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MARINE MACRO FOULING: A REVIEW OF CONTROL TECHNOLOGY IN THE CONTEXT OF AN ON-LINE

EXPERIMENT IN THE TURBINE CONDENSER WATER BOX OF AL-JUBAIL PHASE-I POWER/MSF PLANTS1

P. K. Abdul Azis, Ibrahim Al-Tisan, Mohammed Al-Daili, Troy N. Green and Khalid Ba-Mardouf

Saline Water Conversion Corporation

P.O.Box 8328, Al-Jubail -31951, Saudi Arabia Tel: + 966-3-343 0012, Fax: + 966-3-343 1615

Email: rdc@swcc.gov.sa

&

Saeed Ali-Al-Qahtani & Khalid Al-Sabai

Desalination and Power plants, Al-Jubail 31951 Kingdom of Saudi Arabia.

ABSTRACT The problem of macrofouling has serious implications in the performance of

desalination and power plants. Intake structures, screens, seawater piping systems and

heat exchanger tubes are the sites worst affected in the plants causing overall decline

in plant efficiency at great economic cost. The last half a century has witnessed

significant advancements in the development of macrofouling control technologies.

Materials of inherent antifouling properties are widely used in the construction sector.

Control technologies available include antifouling paints and coatings, injection of

biocides, marine bio-active compounds materials of inherent antifouling properties,

heat treatment, pulse-power devices, UV and nuclear radiation, scrubbing devices,

biological control, etc. Literature search carried out during the last few years has

yielded about 450 references. The paper presents, in a very concise manner, state-of-

the- art macrofouling control technologies pertinent to desalination and power plants

in the Kingdom. The paper also discusses the issues of biofouling control in the Al-

Jubail plants based on the results of an on-line macrofouling experiment conducted in

one of the turbine condensers of Al-Jubail Phase-I MSF/ Power plants.

1 Presented at the 3rd Acquired Experience Symposium, Al-Jubail, Saudi Arabia, 4-6 Feb. 2002. and also published in Desalination 154 (2003) 277-290.

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1. INTRODUCTION AND REVIEW Man has been aware of the problem of biofouling ever since he ventured into the sea. In

the 4th century B.C. Aristotle, the Greek Philosopher, had referred to the slowing down

of ships due to their hulls being covered by barnacles. Macrofouling has been defined

as the attachment and subsequent growth of a community of visible plants and animals

on structures and vessels exposed to water [1]. A precursor to macrofouling is the

microfouling caused by bacteria, fungi and other microscopic organisms. Because of

the proximity of desalination plants to the marine environment, marine macrofouling

has become a serious problem of concern to utility managers everywhere. There has

been a significantly laudable effort in the world to understand the phenomenon of

biofouling and evolve strategies for its prevention and control [2,3]. About 5000

biological species have been listed as involved in the fouling of structures exposed to or

immersed in water, the composition and community assemblages showing wide

variations from site to site. An earlier study in the intake bay of the Jubail Desalination

and power plants showed the involvement of 31 genera of organisms in the biofouling

settlement on glass coupons [4]. Two of the most significant groups associated with

fouling are bacteria and diatoms. Once attached to a surface, they rapidly divide and

form a slime film of great importance to the emerging fouling community. Mold and

fungi also occur besides a variety of algae of which some live as single cells, and

others, such as seaweeds live as large filamentous or branching plants. Representatives

of the animal kingdom range from protozoans to chordates. Animals involved in

macrofouling consists largely of barnacles, mussels, bryozoans, hydroids, tunicates and

serpulid worms. Corals, sea anemones, sponges, echinoderms, amphipods, isopods,

nemerteans and platyhelminthes also occur. Problems of biofouling are most common

on ship hulls, navigational buoys, underwater equipment, seawater piping systems,

beach well structures, industrial intakes, Ocean Thermal Energy Conversion Plants

(OTEC), offshore platforms, moored oceanographic instruments and submarines. Water

lines lose their carrying capacity and speed of flow due to biofouling growth along

pipelines. Due to attachment of fouling organisms, the performance of heat exchanger

tubes declines. Biofouling also causes corrosion of materials. The marine industry in

the world incurs an estimated expenditure of 10 billion sterling pounds a year to combat

the problems associated with biofouling. About 450 papers on the subject of biofouling

have been reviewed for the purpose of this presentation. The literature collected under

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this project through the database available at the National Institute of Oceanography,

Goa, India has been deposited at the Library of the SWCC Research and Development

Center, Jubail [5]. These publications deal with the fundamental aspects of biofouling

[6-19] as well as the large number of control technologies developed around the world

[20-26]. The readers are advised to refer the bibliography compiled by Abdul Azis [5]

for details of references listed in Table 1.

The R&D Center had undertaken a study of macrofouling caused by marine shells in

response to such a request from the Jubail Plant Manager. The project started in

September 1999 would end in March 2002. This paper is based on the online biofouling

experiments conducted in the Jubail MSF/ Power plants. The technology for biofouling

control has been discussed on the basis of an extensive literature survey carried out

during the period. The purpose of this study was to understand the nature and

magnitude of macrofuling inside the water box and the degree and extent of condenser

tube choking due to growth of marine life, scale deposits and accumulation of debris.

Other aspects such as plankton ecology, water quality and environmental biofouling

would be dealt in subsequent publications.

2. EXPERIMENTAL DESIGN AND METHODOLOGY 2.1 Site of experiment The online study of biofouling was carried out in the turbine condenser water box of

Al-Jubail Phase-I MSF /Power plants Unit – 2, for a period of one year covering all the

seasons. The unit that was shut down for overhauling was inspected by the research

team on 10-7-1999 to assess the status of biofouling in the unit. Digital photographs 1-3

indicate the status of biofouling in the unit at the time of shut down. The experiment

was started after cleaning and overhauling. Material specification of the condenser is

given below:

1. Type of Condenser : Radial flow 2. Construction : Rectangular 3. Cooling water : Seawater 4. Capacity of Condenser : 25 tons 5. Number of tubes : 2629 6. Condenser tube length : 8104 mm 7. Condenser tube diameter : 20.96 mm

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8. Pressure drop : 0.15 bar (minimal); 0.23 bar (normal) 9. No. of water pass : One 10.

Flow rate of cooling water : Max.: 14 202 ton/hr; Min.: 10 090 ton/hr Normal : 12 935 ton/hr

11. Condenser tube metal : Titanium ASTM B338 Gr-2 12. Tube Plates : Aluminium Bronze ASTM B171 Alloy

614 13. Cooling surface Area : 2951 m2 14. Water Box metal : Aluminium Bronze ASTM B 171 alloy

630 15. Shell metal : ASTM A 285 Gr-C 16. Internal Supports metal : ASTM A 285 Gr-C

2.2 Experimental coupons and coupon holders Titanium Gr-2 Plate sheet coupons (100 x 100 x 1.5 mm) with 180 grit finish

conforming to ASTM B 265, procured from M/S Metal Samplers (USA), with a

certified Material Test Report were used in the study for all the experiments. The

coupons were holed at the Pilot Plant workshop. Coupon holders that could be fixed to

Anodes were designed and fabricated by the Pilot Plant staff. Coupon fixing device was

designed in such a way that the individual coupons remain away from each other and

each could be retrieved with out disturbing the other (Photograph - 4).

2.3 Methodology Titanium coupons were cleaned, sterilized and weighed before use. The anodes on the

Left and the Right sides of the Inlet and Outlet sides were selected as the site for fixing

the coupons. Four coupon holders each were fixed to the anodes at the Inlet and Outlet

sides. Each holder carried 2 coupons each. The experiment started in September 1999,

was completed in September 2000. Two coupons each were retrieved at intervals of

three months. Accordingly, the first set of coupons remained exposed to the cooling

water for three months, the second set for six months, the third set for nine months and

the last set for 12 months representing the winter, spring, summer and fall seasons

respectively. This design enabled the research team to evaluate the situation of

biofouling during the different seasons of the year. An inspection of the Phase –I Intake

Screens was made on 25-11-2000. The purpose of the visit was to locate the source of

the huge quantities of polyethylene bags, wire ropes, cans, weeds, wood etc., noticed in

the Turbine Condenser Water Box. Operating Data on Residual chlorine for Power

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Plant Phase I Unit- 2 received from the plant have been used to discuss the chlorine

availability in the process stream.

The retrieved coupons were examined for fouling film formation and biofouling.

Weight gain method was used for estimating the degree and extent of fouling materials

getting settled on the surface of coupons. One of the coupons removed from the Inlet

and Outlet sides was dried in an oven for overnight at a temperature of 60oC. The

coupon is taken out, allowed to return to room temperature and re-weighed. Biofilm

thickness of the slime could not be measured, as the film observed was very thin.

Visual inspection of the Water Box and Condenser tubes were made once in three

months when the Water Box was opened for coupon retrieval. Members of the

Research Team carried out inspection of the Water Box once in a quarter, photographed

the situation and prepared notes on the same.

3. RESULTS 3.1 Weight Gain by Coupons Data on the weight gain/loss displayed by the coupons are presented in Figure-1. The

weight of settled material ranged from 0.05 to 0.19 gm per coupon on the Inlet side and

from 0.03 to 0.15 gm on the Outlet side. The weight gained was lower in the coupons

kept at the Outlet side indicating meager settlement on coupon surfaces. The weight

loss displayed by certain coupons indicated a certain degree of corrosion taking place in

the water box. 3.2 Visual Examination Visual examinations were carried out on the Inlet and Outlet sides of the water box and

condenser tubes four times during 1999-2000 covering the winter, spring, summer and

fall seasons to document the status of film formation. At no time was the film thick

enough to take any measurement.

3.2.1 Condition of the coupons The three month exposed coupon on the Inlet side carried black and reddish deposits on

one corner. It also showed the presence of a slime film on both sides, but with out any

biofouling settlement. The six month exposed coupon also showed the presence of a

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slimy film on both sides. The coupon was covered with a strip of polyethylene bag.

This was also covered by a brown film (Photograph-5). The nine month old coupon

taken out in Summer, showed the presence of gelatinous slime in some areas and a

brown slimy film in the remaining areas. The coupon was devoid of any macrofouling

settlement. The 12 month old coupon was deep brown with patches of white and black

deposits. One piece of an algal filament was seen along with a patch of debris. No other

settlement was seen on the coupons. The three months old coupon on the outlet side

showed a greenish slimy film with hard particles stuck to the surface. Red deposits

increased with the duration of exposure. The 12 months exposed coupons showed the

presence of diatoms and protozoans. No macrofouling settlement was observed.

3.2.2 Condition of the Water box and turbine Condenser Tubes The inlet side of the water box was free from any settlement during the first three

months (inspection in winter). Several tubes were partially blocked by white, slime

deposits (Photographs: 6-7). Strips of polyethylene bags were found covering the inlets

of tubes impeding the flow of water. About 5 kg of debris consisting of dead and

broken shells of Balanus sp., mutilated parts of crabs, remains of sea grass, pieces of

polyethylene bags, nylon ropes and stones were removed from the water box. Both the

anodes showed signs of corrosion. Inspection after six months (spring season) showed

that the debris and pieces of polyethylene bags that were found clogging the tubes

during the winter season were no longer present. But more tubes than observed

previously were choked now by white deposits. No marine growth was seen either

inside the tubes or on the walls of the water box. Inspection after nine months (summer

season) showed a recurrence of polyethylene bags, nylon ropes, algal litter and other

debris (Photographs 8&9) covering the inlets of numerous tubes. This was more than

that seen during the spring season observation. A matter of great concern was the

presence of macrofouling organisms, some embedded in tar balls and sediments

(Photographs 10-13).Both the anodes were greatly corroded. During the inspection in

the twelfth month, about 50-60% of the tubes were found to be affected by deposits and

garbage settling (Photograph 14). No organism was seen inside the tubes. The tubes

were largely free from any macrofouling. The walls of the water box showed some

settlement of barnacles that was negligible. However, it was quiet insignificant as to

cause any problem for the smooth operation of the unit under study. On the outlet side,

both the anodes were heavily damaged due to corrosion. None of the debris and

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garbage seen on the inlet side was seen on the outlet side of the water box and

condenser tubes during any of these inspections. However, many tubes were seen

choked due to deposits seen on the inlet side (Photograph 15). Barnacles were found

settled on the roof side of the water box. They were all small and black.

3.3 Chlorine Residual Chlorination is continuously dosed at the Intake itself. The Intake is provided with 6

sets of Sodium Hypochlorite (NaOCl) generators producing about 45.5 kg/h of chlorine

per generator. On a day of full production, about 7200 kg of chlorine is produced and

injected in the Intake Pit. The normal dosing rate is 2ppm where as the shock dosing

rate is 8 ppm. The aim is to get an optimum Residual Chlorine level of 0.20 to 0.50

ppm, considered adequate enough to kill marine life and prevent organisms from

attaching to surfaces. The Residual Chlorine in the seawater intake ranged from 0.24 to

0.35 ppm and that at the Turbine Condenser inlet and outlet ranged from 0.05 to 0.33

ppm. During the period of April to August 2000, Residual Chlorine in the Turbine

Condenser was less than 0.20 ppm.

3.4 Inspection of Phase-I Intake Screens

The entry of trash and garbage was found to be a menacing problem, choking the tube

inlets on many occasions during the year. The following points were checked.

3.4.1 Bar Screen Zone

The Rubber Boom fixed in front of the Intake pit has many gaps in between allowing

floating materials to reach the Bar Screen and enter the intake pump house. Although

this boom was meant for preventing oil from entering the pump house, it prevents the

floating trash and garbage from entering the pumping location.

3.4.2 The Bar Screen The bars were found to be heavily fouled by barnacles and bivalves. The wall of the

intake was also found to be fouled by large Molluscs. These settled organisms make the

spot a location for breeding.

3.4.3 Travelling Screen There are 16 sets of single flow type Travelling Screens designed to filter the feed

seawater before it enters the seawater pumps and the screen wash pumps. The Power

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Plant side is catered by 8 sets of travelling Screens with a maximum screening capacity

of 22,800 kg/h at a maximum design seawater flow rate of 11,556 m3/h/screen/NLWL

(Normal Low Water Level, the elevation of which is - 700 mm). The seawater velocity

through the screen is 0.3 m/s (about 1 km/h). Eight sets of Screens fixed on the

desalination side of the Intake carry a maximum screening capacity of 20,000 kg/h at a

maximum design flow rate of 9,265 m3/h/screen/NLWL. The seawater velocity is

slightly less on this side. The mesh size of the wire cloth fixed to the screen is 9.5 mm

in square.

Each set of the Travelling Screen is installed in the pump pit in front of the seawater

pump through a specially designed concrete slit. When operated, the screen travels in

such a way that the feed water to the pump always flows through it before it reaches the

pump. The moving screen lifts the trash collected by the screen, and when it reaches the

ground level, the trash gets automatically left on a trash collection rack. There was

heavy fouling on the travelling screen. Photographs 16-17 depicts the conditions

observed on one of the screens.

The inspection of the site showed that there is gap left between the screen and the trash

receiving rack as part of the safety margin allowed for the movement of the screen.

Many of the screen blade tips were found corroded creating more space between the

screen and the trash receiving rack. The trash filtered by the screen falls back in to the

bay in front of the seawater pump (Photograph 18). Naturally, these items also get

pumped into the feed stream of the Power and Desalination units.

One part of the screen was found to be heavily biofouled due to settlement of barnacles

and bivalve shells, where as the other part of the screen was free from any settlement. It

is presumed that the Travelling Screen was not operated continuously. Leaving the

screens bathed in the incoming seawater permits biogrowth. Prolonged exposure means

more biofouling. Such massive settlements of organisms eventually create a breeding

ground for these organisms with in the Intake Pit. This is likely to expose the plant

structures to greater biofouling.

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4. DISCUSSION The rationale for the present study has been the problem of fouling caused by

molluscan and crustacean organisms in the Turbine condenser Water Box of the Jubail

Phase I MSF/Power plants, in spite of standard chlorination used as the disinfection

regime at the Intake Pumping bay. The online experiment did not show any

macrofouling settlement during the period of this study except certain occasional

presence of Barnacles during the summer season when the residual chlorine levels were

less than 0.20ppm. Chlorination is widely used to prevent settlement of fouling

organisms in cooling conduits of power stations with varying degrees of results [27].

Macrofouling has been reported when there is only intermittent chlorination or when

residual chlorine levels are very low [28]. Mussels and barnacles, once settled during

no chlorination periods were found to be able to resist the subsequent exposure to

chlorine and during the breaks in chlorination they can actively feed and carry on their

normal life [29]. Flow velocities of less than 1.2 m/second are known to allow larval

settlement. Once established, shell communities can withstand velocities ranging from

1.5 to 2.5 m/second and flow velocities below 0.1 m/second may not provide adequate

food and oxygen for their growth [30]. In the present study, macrofouling has been

noticed on the bar screens and the traveling screen. This has the potential of turning this

area in to a breeding zone for barnacles and mussels with potential release of larvae of

biofouling organisms in the feed stream.

4.1 Control Technology While presenting this overview, we would like to underline the fact that there is no

“silver bullet” offering a universal solution to biofouling problems. In the following

section, control measures have been categorized and briefly discussed with the modes

of their delivery to the fouling zones. These methods have to be carefully selected for

specific applications. Major references in this regard are summarized in Table 1.

4.1.1 Antifouling (AF) paints and coatings They provide, probably, the most cost-effective method to prevent fouling. These are

mixtures that contain sufficient water-soluble resins, pigments, metal salts and inert

fillers. AF coatings remain the most favored delivery system to control biofouling on

most marine structures (other than cooling water systems). The advantages of coatings

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are ease of manufacture, high speed, low cost application, reasonable duration and

relatively low coast. The disadvantages are limited life, the lack of ways to apply

coatings to submerged or wetted surfaces and toxicity of control agents. Copper oxide

coatings remain the most widely used AF coatings, and the basic insoluble-matrix

rosin-copper (I)- oxide coatings (using vinyl, chlorinated rubber, and polyisobutyl

resins) developed in the 1950s remain the same. These coatings are capable of

delivering static barnacle resistance of over 90% for as much as four years. A major

development in AF coatings has been the organotin toxics that became available in the

early 1960s. There are two basic types of organotin coatings: coatings that icorporate

organotin compounds and coatings based on film forming resins that contain a

chemically bound organotin. Antifouling Elastomeres offer an intriguing approach to

long lasting fouling control, with a toxicant reservoir that is much larger than in paints.

4.1.2 Injectable biocides Flowing systems provide marine organisms with a salutary environment for the

settlement of organisms because the moving water stream replenishes nutrients and

oxygen. Injectable biocides with biocidal or biostatic properties have made it possible

to take anitfoulants to areas where coating cannot be provided. They are most often

used in geometrically constrained locations existing in the interior of pipes, heat

exchanger systems or other enclosed and/or remote areas in flowing water systems.

Chlorine, first used as a disinfectant in 1800, was first used on a plant scale in 1879 and

it became the widely used disinfectant since the 1970s. Low-level chlorination is still

the most commonly used method for the prevention and control of biofouling. The

desalination industry is well aware of the benefits of this biocide. Because of the

hazards involved in the transport and storage of this gas, in situ electro-chlorination is

the technique being followed at seawater intakes of power and desalination plants. At

the doses injected now, with a residual chlorine level of 0.20 to 0.50ppm, plants do, at

times, experience macrofouling problems. Long-term exposure of organisms to a

particular toxicant develops in them a certain degree of immunity and the same dose

may not necessarily have the previously known toxicity on a prolonged application

regime. According to experimental studies reported from India, high concentrations of

chlorine (8 mg/l) as sodium hypochlorite was found needed to achieve 100% kill of

marine larvae. Continuous chlorination was found necessary to arrest the growth of

shell in the case of molluscan biofoulers (Mytilus edulis). At 1ppm residual chlorine, 12

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mm size mussels showed 100% mortality only in 504 hours (21 days) whereas at

10ppm residual chlorine they died in 30 hours. 95 mm size mussels died in 48 hours at

10ppm residual chlorine. Assessments are available on the merits of low dose

continuous chlorination, intermittent chlorination (2ppm residual for 1 hour in 8 hours),

targeted chlorination and application of bromine chloride, copper-chlorine mixture, iron

and hydrogen peroxide mixture. The chlorine demand of seawater changes with water

quality variations. In an effort to develop an environment friendly biocide regime the

synergistic effect of chlorine and copper has been put to a combination method that

reduced the required chlorine to about one-tenth and copper to one-sixth. Basically,

bromine chloride and chlorine dioxide were found to be more effective than chlorine

but they were also more expensive. Ozone has been found feasible as an alternative to

chlorination for control of biofouling in once through cooling systems. The use of small

amounts of cationic flocculants (Acrylate additives) at the rate of 2 to 4mg/l with

chlorination has been found to remove biomass from heat exchanger surfaces. Acrylic

films and plastic films have been investigated as potential covering for surfaces.

Except for chlorine, bromine and bromine chloride, little is known about the effects of

these materials, and in the case of halogens, recent works has suggested that their

harmful impacts is significantly greater than previously reported. Marine creosote,

alone or together with copper salts, remains the mainstay for the bio-protection of

wooden structures in the marine environment. In a recent study [30], 47 chemicals

having potential for preventing attachment of zebra mussel were identified and tested.

4.1.3 Marine bioactive compounds The search for environmentally benign antifouling agents has resulted in the isolation

of a large number of marine natural, non toxic compounds that demonstrated significant

antifouling activity with out any side effects. About 200 species of marine organisms

were tested for their antifouling activities with their extracts with many species

exhibiting encouraging results. The antifouling activity of several secondary

metabolites was tested in bioassays using barnacles, algae and bacteria. The

polyhydroxysterols isolated from octocorals has been cited as a breakthrough. It was

found as a more effective substitute for the highly toxic organotin compounds.

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4.1.4 Materials of inherent AF properties There has been a continuous endeavor to develop structural materials that are inherently

fouling resistant. Copper and some of its alloys are the earliest recognized and most

widely used antifouling structural materials. By applying an electric current, its rate of

leaching is increased thereby enhancing the antifouling potential. Leaching of copper

results in improper shell growth and in some cases interfere with various enzymatic

processes. Copper-Nickel alloys are well known for their range of application and

reliable performance because of their inherent resistance to biofouling and corrosion.

The search for cost effective marine alloys that are inherently antifouling and are also

insoluble has produced a new marine alloy, based on copper, manganese, cerium and

gallium with greatly promising results. Conventional concrete structures have been

given antifouling property by incorporating toxic compounds with proven resistance for

biofouling. Monomers and polymers with chemically attached biocides constitute one

of the latest classes of materials, called controlled release biocides that give inherent

protection to marine structures.

4.1.5 Heat treatment Heat treatment is considered a viable alternative and is being practiced by several

utilities in different countries. Marine organisms are significantly more temperature

sensitive than their terrestrial cousins. Warm waters having temperatures between 50-

70ºC can kill nearly all organisms and it has found successful as a localized fouling

control technique if flushed for 1-2hrs in cooling water systems. This technique is

extremely energy intensive and can be considered for small, extremely critical surfaces.

4.1.6 Pulse-Power technology Pulse power technology, the technology of short, high electrical power pulse generation

has made tremendous progress in the past decade. Powerful, long-time, pulse-power

devices are now available to generate electrical pulses of duration shorter than one

nanosecond [32]. Based on experimental studies, it is stated that pulses on the order of

one microsecond are sufficient for preventing biofouling.

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4.1.7 Ultra-violet and Nuclear radiation Effect of UV and nuclear radiation in preventing the primary settlement of biofilm has

been investigated with encouraging results. UV-B radiation has been found to kill

mussel larvae before they get settled on a surface. It is also stated as having an ability to

control zooplankton communities. Nuclear radiation has been attempted in India for

preventing microfouling in the cooling conduits of a Nuclear Power Plant. Paints are

available incorporating a radioactive material. Although many isotopes with stable

properties have been identified and tried with remarkable antifouling effectiveness, it

has not become popular because of extreme concerns on their fallout impact on human

beings and ecosystems.

4.1.8 Scrubbing This is probably the oldest fouling control technology known to man. Here, mechanical

energy is used to keep fouling surfaces clean. The development of diving technology

since the 1950s has made it possible for marine structures and ship hulls to be scrubbed

by divers. Rotating brush devices used for cleaning microbial fouling from the heat

exchanger surfaces of Ocean Thermal Energy Conversion Plants have worked

successfully. Scrubbing technology has become very commercialized and the US Navy

gives worldwide contract for cleaning ship hulls on a routine basis. The use of rods and

brushes to remove highly developed fouling communities in the interior pipes and tubes

is at time the only method possible. Two commercial approaches, namely the sponge-

rubber balls and flow driven brushes, focus on cleaning heat exchanger tubes. While the

ball cleaning system has been found to be useful indeed, it has also been implicated in

tube corrosion and erosion.

4.1.9 Biological control Studies carried out in the USA have brought out encouraging results in this regard. The

captive reared, common map turtle (Graptemys geographixca) was found to feed

heavily on Zebra mussel, one of the most prolific macrofoulers in American waters

opening the prospects of biological control of macrofouling. The fish bull chub

(Nocomia raneyi) has been tested positive for crushing and ingesting hard- shelled

molluscan foulers. In other instances, blue crabs, hermit crabs and stone crabs were

found to prey significantly on oysters (mollusca).

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4.1.10 Other techniques Pressure washing, water jetting, magnetic fields, sonic devices, robotics, Reproductive

control and cathodic protection are the other techniques found feasible by many

investigators and recommended to the industry.

5. CONCLUSION The Turbine Condenser Water Box did not show the previously experienced menace of

biofouling caused by marine shells. Neither the heat exchanger tubes nor the

experimental titanium coupons showed any tendency of macrofouling. The marine

organisms observed were very negligible. Heat exchanger tubes were seen choked by

white deposits and their inlets were seen covered with polyethylene bags and other

debris. Although residual chlorine levels were below the desired 0.20ppm concentration

on certain occasions, it appeared that the intake chlorination was effective in controlling

the ingress of biofouling organisms. An inspection of one of the traveling screens,

carried out independently of the online experiment showed that the gap that exists

between the screen and the trash receiving rack facing the pump, is the source of

polyethylene bags and other trash that were seen inside the Water Box from time to

time. This is a problem that needs to be tackled on a priority basis.

6. RECOMMENDATIONS

1. It is always prudent to maintain a residual chlorine level of 0.20ppm inside the

Water Box. This regime should be carefully managed to avoid the chance of

biofouling settlement.

2. Fouling on the traveling screen needs to be prevented, as the organisms getting

settled and growing thereafter, could breed and release their larvae in large

numbers right in front of the pump which could be sucked into the feed water

line of the plant. Further, idling of the screen should be avoided. Macrofouling

on the screen further enhances the chance of corrosion of the screens.

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3. Some of the methods mentioned above may be examined by the plant personnel

for application in the Condenser Water Boxes and other locations in the plants,

where macrofouling is experienced.

7. RFERENCES 1. Fischer,E.C., Cstelli,V.J., Rodgers,S.D. and Bleile,H.R., (1981), Technology for

control of Biofouling, Technology for Control of Marine Biofouling, 261-299.

2. Woods Hole Oceanographic Institute, (1952), Marine fouling and its prevention. Annapolis, MD: US Patent No.4,123,338, 31 October 78.

3. Crisp, D.J., (1973), The role of the biologist in antifouling research, In Proc. 3rd International Congress on Marine Corrosion and Fouling, Evanston,IL: North Western Univ. Press, 88-93.

4. Abdul Azis, P.K., Al-Tisan, I. And Sasikumar, N., (2001), Biofouling potential and environmental factors of seawater at a desalination plant intake, Desalination, 135, 69-82.

5. Abdul Azis, P.K., (1999), Bibliography on Biofouling Studies, ecology and Marine Biology Department, SWCC R&D Center, Jubail, Kingdom of Saudi Arabia.

6. Page, T.L., Neitzel, D.A., Simmons, M.A. and Hayes, P.F., (1986), Biofouling of power plant service systems by Corbicula, Proceedings of the second International Corbicula Symposium, Little Rock (USA), 41-45.

7. Isom, B.G., (1986), Historical review of Asiatic clam (Corbicula) invasion and biofouling of waters and industries in the Americas, Proceedings of the Second International Corbicula Symposium, Little Rock (USA), 1-5.

8. Li, C., (1989), Biofouling and filter blocking algae in Daya Bay, Collection of Papers on marine ecology in the Daya Bay-1, 3rd Institute of Oceanography, Xiamen, People’s Rep. China, 53-58.

9. Satpathy, K.K., (1989), Biofouling control measures in power plant cooling systems: A brief overview, Pro. Specialist’s meeting on marine biodeterioration with reference to power plants, IGCAR, Kalpakam (India), 153-166.

10. Jones, J.M. and Little, B.J., (1990), USS Princeton: Impact of marine macrofouling (mussels and hydroids) on failure/corrosion problems in seawater piping systems, Naval Oceanographic and Atmospheric Research Laboratory, Stennie Space Cent., MS(USA),19.

11. Huang, Z., Zheng, C., Li, C., Wang, J, Lin, S., Yan, S., Zheng, d. and Lin, N. (1990), Biofouling at water inlet of nuclear power station in Daya bay, Collection of papers on Marine Ecology in Daya Bay-2, 3rd Inst. Ocean., Xiamen, P.R.China, pp.478-488.

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12. Challinor, C.J., (1991), The monitoring and control of biofouling in industrial cooling water systems, Biofouling, 4(4), 253-263.

13. Turpenny, A.W.H. and Coughlan, J., (1992), Power generation on the British coast: Thirty years of Marine Research, Hydroecol., 4(1), 1-11.

14. Al-Ahmad, M. and Aleem, F.A., (1994), Scale formation and fouling problems and their predicted reflection on the performance of desalination plants in Saudi Arabia, Desalination, 96(1-3), 409-419.

15. Sasikumar, N., Azariah, J. and Nair, K.V.K., (1993), Changes in the composition of tropical fouling community at a power plant discharge, Biofouling, 6(3), 221-234.

16. Poulton, W.I.J., Cloet, T.E. and von Holy, A., (1995), Microbiological survey of open circulating cooling water system and their raw water supplies at twelve fossil - fired power stations, Water Sc. As. 21(4), 357-364.

17. O’Neill, C.R. Jr., (1996), The Zebra Mussel, impacts and control, Cornell Coop. Ext. Inf. Bull. No. 238, 62.

18. Venugopalan, V.P., Thyagarajan, V. and Nair, K.V.K., (1997), Marine growth in large seawater intake systems: Problems and their control, Proc. 2nd Indian Nat. Conf. Harb. and Ocean eng., Thiruvananthapuram (India), Vol.1, 640-647.

19. Thyagarajan, V., Venugopalan, V.P., Subramoniam, T. and Nair, V.K., (1997), Macrofouling in the cooling water conduits of a coastal power station, Indian J. Mar. Sci., 26(3), 305-308.

20. Lawrence, C.F., (1997), Chemicals for Zebra Mussel control, Proc. 7 Intl. Zebra Mussel and Aquatic Nuisance Species Conf., New Orleans, LA (USA), 28-31.

21. Singh, I.P., Takahashi, K. and Etoh.H., (1996), Potent attachment –inhibiting and promoting substance for the blue mussel, Mytilus edulis galloprovincialis, from two species of Eucalyptus, Biosci-Biotechn.-Biochem., 60(9), 1522-1528.

22. Ten Hallers, C.C., (1997), Tributyltin and policies for antifouling, Environ. Technol., 18(12), 1265-1268.

23. Lockheed, (1977), Ways to control Biofouling, Sea Technology, 18(11), 30-31.

24. Rajagopal, S., Nair, K.V.K. and Azaria, A., (1995), Response of brown mussel, Perna indica, to elevated temperature in relation to power plant biofouling control, J. thermal Biol.,20(6), 461-467.

25. Neuhauser, E.F., Rhode, M.A., Knowlton, J.J., Wahanik, R.J., Borden, M., Lewis, D.P. and Mackie, g., (1992), Thermal back-flushing to control Zebra Mussels at steam station, J. shellfish Res., 11(1), 234-235.

26. Pickles, S.B., (1997), Medium pressure Ultra-Violet light to control Zebra Mussels, Proc. 7 Intl. Zebra Mussel and Aquatic Nuisance Species conf., New Orleans, LA(USA), 28-31.

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27. Rajagopal, S., Nair, K.V.K., Azaria, A., van der Velde, G and Jenner, H.A., (1996), chlorination and Mussel control in the cooling conduits of tropical coastal Power Station, Mar. Env. Research, 41,201-221.

28. Anderson, D.B. and Richards, B.R., (1966), Chlorination of seawater: effects on fouling and corrosion, Trans ASME, 203-208.

29. Holmes, N.J., 1967), Mussel settlement in the cooling water Intake screens at Power Stations, Central Electricity Research Laboratories, Report No.RD/L/N 1 Leatherhead, Surrey, 6.

30. Jenner,, H.A., (1980), The biology of the mussel Mytilus edulis in relation to fouling problem in industrial cooling water systems La tribune du CEBEDEAU, 33, 13-19.

31. Cope, W.G., Bartech, M.R. and marking,L.L., (1997), the efficacy of candidate chemicals for preventing attachment of Zebra mussel (Dreissena polymorpha), Environ.Toxicol.Chem., 16(9), 1930-1934.

32. Schoenbach, K.H., Abou, G.A., Alden, R.W., Turner, R. and Fox, T.J., (1997), Biofouling prevention with pulsed electric fields, Proc. 7 Int. Zebra Mussel and Aquatic Nuisance species conf., New Orleans, LA (USA), 28-31.

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Table 1: Anti-fouling Technology: available literature sources Anti fouling agents Sources Copper compounds and metal

Cresco, 1996; Rao&balaji, 1994; Mukherjee et al., 1993; Marshall, 1980; Marine engineering, 1980; Chandler, 1979; Mc Naught, 1978; Gibson, 1972.

Organotin compounds and organometallic polymers

Ten Hallera, 1997; Fargasova& Kizlink, 1996;Price et al.,1994; linders, 1994;Fonalik et al., 1983; Kronstein,1980; Talbptt et al., 1980;Drisko et al., 1977; Bennet & Zedler, 1966

Organolead Kronstein, 1977; Henry and Paul, 1969 Elastomers Carderelli, 1963; cuthrell, 1967; Hohman, 1976 Biocides Chlorine

Allonies and Khalanaki, 1997; Venogopal et al., 1997; Menia and DeBruyn, 1997; Thompson et al., 1995; Rajagopal et al., 1995; Satpathy et al., 1994; Fisher, et al., 1994;de Beer et al.,1993; Nayar, 1989; William and Knox, 1989; finger, 1985; Kinelaki, 1985 and Wilde et al., 1983.

Chlorine dioxide Holte and Ryan, 1997. Copper-chlorine Knox-Holmes, 1993. Hydrogen peroxide Characklis, 1980; Nishimura et al., 1988. Bromine& Iodine Bidwell et al., 1992; Koening et al., 1995. Potassium and Chloramine

Dekan, 1995; Matissof, 1992.

Ozone Meldrim et al., 1981; Nakayama et al., 1980; Paller, 1979. Creosote Anderson, 1981.

Marine organisms used

Eel grass Zimmerman, 1993. Ascidians e Teo&Ryland, 1995. Marine sponge, Nudibranch, Holothurians

Haltori et al., 1996; Tsukamoto et al., 1996; Mokashe et al.,1994; Henrikson&Pawlik, 1995.

Corals Mary et al., 1997;Mizobatchi et al.,1993, 1996; Alizobuchi et al., 1994.

AF Materials Copper Castelli, 1979; Spears and Stone, 1969; Karande, 1977; Copper-Nickel Ansuini et al.,1978; Gaffoglio, 1987 Copper-Manganese-Cerium-Gallium

Mukherjee, 1997

Titanium Maruthamuthu et al., 1995. Controlled release materials

Parks et al., 1981; Talbot et al., 1980.

Heat treatment Payne, 1997; Rajagopal et al.,1994&1995; Neuhauser et al. 1992; Jones et al., 1990; Somerville, 1986.

Pulse-power Shoenbach et al.,1997; Fear & Macko, 1997; Okochi et al., 1994; Useami et al., 1994; Nakasone et al., 1993.

UV & Nuclear Pickles, 1997; Chalker, 1992; Seki et al., 1985; Nair, 1990.

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Radiation Scrubbing Burnett, 1980; Mitchell&Bensen, 1980; Leventhal, 1978;

Sato et al., 1972; Santhakumaran, 1970. Biological control Richards et al., 1997; Rickard et al., 1997; Serrouyu et al.,

1985; Cloe et al., 1995. Others Pressure washing Rickard et al., 1997. Water jetting Bain, 1981. Magnetic devices Smythe et al., 1997. Sonic devices Menezes, 1992; Zipts et al., 1990; Murphy&Latour, 1979;

Suzuki&Konno, 1970; Iskra, 1960. Robnotics Martin&Landsberger, 1992. Reproductive control Fingerman et al., 1994; Ram et al., 1992. Cathodic protection Easwar et al., 1995; Perez et al., 1994; sawant&Wag,1994;

Little&Wagner, 1993.

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-0.6

-0.4

-0.2

0

0.2

0.4

Wei

ght (

gm)

Fall Winter Spring Summer

Fig. a

Weigh GainedQuarterly increase/decrease

-0.6

-0.4

-0.2

0

0.2

0.4

Wei

ght (

gm)

Fall Winter Spring Summer

Fig. bFigure I: Fouling in Heat Exchanger/Water Box at the Al-Jubail Desalination/ Power Plant(1999-

2000).

Weight GainedQuarterly increase/decrease

(a): Inlet side (b) Outlet

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Digital Photograph: Different stages of fouling in the turbine condenser Water Box. 1-3: Visual Inspection at the time of shut down in July 1999; 4-: Coupon holder fixed on the anode. After 3 months: 5-: titanium coupons with polyethylene pieces on it; 6-7- Condenser tubes clogged with deposits. After 6 months: 8-: Polyethylene bags, ropes & debris. After 9 months: 9-:Balanus settled on a bag. 1

2

3

4

5

6

7

8

9

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Digital Photographs: Materials observed in the Condenser Water Box inlet side. Inspection after 9 months: 10 -: Tar ball with a Serpulid worm; 11- Bivalve Molluscs; 12- Balanus clusters with tar balls; 13-Crabs. Inspection in September 2000: 14- Polyethylene bags and other debris on Turbine Condenser Tubes; 15-Tubes getting clogged; 16&17 macrofouling settlement on the Travelling Screen; 18- Travelling Screen (Pump front) showing polyethylene bags, seaweeds & other debris that could fall in the bay and carried into the feed stream. 10

11

12

13

14

15

16

17

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