ozone has been shown to reduce
swine slurry odor and be more effective than stripping
with nitrogen or oxidizing with O2 [6]. Ozonation facili-
ties in the United States have become more common and
have been shown to provide a safe treatment option for
municipal waste water [4]. However, most ozone treat-
ment systems are too expensive for use in livestock op-
Increased levels of odor can reduce growth and in-
crease susceptibility to disease in swine housing units.
Nuisance odors from agriculture such as swine slurry
could have psychological affects [7]. Cognitive per-
formance and physiological response can be affected by
strong odors [8].
The transformation within the swine industry from
smaller producers to large concentrated animal feeding
operations (CAFO) will continue to accumulate large
Treatment of Swine Slurry by an Ozone Treatment System to Reduce Odor
quantities of swine slurry resulting in land-limited-
conditions [9]. Integrated swine production and increased
urbanization leads to an increase in complaints and con-
cerns about air quality. Warranted regulation due to soci-
ety concerns has been hindered by the lack of federal
guidelines caused by difficulty in defining odor limits
including measurement and evaluation. Odor is presently
considered a nuisance that is handled by local and state
agencies based on public complaints [2]. Advancement
in technologies that utilize ozonation to reduce odor dur-
ing storage and application of swine slurry could lead the
livestock (swine) industry to prevent potential health
problems and complaints, as well as meet future regula-
Little research has been conducted on production scale
ozone treatment systems that are capable of reducing
swine slurry odor during storage and subsequent land
application. Smart Earth Technologies® Manure Odor
Control Unit (MOC) may reduce the intensity and/or
offensiveness of odor produced from swine slurry. The
MOC system was originally designed and is currently
used to treat bacteria and prevent odor of waste wash
water so the water can be reclaimed for use in commer-
cial car wash systems. The MOC system has been util-
ized within the steel industry to reclaim water used to
wash oil film from steel in preparation for painting.
The objective of this study was to evaluate the ability
of the MOC system to reduce both offensiveness and
intensity of the smell of swine slurry under production
scale conditions. An additional purpose of this study was
to evaluate the MOC system’s effect on slurry character-
istics. The hypothesis was that the MOC system would
improve odor offensiveness and reduce odor intensity
without changing slurry characteristics.
2. Materials and Methods
2.1. Sample Collection
The MOC system was tested to reduce odor in a curtain
sided finishing facility containing 500 grow-finish mar-
ket hogs. This building spanned from east to west and
utilized wet/dry feeders equipped with nipple waterers.
The facility used slatted floors that allowed wastes to
collect into a 12.2 m wide × 25.9 m long × 2.4 m deep
concrete manure pit. The pit, capable of holding 770,142
l of slurry contained 577,607 l during the testing period.
During the trial period the average percent humidity was
recorded along with the high and low daily temperatures.
Slurry samples were collected at 4 time intervals (0 h,
24 h, 48 h, 96 h). Two, four-liter slurry samples were
collected at each interval using a 3.05 m probe. The
slurry samples were immediately transported to the Illi-
nois State University Analytical Laboratory for analysis.
The 0 h collection was before any processing began and
represented unaerated slurry. Samples collected at 24, 48
and 96 h were collected from aerated slurry.
During air sample collection all ventilation fans were
turned off. An SKC® Air Sample Pump (SKC Inc.,
Eighty Four, PA, USA) was used to collect six, 10-L
samples at each collection time. Samples were collected
by lowering an air tube approximately 12 inches above
the slatted floor from three locations along the center isle
of the building representing the east one third, center, and
west one third of the building. Each mechanical locking
airbag was prefilled with air for two minutes, emptied of
air by manually pressing on the bag and then refilled
with air for five minutes and sealed.
2.2. Ozonation Pump
The ozonation pump/reactor used for slurry treatment is
patented by Smart Earth Technologies®. It treats slurry
with ozone (O3) created by exposing air to ultraviolet
light (UV light). Once O3 is formed it is injected into a
continuous flow slurry line at a rate of 0.08 cubic meters
per minute. The pump consists of a 5 hp single phase
motor with a power consumption of no more than 28
amps. It is capable of sustaining a flow rate of 851.6 l/m
or 51,097 l/h. The entire slurry within the pit was poten-
tially exchanged every 11.3 h.
The intake hose was placed approximately 0.8 m off
the bottom of the pit and pumped slurry from the east end
of the building. The discharge line traveled to the west
end of the building returning slurry to the pit approxi-
mately 0.7 m below the slurry surface.
2.3. Odor Analysis
The odor analysis protocol was approved by the Purdue
University Institutional Review Board. Following collec-
tion, air samples were sent (once daily) to the Purdue
Agriculture Air Quality Laboratory where they were
evaluated for intensity and hedonic tone at both recogni-
tion and full strength. Using the Triangular Force Choice
test method, eight trained panelists evaluated each sam-
ple using an AC’SCENT International Olfactometer® (St.
Croix Sensory; Lake Elmo, MN, USA). Intensity was
measured on a scale of 0 - 5, with 0 equal to no detect-
able odor and 5 equal to extremely strong odor. Intensity
levels were determined by comparison to a reference
odor of n-butanol. Hedonic tone (offensiveness) scales
ranged from –10 (extremely unpleasant) to 10 (pleasant).
2.4. Slurry Analysis
Slurry samples were analyzed using duplicate sub-
samples to evaluate pH, dissolved oxygen (DO), chemical
oxygen demand (COD), solids dry weight (SDW), set-
tleable solids (SS), total suspended solids (TSS), total N,
Copyright © 2011 SciRes. JEP
Treatment of Swine Slurry by an Ozone Treatment System to Reduce Odor
Copyright © 2011 SciRes. JEP
total P, total K, and ammonia (NH3). A Corning® pH
meter, model 7 (Corning Inc.; Corning, NY, USA) was
used to measure pH in standard 0 - 14 pH scale units and
DO was measured using a Hanna® (Hanna Instruments;
Woonsocket, RI, USA) DO meter. A Hach® DR 2000
Colorimeter (Hach Corporation; Loveland, CO, USA)
was used to measure COD as determined by Hach method
8000 microdigestion procedure. Slurry samples were
dried at 105 according to Method 2540 B in Standard
Methods for the Examination of Water and Wastewater,
20th edition [10] to determine SDW. Settable solids were
determined by transferring samples to 1.0 l Imhoff cones
according to method 2540F in Standard Methods for the
Examination of Water and Wastewater, 20th edition [10].
Total Suspended Solids were determined by Hach method
8006 using a Hach® DR700 Colorimeter (Hach Corpora-
tion; Loveland, CO). Total N was analyzed by a LECO®
nitrogen determinator, model FP528 (LECO Corporation;
St. Joseph, MI, USA). Phosphorus and potassium were
determined by the nitric acid/hydrogen peroxide digestion
method described by the Association of Analytical
Chemists [11] and subsequent analysis using an IRIS
Plasma Spectrometer (ICP), model number 13283200,
(Thermo Jarrell Ash; Franklin, MA, USA). The Hach
method 10001 using a Hach® ammonia probe, model
51927-00 and a Hach® sension2 ISE meter, model
5172518 (Hach Corporation; Loveland, CO, USA) was
utilized to determine NH3.
2.5. Statistical Analysis
Statistical Analysis for odor data: intensity at recognition
(IR), offensiveness at recognition (OR), intensity at full
strength (IFS), and offensiveness at full strength (OFS) for
time periods (0, 24, 48, 96 h) were conducted using SPSS
PASW Advanced Statistics (SPSS®, version 18, 2009;
SPSS Inc., Chicago, IL). Multivariate Wilks’ Lambda,
Huynh-Feldt, and Tests of Within-Subjects Contrasts
where used to analyze the odor data. Wilks’ Lambda was
used to determine significance. Slurry characteristics SS,
TSS, SDW, pH, COD, P, N, K, and NH3 for the time
periods (0, 24, 48, 96 h) were analyzed using SPSS 18
ANOVA® (SPSS®, version 18, 2009; SPSS Inc., Chicago,
IL). All statistical significance values were determined at
the 95% confidence interval (P < 0.05 level).
3. Results
Recorded temperatures and percent humidity for each
day’s samples are presented in Table 1. Over the five
days during which samples were collected the mean low
temperature was 23 ± 1.82˚C (73) and the mean high
temperature was 31 ± 0.55˚C (88). The mean percent
humidity over the sampling period was 91% ± 5%.
Slurry characteristic mean ± SD and P values are
shown in Table 2. Ammonia was the only characteristic
Table 1. Temperature(˚C) and humidity(%) outside of the swine building during sample collection.
Date High Temperature Low Temperature Humidity
7/19/2010 32 22 85
7/20/2010 31 23 98
7/21/2010 31 23 88
7/22/2010 29 23 92
7/23/2010 34 22 94
Mean ± SD 31 ±0.55 23 ±1.82 91± 5
Table 2. Slurry characteristics (me an ± SD).
time SDW (%) SS (ml/L) TSS (mg/L) COD (mg/L) N (%) P (ppm) K (ppm) DO
(mg/L) Ammonia (ppm)pH
t (0 h) 13.62 ± 4.62 850 ± 70.71 54,200 ± 4384.06 61,050 ± 12,657.210.86 ± 0.14 4902 ± 32,665.794473 ± 130.82 BDLa 2544 ± 4.95b 7.60 ± 0.78
24 h 9.64 ± 0.36 525 ± 106.0743,375 ± 3005.20 59,050 ± 1484.920.75 ± 0.011903 ±71.42 4346 ± 219.91 BDL 2046 ± 223.45c7.49 ± 0.02
48 h 10.12 ± 0.13 590 ± 70.71 44,050 ± 5161.88 60,450 ± 7919.600.75 ± 0.011792 ± 277.193163 ± 1503.31 BDL 1190 ± 118.79d7.57 ± 0.07
96 h 8.42 ± 0.65 570 ± 155.5641,775 ± 3641.60 59,025 ± 7459.980.75 ± 0.011520 ± 343.653715 ± 120.21 BDL 1760 ± 181.02e7.54 ± 0.01
(24, 48, 96 h)9.39 ± 0.85 562 ± 94.75 43,067 ± 3298.43 59,508 ± 4964.620.75 ± 0.001739 ± 266.723741 ± 862.92 BDL 1665 ± 413.877.53 ± 0.05
P Value 0.282 0.115 0.117 0.992 0.430 0.175 0.401 BDL 0.004 0.176
BDLa=below detection limits, bcdeMeans within a column with different superscripts differ significantly.
Treatment of Swine Slurry by an Ozone Treatment System to Reduce Odor
that significantly changed. Concentrations of NH3 de-
creased 20% between pre-treatment and the treatment
group mean. Ammonia did not decrease significantly
between 0 h and 24 h with only a 10% decrease. Between
0 h and 96 h NH3 significantly decreased comparing
2544 ppm and 1760 ppm, respectively, representing an
18% drop. Concentration reductions of 24% for SDW,
20% for SS, 12% for TSS, 2% for COD, 6% for N, 52%
for P, 10% for K, and 1% for pH were not significant.
Dissolved oxygen was below detectable limits at all col-
lection times.
Odor analysis for Intensity at Recognition (IR), Offen-
siveness at Recognition (OR), Intensity at Full Strength
(IFS), and Offensiveness at Full Strength (OFS), are
shown in Table 3. Panelists found IR was significantly
reduced between 0 h to 24 h and 0 h to 48 h. Odor IR in-
creased after 48 h and between 0 h and 96 h IR was not
significant. Between 0 h and 48 h IR was reduced 18%.
Odor OR and IFS were significantly reduced 20% and 6%
respectively between 0 h and 96 h. Offensiveness at full
strength was not significantly reduced between 0 h and 24
h. However, OFS was significantly reduced between 0 h
to 48 h and 0 h to 96 h. Overall OFS was reduced 11%
between pretreatment and 96 h. The greatest change for
all four treatments occurred between 0 h and 48 h.
Odor panel members’ subjective descriptive phrases
characterizing the air samples at full strength evaluated at
0 h, 48 h and 96 h are shown in Table 4. The descriptors
may be considered less harsh with increased time of
treatment with the MOC system. Panelists’ subjective
evaluations of the samples suggest an overall reduction
in odor at full strength, but the descriptive phrases are
subjective and no attempt was made to statistically eva-
luate these subjective descriptive phrases.
Table 3. Odor analysis.
Collection Time Intensity at Recognition Offensivness at RecognitionIntensity at Full Strength Offensiveness at Full Strength
Mean ± SD Mean ± SD Mean ± SD Mean ± SD
Pretreatment 0h 1.56 ± 0.802a 4.33 ± 2.832a 3.48 ± 0.974a 7.03 ± 2.201a
24 h 1.33 ± 0.646b 2.50 ± 1.271b 3.09 ± 0.919b 6.25 ± 2.499a
48 h 1.09 ± 0.451c 2.63 ± 2.148b 2.89 ± 0.944c 5.23 ± 2.019b
96 h 1.36 ± 0.862a,b 2.85 ± 2.140b 3.03 ± 0.980b,c 5.53 ± 2.157b
P Value 0.04 0.003 0.007 0.001
abcdMeans within a column with different superscripts differ significantly.
Table 4. Panel members’ subjective desc riptors of odor at full strength.
0 h 48 h 96 h
molds, mildew farm fermented feces
feces wastes death animal H2S feces
sour sharp fecal feces sour, fecal, animal
sewage, feces, acidic animal fecal, sour feces, rotting, melted plastic
foul & chicken poop like animal fecal , faint gas/exhaust H2S + soil
farm H2S + petroeum foul, weak, chicken poop
rotten leaves foul, chicken poop slightly foul
foul, burnt, smoke manure, farm farm
sour sharp fecal fungus rotten egg
waste water fermented decomposed
hydrogen sulfide H2S + onion + plastic
dead animal urine
dfecal, septic mold mildew
sewage, sour acidic poop, sulfur
animal waste
strong foul
H2S, rotten eggs 
feces 
Copyright © 2011 SciRes. JEP
Treatment of Swine Slurry by an Ozone Treatment System to Reduce Odor 871
4. Discussion
Evaluation of slurry characteristics found NH3 as the
only characteristic that significantly changed over the
treatment period. Ammonia concentration decreased
from 0 h to 48 h, then rose at 96 h. The cause of the ini-
tial NH3 decrease in this experiment may be caused by
the high volume of slurry turnover resulting in an in-
creased amount of agitation and aeration of the swine
slurry, followed by a steady-state of NH3 production in
equilibrium with NH3 emission. This is opposed to the
findings of Wu [6]. Wu found that NH3 increased while
being stored and treated with ozonation. Wu’s study was
conducted over a period of four weeks as opposed to four
days (96 h). The pH of the swine slurry used in the Wu
study was 8.93 which is above the pH (> 8.5) recognized
to produce excess NH3 from aqueous ammonia ions [12].
The neutral pH of this study (pH = 7.6) may have re-
sulted in less NH3 production compared to the increased
slurry pH during Wu’s slurry storage [6]. Within a con-
trolled environment Li [13] showed that ozonation has no
significant impact on NH3 concentrations. Additional
tests investigating different conditions (temperature, pH,
moisture, and time period) are needed to 1) explain the
inconsistency in results of the affect of ozone on NH3
concentrations in swine slurry and 2) determine why or
how the MOC system reduced NH of the slurry. Wil-
liam’s [14] evaluation of swine slurry odor suggests that
NH3 contributes little to the offensiveness of slurry odor.
Reduced NH3 emissions from animal feeding operations
can be advantageous to the environment, however, as
NH3 can be a major source of nitrogen enrichment and
pollution of air, water and soil [15].
No significant differences (changes) in other slurry
characteristics were observed, though some characteris-
tics decreased numerically. Settable solids, P and K de-
creased which could be accredited to settling. Total sus-
pended solids should increase with agitation, however, it
decreased. This decrease in TSS is additional evidence
that increased surface layer agitation may have still al-
lowed settling. Dissolved oxygen within the slurry was
below detection limits and this agrees with the findings
of Walker and Wade [16] and Walker [17]. Consistent
slurry characteristics suggest that an increase in aerobic
microorganisms may have caused odor reduction and
aroma improvement. Odor was reduced in both offen-
siveness and intensity suggesting that anaerobic odor
producing microorganisms were reduced. Ozone has
shown to be a safe treatment of wastewaters [4] and ca-
pable of oxidizing bacteria [5]. Another explanation is
that continuous turnover of the slurry (approximately two
complete turnovers every 24 h) simply diluted odor con-
tributing compounds (volatile organic compounds, NH3,
etc.). Treatment of swine slurry by Wu [6] showed ozone
to not only reduce odor, but ozone was more effective
than oxygen, hydrogen peroxide, or stripping with nitro-
gen. Ozone use in this study, also, was shown as an ef-
fective odor treatment over the 96 hour treatment period.
The treatment of slurry was most effective between pre-
treatment and 48 h suggesting an increase of odor be-
tween 48 h and 96 h. This may be caused by a regrowth
of anaerobic bacteria after 48 h or the increase of odor
may have been the result of steady-state conditions being
reached. Further investigation into the relationship be-
tween the length of treatment time and odor reduction is
needed in order to suggest the proper length of treatment
in order to reduce treatment expense. No determination
of microorganism species or populations was conducted
in this study. Ozonation with the MOC system has prac-
tical application to minimize emissions leading to fewer
complaints, and reduced adverse health effects to animals
and humans, in addition to enhancing air quality. The
assessment of odor by the human nose (panelists) intro-
duces two kinds of subjectivity into evaluation. Subjec-
tivity of the human nose itself and subjectivity of the
human language used in the description of the odor [18].
Even so, this method of odor evaluation may be the most
effective assessment as under production scale conditions
individual human assessment is the evaluation in the
court of public opinion.
The MOC system performed within a production scale
environment. Pit turnover was theoretically sufficient to
allow incorporation of ozone throughout the slurry. The
MOC system reduced odor during storage. Additional
tests are needed to investigate odor production after
treatment during storage and after treatment during land
application. Further investigation describing and charac-
terizing bacteria populations should be conducted. In
addition, an economic analysis of the MOC system is
warranted to determine if the capital expenditure and cost
of operation is justifiable.
Treatment of swine slurry with the MOC system de-
creased NH3 concentrations. The MOC system signifi-
cantly reduced odor intensity and offensiveness within 48
h and maintained reduced odor through 96 h of operation.
Operation of the MOC system in this study suggests it
can function successfully under production scale condi-
tions to reduce swine slurry odor.
5. Acknowledgements
This study was partially funded by Sobrite Technolo-
gies® Inc. (Eureka, Illinois).
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