Treatment of Hazardous Air Pollutants (HAP)s in Ethanol Plant Exhaust by Using a Bio-Trickling Filter
Production of ethanol from the fermentation of corn creates an American produced renewable fuel source. During this process however, hazardous air pollutants (HAPs) are released as exhaust fumes from the fermentation tanks and solids drying. The generated HAPs are composed of mainly a mixture of acetaldehyde, formaldehyde, and methanol in addition to large fraction of ethanol fumes. In order to treat these HAPs, both CO2 scrubbers and thermal oxidizers are currently being used. The current treatment processes use a significant amount of water and energy to operate. In this study, a bio-trickling filter (BTF) is proposed as an innovative industrial HAPs treatment technology that uses less water and energy. BTFs provide a media for bacterial growth nurtured by nutrients supplied by the trickling liquid. They need to be initially seeded with either bacteria from a wastewater treatment plant (WWTP) or a compost. HAPs in an exhaust stream are removed as they pass through the column due to bacterial respiration. A lab-scale BTF has been set up to treat mixtures of HAPs that are common in an ethanol plant exhaust stream. The sampling plan includes 4 locations along the column depth; one at the top, two in the middle, and one at the bottom. Gas chromatography with mass spectrometry (GC/MS) and Fourier Transform Infrared (FTIR) analyzer were used to measure the individual HAP concentrations at each sampling point. Removal efficiency varied by compound and more analysis is needed to determine the effectiveness of the BTF as a treatment method from ethanol plant exhaust.
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[00:00:01.200]Hi. My name is Katie Mowat and I am a second year
master's student in environmental engineering
[00:00:06.880]at UNL. My research is on the treatment
of hazardous air pollutants or (HAP)s
[00:00:12.800]in ethanol plant exhaust by
using a bio-trickling filter.
[00:00:22.800]Ethanol is an alternative biofuel that
can be produced here in the United States.
[00:00:27.840]When you go to fill up your car at the gas station
there is usually an option to fill up with gas
[00:00:31.520]containing 10% ethanol. In 2018, the US consumed
14.4 billion gallons of ethanol. This ethanol is
[00:00:40.720]created from the fermentation of organic matter
at ethanol plants. There are 24 of these plants
[00:00:47.840]located in the state of Nebraska. During the
fermentation of organic matter, such as corn,
[00:00:54.240]hazardous air pollutants or (HAP)s are
released. Currently regenerative thermal
[00:01:00.160]oxidizers and CO2 scrubbers are used to
treat the exhaust from ethanol plants before
[00:01:05.520]it's released back into the atmosphere.
These are located in red on this diagram.
[00:01:17.040]The goal of this project is to use a bio-trickling
filter instead of the fore-mentioned, or in tandem
[00:01:23.440]with fore-mentioned, treatment methods to
treat this exhaust. The reason we want to
[00:01:29.280]do this is it uses 0.5% of the water that a CO2
scrubber uses and it also uses no natural gas
[00:01:37.600]which is what the thermal oxidizer needs.
Thus it is more environmentally friendly.
[00:01:45.920]To meet this goal, we have created
a lab scale bio-trickling filter,
[00:01:50.960]about four years ago, and have started by
running single compounds, HAPs, through it.
[00:01:56.320]Such as acetaldehyde, formaldehyde, ethanol, and
methanol. We've been able to prove that it will
[00:02:02.720]treat each of these compounds singularly, but now
have moved on to mixtures such as like a synthetic
[00:02:09.440]ethanol exhaust to run through the columns.
[00:02:18.000]You can see this is a picture of our two
columns. We have two columns due to the fact that
[00:02:25.440]one is run under mesophilic conditions,
which is room temperature, and the others
[00:02:30.560]run at thermophilic or 60 degrees celsius
to represent the two places in the plant
[00:02:37.440]where we could get exhaust and they
can be at different temperatures.
[00:02:43.680]We start with compressed air running at eight
liters per minute and using a syringe pump we pump
[00:02:51.200]the mixtures into lines that go into the columns
and they're volatilized due to the airflow.
[00:02:59.040]They flow into the columns
and then through multiple
[00:03:03.840]points along the column we can measure
through a multi-directional valve
[00:03:07.680]different things by sending the flow
to a GCMS, an FTIR or a microGC.
[00:03:16.160]The BTF gets its name because we trickle
bio-trickling fluid or nutrient solution
[00:03:23.120]through the column. So in this picture we
call it the feed tank and we have a pump
[00:03:27.760]controller and it sends about two liters of
nutrient solution through each column per day.
[00:03:40.960]So far we've run mixtures 1 and 2 from the
mixtures table here through the columns and
[00:03:46.480]have the results on this poster. We also
have the results from carbon oxygen demand,
[00:03:54.960]pH and total suspended solid measurements that
we take once a week and those can be seen here.
[00:04:03.680]For COD there isn't much of a difference
between the mesophilic and thermophilic, or
[00:04:08.080]cold and hot columns. It varies between 0.5 and 3
milligrams per liter for total suspended solids.
[00:04:17.600]You can see it's very very low. There's a tiny
bit more in the mesophilic than the thermophilic
[00:04:24.480]for pH. It was interesting, you can see the
gray dots are the nutrient solution or the
[00:04:30.960]influent and the effluent from the hot column or
thermophilic decreased the pH slightly, whereas,
[00:04:40.560]the cold column increased slightly. This could
be due to the heat or the cold spells we've
[00:04:46.960]had during the winter or the nutrient solution
rate changing depending on controller.
[00:04:55.600]The results from mixture 1 can
be seen here. The mesophilic
[00:05:02.560]or cooler column did better for removal efficiency
[00:05:06.480]across the board except for the methanol which
is a little bit higher in the thermophilic.
[00:05:14.160]In the thermophilic, we also found that
the ethanol didn't show up really well
[00:05:18.320]which is a problem we're working on.
[00:05:22.240]As we move into mixture 2 we have a higher ethanol
concentration and it's showing up a lot better.
[00:05:30.800]You can see the means are certainly higher in
the first mixture and the second mixture both
[00:05:37.600]mesophilic and thermophilic columns are very
similar in the results for removal efficiency.
[00:05:50.400]Some conclusions we've learned from this
research is it takes about two weeks to equalize
[00:05:55.040]the column to a new mixture before
you get standardized results.
[00:05:59.920]The amount of nutrient solution flowing
through the columns does affect the readings.
[00:06:05.440]And also the fact that we're running
mixtures is affecting the readings as well
[00:06:09.680]for the GCMS. The ions for acetaldehyde
and ethanol some of them are the same
[00:06:14.240]and that affects the peaks and gives some
uncertainty to our analysis and calibration.
[00:06:21.360]The FTIR also has some trouble with the methanol
readings due to mixtures affecting the wavelengths
[00:06:26.800]for that. So thus future work we're going to
run mixtures 3, 4, and 5 through the columns to
[00:06:33.680]get a bigger picture, fuller picture ,of what the
exhaust running through the bio-trickling filter,
[00:06:41.040]how well we can remove it. And create
more robust calibration curves.
[00:06:46.240]Add more points along the curve. I'd like to
acknowledge and thank my advisors Dr. Bruce Dvorak
[00:06:52.960]Dr Ashraf Aly Hassan. For all the lab help, I've
had multiple undergrads and grad students working
[00:06:59.120]under me and with me and that's been wonderful.
And for funding the Nebraska Public Power District
[00:07:05.920]and the Nebraska Center for Energy Science
Research helped fund this project. Thank you.
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