JP2014195779A - Treatment method and apparatus of an organic effluent combining a hydrothermal treatment and an anaerobic treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably and efficiently treating, anaerobically together with an organic effluent, a liquid matrix obtained by liquefying, in a high efficiency, a solid biomass via a hydrothermal reaction by using an organic acid-containing liquid in place of water based on the permeation of both through an anaerobic treatment apparatus.SOLUTION: The provided anaerobic treatment method of an organic effluent targeting an effluent treatment apparatus including an acid generation tank and an anaerobic reaction tank is furnished with the following steps: a step of introducing, together with a solid biomass, a portion of an organic acid-containing liquid obtained as an effluent from the acid generation tank into a hydrothermal treatment apparatus and then obtaining a liquid matrix by liquefying both via a hydrothermal reaction under subcritical water conditions; and a step of returning the obtained liquid matrix into the acid generation tank, whereas the solid biomass and the organic effluent are anaerobically treated within the identical anaerobic reaction tank; an effluent treatment apparatus for implementing this method is also provided.

Description

  In the present invention, a liquid substrate obtained by liquefying solid biomass with high efficiency by hydrothermal reaction using an organic acid-containing liquid instead of water is stably passed through an anaerobic treatment apparatus together with organic waste water. The present invention relates to a method for anaerobic treatment efficiently.

In general, water-insoluble food-based organic waste such as green tea and coffee beans from food manufacturing processes such as tea and coffee beverage factories are incinerated or used as livestock feed, fertilizer, etc. .
In the incineration process, the heat generated by the combustion of the green tea bowl or the like is recovered, but it is not recovered as methane gas in the anaerobic process described below.

As described in Patent Document 1 below, the method of anaerobically treating organic wastewater in an anaerobic reaction tank, for example, an upflow anaerobic sludge bed (UASB) type anaerobic reaction tank, via an acid generation tank is as follows. Are known.
The UASB method, that is, the Upflow Anaerobic Sludge Blanket Process, granulates anaerobic bacteria (methanogenic bacteria) into self-granulating or core material without using adherent carriers. This is a method in which raw water is passed upward in a reaction tank that forms a sludge bed (sludge blanket) of granulated sludge (granule) and retains high-concentration microorganisms in the UASB reaction tank. Therefore, it is a method capable of efficiently decomposing and removing organic substances in organic wastewater by high load treatment. Therefore, compared to the aerobic activated sludge method, the UASB type anaerobic treatment apparatus has a higher organic substance load per reaction tank volume, does not require energy for aeration, and can recover energy as methane gas. In recent years, it is becoming popular for food factory wastewater and the like because it has excellent features such as a small amount of excess sludge generation and a simple tank internal structure.

  On the other hand, as described in Patent Documents 2 and 3 below, food-based organic waste such as waste yeast, wheat straw, and garbage is liquefied by hydrothermal reaction under subcritical water conditions. The technology to do is known. Further, Patent Documents 2 and 3 describe that methane gas is recovered at a processing tank position including a hydrothermal reaction processing apparatus that performs such a hydrothermal reaction and an anaerobic processing apparatus.

JP-A-8-155486 JP 2002-102897 A JP 2009-119378 A

  In the anaerobic treatment apparatus described in Patent Documents 2 and 3, the object to be treated is solid biomass such as waste yeast, wheat straw, and garbage, and the solid biomass is first liquefied by a hydrothermal reaction, Since it is an apparatus which anaerobically treats this and collect | recovers methane gas, processing an organic waste water and solid biomass together is not assumed. Further, the hydrothermal reaction in the techniques described in Patent Documents 2 and 3 can liquefy solid biomass insoluble in water, but water and heat for making water into subcritical water conditions for liquefaction. And reaction time until liquefaction is required. Furthermore, the methods described in Patent Documents 2 and 3 are batch processes, and in particular, in Patent Document 3, after hydrothermal treatment is performed in order to reduce the amount of flocculant used in the subsequent methane fermentation tank. The processed product which has not been liquefied is supplied to the methane fermentation tank.

  The problem to be solved by the present invention is that hydrothermal reaction of solid biomass using an organic acid-containing liquid instead of water promotes hydrothermal reaction rather than hydrothermal reaction using water, and liquefies. An object is to provide a method and an apparatus for anaerobically treating the obtained liquid substrate together with organic waste water through an anaerobic treatment apparatus in a stable and efficient manner.

  As a result of intensive studies and experiments to solve such problems, the present inventors have conducted anaerobic treatment of organic wastewater in a wastewater treatment apparatus including an acid generation tank and an anaerobic reaction tank, instead of water. The present inventors have found that the above-mentioned problems can be solved by using organic acid-containing water, which is an outlet liquid of an acid generation tank, for hydrothermal treatment, and have completed the present invention.

That is, the present invention is as follows.
[1] In the anaerobic treatment method for organic wastewater in a wastewater treatment apparatus including an acid generation tank and an anaerobic reaction tank, the following steps are performed:
Part of the organic acid-containing liquid that is the effluent of the acid generation tank and solid biomass are introduced into a hydrothermal treatment apparatus, and liquefied by a hydrothermal reaction under subcritical water conditions to obtain a liquid substrate.
The obtained liquid substrate is returned to the acid generation tank.
The solid biomass and the organic waste water are subjected to anaerobic treatment in the same anaerobic reaction tank.

  [2] The method according to [1], wherein heat exchange is performed between a liquid substrate which is an outlet liquid of the hydrothermal treatment apparatus and an organic acid-containing liquid introduced into the hydrothermal treatment apparatus.

  [3] The method according to [1] or [2], wherein the anaerobic reaction tank is an upward flow anaerobic sludge bed (UASB) type anaerobic reaction tank.

  [4] The method according to any one of [1] to [3], wherein the solid biomass is waste discharged from a food manufacturing process such as a beverage factory.

  [5] A wastewater treatment apparatus for organic wastewater including an acid generation tank, an anaerobic reaction tank, and a hydrothermal treatment apparatus, a part of the organic acid-containing liquid that is an effluent of the acid generation tank, and solid biomass Is introduced into the hydrothermal treatment apparatus and liquefied by a hydrothermal reaction under subcritical water conditions to obtain a liquid substrate. The obtained liquid substrate is returned to the acid generation tank, and the solid biomass and the organic The wastewater treatment apparatus is characterized in that anaerobic wastewater is anaerobically treated in the same anaerobic reaction tank.

  [6] The wastewater treatment apparatus according to [5], wherein heat exchange is performed between a liquid substrate which is an outlet liquid of the hydrothermal treatment apparatus and an organic acid-containing liquid introduced into the hydrothermal treatment apparatus.

  [7] The waste water treatment apparatus according to [5] or [6], wherein the anaerobic reaction tank is an upward flow anaerobic sludge bed (UASB) type anaerobic reaction tank.

  [8] The wastewater treatment apparatus according to any one of [5] to [7], wherein the solid biomass is waste discharged from a food manufacturing process such as a beverage factory.

In the anaerobic treatment method of the present invention, a part of the organic acid-containing liquid that is the effluent of the acid generation tank and the solid biomass are introduced into a hydrothermal treatment apparatus, and are liquefied by a hydrothermal reaction under subcritical water conditions. Converting solid biomass into a liquid substrate containing sugars and organic acids in a shorter hydrothermal reaction time than hydrothermal reactions using water, because organic acids promote hydrothermal reactions to produce liquid substrates As a result, the amount of heat required for the hydrothermal reaction is reduced, contributing to energy saving.
The obtained liquid substrate can be returned to acid generation and finally anaerobically treated in an anaerobic reaction tank, for example, a UASB type anaerobic reaction tank, so that the solid biomass and the organic waste water can be removed. It is possible to perform anaerobic treatment in the same anaerobic reaction tank and recover methane gas.
Furthermore, since the effluent of the acid generation tank is introduced into the hydrothermal treatment apparatus and used for the hydrothermal reaction of the solid biomass, no external water supply is required in the hydrothermal treatment apparatus, and the running cost can be reduced.
Moreover, it contributes to further energy saving by exchanging heat between the liquid substrate which is the outlet liquid of the hydrothermal treatment apparatus and the organic acid-containing liquid introduced into the hydrothermal treatment apparatus.
That is, according to the present invention, hydrothermal treatment is applied to a method of anaerobic treatment by passing organic wastewater through a wastewater treatment apparatus including an acid generation tank and an anaerobic reaction tank, without reducing the stability and efficiency of the method. Rather, it is possible to recover solid biomass that has been disposed of by incineration or the like as methane gas by increasing efficiency and incorporating it.

It is a flowchart of the anaerobic waste water treatment method of this invention. It is a flowchart in the case of exchanging heat between the liquid substrate that is the outlet liquid of the hydrothermal treatment apparatus and the organic acid-containing liquid introduced into the hydrothermal treatment apparatus. The Brix value of the solution obtained by hydrothermally treating using normal water and the organic acid-containing liquid that is the effluent of the acid generation tank at a reaction temperature of 140 ° C. is used as the solid biomass. It is a graph to show. The Brix value of the solution obtained by using a green tea bowl as solid biomass and hydrothermally treating each of the normal water and the organic acid-containing liquid that is the effluent of the acid generation tank at a reaction temperature of 180 ° C. It is a graph to show. Using green tea cake as solid biomass, obtained by hydrothermal treatment using normal water and organic acid-containing liquid that is the effluent of the acid generator at reaction temperatures of 140 ° C, 160 ° C, and 180 ° C, respectively. It is a graph which shows the increase part of the saccharide | sugar + organic acid density | concentration (carbon reference | standard) of the dissolved solution.

First, referring to FIG. 1, in a wastewater treatment apparatus including an acid generation tank and an anaerobic reaction tank, wastewater treatment using an anaerobic reaction tank of an upflow anaerobic sludge bed (UASB) type as an anaerobic reaction tank. A method for anaerobic treatment by passing organic wastewater through the apparatus will be described.
Organic (factory) wastewater from the manufacturing process of green tea, coffee beverages, etc., which is the waste discharged from the food manufacturing process of beverage factories, etc., is sent to the acid generation tank, where sugar, protein, etc. in the wastewater are removed. It is decomposed into lower fatty acids such as lactic acid, propionic acid, butyric acid and acetic acid. That is, in the acid production tank, acid producing bacteria are present in a floating state or fixed to a carrier, and a decomposition reaction into lower fatty acids is performed. That is, the effluent of the acid generation tank is an organic acid-containing liquid.

  The effluent of the acid generation tank is introduced into an upflow anaerobic sludge bed (UASB) type anaerobic reaction tank. In order to prevent an extreme decrease in pH due to acid generation and increase the acid generation rate, the acid generation tank is usually added with an alkali as necessary so that the pH is in a weakly acidic state of 5.5 to 6.5. (Not shown). Further, if necessary, a pH adjusting agent is added to the acid production tank effluent, and a predetermined amount of the treatment liquid in the UASB type anaerobic reaction tank is circulated in the acid production tank (not shown). By such circulation, it is possible to reduce the amount of alkali added for adjusting the pH of the acid generation tank.

As described above, a part of the anaerobic treated water in the UASB reaction tank is circulated to the acid generation tank by piping, and the remaining part is discharged to the coagulation sedimentation tank by piping. After solid-liquid separation in the coagulation sedimentation tank, the treatment liquid is subjected to aerobic treatment as necessary, and COD (CODMn; chemical oxygen demand, by the potassium permanganate method) is reduced to a concentration below the discharge standard, and After processing to meet the discharge standard other than COD as necessary, it is discharged into general sewage or rivers.
Excess sludge in the coagulation sedimentation tank can be extracted by piping and dehydrated and landfilled in the same manner as before, but it can also be effectively used as fertilizer after drying.

  From the upper part of the UASB reaction tank, biogas (methane gas) generated by methane fermentation from an organic acid is generated by methanogenic bacteria present in the granular sludge. The generated methane gas is collected, used for boilers and generators, and recovered as steam and electrical energy.

Next, hydrothermal treatment will be described.
As hydrothermal treatment, waste treatment with subcritical water is known.
The critical point of water is a pressure of 22.12 MPa and a temperature of 374.15 ° C (647.30K). Water follows the vapor pressure curve up to a critical point, and maintains a liquid state when a certain pressure or higher is applied. Water in this state (lower limit is atmospheric pressure, 100 ° C) is called subcritical water. Furthermore, water with pressure and temperature conditions above the critical point is called supercritical water. Subcritical water has an ionic product higher than that of water at normal temperature and pressure, and has higher concentrations of oxonium ions and hydroxide ions. For example, this hydroxide ion hydrolyzes a peptide bond of a protein to produce an amino acid, and lipids and carbohydrates are also hydrolyzed to fatty acids and glucose, respectively, by the same mechanism. Supercritical water breaks down stainless steel, decomposes protein to ammonia, and causes a strong reaction.However, this is too strong to handle, so the temperature is 374 ° C or lower and the pressure is 22MPa or lower. Critical water is used. Subcritical water hardly oxidizes, and organic matter decomposes to molecules such as amino acids and fatty acids, but does not generate carbon dioxide. Therefore, subcritical water is used for decomposing natural organic matter such as garbage, waste wood, waste paper, animal manure, sewage sludge, and waste oil.

  In the present invention, instead of normal water, a part of the organic acid-containing liquid that is the effluent of the acid generation tank and solid biomass such as green tea bowl or coffee bean cake are introduced into the hydrothermal treatment apparatus, A liquid substrate is obtained by liquefaction by a hydrothermal reaction under subcritical water conditions. Thereby, liquefaction can be advanced with high efficiency. That is, the ion product in subcritical water derived from normal water is higher than that of water at normal temperature and pressure, and the concentration of oxonium ions and hydroxide ions is increased. It is thought that the concentration of nium ions is increased, which promotes the decomposition of solid biomass.

  Subcritical water conditions can be, for example, 140 to 250 ° C. and 28 to 40 atmospheres (2.8 to 4 MPa). By adjusting such subcritical water conditions, it is possible to control how much sugar, organic acid, etc. are decomposed. If too harsh conditions are used, the decomposed product will be polycondensed or become a carbide or gas. Therefore, in this invention, it is preferable that it is subcritical water conditions which decompose | disassemble solid biomass to the grade of the organic acid produced | generated by an acid production tank.

In the present invention, the liquid substrate obtained by liquefaction by the hydrothermal reaction under such subcritical water conditions is returned to the acid generation tank, so that the solid biomass and the organic waste water are the same UASB type anaerobic. An anaerobic treatment can be performed in the reaction tank.
That is, according to the present invention, organic wastewater is passed through an acid generation tank through a wastewater treatment apparatus including an upflow anaerobic sludge bed (UASB) type anaerobic reaction tank, and an anaerobic treatment is performed. By incorporating the heat treatment without increasing the stability and efficiency of the method, but rather increasing the efficiency, it is possible to recover the solid biomass that has been disposed of by incineration or the like as methane gas.

  In the above description, the case of an upflow anaerobic sludge bed (UASB) type anaerobic reaction tank is described as the anaerobic reaction tank, but an anaerobic fixed bed type anaerobic other than the UASB type anaerobic reaction tank. Even in reaction tanks, anaerobic fluidized bed anaerobic reaction tanks, and expanded sludge bed (EGSB) type anaerobic reaction tanks, solid biomass and organic wastewater are the same as in the UASB type anaerobic reaction tank. It is possible to perform anaerobic treatment in the anaerobic reaction tank.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
[Example 1: Measurement of Brix value of dissolved solution before and after hydrothermal treatment]
Using green tea cake as solid biomass, normal water and an organic acid-containing liquid that is the effluent of the acid generation tank, respectively, were used for hydrothermal treatment at a reaction temperature of 140 ° C. and 180 ° C., respectively. The Brix values are shown in FIGS. 3 and 4, respectively.
When an organic acid-containing liquid was used instead of normal water, the sugar content in the hydrothermal treatment increased.

[Example 2: Measurement of concentration of sugar and organic acid in solution before and after hydrothermal treatment]
Using green tea cake as solid biomass, using normal water and waste water discharged from the beverage production plant collected at the outlet of the acid generation tank containing organic acid, reaction temperatures of 140 ° C. and 160 ° C., respectively. FIG. 5 shows the sugar and organic acid concentrations of the solution obtained by hydrothermal treatment at ℃ and 180 ℃. In addition, FIG. 5 has shown the blank subtraction part for a sugar and an organic acid density | concentration raise.
When wastewater containing organic acid is used, the sugar and organic acid concentrations in the hydrothermal treatment increase in a shorter reaction time than when water is used, and a more remarkable effect is obtained when the reaction temperature reaches 180 ° C. You can see that it is played.

  According to the present invention, hydrothermal treatment is applied to a method of anaerobic treatment by passing organic wastewater through a wastewater treatment apparatus including an acid generation tank and an anaerobic reaction tank, rather than reducing the stability and efficiency of the method. By promoting and incorporating the hydrothermal reaction, solid biomass that has been disposed of by incineration or the like can be recovered as methane gas. Therefore, the present invention can be suitably used for the treatment of waste from food manufacturing processes such as tea and coffee beverage factories.

Claims (8)

In the method for anaerobic treatment of organic wastewater in a wastewater treatment apparatus including an acid generation tank and an anaerobic reaction tank, the following steps are performed:
Part of the organic acid-containing liquid that is the effluent of the acid generation tank and solid biomass are introduced into a hydrothermal treatment apparatus, and liquefied by a hydrothermal reaction under subcritical water conditions to obtain a liquid substrate.
The obtained liquid substrate is returned to the acid generation tank.
The solid biomass and the organic waste water are subjected to anaerobic treatment in the same anaerobic reaction tank.   The method according to claim 1, wherein heat exchange is performed between a liquid substrate which is an outlet liquid of the hydrothermal treatment apparatus and an organic acid-containing liquid introduced into the hydrothermal treatment apparatus.   The method according to claim 1 or 2, wherein the anaerobic reaction tank is an upflow anaerobic sludge bed (UASB) type anaerobic reaction tank.   The method according to any one of claims 1 to 3, wherein the solid biomass is waste discharged from a food manufacturing process such as a beverage factory.   A wastewater treatment apparatus for organic wastewater including an acid generation tank, an anaerobic reaction tank, and a hydrothermal treatment apparatus, wherein a part of the organic acid-containing liquid that is an effluent of the acid generation tank, and the solid biomass, Introduced into a hydrothermal treatment device, liquefied by a hydrothermal reaction under subcritical water conditions to obtain a liquid substrate, the obtained liquid substrate is returned to the acid generation tank, and the solid biomass and the organic waste water are The waste water treatment apparatus is characterized in that anaerobic treatment is performed in the same anaerobic reaction tank.   The wastewater treatment apparatus according to claim 5, wherein heat exchange is performed between a liquid substrate which is an outlet liquid of the hydrothermal treatment apparatus and an organic acid-containing liquid introduced into the hydrothermal treatment apparatus.   The wastewater treatment apparatus according to claim 5 or 6, wherein the anaerobic reaction tank is an upflow anaerobic sludge bed (UASB) type anaerobic reaction tank.   The wastewater treatment apparatus according to any one of claims 5 to 7, wherein the solid biomass is waste discharged from a food manufacturing process such as a beverage factory.

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