Available at www.sciencedirect.com

.els

ind

Ram Prasad, Gary C. Schafran

a r t i c l e i n f o

Article history:

Received 10 August 2004

Received in revised form

26 October 2005

Accepted 11 November 2005

Available online 6 January 2006

the full-scale plant and may be associated with polymer carry through.

oceangoing vessels estimated to use TBT-containing paints

us in

and

and

t al.,

Concern about the presence of TBT in the environment has

ARTICLE IN PRESS

WAT E R R E S E A R C H 40 ( 2006 ) 453 462Corresponding author. Tel.: +1 757 683 3753; fax: +1 757683 5354.(de Mora, 1996; Champ and Seligman, 1996). As an anti-

fouling agent, it inhibits the settlement and attachment of

marine organisms (e.g. barnacles) to ship hulls by continu-

ously releasing the paint into the surrounding water. It is

grown over the past three decades due to its known

toxicological characteristics. To date, TBT has been the

subject of over 400 studies of its occurrence and the negative

health impacts on various marine organisms associated with

0043-1354/$ - see front matter & 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.watres.2005.11.024

E-mail addresses: rampa_mys@yahoo.com (R. Prasad), gschafra@odu.edu (G.C. Schafran).(biocide) in marine paints applied to ship hulls for more than

30 years. Its use has been widespread with up to 70% of 2004).1. Introduction

Tributyltin (TBT) has been used as an anti-fouling agent

widely present in marine coastal systems and ubiquito

the water column and sediments in regions near ports

shipping activities (Kram et al., 1989; Quevauviller

Donard, 1990; Dowson et al., 1992; Hoch, 2001; Wade e& 2005 Elsevier Ltd. All rights reserved.Keywords:

Tributyltin (TBT)

Coagulation

Treatment

Granular activated carbonent, Old Dominion University, Norfolk, VA 23529, USA

A B S T R A C T

Characterization and treatment studies were conducted in an effort to evaluate treatment

options capable of removing tributyltin (TBT) in shipyard waters from above 1,000,000ng/L

to effluent concentrations below 50ng/L. Laboratory studies and operation of a full-scale

treatment plant were used to examine treatment options for TBT removal and included

physicochemical treatment processes of coagulation-clarification, filtration, and granular

activated carbon (GAC) adsorption.

Significant variability was observed in TBT-containing shipyard waters (generated from

different ships) in terms of their particulate solids, conductivity, and TBT and dissolved

organic carbon concentrations. Laboratory tests with aluminum sulfate and ferric sulfate

showed that on average 90% of TBT in shipyard waters could be removed by coagulation-

flocculation-clarification under optimum conditions. No statistically significant difference

was found in TBT removal capabilities between the two metal salts when compared at

equivalent metal doses and coagulation pH. Much lower removals were observed for the

coagulation-flocculation-clarification portion of the full-scale plant while the complete

full-scale treatment plant averaged 99.8% TBT removal over a period of 3 years. While

relatively high % removals were achieved, the total treatment process did not consistently

remove TBT to levels that wouldmeet the regulatory requirements proposed (50ng/L) at the

time the study was conducted. Based on the results from limited efforts to characterize the

dissolved and particulate TBT fractions in the full-scale treatment plant effluent,

particulate TBT was observed to be the dominant component of the effluent TBT fromCivil and Environmental Engineering Departmjournal homepage: www

Characterization of tributyltinremoval through laboratory anevier.com/locate/watres

shipyard waters andfull-scale treatment

and high concentrations of organic particulate material. The

ability to degrade TBT by ultraviolet (UV) photolysis using a

ARTICLE IN PRESS

0 (its presence in the aquatic environment (Alden et al., 1996). In

situ and ex situ studies have been conducted in many waters

and under various conditions and consistent observations of

growth inhibition and interference with organism reproduc-

tion have been reported (Hoch, 2001). Recent studies have

shown that TBT is a potent endocrine disruptor for lower level

organisms while it has been observed to be a dopamine

inhibitor in mammals (Kim et al., 2002). Lower level organ-

isms typically have shown impairment at concentrations as

low as 1ngTBT/L while higher-level organisms show health

impairment at concentrations as low as 1mgTBT/L (Hoch,

2001). The ability to cause imposex in molluscs at concentra-

tions in water of 1ngTBT/L has been reported repeatedly

(IPCS, 1999 (TBTO)) and particularly illustrates the potential

consequence of TBT being present in the aquatic environ-

ment.

TBT is an organometallic molecule that exhibits character-

istics of both its organic and metallic moiety and these

characteristics influence its fate in the environment. The

molecule carries a monovalent charge in the absence of

complexation with an anionic ligand and exhibits pH-

dependent solubility with minimum solubility at approxi-

mately pH 7 (Inaba et al., 1995). It has a high affinity for

organic matter and strongly partitions to the surface of

particulate matter present in water (Unger et al., 1988; Harris

et al., 1996). Because of these characteristics, its presence in

dissolved form in water is generally thought to be brief and it

has been observed to accumulate in sediments (Watanabe et

al., 1995; Langston and Pope, 1995).

National governments and regulatory agencies have moved

to limit or ban the release of TBTwhere the need for aquatic

life protection has been indicated. A number of governments

have instituted outright bans on the use of TBT-containing

paints while others such as the US have instituted a ban on its

use on vessels under 25m in length. Within the US, the

Commonwealth of Virginia was the first state-level govern-

ment to impose controls on its release by instituting a limit on

water discharges of 50ngTBT/L under the state-administered

National Pollutant Discharge Elimination System (NPDES)

permit. The imposition of this limit prompted Virginia

shipyards, beginning in the mid-1990s, to examine options

to reduce TBT in shipyard discharges to less than 50ngTBT/L.

Activities in shipyards, primarily ship repair/maintenance

activities, can produce TBT-containing water in several ways.

When a ship is placed in dry dock, washing the hull to remove

any attached organisms/slime layer is conducted so that the

condition of the hull paint can be inspected. Water generated

by this lower pressure cleaning is referred to as washwater in

this paper. After cleaning and inspection, if the hull is to be

painted, hydroblasting (high-pressure water spray) is often

used to remove either the surface paint coating or remove all

the paint layers to bare metal. Hydroblasting pressures can

range from 1000 lb in2 (7MPa) to approximately 30,000 lb in2

(210MPa) but were not recorded in this study. Volumes of

water generated depend on the size of the ship and the

amount of hull work to be conducted but well over a million

liters of water can be generated by these operations on large

(300-m long) vessels. In addition, any precipitation that falls

WAT E R R E S E A R CH 4454at any point during the time when a ship with TBT-paint is in

dry dock produces TBT-containing water. TBT-containingmercury lamp was examined and confirmed by Fletcher and

Lewis (1999) in a laboratory study where synthetic and dry

dock samples were treated with a low output UV light. They

observed solution pH, turbidity, organic matter content, and

composition of the anti-fouling paint as important variables

affecting removal.

In the study reported here, characterization of shipyard

TBT-containing waters, bench-scale coagulation studies, and

evaluation of TBT removal with a full-scale process train

consisting of coagulation-flocculation-clarification, filtration

and granular activated carbon (GAC) are presented. The

studies reported here were conducted to characterize the

composition of TBT-containing shipyard waters collected

from different shipyards and different regions, to evaluate

in bench-scale studies the effectiveness of a ferric salt and

alum, and to evaluate the long-term performance (ability to

meet a 50ng/L discharge standard) of a full-scale treatment

plant used to treat all TBT-containing waters discharged from

Virginia shipyards during the course of this study.

2. Materials and methods

In Phase 1 of the study, waters from a number of ships at

various shipyards were collected and analyzed. The TBT-

containing waters were collected in one or two 20-L poly-

ethylene containers from shipyards in southeastern Virginia,

the Gulf Coast, and the Pacific Northwest during this effort

from November 1999 through June 2000.

Samples generated in Virginia were packed in ice and

returned to the laboratory within a few hours of sample

collection. For samples collected outside of the region, they

were returned on ice by overnight mail for analysis at Old

Dominion University. In addition to the water samples

generated from ship hull washing or paint removal, one

sample was generated from washing down a steel plate that

had been freshly painted and then dried for 3 days before

washing. Total and dissolved (determined following filtra-water can also be generated in smaller volumes (o100,000L)at shipyards through replacement of water inside certain

hull-mounted radar domes. Additional details on the genera-

tion of TBT-containing water at shipyards can be found

elsewhere (Schafran et al., 2003).

The promulgation of an effluent TBT discharge standard in

Virginia prompted the studies reported in this paper. While

considerable research has been conducted on occurrence and

health effects of TBT, little has been published on treatment

processes to remove TBT from solution (Messing et al., 1997).

Argamen et al. (1984) and Fent and Muller (1991) examined

TBT in domestic wastewater and observed that 8090% in

untreated wastewater was associated with particulate matter

and was removed when the particulate material was retained

during treatment. Donard et al. (1993) and Fent (1996)

confirmed the findings of Fent and Muller but all of these

studies examined low TBT concentrations (o 200ngTBT/L)

2006 ) 453 462tion with a 0.45mm polycarbonate filter) fractions of TBT

were determined, as well as total suspended solids (TSS),

ARTICLE IN PRESS

0 (conductivity, pH, and dissolved organic matter measured as

dissolved organic carbon (DOC).

The Phase I waters used for characterization were also

utilized for laboratory-scale treatment evaluation that in-

cluded coagulation. Since most TBT-containing shipyard

waters contain high concentrations of suspended solids and

TBT has a propensity for partitioning to particles, efforts to

remove particulate matter were determined to be essential

for high levels of TBT removal. Removal of dissolved TBTwas

targeted to occur primarily on GAC, since it was observed that

TBT had a high affinity for this material based on preliminary

testing. In this paper, TBT removal on GAC is presented only

for the full-scale treatment process. Laboratory observations

of TBT removal by GAC and destruction by advanced

oxidation process studies will be presented elsewhere.

Two coagulants were utilized during the laboratory coagu-

lation studies to assess the removal of TBT; commodity-grade

alum (Al2(SO4)3 14H2O, 58gAl/L, General Chemical) and ferricsulfate (Fe2(SO4)3, 190 gFe/L, Midland Resources). Both coagu-

lants were used as received and without dilution before

addition to wash water during the coagulation studies. Prior

to conducting a jar test for each water, portions of the sample

were poured out and dosed at the desired coagulant doses

and then subsequently titrated with base to the desired pH

values (pH 5.510.0) for subsequent coagulation evaluations

(i.e. jar tests). This procedure was followed so that the

amount of base needed to obtain a target coagulation pH

could be determined. Following the base dose requirement

determination, a 2-L aliquot of sample was poured into a

square beaker (gator jar) and placed on a gang stirrer (Phipps

and Bird) where mixing was begun. The previously deter-

mined base dose was then added and allowed to mix for

several seconds and then followed by coagulant addition.

Coagulant doses for alum ranged from 22 to 242mg/L as alum

and for ferric sulfate 15164mg/L as ferric sulfate and were

based on preliminary treatment of shipyard waters prior to

this study. Rapid mixing was conducted at 200 rpm for 2min

followed by slow mixing (simulating flocculation) for 20min

at 20 rpm. While it is common to conduct multiple coagulant

tests simultaneously with a gang stirrer, in this study only

one sample at a time was treated. This procedure allowed for

continuous monitoring of the solution pH during each test

and allowed for small additions of acid (0.01N HCl) or base

(0.01N NaOH) as needed to maintain the target pH. Following

the 20-min slow mixing period, mixing was stopped and the

flocculated suspension was allowed to settle for 3h. A 500mL

sample was then removed from each jar and analyzed for

TBT, turbidity, and DOC.

A laboratory study involving coagulant aids (i.e. organic

polymers) to evaluate the potential affinity of TBT for these

molecules was also conducted. Five polymers (one cationic,

three anionic, and one non-ionic) acquired from a single

manufacturer were used in a modified jar test to evaluate

whether TBTpolymer interactions occur and whether a

polymer migrating through the treatment process train could

cause TBT to similarly carry through the process train. A

single TBT solution made to a dose of 2400ng/L was divided

into 2-L solutions and dosed with polymer at 1mg/L as

WATER RESEARCH 4product with one jar serving as a control (no polymer

addition). Sample aliquots were removed from each jar withone being filtered through a 0.45mm polycarbonate filter and

the other aliquot unfiltered. The polymers used in coagulation

were all large (long-chain, high molecular weight) molecules

capable of being substantially removed through filtration with

a 0.45mm membrane filter. Consequently, if polymer-treated

waters exhibited low concentrations of TBT after filtration, it

was deemed to be the result of removal of the polymer and

associated TBT.

A major component of this research effort was the

demonstration of TBT removal using a full-scale treatment

plant that was mounted on a barge and transported among

the shipyards as needed to provide treatment of TBT-contain-

ing waters. The treatment plant was designed and con-

structed for this study with a capability of treating water at

380L/min but was operated during the study at 190225L/

min. The treatment process train consisted of rapid mix and

flocculation units followed by a dissolved air flotation (DAF)

tank for clarification and a sand filter and two activated

carbon columns (GAC1 and GAC2) operated in series. Coagu-

lation was studied using alum for a limited period of time and

ferric sulfate the majority of the time. Hydrated lime was

added in the rapid mix tank with the coagulant while an

organic polymer was added at the entrance to the flocculation

tank to promote floc development. Retention times in the

treatment plant were approximately 2min in the rapid mix

tank, 20min in flocculation, and 75min in the DAF tank based

on the theoretical hydraulic residence time calculations and

16min in the sand filter, GAC1 and GAC2 based on tracer

study results at 190 L/min. Water passing through the full-

scale treatment plant was typically coagulated at higher pH

values (between 9 and 10) based on optimizing particle

removal in the DAF. During the early part of the study, the

water was applied to the filter and activated carbon columns

at this higher pH while after October 2000 the water was

acidified to pH 7 before passing through the sand filter and

the activated carbon columns. During all phases of the study,

a state-licensed wastewater treatment plant operator oper-

ated the full-scale plant in compliance with state discharge

permit requirements.

TBT sample concentrations varied by over six-orders of

magnitude in this study necessitating extreme care to prevent

cross-contamination of samples. A quality assurance protec-

tion plan (QAPP) and quality management plan (QMP) for the

study following EPA guidelines was developed at the begin-

ning of the study (Champ et al., 2000) and included standard

operating procedures for all aspects of sample collection,

handling, processing, analytical analyses, and data manage-

ment. All samples were collected in pre-cleaned polycarbo-

nate bottles since TBT has been shown not to adsorb to this

material (Unger, 1999). All sample containers were washed

with soap, methanol, and HCl and copiously rinsed with

dionized distilled water between each wash. Only new

sample containers were used for collection of samples from

the effluents of the first (GAC1) and second stage (GAC2) GAC

contactors as a precaution to prevent contamination. During

field sampling, samples collected from the influent, post-DAF,

and post-sand filter were placed in separate coolers on ice

from the samples collected after GAC1 and GAC2. This

2006) 453 462 455separation continued at the laboratory where separate cold

storage facilities (in separate rooms) were used prior to

sample analysis. Sample preparation prior to analysis also

occurred in these separate rooms prior to transporting the

samples to the analytical laboratory. After returning field

samples to the laboratory, the outside of the sample contain-

ers was washed with tap water and dried before opening.

Aliquots of sample were then removed for TSS, DOC, and

conductivity analysis, and then the samples were acidified to

pHo2 with trace metal grade HCl. Influent and post-DAFsamples were placed on a shaking table for 24h after

acidification to promote dissolution of particulate TBT.

After 24h of shaking, these samples were removed and an

aliquot of sample was filtered through a 0.45mm polycarbo-

nate filter and then saved for TBT analysis.

Use of field and trip blanks were incorporated into the study

and no incidents of contamination were detected during the

study. Analytical blanks and spike recoveries were examined

on a daily basis and any spike recovery outside of 720% was

cause for rejection of all analyses conducted on that date.

Similar care and procedures were exercised when handling

depending on the pH range of samples. Calibration was

conducted and Nernstian response (D5973mV/DpH) checked

daily.

Conductivity was measured with a YSI Model 35 conduc-

tance meter. The instrument was calibrated using Standard

KCl solution of 0.00100M (Clesceri et al., 1998; Method 2510B).

TSS measurements were conducted following SM 2540D

(Clesceri et al., 1998) with copious amounts of DI water used

to rinse the filter following sample filtration.

3. Results and discussion

3.1. Characterization of TBT-containing shipyard waters

Shipyard TBT-containing waters in the characterization and

laboratory treatment study (Phase I; 19992000) were ob-

served to be highly variable in TBT concentration spanning a

ARTICLE IN PRESS

stic

tivi

,300 7.6 696 21.5

610 6.5 2130 45.5

350

,00

,50

287

56

108

89

000

251

WAT E R R E S E A R CH 40 ( 2006 ) 453 462456untreated water and treated samples generated in the

laboratory (e.g. following coagulation studies). All samples

were acidified and held in cold storage (4 1C) prior to analysis.

TBTwas analyzed by the hydride generation-AAS detection

method of Hodge et al. (1979) using an atomic absorption

spectrophotometer (Buck Scientific Model 210 VGP) fitted with

a custom quartz burner. Standards were made by serial

dilution of stock solutions (all from Sigma-Aldrich) of TBT

chloride (TBT, 96%), dibutyltin dichloride (DBT, 96%), and MBT

(butyltin trichloride, 95%) to quantify organotin concentra-

tions. The analytical detection limit was determined to be

1243ng/L (mean 23ng/L). Analytical determination of DOCwas conducted using a high-temperature catalyzed oxidation

procedure (Clesceri et al., 1998; SM 5310B) with a Shimadzu

TOC 5000 with four standards bracketing the range of

samples. Turbidity was measured with a Monitek TA1

nephelometer calibrated daily. pH values were determined

with an Orion Model 520 pH meter with Ross electrode and

calibrated with pH 4 and 7 or 7 and 10 buffer solutions

Table 1 Phase I shipyard TBT-containing water characteri

Ship ID TBT (ng/L) Conduc

Total Dissolved

CV1Fa 1,150,000 n.a. 11

CV1Ha 1,440,000 n.a.

CV3a 1,830,000 12,900 1

CV4 53,400 5050 11

CV5 8290 740 18

CV6a 6,260,000 926,000

CV7 5500 330

CV8 41,200 390

CV9 39,400 160

CV10 20,900 3138 9

CV11b 28,700 9220

n.a.not analyzed.

a Hydroblast water; all others are washdown (lower pressure) waters.b Freshly painted steel plate.6.8 574 13.9

0 7.4 119 7.1

0 7.2 14 3.4

7.1 4340 24.8

7.2 17 3.0

7.3 540 10.2

7.3 1030 13.4

7.3 17 7.4

7.4 15 4.3range of less than 55006,260,000ngTBT/L (Table 1). Higher

TBT concentrations were observed in water generated

from hydroblast operations (median concentration 1.6106ngTBT/L) while TBT concentrations in wash water were

lower in comparison (median concentration 2.9105).Based on the limited observations presented here it appears

that elevated concentrations (41,000,000ngTBT/L) can occur

through the removal of TBT hull coatings particularly when a

minimum of water is used and dilution with other waters (e.g.

rain, non-contact cooling waters) is minimized or prevented.

The TBT in these waters was primarily associated with

particles as dissolved TBT averaged only 9.8% of total TBT.

This large proportion of TBT associated with particulate

material clearly illustrates the need for effective particle

removal to lower TBT concentrations in these waters. It also

illustrates the likelihood that the fate of previous TBT

discharges from these sources to waterways surrounding

shipyards was removal from the water column through

settling.

s

ty (m

A

) pH TSS (mg/L) DOC (mg/L)

Concentrations of organic matter (DOC) in these waters

were also variable ranging from 3.0mgC/L (only slightly

higher than the source potable water) to 45.5mgC/L). Elevated

concentrations of DOC can potentially impact treatment

since aqueous organic matter has been observed to complex

with TBT potentially making it more difficult to remove from

solution (OLoughlin et al., 2000). A distinct difference in the

concentration of DOC was observed between hydroblast-

generated waters (mean7s.d. 26.4713.5mgC/LDOC) andwashwaters (mean 7.474.0mgC/LDOC). A similar differ-ence between source waters was noted for TSS with higher

concentrations of TSS associated with hydroblast waters

4. Coagulation studies

The large proportion of TBT associated with particulate

material in TBT-containing shipyard waters necessitates a

high level of particle removal to achieve low TBT concentra-

tions before these waters can be discharged to a receiving

water. To determine the influence of coagulation conditions

on TBT removal, 10 of the 11 waters (Table 1) collected for the

Phase I characterization and laboratory treatability study

were coagulated under laboratory conditions and examined

for TBTremoval. In this effort, coagulant type, coagulant dose,

and coagulation pH value were the variables examined for

their influence on the removal of TBT. As noted previously,

coagulant doses for alum and ferric sulfate ranged from 22 to

121mg/L and 15164mg/L (0.372.0104M as metal for each

ARTICLE IN PRESS

Fig. 2 Comparison of TBT removal by ferric sulfate and

WATER RESEARCH 40 (2006) 453 462 457(1940mg/L) compared to wash waters (250mg/L).

The higher DOC concentrations in the hydroblast waters

are likely the result of solubilization of organic material from

the paint matrix (present in the water as fine particulate

material) after removal of the paint from the ship hulls. The

significance of higher DOC concentrations in waters with

higher TBT concentrations is that any treatment process that

employs a sorption process where both TBT and organic

matter both compete for the same surface sites will have

greater difficulty in achieving lower effluent TBT concentra-

tions. The interference of DOC in the sorption of TBT on GAC

has been clearly shown in batch isotherm studies (Unger and

Schafran, 2003) and similar interference would be expected in

a continuous flow process.

A greater number of TBT-containing water samples was

collected and analyzed during full-scale treatment efforts

over a 3-year period (December 1999 through November 2002)

and the samples collected during this effort can be used to

further characterize TBT-containing waters generated at

shipyards. During this effort, there were 136 days of treatment

in which a discharge occurred to a receiving water and 119

influent samples were analyzed. Influent concentrations

ranged from a low of 800 up to 1.3106ngTBT/L with meanand median values of 253,000 and 137,000ngTBT/L, respec-

tively. A number of the wash and hydroblast waters were co-

mingled before treatment so no attempt was made to

characterize concentrations by the water generation activity.

The distribution of concentrations for these waters is

illustrated in Fig. 1. Based on these influent concentrations

the treatment requirement to reach 50ng/L was observed to

vary between minimum and maximum values of 93.7% and

99.996%, respectively, with a median value of 99.96% TBT

removal required to reach 50ng/L.

0

0.2

0.4

0.6

0.8

1

1.2

100 1000 10000 100000 1000000 10000000

Frac

tion

of V

alue

s Le

ss th

an In

dica

ted

Conc

entra

tionInfluent Total TBT (ng TBT/L)

Fig. 1 Influent TBT distribution for the full-scale treatment.coagulant), while coagulation pH values ranged from 5.4 to

10.0. The influence of a coagulant aid (organic polymer) was

not examined in the laboratory studies, in part due to

limitation in the amount of water available for coagulation

studies.

A significant finding of the coagulation study was that there

was no statistically significant difference (paired Students t-

test, 95% confidence interval, p 0:4428, n 47) in TBTremoval when comparing alum and ferric sulfate treatment

under similar coagulation conditions (Fig. 2). Mean values for

TBTremoval were 87.1% and 86.8% for alum and ferric sulfate,

respectively, and most likely reflected removal of TBT

associated with particulate matter in these solutions. Mean

turbidity removal values of 96.0% and 95.0% for alum and

ferric sulfate indicate a higher level of particle removal than

TBT in these waters. These results likely reflect dissolved TBT

remaining in solution after coagulation and/or a greater

proportion of TBT associated with small colloidal material

remained than the particulate material removed via coagula-

tion. Overall, no statistically significant correlation between

TBT and turbidity removal was observed.

The influent characteristics of the waters treated in the

coagulation study were widely variant in terms of DOC

concentrations and conductivity (i.e. salinity) as well as

particulate matter and total and dissolved TBT (Table 1).

It was expected that DOC removal would increase with

40

50

60

70

80

90

100

40 50 60 70 80 90 100% TBT Removal with Alum

% T

BT R

emov

al w

ith F

erric

aluminum sulfate under comparable coagulation

conditions.

near the end of each treatment event is presented in terms of

ARTICLE IN PRESS

0 (increased coagulant dose and conditions that favored TBT

removal, since DOC is frequently removed to a significant

extent when natural waters are coagulated (Dempsey et al.,

1984). However, DOC removal from these waters was often

poor and under many conditions an increase in DOC was

detected following coagulation (not shown). These observa-

tions may reflect the formulation of the paints that are

designed to ablate (dissolve) and possibly that a significant

hydrophilic fraction of organic matter that is not well

removed by coagulation was present in these waters.

Solution conductivity in these waters exceeded two-orders

of magnitude and potentially might play a role in TBTremoval

since it can influence electrostatic conditions near the surface

of particles, the moiety of ionic organic compounds, and the

binding that can occur between TBT and natural organic

matter (OLoughlin et al., 2000). Examination of these para-

meters revealed no correlation between conductivity (sali-

nity) and TBT, DOC, or turbidity removal in the laboratory

coagulation studies.

Of particular interest in understanding the fate of TBT

during coagulation is whether dissolved TBT is removed

through interaction with the precipitate of the metal coagu-

lant formed during coagulation. Many dissolved organic

molecules can adsorb to or form surface complexes with

ferric and aluminum hydrous oxides and be removed from

solution by this mechanism (Pommerenk and Schafran, 2005).

To evaluate whether dissolved TBT could be removed via a

similar mechanism, a jar test study evaluating TBT removal

from a synthetic solution (100,000ng/L TBT, 40g/L NaCL) was

conducted using ferric sulfate at coagulant doses of

14326mg/L and at coagulation pH values of 6.5, 7.5, and

8.5. Removal of TBT was similar for pH 6.5 and 7.5

(mean 63% and 64% TBT removal, respectively) while TBTremoval did not occur at pH 8.5 (mean 5% TBT removal).These results indicate the importance of coagulation pH in

terms of removing dissolved TBT.

The lower removal of TBTat pH 8.5 may be related to effects

on the coagulant metal or the solubility of the TBT molecule

or a combination of the two. The net electrical surface charge

on the precipitated ferric hydrous oxide would be expected to

be near zero or slightly negative at pH 8.5 while at pH 6.5 and

7.5 the charge on the precipitate would be positive (Dzombak

and Morel, 1990). This condition suggests that the interaction

(sorption) between dissolved TBT and hydrous oxide is

favored when a hydrous metal oxide is positively charged.

The influence of the coagulation pH value on TBT removal

may also be related to the form of TBT present in solution.

TBT solubility has been reported to be minimum in the

neutral pH range (pH 68) at approximately 1mgTBT/L and

more soluble at lower and higher pH values (Inaba et al.,

1995). TBT solubility in solution has also been reported to be

negatively correlated to salinity (Inaba et al., 1995) but little

change occurred in total ionic composition under the

coagulation conditions examined here so it is expected that

variations in ionic strength had little influence on solubility.

Hydroxide complexes of TBT (TBTOH) can occur and

would be favored at higher pH values while at decreasing

pH values it would be expected that cationic TBT species

WAT E R R E S E A R CH 4458would become dominant. A similar influence of pH on the

sorbent surface charge would be observed with a positivelya probability distribution to illustrate the effectiveness of the

full-scale treatment plant in meeting the 50ng/L treatment

goal (Fig. 3). During the 136 days of treatment the o50ng/Lgoal was achieved 41% of the time and exceeded 59%. When

examined in terms of the level of treatment achieved the

treatment plant was able to treat consistently to greater than

90% TBT removal and achieved 99.9% TBT removal in more

than 75% of the time. There was no statistically significant

relationship observed between paired influent and effluent

TBT concentrations (Fig. 4) and there was generally a two-

orders of magnitude difference in TBT removal observed

across the range of influent concentrations treated. It is not

surprising that there is scatter in this relationship since thecharged surface at lower pH and negatively charged surface at

higher pH (Stumm, 1992). If ionic interaction is important in

TBTremoval, the change in speciation of both the sorbent and

the sorbing species may favor removal in a narrow pH range

where charges are opposite or where they are substantially

lowered allowing non-ionic forces to affect attraction be-

tween the TBT molecule and the sorbent surface. Hoch et al.

(2002) observed this narrow pH range effect for TBT adsorp-

tion with four mineralogically distinct clay-enriched sedi-

ments and postulated a zone of maximum adsorption in the

pH 67 due to favorable ionic charges between the soluble

species and the sorbent in this pH range.

5. TBT removal in the full-scale treatmentplant

The primary focus of the full-scale treatment study was to

determine whether a conventional treatment process train

that is present in many shipyards to treat waters containing

trace metals would be capable while operating in shipyards

under shipyard conditions of meeting the treatment

objective of o50ng/L TBT. The full-scale treatment plantwas operated in this study from December 1999 until

November 2002 treating TBT-containing waters typically

shortly after they were generated. During this effort a number

of operational and treatment conditions were evaluated

including dose and type of coagulant, coagulation pH, water

flow rate (and contact time in GAC contactor columns), use of

hydrogen peroxide, and use of powdered activated carbon

(PAC). While there were multiple treatment variables exam-

ined in this study, these conditions were varied over short

durations and the majority of the time the treatment plant

was operated using ferric sulfate (2872mg/L; mean 52mg/L) at a coagulation pH of 910, using a coagulant aid

(2.810.2mg/L; mean 7.5mg/L polymer), no PAC, no hydro-gen peroxide, and operated for a duration of less than 12h.

One significant change that was made in October 2000 was

the depression of pH from 910 to approximately 7 as water

exited the DAF unit entering the filter. This change was made

in an effort to improve TBT removal on the GAC columns

based on observations in batch laboratory studies (not

reported here).

The TBT concentrations measured in samples collected

2006 ) 453 462waters being treated varied greatly in composition (e.g.

2.136.9mgC/L DOC and 42020,400 m

A

/cm conductivity),

and the distribution between dissolved and particulate TBT

likely also varied.

If improvements are to be made in the removal of TBT from

these waters it is imperative to understand the fate of TBT in

the treatment process train. Toward this goal, samples were

collected on a number of occasions immediately following

each unit process and examined to determine the effective-

ness of each unit process in removing TBT. The results for one

period of treatment when the influent concentrations were in

the upper 20% of observed values during the study are

provided in Table 2. The first removal process in the treatment

process train is the DAF clarifier and during this period an

average of 46.1% TBT removal occurred within the DAF unit.

Since this process removes the majority of particulate

material contained in the influent water it is apparent that

a substantial amount of dissolved TBTor TBT associated with

fine particulate material is carried through this process. The

performance of the DAF clarifier was well below the removals

observed in the Phase I coagulation studies but this perfor-

mance is likely due to the optimal conditions and extended

settling time provided in laboratory jar tests (corresponding to

a loading rate of 0.033Mh1) versus the considerably higher

loading rate occurring in the DAF (1.7Mh1). Wave action on

the barge was also observed to periodically cause water in the

DAF to slosh back and forth and cause floating solids on the

surface to carry over. This may also have decreased the TBT

removal efficiency of the DAF.

concentrations in the GAC2 influent, a lower concentration

gradient, and a lower resultant mass flux to the GAC surface.

ARTICLE IN PRESS

0

0.2

0.4

0.6

0.8

1

1.2

1 10 100 1000 10000

Effluent TBT (ng/L)

Frac

tion

of V

alue

s Le

ss th

an

Indi

cate

d Co

ncen

tratio

n

50

Fig. 3 Effluent TBT concentrations from the full-scale

treatment plant measured for regulatory

compliance.

100

1000

10000

BT (n

g/L)

99% Removal 99.9% Removal99.99% Removal

erc

WATER RESEARCH 40 (2006) 453 462 4591

10

100 1000 10000 100000 1000000 10000000

Influent TBT (ng/L)

Efflu

ent T

Fig. 4 Relationship between influent and effluent TBT

concentrations for the full-scale treatment plant.

Table 2 Summary statistics for TBT concentrations and p30December 7, 2000 Period

Influent DAF effluent

Mean conc. (ng/L) 514,500 277,167

Median conc. (ng/L) 405,000 235,000

% Removal based on mean N/A 46.1

% Removal based on median N/A 42.0N/Anot applicable.It was suspected that the TBT in the influent to GAC2 may

also include a fraction of TBT not as amenable to removal as

the TBT entering the GAC1 column and that this TBT fraction

carried through to the effluent. The passage of particulate

TBT through the TBT treatment plant and the GAC2 contactor

column was suspected and efforts to investigate this source

issue are described below.

6. Fractionation of TBT in the full-scaletreatment plant effluent

TSS concentrations were monitored in the effluent of the full-

scale treatment plant under requirements of the discharge

permit and were measured for the 136 days of full-scale

treatment (effluent requirement was o60mg/L TSS). The TSSconcentration in the effluent ranged from less than 1mg/L up

to a maximum of 30mg/L with a median value of 2.3mg/L.

While the potential of particulate TBT to contribute to the

final effluent exists, a regression analysis of effluent TBT

and TSS concentrations showed there was no statistically

ent removal by individual unit process for the November

Sand filter effluent GAC1 effluent GAC2 effluent

257,000 1420 368

190,000 428 262

3.9 99.40 74.1

11.1 99.80 38.80The sand filter was capable of removing additional TBT of

3.9% (mean for the period) with this removal likely represent-

ing retention of TBT associated with fine particulate matter.

The GAC1 contactor provided the highest level of TBTremoval

in the treatment process train removing over 99% of the TBT

contained in the influent to the GAC1 column. This removal is

most likely related to the removal of dissolved TBT though

additional fine particulate TBT may also be removed at this

stage. The GAC2 contactor column removed 74.1% (mean) of

the TBT entering the column but on average only 0.4% (1050

vs. 256,000ng/L) of the amount of TBT removed by the GAC1

column. This low removal of TBT in the GAC2 column was

observed throughout the study and is consistent with low

through the DAF, sand filter, and two carbon contactors in

tion with TBT, it is clear that TBT can associate (e.g. sorb,

ing TBT generated at shipyards illustrates that TBT concen-

trations vary widely (total TBT concentrations between 5500

and 6,260,000ngTBT/L and that TBT concentrations are

dominated by the particulate fraction. Dissolved organic

matter and solution conductivity also were observed to vary

dramatically, which can potentially impact TBT removal via

various treatment processes.

Both ferric sulfate and aluminum sulfate (alum) were used

in coagulation studies of TBTremoval and both were observed

capable of substantial particulate solids and TBT removal.

When compared at comparable coagulation conditions (coa-

gulation pH andmolar metal dose) no significant difference in

treatment was observed between the two coagulants.

Treatment of shipyard TBT-containing waters with the full-

scale treatment plant demonstrated that TBT concentrations

could be lowered by typically over three-orders of magnitude

(99.9%). The DAF and GAC1 were the primary sites of removal

with the DAF unit removing primarily particulate TBT and

ARTICLE IN PRESS

0 (series. Consistent with these observations were those re-

ported by Rowland et al. (2000) and de Rosemond and Liber

(2004) where toxicity in the effluent of municipal and

industrial wastewater treatment processes was observed

and attributed to the passage of polymers, added during the

treatment process, through to the final effluent.

A brief study to discern whether it was possible for TBT to

associate with (e.g. sorb, complex) organic polymers was

conducted by evaluating five different polymers made up in

separate solutions and exposed to a concentration of 2400ng/

L TBT. Both filtered and unfiltered aliquots were analyzed

from each solution to assess whether TBT interacted with the

polymer used in each solution. The TBT concentrations in

unfiltered aliquots taken from the control (no polymer) and

all waters dosed with polymer were similar in TBT concen-

tration indicating that the presence of the polymer in solution

did not inhibit the analytical determination of TBT (Fig. 5).

The filtered control sample was slightly lower (8.5%) than the

unfiltered control and within the analytical uncertainty of the

method. The filtered aliquots of the polymer-treated waters

were all substantially lower than the unfiltered aliquots

(2791% lower) indicating that the polymer removed during

filtration was clearly also causing the removal of TBT. Thesignificant relationship, indicating that TSS cannot be used as

a surrogate indicator of TBT concentrations.

To determine to what extent TBT concentrations in the

effluent could be associated with particulate matter, samples

collected from the effluent of the full-scale plant during the

first 2 weeks of November 2000 were analyzed for both total

and dissolved TBT (n 10). Effluent total TBT concentrationsranged from 67 to 1470ng/L, dissolved TBT concentrations

ranged from 52 to 276ng/L and total TBT removals across the

treatment plant ranged from a minimum of 99.7% to a

maximum of 99.97% (median removal 99.88%). During theperiod of study particulate TBTwas consistently observed to

be the dominant fraction in the effluent. Particulate TBT

represented 090% of the total TBT concentration during this

period with mean and median values of 63% and 73%. TSS

concentrations during this effort ranged from 2 to 24mg/L

(median 4mg/L) and exhibited no trend with regard toparticulate TBT concentrations. The results indicate that a

significant proportion of the TBT in the final effluent of the

full-scale treatment plant was associated with particulate

matter, but also that TSS does not correlate well with the

particulate TBT fraction.

7. Polymer carry-through

The possibility that polymer added during the coagulation

process could potentially influence the movement of TBT

through the treatment process train to the final effluent was

investigated following a short study where a microfiltration

membrane (0.1mm) was used to treat effluent from the full-

scale treatment plant. The membrane repeatedly fouled over

a short period of time (days) and upon visual examination

appeared to be coated with polymer and iron that had passed

WAT E R R E S E A R CH 4460non-ionic polymer showed the lowest polymer-effect on TBT

removal but, because of the few polymer types examined,complex) with the polymer and that passage of polymer

through the treatment process train may cause TBT to also

pass through the process train. Because the polymerTBT

molecule can be filtered out with a 0.45mm filter, it is possible

that some of the particulate TBT determined in the

November 2000 fractionation effort may have been polymer-

associated TBT.

Analysis of the test polymers found one polymer to contain

TBT at a concentration of 120ngTBT/mg polymer; this

polymer was excluded from these experiments. This un-

expected finding suggests a possible external source of TBT to

the treatment process train but analysis of the polymer used

in the full-scale treatment plant confirmed it to be TBT-free.

8. Conclusions

The analysis of wash waters and hydroblast waters contain-there is insufficient information to conclude the influence on

TBT removal by a particular polymer type. Regardless of

whether a particular polymer type shows a greater associa-

0

500

1000

1500

2000

2500

Control Anionic E-42

Nonionic E-30

Cationic ZE 7873

Magnafloc-1011

(Anionic)

Selfloc-2250

(Anionic)

TBT

(ng/L)

UnfilteredFiltered

Fig. 5 Fate of TBT in solutions dosed with organic polymer.

2006 ) 453 462GAC1 removing what would be expected to be primarily

dissolved TBT. The final effluent from the full-scale treatment

mine effluent. Environmental Toxicology and Chemistry 23,22342242.

in Natural Systems. Wiley, New York, p. 428.

ARTICLE IN PRESS

0 (Donard, O.F.X., Quevauviller, P., Bruchet, A., 1993. Tin andorganotin speciation during wastewater and sludge treat-ment processes. Water Res. 27 (6), 10851089.

Dowson, P.H., Bubb, J.M., Lester, J.N., 1992. Organotin distributionin sediments and waters of selected east coast estuaries in theUK. Mar. Pollut. Bull. 24 (10), 492498.

Dzombak, D.A., Morel, F.M.M., 1990. Surface ComplexationModeling: Hydrous Ferric Oxide. Wiley, New York.plant exceeded the o50ng/L treatment goal 59% of the timeand may in part be due to fine, particulate TBT passing

through the treatment system. Evidence of organic polymers

being able to interact with TBT in a manner that could cause

carry through in the treatment system was observed in

laboratory studies.

Acknowledgements

Funding for portions of the work presented in this paper has

been provided through the USEPA, Virginia Department of

Environmental Quality, the Maritime Administration, Na-

tional Shipbuilding Research Program (NSRP), and the Virginia

Center for Innovative Technology. We wish to thank the NSRP

SP-1 Environmental Panel for assisting with acquiring TBT-

containing shipyard waters for the characterization and

laboratory treatment efforts. We specifically acknowledge

the many and varied contributions of T. Fox, M.A. Champ, T.

Tekleab, M. Unger, S. Tanaka, A. Diaz, J. Hirschman, A. Quick,

R. Sherman, P. Ford, K. Ogburn, F. Thorn, J. Soles, M. Ewing, F.

Wheatley, J. Bingham, and A. Rainsberger with this project.

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ARTICLE IN PRESS

WAT E R R E S E A R CH 40 ( 2006 ) 453 462462

Characterization of tributyltin in shipyard waters and removal through laboratory and full-scale treatmentIntroductionMaterials and methodsResults and discussionCharacterization of TBT-containing shipyard waters

Coagulation studiesTBT removal in the full-scale treatment plantFractionation of TBT in the full-scale treatment plant effluentPolymer carry-throughConclusionsAcknowledgementsReferences