JP2006326534A - Organic waste treatment method and treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide organic waste treatment method and treatment apparatus capable of stably carrying out membrane separation treatment of a methane fermentation solution at a high permeation flux for a long duration. <P>SOLUTION: A portion of a methane fermentation solution is taken out a methane fermentation tank and subjected to membrane separation treatment by a pressure type membrane separation apparatus equipped with a circulation line for the methane fermentation solution and then the concentrated methane fermentation solution is turned back to the methane fermentation tank. The membrane of the membrane separation apparatus is hardly clogged by making the apparatus have the above described structure and no blower is required for the biogas and thus the apparatus can be compact. Further, the valve opening of the return line of the concentrated methane fermentation solution is changed in accordance with the membrane-permeating solution amount of the pressure type membrane separation apparatus, so that in-plane membrane pressure difference in the pressure type membrane separation apparatus can be adjusted and a prescribed membrane-permeating solution amount can be maintained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method and apparatus for treating organic waste such as garbage and food waste by methane fermentation.

  An anaerobic digestion method that biologically decomposes organic matter using anaerobic microorganisms such as methane bacteria is a method for treating high-concentration organic waste such as manure, food waste, food waste, and septic tank sludge. In this methane fermentation method, high-concentration organic waste is introduced into the fermenter, the organic waste is decomposed by fermentation with methane bacteria, and the resulting fermented sludge is extracted outside the methane fermenter. The withdrawal amount is generally equal to the input sludge amount. And it is also possible to use the gas which has methane as a main component as a fuel (patent documents 1, 2).

Here, when the fermentation sludge is extracted from the methane fermentation tank, the methane bacteria also flow out of the tank together with the fermentation sludge, so it was difficult to maintain the methane bacteria concentration in the methane fermentation tank at a high concentration. As a method for solving this problem, fermented sludge is circulated between a fermenter and a membrane separator forming a closed region, and the fermented sludge is solid-liquid by a membrane separator (immersion type membrane separator) immersed in the membrane separator. A methane fermentation method that maintains the concentration of methane bacteria in the fermenter by separating (concentrating) and removing the membrane permeate from the membrane separator out of the system, and pulling out excess fermentation sludge from the bottom of the fermenter is a patent document. 3 is disclosed.
JP-A-11-28445 Japanese Patent Laid-Open No. 11-300323 Japanese Patent Laid-Open No. 2000-24661

  However, in the method disclosed in Patent Document 3, the fermentation broth is concentrated by the submerged membrane separation apparatus having a transmembrane pressure difference of about 30 to 40 kPa, and therefore the permeate flux of the fermentation broth is small. For this reason, a membrane with a large area is required, and the membrane separation apparatus must be enlarged.

  In addition, in order to keep the fermentation liquid in an anaerobic state, the membrane surface is washed by blowing biogas generated from the methane fermentation tank (anaerobic gas mainly composed of methane) in the membrane separator. For this reason, there is also a problem that bubbles permeate the membrane surface and the permeation flux is likely to further decrease. Further, since the permeation flux is low, a large membrane separation apparatus is necessary.

  An object of the present invention is to provide an organic waste treatment method and a treatment apparatus that have a high permeation flux and that can stably perform membrane separation treatment of a methane fermentation broth for a long period of time.

  As a result of intensive studies to solve the above problems, the present inventor has maintained a high permeation flux for a long period of time by using a pressurized membrane separator equipped with a fermentation liquid circulation line as a means for concentrating methane fermentation liquid. As a result, the present invention has been completed.

  Specifically, the present invention is a method for decomposing organic waste by methane fermentation in a methane fermenter, comprising a fermentation liquid circulation line for circulating a part of the fermentation liquid in the methane fermenter. By concentrating with a pressurized membrane separator, discharging the membrane permeate out of the system, and returning the concentrated fermentation broth to the methane fermenter, the solids concentration of the fermented liquor in the methane fermenter is reduced to methane. It is the processing method of the organic waste characterized by maintaining to the suitable value of fermentation (Claim 1).

The present invention also provides a methane fermentation tank for methane fermentation of organic waste,
A fermentation liquor extraction line for taking out part of the fermentation liquor in the methane fermentation tank by suction means;
A pressure-type membrane separation device comprising a fermentation liquid circulation line connected to the fermentation liquid extraction line and circulating the fermentation liquid from the fermentation liquid extraction line by a pressurizing means;
An organic waste product comprising: a concentrated fermented liquid return line that is connected to the fermented liquid circulating line and returns the concentrated fermented liquid circulating in the fermented liquid circulating line to a methane fermentation tank. A processing device (claim 7).

  The organic waste processing method and processing apparatus of the present invention uses a pressure membrane separator for concentration of methane fermentation liquor, and therefore has a larger transmembrane pressure difference than when a submerged membrane separator is used. High permeation flux and short processing time. Moreover, since a large membrane area is not required, the membrane separation apparatus is compact.

  Moreover, the processing method and processing apparatus of the organic waste of this invention wash | clean a membrane surface with the circulation flow of a methane fermentation liquid, when a pressurized type membrane separator is provided with the fermentation liquid circulation line which circulates a methane fermentation liquid. be able to. For this reason, compared with the case where the normal pressurization type | mold membrane separator which does not have a fermented liquid circulation line is used, it becomes difficult for solid content to adhere to a film | membrane, and it becomes possible to maintain the permeate amount high for a long time. In addition, the apparatus can be made more compact than a normal pressure type membrane separation apparatus. Furthermore, since blowing with biogas is not required, bubbles adhere to the membrane surface and the effective permeation area does not decrease.

  It is preferable that the membrane surface flow rate of the fermentation liquor in the pressurized membrane separator is 0.6 m / second or more (Claims 2 and 8). If the flow rate at the membrane surface is less than 0.6 m / sec, the solid matter tends to adhere to the membrane surface of the pressurized membrane separator, or the solid matter is deposited between the membranes in the membrane separator, causing the flow of the fermentation broth. This is not preferable because the road may be blocked.

  The pressure difference on the membrane surface in the pressure type membrane separator is preferably 50 kPa or more and 200 kPa or less (Claims 3 and 9). By setting the transmembrane pressure difference of the pressure type membrane separation device within the above range, the power consumption of the circulation pump is not excessive compared with the immersion type membrane separation device in which the transmembrane pressure is usually about 30 to 40 kPa. Rapid concentration of methane fermentation broth is possible.

The amount of membrane permeate discharged from the pressurized membrane separator is measured by a measuring means provided in the membrane permeate discharge line,
When the amount of the membrane permeate decreases below the reference value, the control means adjusts the valve provided in the concentrated fermentation liquid return line to throttle, thereby increasing the membrane surface differential pressure in the pressurized membrane separator, On the other hand, when the amount of the permeated liquid increases from the reference value, the control means adjusts the valve provided in the concentrated fermented liquid return line to open the pressure difference in the pressure type membrane separator. (Claims 4 and 10). By adopting such a configuration, (1) When the organic substance concentration, viscosity, etc. of the methane fermentation liquid increase and the membrane treatment efficiency of the methane fermentation liquid decreases, it is provided in the concentrated sludge return line to the methane fermentation tank By closing the valve, the transmembrane pressure difference increased and the membrane permeation amount increased, and (2) the organic substance concentration and viscosity of the methane fermentation broth decreased and the membrane treatment efficiency of the methane fermentation broth increased. In this case, by opening the valve provided in the concentrated sludge return line to the methane fermentation tank, the transmembrane pressure difference can be reduced and the membrane permeation amount can be reduced.

  An independent acid fermenter may be provided, and a two-phase anaerobic decomposition process in which organic waste is decomposed by acid fermentation in the acid fermenter before the methane fermentation treatment.

  A nitrification denitrification tank may be provided, and after the methane fermentation treatment, the membrane permeate may be further subjected to nitrification denitrification treatment (Claims 6 and 12).

  The organic waste processing method and processing apparatus of the present invention can solve the problems of the prior art, can concentrate the methane fermentation liquor quickly and stably for a long period of time, and further, methane fermentation. Less maintenance is required for the liquid membrane separator. Further, it is possible to reduce the size of the methane fermentation broth membrane separation apparatus.

  Embodiments of the present invention will be described below with reference to the drawings as appropriate. The present invention is not limited to these.

  First, when organic waste containing solids such as raw garbage is subjected to methane fermentation, it is roughly crushed using a coarse crusher such as a uniaxial crusher (particle size 20 to 100 mm), and then a compression crusher or the like is used. Then, it is compressed and crushed into paste-like organic waste, and then fermented.

  When organic waste having a low solid matter concentration such as manure or septic tank sludge is subjected to methane fermentation, solids are concentrated by precipitation or filtration, and the concentrate is subjected to fermentation treatment. Moreover, about an organic waste liquid with a low solid substance density | concentration and a high soluble organic substance density | concentration, you may perform a fermentation process, without concentration of a solid substance.

  FIG. 1 is a diagram showing a flow in the organic waste processing method of the present invention. The organic waste subjected to the pretreatment as described above (step S1) is subjected to acid fermentation for a predetermined time with stirring, and the organic matter is decomposed into organic acids such as acetic acid, butyric acid, propionic acid by the action of acid-producing bacteria. (Step S2).

  Next, the concentration and temperature of the acid fermentation liquor are adjusted as appropriate, and methane fermentation is performed under anaerobic conditions (step S3). At this time, the organic acid in the acid fermentation broth is decomposed into methane, carbon dioxide and the like by the action of methane bacteria. The temperature in the methane fermentation tank is adjusted to 50 to 60 ° C. in the case of high temperature methane fermentation, and 30 to 40 ° C. in the case of medium temperature methane fermentation.

  Next, a part of the methane fermentation liquor is taken out and subjected to membrane separation treatment by a pressure type membrane separation apparatus equipped with a circulation line for the methane fermentation broth (step S5). Membrane separation of the methane fermentation liquid increases the sludge concentration in the methane fermentation tank, and at the same time, substances dissolved in the methane fermentation liquid, such as organic acids and ammonia nitrogen, are discharged from the pressurized membrane separator as a membrane permeate. Is done. In addition, in order to prevent a sludge density | concentration rising too much, a part of methane fermentation liquid is suitably extracted from a methane fermentation tank, and is discarded (step S4).

  Next, the concentrated methane fermentation liquid is returned to the methane fermentation tank (step S6). At this time, the membrane permeate of the pressurized membrane separator is sent to the wastewater treatment step.

  In the flow of FIG. 1, an acid fermentation tank and a methane fermentation tank are separately provided, and an example of a two-phase digestion treatment method in which an acid fermentation treatment and a methane fermentation treatment are sequentially performed is shown. Acid fermentation and methane fermentation may be performed simultaneously in a single tank. That is, step S2 and step S3 may be performed simultaneously in one tank. However, acid fermentation and methane fermentation differ in optimal organic matter concentration, reaction temperature, etc., so when using a single anaerobic digestion method, digestion efficiency is reduced compared to the two-phase digestion method. Moreover, since it is necessary to lengthen the residence time, a large digester is required. For this reason, it is preferable to employ a two-phase digestion method from the viewpoint of space saving and digestion efficiency.

  The concept of the organic waste processing method of the present invention has been described above with reference to FIG.

Example 1
Next, as Example 1 of the present invention, a part of the configuration of the organic waste treatment apparatus will be further described in comparison with the corresponding part of the conventional organic waste treatment apparatus. In addition, a present Example is an example of a single anaerobic digestion processing apparatus.

  First, FIG. 2 is a diagram showing a partial configuration of a methane fermentation tank and a membrane separator of a conventional organic waste treatment apparatus. In the conventional organic waste processing apparatus, the organic waste 1 that has been pretreated is appropriately put into the methane fermentation tank 2 to perform acid fermentation and methane fermentation. And the sludge in the methane fermenter 2 is taken out from the bottom as the sludge 3 and appropriately taken out and discarded.

  A part of the fermentation broth 5 in the methane fermentation tank 2 is sent to the submerged membrane separation device 8 by the pump 6. The fermented liquid 15 concentrated by the submerged membrane separator 8 is returned to the methane fermentation tank 2.

  The submerged membrane separator 8 accommodates a plurality of submerged membranes 9 in parallel at appropriate intervals, and a blower 13 and a diffuser for aerating the biogas 4 generated from the methane fermentation tank 2 at the lower part of the membrane module. A gas device 14 is provided. And the surface of the immersion film 9 is anaerobically cleaned by aeration of the biogas 4 from the aeration device 14.

  However, since bubbles of the biogas 4 adhere to the surface of the immersion film 9, there is a drawback that the effective transmission area is reduced even if the immersion film 9 is washed. Moreover, since the transmembrane pressure difference of the submerged membrane separator 8 obtained by the drawing pump 10 is usually 30 to 40 kPa, it is difficult to concentrate the fermentation broth quickly.

  Next, FIG. 3 is a figure which shows the partial structure of the methane fermenter of the organic waste processing apparatus of a present Example, and a membrane separator. The organic waste treatment apparatus of the present embodiment sends a part of the methane fermentation solution 5 from the methane fermentation tank 2 to the pressurized membrane separator 20 having the fermentation solution circulation line 17 to concentrate the methane fermentation solution 5. It is characterized by performing.

Here, the specific structure of the pressure type membrane separation apparatus 20 is shown in FIGS. The pressure-type membrane separation apparatus 20 includes an envelope-like flat membrane element 62 formed by superposing polyethylene treated water spacers and flat membranes on both sides of an ABS support plate one by one and sealing the outer periphery. The spacer 61 is laminated in multiple layers.
The spacer 61 is for preventing the cleaning waste water from leaking out from the envelope-like flat membrane element 62. The envelope flat membrane element 62 thus laminated in multiple layers is accommodated in a flat membrane element sandwiching body 64 composed of a pair of halves 63 and halves 63 as shown in FIG. Furthermore, as shown in FIG. 7, it is accommodated in a pressure vessel 65 and configured.

  The pressure vessel 65 has an inlet 66 for introducing the methane fermentation liquid at one end, and an outlet 67 for the concentrated methane fermentation liquid at the other end. A permeate discharge path 68 is formed inside the flat membrane element sandwiching body 64 and on the side of the envelope-shaped flat membrane element 62 laminated in multiple layers. A through-hole 69 is formed in the envelope flat membrane element 62 laminated in multiple layers, and the through-hole 69 is in communication with the permeate discharge path 68.

  A pipe 70 for supplying the permeated liquid that has permeated through the envelope flat membrane element 62 to the permeated liquid discharge path 68 is inserted into the through hole 69. Reference numeral 71 denotes a current plate provided in the vicinity of the inlet 66 side.

  As another form of the pressure-type membrane separation apparatus, a structure accommodated in a rectangular tubular pressure vessel as shown in FIG. 8 can be used. Here, FIG. 8 (a) shows a schematic cross-sectional view of the membrane separation device, FIG. 8 (b) shows a schematic cross-sectional view taken along the line BB of FIG. 8 (a), and FIG. ) Shows a schematic cross-sectional view taken along the line CC in FIG. In FIG. 8, the same components as those in FIGS. 6 and 7 are denoted by the same reference numerals and description thereof is omitted.

  This pressure type membrane separation apparatus includes a rectangular tubular pressure vessel 80, a flat plate membrane element sandwiching body 82 provided in the pressure vessel 80, and two paired water collecting portions 82. The flat membrane element group 81 is used. The flat membrane element group 81 is configured by laminating a plurality of envelope-like flat membrane elements 62 and spacers 61 provided on each envelope-like flat membrane element 62.

  Then, as shown in FIG. 8 (a), the membrane separation device main body portion holds a flat membrane element group 81 between a pair of flat membrane element holding bodies 82, and uses a fastening band 83 to The flat membrane element group 81 is fixed. As shown in FIG. 8 (c), the water collecting portion 82 has a width dimension substantially the same as that of the flat membrane element group 81, and the fastening band 83 is an end portion of the water collecting portion 82 and the flat membrane element group 81. The flat membrane element group 81 is sandwiched between the pair of flat membrane element sandwiching bodies 82 so as to be in contact with each other.

Here, a membrane for the membrane treatment of methane fermentation broth using a small-sized tester (using a membrane area of 32 cm ² , material polyethersulfone, and a molecular fraction of 50,000) using a pressurized membrane separator The results of measuring the differential pressure (kPa) and the amount of permeate (flux: m ³ / m ² / day) are shown in FIG. When the transmembrane pressure is 20 kPa, the permeate volume is 0.016 m ³ / m ² / day. When the transmembrane pressure is 5 times 100 kPa, the permeate volume is also about 5 times 0.075 m ^3. / m ² / day. Since the transmembrane pressure difference of a pressurized membrane separator is usually 100 kPa or more, the pressurized membrane separator has a larger amount of permeate compared to a submerged membrane separator using the same membrane area and the same membrane area. It is clear from FIG. 4 that the concentration processing speed of the methane fermentation liquid is high.

次に、うどん主体の麺廃棄物を、発酵容積：2m³のメタン発酵槽を用いて単一嫌気性消化処理し、メタン発酵槽内のメタン発酵液を膜分離処理しない場合と加圧型膜分離装置を使用して膜分離処理する場合について、限界CODcr容積負荷、SS除去率、COD除去率を比較した結果を、表１に示す。ここで、CODcr及びSSは、それぞれJISに定めるクロム酸カリウム法による化学的酸素要求量及び固形分を表し、それらの除去率とは、メタン発酵前後の測定値の差を、メタン発酵前の測定値で除し、100を乗じて算出した数値である。また、限界CODcr容積負荷は、１日にメタン発酵槽1m³当たりに処理可能な有機性廃棄物量を表す。なお、有機性廃棄物の処理量は、膜分離なしで運転する場合30kg/日、加圧型膜分離装置（株式会社神鋼環境ソリューション製：商品名「UFキューブ」（膜面積0.17m²））を運転する場合、90kg/日という条件でメタン発酵処理を行った。

Then the noodles waste noodles mainly fermentation volume: using methane fermenter 2m ³ and single anaerobic digestion process, if not the membrane separation process methane fermentation liquid in the methane fermentation tank and the pressure type membrane separation Table 1 shows the results of comparison of the critical CODcr volumetric load, SS removal rate, and COD removal rate in the case of membrane separation using the apparatus. Here, CODcr and SS represent the chemical oxygen demand and solid content by the potassium chromate method specified in JIS, respectively, and their removal rate is the difference between measured values before and after methane fermentation, measured before methane fermentation. It is a numerical value calculated by dividing by 100 and multiplying by 100. The limit CODcr volumetric load represents the amount of organic waste that can be treated per 1 m ³ of methane fermenter per day. The amount of organic waste processed is 30 kg / day when operated without membrane separation. Pressurized membrane separator (made by Shinko Environmental Solution Co., Ltd .: trade name “UF Cube” (membrane area 0.17 m ² )) When operating, the methane fermentation treatment was performed under the condition of 90 kg / day.

  SS removal rate and CODcr removal rate are compared with the case where the membrane treatment is not performed when the methane fermentation broth is concentrated using a pressurized membrane separator and the concentrated methane fermentation broth is returned to the methane fermentation tank. Increased 2.1% and 7.5% respectively. On the other hand, the critical CODcr load increased up to 3 times, and it was shown that the methane fermentation treatment can be accelerated by performing membrane separation treatment.

  However, if the submerged membrane separator 8 in FIG. 2 is simply replaced with the pressurized membrane separator 20, the membrane 19 may be immediately impeded by the solid content in the methane fermentation broth 5, i.e., lack of practicality. Problems arise.

  Therefore, in the organic waste treatment apparatus of the present embodiment, as shown in FIG. 3, a fermentation liquid circulation line 17 for circulating the methane fermentation liquid is installed in the pressurized membrane separator, and the fermentation liquid circulation line 17 The membrane 19 is prevented from clogging by continuously circulating the methane fermentation broth.

  First, the methane fermentation solution 5 taken out from the methane fermentation tank 2 by the pressurizing pump 6 is pressurized to a predetermined pressure and sent to the fermentation solution circulation line 17. The methane fermentation liquor is circulated through the fermentation liquor circulation line 17 and the pressurized membrane separator 20 by the circulation pump 18, passes between a plurality of membranes 19 arranged in parallel, and is concentrated by membrane treatment. Thus, by making the permeation | transmission direction of the film | membrane 19 and the flow direction of a methane fermentation liquid perpendicular | vertical, the clogging of the film | membrane 19 by the solid content in a methane fermentation liquid does not occur easily. The circulation pump 18 has a function of increasing the membrane surface flow rate in the pressurized membrane separator 20 and a function of compensating for pressure loss in the fermentation liquid circulation line 17 and the pressurized membrane separator 20.

  As the type of the flat membrane 19, an ultrafiltration membrane or a microfiltration membrane is used. The material of the flat membrane 19 is preferably a polymer membrane such as polyethylene, polyethersulfone, polyacrylonitrile, etc., and the length of the methanogen is 0.5 μm or more, so the average pore diameter is 0.5 μm or less. Is preferred.

  From the viewpoint of rapid processing of the methane fermentation broth 5, it is preferable to set the pressure in the fermentation broth circulation line 17 (equal to the pressure in the pressurized membrane separator 20) to 50 kPa or more, and this pressure is the transmembrane pressure difference. Thus, the methane fermentation broth 5 is subjected to membrane treatment. As the pressure is increased, the amount of permeate (permeation flux) of the methane fermentation liquid increases, but the power consumption of the pressure pump 6 also increases. Further, as shown in FIG. 4, when the transmembrane pressure exceeds 200 kPa, the increase in the membrane permeation amount reaches a peak. For this reason, it is practical to set the pressure in the pressurized membrane separator 20 to 50 kPa or more and 200 kPa or less, and from the viewpoint of obtaining a high permeate amount, it is more practical to set the pressure to 100 kPa or more and 200 kPa or less. . The membrane surface differential pressure in the pressurized membrane separator 20 can be measured by the pressure gauge 25.

  Here, in order to prevent clogging of the membrane 19, it is important to set the membrane surface flow rate of the fermentation broth in the pressurized membrane separator 20 to 0.6 m / second or more. If the membrane surface flow rate of the methane fermentation solution in the pressurized membrane separator 20 is less than 0.6 m / sec, it is difficult to prevent clogging of the membrane 19. On the other hand, if the membrane surface flow rate is higher than 0.6 m / sec, the prevention effect is improved, and the permeate volume (permeation flux) of the methane fermentation liquid is further increased. The increase will be peaked. For this reason, the membrane surface flow rate of the methane fermentation solution in the pressurized membrane separator 20 is preferably 0.6 m / sec or more and 1.2 m / sec or less, more preferably 0.8 m / sec or more and 1.0 m / sec or less. The membrane flow rate of the methane fermentation liquid in the pressurized membrane separator 20 can be measured by the flow meter 26.

  Next, the methane fermentation solution in the fermentation solution circulation line 17 is subjected to membrane treatment by the membrane 19, and soluble substances such as volatile organic acids are taken out from the pressurized membrane separator 20 as the membrane permeate 11. Then, the membrane permeate 11 containing such a substance is sent to the wastewater treatment process, and the concentrated methane fermentation solution 15 passes through the concentrated fermentation solution return line 16 connected to the fermentation solution circulation line 17, and is subjected to methane fermentation. Returned to tank 2.

  When the organic substance density | concentration of a methane fermentation liquid becomes high, or when the viscosity becomes high, the amount of membrane permeate will reduce and the membrane separation efficiency of a methane fermentation liquid will fall. In such a case, the membrane permeate amount can be increased by closing the valve 21 provided in the concentrated methane fermentation liquid return line 16 to increase the membrane pressure difference in the pressurized membrane separator 20. It becomes possible.

  In the example shown in FIG. 3, the membrane permeate amount of the pressurized membrane separator 20 is measured by the measuring device 23 installed in the membrane permeate discharge line 22, and the measured amount is transmitted to the valve opening / closing control device 24. . The valve opening / closing control device 24 sends a signal for closing the valve to the valve 21 when the amount of the membrane permeate decreases from a reference value inputted in advance. When the valve 21 is closed, the membrane surface differential pressure in the fermentation broth circulation line 17 and the pressurized membrane separator 20 is increased, and the amount of membrane permeate can be increased.

  Thereafter, when the organic substance concentration of the methane fermentation liquid becomes low or the viscosity becomes low, the amount of the membrane permeate increases more than necessary. Therefore, when the amount of the membrane permeate increases from the reference value previously input to the valve opening / closing control device 23, the valve opening / closing control device 24 sends a signal to the valve 21 to open the valve. By this control, the membrane surface differential pressure in the fermentation liquid circulation line 17 and the pressurized membrane separator 20 is reduced, and the amount of membrane permeate can be reduced.

In the concentrated methane fermentation solution 15 returned to the methane fermentation tank 2, methane fermentation bacteria remain, and the concentration of the methane fermentation bacteria in the methane fermentation tank 2 can be maintained. Moreover, the organic substance density | concentration in the methane fermenter 2 can also be maintained at the density | concentration preferable as methane fermentation (5000-20000 mg / L as suspension substance density | concentration).
(Example 2)
Next, as Example 2 of the present invention, an overall configuration of an organic waste treatment apparatus different from Example 1 is shown in FIG. The configurations and operational effects of the methane fermentation tank and the pressurized membrane separator are the same as the partial configuration of the organic waste treatment apparatus shown in FIG. In addition, a present Example is an example of a two-phase type anaerobic digestion processing apparatus.

  First, the organic waste 31 is separated, crushed, diluted, etc. by the pretreatment device 32. The organic waste that has become the organic slurry 33 is sent to the acid fermentation tank 34 and subjected to acid fermentation. The acid fermenter is retained for a predetermined time while maintaining an anaerobic atmosphere at a temperature of about 55 to 65 ° C.

  Next, the acid fermentation liquid 35 is sent to the methane fermentation tank 36 and subjected to methane fermentation treatment. The methane fermenter is retained for a predetermined time while maintaining an anaerobic atmosphere at a temperature of about 30 to 60 ° C. Specifically, in the case of high temperature methane fermentation, it is retained at 50 to 60 ° C. for about 10 to 20 days, and in the case of medium temperature methane fermentation, it is retained at 30 to 40 ° C. for about 20 to 40 days.

  It is shown in FIG. 3 that the methane fermentation liquid 38 is subjected to membrane separation treatment by a pressurized membrane separator 39 equipped with a methane fermentation liquid circulation line (not shown) and the concentrated methane fermentation liquid 40 is returned to the methane fermentation tank 36. It is the same as the apparatus shown.

  The membrane permeate 41 discharged from the pressurized membrane separator 39 is sent to the denitrification tank 45. In the denitrification tank 45 and the nitrification tank 46, the ammonia nitrogen in the membrane permeate 41 is biologically nitrified and denitrified and decomposed into nitrogen gas 48 and the like. The treated water 49 after the nitrification denitrification treatment is further subjected to advanced wastewater treatment.

  On the other hand, the extracted sludge 42 extracted from the bottom of the methane fermentation tank 36 is solid-liquid separated by a solid-liquid separator 43 such as a centrifugal separator, and the desorbed liquid 50 (liquid component) is sent to the denitrification tank 45. Although it can be denitrified in the same manner as the membrane permeate 41, it can be returned to the acid fermenter 34 to increase the concentration of organic matter and promote acid fermentation. The solid residue 44 is appropriately treated separately.

  As described above, the organic waste treatment method and treatment apparatus of the present invention can maintain a rapid membrane separation treatment of methane fermentation broth for a long period of time. Moreover, by employing the two-phase anaerobic digestion method, acid fermentation and methane fermentation can be performed under optimum conditions, respectively, and the processing efficiency of organic waste is improved. Furthermore, by combining with the nitrification denitrification treatment, the methane fermentation liquor and the effluent from the drawn sludge of the methane fermentation tank can be denitrified, and the burden of wastewater treatment can be reduced.

  The organic waste processing method and processing apparatus of the present invention are useful as an efficient processing method and processing apparatus for organic waste such as garbage and food waste.

It is a figure which shows the flow of the organic waste processing method of this invention. It is a figure which shows a part of structure of the conventional organic waste processing apparatus. It is a figure which shows a part of structure of the organic waste processing apparatus based on Example 1 of this invention. It is a figure which shows the relationship between transmembrane differential pressure and the amount of permeate in the small test machine of a pressurization type membrane separator. It is a figure which shows the whole structure of the organic waste processing apparatus based on Example 2 of this invention. It is a figure which shows the structure of the flat membrane element clamping body of a pressurization type membrane separator. It is a figure which shows the structure about an example of the pressure vessel of a pressurization type membrane separator. It is a figure which shows the structure about another example of the pressure vessel of a pressurization type membrane separator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,31: Organic waste 2,36: Methane fermentation tank 3,42: Extracted sludge 4,37: Biogas 5,38: Methane fermentation liquid 6: Pump 7: Methane fermentation liquid extraction line 8: Immersion type membrane separation Apparatus 9: Submerged membrane 10: Extraction pump 11, 41: Membrane permeate 12: Blower biogas line 13: Blower 14: Air diffuser 15, 40: Concentrated methane fermentation liquid 16: Concentrated methane fermentation liquid return line 17: Fermentation Liquid circulation line 18: Circulation pump 19: Flat membrane 20: Pressurized membrane separator 21: Valve 22: Membrane permeate discharge line 23: Membrane permeate amount measuring device 24: Valve opening / closing control device 32: Pretreatment device 33: Disposal Waste slurry 34: acid fermentation tank 35: acid fermentation liquid 43: solid-liquid separator 44: solid residue 45: denitrification tank 46: nitrification tank 47: nitrification treatment liquid 48: nitrogen gas 49: treated water 50: desorption liquid 61 :spacer 2: Envelope-shaped membrane element 63: Half body 64: Flat membrane element clamping body 65: Pressure vessel 66: Inlet part 67: Concentrated methane fermentation liquid outlet part 68: Permeate outlet part 69: Through hole 70: Pipe 71: Current plate 80: Rectangular tubular pressure vessel 81: Flat membrane element group 82: Water collecting part 83: Clamping band

Claims (12)

  In this method, organic waste is decomposed by methane fermentation in a methane fermentation tank, and a portion of the fermentation liquor in the methane fermentation tank is concentrated by a pressurized membrane separator equipped with a fermentation liquid circulation line for circulating the fermentation liquid. In addition to discharging the membrane permeate out of the system and returning the concentrated fermentation liquor to the methane fermentation tank, the solids concentration of the fermentation liquid in the methane fermentation tank should be maintained at an appropriate value for methane fermentation. A method for treating organic waste.   The method for treating organic waste according to claim 1, wherein the membrane surface flow rate of the fermentation broth in the pressurized membrane separator is 0.6 m / sec or more.   The method for treating organic waste according to claim 1 or 2, wherein the pressure difference on the membrane surface in the pressurized membrane separator is 50 kPa or more and 200 kPa or less. Measure the amount of membrane permeate discharged outside the system,
When the amount of membrane permeate decreases below the reference value, the valve of the return line from the fermentation liquid circulation line to the methane fermentation tank is throttled, and the membrane surface differential pressure in the pressurized membrane separator is increased,
When the membrane permeate amount exceeds the reference value, the valve of the return line from the fermentation liquid circulation line to the methane fermentation tank is opened to reduce the membrane surface differential pressure in the pressurized membrane separator. The organic waste processing method according to claim 1, wherein the organic waste processing method is controlled.   The organic waste treatment method according to any one of claims 1 to 4, wherein the organic waste is decomposed by acid fermentation in an acid fermenter before methane fermentation.   The method for treating organic waste according to any one of claims 1 to 5, wherein the membrane permeate is further nitrified and denitrified after methane fermentation. A methane fermentation tank for methane fermentation of organic waste,
A fermentation liquor extraction line for taking out part of the fermentation liquor in the methane fermentation tank by suction means;
A pressure-type membrane separation device comprising a fermentation liquid circulation line connected to the fermentation liquid extraction line and circulating the fermentation liquid from the fermentation liquid extraction line by a pressurizing means;
An organic waste product comprising: a concentrated fermented liquid return line that is connected to the fermented liquid circulating line and returns the concentrated fermented liquid circulating in the fermented liquid circulating line to a methane fermentation tank. Processing equipment.   The apparatus for treating organic waste according to claim 7, wherein the membrane surface flow rate of the fermentation liquid in the pressurized membrane separator during the membrane separation operation of the fermentation liquid is 0.6 m / sec or more.   The organic waste treatment apparatus according to claim 7 or 8, wherein a membrane surface differential pressure in the pressure-type membrane separation apparatus during the membrane separation operation of the fermentation broth is 50 kPa or more and 200 kPa or less. A membrane permeate discharge line for discharging the membrane permeate from the pressurized membrane separator;
A membrane permeate amount measuring means provided in the membrane permeate discharge line;
A valve provided in the concentrated fermented liquid return line;
Control means for adjusting the opening of the valve,
When the membrane permeate discharge amount measured by the measuring means decreases below a reference value, the control means adjusts the opening so as to throttle the valve, and increases the membrane surface differential pressure in the fermentation liquor circulation line. To control and
When the membrane permeate discharge amount measured by the measuring means increases to a reference value or more, the opening degree is adjusted so that the control means opens the valve, and the membrane surface differential pressure in the fermentation liquor circulation line is reduced. The organic waste processing apparatus according to any one of claims 7 to 9, characterized by being controlled as follows.   The organic waste treatment apparatus according to any one of claims 7 to 10, further comprising an acid fermentation tank for decomposing the organic waste by acid fermentation prior to methane fermentation. The apparatus for treating organic waste according to any one of claims 7 to 11, further comprising a nitrification / denitrification tank for nitrifying / denitrifying the membrane permeate after methane fermentation.

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