Air scrubber for organic solvent removal

An air scrubber is described, comprising a closed cabinet; a layer of permeable growth medium for the growth of microorganisms near the bottom of the cabinet wherein a portion of the growth medium is submerged in water, and an air space above the growth medium for accommodating growing plants wherein air is passed upwardly through at least a portion of the submerged growth medium. In normal operation, the air scrubber operates in a closed loop with a glove box. Air is circulated between the air scrubber and the glove box.

FIELD OF THE INVENTION 
This invention relates to a closed ecological system including humans, 
which is completely isolated from the earth's environment insofar as 
transfer of matter is concerned. The isolated, experimental environment 
requires constant monitoring. Therefore, experimentation that includes the 
use of toxic and volatile organic solvents is required. To maintain the 
purity of the air in the closed environment, it is important to remove 
these volatile organic pollutants from the air. An air scrubber for this 
purpose is described. The scrubber can also be utilized in non-closed 
systems to eliminate pollution by volatile organic chemicals. 
BACKGROUND OF THE INVENTION 
The earth comprises a biosphere in which microorganisms, plants, and 
animals, including humans, exist in a more-or-less steady state, wherein 
matter is a finite resource which is continually recycled. There is 
continual energy input in the form of solar radiation. The quantity of 
matter gained or lost to space outside the earth's atmosphere is minute. 
It is desirable to provide a microcosm of the biosphere known as earth to 
study the interaction of components and for the development of techniques 
for influencing our environment. Such experiments are difficult at best in 
the open system provided on earth, since matter is exchanged between the 
earth's environment and the experiment. It is, therefore, desirable to 
provide a system that is completely enclosed so that no matter is 
exchanged with the earth's environment. It is desirable to have humans 
within this miniaturized biosphere to provide control and to conduct 
scientific research within a closed system, where conditions can be varied 
as desired. 
Currently, a closed ecological system, referred to as Biosphere 2, is being 
established near Oracle, Ariz. The system completely encloses about one 
hectare of land and 175,000 cubic meters of space, isolated from the 
earth's environment by an impermeable skin so that no matter is 
transferred. 
The closed environment requires constant monitoring to obtain data of 
scientific interest, such as the changes that occur with time in the 
isolated environment. Additionally, the monitoring is performed to provide 
data for determining what adjustments to the internal systems of the 
biosphere may be required to ensure its proper functioning. 
Such monitoring involves experiments that use organic solvents. Many of 
these solvents are toxic and volatile and produce a form of pollution that 
can contaminate the isolated environment of the biosphere. If such 
pollution is not removed from the biosphere's environment it will 
accumulate, since there is no exchange of matter with the biosphere and 
the atmosphere outside the biosphere. Therefore, it is important to 
provide a system to not only contain fumes generated by the use of the 
organic solvents in the experiments or by accidental spills, but also to 
completely remove such fumes or accidental spills from the containment 
system, to prevent contamination of future experiments. 
It is therefore desirable that the experiments using organic solvents are 
contained in a closed environment, such as a glove box. Additionally, it 
is desirable that the glove box is in a "closed loop" with an 
air-purification system or air scrubber. The air scrubber removes the 
volatile organic pollutants from the air and provides a means for 
decomposing the pollutants to non-toxic compounds which, preferably, can 
be recycled. 
SUMMARY OF THE INVENTION 
The present invention relates to an air scrubber for removal of volatile 
organic pollutants from air. The air scrubber comprises a closed cabinet, 
a layer of permeable growth medium for the growth of microorganisms near 
the bottom of the cabinet, means for maintaining a portion of the growth 
medium submerged in water, an air space above the growth medium for 
accommodating growing plants, and means for passing air upwardly through 
at least a portion of the submerged growth medium. 
The plants and microorganisms exist in a symbiotic relationship in which 
the microorganisms convert the organic pollutants to carbon dioxide for 
use by the plants. The plants convert the carbon dioxide into complex 
organic material and provide aeration for the microorganisms. 
In normal operation, the air scrubber operates in a closed air loop, 
comprising a glove box in which organic pollutants are produced, and an 
air scrubber, where the organic pollutants are removed from the air.

DETAILED DESCRIPTION 
The biosphere's closed environment requires constant monitoring to obtain 
experimental data of scientific interest relating to changes that occur, 
with time, in the isolated environment of Biosphere 2. Additionally, 
experimentation is required to provide information necessary to make 
adjustments to the internal systems of Biosphere 2, to ensure that they 
are functioning as required. 
Such monitoring involves experiments and analyses that use toxic and 
volatile organic solvents. To prevent the environment of Biosphere 2 from 
becoming contaminated with the fumes generated by the use of the organic 
solvents and those generated by accidental spills, the organic pollutants 
must be removed from the atmosphere of the biosphere. Preferably, the 
material is not only removed from the biosphere's atmosphere, but is also 
disposed of in a non-toxic form. More preferably, the toxic material is 
recycled into non-toxic and usable products, since all waste products that 
cannot be recycled must be stored within the biosphere. Such storage takes 
up valuable space and limits the time the system can remain isolated or 
closed. 
It is therefore desirable to recycle the fumes and waste material from the 
experiments using organic solvents. Experiments involving organic 
materials are contained within a glove box that is part of a closed loop 
with an air scrubber. 
The air scrubber is designed to remove and decompose the pollutants, 
generating non-toxic end products, by using a symbiotic combination of 
microorganisms and plants. Air within the closed loop can be continually 
cycled from the glove box, where the pollutants are generated, to the air 
scrubber, where the pollutants are removed from the air. The purified air 
is then returned to the glove box. 
The air scrubber 10, shown in FIG. 1, comprises a cabinet 12 having a total 
volume of about 0.8 cubic meters. At the bottom of the cabinet is a sump 
14, which acts as a water reservoir. Water, for use in the cabinet, is 
removed from the sump via an outlet port 16, located at the bottom of the 
sump. Excess water, from the cabinet, is returned to the sump via the 
manifold outlet 18 at the top of the sump. The sump is separated from the 
remainder of the cabinet by a water-tight partition 20. The cabinet and 
partition are conveniently made from transparent acrylic or other suitable 
material. 
A plurality of diffuser pipes 22, located on the upper side of the 
partition, are embedded in a layer of pea gravel 24. The diffuser pipes, 
shown in FIG. 2, are semi-circular pipes of polyvinyl chloride (PVC), or 
other suitable material, fixed to the upper surface of the partition. 
Perforations 26 are included in the diffuser pipes so that air can escape 
into the layer of pea gravel. Percolating the air through the pea gravel 
aids in the diffusion of the air. 
A carbon layer 28 is layered over the pea gravel. The carbon in the carbon 
layer is in the form of granules of 3-6 mm in size. The carbon layer 
functions to remove the organic pollutants from the diffused air. Carbon 
is preferred as a medium for removing the pollutants from the air, since 
it has a large surface area and a high affinity for organic pollutants. 
The carbon layer also provides an environment for the growth of 
microorganisms. 
The microorganisms contained within the carbon layer are aerobic and are of 
a type that is capable of digesting organic pollutants, such as acetone, 
hexane, or the like, which become trapped in the carbon layer and of 
converting them to carbon dioxide. Microorganisms with the capacity to 
digest these organic compounds can be selected from nature, or they can be 
genetically engineered to have the desired properties required for the 
digestion of the organic solvents used within Biosphere 2. Preferably, 
when naturally-occurring microorganisms are used, the carbon layer is 
inoculated with a broad spectrum of microorganisms. The microorganisms 
that are best suited for survival under the prevailing conditions in the 
air scrubber will grow and flourish. Microorganisms that are poorly suited 
to the prevailing environment of the air scrubber will not survive, since 
they are unable to compete for nutrients and space. Therefore, the 
selection of the microorganisms used in the air scrubber is based on 
survival of the fittest. 
It is desirable that the carbon layer is inoculated with a variety of 
microorganisms, since it is unlikely that the carbon layer naturally 
contains a significant population of microorganisms. Without inoculation, 
it can take some time to build up a sufficient population of 
microorganisms for thorough removal of pollutants from the air. Without 
inoculation, a substantial time may elapse before effective pollution 
removal is obtained. 
The microorganisms that are preferred for inoculating the carbon layer of 
the air scrubber are the naturally-occurring aerobic symbionts found in 
conjunction with the plant species used in the system. 
To further support the growth of the microorganisms, the carbon layer is 
partially submerged in water. The water provides a medium suitable for the 
establishment of cultures of some of the desired microorganisms and the 
dry area for others. 
It is also desirable that the end product of the microorganisms' digestion 
of the organic compounds is complete oxidation to carbon dioxide. Since 
carbon dioxide is the desired end product, oxidative catabolic processes 
and, therefore, aerobic growth conditions for the microorganisms are 
preferred. To obtain the aerobic conditions, aeration of the carbon layer 
is helpful. Partial aeration of the carbon layer is provided by the 
diffused air, carrying the organic compounds, as it percolates through the 
carbon layer. 
Primary aeration is provided by the root system of suitable plants. 
Preferably, the plants are marsh plants, such as Typha latifolio, 
Phragmites communis, and Eicchornia crassioes. Marsh plants are preferred 
for use in the air scrubber, since they translocate oxygen to their roots. 
The root system of these plants, therefore, provides a simple and 
efficient means of aerating the carbon layer. An additional reason for 
preferring marsh plants is that they are very tolerant of having their 
roots continually submerged in water, whereas other plants, under similar 
conditions, would rot. It is important that the plants are tolerant of 
continual exposure to water, since this type of environment is preferred 
as a growth medium for the microorganism cultures established within the 
carbon layer. 
To support the growth of the plants, a layer of soil 30 is layered over the 
carbon layer. The soil layer provides mineral nutrients important for 
maintaining the plants' optimal growth rates and also provides a medium 
for anchoring the roots of the plants. 
The plants and the microorganisms exist in a symbiotic relationship with 
each other inside the air scrubber. The plants, on the one hand, provide 
aeration of the microorganisms' medium, which promotes the aerobic growth 
of the microorganisms. The microorganisms, on the other hand, metabolize 
the organic pollutants to carbon dioxide, thus providing an essential 
carbon source for the plants. 
The soil used in the air scrubber is a porous hydrophilic medium. The soil 
can comprise soil indigenous to the area and may be augmented with organic 
additive, compost, peat moss, sand and clay mixtures, small ceramic or 
plastic particles, or commercially-available potting soil or the like. 
Rich, aerated soil contains an ample variety of microorganisms for 
inoculating the carbon layer. Some soil may be mixed in for inoculation, 
or one may simply wait for natural spread of organisms from the soil layer 
and plant roots into the carbon layer. 
So-called "potting soil" is preferred, since it is hydrophilic, rich in 
organic nutrients, stable, permeable, readily available, and inexpensive. 
Typical potting soils include sand, a small amount of clay, other mineral 
grains, and organic particles or fibers, and can include conventional 
chemical fertilizers and adjuvants. 
A closed plant chamber 32 is located above the soil layer. The plant 
chamber provides a space for the growth of the plant foliage. The plant 
chamber also provides a space in which the carbon dioxide, produced by the 
action of the microorganisms, is collected and exposed to the leaves of 
the plants. The accumulated carbon dioxide is removed by the plants from 
the atmosphere of the plant chamber and is converted into complex organic 
material, in the form of plant matter, by the process of photosynthesis. 
The plant matter is harvested periodically to prevent overgrowth of the 
plant chamber. The harvested plant matter, or similar plant matter, is 
made into compost and returned to the air scrubber. Returning the compost 
back to the air scrubber replenishes the valuable nutrients and minerals 
of the soil. Such replenishment promotes the continued growth of both 
microorganisms and plants within the air scrubber. 
An additional requirement for the growth of the plants is light, since 
light is an essential requirement for photosynthesis. A lamp 34, which 
emits light of a wavelength suitable for promoting the photosynthetic 
reactions of the plants, such as a haline or other suitable lamp, is 
attached to the top of the cabinet. 
A method for controlling the growth of the plants in the plant chamber is 
by regulating their light supply. When the air scrubber is not in use, the 
lights over the air scrubber can be turned off. In the absence of light, 
the plants' rate of growth is suppressed. Therefore, the need to harvest 
the plants in the plant chamber can be minimized or reduced by limiting 
the light available to the plants, if desired. 
As discussed above, an additional requirement for the growth of the plants 
and microorganisms in the air scrubber, is water. A watering system 36 is 
provided for supplying water, as it is required, to the plants and 
microorganisms. The outlet port 16 of the sump is connected to the inlet 
42 of a liquid-transfer pump 38 by a pipe 40. The outlet 44 of the 
liquid-transfer pump is connected to a vertical pipe 46. An L-shaped joint 
48 is made with a second pipe 50. A shower nozzle 52 is at the open end of 
pipe 50. The shower nozzle is located at the top of the plant chamber. 
The plants are watered by pumping water from the sump to the shower nozzle 
and spraying it from the shower nozzle onto the plants in the plant 
chamber. However, once the air scrubber is established and the plants and 
microorganisms in it are growing as desired, water is not routinely added 
to the air scrubber. Rather, water is added only periodically, to clean 
and refresh the foliage of the plants. Once the level of water in the air 
scrubber has been adjusted to the desired level, for optimum growth of the 
plants and microorganisms, additional water will not be needed, since the 
air scrubber is in a closed loop with a glove box 74, and there is little 
or no water loss from the system, except in harvested biomass. 
The water level in the air scrubber is an important factor in the 
determination of the satisfactory growth of the microorganisms and plants. 
An inadequate level of water results in a limited population of 
microorganisms, since the volume in which they can grow is smaller than 
desired. Alternately, a level of water that is too high will result in 
rotting of the plants and an inability on the part of the plants to anchor 
themselves into the soil, due to a lack of a solid support medium. 
Therefore, it is desirable to provide a means of adjusting the level of 
the water in the pea gravel, carbon, and soil layers, so that the growth 
of the microorganisms and plants can be optimized and to simulate 
naturally-occurring, seasonal, periodic "drawdowns." 
A drain manifold 54 is provided to adjust the level of water in the growth 
mechanism, so that growth of plants and microorganisms can be optimized. 
The drain manifold comprises a series of pipes 56 connected at one end to 
the cabinet. Each pipe is connected to the cabinet at a different depth 
within the cabinet. Some pipes are connected at the level of the soil 
layer, some are connected at different levels in the carbon layer, and 
some are connected in the pea gravel layer. 
On the inside of the cabinet, and located to cover the inlets of the pipes, 
is a PVC pipe, cut in half to form a semi-circular shell 58. The 
semi-circular shell is affixed to the inside of the cabinet wall 59. 
Perforations 61 are included in the shell to allow water to pass through 
the shell to the pipes of the manifold. Preferably, the perforations are 
small enough to inhibit the soil, carbon granules, and pea gravel from 
entering and clogging the manifold pipes. Also, the perforations retain 
the soil, carbon granules, and pea gravel in the air scrubber. 
Each of the manifold pipes has a ball valve 60 to control the water level. 
When a ball valveiis in the off position, water is unable to flow out of 
that particular manifold pipe so that the water level in the cabinet is 
maintained at a height greater than that of the "closed" pipe. When a ball 
valve is in the open position, water is able to flow out of that 
particular manifold pipe so that the water level in the cabinet is 
maintained at a height equal to that of the "open" pipe. 
The other end of each of the manifold pipes is connected to a collector 
pipe 62. The collector pipe is connected to the manifold outlet 18 in the 
sump. The drain manifold 54 provides a means of returning any excess water 
to the sump. The air scrubber, therefore, is a "closed loop" with respect 
to water. As a result of the closed nature of the air scrubber, little or 
no water needs to be added to the plant chamber once the desired water 
level has been established. 
The air scrubber is designed to remove pollutants from air. Therefore, it 
is important to provide an aircirculation system to bring polluted air 
from the experiment work area, where organic solvents are used in various 
experimental procedures, to the air scrubber, where the pollutants are 
removed, and then return the purified air to the experiment work area. The 
air-circulation system also provides a "closed loop" with respect to air. 
The air-circulation system is driven by a direct-drive blower 64. The 
outlet of the blower is connected to a T-conduit 66. One end 68 of the 
T-conduit is connected to the plant chamber 32, and the other end 69 is 
connected to the diffuser pipes 22. The flow of air to the diffuser pipes, 
or to the plant chamber, can be regulated by means of a valve 70. The 
valve directs air flow to either the diffuser pipes or directly to the 
plant chamber. Air that is introduced into the air scrubber via the 
diffuser pipes is diffused into small bubbles as the air is released from 
the perforations in the diffuser pipes. Further diffusion of the air is 
achieved by bubbling the air through the granules of the pea gravel. A 
small bubble size is preferred, since small bubbles present a large 
surface-area-to-volume ratio to the carbon granules, and the organic 
pollutants that they are carrying are more readily adsorbed. As the air 
bubbles rise through the carbon layers, the organic pollutants are 
adsorbed onto the carbon and soil particles. Once the pollutants have been 
adsorbed, they are then available to the microorganisms as a carbon source 
for metabolism. The small air bubbles also help to oxygenate the carbon 
layer and, therefore, promote oxidative catabolism of the organic 
pollutants by the microorganisms. 
As the microorganisms digest the pollutants, they generate carbon dioxide. 
The carbon dioxide and the air bubbles, which have had the pollutants 
removed, then percolate through the soil layer and out into the plant 
chamber. The carbon dioxide is then available to the plants in the plant 
chamber as a carbon source which they can metabolize into complex organic 
material, i.e., starches, etc. 
The air bubbles not only percolate through the solid layers of pea gravel, 
carbon, and soil, but also through water. As a result, the air becomes 
very humid. 
The humidity of the air is also increased by the warmth of the air 
scrubber, generated by the heat of the lamps, as well as the ambient 
external temperature. The temperature of the air scrubber is preferably at 
25.degree. to 38.degree. C. This temperature range is preferred, since it 
promotes the rapid growth of the microbial cultures in the carbon layer. 
Additionally, the plants selected for use in the air scrubber are 
naturally found in temperate and tropical climates and are best adapted to 
growth at these temperatures, although, at lower temperatures, microbial 
action continues even though the plant growth is inhibited. 
It is desirable to prevent condensation of the water from the moist, warm 
air from the air scrubber as it cools down when it is returned to the 
glove box. If the water is not cooled prior to its return to the glove 
box, water may condense and accumulate in the glove box and the air lines 
leading to it. The presence of water in the glove box and the air line 
would likely interfere with the experiments that are being conducted in 
the glove box. Any water that reached the glove box would have to be 
continually removed. As a result, water would be continually removed from 
the air scrubber system. Since it is preferred that the air scrubber is a 
closed system with respect to air and water, it is preferable to remove 
the moisture from the air before it is returned to the glove box. 
An air cooler 72, located at the top of the plant chamber, is provided to 
cool the air and reduce its moisture content before the air is returned to 
the glove box 74. The air cooler also forms the air outlet of the plant 
chamber. In addition to preventing condensation of water in the glove box, 
the air cooler also ensures that water is not removed from the plant 
chamber. If water were continually being removed from the plant chamber in 
the form of humidity, the water would have to be replenished. The air 
cooler provides a means of cooling the air and returning the excess 
moisture to the plant chamber. 
Experiments in the glove box will not always be in progress, but rather 
will be conducted on an intermittent basis. Therefore, when the glove box 
is not in use, there will be no organic pollutants being generated, or, at 
most, there will only be residual amounts of pollutants within the system. 
At times when the level of pollutants is very low, the air scrubber need 
only be run at a slow or idling rate. The flow rate of the air through the 
air scrubber is about 7.1 liters/second when it is idling and removing low 
levels of pollution. 
At other times, when experiments are in progress, the level of pollutants 
in the air from the glove box will be at an intermediate level. The flow 
rate of the air through the air scrubber is about 14.2 liters/second when 
the air scrubber is being operated at an intermediate level and removing 
normal levels of organic material that is generated in the normal course 
of an experiment. 
At still other times, accidental spills are expected to occur within the 
glove box and, as a result, will generate high levels of pollution. At 
such time, the air scrubber is required to operate at its maximum 
capacity, to remove all of the organic pollutants from the air. The flow 
rate of the air through the scrubber is at a rate of up to 14.2 
liters/second when the air scrubber is removing high levels of pollution 
resulting from spills of organic solvents. 
When the air scrubber is removing low levels of pollution, a single passage 
of the air through the scrubber may be sufficient to purify the air. 
However, when there is a high level of pollution, such as that resulting 
from accidental spills, the polluted air may have to be passed through the 
air scrubber several times before all the organic pollutants are removed 
and the air is purified. 
Low levels of pollution are about 125 milliliters (ml) of solvent per week. 
High levels of pollution, such as levels that might result from spills, 
are up to about 300 ml per incident. 
The present invention is described in relation to only one working 
embodiment and is for illustration purposes. Variations will be apparent 
to those skilled in the art. For example, the air scrubber described is 
for small-scale, experimental procedures that can be conducted in a glove 
box. However, it would be possible to "scale up" the air scrubber so that 
it could be used to purify the air from a whole room, or even from an 
industrial-sized installation. Additionally, other types of plants, and 
the growth conditions of plants and microorganisms, may be used to obtain 
digestion of organic pollutants. Therefore, the present invention is not 
intended to be limited to the working embodiment described above. The 
scope of the invention is defined in the following claims.