JPH02131196A - Treatment process for organic waste water - Google Patents

Abstract

PURPOSE:To increase efficiency by adding iron family metal salt as a reaction accelerator, branching a part of generated gas by the given ratio, passing the same through an acid absorption tower, measuring the remaining gas volume and adjusting the adding volume in digesting under the anaerobic condition. CONSTITUTION:Organic waste water 2 is fed into a digestion tank 1, methane fermented and disgested under anaerobic condition, and at least one kind of water solution of iron family metal salt is added from a tank 5 by a pump 6 in said process, and the same is separated into digestion elimination liquid 3 and sludge 4 to be discharged out of a system. Generated gas is stored in a storage tank 8 through a drawn tube 7, a part of which is branched by the given ratio passed from a branching valve 7a through an acid absorption tower 9, and CO2, H2S and the like in the branched gas generated are removed. The volume of the remaining gas, turned into CH4 gas by almost 100%, is metered by a flow meter 10, from which adding volume of metal salt solution is computed by a control section 11 to control the flow rate of the pump 6. Thus, organic waste water can be treated efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for treating organic wastewater by anaerobic digestion of wastewater containing organic substances.

Conventional technology One method for purifying organic wastewater containing large amounts of organic matter, such as domestic wastewater, human waste, and industrial wastewater, is called methane fermentation, which decomposes organic matter anaerobically at a temperature of 37°C to 55°C. Anaerobic digestion is widely used. The advantages of this method are that the amount of sludge generated is small, the power consumption required for treatment is lower than that of aerobic treatment methods such as activated sludge method, and the generated gas can be used as an energy source.

Problems to be Solved by the Invention The above-mentioned anaerobic digestion treatment, that is, methane fermentation, usually involves three steps.
It is carried out at a substantially constant temperature of about 7° C. to 55° C. and under a fixed residence time, that is, a fixed organic matter load.

In this case, the methane fermentation rate is extremely slow, and the residence time is generally very long, about 30 days. Therefore, it is necessary to increase the number and size of digesters, etc., and this requires a vast amount of land for installation. As a countermeasure against these problems, there is a strong demand for increasing the speed of so-called methane fermentation and reducing the size and number of digesters.

The present invention solves the above problems, and aims to provide a method for treating organic wastewater that can be efficiently treated by increasing the speed of anaerobic digestion, that is, methane fermentation.

Means for Solving the Problems In order to solve the above problems, the method for treating organic wastewater of the present invention includes at least one salt of an iron group metal when digesting organic wastewater under anaerobic conditions. A part of the gas generated from the digestion tank is taken out at a predetermined ratio and passed through an acid absorption tower, the amount of remaining gas is measured, and the amount of the metal salt is determined based on the amount of remaining gas. It is characterized by adjusting the amount added.

In the present invention, organic wastewater is digested under anaerobic conditions, organic matter in the wastewater is decomposed by methane fermentation using anaerobic bacteria, particularly methane bacteria, and methane gas is extracted as a decomposition product. In this process, salts of iron group metals, namely iron (Fe), :+balt (Co), are used as reaction accelerators.
), :-7 #(Ni) halide. Sulfates, nitrates. Add one or more salts such as carbonates, acetates, etc. The addition of this metal salt activates the methane bacteria in the digester in its metabolic process, increasing the rate of methane production. As a result, the time that organic matter in wastewater remains in the digestion tank for digestion processing can be shortened, and the installation space for the digestion tank etc. can be reduced.
Alternatively, the organic matter load to the digester can be increased. The amount of these metal salts added varies greatly depending on the target organic substance, but
For example, Fe: 5 to 20mM to the loaded organic matter.
, Co:o. s ~ smM, Ni: 0.0
Selection is made as appropriate within the range of 2 to 0.2mM. Further, salts of Mo and other metals other than at least one of the metal salts mentioned above may also be added if necessary.

By adding the metal salts to wastewater at appropriate times and amounts during the methane fermentation process, it is possible to accelerate the reaction at the start of methane fermentation and maintain the maximum methane production rate during the fermentation process. . In other words, the amount and composition of gas, mainly methane gas, generated when wastewater in the digestion tank is digested by methane fermentation changes depending on the progress of methane fermentation. By adjusting the amount of metal salt added, the methane production rate can be kept at a maximum. In order to understand the progress of this methane fermentation, the amount of methane gas in the generated gas is measured. That is, a part of the generated gas is taken out at an arbitrary predetermined ratio and passed through an acid absorption tower, and the H! After absorbing S, Co, and almost 100% methane (CH), the amount of residual gas is measured to understand the amount of methane gas in the generated gas, and the conditions set in advance are set in accordance with this amount of methane gas. The amount of metal salt to be added is determined and added based on the following. In this way, by adjusting the amount of metal salt added according to the progress of methane fermentation, the production rate of methane gas can be maintained at the maximum, and the rate of methane fermentation increases accordingly, reducing the residence time in the digester. It is possible to reduce the installation area of the equipment or increase the organic load on the digester.

Effect With the above structure, when wastewater containing organic matter is digested under anaerobic conditions, at least one salt of an iron group metal is added, and the amount of the metal salt added is adjusted to the amount of gas generated by removing a part of the generated gas. By determining the amount of methane gas generated by measuring the amount of methane gas generated, the system promotes methane fermentation in the digestion process to maximize the generation of methane gas, shortens the residence time of wastewater in the digester, and reduces the equipment installation area. Or,
It becomes possible to increase the organic load on the digester.

Example The present invention will be explained below with reference to Examples.

FIG. 1 is an explanatory diagram illustrating a method for treating organic wastewater according to an embodiment of the present invention. First, organic wastewater 2 containing organic matter is supplied to a digestion tank 1 and digested by methane fermentation by methane bacteria under anaerobic conditions. After the digestion process has been completed, the treated liquid is separated into a digested and desorbed liquid 3 and sludge 4, and each is drawn out of the system. In the process of the digestion treatment, a predetermined amount of an aqueous solution of at least one salt of an iron group metal (Fe, Co, Ni) is added from a metal salt solution tank 5 by a pump 6. Further, the generated gas generated during the digestion process is stored in the generated gas storage tank 8 through the gas extraction pipe 7, and a part of the generated gas is transferred at a fixed ratio through a branch valve 7a installed in the gas extraction pipe 7. The branched gas is passed through an acid absorption tower 9, and the carbon dioxide (CO2) in the branched gas is removed by the acid absorption tower 9.
After absorbing and removing sulfide water fX (R2 b ) and the like, the amount of the remaining gas, which is almost 100% methane (CH4) gas, is measured with a flow meter 10 and then stored in the generated gas storage tank 8 . On the other hand, the measured value of the flow rate of the remaining gas is input to the control unit 11, and this control unit calculates the generated gas, that is, the amount of methane gas generated, from the flow rate of the remaining gas, and uses this value to determine the amount of generated gas, that is, the amount of methane gas generated, so that the rate of generation of methane gas is maximized. The amount of metal salt solution added is calculated based on preset conditions, and the flow rate of the pump 6 is controlled.

By treating organic wastewater with the above method, methane fermentation in the digestion process can be promoted to the maximum generation of methane gas, and the rate of methane gas generation can be maintained at the maximum. Residence time can be significantly shortened, the installation area of each device can be reduced, and the organic load per unit size of the digestion tank can be increased or the energy consumption required for heating etc. can be reduced.

Effects of the Invention As described above, according to the present invention, when organic wastewater containing organic matter is digested under anaerobic conditions, methane fermentation in the digestion treatment is promoted to maximize the generation of methane gas, and the methane gas is The generation rate can be maintained at maximum, the digestion rate can be increased, the residence time of wastewater in the digester can be significantly shortened, the installation area of each device can be reduced, and the organic matter load per unit size of the digester can be reduced. It is possible to increase the energy consumption or reduce the energy consumption required for heating.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram illustrating a method for treating organic wastewater according to an embodiment of the present invention. Engineering: Digestion tank, 2: Organic wastewater, 5: Metal salt storage tank, 9: Acid absorption tower, 1o: Flow meter, 1
1...control unit.

Claims (1)

[Claims] 1. When digesting organic wastewater under anaerobic conditions,
At least one salt of an iron group metal is added as a reaction accelerator, and a part of the gas generated from the digestion tank is taken out at a predetermined ratio and passed through an acid absorption tower, and the amount of remaining gas is measured. A method for treating organic wastewater, comprising adjusting the amount of the metal salt added based on the amount of residual gas.