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Development of a Sulfate-Reducing Biological Process to Remove Heavy Metals from AcidMine DrainageAuthor(s): Vicki S. Steed, Makram T. Suidan, Munish Gupta, Takashi Miyahara, Carolyn M.Acheson, Gregory D. SaylesReviewed work(s):Source: Water Environment Research, Vol. 72, No. 5 (Sep. - Oct., 2000), pp. 530-535Published by: Water Environment FederationStable URL: http://www.jstor.org/stable/25045418 .Accessed: 23/01/2012 19:40

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Development of a Sulfate-Reducing

BiologicalProcess To Remove

HeavyMetals from Acid Mine Drainage

Vicki S. Steed, Makram T. Suidan, Munish Gupta, Takashi Miyahara, Carolyn M. Acheson,Gregory D. Sayles

ABSTRACT: The feasibility of using sulfate-reducing bacteria to

remove heavy metals from aqueous streams such as acid mine drainagewas evaluated using three anaerobic reactors: an upflow anaerobic

sludge blanket (UASB) reactor, a packed filter reactor, and a filter

reactor that was partially packed with floating plastic pall rings. The

packed filter reactors removed more than 99% of the influent metals.

The performance of the partially packed reactor was superior based on

effluent metal and sludge concentrations. Although the UASB reactor

reduced the concentration of dissolved iron, the effluent concentration of

total suspended solids remained greater than 18 g/L. This elevated solids

concentration indicated that the UASB reactor was not operating as an

effective clarifier, and, as a result, UASB reactor operation was

discontinued after 4 months. The packed filter reactors were operatedin parallel and received influent containing a combination of heavy

metals. By withdrawing sludge from the bottom of these reactors, the

accumulation of solids such as metal precipitates and biomass was

controlled. The effluent concentrations of most metals were low, often

less than drinking water standards, with the exception of manganese.

Water Environ. Res., 72, 530 (2000).

KEYWORDS: acid mine drainage, sulfate-reducing bacteria, anaerobic

reactors, metal sulfide precipitation.

IntroductionAcid mine drainage (AMD) is characterized by low pH (1.5 to

3.5) and large concentrations of sulfate and dissolved heavy metals

such as iron, manganese, aluminum, zinc, and copper. The ions

and concentrations present are site specific and vary considerably

depending on factors such as location and type of mine and, to a

large extent, the sampling site within the mine.

Typically, these metal bearing wastes have been treated by

chemical precipitation such as in situ addition of lime, calcium, or

sodium hydroxide or by sorption to materials such as ion-exchange

resins or the biomass-based sorbent Algasorb (Bio-Recovery Sys

tems, Inc., Las Cruces, New Mexico). Less costly technologies are

needed to remediate many sites that have been affected by metal

contaminated liquids and solids such as soils, sludges, and sedi

ments.

Bacterial sulfate reduction has been identified as a potentially

cost-effective means to remove metals from AMD (Dvorak et al.,

1992, and Kuyucak et al., 1991). Sulfate-reducing bacteria (SRB)can convert sulfate to sulfide using an organic carbon source as an

electron donor (for chemical reactions, see Table 1). This sulfide

reacts with many of the metal ions present. The low solubility of

metal sulfides under sulfate-reducing conditions results in a low

residual concentration of dissolved metal species (Hammack et al.,

1994). In addition, as the sulfate-reduction process mineralizes the

organic energy source, carbon dioxide is produced. Based on

chemical equilibria under sulfate-reducing conditions, pH and

alkalinityof the waste will increase. Furthermore, the carbonate

and hydroxide ions generated as the pH rises may also form metal

precipitates (Dvorak et al., 1992). The ability to reduce dissolved

metal concentrations and neutralize AMD acidity makes SRB

useful catalysts in treating AMD and other metal contaminated

materials.

To effectively treat metal contaminated wastes, an anaerobic

environment supporting sulfate reduction must be established for

metal precipitation, and clarification must be provided to remove

metal precipitates from the effluent. Because solids (metal precipitates and biomass) accumulate in the reactor and may eventually

clog it, a method of solids removal or cleaning is an importantconsideration in reactor selection. Two reactor types were evalu

ated in this study:an

upflow packed anaerobicfilter with

recycleand an upflow anaerobic sludge blanket (UASB) reactor. To clean

the UASB reactor, solids can be removed from the bottom of the

reactor. The same technique can be used for the filter reactor;

however, the presence of packing material complicates the process. Therefore, evaluation of reactor cleaning was another objective of the research. As a result, two configurations of the filter

reactor were evaluated: a reactor that was completely packed and

a reactor that was partially packed (60% by volume).

MethodologyThe reactors were constructed of plexiglass (1.07 m height, 170

mm diameter). Polypropylene pall rings (Glitsch Ballast Rings[Koch-Glitsch Mass Transfer Technology, Wichita, Kansas], 26

mm diameter) were used as the packing material in the filter

reactors. Pall rings were selected because of the large surface area

per unit volume, high porosity, and chemical resistance in the

corrosive environment of the sulfate-reducing system. Because the

packing was lighter than water, the packing material floated to the

top of the partially packed filter reactor leaving an open area at the

bottom. The reactors were kept completely mixed by recirculating

the effluent at a recycle ratio of 20:1. Because the influent was

acidic, recirculating the effluent moderated the pH and promotedmore efficient sulfate reduction. Figure 1 shows a schematic dia

gram of the filter reactors.

The reactors were seeded with a mixture of primary and anaer

obic digestor sludge obtained from the Mill Creek wastewater

treatment plant, Cincinnati, Ohio. Primary sludge was used be

530 Water Environment Research, Volume 72, Number 5



_Steedet al.

Table 1?Pertinent reactions and equilibria of SRB bio

logical process.9

Type Reaction

Sulfate

reducing

Acid/base

CHXOO- + SO2" + 3H+ -> 2CO? + 2H20+ HoS

2CH3COO 2S02+ 2HCO?

+ 3H+ -? 2C02HS" + H2S

CH3COO- + H20->

CH4 + HCO3

CH3COOH ^ H+ + CH3COO2HS07 ** 2S02~ + 2H+

HCO3<-> 2H+ + CO?

C02(g) + H20l20

<-> H+ + OhT

US <* H+ + HS" ^ 2H+ + S"

Metal

precipitation0 2M+n + nS-2 <^M2Sn

M+n + nOH~ *+M(OH)n

2M^n + nC03"2*?

M2 (C03)n

aTypical values for dissociation constants and thermodynamic

properties can be obtained from sources such as Lide (1991).bWhere M represents a generic metal ion, and n represents the

charge on a metal ?on.

cause of the long sewer lines in Cincinnati and the abundant

release of hydrogen sulfide from manholes located close to the

wastewater treatment plant. Also, primary sludge from the same

source had been used in previous experiments with SRB (Gupta et

al., 1996).

Acetic acid was selected as the carbon and energy source for

two reasons. Because acetic acid can be used to leach metals from

solids in thetoxicity

characteristic leachateprocedure (TCLP) test,

selecting acetic acid as the carbon and energy source for the SRB

biological process enhances the compatibility of this biological

process with other metal remediation efforts, such as the leachingof metals from mine tailings. The effectiveness of an aqueous

solution of acetic acid in leaching heavy metals from contaminated

soils needs to be verified. In addition, acetic acid is relatively

inexpensive.

Tables 2 and 3 show the composition of the feed. A synthetic

Gas Sampling Port

Effluent

Acid MineDrainage

Buffersolution

Sludge Withdrawal Port

Figure 1?Schematic diagram of the anaerobic filter reactor.

Table 2?Composition of reactor feed (iron-only feed).8

Components Concentration0

Acetic acid 3000Iron (ferrous) 1490Iron ferric) 840

Chloride 3480Hydrochloric acid 2.75c

Stock salt solution 32c

Vitamin solution 8C

Sulfate0 5200Sodium 5370Carbonate 870

Hydroxide 1630

aMetal concentrations are not based on a specific mine effluent

but are characteristic of types of effluent from hard rock mines.b

Inmg/L, except where noted.c

InmL/L.d

Sulfate was fed as sodium sulfate.

wastewater containing metals, sulfate, and acetate was fed to the

reactors. The concentration of metals in AMD can change drasti

cally from mine to mine and even along the depth of the water in

a pit as demonstrated at the Berkeley Pit in Butte, Montana (Davis,

1989). The combination and concentration of metals selected for

the synthetic wastewater used in this experiment was provided bythe U.S. Environmental Protection Agency as being characteristic

of mines in Montana and Colorado (Sayles, 1994). The concen

tration of acetic acid added was stoichiometrically calculated so

that the amount of sulfide produced from sulfate could precipitate

Table 3?Composition of reactor feed (metal mixture

feed).3

Components Concentration5

Acetic acid 3000Iron (ferric) 840

Zinc 650

Manganese 275

Copper 127Cadmium 2.3

Arsenic0 2.1

Lead 1.5

Chloride 2800Stock salt solution 24d

Vitamin solution 6d

Sulfate9 5000Sodium 7300Carbonate 700

Hydroxide 1700

aAll metals, except arsenic, were fed as their respective chloride

salts. Metal concentrations are not based on a specific mine

effluent but are characteristic of types of effluent from hard rock

mines.b

Inmg/L, except where noted.c

Arsenic was fed as arsenic trioxide.

d InmL/L.e

Sulfate was fed as sodium sulfate.

September/October 2000 531



Steed et al.

Table 4? Stock salt solution.

Component Concentration8

Trace salt solution 33.1b

Magnesium chloride (MgCI2 6H20) 8.13

Sodium acid phosphate (NaH2P04 H20) 8.28

Potassium acid phosphate (KH2P04) 13.6Ammonium chloride (NH4CI) 30.33Calcium chloride (CaCI2 2H20) 5.88

aIn g/L, except where noted.

b InmL/L

all metals present in the wastewater. A solution containing essen

tial vitamins for the microorganisms and a stock salt solution

containing essential minerals were added to the metal solution (see

Tables 4, 5, and 6).

A pH set-point of 7.2 was selected for optimal SRB growth

(Barton, 1995). A buffer solution (containing sodium carbonate,

sodium hydroxide, and sodium sulfate) was fed to the reactors to

control pH. The concentration of sodium hydroxide in the buffer

solution was determined experimentally as the concentration nec

essary to achieve the desired pH set-point.The flow rates of the synthetic AMD and buffer solutions were

monitored using calibrated carboys. The solutions were fed to the

reactors using Cole-Parmer Masterflex pumps (Cole-Parmer In

strument Company, Vernon Hills, Illinois) operating at 2 r/min.

Power to the Masterflex pumps was channeled through electronic

Chrontrol timers (Lindberg Enterprises, Inc., San Diego, Califor

nia). These timers adjusted flows to obtain proper hydraulic resi

dence time. Both AMD and buffer flows were intermittent, cycling

every1 to 2 minutes. For the initial

comparisonof the UASB

reactor with the filter reactors, the combined flow rate of the

synthetic AMD and buffer was 2.0 L/d corresponding to a hydrau

lic detention time of 8.4 days.All reactors were operated at 30 ?C. The UASB reactor temper

ature was maintained by heating the recycle line and insulating the

reactor. The temperature of the filter reactors was maintained with

a Fisher Scientific (Pittsburgh, Pennsylvania) Isotemp WaterbathModel 28L-M.

All pH determinations were made on unfiltered samples imme

diately after collection using an Orion Model 720A pH meter

(Orion Research, Beverly, Massachusetts). All other effluent sam

ples (except total metals) were filtered with a 0.45-|xm MAGNA

Nylon membranefilter

(MSI, Westboro, Massachusetts)before

analysis. Whenever possible, measurements were determined on

Table 5?Stock trace salt solution.

Concentration,

Component g/L

Ammonium molybdate ((NH4)6Mo7024 4H20) 0.52

Sodium borate (Na2B407 10H2O) 1.15

Nickel chloride (NiCI2 6H20) 3.00

Manganese chloride (MnCI2 4H20) 4.74

Cobaltic chloride (CoCI2 H20) 2.86

Zinc chloride (ZnCI2)3.27

Copper(ll) chloride (CuCI2 2H20) 2.05

Table 6?Vitamin solution.

Component Concentration, g/L

p-Aminobenzoic acid 0.01

Biotin 0.003 9

Cyanocobalamin 0.000 2

Folie acid 0.003 9Nicotinic acid 0.01

d-Pantothenic acid 0.01

Pyridoxine hydrochloride 0.02

Riboflavin 0.01

Thiamine 0.01

Thiotic acid 0.01

the day samples were collected. Flow rate, pH, and temperaturewere monitored daily.

Samples for metal analysis were taken twice weekly. Metal

concentrations were analyzed using a PerkinElmer Atomic Ab

sorption Spectrophotometer Model 3100 with AS90 (flame) andHGA 600 and AS60 (furnace) according to the SW 846 method

(Office of Solid Waste, 1986). Total (unfiltered) and soluble (filtered) effluent samples were preserved with nitric acid (HN03)

(trace metal grade) before analysis. Sludge samples, diluted 1:200,

were also digested with HN03 before analysis.

Acetic and propionic acid concentrations were determined usinga Hewlett Packard (Palo Alto, California) Series 1050 LC diode

array detector with Bio Rad Aminex HPX-87H (300 X 7.8 mm

column). Chemical oxygen demand (COD) was determined usingHach (Loveland, Colorado) COD glass vials, a Hach COD ReactorModel 45600, and a Bausch & Lomb (Rochester, New York)

Spectronic70

spectrophotometer followingStandard Methods

(method 508 C; APHA et al., 1995). Total organic carbon (TOC)was determined using a TOC analyzer (Shimadzu TOC-5000

[Shimadzu Scientific Instruments, Inc., Columbia, Maryland]).Gas composition was determined using a Hewlett Packard 5890

Series II GC, TCD detector, HP 45/60 Molecular Sieve column,and HP 80/100 Hayesep Q column. Carbon dioxide, oxygen,nitrogen, and methane were measured and expressed as fractions

of the total sample. The above variables were analyzed weekly.

Sulfate concentration was determined using the gravimetric

method with drying of the residue as described in Standard Methods (method 4500-D; APHA et al., 1995). Dissolved sulfide con

centrations were determined using an Orion silver/silver sulfide

electrode onsamples prepared

with0.45-p-m

MAGNANylon

syringe filters (MSI) and mixed in equal portions with a sulfide

anti-oxidizing buffer (Orion). Sulfates and sulfides were analyzed

weekly.

Results and DiscussionThe reactors were evaluated in two comparisons. Initially, the

fully packed filter was compared to the UASB reactor using an

iron-only feed with an iron concentration of 32 mmol/L (see Table

2). The filter reactors reduced the effluent concentrations to 0.11

mg/L dissolved iron and 0.51 mg/L total suspended solids. Al

though the UASB reactor reduced the concentration of dissolved

metals to less than 0.25 mg/L, the concentration of total suspended

solids varied between 18 and 22 mg/L. No sludge granulation

occurred within the UASB reactor. Performance of this reactor




_Steedet al.

1 I I I I I I I I I I s

Total fed s^

s' Total removed

^sin sludge 1

^/Remaining_ _

S^ In reactor

I Total removed in effluent~

J_I_I_L_. -L_U.. T 1.1.1.1.1.

Time, days

Figure 2?Idealized metal balance for the anaerobic filter.

indicated that it did not operate well as a clarifier, and, as a result,

UASB reactoroperation

was discontinued after 4 months.

During the comparison of the UASB and packed bed filter

reactors, solids accumulation in the filter reactor was controlled by

removing a fixed volume from the reactor every three hydraulic

retention times or 26 days. In time, performance of the reactors

deteriorated. The effluent COD, acetate, and dissolved metals

concentrations increased. Propionate was detected in the effluent,

indicating that the system was under stress. In addition, the total

effluent metal concentrations increased, indicating decreased per

formance of the filter reactors with respect to clarification.

Increasing the solids removal frequency did not improve reactor

performance. Both reactors were cleaned by removing the packing

material. The solids in the lower half of each reactor accumulated

tothe

extentthat the packing

wascompletely clogged. Approxi

mately 40% of the packing material was removed from one of the

reactors to provide a larger volume for the accumulation of solids.

In the second comparison, both filter reactors were restarted, and

hydraulic retention time was increased to 12.9 days (a decrease in

the combined flow rate to 1.3 L/d). The feed composition was

changed to include a combination of heavy metals (see Table 3).

Solids were withdrawn from the bottom of the reactors to remove

accumulating metal precipitates and biomass (sludge) in the reac

tor to avoid plugging of the reactor and allow continuous opera

tion. During the initial 3 to 4 weeks of operation, no sludge was

wasted from the reactors to allow for the accumulation of biomass.

After this initial phase, sludge was wasted based on a metal

balance for each reactor. It is interesting to note that neither reactorexhibited signs of inhibition resulting from exposure to oxygen

during cleaning.

Figure 2 shows an idealized metal balance for the anaerobic

filter reactor. One liter of sludge was wasted every week from each

of the reactors. The concentration of metals in the feed solution, in

the sludge, and in the unfiltered effluent was measured as previ

ously discussed. The total mass of metals remaining in each reactor

was calculated as the difference between total mass of metals fed

to the reactor and total mass of metals removed in the sludge and

effluent. If the total mass of metals removed in the sludge was less

than the total mass of metals fed to the reactor, then additional

sludge was wasted from the reactor to maintain a continually

constant mass of metals in the reactor. Performing a mass balance

for each reactor was necessary because the density of wasted

ECD

sludge varied; therefore, removing a constant volume of sludgewould not always equate to maintaining a constant mass of metals

within the reactor.

Figures 3 and 4 show the actual metal balance for the two most

prominent metals in the reactor feed and sludge. In Figures 5 and

6, the total mass of metals remaining in the completely packed and

partially packed filter reactors, respectively, is presented as a

function of time. As illustrated in these figures, the total mass of

metals increased in the beginning (during the period when no

sludge was wasted); however, over time, the rate of accumulation

slowed considerably.

As shown in Table 7, COD and acetic acid were reduced bymore than 95%. Based on the reactions given in Table 1, if the

reduction in COD and acetic acid was solely the result of SRB

activity, the sulfate concentration should be reduced to the same

level. (Acetate concentration was reduced from 50 to 0.83

mmol/L; therefore, sulfate concentration should have been reduced

from 52.1 to 2.9 mmol/L.) However, a sulfate residual of approx

imately 25% of the influent concentration (12 mmol/L) was

present.One possible explanation could be that methanogenesis was

responsible for the 9 mmol/L of acetate consumed that could not

be accounted for by sulfate reduction. If methanogenesis occurred,

methane should have been detected in the weekly gas samples.

However, the gas production was negligible, and the amount of

methane in the headspace was always less than 10% and frequentlybelow the detection limit. Another possible explanation could be

the presence of a consortium of bacteria, including non-SRB, that

used the acetic acid but not the sulfate. This is possible because the

reactor was seeded with sludge from a wastewater treatment plantrather than a pure culture of bacteria.

Based on the metal mass balance, the reactors are now operatingat

steadystate

with respectto

themass

of metals, except formanganese, remaining in the reactor. Stable operation was con

firmed by operating the reactors for more than three retention times

(40 days) at steady state, based on the metal mass balance with

respect to the mass of sludge in the reactor.

As shown in Tables 8 and 9, both filter reactors performed wellwith respect to the removal of metals, and the concentration of

soluble metals in the effluent, except manganese, was reduced to a

concentration less than drinking water standards. Both filter reac

tors, unlike the UASB reactor, worked well as clarifiers, and total

metal removal efficiencies exceeded 99%. However, the effluent

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Time, days

Figure 3?Iron balance for the partially packed filter.




Steed et al.

O 10 20 30 40 50 60 70 80 90 100 110 120 130

Time, days

Figure 4? Zinc balance for the partially packed filter.

total metal concentrations for iron, zinc, and manganese were

larger for the completely packed reactor than for the partially

packed reactor. Analysis of effluent total metal concentrations

using a Student t test with a 95% confidence interval confirmed

that the difference in iron and zinc concentrations was statistically

significant. However, there was no statistically significant differ

ence in soluble metal concentrations. This indicates that the par

tially packed reactor was a more effective clarifier than the com

pletely packed reactor.

One of the reasons for this observation may be the mechanism

of sludge accumulation. As shown in Table 10, analysis of total

solids indicated that the partially packed reactor produced a

slightly more compact sludge. The absence of packing in the

bottom part of the partially packed reactor may have producedmore dense sludge, which may have provided additional filtration

capability. Analysis of total solids using a Student t test with a 95%confidence interval indicated no statistically significant difference

between the two reactors. However, analysis found iron concen

trations to be significantly higher in the sludge in the partiallypacked reactor.

Conclusions

Compared to a UASB reactor, an upflow anaerobic filter reactor

was superior for treating water contaminated with heavy metals.

The filter reactor, unlike the UASB reactor, worked well as a

90 M . I I | I I I | I I I I |M . I | I IM | I I . I | , , I I |M I I |M I I , . I I |M I I | . , I , | I I I | IH

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Time,days

Figure 5?Total metals remaining in the completelypacked filter.

120 M I I I |M I I | I I I I | I I I | I IM | I I I | I I I I | , I I I | , I I | I I I , | I , | I I I I | , I , , | ,||

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Time, days

Figure 6?Total metals remaining in the partially packedfilter.

clarifier, and all metals, except manganese, were reduced to a

concentration close to drinking water standards. Sludge with

drawal from the bottom of the filter reactor can be used to remove

accumulating metal precipitates and biomass, and therefore, the

reactor can be operated continuously. Sludge levels can be con

trolled in the filter reactors using a mass balance for metals that

compares feed to effluents, including sludge withdrawal and liquideffluent. Among the two configurations of filter reactors, the par

tially packed reactor was more effective because it produced an

effluent with smaller metal concentrations.

AcknowledgmentsCredits. The U.S. Environmental Protection Agency (U.S.

EPA) through its Office of Research and Development funded and

managed the research described here under Cooperative Agreement CR-821029 to Makram Suidan. This paper has not been

subjected to an agency review and therefore does not necessarily

reflect the views of the U.S. EPA. No official endorsement should

be inferred.

Authors. Vicki Steed is a researcher with Battelle Memorial

Institute, Columbus, Ohio. At the time the research was performed,she was a research assistant at the University of Cincinnati, Cin

cinnati, Ohio. Makram Suidan is Professor of Environmental En

gineering, Department of Civil and Environmental Engineering,

University of Cincinnati. Munish Gupta is with Parsons Engineer

ing Sciences, Atlanta, Georgia. At the time the research was

performed, he was a research associate at the University of Cin

Table 7?Comparison of filtered liquid effluent concen

trations for the two filter reactors to influent.

Concentration, mg/L

Completely PartiallyComponent Influent packed packed

Chemical

oxygendemand 3500 85.2 ? 23.1 83.7 ? 22.6

Acetic acid 3000 46.9 ? 26.7 14.9?

2.7Sulfate 5000 1148 ?364 1155 ?317Sulfide 0 156.7 ? 20.2 180.0 ? 18.7




_Steedet al.

Table 8? Comparison of total liquid effluent metal con

centrations for the two filter reactors to influent.

Concentration, mg/L

Component InfluentCompletely

packed

Partiallypacked

Iron

Zinc

Manganese

CopperTotal

840650275127

1894

1.28 ?0.36

0.927 ? 0.229

8.06 ? 1.77

0.036 ? 0.021

10.32 ? 1.49

0.343 ?0.18

0.205 ?0.176

6.99 ? 1.13

0.024 ?0.018

7.60 ? 1.94

cinnati. Takashi Miyahara is assistant professor, Department of

Civil Engineering, Tohoku University, Sendai, Japan. At the time

the research was performed, he was a visiting scientist at the

University of Cincinnati. Carolyn Acheson and Gregory D. Saylesare with the U.S. EPA National Risk

ManagementResearch Lab

oratory, in Cincinnati. Correspondence should be addressed to

Makram T. Suidan, Department of Civil and Environmental En

gineering, University of Cincinnati, Cincinnati, OH 45221-0071.

Submitted for publication November 18, 1997; revised manu

script submitted September 7, 1999; accepted for publication April

27, 2000.

The deadline to submit Discussions of this paper is January 15,

2001.

Table 9?Comparison of effluent metal concentrationsfrom the partially packed filter reactor to drinking water

standards (Pontius, 1996).

Concentration, mg/L

Component Total Soluble

Maximum

contaminant

level

Iron

Zinc

Manganese

Copper

0.343 ?0.18

0.205 ?0.176

6.99 ? 1.13

0.024 ? 0.018

0.097 ? 0.073

0.025 ? 0.023

6.66 ? 1.68

0.017 ?0.015

0.30

5.00

0.05

1.30

Table 10? Comparison of sludge concentrations for thetwo filter reactors.

Concentration, g/L

Completely PartiallyComponent packed packed

Total solids 24.2 ? 5.2 27.8 ? 10.6

Iron 5.07 ?0.87 5.76 ?1.24

Zinc 3.49 ? 0.71 3.54 ? 0.62

Manganese 0.96 ? 0.22 0.98 ? 0.22

Copper 0.61 ?0.10 0.61 ?0.17

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Examination of Water and Wastewater. 19th Ed., Washington, D.C.

Barton, L.L. (Ed.) (1995) Sulfate-Reducing Bacteria. Plenum Press, New

York.

Davis, A., and Ashenberg, D. (1989) The Aqueous Geochemistry of the

Berkeley Pit, Butte, Montana, U.S.A. Appl. Geochem., 4, 23.

Dvorak, D.H.; Hedin, R.S.; Edenbom, H.M.; and Mclntire, P.E. (1992)Treatment of Metal-Contaminated Water Using Sulfate Reduction:

Results from Pilot-Scale Reactors. Biotech. Bioeng., 40, 609.

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Situ Bacterial Treatment of AMD inOpen

Pits. 2nd Intl.Conf.Abatement Acidic Drainage, Montreal, Canada.

Lide, D.R. (Ed.) (1991) CRC Handbook of Chemistry and Physics. 71st

Ed., CRC Press, Boca Raton, Fla.

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