JP4386409B2 - Pressurized biological wastewater treatment method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to the biological wastewater purification treatment technical field represented by the activated sludge method, and further belongs to the technical field of increasing the dissolved amount of gas in the biological reaction tank by pressurization.
[0002]
[Prior art]
In order to purify the wastewater, biological treatment represented by the activated sludge method is widely adopted. The activated sludge method is a method in which microorganisms and oxygen are used for biological treatment, organic pollutants in the wastewater are fixed as activated sludge, and part of them is decomposed into water and carbon dioxide (self-digestion) and removed. is there.
In biological wastewater purification processes such as the activated sludge method, dissolved oxygen is indispensable in the reaction system, and supply of dissolved oxygen to the reaction system is often the rate-limiting condition.
In order to promote the biological reaction in the reaction system, air was supplied using a bubbling device. However, the bubble size of the gas supplied to the treated water by the diffuser is very large, and most of the gas rapidly rises in the treated water and dissipates from the water surface, so the oxygen utilization efficiency is very low. It was a thing.
[0003]
Therefore, oxygen is enriched instead of standard air aeration, pure oxygen aeration is employed, or a large aeration amount aeration is attempted. In the conventional aeration technique, it is said that the dissolution efficiency of air or the like is usually 5 to 6%, or at most about 10%.
When a reaction gas such as a hardly soluble oxygen gas is dissolved in a solution, it is known that the amount of gas dissolved increases as the pressure increases. The conventional reaction tank is based on a biological reaction under atmospheric pressure, and the pressure factor only uses the water depth pressure of the reaction tank (usually an effective water depth of 5 m and a pressure of about 0.05 MPa).
It seems that attempts have been made to increase the depth of the tank (tank) and use the water pressure. There is an example in which the depth of the deep shaft reaches 40 to 150 m.
[0004]
However, in order to draw oxygen gas (air) bubbles to that depth, it is necessary to increase the flow rate of the water to be treated which is raised after being lowered in the deep shaft to 2 m / sec or more, The consumption efficiency of oxygen gas is 90% due to the increased consumption of aeration power, the lack of suitable grounds (bedrock) where there is no risk of water leakage, and excessive construction costs for the reaction tank installation. % Can be realized, but it has hardly spread.
Although the idea of a pressurized reaction tank was not necessarily absent, the load generated by pressurization of 0.1 MPa, which is the water depth pressure of a normal reaction tank, was about 10 tons / m ² , and the daily flow rate was several tens of thousands. The cost of making a reaction tank in a public sewage treatment plant that reaches tens of thousands of tons is hermetic and pressure resistant is enormous, and as long as the utilization efficiency of oxygen (air) at the current aeration technology level is assumed The improvement effect has a limit in terms of cost effectiveness and is not adopted.
[0005]
In addition, as a measure for reducing the volume of surplus activated sludge, ozone gas is also applied to a wastewater treatment system using an activated sludge method (see Patent Document 1, Patent Document 2, and Patent Document 3). Even here, the dissolution / dispersion efficiency in the gaseous liquid was almost the same as the conventional aeration technology.
The present inventor has invented an invention for dispersing and storing a gas as (ultra) fine bubbles in a liquid with regard to wastewater purification by an activated sludge method (see Patent Document 4).
In this case, since the gas is dispersed and stored as (ultra) fine bubbles in the liquid using a stirrer (see Patent Document 5), the function of dissolving and storing the gas in the liquid is drastically improved. The utilization efficiency of the gas state was able to reach almost 100%. However, since the activated sludge reaction system is generally performed in an open form under atmospheric pressure, further improvement is desired in terms of reducing the amount of excess sludge produced as a result of the purification of wastewater. ing.
[0006]
[Patent Document 1]
Japanese Patent Publication No. 5-85236 [Patent Document 2]
JP-A-6-206088 [Patent Document 3]
Japanese Patent Publication No.57-19719 [Patent Document 4]
Japanese Patent Application No. 2002-212598
[Patent Document 5]
Japanese Patent Laid-Open No. 7-124577
[Problems to be solved by the invention]
If the biological wastewater purification reaction is carried out under pressure, further improvements can be expected in terms of further improving gas utilization efficiency and reducing the amount of excess sludge produced as a result of wastewater purification. .
In the present invention, when introducing the liquid mixed and stored into the wastewater to be treated in the reaction tank, the inside of the reaction tank is brought into a pressurized state to improve the utilization efficiency of the gas state and further increase the amount of surplus sludge produced. It is an object of the present invention to provide a reaction system that can simultaneously achieve reduction.
[0008]
[Means for Solving the Problems]
The pressurized biological wastewater treatment method of the present invention includes a gas-liquid pressure feed pump that feeds a mixture of gas and liquid, a stirring device that stirs the gas and the liquid pumped from the gas-liquid pressure feed pump, Is a pressurized biological wastewater treatment method using a gas-liquid mixing device that generates cavitation ultrafine bubbles with a bubble diameter of 1 nm to 1,000 nm, and is a reaction comprising sludge water from a sedimentation tank, oxygen and ozone A solution of ultrafine bubble reaction gas having a bubble diameter of 1 nm to 1,000 nm obtained by pumping gas to the stirring device by the gas-liquid pump is fed into the pressurized biological reaction tank at a high pressure. . Moreover, it is preferable that the ultrafine bubble reaction gas of 1 nm to 1,000 nm is dissolved within the time for passing through the stirring device . Furthermore, it is preferable to equip the pressurized biological reaction tank with a microorganism carrier as means for increasing the population density of microorganisms and retaining the microorganisms .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The present invention uses a gasification liquid technique in which a gas body containing oxygen or a gas body containing ozone is dissolved in a liquid at a high concentration and stored by a line atomizer disclosed in detail in Patent Document 4, using a high pressure The treated wastewater in the reaction tank is directly converted into a gasified liquid, or a high-pressure gasified liquid is supplied to the treated water to promote biological or chemical reactions, and the organic matter in the treated wastewater is made as much as possible. Basically, it decomposes into gas and water.
Hereinafter, the present invention will be described in detail.
The treated wastewater to be treated in the present invention is not particularly limited as long as it contains organic matter to be decomposed and removed, such as domestic wastewater, sewage, factory wastewater, and stagnant water containing sludge. It is possible even in a seawater system.
[0010]
The pressurized reaction vessel is a container that can withstand a pressure of about 0.3 to 3 MPa. The pressurized reaction tank may be a pressurized reaction tank or a pressurized reaction tower. But also particularly any shape or manner, for example, pressurized reactor vessel to be installed may be plural, if necessary parallel, may be arranged Yibin suitable for series. Moreover, the structure of the reaction tank can be a single tank type horizontal cylindrical tank or can be two tanks or more.
The pressurized reaction tank is provided with an inlet for raw wastewater to be treated, an inlet for gasified liquid, and an outlet for treated exhaust liquid. The raw wastewater to be treated is supplied to the pressurized reaction tank via an atomizer or directly by a gas-liquid pressure feed pump. A gas (such as carbon dioxide) that is decompressed at the tip of the discharge port and generated by the reaction is separated from the discharge liquid during the pressure reduction.
[0011]
The discharged liquid may be discharged to the outside of the system as usual via a settling tank (pond) or, if necessary, after being subjected to other necessary treatments, discharged to the outside of the system. The gas produced by the reaction may basically be released to the outside, but may be treated secondarily if necessary from the viewpoint of preventing global warming.
A gas-liquid mixing device (line atomizer system) desirably used in the present invention includes a gas-liquid pressure feed pump capable of feeding a gas-liquid mixture without causing a gas lock and an air lock, and an ultrasonic wave. And an atomizer having a function of generating cavitation and a device for supplying oxygen and / or ozone.
[0012]
As the atomizer, any atomizer may be used as long as it can be efficiently dispersed and mixed in fine (ultrafine) bubbles and stored in a liquid.
As the atomizer, for example, a static mixer can be used in multiple stages or in parallel according to function. As a more preferable example of the atomizer, “agitator” used in “ozone reactor” (see Patent Document 5) can be mentioned.
[0013]
The stirring device (gas-liquid mixer) is as shown in FIG. In FIG. 1, two semi-elliptical blades 2 having substantially similar shapes are arranged on the fluid inflow side of the tube 1, the chord side edges 3 of the blades 2 are faced to each other, and the axis of the tube is Crossed symmetrically, and closed between the chord side edges 3 of the two blades 2 located on the fluid inflow side from the intersecting portion with a triangular partition plate 4 that bisects the transverse section of the tube, A current transformation part formed by fixing the arcuate edge of the blade (the edge opposite to the chord side edge 3 of the blade 2) to the inner peripheral wall 6 of the tube 1, and the tube following the current transformation part One or more protrusions 9 integrally formed with a hemispherical head 7 with the top of the inner wall 6 oriented in the axial direction of the tube and a reverse-mounting truncated-conical leg 8 , And a reaction part formed radially with respect to the axis of the tube 1.
[0014]
According to this stirring device (also referred to as an OHR line mixer), if gas and liquid can be fed to the gas-liquid mixer with a single unit, the bubble diameter is 0.5 to within a short time required to pass through the gas-liquid mixer. Ultrafine bubbles of about 3.0 μm, and further 1 nm to 1,000 nm can be uniformly dispersed and mixed in the liquid.
Gas and liquid are pumped to the atomizer using a gas-liquid pump. In that case, it is desirable that the pumping capacity does not decrease even if the gas mixing ratio is increased to 3% by volume or more.
A normal pump for feeding a liquid causes a gas lock and an air lock when a gas is mixed in the liquid, and the feeding capacity is drastically lowered. When the mixed gas reaches 6 to 8% by volume, it is substantially reduced. Can not be delivered to.
[0015]
As the pump for pumping the liquid in which the gas is mixed, it is more preferable if it is a gas-liquid pump that does not decrease the pumping capacity even if the gas ratio increases. As such a pump, for example, there is a “Mono pump” commercially available from Hyojin Equipment Co., Ltd.
As shown in FIG. 2, the “Monopump” has a spiral with a large pitch and a circular cross section in the female screw space in the stator 10 in which a female screw space having an oval cross section is perforated. When the rotor 11 is rotated, the gap formed by the stator and the rotor moves sequentially, and the substance present in the gap moves. In the lower part of FIG. 2, the relationship between the rotor and the space formed in the stator at each position is shown. According to this, it can be seen that one pitch of the space formed in the stator corresponds to two pitches of the spiral of the rotor.
[0016]
According to the “Monopump”, gas-liquid mixed fluid with 90% by volume or less of gas to be mixed can be pumped without lowering the pumping capacity, and the mixing ratio and flow rate of gas and liquid can be adjusted and varied. Can be done freely. The feeding amount per unit time can be adjusted by the rotational speed of the rotor. Reverse feed is also possible by rotating the rotor in reverse.
As an apparatus for supplying oxygen and / or ozone, an ozone generator that can control supply of oxygen and generation of ozone can be used. For example, an ozone generating element having an electrode formed on a dielectric, and a high-frequency high-voltage power source that applies a high-frequency alternating voltage to the ozone generating element, while supplying an oxygen-containing gas to the ozone generating element, And / or the amount of ozone generated can be adjusted by operating the frequency with a regulator.
[0017]
Moreover, it is possible to provide an oxygen / ozone cycle generator that adjusts the amount of oxygen and ozone to be supplied as a process mainly including supplying oxygen and a process mainly including oxidative decomposition with ozone.
The reactive gas containing oxygen to be supplied may be air, oxygen-enriched air, or pure oxygen. It is also possible to send out the supplied gas as it is, with the amount of ozone generated being zero.
Pressure can be applied to the liquid passing through the line atomizer. Before introducing the gas body into the liquid, pressure may be applied by providing an appropriate pressurizer, and the inlet diameter and outlet diameter of the gas-liquid pressure feed pump or the inlet diameter and outlet diameter of the atomizer are made different. Also, the pressure can be changed.
[0018]
Therefore, generally, since the solubility of gas becomes high under high pressure, it can contribute to dissolution of the gas body in the liquid.
As the liquid to be mixed with gas, sludge water and supernatant water from the sedimentation tank (pond) of the wastewater treatment system may be used, fresh water outside the system may be used, or the influent wastewater to be treated It may be used.
A gas-liquid mixed fluid in which liquid and gas are mixed by a line atomizer is introduced into the raw water to be treated. The introduction position is introduced directly into the pressurized reaction vessel. Further, when the gas supplied through the line atomizer is made different between a gas mainly containing oxygen and a gas containing ozone, a plurality of pipes for introducing each of them can be provided in the pressurized reaction tank.
[0019]
In an atomizer, a solution and a desired gas are mixed under pressure, and the gas state is changed to an ultrafine bubble state with a bubble diameter of 300 μm or less, thereby increasing the dissolution rate of the gas into the liquid and making the dissolved gas, The remaining gas state is made into an ultrafine bubble state and can be dispersed, retained and stored, and sent into the reaction vessel at a high pressure.
When the remaining gas state is dispersed, retained, stored, and sent as ultrafine bubbles, when dissolved gas is consumed in biological or chemical reaction, it is dispersed in the reaction vessel. The dissolved gas is instantly converted and replenished from the ultrafine bubble state, and the reaction is not delayed due to the lack of dissolved gas.
[0020]
The present invention can be applied as a biological wastewater treatment method such as an activated sludge method regardless of existing or new establishment. In particular, when installing in an existing treatment facility, a small-sized (about 1/10 to 1/100 capacity of the existing reaction tank) pressurized reaction tank is provided at an appropriate portion corresponding to the existing reaction tank, It can be easily carried out by installing a reaction tank and / or a reaction tower (represented by a pressurized reaction tank). In other words, a pressurized reaction tank was installed at an appropriate location in the flow of a biological wastewater treatment facility such as the activated sludge method, and wastewater to be purified and reaction gases such as pure oxygen and air necessary for the reaction were mixed. Gas-liquid is pressurized and delivered to the reaction tank, and preyed and decomposed by microorganisms that live and are retained in the pressurized reaction tank.
[0021]
The present invention can increase the dissolution amount of reactive gases such as hardly soluble oxygen and air, thus rapidly promoting the activation and growth of microorganisms and precipitating soluble organic matter in wastewater in a short time.・ Can be disassembled. In addition, by using a pressurized reaction tank, the volume of a conventional reaction tank that uses only water depth (about 0.05 MPa) is reduced to about 1/10 to 1/100, and the wastewater treatment facility is greatly increased. Can be downsized.
In the present invention, since the reaction gas such as oxygen necessary for microorganisms is sufficiently supplied in a pressurized reaction tank in a high concentration dissolved state or in an ultrafine bubble state, the population density of microorganisms is reduced. The effect can be remarkably enhanced by equipping the carrier for enhancing. By installing a carrier that increases the population density of microorganisms in the pressurized reaction vessel, the volume of the pressurized reaction vessel can be significantly reduced compared to a reaction vessel that is not equipped with a carrier. And since a sufficient amount of microorganisms necessary for the reaction adheres and inhabits on the carrier or on the periphery of the carrier, the microorganisms remain in the body pressure reaction tank and do not flow away, but are returned as in the conventional activated sludge method. There is no need to supply microorganisms (activated sludge) with sludge.
As a carrier that increases the density of microorganisms, for example, a carrier that can increase the concentration of microorganisms such as “jellyfish” using PVA as a raw material, enhance the BOD removal ability, and can cope with high load drainage.
[0022]
In the present invention, activated sludge can be further decomposed by supplying a gas containing ozone as necessary. In addition to microbial self-digestion, decomposition of activated sludge by ozone is expected to significantly reduce the generation of sludge from the reaction tank, and it can be expected not to see the generation of sludge. .
In the present invention, a biological reaction or a chemical reaction is performed under pressure using a pressurized reaction tank, so that the ozone utilization efficiency can be made 100%. Such exhaust ozone treatment is not required at all.
[0023]
Taking the case of implementing the present invention as an example in the general process of public sewerage facilities adopting biological wastewater treatment,
1. When the water depth of the conventional tank water depth pressure aeration tank is 5 m, the average value of the tank pressure due to the water depth is 0.25 kg / cm ² , and the gas dissolution efficiency when air aeration is used is about 0.2%. (Temperature 20 degrees).
On the other hand, under the above conditions, when a pressure of 5 kg / cm ^{2 is applied to} the pressurized reaction tank in the present invention, the gas dissolution efficiency is 10%, which is about 50 times the dissolution concentration (Henry's law).
[0024]
2. If 90% pure oxygen is used instead of air under the above conditions, a 215-fold oxygen dissolution concentration can be achieved.
3. The Unox method, which had a world patent for a 90% pure oxygen aeration method, was a surface aeration method, and thus it took a long time to dissolve oxygen. In the present invention, dissolution at a rate several tens of times higher. It is possible to reduce the size of the reaction tank to several tenths to hundreds of the conventional method, and the installation space and the construction cost are greatly reduced.
4). The increase in dissolution efficiency saves oxygen / ozone production power and aeration power, realizing energy saving and cost reduction effects.
[0025]
【The invention's effect】
According to the present invention, the mixing of the ultrafine bubbled gas state such as oxygen is remarkably enhanced by using a pressurized reaction tank, both the mixing speed and the mixing amount, and the biological reaction or chemical reaction of the reaction gas such as oxygen. As a result, the wastewater treatment facility can be greatly downsized, and it has become possible to incorporate a pressurized reaction tank into wastewater treatment technology.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an example of a gas-liquid mixer that can be suitably used as an atomizer of the present invention.
FIG. 2 is an explanatory diagram showing an example of a gas-liquid pump that can be optimally used in the present invention.
[Explanation of symbols]
1: tube 2: blade 3: chord side edge 4 (of blade) 4: partition plate 6: inner peripheral wall 7: hemispherical head 8: leg 9: projection 10: stator 11: rotor

Claims (3)

A gas-liquid pressure-feed pump that feeds a mixture of gas and liquid; and a stirring device that stirs the gas and the liquid pumped from the gas-liquid pressure-feed pump, and has a bubble diameter of 1 nm to 1,000 nm. A pressurized biological wastewater treatment method using a gas-liquid mixing device that generates cavitation ultrafine bubbles ,
Pressurize the dissolved liquid of ultrafine bubble reaction gas with a bubble diameter of 1 nm to 1,000 nm obtained by pumping the reaction gas consisting of sludge water, oxygen and ozone from the settling tank to the stirring device by the gas-liquid pressure pump. A pressurized biological wastewater treatment method characterized by feeding the biological reaction tank with high pressure. 2. The pressurized biological wastewater treatment method according to claim 1, wherein the ultrafine bubbled reaction gas of 1 nm to 1,000 nm is dissolved within a time passing through the stirring device . In the pressurized圧生thereof reactor, increasing the population density of the microorganisms, as a means of retention of the microorganism, or claim 1, characterized in that to equip a carrier microorganisms pressurized biological wastewater treatment according to claim 2 Law.

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