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Pacific Southwest Conference
American Society of Civil Engineers
Environmental Competition
Team members
Andrew Dunavent — Team Captain
Daniel Defever
Omar Fojaco
Sean Papenhousen
Federick Pinonogcos
Patrick Poon
Darin Sanchez
Gabbi Staehle
Willie Valle

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Introduction
Chromium(VI) and copper(II) have been compounds kept under close govern by the
Environmental Protection Agency (EPA) to ensure public safety from the harmful ions. To
ensure the regulation, the US EPA establishes maximum contaminant level goals (MCLG),
advising citizens on potential health risks from lifetime exposure to a substance, maximum
contaminant levels (MCL) are also established. MCLs are levels at which scientific experiments
have proven a correlation from the substance exposure to health problems.
Chromium(VI) in water is a known carcinogen and poses a huge problem mainly in ground
water as a result of industrial waste and chromium contained with sediment. Upon discharge and
runoff and other various methods of transport, hexavalent chromium ultimately ends up in water
sources where it has potential to be consumed. The EPA has set an MCL for total chromium
based upon an assumption that all chromium of the sample of water being tested is hexavalent
chromium to error on the side of caution, leading to an MCL of 10 ppb as of July 1, 2014 (Water
boards 2014).
Copper (II) comes from many sources in industry including fungicides/herbicides/pesticides,
which use copper sulfate as the main ingredient. The chemicals then combine with the runoff of
a wet weather event and ultimately end up in water streams. Copper(II) within the human body
serves as an irritant that causes various forms of irritation and inflammation that upon
accumulation of the ion can lead to severe nausea, and gastrointestinal distress that requires
medical attention. The EPA has set an MCL for copper to be 1.3mg/L (ATSDR 2000).
For this design project, chromium(VI) and copper(II) will be added in the forms of potassium
dichromate and copper sulfate, respectively, to the influent. The process will treat the

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contaminated water to yield an effluent that meets the MCL set by the EPA for both total
chromium and copper.
Methods
For removal of the hexavalent chromium and divalent copper, an oxidation-reduction reaction
was chosen to reduce the toxic forms of the ions to a less toxic and precipitate forming ion. To
reduce the ions, ferrous sulfate and iron(0) were chosen as the reducing agents for the reaction.
Upon being put into solution, the ferrous sulfate (FeSO4) dissociated into ferrous iron (Fe2+
) and
the sulfate ion (SO4
2-
). The ferrous iron served as the reducing agent for the chromium while the
iron(0) acted as a reducing agent for the copper. For the reaction, the pH value were not altered
because the reduction process itself was not readily affected by it, only the precipitation of the
products of the reduced ions was. The reaction was left to run for 60 minutes, which proved to
be ample time for equilibrium to be reached for both
the chromium and copper.
The hexavalent chromium required three equivalents
of ferrous iron to be reduced since it takes three
electrons to reduce hexavalent chromium to the less
toxic and much more immobile trivalent chromium.
Taking into consideration the given time domains
and necessary reaction rates, the amount of ferrous
iron used was calculated using a 10:1 mass ratio of
ferrous iron the chromium (VI) (Figure 1). The excess of iron (II) aided the reaction in speed,
allowing for equilibrium to be reached in a shorter amount of time in addition to ensuring that as
Figure 1. Mechanism of Chromium (VI) Reaction

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much chromium as possible was reduced to the trivalent state. Upon reduction, the trivalent
chromium would either remain in solution in its ionic state, or form Cr(OH)3 and precipitate out
of the solution. Regardless of the fate of the trivalent chromium, the hexavalent chromium had
been removed and reduced to a trivalent state that is much less toxic and easier to be treated.
According to the calibration curve used based upon absorbance from the lab experiments, a
chromium removal of 96.4% was yield by preparing a concentration of potassium dichromate
solution.
The copper(II) was reduced
using the iron(0) which
became a solid present in
the solution. The sulfate ion had a much higher affinity for the iron metal than the copper metal,
which allowed copper to be reduced to copper (0) while the iron oxidized to iron (II). The use of
the solid iron (0) was ideal because the copper (0) would precipitate out on the surface of the iron,
allowing for removal from solution completely.
An advantage of the formation of the ferrous sulfate in the reaction is the ability to speed up and
increase the yield for the reduction reaction of the ferrous sulfate and chromium (VI) that will be
occurring at the same time to help shift the equilibrium. From the experiments, the iron dosing
based upon excess and the use of 6 grams of iron powder suspended in the solution which at a
pH of 6.8, had an 82% yield for removal of the copper (II).
The reason for choosing ferrous sulfate for the reduction of the chromium came from the
consideration of multiple factors. The biggest consideration was the time constraints. In industry,
elemental iron is used in groundwater applications when the remediation process is extended
Figure 2. Mechanism of Cupper (II) Reaction

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over a long period of time, but given the two-hour time frame and research of reaction rates for
the reduction of chromium using elemental copper, it was concluded that the reaction must occur
at a faster rate. The solution to the problem was to select ferrous sulfate as the reducing agent in
excess because it achieved reduction yields greater than elemental iron at a much faster rate,
allowing for equilibrium to be reached before the end of the two-hour period. On the other hand,
elemental iron was chosen for the copper(II) because it serves as not only a reducing agent for
the copper, but also a great sink for the copper as it is removed from the solution due to its
formation of solids on the surface of the solid iron. Both reactions also serve to be ideal because
they do not require manipulation of the pH of the solution or temperature, allowing for minimal
manipulation and maintenance of the reaction.
Design
The basis of the design is to use a
batch reactor to house and perform
the reduction oxidation reaction of
ferrous sulfate and elemental iron
with the chromium (VI) and copper
(II) ions. Within the batch reactor, a
stirring mechanism will be placed
to stir the reaction to maximize mixing and contact times. Upon completion of the reaction, a
timed valve at the bottom of the reactor will open up, letting the treated effluent water to flow
through a pipe containing activated carbon, which will act as a filter to remove and precipitates
that formed during the reaction. At the end of the effluent pipe a basin is placed which will
collect the final treated water.
Figure 3. Schematic Diagram of the Design

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For the batch reactor, a five-gallon bucket is used with an opening in the bottom to allow the
effluent to leave once the reaction has reached completion. The chemicals will be placed in
solution and placed in the reactor prior to addition of the contaminated water. A plastic bucket
was picked as the ideal batch reactor because of the inert qualities of the plastic, meaning that it
will not react or interfere with the reaction occurring inside in addition to it proving to be one of
the cheapest alternatives.
The stirring mechanism of the batch reactor consists of a salvaged old car seat motor with a paint
stirring extension placed on the end. The mechanical stirring of the solution aids in increasing the
reaction rate in addition to ensuring that all of the chemical constituents contact each other to
give the highest yield. In picking the mechanism for stirring, an electrical motor that operates at a
high torque and low rpm would be ideal for stirring the solution. The low rpm and high torque
nature of the motor allows for complete mixing of the water with a large blade with minimal
cavitations and centrifugal force placed on the mechanism that could lead to failure in the
assembly. Since the motor roots from an automobile, a 12-volt transformer is used to regulate the
voltage from a standard outlet to the 12 volts necessary for the motor.
Upon completion of the reaction (60 minutes), an electrical timer will trigger the valve at the
bottom of the batch reactor to open up, allowing the reacted water to flow through 3/4” PVC
piping, with a 6 inch section of the piping packed with pelletized activated carbon. The activated
carbon in the pipe serves as a filter to remove the precipitates that form during the reaction by
adsorption.

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Economics
Since the goal of this project is to minimize the cost of the project, some materials were
purchased from noncommercial hardware stores and testing chemicals were provided from
companies. Few of the materials and tools used were recycled and considered as regular common
household tools. The whole project was estimated to have cost about $57.71. The cost
breakdown is as follows:
Completely Mixed Batch Reactor
Big Button timer .................................................................................................................................................$ 5.27
Bucket with spigot (recycled) ...........................................................................................................................$ 0.00
3.5 gal bucket ...................................................................................................................................................... $ 3.78
Electric in line valve ..........................................................................................................................................$ 7.00
Gaskets ................................................................................................................................................................ $3.00
Helix paint mixer …………………………………………………………………………………..$ 4.98
Replacement Transformer ………………………………………………………………………...$14.96
SS Clamp 3/4” (3) …………………………………………………………………..…………….. $ 5.08
Turkeyfryer stand (recycled) …………………………………………….……………………........$ 0.00
Vinyl Tube ………………………………………………………………….…………………..…$6.00
Tape: Electric, Teflon (recycled) ……………………………………….……………………….......$ 0.00
Seal tape .............................................................................................................................................. $ 2.97
3/4" x 20" Riser ………………………………….…………………………………………. $2.89
3/4" PVC Coupling ………………………………………………………………………… $0.44
3/4" MPT x 1/2” FPT Elbow ……………………………………………………………….. $0.41
3/4" PVC Coupling FPT/XFPT ……………………….......…………………………. $0.93
Total Project Cost: $57.71

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Electricity
The system requires 3 Amps and 120 Volts which results in 360 Watts. With Arizona having an
estimated commercial electric rate of 9.33 cents per kilowatt-hour, the system will cost about
$0.10 cost of power when it runs for 2 hours (EIA 2015).
Electricity Cost: $ 0.10
Reaction
Taking into consideration that the maximum amount of concentrations of each compounds might
be given, the experiments showed a removal of 20.5mg of copper (II) based upon a concentration
of 25 mg/l and 42 mg of chromium (VI) based upon 4 mg/l. The chemical cost for removing
copper(II) was $0.32, while the cost for chromium(VI) was $1.04.
Reaction Cost: $1.36
When it runs at the conference, the whole system will approximately cost about $59.17, with a
removal of 20.5 mg of copper(II) and 42.0 mg of chromium(VI).
Moving Forward
As mentioned above, water can be contaminated with hexavalent chromium both from natural
processes such as mineral erosion or manmade processes such as mining and manufacturing.
Chromium(VI) is highly toxic and in addition to being classified as a carcinogen, symptoms of
ingestion usually include: occupational asthma; kidney and liver damage; and pulmonary
congestion and edema. One of the largest sources of chromium(VI) contamination stems from
the production of stainless steel, in which an alloy known as ferrochromium (FeCr) is used. This
alloy is manufactured from chromite ore, which is most prevalently found in South Africa. In
fact, South Africa held nearly 75% of all known viable chromite ore deposits until recently when
China exponentially increased its own stainless steel production. The problem associated with

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stainless steel production in these areas is that a large portion of FeCr smelters are built over
subterranean water tables. Because of this, the Cr(VI) found in their waste has been leeching into
the groundwater and poisoning nearby communities that use well-water as their primary source
of fresh water.
Many of these communities are too far removed from cities to receive treated freshwater via
pipeline and some do not even have access to electricity. Therefore, conventional methods such
as chemical precipitation, reverse osmosis, or electrodialysis would not be viable options. These
methods, while effective in some areas, require trained staff to operate and have generally high
operational and waste removal costs. Communities without access to such methods would
benefit the most from cheap water filtration systems such as the ferrous sulfate batch reactor
discussed in this article. Although the reactor used in this instance uses an electrical motor to stir
the water in the tank, it could easily be modified to use a magnetic or hand operated stirrer,
which would be better suited for environments without access to electricity. In addition, the
components of the reactor could be redesigned to a variety of specifications and assembled on
site without the use of powered tools. Given its versatility and cheap operational costs, this
system could be deployed in a variety of rural communities and provide fresh water to the people
that need it most.

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References
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"Chromium in Drinking Water." Chromium in Drinking Water. US Environmental Protection
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<http://water.epa.gov/drink/info/chromium/>.
Cone, Marla. "Chromium in Drinking Water Causes Cancer." Scientific American Global RSS.
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