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.
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