This document summarizes research on developing an ammonia scrubber system for poultry and swine facilities that uses acid-tolerant nitrifying bacteria to generate the acid needed to capture ammonia. Key points:
1) The researcher developed acid-tolerant nitrifying bacteria that can generate acid via nitrification at low pH levels.
2) This bacteria was used to inoculate an ammonia scrubber, which successfully captured ammonia using the acid produced by the bacteria.
3) However, the bacteria only thrive at warm temperatures, so further research is needed to develop strains that can also tolerate colder conditions to make the system practical year-round.
Similar to Utilizing Acid-tolerant Nitrifying Bacteria to Generate the Acidity Needed to Operate Ammonia Scrubbers on Poultry and Swine Facilities (20)
Utilizing Acid-tolerant Nitrifying Bacteria to Generate the Acidity Needed to Operate Ammonia Scrubbers on Poultry and Swine Facilities
1. Utilizing Acid-tolerant Nitrifying Bacteria to
Generate the Acidity Needed to Operate Ammonia
Scrubbers on Poultry and Swine Facilities
Philip Moore
USDA
Agricultural Research Service
Poultry Production and Product Research Unit
Fayetteville, Arkansas
2. • According to the EPA, the biggest source of atmospheric NH3 in the
U.S. is animal manure. Roughly 27% of the total NH3 emissions are
believed to originate from poultry manure (Battye et al., 1994).
• We found over half of the N excreted by broilers is lost to the
atmosphere as NH3 before the manure is removed from the barns
(Moore et al., 2011).
• The NH3 emission factor for 50 day old broilers found in that study
was 46 g NH3/bird (about 1/10th
of a pound per bird).
• This not only causes air and water pollution, it results in the loss of
about 100 million pounds of NH3/year in Arkansas alone, where
over one billion broilers are produced. This represents a huge waste
Ammonia emissions from poultry manure
3. • Nitrogen entering lakes and rivers via atmospheric wet and dry NH3
deposition contributes to eutrophication in the same manner as N
entering from runoff.
• When NH3 reacts with NOx or SOx compounds in the air, it can form
fine particulate matter (PM-2.5), which can cause human health
problems when inhaled.
• When NH3 is deposited onto soil via wet or dry fallout, it is
converted to NO3
-
(nitrate) via nitrification, which is an acid-forming
reaction.
• In Holland, the national forests begin dying in the 1980s due to soil
acidification. Researchers found that 45% of the acid deposition
was due to NH3 and 85% of the NH3 originated from livestock
Eutrophication, PM-10s, and soil acidification
4. • Currently, the only technology used in the U.S. to control NH3
emissions from poultry houses is litter acidification using chemicals
like aluminum sulfate or sodium bisulfate.
• Another technology used to control NH3 emissions from animal
rearing facilities in Europe is the use of acid scrubbers.
• With acid scrubbers, exhaust air from barns is passed through a
reactor and an acid solution is sprayed through the air, transferring
the NH3 from the gas to liquid phase.
• Acid scrubbers also remove odors and dust from air. Dutch
scrubbers have shown a 30% removal efficiency for odor and a 62-
93% removal efficiency for PM-10 particles from air (Melse and
Ogink, 2005).
Capturing Ammonia with Acid Scrubbers
5. • Dutch acid scrubbers are
very effective, but cost about
$250,000/house.
• These scrubbers use sulfuric
acid to scrub ammonia.
• Almost all of the scrubbers
on farms in Holland are on
swine farms, since heavy
dust loadings in air from
poultry farms clogs the
packing material in
scrubbers.
European Acid Scrubbers
6. • The goal of our research on acid scrubbers was to develop a
scrubber that can handle very heavy dust loadings, which is
typical from exhaust air from broiler houses, without clogging.
• Another goal was to develop a scrubber that was both simple and
safe enough that a grower could operate it without outside
technical assistance.
• In a perfect world, the scrubbers would be cost-effective to
operate.
Capturing Ammonia with Acid Scrubbers
7. Fertilizing Crops with N from Scrubbers
• In some watersheds, growers cannot apply litter because of soil test
P thresholds and must purchase commercial fertilizer to meet the N
needs of their pasture.
• If a scrubber could be developed that would trap an average of 5
lbs N per day, then the grower would recover 1825 lbs N/unit/year.
• Assuming the grower has 2 units on each chicken house and a total
of four houses, then he/she could recover 14,600 lbs N/year. This
would be almost enough N to supply 150 lbs N/acre to 100 acres of
cropland.
• Air and water quality would also benefit.
8. The current version has
two scrubbers; one for
dust and the second for
ammonia. The dust must
be removed first or acid
will be wasted
neutralizing the dust.
The shells are made out
of fiberglass. Each has
a 360 L reservoir.
These scrubbers are
made for minimum vent
fans on broiler houses in
order to get the most N
per dollar spent (Melse et
al., 2006).
Dust
scrubber
Ammonia
scrubber
9. The dust scrubber can hold
up to 8 rows of 11 wooden
slats at 45 degree angles.
10. The dust scrubber has a screen above the reservoir to catch feathers and very
large particulate matter.
feather
trap
11. water curtains acid curtains
cool cell
water reservoir acid reservoir
wooden slats
ARS Air Scrubber
feather trap
dust scrubber ammonia scrubber
12. Initially we included plastic cool cell
material on the exhaust end
of the scrubber.
It was enclosed in a stainless steel
frame and was on hinges,
allowing for easy access into the
scrubber.
This material is an effective medium
for acid scrubbing and
is used in Dutch and German
scrubbers. We thought it would
improve performance. However, it
clogged after 3-4 weeks.
13. • Currently studies are underway
to evaluate the scrubbers at
commercial broiler farms in
AR, DE and PA.
• We have used several different
types of acid in the scrubbers,
including sodium bisulfate,
alum and sulfuric acid.
• This work is funded by a
Conservation Innovation Grant
(CIG) from NRCS with Hong
Li at Univ. of Delaware.
On-farm Evaluation of Ammonia Scrubber
14. 1. Evaluate the effectiveness of the scrubbers in reducing
ammonia, dust, and odors from the exhaust air of poultry
houses.
2. Determine how much nitrogen is captured with the scrubber
under various conditions.
3. Determine the amount of acid, electricity, water and labor
needed to operate the scrubber.
4. Determine the cost-effectiveness of this BMP.
Objectives
15. Energy and water use by the scrubbers
• The average electricity use for the scrubbers was 544
Kwh/scrubber-flock ($27.20/scrubber-flock assuming
$0.05/Kwh).
• The average amount of water used by a scrubber for one flock
was 970 gallons (3,671 L).
16. Ammonia capturing efficiency. Each run was conducted with 22.7 kg (50
lbs) of sodium bisulfate (PLT).
Sampling time
Mass NH3-N in
exhaust (kg )
Mass NH3-N
captured (kg) Efficiency,%
Run 1
12 hr 1.82 1.41 77
24 hr 3.60 1.59 44
Run 2
24 hr 3.98 2.20 55
48 hr 7.77 2.92 38
Run 3
12 hr 1.98 1.18 60
48 hr 7.94 4.54 57
17. Economics
• Although the efficiency of the scrubber when we used PLT wasn’t
too bad (average = 55% reduction in NH3), the cost-effectiveness
was ugly.
• The average amount of N captured with 50 lbs of PLT was 3.02
kg N or 6.64 lbs N. A 50 lb bag costs $15.50.
• This is equivalent to $2.33/lb N. Of course that price doesn’t
include the price of the scrubber or the cost of electricity, water
and labor to operate it.
• Since poultry production is not affected with scrubbers, the only
economic benefit is the capture of lost nitrogen.
18. Free acid is needed to make this cost-effective
• The economics of using any type of acid to capture ammonia
from poultry houses looks questionable, particularly since the
scrubbers themselves are so expensive.
• Sulfuric acid poses a significant safety risk when used by typical
producers and is not cheap in small quantities. When bought in
quantities manageable by a grower (30 gal drum), sulfuric costs
$10-15/gal, which is about the same cost as PLT when converted
to moles acid/dollar. Most growers don’t want a semi load.
• We looked for “free” acids to use for this purpose, but waste acids
are often contaminated and transportation costs alone makes them
unattractive.
• Therefore we decided to try to develop a biological system in
19. Nitrification of ammonia produces acid
• Nitrification is a process carried out by bacteria in soil and water,
where ammonium (NH4
+
) is converted to nitrate (NO3
-
).
• Two moles of acid are formed for every mole of ammonium
oxidized:
NH4
+
+ 1.5O2 NO2
-
+ 2H+
+ H2O
NO2
-
+ 0.5O2 NO3
-
• We hypothesized that a system could be developed to use
ammonia-oxidizing bacteria, such as Proteobacteria,
Nitrosomonas and Nitrosococcus to generate the acid needed to
capture ammonia in the scrubbers.
20. Can bacteria produce the acid via nitrification?
• The idea was as follows: if every mole of ammonia scrubbed from
the air resulted in two moles of acid, and the new acid then
captured more ammonia that was nitrified, and the cycle
continuously repeated itself, then we would have a free acid
source.
• The only problem is the bacteria responsible for nitrification will
not grow under acidic or even slightly acidic conditions. In nature,
nitrification is greatly inhibited below pH values of 6.5.
• However, in order for scrubbers to work, the pH needs to be less
than 4.5.
• Hence, we needed to develop acid-tolerant nitrifying bacteria.
21. Developing acid-tolerant nitrifying bacteria
• In order to do this we built a reactor in the lab which was
inoculated with sewage taken from the aeration basin of the
wastewater treatment plant in Rogers, AR.
• Then a feed solution containing ammonium chloride and a base
(sodium bicarbonate) was slowly pumped through the reactor.
Oxygen was metered into the system at rate needed to achieve at
least 10 ppm dissolved O2.
• The reactor effluent was analyzed for ammonium, nitrate and pH.
As the bacteria grew, the ammonium concentration was increased
to very high levels. Then, over time, we reduced the sodium
bicarbonate in the feed solution, which caused the pH to drop.
• The organisms that survived were very acid tolerant.
22. Oxygen Tank
feed solution
Feed Pump
Circulation
Pump
Filtralite
flow
flow
flow
flow
flow meter
Reactor
Dissolved oxygen
sampling port
waste
Mixing
vessel
NH Cl4
Laboratory reactor for developing acid-tolerant nitrifying bacteria
24. 0 50 100 150 200 250
4
5
6
7
8
Time (days)
EffluentpH
Influent pH
The effluent pH decreased to values as low as 4.2 as the sodium bicarbonate
concentration was reduced in the feed solution. Chemical analysis of the water
indicated that 98% of ammonia was nitrified.
25. Clay medium was used to inoculate scrubbers with acid-tolerant nitrifiers
The clay was wrapped in cheesecloth, which was stapled to the slats
27. A short time later we observed this bacterial slime growing on the slats. We also
measured high levels on nitrate in the scrubber for the first time.
28. The system worked. In just over a month we captured 20 kg (44 lbs) of N,
even though only 3 slats out of 88 were used. About half of the nitrogen was
ammonium and half was nitrate.
29. feather trap
wooden slats
water curtains water curtains
Dust Scrubber Ammonia Scrubber
poultry house
exhaust fan
air
flow
bacterial biofilms growing from nylon mesh
Nitrification-enhanced ammonia scrubber (patent pending)
30. Conclusions
• Acid scrubbers can remove NH3 from broiler house exhaust air,
but they are currently not cost-effective.
• Although sodium bisulfate is safer than strong acids, it is not
practical because of sodium toxicity. We’re currently testing
sulfuric acid and alum, but the economics are much better.
• Poultry production is not improved when acid scrubbers are used
to capture NH3in air exhausted from poultry houses, so the only
economic benefit is the value of the N, which is cheap.
• Bottom line – It’s much easier and more cost-effective to prevent
NH3 emissions from broiler houses using litter amendments like
alum, than to use scrubbers to capture the N.
31. Problems/Future Research
• The acid-tolerant organisms we developed thrive at very warm
temperatures (80 - 90o
F). The scrubbers are located on the outside
of the poultry houses. To keep the water heated to 90o
F in the
winter would take an enormous amount of energy.
• Hence, our next step is to try to develop a strain of acid-tolerant
nitrifying bacteria that are also tolerant of cold conditions. So we
have set up the lab microcosm again and are using a big aquarium
cooling system to slowly reduce the temperature.
• We are hoping to develop a nitrification-enhanced ammonia
scrubber that is practical and works year round.
• However, bacteria are living things which require just the right
combination of temperature, oxygen, and nutrients to thrive.
Hence, this is challenging.