http://www.physorg.com/news/2011-01-electrifying-dirty.html
January 6, 2011
Electrifying new way to clean dirty water
(PhysOrg.com) -- University of Utah researchers developed a new
concept in water treatment: an electrobiochemical reactor in which
a
low electrical voltage is
applied to microbes to help them quickly and efficiently
remove pollutants from mining, industrial and agricultural
wastewater.
The patented
electrobiochemical
reactor (EBR) process replaces tons of chemicals with a
small amount of electricity that feed microbes with electrons.
Tests have shown that the electrons accelerate how quickly the
microbes remove pollutants such as arsenic, selenium, mercury and
other materials, significantly reducing the cost of wastewater
cleanup.
The research is now being used by a University of Utah startup
company named INOTEC, which was honored at the 2010 Cleantech Open
competition in San Jose, Calif. INOTEC and its EBR technology won
the $40,000 Rocky Mountain regional award in what is nicknamed the
"Academy Awards of Clean Technology." INOTECH was one of 18 teams
that became finalists out of 271 in the event.
Metallurgical engineer
Jack
Adams of the College of Mines and Earth Sciences
pioneered the process. He and graduate student
Mike Peoples, who co-founded
INOTEC, say the award is validation that their research can save
the wastewater industry money.
"It is great to be recognized for an innovative clean technology,"
says Adams, president of INOTEC and a research professor in the
Department of Metallurgical Engineering. "We're currently in the
early stages of growing the company, and every bit of recognition
and support we get fits in with our go-to-market model. It will
open new opportunities for securing partnerships and investor
funding that will allow us and a partner to take the technology
further faster."
Adams says the new method can enhance just about any type of
wastewater treatment. It now is being tested primarily for
removing metals from mining wastewater, but also could be used for
other industrial and agricultural wastes, he adds.
INOTEC has received support and an exclusive license to the EBR
technology from the University of Utah's Technology
Commercialization Office, which protects and manages the
university's intellectual property and helps faculty members
create startup companies. INOTEC is working with the office's new
Energy Commercialization Center to secure business partners and
funding.
In conventional wastewater treatment, microbes or chemicals alter
or remove contaminants by adding or removing electrons. The
electrons come from large excesses of nutrients and chemicals
added to the systems to adjust the reactor chemistry for microbial
growth and contaminant removal. Those large excesses must be added
to compensate for changes in water chemistry and other factors
that limit the availability of electrons to remove pollutants.
The electrobiochemical reactor or EBR system overcomes these
shortcomings by directly supplying excess electrons to the reactor
and microbes using low voltage and no current, unlike other
systems that provide large electrical currents. One volt supplies
about one trillion trillion electrons (note: trillion twice is
correct). These electrons replace the electrons normally supplied
by excess nutrients and chemicals, at a considerable savings and
with greater efficiency.
The electrons needed for a full-scale facility can easily be
supplied by a small solar power grid. "The provided electrons make
reactors more efficient, stable and controllable," Adams says.
The researchers, through INOTEC, have successfully completed five
laboratory tests of waters from various metal and coal mines in
North America containing selenium, arsenic, mercury and nitrates.
INOTEC recently completed its first on-site, pilot-scale contract,
treating wastewater containing arsenic and nitrate from an
inactive gold mine. This demonstration was partially funded
through a University of Utah Virtual Incubator Program grant.
INOTEC has also secured its own contract for a second pilot-scale
test at a mine for silver and other metals in the Yukon in spring
2011.
http://www.earthtimes.org/pollution/electric-technology-zaps-water-pollution/256/
11 Feb 2011
Electric technology zaps away water pollution
by Laura Goodall
Zapping microbes with electricity could replace tonnes of
chemicals used in cleaning up mining wastewater, thanks to
scientists who have developed a new water treatment system.
Microbes are already used in conventional wastewater treatments to
mop up contaminants by adding or removing electrons. But to work
effectively, they need to be 'fed' using vast amounts of nutrients
and chemicals.
The researchers from the University of Utah say that their
electrobiochemical reactor (EBR) system bypasses the addition of
excess chemicals by feeding electrons directly to the microbes.
This boosts how quickly they can clean up pollutants, such as
arsenic, mercury, selenium, nitrates and sulphates.
''We've seen that microbes with the EBR system work between
2 and 10 times faster than the same
process without the added voltage,'' says Jack Adams, the
research professor at Utah's Department of Metallurgical
Engineering who pioneered the system. ''Because the microbes are
at least twice as efficient, we can reduce the amount of chemicals
by over 50% and still effectively remove the contaminants.''
He adds, ''The metal contaminants are removed and collected in a
form that can be recycled. Similarly, the concept behind the EBR
may make it possible to recover more of the valuable product
itself and with similar environmental benefits.''
The low voltage used by the EBR can also easily be generated using
a small solar power grid, helping to minimise the overall
environmental impact.
Following their successful trial in treating wastewater at an
inactive gold mine, Adams and his colleagues are now embarking on
a second pilot-scale study at a mine for silver and other metals
in Canada's Yukon Territory.
''This research will help us to gain insight into how we can
improve the system even further, and we anticipate that the
pilot-scale tests will lead to full-scale treatment systems,'' he
says.
Although the research team are focusing on removing metals from
mining wastewater, Adams points out that EBR has great potential
for other applications.
''Essentially, all biological and chemical reactions involve
electrons being added and removed, which the EBR delivers in a
controlled way,'' he explains. ''This makes it possible for many
other microbial and chemical systems to be better controlled and
more efficient as well as better for the environment.''
http://www.inotec.us/
Electrobiochemical reactor
WO2010002503 // AU2009265058
Inventor(s):
MILLER JAN D;
NANDURI MADHURI; ADAMS JACK; PEOPLES MIKE; NEWTON NICOL + (JAN
D. MILLER, ; MADHURI NANDURI, ; JACK ADAMS, ; MIKE PEOPLES, ;
NICOL NEWTON)
Applicant(s): UNIV UTAH RES FOUND + (UNIVERSITY OF UTAH RESEARCH
FOUNDATION)
Classification:- international: C12M1/33;
C12M1/42 - European: C02F1/46B; C12M1/42
Abstract -- A method for
removing a target compound from a liquid can include arranging two
active surfaces so as to be separated by a distance. The active
surfaces can be placed within a flow of the liquid and can be
capable of supporting an electrical charge, biological growth,
and/or enzymes and proteins. The method can further include
developing a population of microorganisms concentrated on the
active surfaces where the population of microorganisms is
configured to or capable of transformation of the target
compounds. The method can further include developing enzymes or
proteins concentrated on the active surfaces where the enzymes or
proteins are configured to or capable of transformation of the
target compounds. The method can further include applying a
potential difference between the two active surfaces.; The
microorganisms and the potential difference can be sufficient in
combination and/or with specific nutrients to remove the target
compound from the liquid and maintain the population of
microorganisms. The enzymes and proteins and the potential
difference can be sufficient in combination to remove the target
compound from the liquid.
Description
BACKGROUND OF THE INVENTION
Metals and other inorganics like arsenic, selenium, mercury,
cadmium, chromium, nitrogen, etc. are difficult to remove to
levels that meet current drinking water and discharge criteria in
many countries. For example, in the United States, the 2006
maximum arsenic level in drinking waters was set at 10 ppb; this
may soon be the case in other countries. Maximum contaminant
levels (MCL) of metals in drinking water in the United States can
range 0.0005 to 10 mg/L, and can be even lower. Commonly regulated
metals and inorganics include antimony, arsenic, asbestos, barium,
beryllium, cadmium, chromium, copper, cyanide, fluoride, lead,
mercury, nitrate, nitrite, selenium, and thallium.
There are various kinds of treatment methods for metal,
inorganics, and organics removal. Technologies used to treat metal
and inorganic-contaminated soil; waste and water mainly include:
solidification/stabilization, vitrification, soil washing/acid
extraction, reverse osmosis, ion exchange, biological treatments,
physical separations, pyrometallurgical recovery, and in situ soil
flushing for soil and waste contaminant treatment technologies.
Precipitating/co-precipitation, membrane filtration, adsorption,
ion exchange, and permeable reactive barriers are more common
treatment technologies for treating contaminant water, while
electrokinetics, phytoremediation, with biological treatment being
a common treatment technology for removing contaminants in soils,
wastewaters, and drinking waters.
SUMMARY OF THE INVENTION
A method for removing a target compound from a liquid can include
arranging two active surfaces so as to be separated by a
predetermined distance. The active surfaces can be placed within a
flow of the liquid and can be capable of supporting an electrical
charge and biological growth. The method can further include
developing a population of microorganisms concentrated on the
active surfaces where the population of microorganisms is
configured to or capable of acting on, transforming, or binding
the target compound. The method can further include applying a
potential difference between the two active surfaces. The
microorganisms and the potential difference can be sufficient in
combination to remove the target compound from the liquid and
maintain the population of microorganisms.
Additionally, a system for removing a target compound from a
liquid can include two active surfaces arranged a distance apart,
and substantially parallel to each other. An electrical source can
be operative Iy connected to each of the active surfaces in a
manner so as to provide a potential difference between the two
active surfaces. In another configuration, a population of
microorganisms can be present on each of the two active surfaces.
Additionally, the system can include a flow path sufficient to
direct a majority of the liquid to contact each active surface and
sufficient to direct a majority of the liquid across the distance.
The more important features of the invention have been outlined,
rather broadly, so that the detailed description thereof that
follows may be better understood, and so that the present
contribution to the art may be better appreciated. Other features
of the present invention will become clearer from the following
detailed description of the invention, taken with the accompanying
drawings and claims, or may be learned by the practice of the
invention.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a dominance
diagram for As2S3 precipitation in equilibrium with various
chemical species as reported in the literature.
Figure 2 is an Eh-pH
diagram for various arsenic species.
Figure 3 is an Eh-pH
diagram for N2-O2-H2O systems.
Figure 4 A and 4B are
Eh-pH diagrams for various selenium systems.
Figure 5 is an
electrobiochemical reactor having an open channel which flows
parallel to and past charged electrodes in accordance with one
embodiment of the present invention.
Figure 6 is an
electrobiochemical reactor having a bed of high surface area
conductive material permeable to solution in a channel which flows
perpendicular to and across charged electrodes in accordance with
another embodiment of the present invention.
Figures 7A and 7B are a
depiction of an electrobiochemical reactor system tested without
(7A) and with applied potential (7B) and used to evaluate arsenic
removal in accordance with one embodiment of the present
invention.
Figures 8 A and 8B are a
depiction of an electrobiochemical reactor system tested with (8A)
and without (8B) applied potential to evaluate selenium removal in
accordance with one embodiment of the present invention.
Figure 9 is a graph of
measured potentials across the EBR and conventional bioreactor
used to remove arsenic from test waters.
Figure 10 is a graph of
arsenic removal from several test solutions comparing the EBR with
a similarly constructed reactor operated without applied voltage.
Figure 11 is a graph of
selenium removal from several mine waters using a two stage
conventional bioreactor without applied potential and a retention
time of 44 hrs and a single stage EBR with a retention time of 22
hr and an applied potential of 3 volts.
DETAILED DESCRIPTION
Reference will now be made to exemplary embodiments, and specific
language will be used herein to describe the same. It will
nevertheless be understood that no limitation of the scope of the
invention is thereby intended. Alterations and further
modifications of the inventive features illustrated herein, and
additional applications of the principles of the inventions as
illustrated herein, which would occur to one skilled in the
relevant art and having possession of this disclosure, are to be
considered within the scope of the invention. Definitions In
describing and claiming the present invention, the following
terminology will be used in accordance with the definitions set
forth below.
It must be noted that, as used in this specification and the
appended claims, the singular forms "a," "an," and "the" include
plural referents unless the context clearly dictates otherwise.
Thus, for example, reference to "an active surface" includes one
or more of such active surfaces and reference to "a developing
step" includes reference to one or more of such steps.
As used herein, "substantial" when used in reference to a quantity
or amount of a material, or a specific characteristic thereof,
refers to an amount that is sufficient to provide an effect that
the material or characteristic was intended to provide. The exact
degree of deviation allowable may in some cases depend on the
specific context. Similarly, "substantially free of or the like
refers to the lack of an identified material, characteristic,
element, or agent in a composition. Particularly, elements that
are identified as being "substantially free of are either
completely absent from the composition, or are included only in
amounts that are small enough so as to have no measurable effect
on the composition.
As used herein, a plurality of items, structural elements,
compositional elements, and/or materials may be presented in a
common list for convenience. However, these lists should be
construed as though each member of the list is individually
identified as a separate and unique member. Thus, no individual
member of such list should be construed as a de facto equivalent
of any other member of the same list solely based on their
presentation in a common group without indications to the
contrary.
Concentrations, amounts, thicknesses, parameters, volumes, and
other numerical data may be expressed or presented herein in a
range format. It is to be understood that such a range format is
used merely for convenience and brevity and thus should be
interpreted flexibly to include not only the numerical values
explicitly recited as the limits of the range, but also to include
all the individual numerical values or sub-ranges encompassed
within that range as if each numerical value and sub-range is
explicitly recited. As an illustration, a numerical range of
"about 1 to about 5" should be interpreted to include not only the
explicitly recited values of about 1 to about 5, but also include
individual values and sub-ranges within the indicated range. Thus,
included in this numerical range are individual values such as 2,
3, and 4 and sub-ranges such as from 1-3, from 2-4, and from 3-5,
etc. This same principle applies to ranges reciting only one
numerical value. Furthermore, such an interpretation should apply
regardless of the breadth of the range or the characteristics
being described.
Embodiments of the Invention
An improved method for removing a target compound from a liquid
can include arranging two active surfaces so as to be separated by
a distance. The active surfaces can be placed within a flow of the
liquid and can be capable of supporting an electrical charge and
biological growth. The method can further include developing a
population of microorganisms concentrated on the active surfaces
where the population of microorganisms is configured to or capable
of acting on or transforming the target compound. The method can
further include applying a potential difference between the two
active surfaces. The microorganisms and the potential difference
can be sufficient in combination to remove the target compound
from the liquid and maintain the population of microorganisms.
In one aspect, the target compound or compounds are recovered from
the liquid. The method can be utilized to remove one or a
plurality of target compounds. The active surfaces can be the same
or different and can comprise a homogeneous material or a
heterogeneous material. In one embodiment, the two active surfaces
comprise or consist essentially of various forms of activated
carbon. The step of developing a population of microorganisms can
occur before or after the step of applying a potential difference.
The potential difference can be adjusted to optimize results,
although the potential is relatively low. As a general guideline,
the voltage can be from about 1 to about 110 V, and often from
about 1 to about 10 V. The amount of voltage that can be applied
is generally application dependent, but should range between the
minimal amount that effectuates an improvement in the removal or
recovery of the target compound, and an upper range that is less
than an amount that damages or reduces the microorganism
population. While there are water treatment applications wherein
voltage is utilized to reduce or eliminate microorganisms, the
present application of voltage is to enhance the activity of the
microorganism population in removing target compounds, and as
such, a voltage sufficient to cause damage to the microorganism
population inherently lessens the efficacy of the system.
Variations in size of reactor, particular microorganisms utilized,
and other parameters of reactor design can affect the amount of
voltage that is optimal.
The charged surfaces described herein can have a high surface area
and can include or consist essentially of activated carbon, metal
and/or functional group impregnated activated carbon, metals such
as platinum, graphite and many other metal alloys, conductive gels
and plastics in multiple configurations. Electrode configurations
can include electrode rods, plates, fabrics, pellets, granules,
etc. present in high surface area configurations. These materials
can also contain immobilized, incorporated, or bound bacteria
and/or specific microbes or microbial materials, such as proteins
and enzymes known for their ability to bind, transform, or degrade
various metals, inorganics, or organics.
The applied voltage supplies a continuous supply of electrons and
an electron sink that enables the microbial bio films or enzyme
impregnated surfaces to remove or transform contaminants more
effectively.
Additionally, a system for removing a target compound from a
liquid can include two active surfaces arranged a distance apart,
and substantially parallel to each other. An electrical source can
be operative Iy connected to each of the active surfaces in a
manner so as to provide a potential difference between the two
active surfaces. A population of microorganisms can be on each of
the two active surfaces. Additionally, the system can include a
flow path sufficient to direct a majority of the liquid to contact
each active surface and sufficient to direct a majority of the
liquid across the distance. In one aspect, the system can be
arranged in-situ. In a further aspect, the in-situ arrangement can
include a stream or other flowing body of water, wherein the
natural stream of flowing body provides the flow path. In another
example, the system can be part of a permeable reactive barrier
which treats underground wastewater along a plume, portions of a
water table, or the like.
The microorganisms can act to remediate a target compound.
Inorganic solution components, nutrients, including carbon or
energy sources (e.g. molasses, yeast extract, proteins, and the
like), may at times be a limited material for microbial cell
synthesis and growth. The principal inorganic nutrients needed by
microorganisms are N, S, P, K, Mg, Ca, Mg, K, Fe, Na, and Cl. In
one embodiment, microbes can convert nitrates or nitrites to
nitrogen gas using them as terminal electron acceptors. Excess
nitrate or nitrite present receives electrons from the system. In
another embodiment, selenates and selenites are reduced to
elemental selenium. In still another embodiment, As(V) can reduce
to As(III) and, in the presence of sulfides, As(III) can
precipitate as As2S3, as shown in Figure 1. As such, the present
invention provides electrobiochemical reactors that can create
enough reductive conditions such that these inorganics are
converted to insoluble forms or degraded to carbon dioxide and
other gases, e.g. nitrogen.
Generally, redox processes can be mediated by microorganisms,
which serve as catalysts in speeding up the reactions. These
microorganisms, including many bacteria, can use redox reactions
in their respiratory processes. In oxygen-rich environments,
oxygen can be the natural electron acceptor, but other electron
acceptors can also be used and will generally follow a distinct
order when the previous electron acceptor has been consumed or
nearly consumed based on their redox potential. As a guideline,
the order is based on the amount of energy available to the system
from the electron acceptor. For example, oxygen provides the
highest amount of energy to the system; nitrate provides a
slightly smaller amount. This is shown in Table 2.
The term redox represents a large number of chemical reactions
involving electron transfer. When a substance is oxidized, it
transfers electrons to another substance, which is then reduced.
The point at which a given reaction can take place is determined
by the electrical potential difference or redox potential (Eh) in
the water; some reactions liberate energy, other require energy
input. Redox potential and pH can be important factors controlling
inorganic speciation and mobilization. An Eh-pH diagram for
arsenic is shown in Figure 2. The diagram represents equilibrium
conditions of arsenic under various redox potentials and pH.
Arsenate [As(V)] is dominant in oxygenated water, which tends to
induce high Eh values, whereas arsenite [As(III)] is dominant in
non-oxygenated water. The conversion of As(V) to As(III) may take
a long time due to bio geo chemical processes in the environment.
This may be one of the reasons why As (V) can be found in some
anoxic waters. The sequence begins with the consumption of O2 and
thereafter N(V is used.
Manganic oxides dissolve by reduction OfMn<2+> and
thereafter NH4<+> is produced through ammonification. Thus,
in the absence of oxygen nitrates readily degenerate to nitrogen
gas when used as electron acceptors.
These processes can be followed by the reduction of hydrous ferric
oxides to Fe<2+>. Finally, SO4<2"> can be reduced to
H2S and CH4 is produced from fermentation and methano genesis.
As(V) reduction is normally expected to occur after Fe(III) -
oxide reduction, but before SO4<2"> reduction. The
thermodynamic information describes only the system at equilibrium
and generally indicates the direction in which a non- equilibrium
system will move.
Figure 3 provides an Eh-pH stability diagram for nitrate.
Generally, nitrate (N(V ) can be present in significant quantities
in waters containing free oxygen. Additionally, ammonium ion and
ammonia can be present in very reducing waters. The nitrogen cycle
can be quite complicated, and although not shown by the
equilibrium Eh-pH diagram, transformation among the various
oxidation states can occur almost entirely under the influence of
microbes. Figure 4 provides a Eh-pH diagram for selenium and
selenium- iron, respectively. As shown from Figures 3 and 4, the
present electrobiochemical reactors can advantageously use redox
potentials to remediate target compounds through reactions with
microorganisms, as previously discussed.
Reduction of other species can be accomplished using similar
reduction mechanisms. Table 1 illustrates a sample of some
exemplary reduction mechanisms which can occur under conditions of
the present invention.
Table 1
Although not intended to be limiting, these mechanisms include
respiration, denitrification, manganese reduction, ammonification,
iron reduction, sulphate reduction, and methanogenesis,
respectively. The present invention can be geared towards a
specific target chemical in a fluid, and can provide specific
design considerations for removing the target chemical, as well as
the specific equipment that can be used. However, it should be
understood that, while the embodiments discussed in the disclosure
can be specific, the applicability of the method and equipment can
be used for numerous target compounds. Indeed, the present method
and equipment described herein can equally be applied to the
targeting and removal of various target compound(s) from a fluid,
wherein microorganisms and a potential difference together affect
the compounds chemical make-up, solubility, dispersibility,
binding, and/or transformation, or otherwise enhance removal or
recovery of the target compound or compounds. For example, in one
embodiment, the present electrobiochemical reactors can treat mine
wastewater containing nitrate-N and arsenic. As previously noted,
a system for removing a target compound from a liquid can include
two active surfaces arranged a distance apart, and substantially
parallel to each other. Two non- limiting configurations of
electrobiochemical reactors of the present invention are shown in
Figures 5 and 6. Figure 5 shows a plug flow reactor 10 having
parallel electrodes plates 12 oriented parallel to the direction
of fluid flow 14. These electrodes include an electrically
conductive high surface area material 16, which supports growth of
desired microorganisms 18. Figure 6 illustrates another plug flow
configuration 20 where the electrodes 12 are oriented
perpendicular to the direction of fluid flow 22. A feed solution
inlet 23 can introduce the fluid into the reactor 20 and the
treated fluid having a reduced concentration of target compound
can be removed via effluent line 25. In this case, the fluid to be
treated flows across the electrodes in contrast to the embodiment
of Figure 5 where the fluid flows past or along the electrodes.
The active surfaces can be any material having a high surface area
that can support an electrical charge (conductive), and can
further support microorganism growth. Furthermore, in one
embodiment, the active surface can be moderately resistant to
plugging, overgrowth, and/or decay. As a very general guideline,
suitable active surface materials can include, but are in no way
limited to, plastics, zeolites, silicates, activated carbons,
starches, lignins, celluloses, plant materials, animal materials,
biomaterials, and combinations thereof. In another specific
embodiment of the present invention, the substrate can be a
mesoporous material. Activated carbon surfaces and/or platinum-
containing materials, including activated carbons, can be
effective materials for use as the primary conductive surfaces.
These primary surfaces can be in contact with other more
economical conductive high surface area materials, e.g., secondary
conductive high surface area materials, providing an extended
large surface area for contaminant transformation and/or binding.
For example, plastics, biopolymers, pumice, aluminum or iron
impregnated materials can be used as primary and/or secondary
substrate material. Biological support materials can have
functional groups, which are selected and optimized for a
particular target material to be removed. For example, and in
order of increasing basicity, inactive hydrogen, carboxyl,
lactone, phenol, carbonyl, ether, pyrone, and chromene groups are
non- limiting examples of suitable functional groups for a
biological support material in accordance with the present
invention.
An electrical source 24 can be operative Iy connected to each of
the active surfaces in a manner so as to provide a potential
difference between the two active surfaces as shown in Figures 5
and 6. A population of microorganisms can be on each of the two
active surfaces and more economical high surface-area conductive
materials.
Additionally, the system can include a flow path sufficient to
direct a majority of the liquid to contact with each primary
active surface and sufficient to direct a majority of the liquid
across the distance.
The electrobiochemical reactor (EBR) can be formed using
cylindrical vessels as part of the flow path, oriented so as to
have a diameter substantially vertical as shown in Figures 6-8. A
perforated plate can be used to suspend carbon at the bottom and
another at the top, thus forming active high surface areas. The
plate can act as a substrate for the active surfaces. Therefore,
the plate can be formed of any suitable material which may be
conductive (e.g. metal) or non-conductive (e.g. plastic). In some
cases, non- conductive plates can be useful in order to avoid
disintegration due to electrochemical erosion.
The reactor can be inoculated, wherein a population of
microorganisms is developed on the active surfaces, in a variety
of ways and at different times. At times, it may be necessary or
useful to deliberately inoculate the active surfaces. At other
times, the fluid, such as water to be treated, may have a minor
microorganism population associated with the fluid that may, with
adequate time and conditions, naturally inoculate the active
surfaces.
A number and variety of microorganisms can be utilized to
inoculate the active surfaces, either alone, or in combination.
Non-limiting examples of bacteria and algae that may be utilized
include Cyanobacteria, Diatoms, Alcaligenes sp., Escherichia sp.,
Pseudomonas sp., Desulfovibrio sp., Shewanella sp., Bacillus sp.,
Thauera sp., P. putida, P. stutzeri, P. alcaligenes, P.
pseudoalcaligenes, P. diminuta, Xanthomonas sp. including X.
(Pseudomonas) maltophilia, AIc. Denitri[beta]cans, various
Bacillus species Bacillus species that are versatile
chemoheterotrophs including B. subtilis, B. megaterium, B.
acidocaldarius, & B. cereus, Cellulomonas and Cellulomonas
Fermentans, various sulfate reducing bacteria including
Desulfobacter, Desulfobulbus, Desulfomonas, Desulfosarcina,
Desulfotomaculum, Desulfurocococcus, Desulfotomaculum, and
Desulfuromonas species, Nitrosomonas, Nitrobacter, Rhodobacter,
Thiobasillus, and Geobacter species, E. coli, and various Achaea
bacteria and combinations thereof. The premix consortium of
identified microbes were grown to high concentration and added to
the electrobiochemical reactors. Although up-flow type reactors
are shown in Figures 6-8, it should be noted that a variety of
designs could be utilized, including a down- flow, horizontal
flow, flow along any pathway, plug flow, semi-continuous, batch,
fluidized bed, etc. Furthermore, wherein a flow path is
pre-existing, active surfaces could be inserted a distance apart
to form a system for removing a contaminant or target compound.
Such is the case with an in-situ formation of an
electrobiochemical reactor in a runoff stream.
Turning now to Figure 8b, a system for removing at least one
target compound from a liquid can comprise a) a first
electrobiochemical reactor 30, comprising i) two active surfaces
arranged a distance apart and arranged substantially parallel to
each other, ii) an electrical source operatively connected to each
of the active surfaces to provide a potential difference between
the two active surfaces, and iii) a population of microorganisms
on each of the two active surfaces. The system can further
comprise a second electrobiochemical reactor 40, comprising i) two
active surfaces arranged a distance apart and arranged
substantially parallel to each other, ii) an electrical source
operatively connected to each of the active surfaces to provide a
potential difference between the two active surfaces, and iii) a
population of microorganisms on each of the two active surfaces.
Additionally, the system can comprise a tube 32 that connects the
first electrobiochemical reactor to the second electrobiochemical
reactor such that the liquid exiting the first electrobiochemical
reactor enters the second electrobiochemical reactor. As discussed
above, the system can also include a flow path sufficient to
direct a majority of the liquid to contact each active surfaces of
each electrobiochemical reactor and sufficient to direct the
majority of the liquid across the distances of each
electrobiochemical reactor.
Additionally, the electrobiochemical reactors may include any of
the aforementioned embodiments discussed throughout the present
disclosure. For example, the present system can include the
microorganisms previously discussed. Further, the
electrobiochemical reactors can be the same or different; e.g.,
have the same or different components or target the same or
different target compounds.
EXAMPLES
The following examples illustrate various embodiments of the
invention. Thus, these examples should not be considered as
limitations of the present invention, but are merely in place to
teach how to implement the present invention based upon current
experimental data. As such, a representative number of systems are
disclosed herein.
Example 1 - Removal of
Contaminants from Mining Waste Water
The present example targeted the removal of arsenic, selenium, and
nitrate from various mining waters, and further tested a
combination of microbes exposed to various potential differences.
Two identical reactors with the same features, were tested side by
side, shown in Figure 7 A and 7B. One of the reactors, 7 A, did
not have an applied potential across its electrodes 12 (Reactor
Rl) and the other, 7B, did have applied potential 24 across the
electrodes 12 (Reactor R2). The reactors were fabricated from
transparent plastic. The EBR's tested were of several different
sizes and configurations. In one configuration, both the cathode
and anode carbon beds sat on perforated diaphragms. The carbon
used was of size 2Ox 20 mesh or pelletized activated carbon. The
cathode and anode carbon beds were of different sizes to determine
the effectiveness of different configurations. Embedded in each
carbon bed was a firmly- he Id electrode system sealed to the
outside with silicon gel. The electrodes helped maintain the
reduction potential gradient through the electrobio chemical
reactor. Various tubes, running from the top plate and ending at
different locations within the EBR's tested served the purpose of
sampling and monitoring the transformation of the contaminants
arsenic, selenium, and nitrate-N. The bench-top EBR's tests were
conducted at an ambient temperature of ~25[deg.]C.
The electrobiochemical reactor setup used for arsenic removal is
shown generally in Figures 7A and 7B and includes two
electrobiochemical reactors, respectively: one without an applied
potential (Figure 7A) and a second with applied potential (Figure
7B); two sampling ports on each reactor 26; power source 24; pump
mechanism (not shown) and connecting tubes (not shown); and a
solution feed container (not shown). Figure 8A similarly shows a
single stage electrobiochemical reactor of the present invention
and Figure 8B shows a two-stage biochemical reactor without
applied potential used to test selenium removal as further
discussed in Example 2. In this manner, the present invention can
be compared in performance with and without applied voltage.
Although a variety of microbes could be used, the microbes used
were a consortium of Pseudomonas and sulfate-reducing microbes
that could effectively carry out arsenic reduction from As (V) to
As (III), selenium reduction from selenate and selenite to
elemental selenium (for Example2) as well as denitrification. The
same microbes were introduced into both the standard bio reactors
without applied potential and the electrobiochemical reactors.
Figure 9 shown differences in measured potentials across Reactor
Rl and Reactor R2. Performance variations between the EBR with
applied potential (Reactor R2) and the EBR without applied
potential (Reactor Rl) can be explained by noting that in the case
of the reactor with the applied potential (Figures 7B, 8A), the
cathode provides additional electrons for the reduction of the
nitrogen compounds (nitrates and nitrites) to nitrogen gas, as
well as the reduction of sulfate to sulfide, the reduction of
arsenate to arsenite, and selenium to elemental selenium which
otherwise would have to be provided by means of bacterial action
and additional nutrients. Nutrients are being used to establish a
reducing environment and microbial growth in the reactor without
the applied potential (Figure 7A). The EBR with applied potential
showed a greater efficiency in performance as compared to the EBR
without applied potential. With the applied potential to the EBR
with the iron electrodes, corroding of the iron electrode was
expected to increase thereby increasing the ferrihydrite
suspension in the reactor 2. This enabled additional co-removal of
As (V) with iron precipitation. Iron can also be included in the
feed solution to enhance the iron co-precipitation of arsenic. The
increase in the iron oxide surface with this suspension aided the
reduction of As (V) to As (III) at the top section of the reactor.
In testing for arsenic removal at a flow rate of 5.045 liters/day,
the EBR was able to remove all nitrogen present from the feed
solution. The arsenic concentration of 200 ppb in the feed was
also reduced to 35 ppb as opposed to a conventional bioreactor
that only reduced the feed arsenic concentration from 200 ppb to
75 ppb. Figure 10 shows arsenic removal in an extended run of a
paired bioreactor system; a conventional bioreactor and an EBR
with the EBR running at different voltages. Three volts in this
system produced the best results. Three volts reduced the time
required for arsenic reduction and the amount of nutrients
utilized in the bioreactor system. The improved performance of the
EBR is due to the applied potential which sustained a reduction
potential in the reactor. Therefore, an EBR process, utilizing two
active surfaces arranged a distance apart and having a potential
difference between them, as well as microorganism growth on each
active surface, showed a distinct advantage in efficiency of
removing arsenic from solution.
Thus, the present results show that the EBR was effective in
removal of contaminants. Further, the present results show that
the EBR can be effective even when decreasing the nutrient
requirement; thereby providing lower operational cost. It was also
demonstrated; when mine water was passed through the reactors,
that the designed system could be used to treat a wide variety of
wastewater bodies with different contaminant metals.
In light of the above, a set of such electrobiochemical reactors
having the potential difference, optionally in series with a
filtration system that would remove debris, and coupled with
ultra-violet purification unit, can serve industries and process
plants that intend to recycle their water by treating their plant
effluents. The benefits to be derived are numerous, and include:
lower cost of infrastructure implementation and operation compared
to other treatment methods; use of simple reactors to produce
hundreds to thousands times less sludge than conventional metal
precipitation processes, that permit for the decontamination or
reclamation of a number of target chemicals wherein the
electro-mechanical biochemical reactor can be applied to a number
of liquids as well as a number of target compounds.
Example 2 - Selenium Removal from
Mining Water Waste
In another exemplary embodiment, the electrobiochemical reactor,
and similar methods as presented here, was utilized to remove
selenium from water. Mining water was obtained from an undisclosed
potential mining site.
Three 1.4-liter (approximately) reactors were used for reactor
testing. All the materials used in the reactor were acrylic or
polyvinyl chloride. Two fixed bed reactors packed with pumice and
activated carbon were run in series as shown in Figure 8b. A third
reactor an EBR packed with pumice and activated carbon with
applied voltage using a DC power supply was used separately for
testing selenium reduction in mine water. All three reactors have
similar sampling ports in the head for measuring pH, oxidation-
reduction potential (ORP) and temperature at different depths. The
reactors were maintained under anaerobic conditions.
Lab scale electrobiochemical reactors were constructed to
investigate the applicability of a selected microbial consortium
to remove high concentrations of soluble selenium, as selenate and
selenite and to improve retention times in the electrobiochemical
reactors. Three reactors each having a volume of 0.001387 m were
used for testing. Acrylic columns used for the reactors had a
height of 9.5 inches and radius of 1.5 inches. The reactors were
sealed with polyvinyl chloride caps on the top and bottom having a
radius of 1.5 inches and height 2.5 inches.
Two reactors packed with pumice material (volcanic rock) and
activated carbon were connected in series and further connected to
a pump and feed water. Feed water was actual mine water containing
mainly selenium as selenate. The feed water entered the first
reactor (Reactor 1) from the bottom, passed through the packed bed
supporting microbes in the upward direction, exited out from the
top and then entered from the bottom of the second reactor
(Reactor 2). Effluent was collected from the top portion of the
second reactor. Retention times of 22 and 44 hours were tested for
the reactors connected in series. Anaerobic conditions were
maintained in all the reactors. An electrobiochemical reactor
(Reactor 3) was an electrochemical reactor packed with pumice and
activated carbon and has voltage applied across the reactor
through a set of electrodes imbedded in activated carbon layers at
the top and bottom of the reactor. Pelletized activated carbon
material was used as the electrode in the system. The reaction was
carried out with a mixture of selenate containing substrate and
consortium of microbes having the capability to catalyze the
reduction process and mine water was used for testing.
The feed water was pumped to the third reactor. All the reactors
were provided with 3 sampling ports for measurement of pH,
oxidation-reduction potential (ORP) at different locations in the
reactors. Samples for selenium analysis were collected after the
water comes out from the Reactor 1 (Reactor 1 effluent) and
effluent coming out from the Reactor 2. Sampling for pH, ORP and
temperature were performed once in three days. The third EBR
reactor was tested separately for selenium removal.
Microbial consortia were tested to determine the effects of
different nutrients on growth and selenium reduction. As was
discussed under the testing for arsenic removal (Example 1), many
different carbon amendments were used to stimulate selenate
conversion to elemental selenium in water. Bacteria require three
major nutrient components: carbon, nitrogen and phosphorous for
growth and other activities. Stoichiometric amounts of carbon can
be calculated for various inorganic removals. While these
equations give the amount of carbon needed for metal reduction,
additional amounts of carbon are required for the growth of the
microbe and to create a reducing environment. Hence different
amendments were tested in this research to see the effectiveness
of different nutrients in combination with an applied voltage to
stimulate the reduction of selenate and selenite to elemental
selenium and enhance the growth of the microbes. The design of
this testing of an electrobiochemical reactor has the following
fundamental functions: (1) immobilize the micro-organisms on an
inert media, with an optimal retention time of the mine water for
the organisms to act on the selenium and (2) construct a series of
electrobiochemical reactors connected in tandem by using pumice
(volcanic material) or other high surface area materials as the
material for the active surfaces (3) the natural porosity of
pumice forms a niche for and supports dense bacterial growth (4)
in addition, the pores might help in material transfer (5) another
possible utility with pumice is that it could occlude reduced
selenium in the reactor.
The mine water tested naturally contained selenium as selenate and
was used as the feed water and TSB was used as nutrient. Selenium
analysis was conducted on a daily basis. Different mine waters
were used over the course of the experiment which had pH varying
from 10.2 to 10.3. The pH in the mine water was adjusted to a
concentration ranging between 6.8 to 7.2 before pumping it through
the reactors. This was performed to avoid toxicity of high pH
concentration on the activity of the microbes. The pH and
Oxidation -Reduction potential (ORP) were measured on a daily
basis at different depths in the reactors and room temperature was
recorded frequently. The pH of the water was monitored on a daily
basis to ensure that it is in the range of normal physiological
conditions of the microbes and is not toxic or does not inhibit
the activity of microbes. The pH measurements observed for
different samples fluctuated between pH 6.6 and 7.4 with some
periodicity in both the reactors. This fluctuation can be
attributed to dilution effects of the feed and media addition.
Over the course of the electrobiochemical reactors testing, there
was a continuous decrease in the oxidation- reduction potential
from day 0 to day 83.
Figure 11 provides a graph of selenium removal from several mine
waters using a two stage conventional bioreactor without applied
potential and a retention time of 44 hrs and a single stage EBR
with a retention ime of 22 hr and an applied potential of 3 volts
and Tables 2 and 3 shows a list of metals added and removed from
solution in a conventional bioreactor and an EBR using a composite
metal electrode and mining wastewaters containing selenium.
Table 2
Item ([mu]g/L) Al S Fe Ni Cu Zn
Feed Waters 998.95 460. 67 32.0 6.23 3 00 19.48
BEMR-I Effluent (series 162.63 421. 73 177. 37 8.31 3 00 21.77
with 22 hour retention)
BEMR-2 Effluent (series 58.17 339. 88 255. 68 11.49 4 05 32.51
with 44 hour retention)
EBR Effluent (22 hour 23.21 176. 09 339. 41 10.41 3 04 31.65
retention)
Eluted from Pumice (gm) 200.07 0.00 175. 19 1.22 1 07 7.73
Table 3
The ORP curves showed a drastic change in the values during
initial 40 days in both reactors. Reactor 1 shows negative
oxidation reduction potential after 35 days and Reactor 2
exhibited negative value after 40 days of operation. Similar
trends observed for samples collected from different locations of
reactor indicate characteristics of water being similar throughout
the reactor. Decrease in ORP, initially due to provided nutrients,
could be indicative of metal ion accumulation - i.e., selenium.
Selenate species should exist at higher ORPs when compared to
elemental selenium. Possible explanation for this is oxygen
consumption from the surrounding environment by the bacteria and
nutrient added creating a strong reducing environment.
Transformation of selenate to elemental selenium was also observed
to be higher over the period of negative ORP. The two reactors
were fed in series by adding TSB to the feed water on a daily
basis at a concentration of 3.75 g/L of mine water for a period of
56 days. A retention time of 12 hours corresponding to a flow rate
of 0.96 ml/min was maintained in each reactor for a period of 18
days. When retention time was 12 hours, on an average 73%
reduction in selenate for both the reactors was observed. However,
increasing the retention time to 22 hours in each reactor
increased the selenium reduction to 83% average reduction in the
Reactor 1 effluent. Calculations for the performance of the
reactors were made by excluding the extreme low and high points.
Addition of TSB to the feed water resulted selenium reduction in
the feed water itself. The feed water had a significant drop in
selenate concentration on the 41<st> day. Bioreactors
reactors 1 and 2 in series on an average showed a reduction of
88.2% with a total retention time of 44 hours. The
Electrobiochemical reactor showed an average reduction of 91.5%
with a retention time of 22 hours, Figure 11. Therefore, the two
conventional bioreactors in series having a retention time of 44
hours showed an average reduction of 88.2%, and the
Electrobiochemical reactor 3, having the applied potential with
external electrodes, which is a single unit operation, showed an
average reduction of 91.5% in 22 hours. Electrobiochemical reactor
3 was far more efficient in reducing selenium with only half the
retention time of electrobiochemical reactors 1 and 2, Figure 11.
Once metal and target contaminants are immobilized using the
biochemical reactors of the present invention, these can be
isolated and treated, disposed of, or recovered using any number
of techniques.
It is to be understood that the above-described arrangements are
only illustrative of the application of the principles of the
present invention. Numerous modifications and alternative
arrangements may be devised by those skilled in the art without
departing from the spirit and scope of the present invention and
the appended claims are intended to cover such modifications and
arrangements. Thus, while the present invention has been described
above with particularity and detail in connection with what is
presently deemed to be the most practical and preferred
embodiments of the invention, it will be apparent to those of
ordinary skill in the art that numerous modifications, including,
but not limited to, variations in size, materials, shape, form,
function, and manner of operation, assembly, and use may be made
without departing from the principles and concepts set forth
herein.
