Control of Lethal Poisons with Soil Ecosystem Machinery

1
Control of Lethal Poisons with Soil Ecosystem
Machinery David R. Tilley and Priti
Ganeshan Department of Biological Resources
Engineering and Natural Resources Management
Program, University of Maryland, College Park
dtilley_at_umd.edu, 301-405-8027
Abstract We investigated the capacity of air
biofilters to reduce carbon monoxide (CO)
emissions from the exhaust of a 2.6 kW (3.5
horsepower) gasoline powered engine. CO, a
product of incomplete fuel combustion, is a
lethal poison that kills 500 Americans annually,
sickens thousands and interferes with the
capacity of the Earths atmosphere to destroy
greenhouse gases. Soil ecosystems with their
resident microbes have been identified as the
second largest sink for CO emissions. Tube-shaped
bench-scale biofilters (1 m x 15 cm) were
constructed of clear-PVC, filled with compost or
rock media, inoculated with local urban soil
slurries, and supplied engine exhaust gas
containing between 500 and 1000 ppm-CO for
several weeks. A vacuum pump pulled air at 1.0
liter per minute through the biofilters from
bottom to top. The maximum mean daily reduction
in CO concentration (45) was observed for a
compost biofilter, whereas rock media filters
never reduced CO by more than 20. The
ecological machinery of soils provide a valuable
service by reducing air pollution.
Materials and Methods Figs. 2 and 3 show a
photograph and a diagram, respectively, of the
engine exhaust biofiltration system. Six
bench-scale biofilters (BF), 15 cm in diameter
and 100 cm in height, were constructed of clear
PVC, filled with either poultry litter compost or
Grorox (clay pebbles), inoculated with an urban
soil slurry, and irrigated with de-chlorinated
water to maintain 40-60 moisture content. An
1125 W (1.5 HP) vacuum pump, attached to a top
port, pulled either exhaust from a 2620 W (3.5
HP) four-stroke gasoline engine (Briggs
Stratton, Inc., Wauwatosa, WI) or bottled air
with 1000 ppm CO (Air Gas, Inc., Radnor, PA)
through the BF media. Engine exhaust CO
concentration ranged from 500-1000 ppm. BF inlet
and outlet CO concentrations and flow rates were
measured with a non-dispersive infrared analyzer
(CAI model 200, California Analytical
Instruments, Inc., Orange, CA) and
stainless-steel flow meters (Gilmont Inc.,
Barrington, IL), respectively. With a single
analyzer, inlet and outlet CO concentrations
could not be measured simultaneously, but were
measured periodically.
Results Fig. 4 shows a typical response of the
biofilter to a daily (7 h) dose of continuously
fed CO from an air-mixed bottle. CO outlet
concentrations increased during the first 2 h of
operation, but then leveled to a steady state of
705 ppm-CO (30 removal).
Fig. 7 shows the effect of soil inoculation on
biofilter removal rate of CO. The compost
biofilter was inoculated with the soil slurry
after Day 5, which resulted in a reduction in
outlet CO levels to 840 ppm for six days. By Day
7 CO outlet levels began increasing. A second
soil inoculation was conducted on Day 24, which
again resulted in lowered CO levels. The
experiment was stopped on Day 32 when removal
efficiency was 22.
Fig. 4. CO outlet concentration from a compost
biofilter fed a continuous supply of 1000 ppm CO
from a bottle mixed with air.
In Figs. 5 and 6 the variability of the engine
exhausts CO concentration was noticeably higher
than the outlet concentration of both types of
biofilters tested (compost and rock media).
Whereas the range of the engine CO was 350 ppm
during the three minutes shown, the range of the
biofilter CO was only 20 ppm. The compost
biofilter reduced the engine CO by 45, whereas
the rock filter had an average removal efficiency
of 22.
Fig. 7. Steady state CO outlet levels of a
compost biofilter fed a continuous supply of 1000
ppm CO mixed with air before and after
inoculations with urban soil slurry.
Introduction Carbon monoxide (CO), a product of
incomplete combustion of hydrocarbons (Fig. 1) is
a lethal poison that kills 500 Americans annually
by interfering with the oxygen carrying capacity
of hemoglobin. Estimates of the annual global
production of CO range from 2600 to 3300
teragrams (Conny, 1998). CO reaction with OH- is
the major sink for CO, but the microbial
metabolism of soil ecosystem machinery is the
second largest sink. CO removal of tropospheric
OH- decreases the atmospheres removal capacity
for greenhouse gases like methane. Air biofilters
can remove inorganic and organic compounds like
H2S, NOX and VOCs. Objectives for this study
were to determine the effect of a bench-scale
biofilter on the CO levels emitted from a
gasoline powered engine and canisters of CO/air
mixtures.
Conclusions Bench-scale reactors containing
compost media inoculated with a slurry of soil
from an urban ecosystem reduced the levels of CO
emitted from a gasoline powered engine and CO
discharged from an air mixed bottle. Reactors
containing inoculated rock media removed less CO
than inoculated compost. A human engineered
machine (i.e., small gasoline engine) exhibited
higher variance in CO output than the microbially
mediated soil machine (i.e., biofilter).
Fig. 2. Photograph of air biofilters receiving
exhaust from a small gasoline engine.
Fig. 5. Overlay of two typical inlet and outlet
biofilter CO concentrations during treatment of
gasoline engine exhaust by COMPOST biofilter.

• Machine Definitions
• A device consisting of fixed and moving parts
  that modifies mechanical energy and transmits it
  in a more useful form.
• An intricate natural system or organism, such as
  the human body.
• A system or devicethat performs or assists in
  the performance of a human task.
• Any mechanical contrivance.
• Any mechanical or electrical device that
  transmits or modifies energy to perform or assist
  in the performance of human tasks.
• Ecological Machine A system of living and
  non-living parts that modifies energy and matter
  to perform a life-support service.

Fig. 3. Diagram of air biofilter system.
Literature Cited Conny, J.M., 1998. The isotopic
characterization of carbon monoxide in the
troposphere. Atmospheric Environment
32(14/15)2669-2683
Fig. 6. Overlay of two typical inlet and outlet
biofilter CO concentrations during treatment of
gasoline engine exhaust by ROCK filters.
Fig. 1. Energy systems diagram of global CO cycle
(values from Conny 1998).