Arsenic Removal Tech Comparison.pdf

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ARSENIC REMOVAL FROM INDUSTRIAL WASTEWATER

DISCHARGES AND RESIDUALS MANAGEMENT ISSUES

Ganesh Ghurye

CDM, Texas

Jean-Claude YounanSCANA, South Carolina

Joseph ChwirkaAlbuquerque-Bernalillo County Water Utility Authority, New Mexico

ABSTRACT

Exposure to arsenic, a naturally occurring trace contaminant in drinking water, has recentlyattracted greater regulatory attention in industrial wastewater discharges as well. Thedischarge of arsenic to a receiving stream is subject to compliance with the National

Pollution Discharge Elimination System (NPDES) program. These discharge limitsestablished in the NPDES permit for specific contaminants are determined by the water

quality criteria established for the receiving water, ambient levels of the specific

contaminants, the established low-flow condition of the receiving water, and the design flowof the proposed discharge from the arsenic treatment process. Depending on these factors, the

discharge limit for arsenic in industrial wastewaters can be quite stringent. For example,

some power plants in the United States have recently been limited to arsenic discharges as

low as 4 g/L, which is lower than the 10 g/L arsenic standard for drinking water. This

paper presents best available technologies for the removal of arsenic from industrialwastewaters, and also discusses wastewater quality drivers affecting technology selection and

treatment residuals management issues.

JOURNAL OF EUEC, Volume 1, 2007

2007 Energy and Environment Conference


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Journal of EUEC Arsenic Removal

2007 EUEC 2

BACKGROUND

Prior to discussing arsenic removal technologies, a brief description of issues relating to

arsenic speciation and arsenic removal efficiencies is provided in this section.

Arsenic Speciation

Arsenic can occur in both organic and inorganic forms. In most arsenic-contaminatedwastewaters, the inorganic forms predominate. Inorganic arsenic exists as either As III

(arsenious acid with an arsenic oxidation state of +3 H3AsO3) or As V (arsenic acid with an

oxidation state of +5 H3AsO4). Arsenious acid is a weak monoprotic acid (pKa = 9.22) and

exists predominantly as an uncharged molecule below pH 8.2. Arsenic acid, on the otherhand, is a triprotic acid (pKas = 2.22, 6.98 and 11.4) and exists predominantly as a divalent

anion above pH 7.0.

The normally uncharged arsenic species, As III, is poorly removed by most arsenicremoval technologies. Therefore, for waters containing As III, pre-oxidation prior to

treatment is required for efficient arsenic removal. As III can be easily oxidized usingchlorine, potassium permanganate, ozone, or MnO2-based solid oxidizing media (Ghurye andClifford, 2001, 2004). If pre-oxidation becomes necessary, the discharge limits for oxidizing

chemicals such as chlorine will have to be considered during evaluation of arsenic removal

processes.

Arsenic Removal Efficiency

Unlike the arsenic standard for drinking water, which is set at 10 g/L (U.S. EnvironmentalProtection Agency [EPA], 2001), arsenic limits for industrial wastewater discharges can vary

significantly, and may even be set below the drinking water standard. Typically, NPDES

discharge limits specify a daily and monthly maximum. Therefore, the required arsenicremoval efficiency must first be determined, and subsequently the ability of arsenic treatment

technologies to meet low or very low arsenic discharge limits must be evaluated. It should be

noted that adsorption processes that might otherwise be feasible to meet the drinking waterstandard of 10 g/L may well fail to consistently meet a much lower discharge limit of say 2

to 5 g/L. Sufficient scientific information is available for most technologies to perform adesktop analysis and select one or two of the most promising technologies for further

evaluation.

When performing desktop evaluations of treatment technologies, greater importanceshould be given to technologies that have been studied by third parties. Vendor literature,

though informative, is often cited with incomplete information to allow proper scientific

comparisons with other media/processes.

FEASIBLE TECHNOLOGIES FOR TREATMENT OF ARSENIC-CONTAMINATED

WATERS

A number of technologies are available for arsenic removal from arsenic-contaminatedwaters, and technologies appropriate for a particular application may be identified based on


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2007 EUEC 3

knowledge of water chemistry, the strengths/drawbacks of these technologies, and residuals

management issues. Current state-of-the-art technologies available for arsenic removal are asfollows:

Ion Exchange (IX) (with or without spent brine reuse)

Hybrid Iron-impregnated IX (Fe-IX) Activated Alumina (AAl) & Iron-doped Activated Alumina (Fe-AAl) Ferric Coagulation-Direct Microfiltration (C/MF) Ferric Coagulation-Pressure Filtration (C-PF) Granular Iron Media (GIM) Other Adsorbent Media (Titanium- or Zirconium-oxidebased media).

Technology Selection

Given the wide array of technologies available, technology selection can often be a

challenging aspect of arsenic treatment. A number of technologies cited above, such as the

IX process with spent brine reuse or the ferric coagulation-direct microfiltration process, arenon-proprietary and thus can be freely used/adapted by the end user. Other technologies

require the use of proprietary media, and their advantages/drawbacks may not have beenfully explored. The key steps to selecting the best technology include:

(1) Wastewater Quality understanding the chemistry of arsenic-contaminated waters;(2) Technology Selection understanding the impact of wastewater chemistry on

treatment processes and the ability of selected technology to meet treatment goals;

(3) Desktop, Bench and Pilot Studies determining/verifying process efficiency andobtaining scale-up data;

(4) Residuals evaluating residuals treatment and handling issues; and(5) Cost performing detailed cost evaluations.

The ensuing sections discuss the water quality drivers that affect process selection,

the advantages, and limitations of some proven technologies and residuals managementissues. Since treatment costs are highly site-specific, they are not discussed in this paper.

DISCUSSION

Arsenic removal technologies can be broadly classified as purely adsorption-based

technologies (for example, ion exchange or granular iron media adsorption), purely

membrane-based technologies such as nanofiltration (NF) or reverse osmosis (RO), ortechnologies that use a combination of adsorption followed by filtration/microfiltration (seeFigure 1). Purely membrane-based technologies are generally cost prohibitive for arsenic

removal applications, and, moreover, generate large quantities of arsenic-rich brines that

require treatment/disposal. Therefore, only adsorption processes, and adsorption followed byfiltration (membrane or media filtration), are discussed below.


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Figure 1. Arsenic Removal Processes

ADSORPTION-BASED TECHNOLOGIES

Ion Exchange (IX)

A schematic of an ion exchange with spent brine reuse process is shown in Figure 2.

Developed at the University of Houston (Ghurye, Clifford, and Tripp, 1999; Clifford,Ghurye, and Tripp, 2003), the IX-brine reuse process improved the conventional IX process,

which wasted spent brine following regeneration, by reusing or recycling spent brine

multiple times. The IX-brine reuse process resulted in substantial salt savings, and alsominimized the volume of brine residuals.

Arsenic, which is present as an anion, is exchanged for chloride ions on the ionexchange resin. Rapid kinetics is a significant advantage of IX-based processes and empty

bed contact times (EBCTs), defined as the ratio of the volume of resin including voids to the

flow rate) as short as 1.5 min may be used without compromising arsenic removalperformance. Just before arsenic breakthrough (which may be operationally defined as

4 g/L), the column run is stopped and the resin is regenerated (converted back to the

chloride form) by simply passing a salt (NaCl) solution through the resin. Arsenic, along withother anions such as nitrate and sulfate are removed from the resin during regeneration, withthe waste stream being the spent brine that is typically wasted. If make-up salt is added to

this spent brine to bring its chloride content back to a preset concentration, the spent brine

can be reused several times before it must be finally treated and disposed. Even with multiplereuses or recycles, arsenic concentration in the treated water can be reduced to less than

1 g/L (Clifford, Ghurye, and Tripp, 2003). For ion exchange, arsenic breakthrough is very

sharp (typically occurs in less than 100 bed volumes (BV). Since arsenic breakthroughs are

Arsenic removal processes can be broadly classified into

Raw Water

Treated Water

Raw Water

Treated WaterReject Stream

Adsorption

IX

GIM

AAlCMF

Membrane

NF

RO Mem

brane

Membr

ane

Adsorption Processes Membrane Processes

M

E

D

I

A

Arsenic removal processes can be broadly classified into

Raw Water

Treated Water

Raw Water

Treated WaterReject Stream

Adsorption

IX

GIM

AAlCMF

Membrane

NF

RO Mem

brane

Membr

ane

Adsorption Processes Membrane Processes

M

E

D

I

A


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relatively sharp, virtually all of the arsenic adsorption capacity of IX resins may be utilized

prior to terminating a run.

Figure 2. Schematic of Ion Exchange with Spent Brine Reuse Process

Water Quality Drivers for the IX Process

Of the major anions found in arsenic-contaminated waters, only sulfate has any significant

adverse impact on IX capacity for arsenic. This is because sulfate has a greater affinity for aresin than arsenic, and it eventually drives accumulated arsenic off the resin. Unlike granular

iron adsorbent media, IX is unaffected by pH (in the range of 5-9), silica, phosphate, or

vanadate.

Advantages of IX

Simple, easily automated process, fast kinetics (EBCT 1.5 min) Requires inexpensive salt for regeneration

Cost effective for waters containing high silica/phosphate and low sulfate High ( 99%) arsenic removal efficiency, and the IX process can be tailored to provide

effluent arsenic concentration below detection limits (< 2 g/L) at all times Proven track record in full-scale treatment plants In many cases, sufficient data exist to provide accurate predictions of cost and

performance without bench testing

Disadvantages of IX

Raw Water NaCl to Regenerate

Arsenic-free (< 2 ppb)

Treated Water

Backwash

Water

Cl2 to

Oxidize

As III

As III or As V

pH 6.5 9.0

Bicarbonate

Nitrate

Sulfate

Silicate

Phosphate

Fluoride

Spent

Backwash

Water

Chloride-form

SBA

Resin

0.3-0.6 mm

1 m deep

1.5 min EBCT

Chloride-form

SBA

Resin

0.3-0.6 mm

1 m deep

1.5 min EBCT

Spent Brine

Recycle

Recycle

Spent Brine:

Arsenic, NaCl,

Na2SO4, NaHCO3

Recycle

Spent Brine:

Arsenic, NaCl,

Na2SO4, NaHCO3

Make-up

NaCl

FeCl3 to

co-precipitate

Fe(OH)3.As

pH = 5.5

Fe/As=20 (m/m)

99.5% As Rem.

Fe(OH)3.As

Sludge

Raw Water NaCl to Regenerate

Arsenic-free (< 2 ppb)

Treated Water

Backwash

Water

Cl2 to

Oxidize

As III

As III or As V

pH 6.5 9.0

Bicarbonate

Nitrate

Sulfate

Silicate

Phosphate

Fluoride

Spent

Backwash

Water

Chloride-form

SBA

Resin

0.3-0.6 mm

1 m deep

1.5 min EBCT

Chloride-form

SBA

Resin

0.3-0.6 mm

1 m deep

1.5 min EBCT

Spent Brine

Recycle

Recycle

Spent Brine:

Arsenic, NaCl,

Na2SO4, NaHCO3

Recycle

Spent Brine:

Arsenic, NaCl,

Na2SO4, NaHCO3

Make-up

NaCl

FeCl3 to

co-precipitate

Fe(OH)3.As

pH = 5.5

Fe/As=20 (m/m)

99.5% As Rem.

Fe(OH)3.As

Sludge


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2007 EUEC 6

Requires prefiltration for iron, manganese, and TOC (total organic carbon), which canfoul IX resins

Adversely affected by sulfate, arsenic concentration in the effluent can peak above itsinfluent value

Requires a large amount of salt (up to 1,660 lbs NaCl/million gallons [MG] treatedeffluent)

Produces a large volume of waste brine (5,000 gallons/MG treated effluent) Waste brine can contain very high arsenic concentrations (up to 20.000 g/L) and will

require treatment prior to disposal

Residuals

High arsenic spent brines will likely trigger classification of the treatment facility as alarge quantity hazardous waste generator (LQHWG) under the Resource Conservation

and Recovery Act (RCRA).

Fe-Doped Ion Exchange (Fe-IX)

Recently developed hybrid iron-resin ion exchangers reportedly have many advantages overconventional strong base anion exchange resins. In addition to functioning as ion exchangers,

these hybrid resins also have ferric (hydr)oxide functional groups, which have a high

capacity for arsenic adsorption. These new hybrid resins also require regeneration with analkaline brine solution. Arsenic concentration in waste brine from Fe-IX resins is expected to

be several times greater than with conventional IX resins. Therefore, these waste brines willalso be classified as hazardous wastes.

Based on the chemistry of the Fe-IX process, arsenic breakthroughs will be gradual

and not sharp as in the IX process. The Fe-IX process will produce effluent arsenic levels

below detection during the initial part of its run, and arsenic concentration will then gradually

increase over a period of several hundred bed volumes (one bed volume [BV] is defined asthe volume of the media bed including voids). Thus, an Fe-IX run may be terminated to

provide an average arsenic effluent concentration of < 2 g/L at all times, but the drawbackto this approach is that a bulk of the arsenic adsorption capacity will be left unutilized prior

to regeneration, resulting in poor capacity utilization of the Fe-IX resin and concomitantly,

resulting in a much greater requirement of salt and base for regeneration per unit throughputof arsenic contaminated water. For example, it may take approximately 20,000 BV for the

effluent arsenic concentration to increase from 1 g/L to 5 g/L and an additional 25,000 BV

for the effluent arsenic concentration to increase to 10 g/L (Boodoo, 2005).

Water Quality Drivers

Since Fe-IX resins contain both a resin and ferric (hydr)oxide functionality, they should beaffected by the presence of sulfate, silicate, phosphate, and vanadium. However, vendorliterature has indicated that Fe-IX resins are unaffected by sulfate, which is the limiting

factor in a conventional IX processes. The non-effect of sulfate is plausible, given that an

Fe-IX resin may be expected to continue arsenic removal long after the resin sites havereached their arsenic and sulfate capacity. Often contrary to vendor claims, Fe-IX media are

affected by the presence of other co-occurring species such as silicate, phosphate, and

vanadium all of which reduce arsenic removal capacity. Further, species such as silica may


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not be readily removed during regeneration leading to a substantial (up to 30%) loss of

capacity on subsequent reuse.

Advantages of Fe-IX

Longer run lengths (throughput) than conventional IX media as arsenic capacity is notaffected by sulfate concentration

High arsenic removal efficiency; arsenic removal to less than 4 g/L possible, but maylead to inefficient use of media capacity

Media more robust than friable granular iron media or activated alumina Some vendors offer off-site regeneration facilities

Disadvantages of Fe-IX

Requires prefiltration for iron, manganese, and TOC which can foul IX resins Arsenic capacity is reduced by the presence of silicate, phosphate and vanadate Bench and/or pilot testing will be required to predict performance and costs Requires a large amount of salt and sodium hydroxide for regeneration Vendor claims of multiple regeneration with minimal loss of capacity remain unproven If not regenerated off site, the large volume of alkaline waste brine containing very high

concentrations of arsenic will require treatment prior to disposal

Residuals

The extremely high arsenic waste brines will trigger classification as a large quantityhazardous waste generator (LQHWG) under the Resource Conservation and Recovery

Act.

Activated Alumina (AAl) & Fe-doped Activated Alumina (Fe-AAl)

The use of activated alumina for arsenic removal has been known since the early 1980s, andis a proven technology for arsenic removal (Clifford, 1999; Wang, Chen, and Fields, 2000).More recently, activated aluminas have been doped with iron to increase arsenic removal

capacity (Rubel, 2003). Conventional and iron-doped aluminas remove arsenic via a surface

adsorption/complexation reaction. While conventional aluminas require a low operating pHof around 5.5 to 6.5 (capacities are poor at pH > 6.5), the iron-doped aluminas can be

operated at pH values up to 7.5. Note that for both aluminas, adsorption capacities increasewith decreasing pH. Due to the incorporation of iron, Fe-AAl media possess greater arsenic

capacity than conventional aluminas. Both media suffer from poor kinetics, and require long

EBCTs in the range of 5 to 12 min. Comparatively, IX can be operated at an EBCT as low as1.5 min. The longer EBCT requirement translates to much greater media requirement. Both

media are generally used as throwaway media, and are expected to pass the ToxicityCharacteristic Leaching Procedure (TCLP) test. A typical process schematic for an adsorbent

media process is shown in Figure 3. Typically, raw water is chlorinated/pH-adjusted asnecessary and passed through the adsorbent media. The media may be typically backwashed

once every month, and is replaced with new media once it reaches a user-defined set-point

for effluent arsenic concentration. Usually adsorbent media columns are operated in series (alead column and a lag column) to maximize their capacity for arsenic and keep effluent

arsenic concentrations at a low level.


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2007 EUEC 8

Figure 3. Schematic for Arsenic Removal using Adsorbent Media

Arsenic breakthrough curves using AAl or Fe-AAl are usually prolonged and may

take several thousand bed volumes from the time that arsenic initially makes an appearance

in the effluent to complete breakthrough. However, as with Fe-IX, arsenic adsorptioncapacity utilization will be poor if low arsenic discharge limits are required.

Water Quality DriversSince the mechanism is one of surface complexation (ligand exchange), arsenic removal via

conventional or iron-doped media is affected by pH, and adversely affected by the presence

of silicate, phosphate and vanadate. Sulfate has no effect on arsenic removal via aluminas,and in fact, sulfuric acid may be used for pH depression prior to treatment via activated

aluminas.

Advantages of AAl and Fe-AAl

Low cost, non-regenerable (not efficiently regenerated), throwaway media. Proven technology; typical arsenic removal efficiencies are in the range of 9095%. Depending on water quality, capacities may be greater than IX media.Disadvantages of AAl and Fe-AAl

Will require bench and/or pilot testing to determine performance and cost May not be able to meet low arsenic discharge limits on a consistent basis Requires prefiltration for iron, manganese and TOC, which can foul media Lower capacity than granular iron media, more frequent media replacement

Chlorine/Oxidant

AdsorbentMedia

Acid or Base

(If needed)

RawWater

Filtrate toDischarge

Backwash to Waste

Chlorine/Oxidant

AdsorbentMedia

Acid or Base

(If needed)

RawWater


Backwash to Waste


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2007 EUEC 9

Slow kinetics compared with IX and Fe-IX media, requires a 5- to 12-min EBCT andhence increased media requirement

Adversely affected by silicate, phosphate, and vanadium, which compete with arsenic foradsorption sites

Friable media and not as robust as IX or Fe-IX media

Residuals

Spent media may pass the TCLP test and be classified as a non-hazardous waste

Granular Iron Media (GIM) Adsorption

The adsorption of arsenic onto a fixed bed iron-based media has been shown to be effective

at removing arsenic from drinking water (Rubel, 2003). These iron-based media are generallyreferred to as granular iron media (GIM). The two most effective GIM available are granular

ferric oxide (GFO) and granular ferric hydroxide (GFH) (no endorsement is implied by the

authors) and they have been pilot tested in a number of installations across the United States.

The GIM adsorption process is similar to the activated alumina process, and occurs by aprocess of surface complexation or ligand exchange. Typical arsenic breakthrough curves for

some various GIM media may be obtained from Badruzzaman, Westerhoff and Knappe

(2004). As with the alumina media, GIM breakthroughs are gradual and may take severalthousand bed volumes to complete breakthrough. To obtain low (< 4 g/L) arsenic effluent

concentrations, the GIM process will have to be operated in series in a lead-lag configuration.

As with the aluminas and Fe-IX, if low effluent arsenic concentrations are required, pooradsorption capacity utilization will result.

Water Quality DriversGIM can generally operate in a higher pH range than activated aluminas due to the higher

point of zero charge (pzc) of ferric hydroxide at pH 8.2. GIM adsorption is adversely affectedby silicate, phosphate, and vanadate. Sulfate, however, has no effect on arsenic removal via

GIM.

Advantages of GIM

GIM have been shown to have higher capacity than other granular media, whichtranslates to longer run times.

Proven technology, simple operation; arsenic removal to less than 4 g/L possible butwill lead to poor capacity utilization.

Of various metal (hydr)oxides available for arsenic removal, ferric hydroxide has thegreatest capacity for arsenic removal.

Disadvantages of GIM

Pilot testing will be required to predict performance and costs. May not be able to meet a low arsenic discharge limit on a consistent basis. Without prefiltration, iron, manganese, and TOC can foul the granular iron media. Slow kinetics compared with IX media, requires 3 to 6 min EBCT, thus increasing media

volume requirement compared with IX.

Adversely affected by silicate, phosphate, vanadium, and TOC, which foul GIM.


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Less arsenic adsorption capacity than freshly generated ferric hydroxide, may not be costeffective for larger flow rates or high arsenic (> 20 g/L) waters.

Friable media and not as robust as IX or Fe-IX media.

Residuals

Spent media may pass the TCLP test and be classified as a non-hazardous waste.

MEMBRANE-BASED TECHNOLOGIES

Previous studies have shown that purely membrane based technologies can effectively

remove arsenic from potable water supplies (Brandhuber and Amy, 1998). However, due to

their comparatively higher costs and the generation of large quantities of contaminant-laded

brines, these technologies are not considered feasible for arsenic removal from industrial

wastewaters (Chwirka, Stomp, Thomson, 2001). Therefore, purely membrane-based

technologies are not further discussed in this paper.

COMBINATION OF ADSORPTION AND FILTRATION TECHNOLOGIES

Ferric Coagulation-Pressure Filtration (CPF)

In the ferric coagulation-pressure filtration process, a coagulant such as ferric chloride (or

ferric sulfate) is added to the arsenic-containing water with mixing typically provided via a

static mixer, followed by a contact tank to provide sufficient time for arsenic adsorption, andfinally arsenic-iron precipitate removal in a pressure media sand filter. Sufficient iron dose is

provided to meet the target arsenic removal. Typically sand or dual media pressure filters

have been used for filtration of the arsenic-precipitated iron solids Fields, Chen, Wang,2000a, 2000b). More recently, robust light-weight ceramic media have been tested that claim

much higher flow fluxes than conventional pressure filters (up to 8 gpm/ft2) and require

lower backwash flow rates, thus minimizing the volume of waste generated. During a typical

filter run, the initial portion of filtrate is recycled back until the filter ripens (evidenced by

reduced effluent turbidity), followed by a production leg where incoming iron-arsenicprecipitate is removed efficiently to produce a low arsenic filtrate. The filter run is terminated

based either on reaching a user-defined headloss across the filter, effluent turbidity, or filter

run time.

Efficient arsenic removal will depend significantly on the efficient filtration of

precipitated solids (ferric hydroxide). Therefore, even a small breakthrough of solids will

render it difficult to achieve low filtrate arsenic concentration using the ferric coagulationpressure-filtration process.


Since arsenic removal occurs via ferric hydroxide, water quality impacts are the same as

those for GIM. Greater ferric doses may be required to reach a target filtrate arsenic

concentration in the presence of competing species such as silicate, phosphate, and vanadate.


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2007 EUEC 11

Alternatively, a lower ferric dose in conjunction with pH reduction via acid addition may be

required to overcome/compensate for the presence of competing ions.

Advantages of Coagulation/Pressure Filtration

Readily automated, simpler operation than CMF process, proven technology for arsenicremoval for small systems.

Ferric dose and pH can be varied independently to achieve a target arsenic removal. Arsenic removal to less than 2 g/L possible but may come at the cost of reduced filter

run times.

Pressure filtration media is not susceptible to fouling by organics in the raw water as isthe case with microfiltration membranes.

Disadvantages of Coagulation/Pressure Filtration

May not meet low arsenic discharge limits on a consistent basis. May not be able to handle surges in influent suspended solids concentrations or may fail

to provide sufficient run time when higher coagulant doses are required.

Backwash water usually contains less than 0.5% solids, and will requirethickening/dewatering prior to disposal.

Requires pilot testing to determine the optimum ferric coagulant dose, filter ripening timeand backwash interval.

Generates a waste sludge that must be handled and dewatered prior to disposal. Precipitation of ferric hydroxides may cause a pH drop (depending on the ferric dose and

buffering capacity of the water) requiring neutralization prior to discharge.

Residuals

Waste sludge may pass the TCLP test and be classified as a non-hazardous waste.

Ferric Coagulation-Microfiltration (C/MF)

A conceptual C/MF process flow diagram is shown in Figure 4 . This process is essentially

the same as the coagulation/pressure filtration process except that microfiltration membranesare used for filtration rather than a media filter. Coagulant (ferric chloride or ferric sulfate) is

typically added at the optimum dose in-line to a rapid mixer, where the coagulant is

instantaneously mixed with the incoming raw water. The coagulated feed stream is thendelivered directly to a microfiltration unit for solids removal. In general, lower treatment

pHs tend to result in better arsenic removal due to the increased fraction of positively ferric

hydroxide surface that results with a decreasing pH. Thus, filtrate arsenic concentrations less

than 4 g/L (often less than 2 g/L) are achievable on a consistent basis (Ghurye, Clifford,

Tripp, 2004; Chwirka, Colvin, Gomez, and Mueller, 2004).The microfiltration units are backwashed on a periodic basis to remove accumulated

ferric hydroxide solids from the membranes. Typically microfiltration systems includecompressed air addition to assist with the backwashing. Submerged filtration systems may

also be used instead of pressurized MF systems but usually require a larger footprint.

Backwashing occurs approximately every 20 to 30 minutes.The flux of the microfiltration unit is a key parameter for effective operation. Flux is

defined as the instantaneous flow per unit area of membrane and is typically expressed in


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2007 EUEC 12

terms of gallons per square foot (of filter surface area) per day or GFD. The microfilter

membranes are tubular in shape and the surface area is calculated based on the outsidesurface of the membrane. Typical fluxes vary from 25 to 75 GFD. Ferric dose, flux, and

backwash intervals are typically optimized during pilot testing. The optimum flux is typically

dependent on the solids loading to the filters and the potential for membrane fouling from

organic carbon in the raw water (Chwirka, Colvin, Gomez, Mueller, 2004).

Figure 4. Ferric Coagulation Direct-Microfiltration Process Schematic

Nominal pore sizes in microfiltration membranes are usually in the range of 0.1 to

0.22 m, leading to a near complete removal of precipitated ferric hydroxide solids. Thus,

the C/MF process is capable of very high filtration efficiencies, and is typically able to meet

effluent arsenic targets using low ferric doses. For example, raw water arsenic concentrations

can be reduced to below detection (< 2 g/L) using a ferric dose 2 to 3 mg/L as Fe (6 to 9

mg/L as FeCl3) in low alkalinity waters (typically containing less than 30 mg/L alkalinity as

CaCO3).


Since removal is via ferric hydroxide, water quality impacts are the same as those for GIMand ferric coagulation-pressure filtration. However, iron-based processes that use freshly

formed orin situ-formed ferric hydroxide typically exhibit greater arsenic removalefficiencies over preformed iron-adsorbent media such as GIM. The reason for the greater

efficiencies (more arsenic adsorbed/unit mass of Fe) is the availability of greater surface area

available for arsenic adsorption. As ferric chloride is dosed into the arsenic-containing water,

and as the ferric hydroxide particles coagulate and agglomerate, a significant amount ofinternal surface area becomes available for arsenic adsorption. In contrast when using GIM,

Rapid Mixer

Chlorine/Oxidant

Coagulant(FeCl3) Acid or Base

(If needed)

CompressedAir

RawWater

MicrofiltrationModule


Backwash toThickening/Landfill

Rapid Mixer

Chlorine/Oxidant

Coagulant(FeCl3) Acid or Base

(If needed)

CompressedAir

RawWater

MicrofiltrationModule


Backwash toThickening/Landfill


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2007 EUEC 13

the ferric adsorbent particles are already formed, and thus only the external surface area of

the adsorbent is available for arsenic adsorption (Ghurye, Clifford, Tripp, 2004).

Advantages of Ferric Coagulation-Microfiltration

One of the most cost-efficient technologies for removing for arsenic removal from high-arsenic waters.

Membranes provide much tighter filtration for removal of arsenic-iron solids compared topressure media filters.

Ferric dose and pH can be tailored independently to achieve target arsenic removals;consistent arsenic removal to less than 4 g/L is possible.

C/MF process exhibits greater arsenic adsorption capacity (arsenic removal/unit mass ofFe) than GIM.

Proven technology.

Disadvantages of Ferric Coagulation-Microfiltration

More complex than GIM adsorption and pressure filtration. Capital cost of membrane systems is much higher compared to pressure filtration

systems.

High TOC-containing waters can result in more frequent cleaning requirements formembranes.

Requires pilot testing to determine the optimum ferric coagulant dosage, backwashinginterval, and flux.

Backwash water, usually containing less than 0.5% solids, will requirethickening/dewatering prior to disposal.

Precipitation of ferric hydroxides may cause a pH drop (depending on the ferric dosageand buffering capacity of the water) requiring neutralization prior to discharge.

Residuals Spent media may pass the TCLP test and be classified as a non-hazardous waste.

SITE-SPECIFIC WASTEWATER QUALITY SAMPLING PLANS

Although not discussed in detail in this paper, it is vitally important to obtain data on

wastewater characteristics including pH and alkalinity, flow, and important inorganic and

organic constituents. This is often achieved through a well-conceived site-specific sampling

plan. The sampling plan should ideally be implemented prior to performing the desktop

analysis, and should be of sufficient duration to capture seasonal variations in wastewater

quality. For example, significant shifts in pH and constituents that interfere with arsenicremoval must be sufficiently characterized to ensure that the treatment technologies selected

for pilot testing are theoretically able to handle upsets in wastewater quality. Of special

importance also are constituents such as total suspended solids (TSS) and total organic

carbon (TOC). Although these two constituents do not directly interfere with arsenic

removal, they can significantly increase the scope of pretreatment that is required upstream

of the treatment processes (Ghurye and Chwirka, 2006).


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2007 EUEC 14

ARSENIC TREATMENT RESIDUALS MANAGEMENT

Toxicity Characteristics

Arsenic-containing wastes are considered hazardous when the arsenic concentration is higher

than certain threshold levels. Under the Resource Conservation and Recovery Act (RCRA), aresidual from an arsenic treatment facility may be defined as being hazardous waste if itexhibits a toxicity characteristic. For arsenic, the hazardous waste toxicity characteristic

criterion is 5.0 mg/L as defined in Title 40 of the Code of Federal Regulations (CFR), Part

261.24. For liquid wastes with less than 0.5% solids, the 5 mg/L criterion is applied to thedissolved concentration of arsenic in the liquid. For liquids, sludges, or solids with a solids

concentration greater than 0.5 %, the Toxicity Characteristic Leaching Procedure is used.

The TCLP is performed on a sample to determine the leachable concentration of arsenic

under mildly acidic conditions. If the concentration of arsenic in the leachate is greater than 5mg/L, the liquid, sludge, or solid is characterized as a hazardous waste.

The TCLP is performed by placing approximately 125 grams of the solid residuals in

a glacial acetic acid solution with a resulting pH of 4.8. This solution is tumble-mixed for 18hours. The solution is then filtered and the filtrate is analyzed for arsenic. The State of

California has modified the TCLP procedure by using citric acid in lieu of acetic acid. This

modification is called the State of California Waste Extraction Test (WET). The CaliforniaWET test is applied in addition to the federal regulations in California.

Under RCRA, a chemical used in the treatment process is not considered a waste until

it is no longer used in the process. At that point, it is considered a waste and if the waste

exhibits a toxicity characteristic, the waste will be characterized as a hazardous waste. This isan important concept in that with several of the technologies discussed above there is an

intermediate liquid waste that may have a sufficiently high concentration of arsenic to be

classified as hazardous. Even though the arsenic can be removed from the hazardous waste at

the facility, the facility will either be classified as a hazardous waste generator or as atreatment, storage, and disposal facility, both of which have specific RCRA requirements. Ifan arsenic-containing waste is discharged to NPDES permitted discharge (such as a

municipal wastewater treatment facility), the RCRA permitting requirements do not apply.

However, this is not a likely option for arsenic residuals classified as hazardous because mostindustrial pretreatment programs prohibit the discharge of hazardous wastes to the sanitary

sewer system.

Large Quantity Hazardous Waste Generators

Arsenic treatment systems which have onsite regeneration (ion exchange and activated

alumina) will be classified as large quantity hazardous waste generators (LQG) if theygenerate brine quantities greater than 1,000 kg per month. This regulation is specified in

40CFR Part 262.34. In addition, depending on the jurisdiction of state, the state permittingagency may define the arsenic facility as a hazardous waste treatment, storage, and disposal

facility. The requirements of 40CFR Part 262.34 also apply if the treatment facility stores

their hazardous waste on site for more than 90 days.


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Composition of Arsenic Treatment Residuals

Some typical residuals produced by technologies evaluated in this paper are summarized

below. Due to the lack of full-scale data, residuals information on some of the newer

technologies such as granular iron media is not available. It should also be noted that most of

the information on residual characteristics comes from potable water treatment plants andlittle to no information is available on residual characteristics from the treatment of arsenic-

contaminated wastewaters from industrial sources. Nevertheless, the information provided in

Table I showing typical residuals generated from the treatment of arsenic-contaminatedpotable waters should provide some idea of the residuals that may be generated from the

treatment of arsenic-contaminated industrial wastewaters.

Table I. Summary of Treatment Residual Characteristics from the Treatment of Potable Arsenic

Contaminated Waters

Technology Type ofResidual Volume Residual(gal/MG) As Concentration(mg/L) Solids Produced(lb/MG) As in Solidsmg/Kg DryWeight

Conventional Coagulation Sludge 4,300 9.3 180 1,850

Chemical Softening Sludge 9,600 4.2 2,000 165

Ion Exchange Liquid 4,000 10 23.4 14,250

Coagulation-Microfiltration Sludge 52,600 0.8 113 3,000

Nanofiltration orReverse Osmosis

Liquid 664,000 0.1 NA NA

General Standards for RCRA Compliance

LQGs accumulating hazardous waste on site under 40CFR Part 262.34(a) must comply with

the preparedness and prevention procedures of Part 265, Subpart C. Further, LQGs must

develop and maintain a contingency plan onsite, as found in Part 265, Subpart D. LQGs mustalso comply with the personnel training requirements referenced in 40CFR Part 265.16.

Before shipping hazardous waste off site to a RCRA facility, a generator must comply with

several pretreatment requirements, including: obtaining an EPA ID number, preparing a

Uniform Hazardous Waste Manifest (EPA Form 8700-22), and complying with severalDepartment of Transportation requirements.

Reporting and Recordkeeping

Generators have several reporting and recordkeeping responsibilities under Subpart D of Part

262. These include reporting requirements for shipping hazardous wastes off site, or for thosewho treat or store hazardous waste on site, submitting a biennial report (EPA form 8700-

13A) to EPA by March 1 of each even-numbered year (40CFR Part 262.41). The biennial

report compiles data collected from off-site shipments of waste during the previous calendaryear. Under 40CFR Part 262.40, the generator must keep a signed copy of the manifest for at

least three years from the date the waste was accepted by the initial transporter. Basins and


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tanks that treat hazardous arsenic residuals are subject to the design and installation

requirements in 40 CFR 264/265.192 under RCRA. The tank system or component must bedesigned with an adequate foundation, structural support, and corrosion protection to prevent

collapse, rupture, or failure of the unit.

DISPOSAL OPTIONS FOR ARSENIC-CONTAMINATED RESIDUALS

The residuals generated from various treatment technologies discussed above will consist of

either liquids, solids, or both. Presented below is a general description of possible disposal

methods for liquidand solid residuals generated from arsenic treatment facilities.

Residuals Disposal Directly to a Receiving Stream

The disposal of liquid residuals containing arsenic directly to a receiving stream will be

subject to compliance with the National Pollution Discharge Elimination System (NPDES)

program. The limits established in the NPDES permit for specific contaminants aredetermined by the water quality criteria established for the receiving water, ambient levels of

the specific contaminants, the established low-flow condition of the receiving water, and thedesign flow of the proposed discharge from the arsenic treatment process. Most NPDES

permits limit solids discharge to around 30 mg/L. Waste streams with solids concentrations

greater than this can not be discharged.

The EPA has established regulations or guidance for arsenic under the Clean WaterAct (CWA) and the Safe Drinking Water Act (SDWA). Under the Clean Water Act, an

ambient water quality criterion for arsenic was established in 1992 for fish consumption to

protect human health. This 1992 criterion for fish consumption was set at 0.14 g/L. Further,if that same water was used for drinking and fish consumption, the ambient water quality

criterion for arsenic was set at 0.0175 g/L to protect human health. These arsenic waterquality criteria represent a one in one million (10

-6) cancer risk for arsenic exposure. The

Safe Water Drinking Act MCL for arsenic is 10 g/L. To protect the natural environment, the

EPA established arsenic criteria for fresh water and marine water chronic and acute

conditions. The ambient water quality criteria that may apply to arsenic discharge are

summarized in Table II.

TableII.Summary of Water Quality Criteria for Arsenic

Arsenic Form Total Arsenic Trivalent Arsenic

Fresh Water Acute, g/L (Dissolved) 360

Fresh Water Chronic, g/L (Dissolved) 190Marine Water Acute, g/L (Dissolved) 69

Marine Water Chronic, g/L (Dissolved) 36

Human Health- Fish Consumption, g/L 0.145Human Health, Water and Fish 0.018 0.0175

Consumption, g/L

SDWA Drinking Water Criteria, g/L (Total) 10


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The water quality criterion presented in Table II will be used by state regulators toestablish discharge limitations for arsenic depending on the classification of the receiving

water. The established arsenic limit will then be written into the NPDES permits. The

discharge limitations are calculated by the following mass balance equation:

M2 = (Q3*M3-Q1*M1)/Q2 (1)

whereM1 = the background arsenic concentration in the receiving stream, g/L

Q1 = the low flow condition of the receiving stream, MGD

M2 = the allowable arsenic concentration of the discharge, g/LQ2 = the design flow rate of the arsenic treatment facility discharge, MGD

M3 = the arsenic water quality criterion of the receiving stream, g/L

Q3 = Q1 + Q2, MGD

The allowable discharge of waters containing arsenic will therefore be impacted by theability of the stream to assimilate the arsenic without exceeding the arsenic standard of the

receiving water. As such, each potential discharge will have specific arsenic discharge limitsestablished by the regulatory agency.

In addition, a discharge will likely be required to pass the whole effluent toxicity

(WET) test. The WET test will determine toxicity of the effluent regardless of the arsenicconcentration and possible synergistic impacts with other contaminants in the water. Given

these considerations, direct disposal of arsenic residuals to the receiving stream will only be

acceptable for residuals with low levels of suspended solids and arsenic concentrations thatcomply with surface water quality standards under the NPDES program. Direct disposal will

also be limited to regions where discharge of high TDS (total dissolved solids) wastewatersto receiving streams is not a concern. Given these constraints and the requirement that the

groundwater treatment facility must be in close proximity to the receiving stream, direct

discharge of arsenic residuals to the receiving stream will only be feasible for a limited

number of facilities.

Discharge of Arsenic Residuals to a Sanitary Sewer

The discharge of arsenic residuals to a sanitary sewer may be a disposal alternative,

providing arsenic concentrations are within the established Technically Based Local Limits(TBLL) of the sewerage authority's Industrial Pretreatment Program. Under NPDES

regulations, wastewater treatment plants (WWTPs) must have an Industrial Pretreatment

Program in effect to protect the operation of the WWTP, prevent violations of the WWTP

NPDES permit, and prevent unacceptable accumulation of contaminants in the WWTPsludge or biosolids.

The residuals generated from an arsenic treatment facility will be classified as

industrial waste since they contains contaminants that may impact the WWTP (metals,caustic and acidic solutions, and high levels of TDS). As such, the arsenic residuals will need

to meet the established TBLLs if they are to be discharged to a sanitary sewer. The TBLLs

are computed for each WWTP to take into account the background levels of contaminants inthe municipal wastewater. In addition, the estimated flow contributed by the industries


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2007 EUEC 18

compared with the municipal flow is used to calculate the allowable contaminant loading to

the WWTP. The TBLL is established by the most stringent of the limits that protect theeffluent water quality of the WWTP, cause process operational upsets, or cause unacceptable

levels of contaminants in the biosolids. The development of TBLLs for each WWTP will

result in specific limitations representative of that wastewater system.

The discharge limitations for arsenic that the WWTP must meet were discussedabove. The computations consider the amount of arsenic removed through the treatment

processes at the WWTP that will accumulate in the sludge. Arsenic removal values reported

by EPA are 11% to 78% for activated sludge facilities (EPA, 1986). Arsenic may causeinhibition of the biological processes if the concentration is high enough. Reported values of

arsenic threshold process inhibition are 0.1 mg/L for activated sludge, 1.5 mg/L for

nitrification, and 1.6 mg/L for anaerobic digestion. Arsenic concentrations should be keptbelow these threshold inhibition values. Note that the arsenic removed in the treatment

processes will accumulate in the biosolids and impact the eventual disposal of these

biosolids.

Based on a number of industrial pretreatment programs established by the authors, the

TBLL for arsenic will typically be limited by the contamination of the biosolids as opposedto discharge limitations or process inhibition. However, if the drinking water standard is

significantly lowered, the effluent limits for streams classified as a domestic water sourcewill be drastically reduced. This will result in a condition in which the effluent limits will

dictate the criteria used to develop local limits, as opposed to the biosolids content.

The allowable concentration of arsenic in biosolids will be governed by the 40CFRPart 503 regulations promulgated in 1989 and amended in 1995. The Part 503 regulations

specify the following arsenic limits in biosolids as a function of the disposal method:

Land Disposal Arsenic Limit....73 milligrams per kilogram (mg/kg)

Land Application Arsenic Ceiling Limit 75 mg/kgLand Application Clean Sludge Arsenic Limit.. 41 mg/kg

Land disposal refers to dedicated sludge disposal sites that are essentially sludge-only

landfills. These facilities are used by municipalities for the disposal of WWTP and watertreatment plant (WTP) residuals and typically referred to as Dedicated Land Disposal (DLD)

sites. The sludge must be applied to DLD sites in conformance with the 40CFR Part 503

regulations. The land application of biosolids refers to the application of WWTP or WTPresiduals to agricultural land for the purpose of nutrient addition and as a soil conditioner.

The residuals are applied at a rate in which the nitrogen content of the biosolids meets the

agronomic nitrogen requirements of the crop grown and also meets the contaminant limitsestablished in the 40CFR Part 503 regulations. The 41 mg/kg arsenic limit is the value listed

in Table III of the Part 503 regulations and has been termed clean sludge. Clean sludge can

be land applied with no limitations.


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Table III. Arsenic Technically Based Local Limits (TBLL) for Various Cities

City Arsenic TBLL, g/L

Albuquerque, NM 51

El Paso, TX 170

Phoenix, AZ 100Tucson, AZ 400

Fresno, CA 320

Newark, NJ 150

Orange County, CA 2,000

If the arsenic concentration of the residual exceeds the clean sludge limit of 41

mg/kg, the biosolids may still be land applied, but the quantity will be limited to a totalcumulative arsenic loading of 41 kg per hectare of land (36.6 lbs/acre). As such, most

municipalities will establish TBLLs based on the clean sludge criteria to avoid landapplication restrictions. To illustrate the impact of the Part 503 regulations on thedevelopment of an arsenic TBLL, consider a limit of 41 mg/kg for land application of

biosolids. The wastewater removal efficiency for arsenic is typically given as 45% through

an activated sludge facility. Assuming that the biosolids production is around 1,200 poundsper million gallons of wastewater treated, the maximum allowable headworks loading will be

around 0.109 pounds of arsenic per million gallons of wastewater treated. This equates to a

total (background and industrial) influent arsenic concentration of around 13 g/L. The

arsenic TBLL will then be calculated based on the background arsenic concentration, theestimated industrial flow, and a factor of safety. For comparison purposes, the arsenic TBLL

for several cities is presented in Table III.

Table III shows a large variation in the arsenic TBLL caused by the specificcharacteristics of the individual wastewater systems. The development of an arsenic TBLL

will be influenced by the arsenic concentration of the water supply and therefore also by the

treatment technology and level of treatment achieved for the water supply. As shown above,when the background arsenic concentration approaches the 13 g/L level, the industrial

pretreatment program will result in a lower arsenic TBLL.

The ability to discharge arsenic residuals to a sanitary sewer will be determined by

the arsenic TBLL and will be different for each community. If the water supply has anarsenic concentration above approximately 13 g/L, it may not be possible to discharge

arsenic treatment residuals to the sanitary sewer. In other words, communities that require

arsenic treatment will likely have higher background arsenic concentrations in thewastewater, and therefore will limit the possibility of discharge of arsenic residuals to the

sanitary sewer. Although a reduction in the arsenic drinking water standard will reduce

background arsenic levels in wastewater, disposal of drinking water arsenic residuals to thesewer will increase the influent arsenic concentration at the wastewater plants. This is

because in arid areas, wastewater flow is significantly less than the domestic water

production rate due to consumptive uses and irrigation. This would also elevate arsenic levelsin wastewater effluent and biosolids.


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2007 EUEC 20

Landfill Disposal of Arsenic Residuals

The disposal of arsenic residuals at a landfill is a potential method of disposal for arsenic

residuals that contain no free water. This means the arsenic residuals must be in a solid form

and not contain free water that could drain out of the residual. In addition, the residuals must

not have toxic characteristics as defined by the TCLP test or the California WET. If thearsenic-containing residual is determined to be non-hazardous and does not have free water,

then it will be accepted at most solid waste landfills.

The arsenic residuals must not contain free draining water if they are to be landfilled.The landfill will typically administer a test called the paint filter test to determine if the

residual has free water. A sample of the residual is placed in a paint filter and if water drains

out, the residual will be rejected. As such, the arsenic residual must be dewatered before itcan be landfilled. Depending on the form of the solid arsenic residual, the residual must be

dewatered to around 20% to 25% solids before it will meet the paint filter test requirements.

Disposal of Arsenic Residuals at a Hazardous Waste Disposal Facility

Arsenic residuals that fail to pass the TCLP (or the California WET test in California) mustbe treated to meet relevant RCRA land disposal restrictions and disposed of at a designated

and licensed hazardous waste facility. These facilities are designed to prevent migration of

the hazardous contaminants to the environment. As such, these facilities have extensivemonitoring and operational requirements that cause the cost of this method of disposal to be

much greater than a typical solid waste landfill.

In addition, if the arsenic residual is a hazardous waste, its transport to the hazardous

waste facility must be manifested and the owner may never be free of the responsibility ofthat waste. The production of an arsenic residual that is determined to be hazardous should be

avoided. Treatment technologies should be evaluated closely to assure that the residualsproduced are not classified as hazardous and require disposal at a hazardous waste facility.

SUMMARY AND CONCLUSIONS

Various technologies are available for arsenic removal from industrial wastewaters. Thesetechnologies generally use either adsorption or adsorption followed by filtration. Based on

the discussion above, the following conclusions are offered:

Based on the characteristics of the receiving stream, arsenic discharge limits inindustrial wastewaters can be quite low, even lower than the drinking water standard

of 10 g/L. The choice of an appropriate treatment technology for arsenic removal depends on

treatment goal, i.e., the efficiency required of a treatment process. Technologies that

may be feasible for arsenic removal from drinking waters may not always work forindustrial wastewaters.

Prior to evaluating treatment processes, a site-specific sampling plan should beimplemented to obtain important wastewater characteristics. The sampling plan


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2007 EUEC 21

should be of sufficient duration to capture seasonal changes (if any) in wastewater

chemistry. A desktop analysis should be performed to evaluate the feasibility of various

available technologies to meet site-specific discharge limits. One or two technologies

should be selected for pilot testing.

Pilot testing should determine the impact of wastewater chemistry on treatmentefficiency and the ability of the treatment process to handle wastewater quality

upsets, develop data for establishing design criteria, prepare conceptual facility

designs, and estimate capital and operations and maintenance costs. Attention must also be focused on residuals handling and disposal issues. Residuals

resulting from pilot plant operation should be collected and analyzed to determine the

toxicity characteristic. Simultaneously, a holistic analysis must be performed toensure that the entire treatment process including waste generation complies with

applicable local, state, and federal regulations.

REFERENCES

Badruzzaman, M., Westerhoff, P., Knappe, D. 2004. Intraparticle diffusion and adsorption of

arsenate onto granular ferric hydroxide (GFH). Water Research, 38 (18):4002-4012.

Brandhuber, P., Amy, G. 1998. Alternative methods for membrane filtration of arsenic fromdrinking water.Desalination 117: 1.

Boodoo, F. 2005. Personal communication.

Chwirka, J.D., Stomp, J., Thomson, B. 2001. Residuals handing issues for arsenic treatment

processes. Presented at the AWWA/WEF Joint Residuals Conference, San Diego,California.

Chwirka, K.D., Colvin, C., Gomez, J.D., Mueller, P.A. 2004. Arsenic removal from drinking

water using the coagulation/microfiltration process.Journal of American Water WorksAssociation, 96 (3):106-114.

Clifford, D.A. 1999. Ion exchange and inorganic adsorption. In Water quality and treatment,

5th ed., chap. 9. New York: McGraw Hill.Clifford, D.A., Ghurye, G.L., Tripp, A.R. 2003. Arsenic removal from drinking water using

ion exchange with spent brine recycling.Journal of American Water Works Association,95 (6):119-130.

Environmental Protection Agency. 1986. Quality criteria for water(EPA 440/5-86-001).

Washington, DC: Environmental Protection Agency.Environmental Protection Agency. 2001.National primary drinking water regulations;

Arsenic and clarifications to compliance and new source contaminants monitoring:

Final rule. Federal Register, Vol. 66, No. 14.Fields, K., Chen, A., Wang, L. 2000a.Arsenic removal from drinking water bycoagulation/filtration and lime softening plants (E.P.A, Office of Research and

Development [ORD] Report, EPA/600/R-00/063). Washington, DC: Environmental

Protection Agency.Fields, K., Chen, A., Wang, L. 2000b.Arsenic removal from drinking water by iron removal

plants (E.P.A, Office of Research and Development [ORD] Report, EPA/600/R-

00/086). Washington, DC: Environmental Protection Agency.


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Journal of EUEC Arsenic RemovalGhurye, G.L., Chwirka, J.D. 2006. Water quality considerations for arsenic removal from

groundwaters. Proceedings NGWA Naturally Occurring Contaminants Conference,Albuquerque, NM.

Ghurye, G.L., Clifford, D.A. 2001.Laboratory study on the oxidation of As III to As V. US

(E.P.A, Office of Research and Development [ORD] Report EPA/600/R-10/021).

Washington, DC: Environmental Protection Agency.Ghurye, G.L., Clifford, D.A. 2004. Laboratory study on the oxidation of As III to As V.Journal of American Water Works Association, 96 (1): 84-96.

Ghurye, G.L., Clifford, D.A., Tripp, A.R. 1999. Combined nitrate and arsenic removal by ionexchange.Journal of American Water Works Association, 91 (10): 85-96.

Ghurye, G.L., Clifford, D.A., Tripp, A.R. 2004. Pilot study of an iron coagulation-direct

microfiltration process for arsenic removal from groundwater.Journal of AmericanWater Works Association, 96 (4): 143-152.

Rubel, F. 2003.Removal of arsenic from drinking water by adsorptive media (E.P.A, Office

of Research and Development [ORD] Report, EPA/600/R-03/019). Washington, DC:

Environmental Protection Agency.

Wang, L., Chen, A., Fields, K. 2000. Arsenic removal from drinking water by ion exchangeand activated alumina plants (E.P.A, Office of Research and Development [ORD]

Report, EPA/600/R-00/088). Washington, DC: Environmental Protection Agency.

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