Paper No. 2005-D09 Tamburri 1

Evaluations of a Ballast Water Treatment to Stop Invasive Species and

Tank Corrosion

Mario N. Tamburri, (V) Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science

Gregory M. Ruiz, (V) Smithsonian Environmental Research Center

ABSTRACT

Invasive species are one of the most destructive environmental problems facing the world today. They can alter

habitats, cause local extinction of native species, and have enormous economic impacts. Because ballast water is the

primary source of aquatic invasions, the International Maritime Organization has recently passed regulations that will

require ocean-going vessels to treat water prior to discharge. It has proven challenging, however, to find an

environmentally friendly treatment that is effective at reducing the potential for invasions and yet also acceptable to

the shipping industry in terms of safety, time and cost. Our work has focused on evaluations of deoxygenation in

general, and Venturi Oxygen Stripping in particular, because of its ability to kill ballast water organisms and to

reduce ballast tank corrosion. Results to date suggest that this approach has the potential to be an effective ballast

water treatment option.

KEY WORDS: Ballast Water Treatment; Invasive Species;

Deoxygenation; Corrosion.

INTRODUCTION

Statement of Problem and Prospectus – Invasions by

non-native aquatic species are increasingly common worldwide

in coastal habitats (Ruiz et al. 2002a,b) and it is widely accepted

that ballast water is the most important vector responsible for

transporting and introducing non-native species to new

biogeographic regions (Carlton and Geller 1993; Cohen and

Carlton 1998). It has proven challenging, however, to find an

environmentally friendly ballast water treatment that is effective

at reducing the potential for introductions and yet also

acceptable to the shipping industry in terms of safety, time, cost,

and space requirements. For instance, the offshore exchange of

ballast water is currently mandated by U.S. Coast Guard (and

other jurisdictions) to reduce introductions, since coastal

organisms are unlikely to invade open ocean areas, and vice

versa. However, the process can be time-consuming (thus

costly), cannot be performed in rough sea conditions, is not

appropriate for some shipping routes that do not travel far

enough offshore, and has limited effectiveness in some

environments and for certain vessel designs (e.g., Cooper et al.

2002; Ruiz et al. in prep.). Because of these reasons, exchange

is considered an interim solution that will likely be phased out

over the next several years as regulations requiring treatment are

implemented.

In the past, the development or identification of feasible and

effective ballast water treatments had been hindered in part by

the lack of accepted standards. However, the International

Maritime Organization (IMO) has recently (February 13, 2004)

adopted the Convention for the Control and Management of

Ships' Ballast Water that includes ballast water standards. The

U.S. Coast Guard and legislative efforts have also made strides

towards regulations that will provide standards for technology

performance to be measured against. However, for any ballast

water management strategy to be successful, the shipping

industry must be able to comply (e.g., non-conflicting with other

regulations such as those designed for crew, vessel, and

environmental safety) and compliance must be measurable.

With the recent progress of promising treatments, the shipping

industry does appear prepared to adopt technologies that are safe

and effective.

Our work indicates that deoxygenation might be such a

treatment, with an added benefit of reductions in ballast tank

corrosion rates (Tamburri et al. 2002; Tamburri et al. 2003). We

have taken a phased approach in the evaluation of

deoxygenation as a treatment to prevent the transport on nonnative species in ballast water and are now at the stage of fieldtesting of a prototype system during normal vessel operations.

The following is a summary of our work to date and our

presentation will focus in particular on results of our ongoing

evaluations onboard the active oceangoing vessels.

PHASE I: PROOF-OF-CONCEPT STUDIES

The vast majority of the world’s ships are constructed of

carbon steel, which corrodes rapidly when exposed to oxygen

and water. The cost to prevent, maintain, and repair corrosion

on individual vessels typically runs into the millions of dollars

and for the entire U.S. marine shipping industry it is estimate at

$2.7 billion annually (Koch et al., 2001). Ballast tank corrosion

in particular is considered to be the most important factor

leading to age related structural degradation of ships (Paik et al.

2003).

In a study completed in 1998, Sumitomo Heavy Industries

found that deoxygenating ballast waters (purging with nitrogen
Paper No. 2005-D09 Tamburri 2

gas to drop oxygen levels to approximately 0.2 mg/l) decreases

the rate of uniform corrosion by 90% and represents a

significant savings for ship owners when compared to other

corrosion prevention approaches currently available

(approximately $80,000/year/vessel saved when compared to

the standard painting and maintenance; Matsuda et al. 1999).

These results are supported by the anecdotal observations of the

Hellespont Group, who state that corrosion in ballast tanks on

their tankers has been “completely arrested” after the addition of

low-sulfur inert gasses, which produces hypoxic conditions.

Continuous hypoxia has also been suggested as a way to reduce

microbial induced corrosion in other marine applications, such

as pipe systems (Lutey 2001; Pope and Pope 2001).

To test whether deoxygenation may also limit invasion, we

carried out laboratory oxygen tolerance experiments on the

larvae of three widely introduced aquatic nuisance species

(Australian tubeworm Ficopomatus enigmaticus, European

zebra mussel Dreissena polymorpha, and European green crab

Carcinus meanas) using oxygen levels comparable to those in

the Sumitomo shipboard corrosion study (< 0.8 mg/l).

Significant levels of mortality were found in nitrogen treated

water after only two or three days (Tamburri et al. 2002). Two

separate literature reviews of oxygen tolerance for various

aquatic species further support the conclusion that few

organisms will be able to withstand extended periods of

exposure to deoxygenated ballast water. For example, by far the

most abundant animals found in ballast water are copepod

crustaceans (Carlton and Geller 1993; Smith et al. 1999) and

shallow water and estuarine species that are unable to withstand

24 hours of exposure to hypoxia (e.g., Roman et al., 1993; Lutz

et al. 1994; Stalder and Marcus 1997).

Small plant and algal parts (fragments, spores, and seeds) as

well as single-celled phytoplankton, protoctists, fungi, and

bacteria are also often transported in ballast water (e.g.,

Hallegraeff and Bolch 1991; Carlton and Geller 1993, Wonham

et al., 2000). These microscopic components of ballast water

have not been thoroughly characterized. However, it appears

from our reviews that their tolerances for low oxygen

environments will vary greatly. There are examples of species

that are very sensitive to hypoxic conditions (e.g., filamentous

fungi, Padgett et al. 1989; zoospores of the seaweed Undaria

pinnatifida, Mountfort et al. 1999), as well as counter-examples

of species that can withstand low oxygen levels (e.g., resistant

cysts of some dinoflagellates, Hallegraeff 1998). Marine

bacteria, in particular, will have dramatically different responses

to the conditions created by simply sparging with nitrogen.

While most obligate aerobic strains will be unable to grow over

extended periods of hypoxia, some facultative and obligate

anaerobic bacteria may actually thrive under the conditions

found in nitrogen treated ballast water. Our previous work

therefore concluded that ballast water deoxygenation alone

(sparging with nitrogen gas maintaining hypoxia as done by

Sumitomo) would likely be highly effective at reducing

introductions of aquatic animals (larvae, juveniles, and adults

stages) but may have mixed success at eliminating introductions

by members of other taxa.

PHASE II: MESOCOSM EXPERIMENTS

Based on initial results, we conducted further evaluations of

deoxygenation, focusing on a specially designed ballast water

treatment system called Venturi Oxygen Stripping (VOS), to

prevent the transport of aquatic species as well as ballast tank

corrosion. VOS was developed and patented by NEI Treatment

Systems, LLC, a U.S.-based environmental engineer firm. In

February 2003, we began our NOAA, Fish and Wildlife Service

and MARAD supported project as our second phase with three

specific goals:

1) Evaluate the abilities and potential of VOS as a ballast

water deoxygenation method,

2) Examine the impact of this oxygen stripping technique

on the immediate and long-term survival of natural

Chesapeake Bay planktonic organisms, and

3) Quantify corrosion rates and establish the corrosion

mechanism under VOS deoxygenated conditions (with

particular emphasis on microbiologically influenced

corrosion).

Optimizing deoxygenation – A key to the success of

deoxygenation as a ballast water treatment is to efficiently

maintain levels of oxygen in tanks that both kills the majority of

aquatic organisms while also reducing corrosion rates; between

0.2 and 1.0 mg/l. Several deoxygenation methods have been

proposed or tested, including nitrogen sparging (described

above), vacuums, horizontally placed diffuser plates, and

biological processes. These oxygen removal techniques vary in

degree of effectiveness (including time required until hypoxic

ballast water is produced), associated costs, and logistic

constraints. However, a broad survey of options concluded that

VOS is currently the most efficient and feasible way to remove

oxygen from ballast water onboard vessels. Therefore,

beginning in 2003, our research into deoxygenation to prevent

aquatic invasions and ballast tanks corrosion has focused on

VOS.

VOS is a rapid (< 10 seconds), in-line, single-pass system

that mixes inert gas directly into ballast water as it is drawn into

the vessel (Figure 1). The inert gas is produced by combusting

low-sulfur marine diesel (generating mostly nitrogen with small

amounts of carbon dioxide and only trace levels of oxygen) in a

device similar to the inert gas generators commonly used on

tankers. The gas is mixed with the ballast water using a venturi

injector manifold that is installed in-line, just down-stream of

the ballast pump. The venturi injectors create a micro-fine

bubble emulsion where dissolved oxygen quickly diffuses out of

the water into the gas. Because adding carbon dioxide in

solution forms both carbonic and carboxylic acid, the pH of

treated water is also reduced to between 5.5 and 6. This system

is designed so that the same inert gas is also used to blanket all

headspaces and the entire ballast tank when empty to maintain

permanent hypoxia. Continuously maintaining a deoxygenated

environment in ballast tanks appears to be a critical factor for

corrosion prevention (Pope and Pope 2001; Lee et al. 2005).
Paper No. 2005-D09 Tamburri 3

Figure 1. Basic schematic of the VOS system onboard a vessel.

Survivorship of natural planktonic organisms – The

mortality rates of planktonic organisms produced by VOS are

higher than predicted for our laboratory scale nitrogen sparging

experiments and published literature on the oxygen tolerances of

aquatic organisms (Tamburri et al. 2003). Although it is clear

that the hypoxic conditions alone are toxic to the majority of

planktonic organisms, it was the combination of reduced oxygen

levels (between 0.2 and 1.0 mg/l), CO2 saturation with lowered

pH (between 5.5 and 6.0), and mechanical disruption as

organisms pass through the venturi injector that is responsible

for the rapid removal of potential invaders. Therefore, VOS is

not simply a deoxygenation treatment but a single unit or

method that produces a combination treatment.

In dockside, mesocosm experiments at the Chesapeake

Biological Laboratory (CBL) in Solomons, MD, the dissolved

oxygen levels and pH in the untreated or control 94-liter tanks

were between 8.18 – 11.01 mg/l and 7.61 – 8.20 respectively.

The dissolved oxygen levels and pH in similar VOS treated

tanks dropped to 0.26 – 0.87 mg/l and 5.46 – 5.62 respectively.

These changes to the physical environment in the treated tanks

led to a greater than 99% mortality of natural zooplankton

(copepods, barnacle larvae, polychaete larvae, cladocerans,

rotifers, crustacean nauplii, bivalve larvae, and nematodes) in

less than 48 hours while the majority of zooplankton survived in

the control cylinders (> 50 % survival even after 96 hours

holding time). In other words, after 48 hours of exposure to the

VOS system, there were only on average 6 (± 9 SD) living

individual organisms greater than 50 μm in size per cubic meter

and zero after 72 hours. Furthermore, no intact individuals

scored as dead after 48 hours recovered after being placed back

in aerated water for 24 hours. Therefore zooplankton are not

simply narcotized but are being killed.

In addition to hypoxia and lowered pH, many of the larger

zooplankton (mostly copepods) also appear to be killed

instantaneously by being damaged (Figure 2) as they passed

through the venturi injector, which creates large amounts of

cavitation and turbulence.

Figure 2. Copepod torn in half by passing

through the VOS system.

Our mesocosm experiments also demonstrate that VOS will

significantly reduce the abundance of phytoplankton (mixtures

of naturally occurring diatoms and dinoflagellates; Tamburri et

al. 2003). Because the dockside, mesocosm experiments were

conducted in the dark to mimic ballast tank light conditions, our

initial measurements of chlorophyll in samples taken from

treated and control tanks are difficult to interpret. It is common

for algae to resorb photopigments when stressed by low light or

other harsh environmental conditions (e.g., Deventer and

Heckman 1996). Although greater decreases were found in

treated water, our results show a dramatic and rapid decline in

total active chlorophyll for both treated and control tanks

through time. Another estimate of impacts of VOS on

phytoplankton is the number of algal cells per unit volume

through time. The main limitation of direct cell counts is that

they do not distinguish between live (or viable) and dead cells

so will typically overestimate abundances. Through direct

counts, we found that while the abundance of phytoplankton did

not change significantly in the control tanks over four days, it

dropped between 70 - 80% of initial concentrations in the

treated tanks. Depending on what time of year the particular

trial was conducted, the numbers of cells per ml decreased to

only a few hundred after 96 hours. While hypoxia is likely the

main factor causing the mortality of zooplankton, CO2 saturation

and pH reduction (5.5 - 6.0) appears to be responsible for the

removal of algae (in addition to the obvious absence of light).

This is not surprising given the recent review of 21 publications

on the response of nearly 40 different species of diatoms and

dinoflagellates that concluded a small pH reduction to 6.5

severely affected phytoplankton growth (Hinga 2002).

Results from our dockside, mesocosm experiments also

demonstrate that there is no significant change in numbers of

total bacteria cells through time or between control and

treatment (Tamburri et al. 2003). Although treated ballast water

contains elevated levels of organic material (i.e., dead plankton),

the VOS system produces a “dead-end” condition of continuous

hypoxia. This dissolved oxygen concentration inhibits the

growth of aerobic microbes but is still toxic to obligate

anaerobic microbes such as sulfur reducing bacteria. In fact,

VOS appears to kill several pathogens that are of particular

concern in ballast water. Although bacteria such as Escherichia

coli and Vibrio cholera are facultative anaerobes and adapted to

acidic conditions found in digestive systems, they are extremely

susceptible to rapid drops in pH with 100% mortality after only

30 minutes of exposure to a 2 unit pH decrease (Merrell and

Camilli 1999). This could explain the recent result of Husain et

al. (2003) which reported a greater than 99% mortality of V.

cholera after a 24 h exposure to hypoxia and a pH of 5.5.

Furthermore, a mixture of low dissolved oxygen (between 0.1

and 1.0 mg/l) and a pH of 5 has also been demonstrated to

effectively reduce the levels of Enterococci form 7.8 x 106 per

100 ml to less than 500 per 100 ml after extended exposure in

batch scale experiment (Awuah et al. 2002). We have also

tested for this effect directly as a response of VOS (see below).
Paper No. 2005-D09 Tamburri 4

Corrosion rates and mechanism – Results from our

corrosion experiments with the Naval Research Laboratory have

confirmed the findings of Sumitomo Heavy Industries (Matsuda

et al. 1999). When the VOS system is operated correctly,

instantaneous corrosion rates are reduced by 50% to 80% (using

IR compensated Linear Polarization Resistance analysis) when

compared to the corrosion of steel under normal ballasting

conditions (Lee et al. 2005).

Additional evaluations of corrosion rates under control and

VOS treatment conditions are also currently underway by BMT

Fleet Technology Ltd. This work is being carried out using

similar methods employed to investigate deterioration of vessel

structural integrity due to chemical treatment of ballast water

(commissioned by the Ship Structure Committee). While this

analysis of corrosion is still ongoing, initial results further

support the conclusion that VOS will dramatically reduce

corrosion rates (Figure 3).

Figure 3. The top row is steel plates from a test tank under typical

oxygenated seawater conditions after 30 days. The bottom row is steel

plates from a test tank with VOS treatment water after 30 days.

The reduction in corrosion as a result of the this

deoxygenation system has the potential to decrease ballast tank

maintenance. It is possible that the amount of material repair

and replacement required during vessel servicing, and the

frequency of vessel servicing, can be reduced significantly.

Furthermore, with reduced wastage rate of ballast tank steel,

ships may remain more structurally sound at advanced ages

(Paik et al. 2003).

PHASE III: PILOT-SCALE EVALUATIONS

We extended our work with funding from the Great Lakes

Fishery Commission (through the Fish and Wildlife Service) to

add an additional key step in the process of evaluating this

ballast water treatment system. A pilot-scale VOS system was

built by NEI at CBL (Figure 4), where local waters are very

productive (high concentrations of plankton) and range

seasonally from temperatures of 6 – 28oC and salinities of 8 – 18

ppt. The system consists of a 1,500 gpm (350 m3/hr) ballast

water pump with 8-inch diameter PVC piping, valves, and

venturi injector; a full-scale inert gas generator; and a series of

replicate mesocosms enclosed in a small work space. This is the

equivalent treatment system for a large-sized cruise ship, but

approximately one-tenth scale for a VLCC tanker.

Figure 4. Pilot-Scale VOS system at the Chesapeake Biological

Laboratory, Solomons, MD.

Mechanical and engineering evaluations have demonstrated

that the VOS system will produce the desired conditions that

will cause the mortality of planktonic organisms and that will

reduce corrosion rates. Long-term (12 hour) reliability tests

have yet to result in any drift in operational performance or

mechanical problems.

Results from pilot-scale biological experiments demonstrate

that the VOS system alone can meet IMO standards for all three

categories (zooplankton, phytoplankton and bacteria) on

voyages of more than four days. Figures 5, 6, and 7 show some

of our results of biological efficacy of VOS at the pilot-scale.

Figure 5. Number of live organisms > 50 μm per cubic meter of water

after replicate trial (n = 3) of 2, 3, 4, 5 and 7 days holding times after

treatment with VOS at the pilot-scale.
Paper No. 2005-D09 Tamburri 5

Figure 6. Results from extractive chlorophyll analyses of natural bay

water just prior to starting the experiment (Initial, n = 1), untreated

water (Control, n = 3), and VOS treated water (Treated, n = 3). Control

and treated water were held in darkened mesocosms for 120 hours and

active chlorophyll quantified immediately after holding time and after

allowed to “regrow” under light and aerated conditions for 24 hour.

Chlorophyll in regrowth water was less than water prior to regrowth

and below method detection limits (*) indicating essentially no viable

phytoplankton after 5 days. Cell counts from fixed samples are still

underway but < 4 organisms between 10 and 50 μm in size per ml in

VOS treated water were found after 7-day trials (IMO Standard is

10/ml).

Figure 7A & 7B. Abundances of E. coli (A) and Entrococci (B) in

seeding experiments with control (n = 3) and VOS treated (n = 3) water

after either 1 hour or 1 day holding periods without light. In separate

experiments, single strains of bacteria were cultured and added to 50 L

of natural bay water at approximately 800 cfu/100 ml. The seeded

water was pumped into replicate 1 L flasks, with control flasks open to

air and treated flask sealed to maintain hypoxic/low pH conditions.

One 100 ml subsample from each flask was analyzed for concentrations

of culturable E. coli or Enterococci using a commercially available

chromogenic substrate method (IDEXX Laboratories, Inc.; Noble et al.

2003).

We were also able to take advantage of the pilot-scale

testing to examine if discharging treated water alters the

environment. Periodic measurements of the temperature,

salinity, dissolved oxygen, and pH of ambient water (up current

> 20 meters from discharge) and at varying distances from the

discharge pipe during all pilot-scale evaluations demonstrated

that there is almost no measurable change to receiving water.

Differences in the physical conditions could only be detected

when measurements were taken within 1 meter of the discharge

pipe but the slight reductions in dissolved oxygen and pH were

still well above harmful levels for aquatic organisms and well

above regulation limits (Table 1). These results hold even after

12 hours of continuous treated water release at 350 m3/hr.

Table 1. Range in values for dissolved oxygen (DO) and pH measured

in ambient water and receiving water (< 1 meter of VOS treated water

release point). The treated water was discharged at 350 m3/hr and for

as long as 12 hours.

Parameters Ambient Receiving

DO (mg/l) 8.7 – 11.3 6.9 – 9.7

pH 7.6 – 7.8 6.7- 7.0

PHASE IV: SHIPBOARD EVALUATIONS

The following is a short summary of a partial and complex

dataset. Not all data has been included and additional test

voyages, analyses, and statistical evaluations are ongoing.

Engineering Efficacy – NEI has furnished and installed a

prototype VOS system for the 40,000 DWT bulk carrier M/V

Pat Cantrell, operated by TECO Ocean Shipping in U.S. waters

of the Gulf of Mexico and Florida’s Atlantic coast (Figure 8).

This particular VOS system operates at 1,000 cubic meters per

hour and has produced the intended ballast water conditions

(dissolved oxygen < 1.0 mg/l, pH approximately 6) on three

consecutive test voyages, from January through May 2005.

Following a fine-tuning process of the prototype to operate

optimally onboard the Pat Cantrell, all mechanical evaluations

(e.g., monitoring ballasting rates and ballast water pressure with

and without treatment) to date have shown that it does not

impact normal vessel operations.

Water Quality Analysis – In addition to monitoring the

specific physical parameters of control and treated ballast water

that are altered by VOS (dissolved oxygen and pH), we have

also considered other potential impacts to treated ballast water

and alterations to harbor water where it is released. For

example, analysis of total petroleum hydrocarbons were

measured and found to be below detection limits in both control

and treated ballast water (Phase Separation Science, Inc., No.

05060316).
Paper No. 2005-D09 Tamburri 6

Figure 8. Shipboard evaluations are underway on the TECO Ocean

Shipping bulk carrier M/V Pat Cantrell (top). Twin 12-inch stainless

steel venturi injectors as part of the VOS system (bottom left).

Biological sampling to determine system efficacy (bottom right).

To date, only one set of measurements has been taken to

quantify impacts of VOS treated water on receiving harbor

water for this full-scale shipboard study because of vessel

logistic constraints. Measurements of dissolved oxygen, pH,

temperature and salinity were taken 10 minutes prior to

(ambient water) and 15 minutes after the Pat Cantrell began

discharging VOS treated water at approximately 1,000 m3/hr.

Table 2 below presents dissolved oxygen as mg/l and pH values.

Table 2. The water in ballast tanks prior to release had dissolved

oxygen levels below 1.0 mg/l and pH values of approximately 6. b Lowest values recorded in VOS receiving water < 1 meter from the

seachest as the instrument was lowered and raised vertically in the

water column. c Lowest values recorded in VOS receiving water 3 meters port and

starboard of the seachest as the instrument was lowered and raised

vertically in the water column.

Date Ambient

Water

Receiving

Water < l mb

Receiving

Water 3 mc

DO

mg/l pH DOmg/l pH DOmg/l pH

5/12/2005 6.4 7.6 5.5 7.2 6.3 7.6

Biological Efficacy – Three biological test voyages have

been completed with two more planned. In all cases, prior to

departure, shipside measurements are made and samples

collected to characterize the water being brought onboard the

vessel (T0) from the St. John’s River (Jacksonville, FL). In

addition to standard measures of temperature, salinity, dissolved

oxygen and pH, we have also been collecting samples for in

vivo chlorophyll, total suspended solids (TSS), particulate

organic carbon (POC) and the presence of Vibrio cholerae.

The biological evaluations are designed to examine the

concentrations of organisms before (T1; immediately after

ballasting), during (T2; mid-voyage/approx. 2 days) and after a

test voyage (T3; prior to discharge/approx. 4 to 5 days) in paired

control and treated ballast tanks (two each, four tanks total).

This allows both estimates of percent reduction in organism

concentration due to VOS treatment by comparison with the

control tank and to determine the amount of time required by

VOS to meet IMO standards.

Organisms have been divided into the size fractionations

and bacterial types described in IMO standards. Zooplankton

are exampled in > 50 microns samples that are collected at each

time period using a specially designed and calibrated

submersible pump/net system. Two replicate 0.5 cubic meter

samples are taken near the surface of the ballast tanks and two

replicate 0.5 cubic meter samples are taken 1 meter above the

bottom of the ballast tanks. For all test voyages, T3 samples

(taken just before the vessel arrives in port) are analyzed for live

and dead zooplankton under a dissecting microscope prior to

fixation. In some case, we also have direct counts of live/dead

for T2 samples. While total abundance and taxonomic

classification for many samples is still being determined, the

live/dead data from the T3 samples have shown reductions in

zooplankton after 4 to 5 days. Initial concentrations of

zooplankton at T1 in ballast tanks have been remarkably high

(in some cases over 500,000 per cubic meter) but as expected,

abundances drop through time in both control and treated tanks.

However, while several thousand are still living in the control

tanks after 4 days, few if any living organism > 50 microns can

be found in VOS treated tanks. Table 3 shows examples from

two test voyages for the numbers of live zooplankton (mostly

copepods, barnacle nauplii and cyprids, trocophores, turbellaria,

rotifers, platyhelminthes, and polychaetes) in replicate control

and treated tanks after voyages just over four days.

Table 3. The mean and standard deviation of live organisms per m3 of

ballast water > μm 50 microns in size in Control and VOS treated

ballast tanks after approximately 100 hours.

* Designates a conservative estimate further analysis is underway.

Date Route Control

(mean ± SD)

VOS

(mean ± SD)

5/12/2005

Jacksonville, FL

to

Port Arthur, TX

> 20,000 * 0 ± 0

5/25/2005

Jacksonville, FL

to

Houston, TX

11,650 ± 4,454 10 ± 9

Protists between 10 and 50 micron in size are quantified in

a similar way using whole water samples. Two replicate 2-l

Kimmerer bottle samples are taken in each test tank near the

surface and two replicate samples are taken 1 meter above the
Paper No. 2005-D09 Tamburri 7

bottom, at each time point described above. Sub-samples are

fixed with standard Lugol’s solution and placed in 250ml amber

bottles for direct cell counts under a microscope (analysis from

the first three test voyages is still underway). Because these

direct cell counts cannot distinguish between live and dead cells,

we have also been measuring in vivo fluorescence for

chlorophyll from the water samples collected from each tank at

each time point, and are conducting regrowth experiments.

Final samples from each test tank (T3) are measured for in vivo

chlorophyll and then placed in flasks (covered but open to air),

with algal nutrients, and under grow-lights. Subsequent in vivo

chlorophyll measurements are taken from each sample after 12,

24 and 36 hours. To date, we have found increasing chlorophyll

concentrations in samples taken from controls but not VOS

treated tanks. While a decrease in chlorophyll concentration in

regrowth experiments is not definitive proof of no viable

phytoplankton, an increase in chlorophyll levels through time

does suggest that at least some viable organisms were present in

the original T3 samples. Complete analysis of data is still

underway.

In addition to quantifying the specific bacteria described in

the IMO standards, we are also determining total bacteria

concentrations. Sub-samples are taken from the Kimmerer

bottles described above, fixed and counted by flow cytometry

(analysis is still underway). Additional sub-samples at T3 are

also analyzed for concentrations of E. coli and Enterococci

using the chromogenic substrate, quanti-tray most probable

number analysis described above. Enterococci have yet to be

detected at any significant level in test tanks after the vessel

arrived in port. E. coli has been detected but on only one test

voyage to date. Concentrations in control and treated tanks for

E. coli were both below 100 cfu with fewer in treated than

control (although not significantly different). Finally, as

mentioned above, V. cholerae is also being measured using

DFA analysis (New Horizon Diagnostics). During one test

voyage (5/25/2005), an average of 25 cells/ml of the serotype 01

were found shipside prior to departure. However, none was

found in VOS treated tanks and only one cell (total, not per ml)

was found in control tanks at T3.

We now also have funding in place from the NOAA Ballast

Water Technology Demonstration Program to extend the scope

of performance testing to include a different ocean basin (with

different biota) and vessel type than is currently being evaluated

and to conduct long-term monitoring of VOS efficacy for an

entire vessel’s ballast water under routine, continuous operations

as part of U.S. Coast Guard’s Shipboard Technology Evaluation

Program (STEP). This final demonstration will involve a

completely automated treatment system and a vessel operating

in the Pacific and is critical to determine the ability of VOS to

continuously meet regulations under normal vessel operations.

SUMMARY AND CONCLUSIONS

Multiple US and international organizations and agencies

rate the invasive species issue as one of the three most

destructive environmental problems facing the world today (e.g.,

United Nation, U.S. Department of State, and Union of

Concerned Scientists) and oceangoing vessel ballast water is

recognized as the primary source of aquatic species invasions

(National Research Council 1996). The newly adopted IMO

Ballast Water Convention will eventually require over 50,000

internationally trading vessels to treat ballast water prior to

discharge.

Although additional real-world testing is still required, our

results to date suggest that Venturi Oxygen Stripping has the

potential to be an effective, safe and practical ballast water

treatment option. The hypoxia, low pH, and mechanical

disruption produced by this system appears to be lethal to

organisms found in ballast water, reducing abundances to IMO

discharge standards after 4 to 5 days of tank holding time. The

VOS system may also directly benefits the shipping industry.

The results of our work, and of others, have demonstrated that

this system can reduce corrosion rates of ballast tanks between

50% and 90%. This reduction in corrosion has the potential to

reduce maintenance cost for ship owners and with reduced

wastage rate of ballast tank steel, ships may also remain more

structurally sound at advance ages. This ballast water treatment

system may therefore represent a rare example of a technology

that simultaneously has benefits for the environment and

industry.

ACKNOWLEDGEMENTS

We would like to thank the NOAA Ballast Water

Technology Demonstration Program and the Great Lakes

Fisheries Commission for supporting much of this work. Peter

McNulty and Kevin McPherson of NEI Treatment Systems LLC

have designed, built and been a critical part of VOS system

testing. We also thank George Smith and Tim Mullady of

Smithsonian Environmental Research Center for their hard work

on the shipboard biological evaluations.

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