Patent Publication Number: US-2004043476-A1

Title: Multi-stage malodorous or noxious gas purification system

Description:
TECHNICAL FIELD  
       [0001] The present invention generally relates to an apparatus for purifying air, and more specifically to a system for purifying malodorous or noxious gas employing a multi-stage method.  
       BACKGROUND ART  
       [0002] In general, malodors produced from domestic electrical appliances, mobile toilets, or in the processes of industrial facilities such as environmental waste treatment facilities are caused by mixed gas mainly comprising hydrogen sulfide H 2 S, ammonia NH 3 , methylmercaptane CH 3 SH, trimethylamine (CH 3 ) 3 N, etc. The causative agents of such malodors and other noxious gas cause pains to people by stimulating the human nerve system, and can give considerable damage to the health of people, which in turn become main reasons for public environmental complaints.  
       [0003] In order to solve such problems of malodorous or noxious gas, various purification techniques are used conventionally, for. example, use of sprays and perfumes to disguise malodors with fragrant smells, absorption of malodorous or noxious gas by using adsorbents such as activated carbon or charcoal, physio-chemical decomposition of the causative agents of malodorous or noxious gas, and use of microorganisms which can decompose the causative agents of malodorous or noxious gas by contacting therewith.  
       [0004] Among such techniques, the use of sprays and perfumes to disguise malodors with fragrant smells is limited to only a small space with temporary effect. The absorption of malodorous or noxious gas by using adsorbents such as activated carbon or the like has an advantage of relatively simple structure and easy maintenance of the apparatus. However, in such a technique, cleansing or replacement of the activated carbon or charcoal is required periodically, and in addition, it is impossible to eliminate stimulative malodorous gas such as ammonia which cannot be adsorbed by the adsorbents. While, in the purification by microorganisms, waste gas is purified through the natural decomposition by microorganisms in the soil or the adsorption by soil particles, by passing the waste gas through a soil layer in which the microorganisms live. This process is quite effective for the purification of high-concentration waste gas, however it requires an enormous amount of installation and maintenance cost including large installation area for the facility.  
       [0005] The purification apparatus using microorganisms improved over such prior art purification systems have been developed, for example, those shown in FIGS.  1  to  3 . FIG. 1 shows an embodiment of a Korea Patent (Patent Registration No. KR-0138050, Feb. 16, 1998), entitled “Method and Device for Biologically Deodorizing Waste Gas”, granted to ENVI SYSTEM CO., LTD (Republic of Korea). A microorganism deodorization device  10  shown in FIG. 1 has a deodorization tower  4  including a plurality of serially arranged unitary deodorization tanks  6  containing wood pieces or bark pieces  8  therein. Waste gas is introduced into an inlet opening  4   a , passed through a humidistat  2 , and purified by the microorganisms in the deodorization tower  4 . Then, the gas is passed through a collector  9  and discharged at an exit opening  4   b  as purified gas. The unitary deodorization tank  6  includes two spaces partitioned by a metal net  6   a , and only one of the spaces is filled with wood pieces or bark pieces  8  so that microorganisms can live therein. Each unitary deodorization tank  6  is adjacent one another with a cross-plate  6   b  positioned therebetween, the cross-plate  6   b  having vents formed therein.  
       [0006] As described above, the deodorization device  10  is configured such that the microorganisms are disposed in multi-layers so as to increase general gas permeability, thereby increasing deodorization effect. In the device  10 , nonetheless, it is difficult to remove and replenish the microorganisms and wood pieces which are the nutritional source for the microorganisms since there is no apparatus for separately feeding or supplying such microorganisms and wood pieces. Further, separation effect of microorganisms can be hardly achieved because there is a high possibility that the microorganisms can move from one layer to another through the openings or vents in the metal net  6   a  or the cross-plate  6   b  and be mixed together. In addition, there is no description about the separation of microorganisms in accordance with their species in the Patent document..  
       [0007] That is, it is necessary to mix various species of microorganisms to purify composite waste gas including causative agents of various malodorous or noxious gases since usually one species of microorganisms has capability to decompose one type of compounds. In the meanwhile, if different species of microorganisms are mixed one another without separation, some struggle between different species can occur, which in turn significantly lowers the efficiency of purification. Moreover, the deodorization device  10  is not flexible to employ various effective microorganisms for purification of waste gas—for example, the species of microorganisms that do not feed on wood pieces, but are greatly effective in deodorization—since the nutritional source for the microorganisms is limited only to wooden materials in the description of the document.  
       [0008] Additionally, there are other examples that include a prior art apparatus for supplying a malodorous or noxious gas purification system with microorganisms and culturing solution shown in FIGS. 2 and 3. FIG. 2 shows a deodorization apparatus  20  of a Korea Patent Application No. 1999-0009239 (filed on Mar. 18, 1999), entitled “Apparatus for Removing Unpleasant Odor and Volatile Organic Compounds Using Microorganism”, by ENBIOTEC CO., LTD (Republic of Korea), and FIG. 3 shows a purification device  30  of a Korea Patent Application No. 2000-0023935 (filed on May 4, 2000), entitled “Deodorizing Device Using Microbe”, by WORLD INDUSTRIAL MACHINERY CO., LTD (Republic of Korea).  
       [0009] The deodorization apparatus  20  in FIG. 2 is constructed such that waste gas is introduced into an inlet opening  21   a  of a decomposition tank  21 , diffused by porous substances  24 , deodorized by carbon filters  23  in which microorganisms live, and then discharged at an exit opening  21   b  as purified gas. In the deodorization apparatus  20 , the microorganisms in a microorganism storage tank  26  are supplied by a pump  28 , and these microorganisms are mixed with neutralizing agents and nutritional agents  29  by passing through a mixer  27  and are injected via nozzles  22  installed within the tank  21 . Into the storage tank  26 , microorganisms cultured at culturing media  25  are fed. The above-described deodorization apparatus  20  has an advantage of easy maintenance of the malodorous or noxious gas purification system, since the proper pH of the microorganisms is controlled and the microorganisms are fed automatically. However, the deodorization apparatus  20  is still not quite satisfactory to apply to composite malodorous gas, because the decomposition tank  21  in which purifying action takes place is not configured as multi-stages. In addition, there is no specific alternative to cause the microorganisms and nutritional agents to remain in the carbon filters  23  for a prolonged time.  
       [0010] While, in the purification device  30  of the prior art shown in FIG. 3, waste gas is sucked through an inlet tube  32   a , arrives at and purified by a deodorization unit  31 , and then the purified gas is discharged through an exit tube  32   b  into the air. Within the deodorization unit  31 , filter media  33  divided into two strata are installed. Microorganisms from a microorganism culture section  36  and culturing solution from a storage tank  39  are fed into the filter media  33 , through injection nozzles  32 . For this device  30 , though the deodorization unit  31  is constructed as two stratum filter media  33 , there is no description on the separation of different species of microorganisms within respective filter media  33 . In addition, although the microorganisms are inhabited in the filter media  33 , there is a high possibility that the microorganisms injected along with culturing solution cannot remain in the filter media for a long time and might be washed away since the filter media  33  used in this case are made of the same material as common air filters. Therefore, the living environment is not quite favorable for the existence of microorganisms.  
       [0011] Accordingly, there is a need for a malodorous or noxious gas purification system in which purification capability of microorganisms which purify malodorous or noxious gas can be effected, by providing habitat spaces for each species of microorganisms, separating/ isolating respective habitat spaces for each species of microorganisms, thereby improving air permeability between the habitat spaces, so as to effectively remove composite causative agents of various malodorous or noxious gas.  
       DISCLOSURE OF INVENTION  
       [0012] The present invention is designed to solve the problems of the prior art malodorous or noxious gas purification systems.  
       [0013] Therefore, it is an object of the present invention to provide a malodorous or noxious gas purification system which can purify malodorous or noxious gas in multi-stages, by isolating and separating one species of microorganisms effective in decomposition of specific ingredients among causative agents of composite malodorous or noxious gas from another species of microorganisms, and at the same time, providing environment suitable for culturing such microorganisms within the purification system.  
       [0014] In order to accomplish the object, a multi-stage malodorous or noxious gas purification system according to the present invention comprises: purifiers for extracting unnecessary ingredients from gas; two or more unitary purification tanks each having a filling space for filling the purifiers therein, each unitary purification tank having an inlet opening and an exit opening for the gas to pass into or out of the filling space; and at least one connecting member for isolatedly connecting the filling spaces of the two or more unitary tanks and for the gas to pass therethrough, each connecting member installed at the inlet opening or the exit opening of the respective unitary purification tanks.  
       [0015] It is preferable to use two or more different kinds of purifiers. At least one kind of the purifiers is a porous substance to adsorb predetermined ingredients among the unnecessary ingredients, or includes microorganisms which can decompose predetermined ingredients among the unnecessary ingredients.  
       [0016] Furthermore, the purifier including microorganisms can comprise habitat members for providing environment for the microorganisms to live in, specific species of microorganisms living in the habitat members, and organic substances as a nutritional source for the microorganisms. The nutritional source for the microorganisms can be fed in liquid with organic substances dissolved. The habitat members, which also serve as the porous substance to adsorb predetermined ingredients, can be carriers consisting mainly of carbon, and preferably, the habitat members can be made of a micro-porous substance with fine pores formed therein, whose size is in the order of several microns.  
       [0017] In addition, each unitary purification tank has a gas-permeable intermediate filter for dividing each filling space into two partitioned spaces. One of the two partitioned spaces can be constructed to be filled with the purifiers. Alternatively, the unitary purification tank further includes a gas-permeable opening filter at the inlet opening or the exit opening so that the space between the opening filter and the intermediate filter can be filled with the purifiers. Additionally, a plurality of inlet openings and exit openings can be formed at the unitary purification tanks.  
       [0018] A closable aperture can be further formed at each unitary purification tank for injecting the purifier therethrough. Furthermore, the unitary purification tank may further comprise an apparatus for automatically feeding microorganisms and culturing solution including organic substances which are the nutritional source for the microorganisms, the apparatus connected to each unitary purification tank.  
       [0019] Each connecting member may comprise a connecting tube one end of which is communicably connected to the inlet opening of one unitary purification tank and the other end of which is communicably connected to the exit opening of another unitary purification tank, and a switch for opening and closing the connecting tube. In addition, the unitary purification tank may further comprise an air blower for forcibly controlling the flow of air passing through the unitary purification tank.  
       [0020] In the multi-stage malodorous or noxious gas purification system in accordance with the present invention, the unitary purification tanks can be arranged serially in one dimension, or may be arranged in two or three dimensions. For one-dimensional serial arrangement, the unitary purification tank may further comprise a chimney-type housing. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0021] These and other features, aspects, and advantages of the present invention will be fully understood with reference to the following description, appended claims, and accompanying drawings, in which like numerals refer to like components. In the drawings:  
     [0022]FIG. 1 is a schematic view of an embodiment of a prior art multi-layer waste gas purification apparatus;  
     [0023]FIG. 2 is a schematic view of an embodiment of a prior art purification apparatus using microorganisms;  
     [0024]FIG. 3 is a schematic view of an embodiment of another prior art purification apparatus using microorganisms;  
     [0025]FIG. 4 is a schematic view of a multi-stage malodorous or noxious gas purification system in accordance with a preferred embodiment of the present invention;  
     [0026]FIG. 5 is a schematic view of a unitary purification tank employed in the multi-stage malodorous or noxious gas purification system in accordance with the invention;  
     [0027]FIG. 6 is respectively a section view and an exploded view of an embodiment of a structure of a filter assembly of the unitary purification tank in accordance with the invention;  
     [0028]FIG. 7 is respectively a section view and an exploded View of an embodiment of a structure of another filter assembly of the unitary purification tank in accordance with the invention;  
     [0029]FIG. 8 is a schematic view of a multi-stage malodorous or noxious gas purification system with a purification path control unit according to the invention;  
     [0030]FIG. 9 is a schematic view of a multi-stage malodorous or noxious gas purification system with an automatic feed apparatus for microorganisms and culturing solution in accordance with the invention;  
     [0031]FIG. 10 is a block diagram illustrating the control relationship of a multi-stage malodorous or noxious gas purification system in accordance with a preferred embodiment of the invention;  
     [0032]FIG. 11 is a schematic view of a multi-stage malodorous or noxious gas purification system configured in chimney-type in accordance with an embodiment of the invention; and  
     [0033]FIG. 12 is a schematic view of a multi-stage malodorous or noxious gas purification system configured in two dimensions in accordance with another embodiment of the invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
     [0034] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.  
     [0035]FIG. 4 shows a multi-stage malodorous or noxious gas purification system  100  in accordance with a preferred embodiment of the present invention, and FIG. 5 shows an embodiment of a unitary purification tank.  140  which can be employed in the multi-stage malodorous or noxious gas purification system.  
     [0036] The multi-stage malodorous or noxious gas purification system  100  as shown in FIG. 4 is used for removing unnecessary ingredients from air, such as causative agents of malodorous or noxious gas contained in the air, and can comprise purifiers, a plurality of unitary purification tanks  140 , and at least one connecting member  160 . The present invention has a structural characteristic in that within each unitary purification tank  140  the purifiers are filled, and in that each of the unitary purification tanks is isolatedly connected with a gas-permeable connecting member  160 .  
     [0037] In a further preferred embodiment, two or more different kinds of purifiers can be used. That is, one of the unitary purification tanks  140  can be filled with a substance that can adsorb the causative agents of malodorous or noxious gas, and another unitary purification tank  140  can be filled with cultured microorganisms that have capability to decompose the causative agents of malodorous or noxious gas. Furthermore, the number of such unitary purification tanks can be 4 or 10 without limitation, as required. Therefore, the present invention can provide a malodorous or noxious gas purification system that can effectively remove and purify causative agents of malodorous or noxious gas, or various causative agents causing air pollution.  
     [0038] As purifiers to extract unnecessary ingredients from the gas to be purified, any substances that purify air can be used. The causative agents of malodors or air pollution exist mixedly in the form of dust or chemical gas in the polluted air. Such causative agents comprise hydrogen sulfide H 2 S, ammonia NH 3 , methylmercaptane CH 3 SH, trimethylamine (CH 3 ) 3 N, etc. Accordingly, it is preferable to select purifiers that are most effective in removing each causative agent and to fill separately such purifiers into respective unitary purification tanks.  
     [0039] That is, at least one kind of the purifiers to be filled in respective unitary purification tanks  140  is a porous substance that can adsorb and collect predetermined ingredients among the unnecessary ingredients so as to purify the air. For. example, adsorbents consisting of wood charcoal or activated carbon can be employed, or common air filters can be used. In addition, it is preferable that at least one kind of the purifiers is a purifier including microorganisms which decompose predetermined ingredients of the unnecessary ingredients. In a still preferred embodiment, the unitary purification tanks, respectively, filled with an adsorbent consisting of the porous substance and a purifier including microorganisms can be properly arranged in stages.  
     [0040] The purifier including microorganisms in accordance with a preferred embodiment of the invention can comprise habitat members, microorganisms and organic substances. The habitat members are a means to provide environment for certain species of microorganisms to live in for a predetermined or semi-permanent period of time, and are made of inorganic substances, preferably, those not affected by the decomposition of corresponding microorganisms. The habitat members also serve as the porous substance to adsorb predetermined ingredients. As a matter of course, it is also possible to use any substances that cannot be decomposed by the microorganisms as habitat members, even though the substances include organic substances. Any microorganisms that have capability to decompose and convert certain chemical substances, especially, gases harmful to human bodies or chemical gases causative of malodors, into un-harmful and non-odorous gas can be employed. Any kind of organic substances that can be decomposed and be the nutritional source for the microorganisms can be also used.  
     [0041] In general, hydrogen sulfide H 2 S, ammonia NH 3 , methyl mercaptane CH 3 SH, trimethylamine (CH 3 ) 3 N, etc. are known as causative agents of malodors. Therefore, it is possible to use certain species of microorganisms that can decompose any one chemical substance among such causative agents of malodors. Since the present malodorous or noxious gas purification system is configured in multi-stages, the system has an effect to remove all, for example four, causative agents of malodorous gas, by separately accommodating each species of microorganisms capable of decomposing specific chemical substances among the causative agents in each stage, and passing malodorous gas through the multi-stages, that is, sequentially passing the malodorous gas through the four unitary purification tanks having respectively four different species of microorganisms therein. Accordingly, there is no need to use microorganisms capable of decomposing simultaneously several causative agents, but it is possible to use microorganisms capable of decomposing just one causative agent, thereby improving the purification efficiency of malodorous or noxious gas.  
     [0042] The organic substances provided as the nutritional source for the microorganisms can be fed in the form of solid pieces or powder. However, it is preferable to feed the organic substances in liquid into which the organic substances are dissolved with water or other solvent. For example, it is possible to spray a culturing solution to the spaces in which the microorganisms live with spray devices. In such spray of organic substances in liquid state, it is easy to adjust an amount of feed, furthermore, it is possible to preclude a possibility that the remaining organic substances become a cause of malodors. In addition, in case the culturing solution is fed in liquid state, since it is easy to mix the microorganisms with the culturing solution, the only thing to do for replacement of purifiers is to mix the microorganisms with the culturing solution in a predetermined ratio and to spray the mixed solution into the unitary purification tanks in a predetermined period of time.  
     [0043] For the habitat members, it is possible to use various substances, for example, plastic materials in the form of woven fabric or sponge, or glass or ceramic materials in the form of fine granules. It is preferable that the size of the granules is more than about 4 mm in diameter, such that the granules cannot be slipped away through the filters or other separation members. In the meanwhile, the habitat members are preferably provided with openings for the gas to pass therethrough.  
     [0044] As the habitat members, a porous substance consisting mainly of carbon and serving to adsorb predetermined ingredients can be also employed. When such porous substance of carbon, for example, wood charcoal or activated carbon is used, the efficiency of air purification is significantly increased due to the combination of the adsorption by the porous substance with the decomposition by the microorganisms. In addition, as is well known in the art, such porous substance of carbon can be an optimum habitat space for the microorganisms, since the microorganisms live well in a porous carrier consisting of carbon components.  
     [0045] Further, the openings formed in the porous substance consisting of carbon are preferably of the size of a few microns. Such openings of the size with a few microns are similar with the size of common microorganisms, so as to be an optimum habitat space especially for microorganisms, and there is little chance for the microorganisms to slip away through the fine openings. In this case, it can be far easier to make a structure that can perfectly isolate specific species of microorganisms within each unitary purification tank and allow only gas to pass therethrough.  
     [0046] The unitary purification tanks  140  of the multi-stage malodorous or noxious gas purification system  100  shown in FIG. 4 have an essentially identical structure. On the other hand, the unitary purification system  140  can be configured differently, as shown in FIG. 5. Each unitary purification tank  140  has a basic structure comprising a filling space for filling various above-mentioned purifiers therein, and an inlet opening and an exit opening for the gas to pass through the filling space.  
     [0047] In accordance with a preferred embodiment, the unitary purification tank is configured such that the filling space is divided into at least two spaces by a partition. This is for better gas-permeability. Preferably, one of the divided spaces becomes a space  147  to be filled with the purifiers, and the other of the divided spaces is a buffer space  145  which is kept empty. In this case, the partition may consist of a filter, or an intermediate filter  148  which allows only gas to pass therethrough. The intermediate filter  148  makes the purifiers remain within the space  147 , and may consist of gas-permeable material. However, the intermediate filter  148  may have an additional function to adsorb causative agents of a certain kind of malodorous or noxious gas.  
     [0048] Further, the unitary purification tank  140  further comprises a gas-permeable filter or inlet filter  146  at an inlet opening  143  or another filter at an exit opening  144 , and the space between the intermediate filter  148  and the inlet filter  146  is preferably filled with the purifiers. Such configuration is desirable especially for the case when microorganisms are used as a purifier, this is because the microorganisms can be filled between the two filters such that the separation effect is increased.  
     [0049] As shown in FIG. 5, a unitary purification tank in accordance with another preferred embodiment of the invention may comprise a plurality of inlet openings  143  and a plurality of exit openings  144 . The inlet openings  143  are formed with respect to the space  147  filled with the purifiers, and the exit openings  144  are formed with respect to the buffer space  145  with no purifier therein. The number of the inlet opening  143  and the exit openings  144  may be varied, as required in accordance with the arrangement of the unitary purification tanks such as in one, two or three dimensions. Alternatively, for example when configuring a 4-stage system, it is possible to configure the system such that a single unitary purification tank is used in stage I, three unitary purification tanks are used in stage II, two unitary purification tanks are used in stage III, and four unitary purification tanks are used in stage IV.  
     [0050] In addition, the unitary purification tank  140  may further comprise an injection opening  142  formed as a closable opening for injecting the purifier, such as the microorganisms and the culturing solution, through which the purifier is injected in the form of powder or liquid. With a manually operable injector  200  in the form shown in FIG. 5, a mixture of microorganisms with culturing solution in liquid state is sprayed into each unitary purification tank. In addition, onto the injection opening  142 , an automatic feed apparatus to be described later with reference to FIG. 9 can be connected.  
     [0051] As shown in FIGS. 4 and 5, the multi-stage malodorous or noxious gas purification system in accordance with a preferred embodiment of the invention has a characteristic in that each unitary purification tank  140  is isolatedly connected one another via a connecting member or connecting tube  160 . The connecting tube  160  is communicably installed at the inlet opening  143  or the exit opening  144  of each unitary purification tank  140 , such that the two or more unitary purification tanks are isolatedly connected. Since it is desirable for the connecting tube  160  to allow gas-permeation only, an opening/closing switch  162  can be installed on the connecting tube  160  for better isolation, or it is possible to fill the connecting tube  160  with other filter material. The connecting tube  160  can be connected to an inlet portion  120  through which gas is introduced, with fastener members such as a joint nut  122 , or can be used to connect different unitary purification tanks  140 .  
     [0052] Another preferred embodiment of the invention may further comprise an air blower  180  for forcibly controlling the flow of the gas passing through the arrangement of the unitary purification tanks  140 . The air blower  180  can be mounted at a rear end of the malodorous or noxious gas purification system as shown in FIG. 4, or can be mounted adjacent to each unitary purification tank  140  as shown in FIG. 5.  
     [0053]FIGS. 6 and 7 show a structure of a filter assembly of the unitary purification tanks in accordance with the invention, and the structure of the filter assembly facilitates replacement of the filters. With reference to FIG. 6, an inlet opening  143  is formed at a portion where one side of the unitary purification tank  140  containing the purifiers  130  connects with the connecting tube  160 , and the part where the inlet opening  143  is formed may be integral with the connecting tube  160 . The outer surface of the part where the inlet opening  143  is formed may be provided with threads  143   a  so as to be screwed into the unitary purification tank  140 . In this structure, unscrewing the connecting tube  160  separates the inlet opening  143  from the unitary purification tank  140 . Accordingly, the replacement of the inlet filter  146  inserted in the inlet opening  143  can be simplified.  
     [0054] In addition, with reference to FIG. 7, the inlet opening  143  formed onto the unitary purification tank  140  comprises a number of vents  143   b . A filter frame  146   a  is attached to the inlet filter  146 , and the connecting tube  160  comprises engageable grooves  160   a  for engaging with the filter frame  146   a , and screwing portions  160   b  for screwing with the unitary purification tank  140 . In this case, the connecting tube  160  and the inlet filter  146  are attached to the unitary purification tank  140  by and along with screws, and thus unfastening the screws on the connecting tube  160  makes replacement of the filter  146  easy.  
     [0055]FIG. 8 shows a multi-stage malodorous or noxious gas purification system with a purification path control unit  320  in accordance with the invention. The purification path control unit  320  can control air flow by forcibly controlling the circulation rate of the air with the air blower  180 , and can control the amount of air which remains in each unitary purification tank  140  and the time during which the air remains in the unitary purification tank  140  by respectively controlling opening/closing switches  162  installed at the connecting tubes  160 . In this case, it is possible to optimize the conditions under which each unitary purification tank  140  can remove a different kind of causative agents of malodorous or noxious gas.  
     [0056] Such control is accomplished by controlling power supply from the power supply unit  310  through respective control lines  322 ,  324 ,  326  and  328  and controlling the operation of a motor of the air blower  180  and respective opening/closing switches  162 , with the purification path control unit  320 . The speed of the motor and the opening/closing time of the switches are determined empirically by taking the capability of the microorganisms being used and/or the concentration of the malodorous or noxious gas to be treated, etc. into account.  
     [0057]FIG. 9 shows a multi-stage malodorous or noxious gas purification system  100  with automatic feed apparatus  200 ′ for feeding microorganisms and culturing solution in accordance with a preferred embodiment of the invention. The automatic feed apparatus  200 ′ are connected to respective unitary purification tanks  140  and used for automatically feeding microorganisms and culturing solution containing organic substances as a nutritional source for the microorganisms. For the automatic feed apparatus, another prior art feed apparatus can be employed.  
     [0058] The automatic feed apparatus  200 ′ as schematically shown in FIG. 9 comprises a storage  220  for the microorganisms and culturing solution, and an injector  260  and nozzles  280  for discharging the microorganisms and culturing solution from the storage  220  into the unitary purification tank  140 . With the operation of an opening/closing switch  222 , a predetermined amount of the microorganisms and culturing solution can be fed from the storage  220  to the injector  260 . The microorganisms and culturing solution fed into the injector  260  can be injected into the unitary purification tank  140  via the nozzles  280 . Though such feed operation can be achieved manually, it is preferable to use a feed control unit  340  including control lines  342 ,  344  and  346  for such operation.  
     [0059] In the block diagram of FIG. 10 illustrating the control relationship of the multi-stage malodorous or noxious gas purification system in accordance with a preferred embodiment of the invention, it is shown that the purification path control unit  320  and the feed control unit  340  control the power supply to the motor and each opening/closing switch from the power supply unit  310 , through time adjustment by a timer  360 . The timer  360  in turn is configured to be automatically controlled by a program unit  380 . Usually, the life expectancy of microorganisms is about four to five days, therefore, preferably the microorganisms and culturing solution are fed automatically in accordance with such life expectancy.  
     [0060]FIG. 11 shows a multi-stage malodorous or noxious gas purification system  400 . configured in chimney type in accordance with an embodiment of the invention. The purification system  400  is a relatively small one among the examples which can be configured as a multi-stage malodorous or noxious gas purification system in accordance with the invention, and the purification system  400  comprises a chimney-type housing  420  to be adapted for outdoor mobile toilets or small waste treatment systems, etc. In the housing  420 , malodorous gas is sucked by the air blower  180  at an inlet  422 , the malodor is removed from the malodorous gas while passing through the arrangement of the unitary purification tanks  140 , and discharged at an exit  428  as purified gas. Within the housing  420 , an automatic feed apparatus  200 ′, a control unit  300 , a power supply unit  310 , etc. can be installed.  
     [0061] Though those embodiments of the unitary purification tanks  140  arranged serially or in one line are mainly described in the foregoing, the embodiments of the invention are not limited to such arrangement but it is also possible to arrange the unitary purification tanks  140  in two or three dimensions. FIG. 12 shows an exemplary configuration of a malodorous or noxious gas purification system  500  in two dimensional arrangement. The waste gas introduced through an inlet  520  is subjected to sequentially passing through a multitude of unitary purification tanks  140  in a purification section  540 , and can be discharged at an exit  560  as purified gas with causative agents of malodorous gas removed. Accordingly, it is possible to configure a malodorous or noxious gas purification system that includes large facilities or that can treat a large amount of waste gas in accordance with such arrangement.  
     [0062] In accordance with a multi-stage malodorous or noxious gas purification system in accordance with the invention as described in the above, the present purification system can improve purification capacity over the prior art malodorous or noxious gas purification systems using purifiers or microorganisms. That is, the invention can provide a malodorous or noxious gas purification system with significantly increased purification capacity, since the causative agents of various malodorous or noxious gases can be removed sequentially and continuously from the gas including such causative agents. Such improvement of purification capacity is easily achieved by the malodorous or noxious gas purification system in accordance with the invention, in which each species of microorganisms that can decompose only certain causative agents of malodorous or noxious gas is isolatedly kept and waste gas is subjected to passing through habitat spaces accommodating such microorganisms.  
     [0063] The malodorous or noxious gas purification system in accordance with the invention as described in the above is highly flexible in its application due to the simple assembly of the system and the adjustability of scale as required. Accordingly, it is also possible to configure a small system such as an apparatus for removing the malodor from domestic electrical appliances such as refrigerators used at home. In addition, the present invention is also applicable to independent convenient facilities such as mobile toilets, and the invention can be employed even in environmental waste treatment facilities or for processing waste gas from industrial facilities, etc. if configured in large scale.  
     [0064] The present invention has been described in detail with reference to some preferred embodiments. However, it should be understood that the detailed description and specific examples are given by way of illustration only. Therefore, those skilled in the art will appreciate that various changes and modifications within the spirit and scope of the invention will become apparent from the detailed description.