JPS621497A - Methane fermentation method - Google Patents

Abstract

PURPOSE:To reduce the building cost of a fermentation tank while increasing the load amount of an org. substance to a large extent, by adding a ferrite carrier to the fermentation tank to form a ferrite carrier sludge bed. CONSTITUTION:Raw water in a fermentation tank 25 is stirred by a stirring impeller 31 and, while the fermentation tank 25 is heated by warm water flowing through a warm water jacket 34 from below to above, a ferrite carrier such as magnetite or heavy metal ferrite and a carrier such as diatomaceous earth with a particle size of 10-500mum or activated carbon with a particle size of 100-500mum are added to said tank 25 and sludge is adsorbed by the carriers to form a carrier/sludge bed. The carriers are mixed by a methane fermentation treated liquid at every 3-4 days in an amount corresponding to about 5% of the charged COD amount loaded during this time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a methane fermentation method used for microbial treatment of organic wastewater.

(Prior art) Conventionally, regarding microbial treatment of organic wastewater, there are an aerobic treatment method using an activated sludge method and an anaerobic treatment method using a methane fermentation method. Two basic methods of sludge powdering are known.

Each of the above methane fermentation methods maintains a high concentration of sludge consisting of microorganisms involved in the methane fermentation reaction such as methane bacteria in the fermenter in order to achieve a high load (high speed). They are different in their methods. In other words, in the fixed bed method, R materials such as gravel or plastic are fixed in the tank, and microorganisms involved in the reaction are grown on this material, and the sludge concentration is reduced by minimizing the flow of these microorganisms out of the tank. Make it darker. In the sludge powder method, the generated gas is separated in the tank, the stirring force of the generated gas in the tank is minimized, and the sludge is naturally concentrated in the tank.

(Problems to be solved by the invention) However, in the aerobic treatment method using the above-mentioned activated sludge method,
There is a disadvantage that oxygen must be supplied, which increases the processing cost.

In anaerobic treatment methods using the fixed bed method or sludge bed method, 30 to 50 g of the methane gas produced by the treatment can be used to heat the fermenter, and the rest can be used as a separate energy source, making it an energy-saving wastewater treatment method. However, it has the disadvantage that the fermenter is large and expensive.

(Means for Solving the Problems) The present invention provides a methane fermentation method (hereinafter simply defined as the ferrite carrier sludge bed method) characterized by adding a ferrite carrier into a fermenter to form a ferrite carrier sludge bed. do.)
By using a ferrite carrier, the amount of organic matter loaded onto the fermenter can be significantly increased without impairing the methane fermentation ability, and the construction cost of the fermenter can be substantially reduced.

(Example) An example of the present invention will be described below with reference to FIGS. 1 to 4.

In the figure, reference numeral 1 denotes an adjustment tank, in which wastewater is temporarily stored, and a ferrite carrier is added to this wastewater.

Reference numeral 2 denotes a fermentation tank, and an adjustment tank 1 is connected to the tank 2 via a pipe 6 so that the waste water containing the ferrite carrier can be introduced and added by a pump (not shown). Is there a pump (not shown) in piping 5? The bottom of the fermentation tank 2 is connected via a pipe 4 so that the liquid in the tank can be mixed with the waste water containing the ferrite carrier. For this reason, wastewater containing ferrite carriers is
The liquid is poured from the adjustment tank 1 into the fermentation tank 2, and at that time, it is mixed with the internal liquid drawn from the bottom of the fermentation tank 2, and is added so as to be uniformly dispersed at the bottom of the tank. When the input wastewater comes into contact with the sludge, a reaction progresses, and at the same time it is separated into mainly methane gas, carbon dioxide gas, and treated liquid.
Ferrite carrier sludge is generated. The generated gas passes through the gas dome 5 at the top of the fermenter 2 and is collected in a gas holder (not shown), and then is used as an energy source for boilers, gas engines, etc., but a portion of it is consumed for heating the fermenter. Ru.

Reference numeral 6 denotes a sedimentation tank in which the treatment liquid and excess carrier sludge, which are led as fermenter effluent from the upper part of the fermenter 2 via piping 7, are stored and separated. The treated liquid is discharged via piping 8, and is further subjected to final treatment using an activated sludge method or the like, if necessary. The carrier sludge is concentrated in the settling tank 6 and discharged, and is usually
The dehydration equipment 9 separates the dehydrated cake into a dehydrated r-liquid. The dehydrated P solution is usually treated together with the settling tank treatment solution. The dehydrated cake is disposed of by dumping or landfilling, or is incinerated in the incineration facility 10, and the incinerated ash is disposed of in a landfill. The carrier sludge concentrated in the settling tank 6 may be partially or completely returned to the fermenter 2 without being subjected to dehydration treatment, depending on the need for load management. Surplus carrier sludge may be disposed of as is, such as in a landfill.

Reference numeral 11 denotes a magnetic field generator, which is installed in the fermenter 2 as required. This device 11 is constructed by mounting a large number of magnet-incorporated pipes, which will be described later, closely on a lattice-shaped pedestal 12 provided in the upper part of the fermenter 2. The magnet-embedded pipe has, for example, an inner diameter of 194 rtrm, an outer diameter of 20 Q in,
A vinyl chloride pipe 16 having a length of 500 wn is provided with mounting holes 14 having a diameter of 25 mm at intervals of 50 mm in the length direction from the upper end and shifted by 60 degrees in the circumferential direction.
A cylindrical permanent magnet 15 with a diameter of 10 m and a thickness of 10 m and opposite polarities at both ends is attached. The permanent magnet 15 is attached by softening the inner periphery of the attachment hole 14 with a conical heating medium such as a soldering iron and fitting the permanent magnet 15 into the hole 14. A vinyl chloride adhesive is applied to the mounting hole 14 that holds the magnet in order to fix the magnet and prevent corrosion.

When the magnetic field generator 11 is installed in the fermenter 2, the ferrite carrier sludge is adsorbed by a large number of permanent magnets 15 and functions as a fixed bed, while the amount of ferrite carrier sludge adsorbed increases. Since the ferrite carrier sludge repeatedly falls away from the permanent magnet 15 due to its own weight and functions as a carrier sludge bed, the sludge concentration in the sludge bed becomes even higher than in the case where no magnetic field generator is installed. Higher load operation is possible.

16 is a disintegration processing device (in the example, an ultrasonic processing device);
a treatment tank 17 for storing concentrated carrier sludge from the settling tank 6;
It is composed of an ultrasonic oscillator 18 for stirring sludge.

When the carrier sludge is ultrasonically stirred by this device 16, the ferrite carrier and sludge are dispersed, and the recovery rate of the ferrite carrier by the magnetic separation device 19, which will be described later, can be improved. Note that the same effect can be achieved even if a mixer is used instead of the ultrasonic treatment device.

Reference numeral 19 denotes a magnetic separator that is put into practical use for ferrite separation during ferrite production, and includes a processing tank 2° for storing the processing tank effluent from the disintegration processing unit 16, and a lower part immersed in the liquid in the tank 20. It is composed of a disk incorporating a magnet, which will be described later, and a scraper 21 for recovering carriers. The magnet-embedded disks have a large number of permanent magnets (not shown) attached to a plurality of rotary disks 22 that are rotatably mounted on the same axis via spacers by a motor (not shown). In this device 19, sludge that has been separated and treated flows into the treatment tank 20 from the upstream side in countercurrent to the rotating disk 22, contacts the permanent magnet of the disk 22, flows out from the downstream side, and is dehydrated. Sent to equipment 9. In the treatment tank 20, the ferrite carrier in the sludge is attracted to a permanent magnet attached to a rotating disk 22, and a scraper 21 is arranged to sandwich the disk 22.
It is collected and collected by On the other hand, on the dehydration equipment 9 side, the incinerated ash discharged from the incineration equipment 10 is collected by magnetic separation. The recovered ferrite carrier is returned to the fermenter 2, and only the amount corresponding to the unrecovered ferrite carrier is newly replenished.

Next, the fifth test example for confirming the effects of the present invention will be described.
This will be explained with reference to FIGS. 9 and 9 and Tables 1 to 5.

Figures 5 to 7 show the test equipment. In the figure, 25 is an acrylic resin fermenter with an inner diameter of 100 mm, and the actual volume is 51 mm.
There is an outlet 26 at a position 650 degrees from the bottom of the tank so that
Further, below the outlet 26, liquid sampling ports 27 of different depths are provided, and at the bottom of the tank there is a raw water inlet 28, and a stirring motor 29 rotatable via a shaft 50. A stirring impeller 31 is provided, and a gas sampling port 32 and a liquid gas sealer 33 for preventing outside air from entering the tank are provided at the top of the tank.

An acrylic resin hot water jacket 64 for heating the fermenter 25 with hot water is provided around the fermenter 25, and a hot water inlet 35 and an outlet 36 are provided at the upper and lower ends of the jacket 34.
is provided.

37 is a raw water storage tank, which is connected to piping 3 by a raw water supply pump 38.
A raw water inlet 28 is connected to the fermenter 25 via a raw water inlet 28 so as to be able to supply raw water to the fermenter 25 in an amount equal to the amount that will flow out from the fermenter 25 .

Reference numeral 40 denotes a constant temperature water tank, which is configured such that the water temperature can be adjusted to 35±0.5° C. by controlling a heater 43 by a temperature regulator 42 while detecting the water temperature by a temperature sensor 41. This constant temperature water tank 4o contains a hot water jacket 64 from the nuclide 40.
A hot water inlet 35 is connected to the hot water supply pump 44 so that hot water can be supplied through piping 45, and a hot water outlet 36 is connected to the hot water jacket so that hot water can be returned through piping 46.

47 is a fermenter effluent storage tank, and the nuclide 47 is communicated with the outlet 26 of the fermenter 25 through a pipe 48, and a liquid level sensor (not shown) for detecting the inflow amount of the fermenter effluent is supplied with raw water. It is provided for quantity control.

Reference numeral 49 denotes a gas discharge pipe, which is connected to the gas sampling port 62 so as to be able to dissipate the gas generated in the fermenter 25 into the atmosphere, and is provided with a gas meter 50 so as to be able to measure the amount of dissipated gas.

Reference numeral 51 indicates a permanent magnet having a length of 6 Q trtM, a width of 40 m1ff, and a thickness of IQrrun, and a plurality of permanent magnets (in the example, 4 permanent magnets are placed on the inner wall of the fermentation tank 25, at a location between 100 and below the liquid level in a centripetal manner in plan view).
5) are mounted via mounting plates 52 at equal intervals, thus constructing a magnetism generating device.

In such test equipment, the raw water in the fermenter 25 is stirred by the stirring impeller 61, and fermentation is carried out by hot water whose temperature is controlled to 35° ± 0.5°C and flows from the bottom to the top inside the hot water jacket 34. While heating the tank 25, one of the various types of carriers described below is added thereto, and the sludge is adsorbed onto this carrier to form a carrier sludge bed, or the sludge is naturally concentrated without adding any carrier. I did it like that.

The carriers used are magnetite (triiron tetroxide Fes Oa) as a ferrite carrier, heavy metal ferrite, and a carrier with a particle size of 10 to 10 as a carrier to be compared with these ferrite carriers.
These are diatomaceous earth with a particle size of 500 μm, activated carbon with a particle size of 100 to 500 μm, fine sand with a particle size of 100 to 500 μm, and a strong anionic ion exchange resin with a particle size of SaO to 550 μm using styrene as a base material. The heavy metal ferrite is a ferrite obtained when heavy metals in smoke washing wastewater of a garbage incinerator are treated by a ferritization method. In general, ferrite is
Refers to a group of iron oxides with the composition MO@Fe2O3, where M is a divalent metal ion (e.g. Mn, , Fe, C
o.

zn2+ etc.) and exhibits ferrimagnetism.

The carrier was loaded every 3 to 4 days during which time the input C0
An amount of carrier corresponding to 5 degrees of Dor amount was mixed with the methane fermentation treatment liquid and added into the fermenter 25 through the lowermost liquid sampling port 27 using a syringe (not shown).

The raw water used is wastewater with the composition shown in Table 1 below, with 152 parts of urea and 2 parts of phosphoric acid per 10 parts of the waste water as nutrients for microorganisms.
．． Supplement 5d and adjust the pH to 5.0 with 7.5N caustic soda.
It has been adjusted to

Table 1 Analysis according to JIS K0102 (1981), the numerical values in the table are average values.

The methane fermentation seed sludge used was acclimated for about 6 months using the same equipment and the same wastewater without adding a carrier.

The load on the fermenter 25 is the chemical oxygen demand C0Do
Based on the amount of waste water input to the fermenter 25 shown in Table 1, the CODcr received in a 1 mS fermenter per day is expressed as 9, based on r. This load was increased stepwise every 5 to 10 days, and the treatment status was monitored as follows: 1) H(
! : Determined by measuring organic acid concentration.

One example will be explained.

FIG. 8 shows the results of an experiment in which heavy metal ferrite was added to the fermenter 25 as described above, and the magnetic field generator described above was installed inside the fermenter 25.

The experiment started with a load of 5 to 0 ODcr/m eD and was increased every 5 days to 2.5 to 7++ C 0 Dcr/m eD. Load is 22K9 * 00Dcr
/m eD, the pH of the fermenter effluent was 7.3 ± 0.1.
The organic acids were stable at a low level of around 200. Immediately after increasing the load from the time when the load exceeded 9·C0 Dor/m eD at 25, a temporary increase in the organic acid level and a temporary decrease in the pH were observed.

Therefore, the period until the load was increased was increased to 10 days, and the fermentation system was sufficiently stabilized before the load was increased. When the load reached 55 Kg-CODcr/m-D, the organic acid level exceeded 10 o aml/l and the rate of decline became slow, so the load was lowered slightly and the increase in load was reduced to I Kg-CODcr/m. The load was increased to a small extent around eD. 37 in this way
We were able to obtain stable processing results up to loads up to Kg-00Dcr/m5・D, but 38Kp・C! 0Dcr
/m5・D, a rapid rise in organic acids occurs, the level exceeds 10,000 μ/l, and the pH also increases to 6.
It became 5 or less. After that, load 35, 20, 0K
Although the g5COD was rapidly lowered to cr/m%D, the methane fermentation function did not recover, and the amount of gas generated was almost no longer observed.

From the above results, the maximum load in this test is 140 test days.
It is determined that the load was achieved between day 154 and day 154, and the average load during this period is 3 7.2Kga C0Dar
/m3-D was determined as the maximum load (RunN in Table 2
[See 14).

The following Table 2 summarizes the maximum load and the average value of the treatment status at the maximum load obtained by conducting experiments on systems with and without the addition of a carrier using the method described above.

In the table, the numerical value of the organic acid at the fermenter outlet is the acetic acid equivalent value determined by the steam distillation method. The numerical value of VSS in the fermenter is the value obtained by subtracting the VTS of the supernatant obtained by centrifuging the fermenter at 12,000 rpm for 10 minutes from the VTS of the solution in the fermenter.

The numerical value of gas generation amount is based on the standard state of gas generation amount in the tank (0℃1
This is the converted value in atmospheric pressure). The value of the gasification rate is the value obtained by dividing the amount of gas generated by the amount of C0Dcr input into the fermenter, and the value differs depending on the wastewater used for the experiment, but for the wastewater used in this experiment, 4
It was around 30 N17 CoDcr, and as the processing situation worsened, this decreased to 60 ONt/4.CoDor. The methane concentration is around 65 degrees, and most of the rest is carbon dioxide gas. The pH and organic acid at the fermenter outlet are indicative of treatment performance. VSS (volatile solids) refers to organic suspended particles in the fermenter and is an indicator of the amount of microorganisms in the fermenter. Note that this in-tank VSS was measured for a liquid that was uniformly and temporarily stirred in the fermenter after the maximum load was obtained and before the next load increase.

Let's discuss the test results shown in Table-2.

In the same table, the relationship between the VSS in the tank, the maximum load of the fermenter, and each experimental condition is summarized in FIG. 9. As is clear from Figure 9, there is an almost perfect correlation between the maximum load and the YSS in the tank, and by increasing the VSS in the tank, the maximum load can naturally be greatly increased. The unknown magnetite
It is found that ferrite carriers such as heavy metal ferrites are significantly superior to other carriers. Furthermore, in the method of installing a magnetic field generator in the fermenter and adding heavy metal ferrite, the maximum load can be increased to 57 Kq・C0Dor/m'・D, which is about 1.3 times that of not installing a magnetic field generator. It turns out that it can be improved dramatically.

Adding the ferrite carrier to the fermenter as described above,
Furthermore, the reason why we were able to significantly increase the load on the fermenter by installing a magnetic field generator in the fermenter is thought to be as follows.

First, the carrier sludge generated by adding a ferrite carrier is
It was observed that in both cases, sludge with good cohesiveness was formed.

Therefore, the sedimentation rates of carrier sludge generated by adding a ferrite carrier and sludge generated without adding a carrier were measured as follows. After collecting 1 g each into a graduated cylinder, the samples were immediately left to stand, and the rate at which each sludge aggregate settled was measured.

The results are shown in Table 6 below.

Table 3 As is clear from Table 3, the sedimentation rate of carrier sludge generated by adding ferrite carrier is 10% higher than that of sludge without additives.
The sedimentation rate was more than twice as high, and clearly faster than the sedimentation rate of carrier sludge generated by adding other carriers.

From the above, adding a ferrite carrier improves the cohesiveness of sludge and increases the specific gravity of sludge.
As shown in Table 2, the concentration of sludge in the fermenter increases,
It is judged that the load could be significantly improved.

Furthermore, by installing a magnetic field generator in the fermenter, the carrier sludge is absorbed by the magnet and prevented from flowing out of the fermenter, making it possible to maintain a higher sludge concentration in the fermenter. It is judged that an extremely high load of 67~.C0Dcr/m3.D was achieved.

As explained above, excellent high-speed methane fermentation can be achieved by manually adding a ferrite carrier to the fermenter and forming a ferrite carrier sludge bed. However, when observing the excess sludge flowing out of the fermenter under a microscope, it was found that
The ferrite carrier, which has become particles of 3 μm, becomes sludge particles (20
It became clear that a large number of them existed in a buried form within the surface (~300 μm). This means that the ferrite carrier is constantly being lost by flowing out of the fermenter along with the effluent, so that the ferrite carrier must always be replenished in an amount corresponding to the amount flowing out. On the other hand, ferrite is produced as triiron tetroxide (Fe30a: magnetite) as a chemical product, and exists as iron sand and magnetite as natural products, but it is an expensive product for use in wastewater treatment.

Therefore, it is important to recover the ferrite flowing out of the fermenter using its magnetism, and to collect only the ferrite after concentrating the ferrite carrier sludge as much as possible in order to configure an optimal methane fermentation process. be.

Next, an example of a method for recovering the ferrite carrier will be explained.

Each ferrite carrier sludge contained in the fermenter effluent was concentrated and separated, and the concentrated carrier sludge was divided into the following four categories, and each of them was subjected to the following recovery treatment.

Category 1: No treatment ■ Category: Put 100 d of carrier sludge into 200 beers,
The above-mentioned permanent magnet with a thickness of 10 mm, width of 40 mm, and length of 60 mm was immersed in it for 10 minutes, and after shaking the magnet gently for 1 minute, the ferrite carrier and sludge adhering to the magnet were wiped off. The procedure was repeated nine times, and the resulting residual liquid was used as the treatment liquid.

■Category Carrier sludge was treated with a household mixer for 6 minutes, and then treated in the same manner as in Category ■O ■Category Carrier sludge was treated with a laboratory ultrasonic cleaner for 5 minutes, and then treated in the same manner as in Category ■ I did it.

Regarding the treatment liquid for each of the four categories of ferrite carrier sludge V
SS and iron concentrations were measured. Iron was measured by incinerating the treated solution, completely dissolving it with 1N hydrochloric acid, and using atomic absorption spectrometry.

The following Tables 4, 5, and 6 show the above experimental results.

Table-4 (Treatment target: Magnetite carrier sludge) Table-5 (Treatment target: Heavy metal ferrite carrier sludge) These Tables-4,
In No. 5, the treatment liquid and the liquid amount are the amounts of the treatment liquid remaining after the ferrite carrier and sludge are adsorbed and removed by the magnet. The VSS concentration and Fe concentration are analytical values of the treatment liquid.

The amount of VSS and Fe remaining in the treated solution were determined for each category from the liquid volume and concentration, and the difference from category ■ (untreated category) was assumed to be recovered by the magnet, and the recovery rate was shown in the section. It is something.

As is clear from the results of this experiment, the recovery rate of the ferrite carrier is 30 to 40 by simply contacting the ferrite carrier sludge liquid with a permanent magnet, and at the same time, the sludge (VSS) is also recovered at approximately the same rate as the ferrite carrier. It will be done.

However, by treating the carrier sludge liquid using a mixer or ultrasonic waves and bringing a permanent magnet into contact with the liquid in which the carrier and sludge have been dispersed, it is possible to increase the recovery rate of the ferrite carrier to 60 to 85%. It has become clear that the recovery rate of sludge can be suppressed to around 1A, which is the recovery rate of ferrite carrier. It was also revealed that ultrasonic treatment was slightly better than mixer treatment in dispersing the carrier and sludge.

Therefore, it is possible to magnetically separate the ferrite carrier from the concentrated solution of ferrite carrier sludge generated by adding the ferrite carrier to a subcap in the fermenter. It has become clear that the high-speed methane fermentation method using an expensive carrier called ferrite is an excellent method that is fully economically viable.

(Effects of the Invention) As described above, according to the present invention, by adding a ferrite carrier, the load on the fermenter can be increased by more than three times that of the conventional method without adding a carrier, and by installing a magnetic field generator in the fermenter. Since it is possible to more than double the volume, the volume of the fermenter can be reduced to 1/3 to 1/4 of that of the conventional method, and the construction cost of the fermenter can be significantly reduced.

Furthermore, the sedimentation rate of ferrite carrier sludge generated by adding ferrite carrier is more than 10 times that of sludge generated without adding ferrite, making it possible to reduce the size of the settling tank to less than 1/1 o. In this respect as well, the construction cost of the settling tank can be significantly reduced.

On the other hand, from the above, it can be said that ferrite carriers do not inhibit the growth of microorganisms involved in reactions, mainly methane bacteria, and are suitable for the attachment and proliferation of these microorganisms, but on the other hand, they are expensive. However, since the ferrite carrier can be almost completely recovered from the ferrite carrier sludge or its incinerated ash by effectively utilizing its properties without changing the performance of the ferrite carrier, there is almost no increase in processing costs.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the processing flow of the present invention, Fig. 2 is a schematic diagram showing the installation situation of the magnetic generation device, Fig. 3 is a perspective view showing one unit of the device shown in Fig. 2, and Fig. 4 is a disaggregation diagram. FIG. 1 is a schematic diagram showing a processing device and a magnetic separation device. Figure 5 is a schematic diagram of the methane fermentation test equipment, Figure 6 is a front view of the magnetic generator used in the equipment shown in Figure 5, Figure 7 is a sectional view taken along the ■-■ line in Figure 6, and Figure 8 is a heavy metal FIG. 9 is a diagram showing the experimental results of adding ferrite and installing a magnetic generator, and FIG. 9 is a diagram showing the relationship between the VSS in the tank and the maximum load of the fermenter under various experimental conditions. 1. Adjustment tank, 2. Fermentation tank, 6. Sedimentation tank, 9. Dehydration equipment, 10. Incineration equipment, 11. Magnetic field generator, 1
6... Disintegration processing device, 19... Magnetic separation device, 25...
Fermentation tank, 26... Outlet, 28... Raw water inlet, 31...
Stirring impeller, 621I・Gas sampling port, 36・・Gas seal device, 64・・Hot water jacket, 67・・Raw water storage tank,
47... Fermenter effluent storage tank, 51... Permanent magnet. (Scream~) Rohiban Figure 2 Figure 3 Figure 5 Figure 6 Figure 8 WtMEPL (F3) Figure 9

Claims (4)

[Claims] (1) A methane fermentation method characterized by adding a ferrite carrier into a fermenter to form a ferrite carrier sludge bed. (2) The methane fermentation method according to claim 1, characterized in that a magnetic field generator is installed in the fermenter to prevent the ferrite carrier from flowing out of the tank. (3) The methane fermentation method according to claim 1 or 2, wherein the ferrite carrier is recovered from the sludge flowing out of the fermenter using a magnetic separator and returned to the fermenter. (4) A disintegration treatment device is provided upstream of the magnetic separation device, and the ferrite carrier is recovered by the magnetic separation device from the sludge treated by the device, according to claim 1 or 2. methane fermentation method.