JP4608765B2 - Biodegradation method of TOC component - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of biodegrading TOC components in raw water by passing raw water through the biofiltration layer, and in particular, downsizing the biofiltration device by enabling downward circulation water to the biofiltration layer, The present invention relates to a biodegradation method of a TOC component that does not require a subsequent membrane separation means.
[0002]
[Prior art]
Since used ultrapure water (recovered water) in the semiconductor manufacturing process contains a small amount of organic substances and other impurities, this recovered water can be used for activated carbon, reverse osmosis membranes, ultraviolet oxidation, biological treatment, etc. After being treated, it is reused as ultrapure water production water.
[0003]
Most of the organic substances contained in such recovered water are organic solvents such as methanol, isopropyl alcohol (IPA), and acetone, and complete removal with activated carbon and reverse osmosis membrane is difficult. UV oxidation and biological treatment are performed. Among these, since the oxidation of ultraviolet rays is expensive, recently, a decomposition method by biological treatment has been widely adopted.
[0004]
Conventionally, as a biodegradation method of TOC components, raw water is passed upward through a filter layer filled with a filter medium such as activated carbon, and the TOC component in the raw water is contacted with microorganisms attached to the filter medium while flowing the filter medium. A method of disassembling them is generally used.
[0005]
Conventionally, the reason why the treatment is performed in the fluidized bed instead of the fixed bed is that when the treatment is performed in the fixed bed, a biofilm is generated on the surface layer of the inlet part of the fixed bed (the uppermost layer in the case of downward circulating water). This is because the filter medium adheres to the biofilm and water cannot pass therethrough. Moreover, when a biofilm is formed in this way, it is difficult to remove it by ordinary backwashing with water, and recovery is very difficult.
[0006]
JP-A-5-64782 describes that the biofilm formed on the filtration layer is removed by regular backwashing with water containing sodium hypochlorite. Even after washing, once a biofilm was formed, it was very difficult to remove it.
[0007]
For this reason, conventionally, in order to prevent the formation of a biofilm, processing in a fluidized bed in which the filter medium is flowed by flowing raw water upward through the biofiltration layer is performed.
[0008]
[Problems to be solved by the invention]
However, with fluidized bed processing,
(1) Since it is necessary to take a long contact time and the water flow rate cannot be increased, the apparatus becomes large.
(2) There is a large amount of bacterial cell outflow. Therefore, it is necessary to provide an ultrafiltration membrane separation device or the like after the biological filtration device to remove the bacterial cell that has flowed out.
There was a drawback.
[0009]
The present invention solves the above-mentioned conventional problems, and in the method of biodegrading the TOC component in the raw water by flowing the raw water downward into the biological filtration layer, it prevents the formation of a biofilm on the surface of the filtration layer, It aims at providing the biodegradation method of the TOC component which aims at size reduction of a filtration apparatus and does not require the membrane separation means of a back | latter stage.
[0010]
[Means for Solving the Problems]
In the biodegradation method of the TOC component of the present invention, the raw water containing the TOC component is passed through the filtration layer filled with granular activated carbon and / or anthracite as a filter medium, and the microorganisms adhered to the filter medium In the method of biodegrading the TOC component in the raw water, the TOC component concentration of the raw water is 1 mg / L or less, and hypochlorite is used as an oxidizing agent in the raw water at an active ingredient concentration of 0.5 to 100 mg / L. It is added and water is passed through the filtration layer.
[0011]
As described above, when raw water is passed through the filtration layer in a downward flow, the biofilm is formed in the uppermost layer portion of the filtration layer.
[0012]
In the present invention, since an oxidizing agent is added to the raw water and water is passed through the filtration layer, the formation of a biofilm in the uppermost layer portion is prevented. The oxidizing agent added to the raw water is decomposed and detoxified by the fungus body in the uppermost layer part of the filtration layer or the activated carbon of the filter medium, so that the fungus body activity inside the filtration layer is maintained, and the filtration layer The TOC component in the raw water is effectively decomposed and removed by the cells inside.
[0013]
In this invention, since processing on a fixed bed becomes possible by downward flowing water as described above, the water flow rate can be increased and the biological filtration device can be miniaturized. Moreover, since there is little outflow of microbial cells, a membrane separation means or the like for capturing the shed microbial cells can be eliminated.
[0014]
The method of the present invention is effective for treating raw water having a TOC component concentration of 1 mg / L or less.
[0015]
Further, use of hypochlorite as an oxidizing agent.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
FIG. 1 is a system diagram showing an embodiment of the TOC component biodegradation method of the present invention.
[0018]
After raw water to oxidant in the raw water tank 1 is added, is processed is passed through by the downflow in biological filtration tower 2 by a pump P.
[0019]
It is an added oxidizing agent, Ru with hypochlorite such as sodium hypochlorite (NaClO). Since H ₂ O ₂ and O ₃ also serve as oxygen sources for microorganisms, they are also effective for the growth of microorganisms in the filtration layer. Two or more oxidizing agents may be used in combination, and an oxidizing agent and a bactericidal agent may be used in combination.
[0020]
The addition amount of the oxidizing agent, Eze prevents too small biofilm formation, too much from the removal efficiency of TOC components affect the bacterial cell activity is reduced, the oxidizing power of the oxidizing agent to be used and sterilized adding an appropriate amount in response to a force. Acid agent is Ru 0.5 to 100 mg / L added pressure to its active ingredient concentration.
[0021]
In the biological filtration tower 2, a filtration layer 2A in which granular activated carbon and / or anthracite is filled as a filter medium is formed in the tower.
[0022]
As the activated carbon and anthracite, those having a particle size of about 10 to 32 mesh are preferable from the viewpoint of contact efficiency with raw water, handling properties, and the like.
[0023]
In the present invention, since the raw water is circulated downward with respect to such a filtration layer 2A, the water flow rate can be made higher than in the case of the upward flow fluidized bed treatment, and the water flow SV5 to 50 hr ^−1. It is possible to process to the extent.
[0024]
Further, by performing such a downward flow treatment, it is possible to prevent bacterial cells from flowing into the effluent water (treated water) of the biological filtration tower 2, so that a downstream membrane separation apparatus such as conventional equipment is used. In addition, the TOC component can be efficiently decomposed and removed without causing an increase in the load on the subsequent deionized water device or the like.
[0025]
Even if the treatment is performed by adding an oxidizing agent to the raw water in this way, a biofilm may be formed inside the filtration layer 2A. That is, as described above, oxidizing agent added to the raw water is decomposed is adsorbed on the inlet side charcoal or decomposed microorganisms in (top layer) of the filtration layer 2A, cell activity in the interior of this for the filtration layer 2A Is retained and the TOC component is decomposed, but there is a risk that bacterial cells grow inside the filtration layer 2A to form a biofilm, and the filter media are fixed to each other to increase water resistance.
[0026]
For this reason, in the present invention, in order to prevent the formation of the biofilm inside the filtration layer 2A, it is preferable to periodically perform air backwashing or water backwashing. This backwashing is different depending passing water conditions and raw water oxidizer concentration, etc. of the raw water, preferably carried out at a frequency of once per water flow of the raw water of 0.5 to 10 days.
[0027]
In the present invention, this backwashing is performed for the purpose of preventing the formation of biofilm and for removing a part of the excess biofilm. Therefore, no special chemical treatment is required, and a sufficient effect can be obtained by backwashing with water or air.
[0028]
Such a biodegradation method of a TOC component of the present invention is effective for treating raw water having a TOC component concentration of 1 mg / L or less, such as recovered water in a semiconductor manufacturing process. That is, when the TOC component concentration in the raw water exceeds 1 mg / L, the filter medium becomes a lump and the water flow load becomes excessive, or the surface area decreases due to lump formation and the treated water TOC deteriorates. In some cases, the effects of the present invention cannot be sufficiently obtained, for example, a load on a subsequent stage is caused by a leak of a living organism.
[0029]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
[0030]
Example 1
In accordance with the method shown in FIG. 1, 0.5 mg / L of NaClO was added to low-concentration TOC actual recovered raw water (TOC component is mainly IPA), and water was passed downward through the biological filtration tower 2.
The quality of this raw water is as follows.
[Raw water quality]
pH: 3.8-4.3
Conductivity: 3.5-4.8mS / m
TOC: 100-150 μg / L
The biological filtration tower 2 was filled with 2500 mL of new coal charcoal-based activated carbon (particle size 10 to 32 mesh), and the raw water was circulated downward with a flow rate of SV 10 hr ⁻¹ .
[0031]
The TOC concentration of the treated water (outflow water of the biological filtration tower 2) at this time was examined, and the change with time in the TOC removal rate is shown in FIG.
[0032]
As shown in FIG. 2, 90% or more of IPA that cannot be adsorbed with activated carbon flows out at the beginning of water flow, but the TOC removal rate is about 33% in about 3 days from the start of water flow, and 90% in 21 days. The TOC removal rate was obtained. In the measurement of the number of viable bacteria in the treated water, the number was about 800 / mL after 3 days from the start of water flow, but decreased to 200 / mL after 21 days.
[0033]
From this result, even when raw water containing NaClO is passed, viable bacteria are supported on the activated carbon which is the carrier, and there is no inhibition on TOC removal, while biofilm formation is prevented, and for a long time. It was confirmed that TOC biodegradation was possible stably.
[0034]
Comparative Example 1
In Example 1, treatment was carried out in the same manner except that NaClO was not added to the raw water, but the amount of treated water was reduced by half after 14 days from the start of water flow, and the water passed through the filter layer after 25 days. It became impossible.
[0035]
When the biological filtration tower was disassembled and the inside was examined, it was confirmed that clogging occurred because the filter media adhered to each other due to the biofilm.
[0036]
【The invention's effect】
As described in detail above, according to the present invention, in the biodegradation method of the TOC component in which raw water is circulated downward to the biofiltration layer, the formation of a biofilm on the surface of the filtration layer can be prevented. For this reason, the process by a fixed bed is attained and the biological filtration apparatus can be reduced in size compared with the conventional fluidized bed process. In addition, since the bacterial cells can be prevented from flowing out, a subsequent membrane separation means for capturing the bacterial cells that have flowed out can be made unnecessary, downsizing the equipment, reducing equipment costs, and reducing maintenance management. In addition, the TOC component can be efficiently decomposed and removed.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of a biodegradation method for a TOC component of the present invention.
2 is a graph showing a change with time of the TOC removal rate in Example 1. FIG.
[Explanation of symbols]
1 Raw Water Tank 2 Biological Filtration Tower 2A Filtration Layer

Claims (1)

A method in which raw water containing a TOC component is passed through a filtration layer filled with granular activated carbon and / or anthracite as a filter medium in a downward flow, and the TOC component in the raw water is biodegraded by microorganisms attached to the filter medium In
TOC component concentration of the raw water is 1 mg / L or less,
A biodegradation method for a TOC component comprising adding hypochlorite as an oxidizing agent in an amount of 0.5 to 100 mg / L as an oxidizing agent to the raw water and passing the filtered water through the filtration layer.

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