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Meeting Nevada DEP-BMRR Profile II

Parameters with Electrocoagulation-

Based Treatment Solutions

B. DENNEY EAMES

Water Tectonics, Inc.

Everett, Washington

BRYAN NIELSEN

Water Tectonics, Inc.

Everett, Washington

CHARLES LANDIS

Halliburton, Inc.

Houston, Texas

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KEYWORDS: Electrocoagulation, water treatment, mining, coagulation, wastewater, arsenic,

antimony, colloids, Nevada Profile II parameters.

ABSTRACT

Although the basic concepts of electrocoagulation (EC) have been known for nearly 100 years,

it was not until the past few years that the technology became commercially viable for large

scale, high flow rate applications. EC now provides an innovative and cost-effective approach to

the treatment of water impacted with colloidal solids, emulsified oils, heavy metals, and other

undesirable constituents. EC has been effectively used to treat mine wastewater from various

mine sites to meet the NDEP/BMRR Profile II parameters, specifically meeting the arsenic and

antimony treatment target levels.

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EXECUTIVE SUMMARY

Although the basic concepts of

electrocoagulation (EC) have been known

for nearly 100 years, it was not until the past

few years that the technology became

commercially viable for large scale, high

flow rate applications. Through innovations

in electric power management, electrode

configuration and geometry, in-line real-time

sensor monitoring and integrated control,

and the ability to efficiently treat large water

flows, EC now provides an innovative and

cost-effective approach to the treatment of

water impacted with colloidal solids,

emulsified oils, heavy metals, and other

undesirable constituents. As a work horse

technology for the removal of total

suspended solids and heavy metals, EC is

an ideal treatment option for the mining

industry and has significant operational

advantages when compared to traditional

coagulation technology.

EC has been effectively used to treat mine

wastewater from various mine sites in the

United States, Australia, and Canada.

Pollutants effectively removed from the

wastewater streams by EC included:

arsenic, antimony, aluminum, iron,

manganese, cadmium, copper, chrome,

nickel, zinc, silica, total suspended solids

(TSS), fats, oils, and grease (FOG), total

petroleum hydrocarbons (TPH), turbidity,

and other contaminants. Ranges of

parameter concentration removal as a result

of EC processing were: up to 95-99.9%

(method detection limit based) for metals

(As, Sb, Cd, Cu, Cr, Ni, Zn, Fe, Al); 55-98%

for manganese; 71-98% for silica; up to

99% of FOG and TPH, up to 98% of TSS;

and 97-99.9% of turbidity.

The focus of this presentation will review the

treatment of impacted mine waters and the

treatment processes used to meet the

Nevada Division of Environmental

Protection (NDEP) and the Nevada Bureau

of Mining Regulation and Reclamation

(BMRR) Profile II parameter targets.

Results of water treated using EC and

electro-oxidation (EOX) will be presented.

PROJECT BACKGROUND

The State of Nevada through the NDEP and

BMRR has established water quality

standards as guidance for permitting of

various activities in the mining industry.

These standards are known as their Profile

II standards, and are accompanied by their

predecessor roster of standards called

Profile I. These parameters cover a broad

range of analytes of concern in waters at

concentrations that require a high level of

analytical rigor to analyze and an even

higher level of reaction optimization to

address. In the state of Nevada, these

parameters consist of three categories;

Profile I, Profile II, and Profile III; and are

used as reference standards for water

permitting projects, including; mine

permitting, mine reclamation, and permitting

related to the treatment and discharge of

water and stormwater to a public waterway

(Reid, Michele R. 2013).

The focus of this paper was to evaluate the

efficacy of using EC to treat mine impacted

water from multiple mine sites with the

target goal of meeting the NEDP/BMRR

Profile II specification. The Profile II

specification is defined in Table 1. Only the

analytes with reference values are listed.

The Profile II specification provided by the

NDEP includes other values that are

monitored but do not have reference values

(NDEP Profile II, July 1, 2014).

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Table 1. Profile II Reference Values

Analytical

Parameter

Description

Units Limit

Value

Aluminum mg/L 0.2

Antimony mg/L 0.006

Arsenic mg/L 0.010

Barium mg/L 2.0

Beryllium mg/L 0.0004

Cadmium mg/L 0.005

Chloride mg/L 400

Chromium mg/L 0.1

Copper mg/L 1.0

Fluoride mg/L 4.0

Iron mg/L 0.6

Lead mg/L 0.015

Magnesium mg/L 150

Manganese mg/L 0.10

Mercury mg/L 0.002

Nickel mg/L 0.1

Nitrate + Nitrite

(as N)

mg/L 10

Nitrogen, Total

(as N)

mg/L 10

pH (standard units) s.u. 6.5 - 8.5

Selenium mg/L 0.05

Silver mg/L 0.1

Sulfate mg/L 500

Thallium mg/L 0.002

Total Dissolved

Solids

mg/L 1,000

WAD Cyanide mg/L 0.2

Zinc mg/L 5.0

Note: All analyses for the dissolved fraction.

Coagulation is one of the most important

physiochemical reactions used in water

treatment. The precipitation of ions (heavy

metals) and colloids (organic and inorganic)

are mostly held in solution by electrical

charges. By the addition of ions of opposite

charges these colloids can be destabilized,

and coagulation can be achieved by

chemical or electrical methods. Typically,

the coagulant is added in the form of

suitable chemical substances. Alum

[3Al2(SO4).18H2O] is a coagulant which is

widely used for water and wastewater

treatment. Ferric Chloride (FeCl3) is also

widely used. Both of these metal salts add

anions in the form of sulfate (SO42-) and

chloride (Cl-) that compete for the ionic

reactions in the water chemistry, and

increase the relative particle size of targeted

contaminants in conjunction with the

coagulant, allowing them to settle out of or

be filtered from a solution.

In addition, when metal salt coagulants are

used to coagulate contaminants, they leave

behind the anion portion of the salts. As

Profile II parameters include both sulfate

and chloride, the use of metal salts as

coagulants may be limited by these

mandated anion concentrations. In some

instances where the TDS concentration is

already close to the limit of 1,000 mg/L, the

use of any chemical coagulant is not

possible. This is because the “residue” left

behind by the chemical causes the treated

water to exceed the TDS limit for Profile II.

The mechanism of coagulation has been

the subject of continual review. It is

generally accepted that coagulation is

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driven primarily by a reduction of the net

surface charge to a point where the colloidal

particles, previously stabilized by

electrostatic repulsion, can approach close

enough for van der Waals forces to hold

them together and allow aggregation. The

reduction of the surface charge is a

consequence of the decrease of the

repulsive potential of the electrical double

layer by the presence of an electrolyte

having an opposite charge.

EC offers an alternative to the use of metal

salts or polymers and polyelectrolyte

addition for breaking stable emulsions and

suspensions. The technology causes

coagulation by introducing highly-charged

polymeric metal hydroxide species. These

species neutralize the electrostatic charges

on suspended solids and oil droplets to

facilitate agglomeration or coagulation and

resultant separation from the aqueous

phase. The treatment prompts the

precipitation of many metals and salts.

In the EC process, the coagulant is

generated in situ by electrolytic oxidation of

an appropriate anode material. In this

process, charged ionic species (metals or

other contaminants) are removed from

wastewater by allowing them to react with

an ion having an opposite charge, or with

floc of metallic hydroxides generated within

the effluent. One advantage to this

technique is that there is no by-product

anion “left behind” as unreacted analytes.

This reaction enjoys several advantages in

water treatment as mentioned by Benefield,

Judkins, and Weand:

Chemical coagulation has been used for

decades to destabilize suspensions and

to effect precipitation of soluble metals

species, as well as other inorganic

species from aqueous streams, thereby

permitting their removal through

sedimentation or filtration. Alum, lime

and/or polymers have been the

chemical coagulants used. These

processes, however, tend to generate

large volumes of sludge with high bound

water content that can be slow to filter

and difficult to dewater. These treatment

processes also tend to increase the total

dissolved solids (TDS) content of the

effluent, making it unacceptable for

reuse within industrial applications.

(1982, p. 212)

Similar findings are expressed by

Tchobanoglous and Burton:

Although the electrocoagulation

mechanism resembles chemical

coagulation in that the cationic species

are responsible for the neutralization of

surface charges, the characteristics of

the electrocoagulated flock differ

dramatically from those generated by

chemical coagulation. An

electrocoagulated flock tends to contain

less bound water, is more shear

resistant and is more readily filterable.

(1991, p. 301-303)

The EC treatment process is shown

conceptually in Figure 1. Direct current

(DC) is applied to a cathode in a water

bath/stream. As the electrons pass

between the cathode and anode, two

simultaneous reactions occur. Water (H2O)

is split at the cathode forming H2 (gas) and

OH-(aqueous) at the cathode. Metal (Me+) is

released through electrolytic oxidation at the

anode. If Iron (Fe) is used the Fe2+ will

quickly oxidize to Fe3+ dependent on the

water characteristics such as pH, oxidation-

reduction potential (ORP), dissolved oxygen

(DO), and others. The coagulation metal

(Me+) and hydroxide (OH-) are suddenly

above the saturation constant and

precipitate and coagulate. These particles

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attract and retain other contaminants in the

water through agglomeration and co-

precipitation, causing a stable floc to form.

This flocculation (“floc maturation”) process

can be encouraged by physiochemical

adjustments such as pH, temperature, and

flow rates/residency times.

Dependent on the floc characteristics of size

and density, a portion of the small amount

of hydrogen gas formed at the cathode

attaches to the floc providing lift and can

form a stable surface floc. Floc particles

with higher density settle to form a sludge

layer (dependent on the fluid hydraulic

characteristics). Figure 1 is a conceptual

diagram of these processes.

Figure 1. EC Treatment Process

Arsenic (As) and antimony (Sb) are found in

many mine wastewaters above the Profile II

limits. Arsenic is typically found in these

wastewaters as Arsenite [As(iii)]. Figure 2

is a diagram of Arsenite species

dissociation in the full pH range.

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Figure 2. Dissociation of Arsenite [As(iii)]

In the neutral pH of 6 to 9, Arsenite is

mostly H3AsO3. This form of Arsenite is

very stable and does not react well or co-

precipitate with iron or other coagulants.

Through oxidation, Arsenite can be changed

to Arsenate [As(v)]. In this same neutral pH

range, Arsenate is found as H2AsO4- and

HAsO42-. These species are much more

reactive with iron and can be co-precipitated

in an iron-hydroxide floc, as shown in Figure

3.

Figure 3. Dissociation of Arsenate [As(v)]

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By controlling the oxidation state of the

species and the pH of a solution, Arsenic

can be very effectively co-precipitated in an

iron-hydroxide floc. Since As and Sb are in

the same group, they have similar electron

outer layers and react in a similar fashion.

The Pourbaix diagrams shown in Figure 4

and Figure 5 illustrate this chemical reaction

for both arsenic and antimony. The

treatment method was designed and

optimized to specifically target As and Sb.

Figure 4. Arsenic (As) Pourbaix Diagram

Figure 5. Antimony (Sb) Pourbaix Diagram

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METHODS

Three different mine water samples were

collected. Each sample collected was

homogenized prior to sampling. Influent

samples were collected from untreated raw

water. Effluent samples were collected after

the following treatment processes were

performed.

Each sample was aerated and the ORP was

raised using an EOX solution generated

onsite. The EOX solution is a salt solution

run through an electrolytic cell to generate a

mixed oxidant mainly consisting of

hypochlorous acid. Following aeration, the

fluid was passed through a laboratory EC

cell at a current setting scalable to a

standard full-scale EC treatment system.

The samples were mixed for floc

development and allowed to settle.

Following settling, the supernate was

filtered using a polyacrylonitrile (PAN)

hollow fiber ultrafiltration membrane.

RESULTS

Mine Water Sample #1 was a mixture of

mine surface water and rain water mixed to

simulate a stormwater sample. The

untreated influent sample contained

elevated antimony and arsenic. All analysis

was conducted by a third-party laboratory.

The treated effluent sample meets the

Profile II parameter limits. The data appear

in Table 2.

Mine Water Sample #2 was collected from a

mine storage pond. The untreated influent

sample contained elevated antimony,

arsenic, and thallium. Duplicate samples of

the EC treated effluent were evaluated by

two independent laboratories. Both of the

treated effluent samples meet the Profile II

parameter limits. There was a very good

correlation in the duplicate data provided by

both labs. The data appear in Table 3.

Mine Water Sample #3 was also collected

from a man-made mine water storage pond.

The untreated influent sample contained

elevated Aluminum, Antimony, Arsenic,

Iron, Sulfate and Thallium. The sample also

had an elevated pH level. The EC treated

effluent sample meets the Profile II

parameter limits. The data appear in Table

4.

Arsenic (As) and antimony (Sb) were found

to be above the Profile II limits in all of the

mine wastewaters. These two

contaminants are very prevalent in many

mine wastewater samples. The EC

treatment method effectively removed these

contaminants without increasing the

chloride or TDS above the Profile II limits.

All other Profile II parameters above the

limit were treated to below the target in the

effluent.

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Table 2. Mine Water Sample #1

Analytical Parameter

Description

Units NV Profile II Influent Effluent

Aluminum mg/L 0.2 ND < 0.2 ND < 0.2

Antimony mg/L 0.006 0.017 ND < 0.005

Arsenic mg/L 0.010 1.5 ND < 0.003

Barium mg/L 2.0 ND < 0.05 ND < 0.05

Beryllium mg/L 0.0004 ND < 0.004 ND < 0.004

Cadmium mg/L 0.005 ND < 0.004 ND < 0.004

Chloride mg/L 400 14 170

Chromium mg/L 0.1 ND < 0.01 ND < 0.01

Copper mg/L 1.0 ND < 0.02 ND < 0.02

Fluoride mg/L 4.0 0.15 0.13

Iron mg/L 0.6 ND < 0.56 ND < 0.56

Lead mg/L 0.015 ND < 0.015 ND < 0.015

Magnesium mg/L 150 3.5 3.5

Manganese mg/L 0.10 ND < 0.011 ND < 0.011

Mercury mg/L 0.002 ND < 0.0005 ND < 0.0005

Nickel mg/L 0.1 ND < 0.05 ND < 0.05

Nitrate + Nitrite (as N) mg/L 10 0.49 0.52

Nitrogen, Total (as N) mg/L 10 1.08 0.94

pH (standard units) s.u. 6.5 - 8.5 7.45 6.57

Selenium mg/L 0.05 ND < 0.005 ND < 0.005

Silver mg/L 0.1 ND < 0.02 ND < 0.02

Sulfate mg/L 500 150 150

Thallium mg/L 0.002 ND < 0.002 ND < 0.002

Total Dissolved Solids mg/L 1,000 250 400

WAD Cyanide mg/L 0.2 ND < 0.005 ND < 0.005

Zinc mg/L 5.0 ND < 0.05 ND < 0.05

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Table 3. Mine Water Sample #2

Analytical Parameter

Description

Units NV Profile II Influent Effluent

Lab #1

Effluent

Lab #2

Aluminum mg/L 0.2 0.09 ND < 0.056 0.0126

Antimony mg/L 0.006 0.03 0.0042 0.0053

Arsenic mg/L 0.010 0.28 ND <0.003 0.0021

Barium mg/L 2.0 0.0959 0.0810 0.0789

Beryllium mg/L 0.0004 ND < 0.0014 ND < 0.0014 ND < 0.0014

Cadmium mg/L 0.005 ND <0.0002 ND <0.0002 ND <0.0002

Chloride mg/L 400 69.9 190 204.4

Chromium mg/L 0.1 ND <0.0006 ND <0.0006 ND <0.0006

Copper mg/L 1.0 0.0034 0.078 0.0069

Fluoride mg/L 4.0 0.5 ND <0.02 ND <0.02

Iron mg/L 0.6 0.27 0.20 0.25

Lead mg/L 0.015 0.052 0.0056 0.0047

Magnesium mg/L 150 30.1 27.4 30.3

Manganese mg/L 0.10 0.047 0.076 0.079

Mercury mg/L 0.002 ND < 0.0001 ND < 0.0001 ND < 0.0001

Nickel mg/L 0.1 0.0066 0.0028 0.0208

Nitrate + Nitrite (as N) mg/L 10 0.05 ND <0.02 ND <0.02

Nitrogen, Total (as N) mg/L 10 0.69 0.72 1.37

pH (standard units) s.u. 6.5 - 8.5 8.22 6.96 7.29

Selenium mg/L 0.05 0.0046 0.0106 0.0086

Silver mg/L 0.1 ND <0.0002 ND <0.0002 ND <0.0002

Sulfate mg/L 500 61 59.6 55.7

Thallium mg/L 0.002 0.0025 ND <0.002 ND <0.002

Total Dissolved

Solids

mg/L 1,000 403 590 585

WAD Cyanide mg/L 0.2 ND < 0.005 ND < 0.005 ND < 0.005

Zinc mg/L 5.0 0.0556 0.0569 0.0571

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Table 4. Mine Water Sample #3

Analytical Parameter

Description

Units NV Profile II Influent Effluent

Aluminum mg/L 0.2 11 ND (< 0.11)

Antimony mg/L 0.006 0.059 0.0058

Arsenic mg/L 0.010 6.3 ND (<0.0033)

Barium mg/L 2.0 0.23 0.1100

Beryllium mg/L 0.0004 ND (< 0.002) ND (< 0.002)

Cadmium mg/L 0.005 ND (< 0.004) ND (< 0.004)

Chloride mg/L 400 47 53

Chromium mg/L 0.1 0.017 ND (< 0.010)

Copper mg/L 1.0 ND (< 0.020) ND (< 0.020)

Fluoride mg/L 4.0 0.55 NS

Iron mg/L 0.6 7.4 ND (< 0.050)

Lead mg/L 0.015 0.0055 ND (< 0.001)

Magnesium mg/L 150 17 12

Manganese mg/L 0.10 0.13 ND (< 0.010)

Mercury mg/L 0.002 0.0075 ND (< 0.0005)

Nickel mg/L 0.1 0.05 ND (< 0.050)

Nitrate + Nitrite (as N) mg/L 10 <0.02 <0.02

Nitrogen, Total (as N) mg/L 10 0.246 NS

pH (standard units) s.u. 6.5 - 8.5 9.29 6.64

Selenium mg/L 0.05 ND (< 0.025) ND (< 0.025)

Silver mg/L 0.1 ND (< 0.020) ND (< 0.020)

Sulfate mg/L 500 590 470

Thallium mg/L 0.002 0.0087 ND (<0.0019)

Total Dissolved Solids mg/L 1,000 810 790

WAD Cyanide mg/L 0.2 ND (<0.005) ND (<0.005)

Zinc mg/L 5.0 0.055 ND (<0.050)

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CONCLUSIONS

The increasingly challenging treatment

targets in mine wastewater treatment

require a constant effort to evaluate new

treatment technologies. The trend to

address relatively high concentrations of

more and more metals, as well as other

contaminants, requires the water treatment

process to complete multiple chemical

reactions simultaneously and more

efficiently than in the past. Treatment

reactions that require trade-offs allowing

one contaminant to be addressed, while

exacerbating another, are no longer

sustainable.

The use of EC technology is an opportunity

to meet this new dimension of compliance.

The NDEP-BMMR Profile II standard is an

excellent example of the breadth of the

treatment obligations now required to

provide flexible reuse of impaired mine

waters. Electrocoagulation is shown to

simultaneously meet the stringent metals

and anion targets by simply targeting

specific anodic materials in optimized water

conditions to meet the Profile II parameters

without trade-offs in other aspects of

compliance.

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References:

Benefield, L. D., Judkins, J. F., & Weand, B. L. (1982). Process Chemistry for Water and

Wastewater Treatment. Englewood Cliffs, NJ: Prentice-Hall.

Kumar, P. R., Chaudhari, S., Khilar, K.C., & Mahajan, S.P. (2004). Removal of Arsenic from

Water by Electrocoagulation. Chemosphere, 55(9), 1245-1252.

Lakshmanan, D., Clifford, D. A., Samanta, G. (2010). Comparative Study of Arsenic Removal by

Iron Using Electrocoagulation and Chemical Coagulation. Water Research, 44, 5641-5652.

NDEP Profile II. (2014, July 1). [PDF]. Retrieved from

http://ndep.nv.gov/bmrr/file/ndep_profile_2.pdf

Reid, M. (2013). Stormwater Discharges Associated with Industrial Activity from Metals Mining

Activities – Sector G Permit No. NVR300000 Fact Sheet. [PDF]. Retrieved from

http://ndep.nv.gov/bwpc/docs/mining_fact_sheet_web_site.pdf

Tchobanoglous, G., & Burton, F. (1991). Wastewater Engineering: Treatment, Disposal, and

Reuse. New York, NY: McGraw-Hill.