JP4339775B2 - Organic waste treatment method and apparatus - Google Patents

Description

  The present invention relates to a method and an apparatus for efficiently recovering phosphorus, nitrogen, and methane in an anaerobic digestion process of organic waste, and in particular, efficient magnesium ammonium phosphate (hereinafter referred to as MAP). The present invention relates to a method and apparatus for treating organic waste, which can recover, increase the amount of methane generated, reduce the volume of sludge, and reduce the scale problem in the digestion tank as compared with the conventional one.

  In a treatment facility for organic wastewater containing phosphorus and nitrogen such as sewage, wastewater, and human waste, first, raw sludge is solid-liquid separated in a sedimentation basin and the separated supernatant is treated with activated sludge to remove organic matter. It was. The activated sludge propagated by the activated sludge treatment is discharged as excess sludge. Anaerobic digestion of organic waste such as raw sludge, surplus sludge, human waste, garbage, etc., decomposes organic matter in the waste by the action of acid-producing bacteria and methanogenic bacteria, reducing sludge. Gas, such as methane gas and carbon dioxide, and wastewater with high nitrogen and phosphorus concentrations are produced. Therefore, studies have been actively conducted on the use of the generated methane gas as a heat source and the use of MAP generated from nitrogen / phosphorus-containing wastewater as a fertilizer and chemical raw material.

  Furthermore, from the viewpoint of further energy recovery and sludge reduction, an anaerobic digester is being made more efficient today. For example, raw sludge, surplus sludge, or mixed sludge mixed with raw sludge and surplus sludge is subjected to physical / mechanical treatment, chemical liquefaction treatment, heating treatment, etc. to promote sludge solubilization and anaerobic We are improving the recovery rate of methane gas in the digestion process and promoting the reduction of sludge. Examples of such physical / mechanical treatment include crushing treatment with a mill, ultrasonic treatment, etc., and chemical liquefaction treatment includes treatment with ozone, hydrogen peroxide, acid, alkali, and heating treatment includes And treatment with thermophilic bacteria. For example, Patent Document 1 describes a method for treating and solubilizing sludge in an ultrasonic treatment process.

JP 2002-336898 A

  As the solubilization is promoted and the efficiency of the anaerobic digestion is increased, the sludge is decomposed to generate waste water having a higher nitrogen / phosphorus concentration. Organic waste contains elements such as nitrogen, phosphorus, and magnesium. When organic waste is solubilized, these elements are transferred into the solution. Nitrogen, phosphorus, and magnesium are components that constitute MAP, and when the concentration becomes high or the alkali rises, the state easily exceeds the solubility product of MAP, and MAP precipitates. Therefore, in the digestion tank, the flow of the digested sludge deteriorates due to the precipitation of MAP in the draft tube, and scale troubles such as clogging at the time of pump withdrawal occur, resulting in sufficient promotion of solubilization. I couldn't do it.

  Therefore, an object of the present invention is to improve the efficiency of anaerobic digestion by promoting solubilization, and to control the precipitation of MAP and to make the apparatus operate stably, To provide an apparatus.

The invention according to claim 1 is an organic waste treatment method for digesting sludge containing organic waste by anaerobic organisms in an anaerobic digestion tank, which is one of the digested sludge in the anaerobic digestion tank. The solubilized step of solubilizing the digested sludge extracted and the extracted sludge by any one of crushing treatment, ultrasonic treatment, chemical liquefaction treatment, heating treatment, biological treatment with thermophilic bacteria, and A gas separation step of depressurizing the digested sludge to separate gas components, and a fine particle separation step of separating fine particles containing magnesium ammonium phosphate from the digested sludge by a physical action, and extracted from the anaerobic digester the digested sludge, the solubilizer step, the gas separating step, the processed in the order of particulate separation step, before at least a portion of the digested sludge after separation of the fine particles in the fine particle separation step A treatment method of organic waste, characterized in that return to the anaerobic digestion tank. By performing the solubilization step and the MAP removal step in parallel, the amount of MAP produced can be controlled while promoting solubilization and improving the efficiency of anaerobic digestion.

Further , the activity of the solution is improved by a gas separation step, and precipitation of MAP and fermentation in an anaerobic digester are promoted.

Moreover , the particle | grains containing a MAP component are efficiently isolate | separated using the difference in specific gravity or a particle size. Of course, a chemical method such as a pH adjusting agent such as sodium hydroxide may be used in combination.

The invention according to claim 2 is an organic waste treatment apparatus for digesting sludge containing organic waste by anaerobic organisms in an anaerobic digestion tank, and is a digestion sludge in the anaerobic digestion tank. Solubilizing means for solubilizing the extracted digested sludge by crushing treatment, ultrasonic treatment, chemical liquefaction treatment, heating treatment, biological treatment with thermophilic bacteria, and the digested sludge Gas separation means for separating gas components by reducing the pressure, and fine particle separation means for separating fine particles containing magnesium ammonium phosphate from the digested sludge by physical action, the solubilization means, the gas separation means, the particulate separation means arranged in series in this order, the processing path is provided for returning at least a portion of the digested sludge after separation of the fine particles in the fine particle separation means to the anaerobic digestion tank A processing apparatus of organic waste characterized by Rukoto.

According to the invention described in claim 1 or claim 2 , MAP can be efficiently recovered by solubilization, increase in the amount of methane gas generated, promotion of sludge reduction, and MAP in the digestion tank draft tube It is possible to provide a treatment method and apparatus that can prevent the deterioration of the flow of digested sludge due to precipitation and blockage of equipment and piping at the time of pump drawing, and can be operated stably.

Embodiments of the present invention will be described in detail with reference to the drawings.
Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments and examples. FIG. 1 is a diagram showing an exemplary flow according to the processing method of the present invention.

  The organic waste treatment process of this embodiment includes a main process for digesting sludge with anaerobic organisms in the anaerobic digestion tank 10 and a part of the sludge in the anaerobic digestion tank 10. A solubilization process, a gas separation process, and a fine particle separation process are performed, and a sub-process for returning the finally treated sludge to the anaerobic digester 10 is performed in parallel. Therefore, in the organic waste processing apparatus of this embodiment, in addition to the main processing path 20 passing through the anaerobic digestion tank 10, a predetermined position (for example, a downstream position) of the anaerobic digestion tank 10 is used. A sub-process for extracting a part of the sludge, transferring it to the solubilizing means, and sequentially returning it to a predetermined position (for example, upstream position) of the anaerobic digester 10 via the gas separating means and the fine particle separating means. A path 30 is provided as a bypass circulation path of the main processing path 20. Pipes and flow paths constituting the sub-processing path 30 are provided with operation equipment such as a transport pump, a valve, and a heater, or a meter such as a flow meter, as necessary.

  As the anaerobic digester 10, a standard single tank type or a multistage type is appropriately used depending on the situation and purpose. As the multistage type, there are a type in which solid-liquid separation is attempted on the rear side, a type in which acid fermentation is performed in the front stage, and methane fermentation is performed in the rear stage. Of course, known methods such as the UASB method, the anaerobic filter bed method, and the fluidized bed method can also be employed. The position for extracting and returning the sludge is appropriately set. Usually, the extraction of the sludge is performed on the rear stage side after a certain degree of processing, and the return is performed on the front stage side.

  The solubilizing means 32 for solubilizing digested sludge includes various means for promoting solubilization of digested sludge. The physical / mechanical solubilization means 32 typically includes a crushing process using a mill and an ultrasonic process using an ultrasonic generator. In the former, sludge particles are refined to promote solubilization, and in the latter, further refinement and microbial cell disruption are performed to promote solubilization. On the other hand, the chemical solubilization means 32 includes treatment with ozone, hydrogen peroxide, acid, and alkali. Heat solubilization treatment utilizing the increase in solubility and reaction rate due to temperature rise is also an important means. Biological solubilization treatment includes treatment with thermophilic bacteria.

  Sludge solubilization increases the concentration of phosphorus, ammonium and magnesium in the liquid as the amount of sludge decreases and the amount of methane generated increases. The elution amount of magnesium varies depending on the type of organic waste, but in the case of sewage digested sludge, it is 0.1 to 1 times that of phosphorus.

  The gas separation step is a step of removing gas components in the digested sludge, and the gas separation means 34 includes means for decompressing a container for storing sludge and a route for conveying. Moreover, you may use the apparatus which has a bottomed sieve body rotated within a vacuum vessel as disclosed by Unexamined-Japanese-Patent No. 7-136406. According to this apparatus, sludge and liquid to be treated can collide with the wall surface in the vacuum container by centrifugal force of the sieve body, and gas in the sludge can be removed and refined at the same time. In addition, since the carbonic acid component in sludge reduces by gas separation processing, in the process in the anaerobic digestion tank 10, the ratio of the carbon dioxide in digestion gas falls significantly.

  In the gas separation step, in addition to removal of dissolved methane, decarbonation and desulfurization are performed. By decarboxylating the digested sludge, the pH of the digested sludge increases. It is known that the precipitation of MAP has a high pH dependency, and the higher the pH, the more MAP precipitates. Therefore, the MAP in the sludge can be efficiently removed before the MAP in the sludge is adhered by performing the fine particle separation step after the MAP is precipitated by performing the gas separation step. In addition, the gas separation process reduces substances that reduce the activity of anaerobic fermentation such as carbon dioxide, hydrogen sulfide, free ammonia, orthophosphoric phosphorus, hydroxide ions, ammonium ions in the liquid, A part of microorganisms is damaged by decompression and becomes a target for decomposition by other microorganisms, and the anaerobic fermentation process is likely to proceed. Therefore, when the gas-separated sludge is returned to the anaerobic digestion tank 10, the decomposition rate of organic substances can be improved in the anaerobic digestion process.

  The fine particle separation means 36 is for separating and separating fine particles contained in the digested sludge mainly by a physical method, and utilizes, for example, a particle diameter difference or a specific gravity difference. Therefore, only MAP is not selected. However, the MAP precipitated in the digestion process and the gas separation process has an appropriately enlarged particle size, and the MAP in the sludge can be separated at a considerably high ratio by separating fine particles having a predetermined diameter or more. Since the separated fine particles contain MAP at a high concentration, they can be further concentrated by an appropriate method and reused as resources.

  Examples of the fine particle separation means 36 that separates using the specific gravity difference between the fine particles and the digested sludge include a hydrocyclone, a centrifugal settling machine, a sedimentation separation tank using gravity separation, and the like, and the fine particle separation means 36 that utilizes the difference in particle diameter. Examples include a vibrating screen, a drum screen, a filtration layer, and a classification layer type separation tank.

  The hydrocyclone has an inverted conical structure at the bottom, and has a sludge inflow pipe, a fine particle discharge pipe, and a sludge discharge pipe. In the hydrocyclone, the digested sludge containing fine particles descends while swirling on the inverted conical wall surface by the pumping pump, and fine particles with a higher specific gravity than the digested sludge move to the lower wall surface side due to the centrifugal force. Collected and concentrated. Concentrated fine particles can be extracted continuously or intermittently.

  Part or all of the sludge after separating the MAP-containing fine particles in the fine particle separating means 36 is returned to the anaerobic digester 10 via the return conveyance path and reprocessed. The MAP concentration in the sludge after separation is lowered, and by returning this to the anaerobic digestion tank 10, the MAP concentration in the digestion tank is lowered, so that the accumulation in the digestion tank is suppressed and the draft tube or the like Clogging can be prevented and a stable anaerobic treatment can be performed. In addition, since the returned sludge has been solubilized by the solubilizing means 32, anaerobic treatment is efficiently performed, and the recovery rate of MAP can be improved and the volume of digested sludge can be reduced.

In the above embodiment, three means, that is, the solubilizing means 32, the gas separating means 34, and the fine particle separating means 36 are arranged in this order in the sub-processing path 30 . In addition, the number of means for performing each step is not necessarily one, and a plurality of means having the same or different configurations may be arranged to operate cooperatively. In that case, but it may also be spaced apart a plurality of means of the same process.

  FIG. 2 shows a processing flow of another embodiment of the present invention. In this embodiment, only the fine particle separation means 36 and the solubilization means 32 are installed in the sub-processing path 30. The configuration, operation, effect, etc. of each means are basically as described above.

  In this embodiment, since the fine particles contained in the digested sludge are removed at the beginning of the sub-processing path 30, it is possible to prevent the fine particles from accumulating and inhibiting the smooth flow in the sub-processing path 30. In addition, since the solubilization is performed while reducing the MAP concentration in the digestion tank, it is the same as in the previous embodiment that improves the MAP recovery rate and reduces the volume of digested sludge while preventing clogging of draft tubes and the like. The effect of can be obtained.

  FIG. 3 shows still another embodiment of the present invention. A plurality of sub-processing paths 30a, 30b, and 30c are provided for each process, and these are arranged in parallel with each other (also with respect to the main processing path 20). It is arranged. That is, the solubilization means 32, the gas separation means 34, and the fine particle separation means 36 are disposed in the middle of the three sub-processing paths 30a, 30b, 30c provided outside the anaerobic digestion tank 10, respectively. The digested sludge extracted from the downstream side of the digestive digestion tank 10 is individually solubilized, gas separated, and particulate separated and returned to the upstream side of the anaerobic digester 10.

  The configuration, operation, effect, etc. of each means of the sub-processing paths 30a, 30b, 30c of this embodiment are basically as described above. In this embodiment, since the three sub-processing paths are individually provided, the pipe diameter, pump capacity, temperature, inlet / outlet position, and the like can be individually set. Therefore, it is possible to derive a favorable processing condition by making settings suitable for the processing steps in the sub-processing paths 30a, 30b, and 30c. Also, in this embodiment, it is needless to say that the same effects as those of the previous embodiment can be obtained, such as improving the recovery rate of MAP and reducing the volume of digested sludge while preventing clogging of the draft tube and the like. Yes.

  FIG. 4 shows still another embodiment of the present invention. The solubilizing means 32 and the gas separation means 34 are placed in the sub-processing path 30d, and the particulate separation means 36 is placed in another sub-processing path 30c in parallel therewith. These are respectively arranged, and are intermediate configurations between the embodiment of FIG. 1 and the embodiment of FIG. In this embodiment, processes effective to be combined and processed in series are selectively arranged in series. Which process is arranged in series can be appropriately set. Also in this embodiment, it is possible to obtain the same effects as those of the previous embodiment that improve the MAP recovery rate and reduce the volume of digested sludge while preventing clogging of the draft tube and the like.

In the following, the present invention is further illustrated by examples. Of course, the present invention is not limited to these examples.
In this example, processing was performed using the processing flow of the embodiment shown in FIG . The target organic waste was obtained by centrifugally concentrating excess sludge from the anaerobic-aerobic method. An ultrasonic treatment apparatus was used as the solubilizing means 32, a vacuum degassing apparatus was used as the gas separating means 34, and a liquid cyclone was used as the fine particle separating apparatus 36.

  The amount of sludge charged into the digester was 90 L / d. The digestion days were 20 days and the digestion temperature was 35 ° C. Digested sludge in the digestion tank was extracted at 450 L / d, vacuum degassed, MAP separation by liquid cyclone, and ultrasonic treatment, and then returned to the anaerobic digester 10. The vacuum degassing step, the MAP separation step, and the ultrasonic treatment step were performed semi-batch. In addition, about 90 L / d was discharged per day as drawn sludge. The vacuum degree of the vacuum deaerator was -93.3 kpa. The oscillation frequency of the ultrasonic oscillator was 20kHz and the power consumption was 1kW. The ultrasonic intensity was 6 kJ / L for the amount of digested sludge (2700 kJ per day).

The input sludge had a TS of 42 g / L, a VS of 35 g / L, and a TP of 920 mg / L. The components of the drawn sludge were 21 g / L for TS, 17 g / L for VS, and 700 mg / L for TP. The VS decomposition rate was 51%, and the reduction rate of TP was 24%. The MAP recovered by the hydrocyclone was 160 g / d (20 g-P / d as phosphorus). The amount of digestion gas generated was 0.46 Nm ³ / kg per VS. TP was reduced by collecting MAP with a hydrocyclone.

(Comparative example)
As shown in FIG. 5, the comparative example 1 is configured such that the sub-processing path 30 is provided with the solubilizing means 32 including an ultrasonic transmitter, and the gas separation means 34 and the fine particle separation means 36 are not provided. .
The input sludge had a TS of 42 g / L, a VS of 35 g / L, and a TP of 920 mg / L. The components of the extracted sludge were 23 g / L for TS, 17 g / L for VS, and 920 mg / L for TP. The VS decomposition rate was 51%, and the decrease rate of TP was almost zero. Since MAP generated spontaneously in the digestion tank was discharged together with the extracted sludge, it is estimated that the decrease rate of TP was zero. The amount of digestion gas generated was 0.46 Nm ³ / kg per VS.

As shown in FIG. 6, the comparative example 2 is a single anaerobic digester 10 in which the sub-processing path 30 is not provided.
The input sludge had a TS of 42 g / L, VS of 35 / L, and T-P of 920 mg / L. The components of the extracted sludge were 25 g / L for TS, 18 g / L for VS, and 920 mg / L for TP. The VS decomposition rate was 49%, and the reduction rate of TP was almost zero. Since MAP generated spontaneously in the digestion tank was discharged together with the extracted sludge, it is estimated that the reduction rate of TP was zero. The amount of digestion gas generated was 0.42 Nm ³ / kg per VS.
Table 1 summarizes the results of Examples and Comparative Examples 1 and 2. As can be seen from this table, there was a large difference in the amount of MAP recovered between the examples and the comparative examples.

  That is, in the above embodiment, MAP can be efficiently recovered through a series of operations, increasing the amount of methane gas generated, promoting sludge reduction, and deterioration of the flow of digested sludge due to MAP precipitation in the digestion tank draft tube, It has greatly contributed to the solution of problems such as blockage of equipment and piping when the pump is pulled out.

It is a figure which shows the flow of the processing method of the organic waste of embodiment of this invention. It is a figure which shows the flow of the processing method of the organic waste of 2nd Embodiment of this invention. It is a figure which shows the flow of the processing method of the organic waste of 3rd Embodiment of this invention. It is a figure which shows the flow of the processing method of the organic waste of 4th Embodiment of this invention. It is a figure which shows the processing method of the conventional organic waste. It is a figure which shows the processing method of the conventional organic waste.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Anaerobic digester 20 Main processing path 30, 30a-30d Sub processing path 32 Solubilization means 34 Gas separation means 36 Fine particle separation means

Claims (2)

An organic waste treatment method for digesting sludge containing organic waste by anaerobic organisms in an anaerobic digester ,
Part of the digested sludge in the anaerobic digestion tank is extracted, and the extracted digested sludge is subjected to any one of crushing treatment, ultrasonic treatment, chemical liquefaction treatment, heating treatment, and biological treatment by thermophilic bacteria. A solubilization step solubilized by treatment;
A gas separation step of depressurizing the digested sludge to separate gas components;
A fine particle separation step of separating fine particles containing magnesium ammonium phosphate from the digested sludge by a physical action ,
The digested sludge extracted from the anaerobic digester is treated in the order of the solubilization step, the gas separation step, and the fine particle separation step,
A method for treating organic waste, wherein at least a part of the digested sludge after separating the fine particles in the fine particle separation step is returned to the anaerobic digestion tank. An organic waste treatment apparatus for digesting sludge containing organic waste by anaerobic organisms in an anaerobic digestion tank ,
A part of the digested sludge in the anaerobic digestion tank is extracted, and the extracted digested sludge is crushed, sonicated, chemically liquefied, heated, or biologically treated with thermophilic bacteria. Solubilization means for solubilization;
A gas separation means for separating the gas components by depressurizing the digested sludge;
Fine particle separation means for separating fine particles containing magnesium ammonium phosphate from the digested sludge by physical action ,
The solubilization means, the gas separation means, and the fine particle separation means are arranged in series in this order,
An organic waste processing apparatus, characterized in that a processing path is provided for returning at least a part of the digested sludge after separating the fine particles in the fine particle separating means to the anaerobic digester.

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