Prevention method of aquatic attaching fouling organisms and its apparatus

This invention relates to a method of preventing or controlling aquatic attaching fouling organisms which comprises covering aquatic organisms attaching portions on the surfaces of submerged structures or intake facilities with a plurality of mutually insulated metallic covers made of iron, magnesium, aluminum or their alloys through an insulating material and a cushion; using each of the metallic covers as an electrode; forming an electric circuit using the metallic covers facing each other as a pair; connecting the electrodes to a D.C. power supply having a polarity reversal function so as to supply a current between both poles either continuously or intermittently; and reversing the polarity of the current so that when one of the metallic covers is an anode, the surface of the metal constituting the metallic cover is dissolved and activated, and attachment of the aquatic fouling organisms to the surfaces of the metallic covers is prevented or controlled.

TECHNICAL FIELD 
This invention relates to a prevention or control method of aquatic 
attaching fouling organisms attaching and breeding on water contact 
surfaces of intake passes of power stations, iron foundries, oil refinery 
plants, ere, using water such as brine as cooling water, intake facilities 
such as screens, and submerged steel and concrete structures to be 
submerged and constructed in sea water such as piers, steel piles and 
steel pipe piles, and equipment used for the method. 
BACKGROUND ART 
Aquatic organisms inhabiting in water such as bacterias, seaweeds, 
shellfishes, etc, attach and breed on water contact portions of various 
harbor facilities such as quays, piers, platform piers, buoys, and 
submerged structures such as ships and greatly lower the functions of such 
facilities and submerged structures. 
The quantity of cooling water or power generation water for various intake 
equipment such as plant intake passes, intake pipes and screens, which is 
used as cooling water in steam power stations, atomic power stations, iron 
foundries, oil refinery plants, etc. or as power generation water of power 
stations, ranges from dozens of thousands of cubic meters to hundreds of 
thousands of cubic meter per hour and is extremely great. Therefore, 
maintenance management of the intake equipment is of great importance. The 
essential points of this maintenance management are corrosion control of 
the facilities and control of attachment of aquatic organisms attaching 
and breeding on the surfaces of the intake facilities in the same way as 
in the submerged structures. Attachment and breeding of the aquatic 
organisms are causes for the occurrence of various troubles in the normal 
operations of equipments and facilities. 
Excellent corrosion prevention engineerings such as the development of 
corrosion resistant materials, the progress in coatings and cathodic 
protection have been developed and put into practical applications as 
corrosion prevention control means of these submerged structures and 
Intake facilities. 
On the other hand, prevention means against attachment of aquatic fouling 
organisms such as marine creatures have long been employed. In other 
words, the following means have been proposed: 
(1) adding chlorine or hypochlorites; 
(2) coating of anti-fouling paints; 
(3) covering with anti-fouling metals; 
(4) formation of chlorine or hypochlorite ions by brine electrolysis; and 
(5) formation of copper ion using a copper anode. 
All of these methods are effective as prevention means against attachment 
of marine organisms, but they are anti-fouling means or methods comprising 
principally the formation of the toxic ions such as chlorine, 
hypochlorite, copper, mercury, tin, and there is the possibility that 
these toxic ions induce secondary environmental pollution. The formation 
and use of these toxic ions require great expenses for installations for 
keeping a suitable concentration or density for a long service life and 
for the maintenance and management of the installations; but mainly 
because they use the toxic ions and may result in environmental 
destruction rather than because of expenses, the use of such installations 
tends to be inhibited. 
Chlorine and hypochlorites can be charged easily, but the concentration 
management is difficult. If any reducing agents or substances exist in 
water, the consumption amount of chlorine becomes greater, and the 
anti-fouling effect cannot be expected in some cases. A great deal of 
labor and expenses are necessary for maintenance and management of a 
chlorine generation apparatus and its concentration management, and 
secondary environmental pollution is not avoidable. Therefore, the use of 
such compounds is now avoided as much as possible. 
Anti-fouling coatings or paints mostly contain metal pigments generating 
toxic ions, and comprise mainly mercury, mercury compounds, copper, copper 
alloys and their compounds. Recently, these materials have been replaced 
gradually by organic stannous compounds (stannates), but the service life 
as the coating is about 2 years. These paints involve the problem of low 
durability resulting from impact, wear and tear. Furthermore, the use of 
such coatings tends to be inhibited from the aspects of environmental 
pollution and safety in the same way as in the case of chlorine. 
Covering with the anti-fouling metals is the method which applies a 
covering of copper or a copper alloy to the submerged area of the 
structure and controls attachment of the aquatic fouling organisms by the 
toxic copper ion slightly eluting from the surface of copper or the copper 
alloy. However, this method needs to cover the entire surface of the 
structure and to perfectly insulate the structure (made of iron steel). 
(If any defect occurs in the covering metals, unusual corrosion occurs in 
the underlayer structure.) For these reasons, the cost of the covering 
work is high. It is one of the anti-fouling methods based on the toxic 
ion, and secondary environmental pollution is not avoidable. 
Anti-fouling means of marine organisms on the wall surfaces of submerged 
structures, particularly the intake facilities of plants using large 
quantities of brine as cooling water, most widely employ the formation of 
chlorine and hypochlorites by electrolysis of brine or the formation of 
the copper ion by the use of a copper anode. 
It is known to generate chlorine, particularly the hypochlorites, by direct 
electrolysis of brine. Various attempts have been made to attain higher 
economy and higher safety. For example, Japanese Patent Publication 
No.(Sho.) 51-41030 (41030/1976) describes a sea water electrolysis system 
for generating hypochlorites. Similarly, Japanese Patent Publication 
No.(Sho.) 54-40472 (40472/1979) discloses an anti-fouling and 
anti-corrosion method using a hypochlorite formation apparatus in 
combination with an iron ion generating system by sea water electrolysis, 
and Japanese Patent Laid-Open No. (Hei.)2-236290 (236290/1990) discloses 
an anti-fouling system using an electrode material obtained by applying an 
insoluble conductive film and a conductive film made of a highly 
conductive material to the submerged structure through an insulating film 
in place of a platinized titanium and carbon electrode as the conventional 
hypochlorite forming anode. 
Sea water electrolytic technique using a copper anode for forming toxic 
ions has long been known. For example, Japanese Patent Publication No. 
(Sho.) 41-5193 (5193/1966) describes a prevention method of aquatic 
attaching fouling organisms by D.C. electrolysis by disposing a copper 
anode and a cathode in the proximity of inner wall surfaces of sea water 
intake underdrains or open drains so as to elute the copper ion by D.C. 
electrolysis, and Japanese Patent Publication No.(Sho.) 45-923 (923/1970) 
describes a method which disposes a pair of copper electrodes on the inner 
surface of a sea water intake pipe and supplies an A.C. or a current 
reversible direct current voltage. Similarly, Japanese Patent Publication 
No. (Sho.) 43-6374 (6374/1968) describes a method which prevents 
attachment of aquatic fouling organisms by sea water electrolyzed by 
copper or copper alloy anode in sea water and adds cathodic protection 
means by using the objective structure as the cathode. 
Japanese Patent Laid-Open No.(Sho.) 59-9181 (9181/1984) describes a 
prevention method of aquatic attaching fouling organisms on the outer 
surfaces of submerged metal structures such as ships by applying a 
plurality of anti-fouling metals (principally copper or copper alloys) on 
time submerged areas. 
Anti-fouling means using other metals in place of copper or using these 
metals in combination with copper has also been proposed. For example, 
Japanese Patent Publication No.(Sho.) 48-39343 (39343/1973) discloses a 
method which prevents fouling of hulls of ships by covering the hulls with 
a zinc layer, uses the zinc layer as the anode while the ships are at rest 
by the use of an auxiliary electrode, and uses the zinc layer as the 
cathode during moving. Japanese Patent Publication No.(Sho.) 59-40361 
(40361/1984) discloses another method which feeds a D.C. current to an 
anode made of copper or a copper alloy and at least one kind of metals 
selected from the group consisting of zinc, aluminum, magnesium and iron, 
and disposed in the proximity, or at an intermediate part, of an intake 
port of a cooling pipe system of sea water or brackish water, which allows 
the copper ions to be adsorbed and concentrated by hydroxide colloid of 
the anode metal, and thus enhances the anti-fouling effect of the aquatic 
attaching fouling organisms and at the same time, inhibits the outflow of 
the copper ion into sea water. 
A method of preventing marine bio-fouling by generating a combination of 
A.C. and D.C. currents in order to elute controlled chlorine and copper 
ions into sea water is disclosed in Japanese Patent National Publication 
No.(Sho.) 63-502172 (502172/1988) (WO 087/03261). 
Anti-fouling means of the aquatic attaching fouling organisms by forming 
the chlorine and hypochlorite ions by the electrolysis of sea water or by 
utilizing the toxic character of the copper ion, etc, by the electrolysis 
using copper or the copper alloy as the anode are effective means, but 
they extirpate useful marine organisms in addition to secondary 
environmental pollution. 
According to Japanese Patent National Publication No.(Sho.) 63-502172 
(502172/1988) described above, the action potential of the marine 
organisms at the nerve/muscle interface is disrupted by the use of the 
A.C., and the possibility of their attachment of the structures is 
lowered. This method is said to be the means which controls attachment of 
the marine fouling organisms but does not extirpates them. As a method not 
involving the formation of the toxic ions, Japanese Patent Publication 
No.(Hei.) 1-46595 (46595/1989) discloses a method which, when the metal 
structures are constructed by valve metals such as titanium, deposit of a 
precious metal oxide catalyst on the surface of the valve metal, connects 
the metal structure to the anode of a D.C. power supply, inhibits the 
formation of chlorine, generates oxygen and hydrogen gases and prevents 
deposit of marine fouling organisms and scales consisting of calcium 
compounds. This method is directed to heat exchanger pipes made of the 
precious valve metal such as titanium. However, it is not industrially 
preferable to cover the surface of facilities, which are great both in the 
quantity and in the number, or the surface of the structures which are 
exposed to marine tidal currents changing incessantly, by the oxide 
catalyst coating valve metal. 
As described above, various anti-fouling means for preventing attachment of 
the aquatic attaching fouling organisms inhabiting and growing on the 
submerged areas of the marine structures have been developed, but none of 
them are entirely satisfactory. In other words, they involve the problems 
that the toxic ions are generated, secondary environmental pollution may 
be induced, maintenance management of the equipments is not easy, the 
running cost is high, and even useful aquatic organisms are extirpated. 
For example, intake facilities of power stations, ere, introducing large 
quantities of sea water as cooling water have the problem of getting rid 
of aquatic fouling organisms expanding over one thousand meters. At 
present, the removing operation is mechanically carried out by a manual 
operation (workers or divers) or using robots. In addition to its low 
removal efficiency, this method involves a large number of safety 
problems, requires an enormous removal cost, and needs a disposal and 
waste site of the marine organisms thus removed. Therefore, not only 
economical but also industrial losses are very large. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a prevention and control 
method of aquatic attaching fouling organisms having high efficiency and 
high economy and its equipments, which do not rely on the generation of 
chlorine and toxic ions, are free from secondary environmental pollution 
and moreover, do not extirpate the aquatic organisms. 
The inventors of the present invention have paid a specific attention to 
the fact that attachment and habitation of marine organisms can be hardly 
observed on the surface of an electrode functioning as an anode in 
conventional cathodic protection which has been applied to corrosion 
control of marine structures such as hulls of ships, harbor facilities, 
etc, by sea water, and have completed the present invention by utilizing 
and applying this phenomenon to intake facilities for which anti-fouling 
measures of marine organisms has been very difficult. The inventors of the 
present invention have realized further that this method can be applied to 
other marine structures, and intake facilities and submerged structures in 
fresh water and brackish water, and have completed the present invention. 
Fundamentally, the present invention is based on the observation that 
attachment and breeding of aquatic organisms can be scarcely observed or 
are drastically controlled on active dissolving portions by anodic 
electrolysis of metals selected from transition metals for generating 
non-poisonous ions, without using metals generating chlorine or toxic 
ions. 
Species and breeding seasons of aquatic organisms are different depending 
on seasons and sites, as will be described in more detail next. The marine 
organisms that cause problems in sea-water, for example, marine structures 
and marine intake facilities, are mussels, barnacles, sea squirts, oysters 
and seaweeds such as sea lettus and green laver. Particularly in the case 
of intake facilities (intake passes) of power stations, mussels account 
for 80% of the fouling organisms and barnacles do the rest, and the 
prevention of attachment of these marine organisms is a great technical 
problem. Generally, their attachment can be hardly observed at low 
temperature in winter season. They attach and grow in a warm season from 
spring to summer, and breed from fall to winter, but new attachment is not 
observed. The aquatic attaching fouling organisms cannot attach unless 
bacteria and slimes attach to a substratum. Therefore, prevention control 
of their attaching can be accomplished by preventing the attachment of 
these bacterias and slimes to the substratum, or even if they do, by 
preventing in advance the growth of their larvae. 
As described above, the present invention does not relate to the prevention 
and control method of the aquatic attaching fouling organisms by their 
extinction by the toxic ions but prevents and controls the method of their 
attachment. 
In other words, the gist of the present invention resides in the following 
points. 
(1) A prevention and control method of aquatic attaching fouling organisms 
comprising: covering attaching portions of aquatic fouling organisms on 
the surfaces of submerged structures or intake facilities with a plurality 
of mutually insulated metallic covers made of iron, magnesium, aluminum or 
their alloys through an insulating material and a cushion material; using 
the metallic covers as electrodes, respectively; composing an electric 
circuit using a pair of the metallic covers facing each other; connecting 
the electric circuit to a D.C. power supply having a current reversal 
function; supplying a current between both of the electrodes either 
continuously or intermittently; and reversing a current polarity so that 
when one of the metallic covers is an anode, the surface of the metal 
constituting the metallic cover is dissolved and activated, and attachment 
of the aquatic fouling organisms is controlled or prevented. 
(2) A prevention and control method of aquatic attaching fouling organisms 
comprising: covering attaching portions of aquatic fouling organisms on 
the surfaces of a submerged structure with a metallic cover made of iron, 
aluminum, magnesium or their alloys through an insulating material and a 
cushion material; connecting the metallic cover to a positive pole of a 
D.C. power supply and using it as an anode; connecting the submerged 
structure to a negative pole of the D.C. power supply to use it as a 
cathode and to form an electric circuit; and supplying a current between 
the cathode and the anode either continuously or intermittently so as to 
prevent or control the attachment of the aquatic fouling organisms to the 
surface of the anode metallic cover by dissolving and activating the 
surfaces of the metallic cover. 
(3) A prevention and control method of aquatic attaching fouling organisms 
comprising: covering attaching portions of aquatic fouling organisms on 
the inner surfaces of an intake facility other than its bottom surface 
with a plurality of mutually insulated metallic covers made of iron, 
magnesium, aluminum or their alloys through an insulating material and a 
cushion material; connecting the metallic covers to positive pole of a 
D.C. power supply and using them as an anode; disposing iron or an iron 
alloy material on the bottom surface of the intake facility and connecting 
it to a negative pole of the D.C. supply to use it as a cathode to form an 
electric circuit; and supplying a current between the cathode and the 
anode either continuously or intermittently so that the surfaces of the 
metals constituting the metallic cover are dissolved and activated, and so 
that attachment of the aquatic fouling organisms to the surfaces of the 
metallic cover is controlled or prevented. 
The structures to which the present invention are directed are submerged 
structures and intake facilities in sea water, fresh water and brackish 
water. 
Here, the term "submerged structures" represents various harbor facilities 
constructed in water such as quays, piers, platform piers and buoys and 
ships, and made primarily of iron steel materials and concrete materials. 
The term "intake facilities" represents intake passes and intake pipes for 
cooling and power generation, and structures using such intake facilities 
are various factories and plants such as steam power or water power 
stations, iron foundries, oil refinery plants. The cross-sectional views 
of the surfaces of these intake facilities are rectangles, circles, ovals, 
squares, etc, and their shapes are arbitrary. 
According to the present invention, the wall surfaces of these submerged 
structures and intake facilities, on which the aquatic fouling organisms 
are likely to attach, are covered with mutually insulated metallic covers 
made of iron, aluminum, magnesium or their alloys, through an insulating 
material and a cushion. A synthetic rubber such as neoprene and silicon 
rubber, and plastics such as PVC, polyethylene and polyester are used as 
the insulating material. Blistered polyethylene sheets, blistered 
polyurethane sheets, etc, are used as the cushion. One of these materials 
may be used as the insulating material and the cushion. A synthetic rubber 
or a plastic of 10 mmt or more is used as this insulating-cushion 
material. The coating of the metallic covers is fixed to the surfaces of 
the submerged structures by the use of customary means as insulating bolts 
and adhesives. 
A pair of these metallic covers facing each other are used as electrodes so 
as to form an electric circuit, and are connected to a D.C. power supply 
having a current reversal function. The current is supplied between both 
electrodes either continuously or intermittently, and the current polarity 
is reversed so that when one of the metallic covers is the anode, the 
surface of the metal constituting the metallic covers is dissolved and 
activated and attachment of the aquatic fouling organisms is controlled or 
prevented. The electric circuit formed hereby may have a combination 
function with A.C. 
To reduce the time during which the metallic cover is the cathode, the 
reversal interval of the current is preferably carried out at the interval 
of 10 seconds to 60 minutes. 
When the current is supplied intermittently, an interval between the 
current supply and the nonsupply is preferably shortened. Generally, this 
gap is preferably from 10 seconds to 60 minutes. When the current is 
supplied for 4 hours per day, this 4 hours' time is preferably divided as 
finely as possible when supplying the current. 
When the structure is the submerged structure, the portions of the 
structures to which the aquatic fouling organisms attach are covered with 
the metallic cover made of iron, aluminum, magnesium or their alloys 
through the insulating material and the cushion material in the same way 
as described above. The metallic cover is connected to the positive pole 
of the D.C. power supply and is used as the anode while the structure is 
connected to the negative pole of the D.C. power supply so as to form the 
electric circuit. The current is supplied between the anode and the 
cathode either continuously or intermittently, so that the surface of the 
metallic cover can be dissolved and activated and attachment of the 
aquatic fouling organisms to the surface of this anode metallic cover can 
be prevented or controlled. In this case, water functions as an 
electrolyte. As a result, attachment of the aquatic Fouling organisms to 
the surface of the metallic cover in contact with water is controlled and 
since the current flows into the submerged structure, surrounding 
corrosion can be controlled. The electric circuit in this case need not 
always have the polarity reversal function. 
Since the electric circuit is formed between the anti-fouling metallic 
cover and the submerged structure in this case, their direct short-circuit 
must be avoided. Therefore, a sheet-like product or molded product having 
a similar shape to the outer shape of the submerged structure is 
preferably used as the anti-fouling metallic cover. 
A protective cover is applied in some cases to water-line portions of the 
submerged structure such as piers for the purpose of corrosion protection. 
In this case, the metallic cover described above may be applied to the 
submerged structure by removing the corrosion protection cover of the 
outermost layer applied below the water line or below water, through the 
insulating material and the cushion in place of this corrosion protection 
cover. In this way, the submerged structure is protected by both the above 
prevention control method of the aquatic attaching fouling organisms and 
the protective cover. 
Generally, sand, mud, etc, are likely stay at the bottom portions of the 
intake facilities and since these portions have insufficient supply of 
oxygen (air), the aquatic fouling organisms can hardly grow up at such 
portions. In such a case, the portions of the intake facilities at which 
the aquatic fouling organisms attach, other than the bottom surface, are 
covered with the insulated metallic cover through the insulating material 
and the cushion material, and this metallic cover is connected to the 
positive pole of the D.C. power supply and is used as the anode. On the 
other hand, iron or its alloy is disposed on the bottom surface of the 
intake facilities, is connected to the negative pole of the D.C. power 
supply and is used as the cathode. These anode and cathode together 
constitute an electric circuit, and the current is supplied between them 
either continuously or intermittently so as to dissolve and activate the 
surface of the metal constituting the metallic cover and to prevent or 
control the attachment of the aquatic fouling organisms. The electric 
circuit obtained In this case need not always have the current reversal 
function. 
In the present invention, active dissolution of the electrode due to the 
anode current prevents or controls attachment of the aquatic fouling 
organisms. Therefore, there is an anode current density which is suitable 
for the prevention or control. Though the anode current density is 
preferably great, it 1s preferably not more than 500 mA/m.sup.2 (0.5 
A/m.sup.2) from the economical and industrial aspects, more preferably 
from 40 to 500 mA/m.sup.2 (0.04 to 0.5 A/m.sup.2) and further preferably, 
150 to 300 mA/m.sup.2 (0.15 to 0.3 A/m.sup.2). It is also preferred to 
regulate the anode current density, either regularly or irregularly, in 
accordance with the species or active living time of the aquatic fouling 
organisms. 
An apparatus preferably used for the prevention method of aquatic fouling 
organisms according to the present invention comprises a multi-layer 
structure fitted to attaching portions of aquatic fouling organisms on the 
surfaces of submerged structures or intake facilities, and comprising an 
insulating material, a cushion material and a metallic cover made of iron, 
aluminum, magnesium or their alloys; and a D.C. power supply capable of 
supplying a current between the metallic covers or between the metallic 
cover and the submersed structure; or comprises a multi-layer structure 
fitted to attaching portions of aquatic fouling organisms on the inner 
surfaces of intake facilities other than its bottom surface, and 
comprising an insulating material, a cushion material and a metallic cover 
made or iron, aluminum, magnesium or their alloys; iron or its alloy 
member disposed on the bottom surface of the intake facility; and a D.C. 
current supply capable of supplying a current between the metallic cover 
and the iron or iron alloy member. 
As the prevention apparatus against the aquatic attaching fouling 
organisms, an apparatus the D.C. power supply of which constitutes an 
electric circuit having a current reversing function, an intermittent 
current supply function or a combination function with A.C. is used 
preferably. 
The present invention uses iron, aluminum, magnesium and their alloys, the 
dissolved ions of which have hardly any toxicity or are said to be 
harmless, as the anode in water. Therefore, the aquatic fouling organisms 
hardly attach to the surface of the metal, and even when they do, their 
adhesive strength to the metal surface is very low and they easily fall 
off from time metal surface. Moreover, the formation of time chlorine gas 
due to electrolysis hardly occurs even in the case of sea water, and the 
formation of the oxygen gas and the hydrogen gas is hardly observed, 
either. 
The reason why attachment of the aquatic fouling organisms is restricted by 
dissolution of the anode metal by the D.C. electrolysis without the 
formation of such toxic ions and gases has not yet been clarified 
sufficiently, but is assumed as follows: Namely, when a D.C. voltage is 
loaded between the anode metal and the cathode metal, active dissolution 
of the anode metal occurs to fall short of attaching conditions of the 
aquatic Fouling organisms, so that these organisms lose their attaching 
abilities.

BEST MODE FOR CARRYING OUT THE INVENTION 
Hereinafter, the present invention will be explained definitely with 
reference to embodiments thereof, but the invention is in no way limited 
by these embodiments. 
EMBODIMENT 1 
Experiments were carried out for the relation between an anode current 
density, the species of aquatic fouling organisms and the quantity of 
their attachment when active dissolution was effected using an iron steel 
as an anode. 
An iron steel sheet (having the inside with an insulating cover) of 3.2 
t.times.350 w.times.450 Lmm was connected to a positive pole of a D.C. 
power supply and was used as an anode Inside a natural marine zone facing 
Suruga Bay, Shizuoka Prefecture, as a substantially average sea area in 
Japan, and another iron steel member disposed separately was used as an 
opposed cathode. A constant current was supplied between the cathode and 
the anode so as to examine the conditions of attachment of marine 
organisms to the surface of the anode iron steel material, a consumption 
rate of the anode and an anode potential. 
The anode current density was set to 14 stages from no-current for control 
to 3,000 mA/m.sup.2 (i.e. 0, 10, 20, 30, 50, 100, . . . , 3,000 
mA/m.sup.2). The period of the current flow started from early winter 
(toward the end of December) during which the marine organisms were said 
to be non-active, passed through active seasons (spring to early summer), 
breeding and best growing season (early summer to early fall) and ended in 
moderate growing season (early fall to early winter) for about one year. 
Fig. 1 shows the quantity of the marine organisms, the anode corrosion rate 
and the anode potential-anode current density relation after the supply of 
power for about a year. In the drawing, a solid line represents the 
quantity of the aquatic fouling organisms for each anode current density, 
a dotted lines represents anode corrosion rate, and a dash line represents 
the anode potential. 
As shown in FIG. 1, the attaching quantity of the marine organisms 
decreased with the increase of the anode current density, and dropped 
drastically when the anode current density exceeded 40 to 50 mA/m.sup.2. 
Furthermore, when the anode current density exceeded 100 mA/m.sup.2, the 
attaching quantity of the marine organisms was below 0.5 kg/m.sup.2, which 
could be substantially neglected, and was close to 0 at 200 mA/m.sup.2. 
On the other hand, the anode corrosion rate was naturally greater than 0.1 
to 0.2 mm/Y of a normal corrosion rate, and became greater with a higher 
current. When the current exceeded 500 mA/m.sup.2, the anode corrosion 
rate became 3 times that of natural corrosion and drastically increased. 
As is obvious from the explanation given above, the anode current density 
is up to 500 mA/m.sup.2, is from 40 to 500 mA/m.sup.2 from the industrial 
and economical aspects as well as from the aspect of environmental 
preservation, and is most preferably 150 to 300 mA/m.sup.2. 
The anode potential somehow got to a noble potential when time anode 
current density exceeded 500 mA/m.sup.2, but was below -600 mV even at 
3,000 mA/m.sup.2 and was hardly polarized from the normal potential of the 
steel. In other words, in comparison with 1.0 V (SCE) as the evolution 
potential of chlorine in sea water, it was by far based and the occurrence 
of chlorine could not at all be considered. 
When the relation between the deposited marine organisms and the anode 
current density was examined in further detail, large quantities of 
various organisms such as mussels, barnacles, sea squirts, tube worms, 
etc, attached to all the surfaces of the electrode without a current, and 
they grew to a thickness of 10 to 20 cm. When the current density was less 
than 40 mA/m.sup.2, large quantities of barnacles and sea squirts 
attached. Though attachment of mussels could be observed partially, this 
attachment dropped drastically or became nil at the current density of 40 
to 50 mA/m.sup.2, and barnacles, sea squirts and tube worms attached 
locally. When the current density was more than 100 mA/m.sup.2, attachment 
of almost all the marine organisms could not be observed, and matured 
lavae of barnacles were observed spottedly or seaweeds could be observed. 
Also, yellow brown products could be observed. These products could be 
easily removed when rubbed with fingers, and the steel surface having a 
metal luster could be observed below these products. 
EMBODIMENT 2 
Activity of the marine organisms exhibits a seasonal change. For example, 
the species and attaching quantity of these marine organisms attaching to 
fixed structures such as intake passes and submerged structures change 
with seasons, that is, four seasons, months, water temperatures, and so 
forth, and their habits also change. In this embodiment, therefore, the 
attaching conditions were tested by dividing a year into four periods 
(first period: the last third of December to the second third of March, 
second period: the last third of March to the second third of June, third 
period: the last third of June to the second third of September, fourth 
period: the last third of September to the second third of December), and 
the attaching conditions in each three month's period were examined 
because the experiments were carried out for full one year in Embodiment 
1. The sea water temperatures were 14.0.degree. C. for the first period, 
16.6.degree. C. for the second period, 24.3.degree. C. for the third 
period and 18.8.degree. C. for the fourth period, and the seasons 
corresponded to these water temperatures, respectively. 
The results of the experiments were tabulated in FIG. 2. In this diagram, a 
solid line represents the attaching quantities of each period (season), a 
dotted line represents the anode consumption rate and a dash line does the 
anode potential. 
The attaching quantity of the marine organisms decreased with an increasing 
anode current density, and this tendency resembled that of the experiment 
for full one year shown in FIG. 1. The attaching quantity of the marine 
organisms was smaller in each period even in the case of the non-supply of 
the current in comparison with the case of the supply of the current, 
because a new steel material was charged in each period. 
When evaluation was made for each period, it was found that the attaching 
quantity of the marine organisms was 0.3 to 0.4 kg/m.sup.2 even when the 
current was not supplied, in the first winter period (average water 
temperature=14.0.degree. C.), and this value was at a negligible level. 
In the second period as the active attaching season when water started to 
warm (average water temperature=16.6.degree. C.), attaching of mussels was 
accelerated, and barnacles, sea squirts and seaweeds started attaching. 
The attaching quantities of these marine organisms to the anode surface 
decreased with the increase in the anode current density, and when the 
density exceeded 40 to 50 mA/m.sup.2, the attaching quantity decreased 
drastically, and could be substantially neglected at more than 120 
mA/m.sup.2 as the quantity dropped to not more than 0.2 kg/cm.sup.2. 
Attachment, growth and reproduction of the marine organisms became 
remarkable irrespective of their species in the third period as the hot 
summer period (average water temperature=24.3.degree. C.). In this period, 
new attachment of mussels could be hardly observed but attachment of 
barnacles and sea squirts became greater. The attaching quantities of the 
marine organisms were the greatest in this period in which the growth and 
reproduction of the marine organisms were vigorous. Although the attaching 
quantities decreased with the increase in the anode current density, the 
attaching quantities were some multiples of other seasons at a low current 
density. The attaching quantity was not more than 0.5 kg/m.sup.2 at 100 
mA/m.sup.2, and could be neglected substantially at more than 130 
mA/m.sup.2 because the quantity was not more than 0.2 kg/m.sup.2. 
Since new attachment of the marine organisms decreased in the fourth period 
(average water temperature =18.8.degree. C.) where activity of the marine 
organisms was stable, the overall attaching quantity dropped and the 
attaching tendency was similar to that of the second period. In this 
period, attachment of barnacles and white sea squirts was observed to some 
extents but new attachment of mussels was hardly observed. 
On the other hand, the anode consumption rate was represented by a 
corrosion rate (mm/Y), and the tendency was similar to a corrosion 
tendency of the year round experiment. In any case, the anode consumption 
rate became great when the anode current density exceeded 500 mA/m.sup.2, 
and this was not advantageous from the industrial and economical aspect 
and also from the conservation of environment. 
The most optimum anode density for limiting the corrosion rate to not more 
than 0.5 mm/Y and minimizing the attaching quantity of the marine 
organisms was 100 to 400 mA/m.sup.2. 
The anode potential, too, was similar to that of the year round experiment, 
and the generation of chlorine could not be believed as described in 
Embodiment 1. 
EMBODIMENT 3 
A critical anode current density for limiting the attaching quantity of the 
marine organisms to less than 1.0 kg/m.sup.2, less than 0.5 kg/m.sup.2, 
less than 0.2 kg/m.sup.2 and 0.1 k/m.sup.2 in the year round experiment 
and the first to fourth periods was measured, and the result was shown in 
FIG. 3. 
As the attaching quantity of these marine organisms was brought closer 
substantially to zero, the critical anode current density had to be 
increased. To limit the attaching quantity to less than 0.2 kg/m.sup.2 
(generally, below 1/100 of the attaching quantity 30 to 40 kg/m.sup.2 of 
the marine organisms under the natural state), the anode current density 
had to be at least 140 mA/m.sup.2 in the year round experiment, but in 
accordance with the periods, the anode current density was less than 20 
mA/m.sup.2 in the first period, 110 mA/m.sup.2 in the second period, 130 
mA/m.sup.2 in the third period and 180 mA/m.sup.2 in the fourth period. 
One of their values in four periods was higher than the anode current 
density in the year round experiment, but these values were 110 mA/m.sup.2 
on an average. In other words, the current could be reduced to 80% of the 
constant current through the year round. 
EMBODIMENT 4 
FIG. 4 is a perspective view showing an embodiment of a prevention 
apparatus against marine attaching organisms according to the present 
invention installed in a box culvert type intake facility, FIG. 5 is a 
sectional view of the apparatus shown in FIG. 4, and FIG. 6 is a side view 
of a portion A-A' in FIG. 5. In FIGS. 4 to 6, reference numeral 1 denotes 
a panel shape laminator (electrode); 2 is an insulating frame (electrode 
support); 3 is fixing means (bolts); and 4 is marine intake facilities 
(cooling water intake pass). In FIG. 4, an arrow represents a water flow 
direction. In FIGS. 4 to 6, a D.C. power supply for supplying a current to 
each panel shape laminator is not shown. The inner wall portion of this 
cooling water intake pass 4 had a width of 2.4 m, a height of 3.0 m and a 
length of 200 m. 
As shown in FIGS. 4 to 6, a plurality of panel shape laminators 1 serving 
as the electrodes were fitted to all the inside wall surfaces (objective 
area=180 m.sup.2) of the cooling water intake pass 4 other than its bottom 
surface. The shape of cross-section of the inside wall surfaces of this 
cooling water intake pass 4 was rectangular as shown in FIG. 5. 
Each panel shape laminator 1 consisted of a multi-laminator (by bonding a 
back surface insulator and a cushion) of an SS 400 steel sheet, and had a 
width of 0.85 m, a length of 1.8 m and a thickness of 1.6 mm. 
The electrode support 2 (width: 0.1 m, length: 4 m) made of FRP (fiber 
reinforced polymer) was used for the insulation between the panel shape 
laminators 1 and fixed support bolts 3 of a resin cure-and -bury type 
(tradename: "Chemical Anchor") were used for fixing. A recess was formed 
on the surface of this FRP electrode support 2 and was filled up with a 
self polishing anti-fouling paint to prevent attachment of the marine 
organisms. 
A definite fixing method is as follows. Each panel shape laminator 1 was 
inserted and clutched into a support groove of the FRP electrode support 2 
fixed to the wall surface of the cooling water intake facility using the 
chemical anchor in consideration of the retention of the strength to the 
flow velocity and uniform consumption of the anode (panel shape laminator) 
1. Furthermore, to prevent vibration of the panel shape structure 1, the 
fixed supporting bolts 3 were applied at the center of the laminator 1 in 
its longitudinal direction with 2 spots between them. 
FIG. 7 shows a lead wiring figure of this prevention apparatus against the 
marine attaching organisms. Reference numerals are the same as those used 
in FIG. 4. Reference numeral 5 represents a connecting wire, 6 is a D.C. 
circuit, 7 is a D.C. power supply, 8 is an A.C. circuit, 9 is a control 
circuit, and 10 is a control box (concentric control apparatus ). 
The D.C. circuit 6 was connected to the D.C. power supply 7 using an intake 
pass cable fitted to the back of each panel shape structure as the 
connecting wire 5 and using a CV cable for the underground portion. The 
panel shape laminators 1 on the facing inside wall surfaces form a pair 
and the D.C. circuit 6 was connected to the D.C. power supply 7 so that 
the panel shape laminators function as the anode and the cathode, 
respectively. The D.C. power supply 7 was of a full wave rectification 
type, has output power of DC 20 V.times.80 A, and selectively supplied 
power in accordance with the instruction from the control box 10 having 
the concentric control function of current reversal and intermittent 
current supply. The control box 10 normally received power of AC 600 V, 3 
.phi., converted it to 200 V, 3 .phi. and supplied it to the D.C. power 
supply 7. At the same time, the control box 10 controlled the operation of 
the D.C. power supply 7 by the concentric control function, and monitored 
the attaching state of the marine organisms on the wall surfaces of the 
intake pass through a monitor. To reduce the power loss due to the voltage 
drop of the D.C. circuit 6 and the material and work costs of the pipings 
and lead wires, the D.C. power supply 7 was divided into five segments and 
were disposed near the cooling water intake pass 4 as shown in the 
drawing. Five D.C. power supplies 7 were disposed as one circuit for each 
of these segments, and each of the D.C. supplies 7 were concentrically 
managed by the control box 10. 
The current was supplied by dividing one hour into three cycles by the 
polarity reversal mechanism assembled in the D.C. power supply. FIG. 8 
shows a time chart as an example of this current supply operation cycle. 
In this operation cycle, the current supplied is 54 A (0.3 A/m.sup.2) and 
the operation was carried out for about 50 days from the spring season as 
the reproduction season of the marine organisms. As a result, attachment 
of the marine organisms on the surface of the panel shape laminators could 
be hardly observed, and the surface exhibited a blackish brown color. 
Thereafter, the current was reduced to 5.4 A (0.03 A/m.sup.2), but 
attachment of the marine organisms was not observed even after the passage 
of 70 days, though attachment of seaweeds was partly observed. In 
contrast, in similar cooling water intake passes not subjected to any 
anti-fouling treatment, marine organisms such as seaweeds, barnacles, 
mussels, etc, attached to the surfaces of the intake passes, and were 
observed growing day by day in this season. 
During the operation, the anode potential of the panel shape structure was 
-600 to -710 mV (SCE) and did not reach 1.1 V (SCE) which was the chlorine 
generating potential in sea water, and chloride was not generated. The 
cathode potential of the panel shape laminator was a less noble potential 
than -900 mV, and was completely corrosion-proofed. Though attachment of 
the marine organisms to these panel shape laminators due to the 
electrolytic reaction was observed, they could be removed easily by 
current reversal. The electrolytic voltage was 2.0 to 4.0 V. When the 
current was reduced to 5.4 A, the voltage showed 1.0 to 1.5 V. 
EMBODIMENT 5 
FIG. 9 is a sectional view showing the prevention apparatus against marine 
organisms according to another embodiment of the present invention. In the 
drawing, like reference numerals are used as in FIGS. 4 to 6, and 
reference numeral 11 denotes a cathode material. 
In this apparatus, a plurality of panel shape laminators 1 as the anode 
were fitted to all the inside wall surfaces of the cooling water intake 
pass 4 other than its bottom surface in the same way as in Embodiment 4 
(objective area: 180 m.sup.2). A cathode material 11 made of a steel was 
disposed on the inside wall bottom surface of the cooling water intake 
pass 4. 
An electric circuit was constituted using a plurality of panel shape 
laminators as the anode and the cathode material 11 as the cathode, and a 
current was supplied under the same condition as that of Embodiment 4. In 
other words, the current was 54 A (0.3 A/m.sup.2), and ON/OFF of the 
current was repeated. One cycle consisted of ON and OFF for 30 minutes, 
respectively, and the operation of 24 cycles/day was carried out. This 
time chart is shown in FIG. 10. 
As a result, attachment of the marine organisms could be hardly seen on the 
surface of the panel shape laminators in the same way as in Embodiment 4 
even after the passage of 50 days, and the surface remained blakish grown. 
The surface area of the cathode was extremely smaller than that of the 
anode panel shape laminators and was under the over-protection state. 
Therefore, a coating consisting of calcium and magnesium was hardly 
deposited to the cathode surface but peeled off, and attachment of the 
marine organisms was hardly observed. 
EMBODIMENT 6 
FIG. 11 is a perspective view showing another embodiment of the present 
invention applied to steel pipe piles of substructures of piers. FIG. 12 
is a sectional view of the steel pipe pile portions of the substructure. 
This embodiment was directed to the steel pipe piles of one block of the 
piers, and one block had a planar shape of a length of 36 m and a width of 
12 m, the outer diameter of the steel pipe piles of the substructure was 
800 mm, and these piles were disposed in an arrangement of 5 rows by 4 
columns. FIG. 11 shows the lead wires in magnification. 
In FIGS. 11 to 12, reference numeral 12 denotes a marine structure (steel 
pipe piles of the pier), 13 is a metal member (anode), 14 is a cathode 
terminal, 15 is a connection box for electrodes, 16 is a D.C. lead wires, 
17 is a distribution box, 18 is a D.C. power supply, 19 is an upper 
structure of the pier, 20 is an insulation/cushion material, 21 is a 
corrosion protecting material, 22 is a corrosion protecting cover, and 23 
is fixing means. Symbol H.W.L. represents a high water level line, and 
L.W.L does a low water level line. 
The steel pipe piles 12 were provided with the corrosion protecting 
material 21 such as a petrolatum paste, petrolatum tape and a plastic 
blistering material, and with the corrosion protecting cover 22 made of 
FRP with the tidal zone being the center. 
As shown in FIG. 12, a part of the FRP protecting cover 22 as the outermost 
layer of this corrosion-proof coating, that is, the marine organisms 
attaching portion, was removed, and a steel sheet 13 (metal member) having 
a thickness of 2.3 mmt was wound through the insulation/cushion material 
20, and was fastened and fixed to the steel pipe piles 12 by the fixing 
means 23. 
To use the steel sheet 13 as anode, an electric circuit contact was 
disposed on the back of the steel sheet and insulation coated wires were 
fitted. The lead wires were extended to the connection box 15 for 
electrode provided on the superstructure of pier and were connected to the 
positive pole of the D.C. power supply 18. On the other hand, another lead 
wire was connected to the steel pipe piles 12, was taken into the 
connection box 15 for electrodes, and was connected to a negative pole of 
the D.C. power supply 18. 
In the steel pipe pile pier shown in FIG. 11, cathodic protection by 
galvanic aluminum alloy anodes was applied to the steel pipe piles which 
was always kept below water surface. Therefore, the prevention apparatus 
against the marine organisms in this embodiment was disposed so as to 
cover the portion 1 m below L.W.L up to H.W.L. 
This prevention apparatus against the marine organisms was practiced for 20 
steel pipe piles of one block, and corrosion protective covering was 
applied to other blocks as usual and cathodic protection was applied to 
the portions kept always below the sea water level. The work was finished 
in the fall season, and the supply of the current was started in early 
spring when the marine organisms started their activity. Observation was 
made after about a year through the active periods of spring, summer and 
fall. 
The continuous current was supplied at a rate of 50 mA/m.sup.2 in the early 
active season of the marine organisms, and at rates of 250 mA/m.sup.2 in 
April to May, 200 mA/m.sup.2 in June to August, 100 mA/m.sup.2 in 
September, 50 mA/m.sup.2 in October, and 20 mA/m.sup.2 in November, 
respectively, but no current was supplied during December to February. 
The ON/OFF supply of the current in a 30 minutes' unit with a constant 
current quantity per day was applied to part of the steel pipe piles 
during April and May as the best reproduction season. 
As a result, attachment of the marine organisms in a thickness of about 15 
to 20 cm was observed on the steel pipe piles not using the prevention 
apparatus of this embodiment below and near the water level, but in the 
case of the steel pipe piles using the prevention apparatus, attachment of 
slimes, seaweeds or extremely small shellfishes was observed in a part of 
the steel pipe piles. When the attaching quantities of the marine 
organisms were measured, the values were 40 to 60 kg/m.sup.2 for the 
former and not more than 0.5 kg/m.sup.2 for the latter, which was below 
1/100 of the prior art. 
EMBODIMENT 7 
FIG. 13 is a sectional view showing the state where the present invention 
was applied to the steel pipe piles for substructures. In this drawing, 
like reference numerals are used to identify like constituents as in FIG. 
12. Reference numeral 201 denotes a cushion material and 202 does an 
insulating material. Since anti-fouling coating was not applied to the 
steel pipe plies 12, a 2.3 mm-thick steel sheet (metal member) 13 was 
applied to the steel pipe piles 12 through the insulating material 202 and 
the cushion material 201 up to a splash zone above H.W.L. In this 
embodiment, too, in order to use the steel sheet 13 as the anode, the 
electric contact bonding part was disposed on the steel sheet, and an 
insulating coating lead wire was fitted, was guided to the connection box 
15 provided on the superstructure of pier 19 and was connected to the 
positive pole of the D.C. power supply 18. On the other hand, another lead 
wire was connected to the steel pipe piles 12, was taken into the 
connection box 15 and was connected to the negative pole of the D.C. power 
supply 18. 
An experiment was carried out using this prevention apparatus against the 
marine organisms in the same way as in Embodiment 6. As a result, although 
attachment of slimes, seaweeds and extremely small shellfishes was 
observed at a part of the steel pipe piles, the attaching quantity was 
extremely small. 
EMBODIMENT 8 
FIG. 14 is a side view showing another embodiment of the present invention 
applied to the ship hull, and FIG. 15 is its sectional view. 
In FIGS. 14 and 15, like reference numerals are used to identify like 
constituents as in FIG. 12. Reference numeral 24 denotes a screw 
propeller, 25 is a rudder, and 26 is an insulation keel, and symbol W.L 
represents a draught line. 
In this embodiment, time steel sheet (metal member ) 13 was fitted through 
the insulation/cushion material 21 in place of an anti-fouling 
anti-corrosion paint applied to the ship hull (marine structure) 12. The 
steel sheet 13 and time insulation/cushion material 21 were produced in 
advance into a unistructure. To fit this unistructure to the ship hull 12, 
an adhesive was applied to time insulation/cushion material 20, and 
fastening was made by the use of stud bolts (fixing means) 23 at necessary 
portions. The head of each stud bolt 23 was shaped by a streamline cap so 
as to minimize the water contact resistance. 
When the experiment was carried out using this prevention apparatus against 
the marine organisms, attachment of slimes and extremely small shellfishes 
was observed partly on the ship hull after the passage of six months, but 
the attaching quantity was extremely small. 
The foregoing embodiments of the invention represent the case of the marine 
structures and sea water intake facilities constructed in sea brine, but 
the present invention can of course be applied in the same way to 
submerged structures constituted in fresh water and brackish water and to 
intake facilities of power generation plants. 
INDUSTRIAL AVAILABILITY 
As described above, the present invention can industrially and economically 
prevent or control aquatic attaching fouling organisms by controlling the 
current density of the anode as the anti-fouling object in accordance with 
the life mode of aquatic fouling organisms. Particularly, the method of 
the present invention is not the method which eliminates the marine 
organisms by generating toxic metal ions or forming chlorine and 
hypochlorites, but is the prevention method of the attaching fouling 
organisms on the basis of active dissolution of intoxic metals. Since the 
anode current density for limiting the quantity deposition of the aquatic 
fouling organisms to an allowable value is now clarified, the operation 
management becomes easy, and the service life of the anode can be 
estimated. 
Furthermore, the reduction of power consumption and a further extension of 
the service life of the anode become possible by regulating the anode 
current density In accordance with the seasons, that is, in accordance 
with activity (active and non-active) of the aquatic fouling organisms by 
grasping the life mode of the aquatic fouling organisms in accordance with 
the season, weather, sites or months.