JP2014205136A - Dinitrogen monoxide(n2o) suppression type sewage treatment technique using carbon fiber packed aerobic bioreactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for sewage treatment which suppresses emission of dinitrogen monoxide (NO) from sewage.SOLUTION: A sewage treatment method includes a step of subjecting sewage to an aeration treatment in the presence of fixed-bed type carbon fibers and suppresses generation of dinitrogen monoxide by utilizing microorganisms accumulated on the carbon fibers.

Description

  The present invention relates to a method for treating organic sewage such as livestock sewage and sewage, and a sewage treatment apparatus used in the method.

The generation of greenhouse gas (GHG) from livestock excreta is said to contribute about 26% of agricultural emissions, and there are high expectations for reduction. In Japan's livestock excrement management category, sewage purification is cited as one of the main sources of GHG methane (CH ₄ ) and dinitrogen monoxide (N ₂ O). In particular, since the global warming potential of N ₂ O is reported to be 298 times that of carbon dioxide (Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report), N ₂ O generated in the dirty water The development of suppression technology is considered to contribute greatly to the reduction of GHG emissions.

In the past, the causes of N ₂ O generated from sewage treatment are as follows: dissolved oxygen deficiency, organic overload, short sludge residence time (SRT), presence of toxic substances, low water temperature, and high ammonia Nitrogen (NH ₄ -N) conditions have been pointed out, and in the denitrification process, the carbon ratio (C / N) of input wastewater is low, the pH is low, and the redox potential (ORP) is high Conditions have been pointed out (Hanaki et al. (2001), Journal of Japan Society on Water Environment, 24 (7), pp. 473-476; Kampschreur et al. (2009), Water Research, 43 (17), pp. 4093-4103; and Masuda et al. (2009), Journal of Japan Society on Water Environment, 32 (3), pp. 147-152). Thus, while N ₂ O generation factors vary widely, it has been reported that the generation of N ₂ O increases when NO _X -N accumulation is observed in the treated water (Hanaki et al. ( 2001), Journal of Japan Society on Water Environment, 24 (7), pp. 473-476; and Kampschreur et al. (2009), Water Research, 43 (17), pp. 4093-4103).

By the way, conventionally, the sewage purification process is performed by the activated sludge method, for example.
The standard activated sludge method is a treatment system consisting of an initial precipitation, aeration, and a final precipitation in this order. In the initial precipitation, a physical treatment is first performed by gravity sedimentation, and then the obtained supernatant is put into an aeration tank. In the aeration tank, aerobic microorganism treatment is performed by activated sludge, and organic matter is decomposed. In the final sedimentation, the activated sludge is settled, and the sludge concentration is adjusted by returning a part of the sludge to the aeration tank. Moreover, the supernatant liquid after final precipitation becomes treated water. In the purification treatment, the standard activated sludge method is used as a general treatment technique. However, operation management such as adjustment of the sludge concentration in the aeration tank and adjustment of the amount of sludge returned from the sedimentation tank to the aeration tank is necessary. In many cases, the nitrogen component is not sufficiently denitrified even after nitrification, but nitrite ions and nitrate ions accumulate. According to reports, N ₂ O release into the atmosphere is attributed to the accumulation of nitrite ions. In the standard activated sludge method, it is estimated that about 5% of the input nitrogen is released into the atmosphere as N ₂ O (Japan Greenhouse Gas Inventory Report, April 2012).

The intermittent aeration method is a modification of the above-mentioned standard activated sludge method, and the standard activated sludge method is a treatment by continuous aeration, whereas the supply of oxygen is stopped by partially stopping aeration in the treatment process. This is a technique that promotes denitrification by making oxygen free. According to the intermittent aeration method, it has been reported that the generation of N ₂ O can be considerably suppressed, while cases in which the generation of N ₂ O has increased have been reported. Moreover, the said method may reduce organic substance resolution | decomposability by temporarily stopping aeration. Therefore, a treatment tank larger than the standard activated sludge method is required. Furthermore, it is necessary to adjust the aeration ON and OFF times according to the concentration of each livestock farmer.

The batch activated sludge method is also a modification of the above standard activated sludge method. Normally, the standard activated sludge method performs treatment with a final sedimentation basin, whereas all treatment steps are completed in one treatment tank. It is a technique. In other words, the batch activated sludge method is a method in which four steps of sewage input, aeration treatment, sludge sedimentation by aeration stop, and discharge of the supernatant liquid separated into solid and liquid as treatment water are repeated in one treatment tank. . It has been reported that the batch activated sludge method can suppress the generation of N ₂ O as in the intermittent aeration method. However, the batch activated sludge method cannot continuously supply sewage, and there is a problem that a large treatment tank is required because the aeration time is limited. Furthermore, although the aeration and sludge settling time can be easily changed according to changes in the amount of sewage and the water temperature, there is a demerit that the knowledge and ability of the manager are required.

According to a report of N ₂ O generation measurement, it was reported that 0.5% or more of N ₂ O was generated in the continuous anaerobic aerobic batch activated sludge process (Itokawa, H. et al. 2001), Water Research, 35 (3), pp. 657-664). In addition, it has been reported that N ₂ O is generated in the continuous activated sludge process by 0.2 to 1.5% of the input nitrogen (Noda, N. et al. (2003), Water Science and Technology 48 (11-12), pp. 363-370).

Thus, in the sewage treatment by the conventional method, generation of N ₂ O could not be sufficiently suppressed.
On the other hand, a method for purifying sewage using a microbial carrier containing carbon fiber is conventionally known.

  Patent Document 1 discloses an at least one type of fiber selected from polyvinylidene chloride, nylon, polyethylene, polypropylene, and carbon fiber, and an acrylic fiber, and a microbial carrier upright so as to form a large number of U-shaped loops in the backbone, and Disclosed is a method for purifying sewage in which aeration treatment is performed using a treatment tank filled with a microorganism carrier.

  Patent Document 2 discloses a sewage treatment apparatus in which a single-filament open tufted filter medium made of carbon fiber is installed in a contact aeration tank as a contact filter medium that holds a biofilm, and a sewage treatment method using the sewage treatment apparatus.

  Patent Document 3 has an anaerobic treatment tank, a support that is long in the vertical direction, fixed in the anaerobic treatment tank, and a plurality of carbons that are partially fixed to the support and arranged in the vertical direction. Disclosed is a water treatment device having a string-like filter medium formed from fibers and the like, and a sewage circulation unit that circulates sewage vertically upward in an anaerobic treatment tank.

  In Patent Document 4, a rod-like support body having a hardness that can maintain a certain form in the air or water and a plurality of carbon fibers and other fiber members protruding obliquely from the support body are arranged in a spiral shape. A septic tank having a water treatment member capable of efficiently collecting sludge such as suspended solids, an anaerobic treatment tank formed so that the major axis direction of the support is the direction in which the treated water flows, and the septic tank Disclosed is a water treatment method using

  In Patent Document 5, a biofilm carrier is formed by PAN-based carbon fiber filaments from which a sizing agent has been removed in advance, and the biofilm carrier binds a large number of ultrafine carbon fiber filaments rich in flexibility and flexibility. Molded to secure a large surface area for attaching microorganisms by being exposed, migrated, and scattered in the water when a large number of carbon fiber filaments are exposed to water when placed in water, compressed, knitted or woven. A broom mold formed into a body by connecting and integrating carbon fiber strands composed of a plurality of carbon fiber filaments to a strand backbone formed by carbon fiber filaments. Disclosed is a contact filter medium in a contact oxidation water purifier constituted of a strand molded body.

  Patent Document 6 discloses a method of immobilizing a carbonophile layer around a carbon fiber into which an oxygen-containing group has been introduced, immobilizing microorganisms around the carbonophile, and immobilizing microorganisms and waste water containing persistent organic substances. Disclosed is a method for purifying waste water, which comprises decomposing a hardly decomposable organic substance and purifying waste water by contacting the waste water.

JP-A-10-276777 JP 2000-325973 A JP 2012-91115 A JP 2011-147886 Japanese Patent No. 2954509 Japanese Patent No. 3328700

As described above, if N ₂ O release can be suppressed in sewage treatment, it is expected to greatly contribute to the reduction of GHG generation. However, in the sewage treatment by the conventional method, the generation of N ₂ O could not be sufficiently suppressed.

The present invention has been made in view of the circumstances described above, and an object thereof is to provide a wastewater treatment method and sewage treatment apparatus which can suppress the release of N ₂ O from sewage.

As a result of diligent research to solve the above problems, we focused on the biofilm method as a method different from the activated sludge method, aiming for treatment with low NO _X -N accumulation, and devised the arrangement of carriers structurally As a result, it has been found that by performing sewage treatment using carbon fiber as a microorganism carrier, release of N ₂ O from sewage can be suppressed, and the present invention has been completed.

The present invention includes the following.
(1) A sewage treatment method including a step of subjecting sewage to aeration treatment in the presence of fixed-bed carbon fibers, and suppressing generation of dinitrogen monoxide (N ₂ O) by microorganisms accumulated on the carbon fibers.
(2) The method according to (1), wherein the sewage is subjected to an aeration treatment in the presence of a fixed bed type microbial carrier including a cylinder and a carbon fiber projecting in a normal direction on the outer peripheral surface of the cylinder.
(3) The method according to (1) or (2), comprising a step of separating the effluent after aeration treatment into sludge and treated water.
(4) The method according to any one of (1) to (3), wherein the sewage is livestock sewage.
(5) A sewage treatment apparatus comprising a fixed-bed carbon fiber filling treatment tank for subjecting sewage to aeration treatment, and suppressing generation of dinitrogen monoxide (N ₂ O) by microorganisms accumulated on the carbon fiber.
(6) The fixed bed type carbon fiber filling treatment tank is a treatment tank filled with a fixed bed type microbial carrier including a cylinder and a carbon fiber arranged so as to protrude in a normal direction on the outer peripheral surface of the cylinder. ) The device described.
(7) The apparatus according to (5) or (6), including a precipitation tank that separates the effluent after aeration into sludge and treated water.
(8) The apparatus according to any one of (5) to (7), wherein the sewage is livestock sewage.

According to the present invention, in sewage treatment, sewage can be purified while suppressing generation of dinitrogen monoxide (N ₂ O) from sewage.

It is a schematic diagram which shows an example of the fixed bed type | mold carbon fiber filling processing tank in this invention. It is a schematic diagram which shows an example of the sewage treatment apparatus which concerns on this invention. 1 is a schematic diagram of a carbon fiber filled aerobic bioreactor in Example 1. FIG. 1 is a schematic diagram of an activated sludge reactor as a control in Example 1. FIG. Is a graph showing the NH _3, N ₂ gas concentration change of O and CH ₄ generated from (a) carbon fiber reactor and (b) activated sludge reactors in operation 130 days to 136 days. Elapsed time 0 (hrs) to 168 (hrs) is an elapsed time from the 130th day to the 136th day of operation. It is a graph which shows the typical example of the change of the water quality and generated gas density | concentration after the sewage injection | pouring of the (a) carbon fiber reactor and the (b) activated sludge reactor in the 131st day of operation. The flora analysis result in a carbon fiber reactor is shown.

  Hereinafter, the present invention will be described in detail.

The sewage treatment method according to the present invention (hereinafter referred to as “the present method”) is a method in which sewage is subjected to an aeration treatment in the presence of carbon fiber fixed bed type (for example, fixed to a cylindrical support). Specifically, the nitrification reaction is accelerated by aerobic microorganisms floating in and around the support (cylinder) on which the fixed-bed carbon fibers are fixed by aeration treatment. On the other hand, a treatment that suppresses the generation of N ₂ O is possible by accumulating and supporting mainly anaerobic microorganisms inside carbon fibers attached to the outside of the support (cylindrical). Organic matter and nitrogen in sewage are removed using the microorganism. According to this method, while effectively treating organic matter and nitrogen in sewage, for example, compared with the conventional activated sludge method, the generation of dinitrogen monoxide (N ₂ O) from sewage is significantly suppressed. can do. In particular, by using a fixed bed type carbon fiber filling treatment tank having this treatment structure, anaerobic microorganisms that are difficult to accumulate by the activated sludge method are retained in the carbon fiber at a high concentration, so that nitrification by accumulated microorganisms is performed. And the denitrification reaction proceeds simultaneously, and the generation of N ₂ O can be significantly suppressed.

Here, the sewage is not limited, and examples thereof include livestock sewage and sewage. Livestock sewage means sewage including manure and washing water, such as a pig barn and a cow barn. For livestock sewage, for example, nitrifying bacteria that perform nitrification reactions (oxidation from ammonium ions to nitrite ions and nitrate ions under aerobic conditions) and denitrification reactions that perform denitrification reactions (reduction of nitrate ions to nitrogen gas) There are bacteria. By accumulating and supporting such microorganisms in sewage sewage in a fixed-bed carbon fiber filling treatment tank, nitrification and denitrification proceed simultaneously, and ammonium ions in the sewage are converted into nitrogen gas. Can be released out of the system and generation of N ₂ O can be suppressed.

  In this method, the sewage can be directly subjected to an aeration process. Alternatively, before the aeration treatment, the sewage can be subjected to solid-liquid separation by a mechanical method or gravity precipitation, and the obtained liquid can be used as an inflow water for the aeration treatment. Examples of the solid-liquid separation method using a mechanical method include pressing and sieving. In pressing, a screw press or a roll press is used. The screw press is a device that removes liquid juice from a small hole or a gap provided in the cylinder by rotating a screw attached in the cylinder to reduce an internal gap and a discharge port to increase pressure. The roll press is an apparatus that separates solid and liquid juice by sandwiching materials between two opposing rolls. On the other hand, sieving means an operation of separating powder particles into large and small particles using a sieving surface, and a fixed sieve, a rotary sieve, a vibrating sieve, or the like is used. The fixed sieve has a fixed mesh surface. The rotary sieve is a mechanism in which the filter mesh is cylindrical, and the rotation shaft is inclined and rotated, and the sieve residue (separated solid matter) generated inside the cylinder moves downward along the inclination axis and is eliminated. The vibration sieve is designed to eliminate the sieve by applying a vibration by slightly tilting the filter mesh, reciprocating or circular arc motion by a crank mechanism, turning motion by an eccentric shaft, resonance of a filter mesh supported by a spring by a vibration motor, etc. It is a device.

  On the other hand, a fixed-bed carbon fiber filling treatment tank is prepared as a tank for performing the aeration process. Here, the fixed bed type carbon fiber (microbe carrier) means a carbon fiber (microbe carrier) that is filled in the tank or fixed so as not to flow. The fixed bed type carbon fiber filling treatment tank means a treatment tank filled with the fixed bed type carbon fiber or fixed so as not to flow.

An example of the fixed bed type carbon fiber filling treatment tank in the present invention is shown in FIG. As shown in FIG. 1, the fixed bed type carbon fiber filling treatment tank according to the present invention is, for example, a fixed bed type biofiber in which a carbon fiber (microorganism carrier) attached to a mesh cylinder (support) is fixed at the center of a cylindrical reactor. Reactor. In this technology, carbon fiber is placed on the outside of the cylinder as a microbial carrier, and aerobic sites and anaerobic sites are formed even under continuous aeration conditions, and nitrogen removal is performed while suppressing the generation of N ₂ O. It is a processing device characterized by being able to. As the microbial carrier, a fibrous carrier can be used in addition to the carbon fiber, and carbon fiber is particularly preferable. The carbon fiber may be commercially available from, for example, Spring Field Limited. The fiber diameter of the carbon fiber is, for example, preferably 3 to 20 μm, particularly preferably 7 to 8 μm so that microorganisms in the sewage can be accumulated. The structure of the microbial carrier is such that the carrier protrudes from the outside of the mesh cylinder so that aeration does not directly hit the carrier so that contact aeration does not occur. As well as suppressing oxygen supply. This structure promotes the formation of a biofilm on the carrier, and anaerobic microorganisms grow on the carrier. In addition, suspended microorganisms not attached to the carrier promote the growth of aerobic microorganisms by supplying oxygen by aeration, causing decomposition of organic matter and nitrification reaction. The biochemical oxygen demand (BOD) load is preferably 0.1 to 0.5 kg / m ³ / day. Accordingly, a processing apparatus is produced which is characterized by promoting the growth of anaerobic microorganisms and suppressing the generation of N ₂ O by arranging and filling the carbon fiber so as not to be contacted and aerated in the processing tank. For example, the treatment tank can be filled as a fixed bed type microbial carrier (microorganism accumulating member) including a cylindrical body (support) and carbon fibers extending in a normal direction on the outer peripheral surface of the cylindrical body. Here, examples of the cylindrical body include a plastic mesh-shaped cylindrical body. For example, as shown in FIG. 1, a plurality of (for example, four) carbon fibers are fixedly arranged on the outer peripheral surface of the mesh body so as to project in the normal direction with respect to the mesh-shaped cylinder body. Furthermore, carbon fibers can be arranged in a plurality of stages (for example, 11 stages) at predetermined intervals in the longitudinal direction on the outer peripheral surface of the mesh-like cylinder. Examples of the method for fixing the carbon fiber to the outer peripheral surface of the mesh-like cylinder include adhesion and welding. In addition, at least one microbial carrier can be disposed in the treatment tank. Examples of the method for arranging the microbial carrier in the treatment tank include a method of installing the microbial carrier so that the entire microbial carrier is immersed in sewage (inflow water). In this case, it is preferable to install so that aeration from a diffuser tube does not hit directly.

  For example, in a treatment tank (bioreactor) composed of a cylindrical column having a diameter of 15 cm, a height of about 120 cm, and a volume of 20 L (effective volume of 10 L) like a carbon fiber reactor in the following example (FIG. 3), the diameter A plurality of carbon fibers with a diameter of 7 μm, a width of 0.5 cm and a length of 5 cm are opposed to the outer peripheral surface of a mesh-like cylinder having a height of 5 cm and a height of 55 cm so as to protrude in the normal direction and at intervals of 5 cm in the longitudinal direction. Arrange in multiple stages.

Next, the sewage or the inflow water after solid-liquid separation is supplied to the fixed bed type carbon fiber filling treatment tank, and the microorganisms in the sewage or the inflow water are accumulated and supported on the carbon fiber. Further, aeration processing is performed in the processing tank by supplying air (venting) into the processing tank. That is, the inside of the fixed bed type carbon fiber filling treatment tank is in an aerobic condition. Aeration is preferably performed continuously. The aeration intensity, include, for example 1~6m ³ / m ³ · h. Moreover, as temperature in an aeration process, 4-40 degreeC, for example, Preferably 20-30 degreeC is mentioned. Further, the pH in the aeration treatment is, for example, pH 5.8 to 8.6, preferably pH 6.0 to 8.0.

  After the aeration treatment, the effluent water is transferred to a settling tank to precipitate sludge. In the precipitation treatment, the effluent after the aeration treatment is separated into sludge (surplus sludge) and treated water by gravity precipitation. The sludge is then generally subjected to a dehydration process. The outflow water from the settling tank becomes purified treated water.

By this method, significantly whether the evaluation could inhibit N ₂ O generated from wastewater, for example using a gas monitor measured N ₂ O during aeration period, N ₂ O of generating a significantly ( (For example, 0.01 gN ₂ ON / gTN (total nitrogen) -load or less, preferably 0.0005 gN ₂ ON / gTN-load or less), it is judged that N ₂ O generation from sewage can be suppressed by this method. can do. In addition, the evaluation of whether or not organic matter and nitrogen in the sewage could be removed significantly, for example, for biochemical oxygen demand (BOD), suspended solids (SS), total nitrogen (TN), etc. that are water quality indicators, This is done by comparing the inflow water after sewage or solid-liquid separation and the outflow water (treated water) from the settling tank. In the effluent (treated water) from the settling tank, these indicators are significantly reduced compared to the influent water after sewage or solid-liquid separation, for example, BOD is 160 mg / L or less, SS is 200 mg / L or less, dissolved When the nitrogenous compound is 100 mg / L or less, it can be determined that the sewage was significantly purified by this method.

As described above, according to the method described, to remove organic matter and nitrogen from wastewater, while purifying wastewater, the N ₂ O generated from the sewage can be suppressed.

  On the other hand, the sewage treatment apparatus according to the present invention (hereinafter referred to as “the present apparatus”) is an apparatus that can perform the present method described above. This apparatus has a fixed bed type carbon fiber filling treatment tank for subjecting sewage to aeration treatment. Further, this apparatus comprises a transfer means for transferring sewage to a fixed bed type carbon fiber filling treatment tank, or a solid-liquid separation tank for supplying sewage to solid-liquid separation and a liquid component (inflow water) obtained by the solid-liquid separation. Transfer means for transferring to fixed bed type carbon fiber filling treatment tank; Transfer means for transferring effluent after aeration treatment to settling tank; and precipitation tank for separating effluent after aeration treatment into sludge and treated water It can be.

FIG. 2 is a schematic view showing an example of the present apparatus including a fixed bed type carbon fiber filling treatment tank.
As shown in FIG. 2, the present apparatus 1 includes a fixed bed type microbial carrier 2 (a fixed bed type microbial carrier including a cylinder 3 and carbon fibers 4 arranged so as to protrude in a normal direction on the outer peripheral surface of the cylinder). A filled fixed-bed carbon fiber filling treatment tank 5 and a solid-liquid separation tank 6 for subjecting sewage to solid-liquid separation before aeration treatment in the fixed-bed carbon fiber filling treatment tank 5 (when sewage is subjected to solid-liquid separation). And a settling tank 7 that separates outflow water after aeration treatment in the fixed-bed carbon fiber filling treatment tank 5 into sludge and treated water. In addition, when not using sewage for solid-liquid separation, this apparatus 1 does not need to be provided with the solid-liquid separation tank 6. FIG. The apparatus 1 further includes a ventilation blower 8 for supplying air as a means for venting the fixed bed type carbon fiber filling treatment tank 5.

  First, when using sewage for solid-liquid separation, sewage is supplied to the solid-liquid separation tank 6 and solid-liquid separation is performed. After the solid-liquid separation, the separated sludge 9 is discharged out of the system, while the separated liquid is supplied to the fixed bed type carbon fiber filling treatment tank 5 as inflow water. An injection pump 10 (transfer means) is disposed in the flow path between the solid-liquid separation tank 6 and the fixed bed type carbon fiber filling treatment tank 5, and the pump is operated at regular intervals (for example, once a day) with a timer or the like. By doing so, inflow water is supplied to the fixed bed type carbon fiber filling treatment tank 5 from the lower part of the treatment tank. Alternatively, when the sewage is not subjected to solid-liquid separation, the sewage is directly supplied to the fixed bed type carbon fiber filling treatment tank 5 by the input pump 10 (transfer means).

  Next, in the fixed bed type carbon fiber filling treatment tank 5, the microorganisms in the sewage or the inflow water supplied from the lower part are accumulated and supported on the carbon fiber 4, and aeration is performed from the bottom through the ventilation blower 8, Perform aeration process. Aeration is preferably performed continuously.

After the aeration process in the fixed bed type carbon fiber filling treatment tank 5 is completed, a certain amount of liquid is withdrawn from the upper part of the treatment tank and supplied to the sedimentation tank 7 as effluent water. A discharge pump 11 (transfer means) is disposed in the flow path between the fixed bed type carbon fiber filling treatment tank 5 and the settling tank 7, and the pump is operated at regular intervals (for example, once a day) with a timer or the like. As a result, a certain amount of liquid is supplied to the settling tank 7. For example, the effluent water is supplied to the settling tank 7 and the inflow water to the fixed bed type carbon fiber filling treatment tank 5 is supplied at an equal amount to the effluent water every predetermined time.
In the sedimentation tank 7, sedimentation of sludge is performed, and the excess sludge 12 and the treated water 13 are separately discharged out of the system.

  In this device, the operation method of the fixed bed type carbon fiber filling treatment tank (aeration tank) is to draw a certain amount of liquid from the upper part at a certain time interval (for example, every day) as described above, and send it to the precipitation tank. The effluent from the tank is treated water, and then a batch type in which sewage of the same amount as the withdrawal amount is introduced from the upper part of the treatment tank, or a constant amount of sewage is always allowed to flow into the lower part of the treatment tank, It can be carried out in any of the continuous processing systems in which the liquid overflowing from the upper part flows down to the settling tank.

According to the present invention described above, compared to the conventional activated sludge method, N ₂ O generation from sewage can be suppressed, and microorganisms in the sewage are accumulated at a high concentration using carbon fiber as a carrier. Because it adheres to the carbon fiber surface and is retained, it is not necessary to return the sludge from the settling tank to the aeration tank, and it is not necessary to adjust the amount of sludge in the reaction tank. Suitable for

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, the technical scope of this invention is not limited to these Examples.

[Example 1] Suppression of N ₂ O generation by swine sewage treatment using a carbon fiber filled aerobic bioreactor
1. Experimental method
(1) Outline of experimental apparatus and operating conditions Figure 3 shows an outline of the experimental apparatus. The aerobic bioreactor used in the test was a cylindrical column having a diameter of 15 cm, a height of about 120 cm and a volume of 20 L, an effective volume of 10 L, and a structure in which aeration was performed from the bottom of the reactor. In the reactor, a carbon cylinder having a diameter of 5 μm and a height of 55 cm and a carbon fiber having a diameter of 7 μm × width of 0.5 cm × length of 5 cm attached in four directions × 11 stages is installed in the reactor. A fixed bed carbon fiber filled aerobic bioreactor (hereinafter referred to as “carbon fiber reactor”) was used.

On the other hand, as shown in FIG. 4, an activated sludge reactor in which activated sludge from an activated sludge treatment facility was used as seed sludge was also operated as a control.
The treatment method was batch, and once every 6 hours, aeration was stopped for 25 minutes in order to settle the sludge.

  As inflow water, pig house sewage was used, and about 400 mL of sewage was introduced into the reactors from the lower part of the reactor once every 6 hours, and the treated water was allowed to flow out from the upper part of the reactor. The residence time was about 6 days on average for both reactors. In both reactors, the test was started after a habituation period.

  The liquid that flowed out of the reactor as treated water was allowed to stand for 30 minutes, the supernatant was collected, and the collected supernatant was subjected to water quality analysis.

In addition, both reactors were operated in a constant temperature room at 20 ° C., and the amount of aeration was tested at 1 L / min (aeration intensity 6 m ³ / m ³ · h) except in the initial operation.

(2) Analysis Method In the collected supernatant, biochemical oxygen demand (BOD) was measured using an automatic measuring device (Hach Company, BOD Trak, USA). Suspended matter (SS) was measured based on the sewage test method (Japan Sewerage Association 1997). Furthermore, total organic carbon (TOC) and total nitrogen (TN) were measured using a total organic carbon meter (Shimadzu, Co. Ltd., TOC-V CSN, TNM-1).

The collected supernatant was subjected to filtration using a 0.45 μm membrane filter (MILLIPORE, IC Millex-LH), and then anion chromatography (TOSOH, IC-2010, TSKgel Super IC-Anion HS) was used. The concentration of nitrate nitrogen (NO ₃ -N) and nitrite nitrogen (NO ₂ -N) was measured, and ammonia nitrogen (NO) was measured using cation chromatography (DIONEX, DX-120, IonPac CS12A column, USA). The concentration of NH ₄ -N) was measured.

Further, gas measurement of ammonia (NH ₃ ), N ₂ O and CH ₄ generated from the reactor was performed using a multi-gas monitor (LumaSense Technologies, Innova 1412 Multi Gas Monitor, USA). The pH, dissolved oxygen (DO), and oxidation-reduction potential (ORP) (Yamagata Toa DKK, YUSB series) were measured continuously at around 10 cm below the reactor surface.

2. Experimental results and discussion
(1) Change in water quality of experimental equipment Table 1 below outlines the water quality of carbon fiber reactor treated water and activated sludge reactor treated water after the inflow water and treated water have stabilized (operations 73-176 days).

As shown in Table 1, the influent NH ₄ -N averaged 165 mg / L, whereas the carbon fiber reactor treated water averaged 9.3 mg / L, and the carbon fiber reactor treated water further. NO ₃ -N averaged 14 mg / L. From this, it was speculated that nitrification and denitrification proceeded and nitrogen was removed in the carbon fiber reactor.

On the other hand, in the activated sludge reactor treated water, NH ₄ -N averaged 21 mg / L and NO ₃ -N averaged 183 mg / L, suggesting that only the nitrification reaction was in progress.

Moreover, almost no accumulation of NO ₂ -N was observed in both reactors.
From these results, it was suggested that the carbon fiber reactor can suppress the accumulation of nitrate ions more than the activated sludge reactor.

(2) Gas generation amount of experimental equipment Fig. 5 shows changes in gas concentrations of NH ₃ , N ₂ O and CH ₄ generated from (a) carbon fiber reactor and (b) activated sludge reactor from 130 days to 136 days of operation. Show. As shown in FIG. 5, in the carbon fiber reactor, NH ₃ is 0.2 mg / day, N ₂ O is 0.3 mg / day, and CH ₄ is 10.0 mg / day, whereas in the activated sludge reactor, NH ₃ was 0.2 mg / day, N ₂ O was 23.5 mg / day, and CH ₄ was 7.1 mg / day. Thus, it was shown that the carbon fiber reactor can suppress generation of N ₂ O by 98% or more than the activated sludge reactor.

The amount of N ₂ O generated per nitrogen input was 0.0003 gN ₂ ON / gTN-load for the carbon fiber reactor and 0.03 gN ₂ ON / gTN-load for the activated sludge reactor. According to the Japan Greenhouse Gas Inventory Report (NIR) 2012, the N ₂ O emission factor in the purification of swine sewage is 0.05 gN ₂ ON / gN, so the carbon fiber reactor in this example is N ₂ It was shown that O generation can be greatly reduced.

Meanwhile, CH ₄ emission per charged sewage organics, the carbon fiber reactor 0.0039 gCH ₄ / gTOC, the activated sludge reactor was 0.0029 gCH ₄ / gTOC. The CH ₄ emission coefficient for purification of swine sewage in the NIR described above was 0.00019 g-CH ₄ / g organic matter, and the amount of CH ₄ generated in this example showed a slightly high value. The global warming potential of CH ₄ is 25 times that of carbon dioxide (IPCC Fourth Assessment Report), and although there is less impact than N ₂ O, the reduction of CH ₄ is a future challenge.

With CO ₂ converted based on the data of the N ₂ O and CH ₄ is a greenhouse gas, in the carbon fiber reactor was 339.4 mg-CO ₂ conversion / day, in the activated sludge reactor 7,180.5 mg-CO ₂ conversion / day. From this, it was shown that the carbon fiber reactor can remarkably reduce greenhouse gases more than the activated sludge reactor.

(3) Behavior of experimental equipment water quality and generated gas by sewage injection Figure 6 shows typical changes in water quality and generated gas after sewage input in (a) carbon fiber reactor and (b) activated sludge reactor on the 131st day of operation. An example is shown. As shown in FIG. 6, the generation of CH _{4 in} both reactors showed a high peak immediately after the introduction of sewage once every 6 hours. Immediately after sewage injection, a decrease in DO was observed temporarily, and it was considered that methane fermentation had progressed due to a decrease in ORP.

Moreover, in the carbon fiber reactor, the generation gas measurement showed that CH ₄ was generated, but NH ₃ and N ₂ O remained below several mg / m ³ .

On the other hand, in the activated sludge reactor, the decrease in DO over 350 to 360 minutes after the introduction of sewage is due to the fact that aeration was temporarily stopped before the treated water was discharged from the reactor. In the generated gas measurement, N ₂ O generation increased when DO and ORP decreased.

(4) Summary The carbon fiber reactor tended to have less accumulation of nitrate and nitrite ions in the treated water, and it was estimated that denitrification proceeded well. On the other hand, in the activated sludge reactor, the accumulation of nitrate ions was high. Since there is a report that the amount of N ₂ O generated increases due to the accumulation of NO _X -N, as a result of measuring the generated gas, the carbon fiber reactor has a significantly higher amount of N ₂ O generated than the activated sludge reactor. It was confirmed that there were few. This indicates that carbon fiber reactors can reduce greenhouse gas (GHG) generation.

[Example 2] Analysis of microorganisms in a carbon fiber-filled aerobic bioreactor after swine sewage treatment DNA flora analysis of DNA samples collected from the carbon fiber reactor after swine sewage treatment in Example 1 was performed. The result is shown in FIG.

  As shown in FIG. 7, 1O / 46 0TUs was detected as a close species of microorganisms capable of nitrate reduction. Specifically, Paracoccus solventivorans (89% sequence identity), Zoogloea resiniphila (97% sequence identity), Zoogloea caeni (98% sequence identity), Ramlibacter tataouinensis (96% sequence identity), Hydrogenophaga pseudoflava (98% sequence identity), Stenotrophomonas rhizophila (91% sequence identity), Terrimonas ferruginea (93% sequence identity), Propioniciclava tarda (93% sequence identity), and Denitrifying Fe-oxidizing bacteria (99% and 96% sequence identities) were detected. In addition, Hydrogenophaga pseudoflava is known as a microorganism capable of nitrite reduction.

Furthermore, 4/46 OTUs are closely related to microorganisms capable of converting nitrates to N ₂ or N ₂₀ , and include Thiobacillus denitrificans (97% sequence identity), Hydrogenophaga pseudoflava (98% sequence identity), Denitrifying Fe- oxidizing bacteria (99% and 96% sequence identities) were detected.

Since many related species of microorganisms capable of reducing nitrate and nitrite were detected, it is presumed that accumulation of nitrate and nitrite was reduced by the action of these microorganisms. Further, it is speculated that the reduction of the accumulation led to the suppression of the decrease in pH, and the generation of N ₂ 0 was suppressed. On the other hand, in nitrification, Candidatus Nitrosoarchaeum limnia (96% sequence identity) is detected as a close species as an ammonia oxidizing bacterium, and Nitrospira sp. (98% sequence identity) is a related species as a nitrite oxidizing bacterium. was detected. Thus, it was revealed that many bacteria involved in nitrogen conversion were growing in the carbon fiber reactor.

1: Sewage treatment apparatus 2 according to the present invention: Fixed bed type microbial carrier 3: Cylinder 4: Carbon fiber 5: Fixed bed type carbon fiber filling treatment tank 6: Solid-liquid separation tank 7: Precipitation tank 8: Aeration blower 9: Sludge 10: Input pump 11: Discharge pump 12: Excess sludge 13: Treated water

Claims (8)

  A sewage treatment method comprising a step of subjecting sewage to aeration treatment in the presence of fixed-bed carbon fibers, and suppressing generation of dinitrogen monoxide by microorganisms accumulated on the carbon fibers.   The method according to claim 1, wherein the sewage is subjected to an aeration treatment in the presence of a fixed bed type microbial carrier comprising a cylinder and a carbon fiber arranged in a normal line direction on the outer peripheral surface of the cylinder.   The method of Claim 1 or 2 including the process of isolate | separating the effluent after an aeration process into sludge and treated water.   The method according to claim 1, wherein the sewage is livestock sewage.   A sewage treatment apparatus comprising a fixed bed type carbon fiber filling treatment tank for subjecting sewage to aeration treatment, and suppressing generation of dinitrogen monoxide by microorganisms accumulated on the carbon fiber.   The fixed bed type carbon fiber filling treatment tank is a treatment tank filled with a fixed bed type microbial carrier comprising a cylinder and a carbon fiber arranged so as to project in a normal direction on the outer peripheral surface of the cylinder. apparatus.   The apparatus of Claim 5 or 6 containing the sedimentation tank which isolate | separates the effluent after aeration process into sludge and treated water.   The apparatus of any one of Claims 5-7 whose sewage is livestock sewage.

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