JP2017176957A - Method of treating waste water using carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of subjecting waste water containing an organic substance to anaerobic waste water treatment at a high load in a stable condition under low temperature.SOLUTION: The anaerobic waste water treatment method of the present invention enables stable, high load treatment even under a high temperature condition, when performing an anaerobic waste water treatment under a low temperature condition by flowing the organic waste water through the reaction vessel 10 having the carrier 14 to bring the organic waste water into contact with a carrier 14, by stirring an organic waste water so that vertically reverse direction flows are generated in the vicinity of a center part of a reaction vessel 10 and in the vicinity of a wall surface inner face part in a whole reaction vessel to stir the interior of the vessel evenly, and enhance the contact efficiency of the carrier 14 with a substrate. The carrier is preferably a polyvinyl alcohol gel. The organic waste water is stirred so that the flow in the vicinity of the center part of the reaction vessel is upward, and the flow in the vicinity of the side wall inner face is downward.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for treating organic waste water. Specifically, in a method of anaerobic treatment with anaerobic microorganisms grown on the carrier by passing water through a reaction vessel holding the carrier under low temperature conditions, the fluidity in the reaction vessel is ensured, and the carrier and substrate are separated. The present invention relates to an anaerobic wastewater treatment method that improves contact efficiency and performs high-load and stable treatment.

  Anaerobic treatment methods that can recover and reuse methane gas are widely used as treatment methods for industrial wastewater as treatment methods for organic wastewater containing organic substances. In particular, the UASB (Upflow Anaerobic Sludge Blanket) method that forms granules with good sedimentation, passes organic wastewater in an upward flow, and performs high-load high-speed treatment, It has been developed as a method for treating high concentration wastewater. Further, as a development of this UASB method, an EGSB (Expanded Granular Sludge Bed) method in which water is passed at a higher flow rate using a tall reactor and anaerobic treatment is performed at a high load. Has also been put to practical use.

  A method using a fixed bed carrier or a fluidized bed carrier is also used. The fixed bed carrier uses a microorganism that grows on the surface of the reaction bed that holds the biofilm on the inside of the reaction vessel. The fluidized bed carrier allows a carrier with adjusted specific gravity and size to flow inside the reaction vessel. Then, the microorganism is grown on the carrier and the treatment is performed.

  In general, the anaerobic treatment is performed in an intermediate temperature region of 35 to 38 ° C., and it is necessary to heat the waste water and the reaction tank in order to keep the reaction tank at an appropriate temperature. There is a method of using biogas generated by anaerobic treatment for heating, but there are many cases where external energy such as steam is required, leading to an increase in running cost. In addition, incidental facilities are also required, which increases the initial cost and increases the installation area.

  On the other hand, when anaerobic treatment is performed in a low temperature region, the activity of microorganisms decreases, so that operation at a high load cannot be performed, and the reaction tank volume increases. In this way, it is necessary to operate at a low load at low temperatures. However, in the UASB method using granules, granule dismantling and outflow occur and the amount of biomass necessary for wastewater treatment cannot be secured. In order to solve this problem, Patent Document 1 discloses that in a UASB-like reaction tank, the treatment water is circulated intermittently to maintain the biomass and improve the contact efficiency between the microorganism and the substrate, and is stable even under low temperature conditions. Methods have been reported that allow processing. However, there is a problem that when the treated water circulation is stopped, the drainage is likely to be short-circuited, and the organic matter decomposition rate is reduced during the circulation operation.

  In general, methanogenic bacteria that are anaerobic microorganisms that decompose organic acids into methane and carbon dioxide are more susceptible to temperature than acid-producing bacteria that are anaerobic microorganisms that decompose sugars and proteins into organic acids. Because it is easy, acid-producing bacteria produce organic acids faster than methanogenic bacteria break down organic acids, leading to inhibition by organic acids and lowering pH, making the treatment unstable ( Non-patent document 1). This is a particular problem in an upward flow type processing apparatus such as the UASB method in that a high concentration of organic acid may accumulate in the vicinity of the microorganism.

JP 2008-036529 A

"Anaerobic biotechnology for industrial wastewater treatment" E. Original by Speed, directed by Saburo Matsui and Masanobu Takashima, Gihodo Publishing, p. 38-39

  In view of the above problems, an object of the present invention is to provide a method for performing anaerobic wastewater treatment with high load and stability under low temperature conditions for wastewater containing organic matter.

  As a result of intensive studies, the present inventors have been able to solve the above-mentioned problem by uniformly mixing the inside of the tank in the reaction tank holding the carrier under low temperature conditions, by stirring the inside of the tank. I found.

  The present invention will be specifically described below.

  In a method for anaerobic treatment of organic wastewater by an anaerobic wastewater treatment apparatus having a reaction tank for holding a fluid carrier, the water temperature in the reaction tank is less than 35 ° C. The organic waste water is agitated so that the flow in the upside down direction occurs in the vicinity of the inner surface.

  The carrier is preferably a polyvinyl alcohol gel carrier.

  It is preferable to stir the organic waste water so that the vicinity of the center of the reaction tank has an upward flow and the vicinity of the inner surface of the side wall has a downward flow.

Hereinafter, embodiments of the present invention will be described in detail.
In the method for anaerobic treatment of organic wastewater, the reaction tank holding the fluid carrier is stirred by the flow in the upside down direction (upstream and downstream) so that the inside of the tank is uniformly mixed with the carrier. The contact efficiency of the substrate is improved, and high load and stable treatment is possible even under low temperature conditions.

It is a schematic block diagram which shows an example of the waste water treatment equipment which concerns on embodiment of this invention. It is a schematic block diagram which shows the example of the conventional waste water treatment equipment.

  In the present invention, organic wastewater is passed through a reaction tank holding a carrier, and the organic wastewater is brought into contact with the carrier to perform anaerobic treatment under low temperature conditions. At that time, the organic waste water is stirred so that the flow in the upside down direction occurs in the vicinity of the center of the reaction tank and the inner surface of the wall surface in the entire reaction tank. By performing such agitation, the inside of the tank is uniformly agitated, and the contact efficiency between the carrier and the substrate is improved, so that a high load and stable treatment is possible even under low temperature conditions.

  In the present invention, the water temperature in the reaction vessel is less than 35 ° C, preferably 20 ° C or more and less than 35 ° C. The temperature of the organic waste water flowing into the reaction tank varies depending on the season and pretreatment conditions, but is often lower than 20 ° C. Therefore, in order to perform anaerobic processing efficiently, it is necessary to heat. In this invention, since it is not necessary to heat up to a medium temperature range (35-38 degreeC), it is excellent in an energy surface and a cost surface. Although it does not specifically limit as a method to heat, For example, you may use the method of adjusting the temperature of a reaction tank with heating apparatuses, such as a heater, and the method of adjusting the temperature of the waste_water | drain which flows into a reaction tank with a heating apparatus.

  The carrier to be used is not particularly limited, but a polymer gel carrier excellent in microbial habitability, particularly a polyvinyl alcohol gel carrier is preferable. The average particle size of the carrier is preferably 1 to 10 mm, particularly preferably 2 to 6 mm.

  The pore diameter in the hole communicating from the surface of the carrier to the inside can be freely controlled, but preferably only microorganisms can inhabit the inside of the carrier, and the pore diameter near the surface is preferably 0.1 μm or more and 100 μm or less, 0.5 μm More preferably, it is 50 μm or less. If the pore diameter near the surface is smaller than 0.1 μm, there is a problem that microorganisms cannot enter the inside, and if it is larger than 100 μm, large organisms other than microorganisms may invade and the efficiency may be lowered. There is no particular limitation on the pore diameter near the center of the carrier.

  The shape of the carrier is not limited, and can be any shape such as a cube, a rectangular parallelepiped, a cylinder, a sphere, or a macaroni. Considering the contact efficiency with methane bacteria, the spherical shape is preferable.

  When there is a carrier separation part that separates the carrier and waste water at the top of the reaction tank, the organic waste water is stirred so that the vicinity of the center of the reaction tank is an upward flow and the vicinity of the inner surface of the side wall is a downward flow. Is preferred.

The means for stirring the inside of the reaction tank is not particularly limited as long as it is a means for stirring so that a flow in the upside down direction occurs in the vicinity of the center of the reaction tank and in the vicinity of the inner surface of the side wall in the entire reaction tank. For example, if a device equipped with a stationary blade at the bottom of the reaction tank and a rotating blade near the liquid level in the reaction tank is used, the vicinity of the center of the reaction tank is an upward flow, and the vicinity of the wall surface is a downward flow. Can be stirred. More specifically, the stationary blade at the bottom of the reaction tank is made of a straight strip and is fixed radially to the bottom. The rotor blade near the liquid level in the reaction tank is fixed at the center of the lower end of the rotation shaft, and rotates near the liquid level in the reaction tank through the rotation shaft by driving a motor (not shown).

  In the present invention, the organic wastewater to be treated is not limited as long as it contains organic matter that can be treated by anaerobic microorganisms, and its CODcr concentration / type is not specified. Production wastewater, general sewage and the like. However, it is not limited to these.

  When the main component of the organic wastewater is a component that does not require an acid-generating reaction such as an organic acid, the treatment can be performed only in the reaction tank holding the carrier of the present invention. Examples of organic substances that do not require an acid generation reaction include low molecular organic acids such as acetic acid, propionic acid, and valeric acid, and methanol. If it is a method of stirring the inside of the tank uniformly as in the present invention, it is possible to prevent local increase in organic acid concentration, so that it is possible to suppress the inhibition of microorganisms and fluctuations in pH. Become.

On the other hand, when an organic substance that requires an acid generation reaction for decomposition of sugar or the like is a main component, it is preferable to provide an acid generation tank in the previous stage of the reaction tank holding the carrier. Examples of organic substances that require an acid generation reaction include sugars, proteins, fats and oils, and amino acids.
Since the acid generation reaction rate is low under low temperature conditions, even when an acid generation tank is provided, an organic substance such as sugar flows into the reaction tank without being subjected to acid generation. When an acid-producing reaction of these organic substances occurs in the reaction tank, a biofilm is generated on the carrier due to the action of acid-producing bacteria, which causes blockage and levitation due to enlargement. Even in this case, if mixing is performed upstream and downstream as in the present invention, there is an effect of physical separation of the enlarged biofilm and a uniform flow of the floating carrier, which enables stable treatment for a long time. It becomes.

  The organic matter concentration of the raw water is not particularly limited, and can be widely applied such as CODcr = 500 to 50000 mg / L. Application in a low-concentration region is preferable because the treatment under low temperature conditions proceeds well. Moreover, although there is no restriction | limiting in particular in pH of the undiluted | stock solution at the time of flowing in into a reaction tank, It is preferable that it is about 6.5-7.5. Regarding the pH adjustment method, it is preferable to adjust the pH of the raw water before passing it through the reaction vessel. The pH adjustment may be performed by any method such as a method of pouring with a pH adjusting tank or a method of performing in a pipe. The pH adjustment in the case of providing an acid generation tank is performed by selecting or combining any of the methods of performing in the preceding stage of the acid generation tank, in the acid generation tank, or between the acid generation tank and the reaction tank. I can do it.

The load on the reaction tank is not particularly limited, but a high load of 5 to ³⁰ kg-CODcr / m ³ · day can be applied.

  Moreover, you may provide the reaction tank which performs an aerobic process in the back | latter stage of the reaction tank which performs anaerobic treatment for the further improvement of a treated water quality. The aerobic treatment may be any generally used activated sludge tank method or carrier method, but is not limited thereto.

  Hereinafter, the present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Example 1]
Using the anaerobic wastewater treatment apparatus shown in FIG. 1, anaerobic wastewater treatment was carried out under the following conditions.

Wastewater type: Sugar-containing wastewater Acid generation tank capacity: 5L
Reaction tank capacity: 5L
Temperature inside the tank: 20 ± 2 ° C
Carrier filled in reaction vessel: polyvinyl alcohol gel carrier (average particle size 4 mm)
Reaction tank carrier filling amount: 40% by volume (relative to tank volume)
Wastewater CODcr concentration: 1000mg / L

The CODcr volumetric load was 5 to 20 kg / m ³ · day, and the removal rate was 80% or more. Although it was operated for about 3 months at a CODcr volumetric load of 20 kg / m ³ · day, it could be processed without problems. During this time, neither enlargement of the biofilm nor floating of the carrier was observed on the carrier.

[Comparative Example 1]
Using the anaerobic wastewater treatment apparatus shown in FIG. 2, anaerobic wastewater treatment with wastewater similar to Example 1 was performed under the conditions shown below.

Wastewater type: Sugar-containing wastewater Acid generation tank capacity: 5L
Reaction tank capacity: 5L
Temperature inside the tank: 20 ± 2 ° C
Carrier filled in reaction vessel: polyvinyl alcohol gel carrier (average particle size 4 mm)
Reaction tank carrier filling amount: 40% by volume (relative to tank volume)
Wastewater CODcr concentration: 1000mg / L

Since the entire reaction vessel could not be sufficiently stirred, some of the carriers floated near the liquid surface, and some of the carriers settled at the bottom of the reaction vessel. The volume loading in 5 to 20 kg / ^{m 3} · day stepwise raising process, seen gradually decrease in removal rate, the removal rate by volume load 20 kg / ^{m 3} · day became 60% or less.

  From the above results, it was confirmed that by controlling the flow in the opposite direction intentionally in the vicinity of the center portion and in the vicinity of the inner surface of the wall surface in the reaction tank, it is possible to stably perform a high load even under low temperature conditions.

1, 2 Wastewater treatment equipment 10 Reaction tank 11 Stirring blade (fixed)
12 Stirring blade 13 Carrier separation part 14 Carrier

Claims (3)

In the method of anaerobic treatment of organic wastewater by an anaerobic wastewater treatment device having a reaction tank holding a fluid carrier,
The water temperature in the reaction vessel is less than 35 ° C.,
An organic wastewater anaerobic treatment method comprising stirring organic wastewater so that a flow in an upside down direction occurs between the vicinity of the center of the reaction tank and the inner surface of the side wall.   The method for anaerobic treatment of organic waste water according to claim 1, wherein the carrier is a polyvinyl alcohol gel carrier. The organic wastewater anaerobic treatment method according to claim 1 or 2, wherein the organic wastewater is stirred so that the vicinity of the center of the reaction tank is an upward flow and the vicinity of the inner surface of the side wall is a downward flow.