Method of purifying lacustrine water and filthy water purification
TECHNICAL FIELD 
     This invention relates to a method of purifying lacustrine water and a filthy water purification boat. 
     BACKGROUND ART 
     In a lake (the word &#34;lake&#34; used herein means a pond, a marsh and the like in addition to a lake), water is hard to move as compared with in the sea or rivers, resulting in stagnating and fails to exhibit a satisfactory self-purifying action, so that pollution of lacustrine water gets worse, to thereby often cause production of algae, odor development and the like. 
     Purification of lacustrine water thus polluted has been conventionally carried out by arranging an aeration system at a lake, installing a water treating system on the land, or drawing up water by means of a pump from a lake for treatment. 
     DISCLOSURE OF INVENTION 
     However, use of the aeration system for evenly purifying lacustrine water requires lots of time. Purification of lacustrine water through the water treating system requires arrangement of a water suction and guide pipe network over a whole lake. Unfortunately, this obstructs navigation of boats, so that it is difficult to evenly purify lacustrine water. The present invention solves the above-described problem by operating, on a lake, a filthy water purification boat mounted with a calcium fluoride electrolyzing device. 
     In accordance with one aspect of the present invention, a method of purifying lacustrine water is provided. The method comprising the steps of operating a boat provided with a calcium fluoride electrolyzing device, a DC power supply device electrically connected to the electrolyzing device and a coagulant pouring device on a lake, and concurrently introducing lacustrine water into the electrolyzing device and pouring coagulant into lacustrine water through the coagulant pouring deivce. 
     In a preferred embodiment of the method of the present invention, the boat is further provided with a flock recovering device for recovering a part or all of the flocks produced. 
     In a preferred embodiment of the method of the present invention, lacustrine water introduced into the electrolyzing device is treated while being stirred. 
     In accordance with another aspect of the present invention, a filthy water purification boat is provided. The boat comprises an electrolyzing device suspendedly arranged at a lower portion of the boat and including a plurality of electrode plates juxtaposed to each other at suitable intervals on struts and a cage arranged between each adjacent two of the electrode plates for receiving fluorite therein; a coagulant pouring device including a pipe provided with coagulant pouring nozzles and arranged forward of the electrode plates and a coagulant tank arranged on the boat; and a DC power supply arranged on the boat and electrically connected to the electrolyzing device. 
     In a preferred embodiment of the filthy water purification boat of the present invention, a flock recovering device of which at least a part is arranged at a rear portion of the boat is further provided. 
     In the present invention constructed as described above, the filthy water purification boat on which the calcium fluoride electrolyzing device, DC power supply and coagulant pouring device are mounted and the flock recovering device may be further mounted as desired is operated on a lake. With operation of the filthy water purification boat, the electrolyzing device is actuated and coagulant is fed to the pipe provided with the coagulant pouring nozzles; so that lacustrine water is caused to flow between the electrodes, during which lacustrine water is fed with fluorine ions (F - ) and coagulant. The fluorine ions cause polluting substances contained in lacustrine water to form flocks and the coagulant causes the flocks to be increased in particle size, so that lacustrine water may be purified. The flocks thus large-sized are recovered through the flock recovering device to the boat or settle on a bottom of a lake due to a decrease in volume of the flocks by a hydrophobic action of the flocks. The purified water is returned to a lake during operation of the boat. Therefore, when the filthy water purification boat is operated on a whole lake, lacustrine water may be evenly purified; whereas the operation of the boat with respect to a limited area of a lake facilitates concentrated or local purification of lacustrine water. 
     Thus, in the present invention, operation of the filthy water purification boat at a local area of a lake permits lacustrine water to be partially selectively treated. Alternatively, operation of the boat over a whole lake permits lacustrine water to be wholly treated. Also, the present invention permits introduction of lacustrine water into the boat and discharge of purified water to a lake to be concurrently and continuously carried out without any other specific operation. 
     Further, the present invention allows lacustrine water to be evenly purified with simple operation, in an energy-saving manner and in a significantly reduced period of time and effectively prevents secondary public nuisance. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a plan view showing an embodiment of a filthy water purification boat according to the present invention; 
     FIG. 2 is a sectional view taken along line II--II of FIG. 1; and 
     FIG. 3 is a left side elevation view of the filthy water purification boat shown in FIG. 1. 
    
    
     BEST MODES FOR CARRYING OUT INVENTION 
     A filthy water purification boat according to the present invention will be described hereinafter with reference to FIGS. 1 to 3. A filthy water purification boat in the form of a double hull boat or catamaran which is generally designated by reference numeral 1 includes a pair of hulls 16 and 17 arranged opposite to each other and a deck 2 arranged so as to extend between the hulls 16 and 17. On the deck 2 are mounted a coagulant storage tank 3 for storing an aqueous coagulant solution such as, for example, an iron coagulant solution in water, a flock storage tank 4 for storing recovered flocks, and a DC power supply 5. To the coagulant storage tank 3 is connected a pipe 8 provided with coagulant pouring nozzles through a pipe line 7 provided with a valve 6. The coagulant pouring nozzles each are adapted to pour the aqueous solution by dropping. Thus, a coagulant pouring system is provided. Also, the boat includes a front strut 10 and a rear strut 11 arranged at a lower portion of the boat and rearward of the pipe 8 having the coagulant pouring nozzles so as to extend between the hulls 16 and 17 and be spaced from each other at a suitable interval in a longitudinal direction of the boat. The struts 10 and 11 are respectively mounted thereon with a plurality of cathode plates 9 1  and anode plates 9 2  electrically connected to the DC power supply 5 in a manner to be alternately arranged at suitable intervals. Rearward of the rear strut 11 is arranged a trough 12 for recovering flocks so as to extend between the hulls 16 and 17. The trough 12 is connected at a bottom thereof through a pipe line 13 and a flock suction pump (not shown) to the flock storage tank 4. Thus, a flock recovery system is provided. 
     Between opposite surfaces of each adjacent two electrode plates 9 1  and 9 2  is suspendedly arranged a cage 14 for receiving fluorite 9 mainly consisting of calcium fluoride and formed into a powder-like, particulate or lump-like shape (the cage 14 and fluorite 19 being omitted in FIG. 1). The electrode plates 9 1  and 9 2 , and cage 14 are dipped in lacustrine water in a flow passage 18 defined between the hulls 16 and 17. The electrode plates 9 1  and 9 2 , fluorite 19 and cage 14 thus arranged cooperate with each other to provide an electrolyzing system. As desired, a means for promoting stirring of water between the electrode plates 9 1  and 9 2  such as baffles or the like may be arranged at suitable places. In the drawings, reference numeral 15 designate a screw propeller. 
     Now, the manner of operation of the filthy water purification boat and the manner of purification of lacustrine water by the boat will be described hereinafter. When the filthy water purification boat is forward driven at a low velocity on a lake, lacustrine water is caused to flow into the tunnel-like flow passage 18 defined by cooperation of the deck 2 with the opposite hulls 16 and 17, then pass through gaps between the electrode plates 9 1  and 9 2  and finally rearward flow out from the boat. 
     With forward movement of the boat, the DC power supply 5 is actuated to apply a DC voltage of 3 V or more between the electrode plates 9 1  and 9 2  and the valve 6 is opened to feed the aqueous coagulant solution through the pouring nozzles of the pipe 8 to the lacustrine water passing through the flow passage by dropping. This causes fluorine ions (F - ) to be produced from the fluorite 19 to fluorinate polluting substances in the lacustrine water, resulting in fluorides of a high polarity being produced. The fluorides coagulate together due to positive and negative charges thereof to form particulate flocks, so that the lacustrine water is purified. To the flocks thus formed adhere fine bubbles of hydrogen gas to cause the flocks to try to rise to the surface of the water, during which iron ions (Fe 3+ ) produced from the iron coagulant lead to further coagulation of the flocks to cause the flocks to have an increased particle size. Then, the flocks flow into the trough 12 and are recovered to the flock storage tank 4, during which most of the purified water rearward flows out through the flow passage 18 between the hulls 16 and 17. 
     The flocks produced by the action of the fluorine ions is allowed to be hydrophobic in about 30 minutes after production of the flocks, so that a part or most of the flocks is reduced in volume by 1/5 to 1/10, resulting in settling on a bottom of a lake and then being cementified in the form of a mixture of clay, calcium silicate, lime and the like, so that they do not form organic sludge. Thus, it is not necessarily required to recover all of the flocks. Also, a calcium ion (Ca 2+ ) produced during the electrolytic treatment combines with a fluorine ion remaining unreacted to form calcium fluoride hard to dissolve, which then settles. Algae such as water-bloom and the like and spores thereof are likewise treated. 
     Another embodiment of the invention may be constructed in such a manner that the above-described electrolytic system and the like are arranged on a barge, which may be towed by a tug-boat. 
     Further, the screw propeller may be vertically moved, so that any sludge accumulating on a bottom of a lake may be subject to an electrolytic treatment while being agitated, resulting in the sludge being treated into a material which does not cause any public nuisance.