JPH0647388A - Treatment of waste water - Google Patents

Abstract

PURPOSE:To eliminate a problem of installation cost or establishment treatment by a method wherein air or oxygen is blown in a contact aeration tank while the capacity load of the oil component in this tank is held to a predetermined value or less and the size of generated air bubbles when the air bubbles reach the surface of the water is set to the specific magnification of that of air bubbles at the time of generation or less to perform intermediate treatment reducing the concn. of the oil component. CONSTITUTION:In the treatment of waste water due to a biological treatment method, a contact aeration tank 3 is packed with a packing material 6 having bacteria immobilized on the entire surface thereof and 400m<3> or more of air or 100m<3> or more of oxygen is blown in the contact aeration tank 3 per 1kg of the oil component at the inlet of the tank 3 while the capacity load of the oil component in the tank 3 is held to 0.3kg/m<3>/day or less. Then, by making the size of air bubbles when air bubbles generated by blowing air or oxygen reach the surface of the water of the contact aeration tank 3 1.5 times or less that of generated air bubbles, intermediate treatment before sewarage discharge reduces the concn. of the oil component in treated water to 30mg/l or less is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment method, and more particularly to a wastewater treatment method suitable for treating water used in baths, washbasins, kitchens and the like (hereinafter referred to as kitchen wastewater).

[0002]

2. Description of the Related Art The quality of wastewater that can be discharged into public sewers is regulated by law. For kitchen wastewater such as hotels, departments, general buildings and condominiums, for example, biochemical oxygen demand (BOD) and suspended solids (SS), If the oil content (mineral oil and animal and vegetable oil) exceeds the regulated amount, detrimental measures must be taken. As a method for treating these substances, various methods such as a pressure flotation method, a biological treatment method such as an activated sludge method and a catalytic oxidation method have been conventionally practiced.

The pressure flotation method is a method in which air dissolved in pressurized water is generated as bubbles by lowering the water pressure, and oil is attached to the air to float and separate the oil, and is most commonly used. This is an abatement method. According to this method, the treated water quality changes due to changes in wastewater,
There is a problem that treatment of sludge generated, odor control, and disposal are very expensive. Biological treatment involves contacting wastewater with microorganisms, aeration of the wastewater to oxidize and decompose harmful substances, and is considered to be a more effective wastewater treatment method than the pressure flotation method, and is particularly effective for removing BOD. It is said that. However, regarding the oil content removal, biological treatment is only possible at a low concentration, and the specific oil content load equivalent to the BOD capacity load is not discussed at present.

Further, when the abatement equipment for carrying out the biological treatment method is installed indoors such as in a department store or a general building in Tokyo, the ceiling height is limited to 3.5 m, so that it is installed on the ground. The effective water depth of the tank is at most 3.0m or less. Normally, these buildings have spring tanks installed,
Although the number of tanks is large, the effective water depth is generally as shallow as 0.8 to 3.0 m, and therefore, the water depth is insufficient for performing wastewater treatment by the conventional biological treatment method. However, if the problem of effective water depth can be solved and a part of the spring tank can be diverted to install the detoxification equipment, the problems of installation location and installation cost can be solved, which is extremely preferable.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been earnestly studied by paying attention to oil removal by a contact aeration tank among biological treatments. It was developed as a result of studying the combination of processing conditions to accelerate the decomposition of the normal hexane extract (oil) even when using equipment with a small water depth, and the purpose was to develop a contact aeration tank with a shallow water depth. An object of the present invention is to provide a wastewater treatment method in which oil, particularly animal and vegetable oil, is decomposed to 30 ppm or less even when used.

[0006]

A wastewater treatment method according to the present invention for achieving the above-mentioned object is a method for filling wastewater treatment by a biological treatment method with a filling material having microorganisms fixed to the entire surface of a contact aeration tank. While maintaining the oil content capacity load in the contact aeration tank at 0.3 [kg-oil content / m ³ · day] or less, 400 m ³ or more of air per kg of inlet oil content or 10
When more than 0 m ³ of oxygen is blown and the bubbles generated by blowing air or oxygen reach the water surface of the contact aeration tank, the diameter of the bubbles is 1.5 times or less than the diameter of the generated bubbles. A feature of the present invention is that an intermediate treatment before discharge of sewerage is performed to reduce the oil concentration to 30 mg / l or less, the residence time in the contact aeration tank is set to 6 hours or less, and the gap of the disc fuser is reduced. 0.5 ~
Aeration is performed from the entire surface of the filling material while maintaining the generated bubble diameter at 3 mm and the generated bubble diameter at 1 to 5 mm, the effective water depth range in the contact aeration tank is 0.8 to 3.0 m, and the contact aeration tank The capacity load of the oil filler inside is 0.5 [kg- oil /
Filler amount m ³ · day] or less is a preferred embodiment.

The kitchen wastewater generally enters the oil-water separation tank 1 shown in FIG. 1 after removing impurities in the wastewater by a fine screen. The oil / water separation tank 1 adopts a natural flotation system, is provided with a partition plate 8 for effective oil / water separation, and has a residence time of 1 hour or more to float / separate the oil component 9 to have an oil concentration of, for example, 100 mg / l. Below. The treated water that has passed through the oil-water separation tank 1 passes through the flow rate adjusting tank 2 and the contact aeration tank 3
Be guided to. The flow rate adjusting tank 2 plays a role of homogenizing the quality of wastewater and adjusting the amount of wastewater sent to the contact aeration tank 3.

The contact aeration tank 3 constitutes a filter medium with a packing material (contact material) 6 to which microorganisms are fixed, and the waste water pumped quantitatively by a pump P is sent from a blower B through an air pipe 7 and scattered. Oxygen is given by the air bubbles released through the trachea, and while retaining oxygen, the microbial membrane on the filter bed surface is contacted and adsorbed and decomposed. As shown in FIG. 1, the filling material 6 is preferably filled on the entire surface of the contact aeration tank, and the aeration is also preferably performed on the entire surface of the filling material 6. If one-sided aeration is used instead of the whole-faced aeration, the oxygen dissolution efficiency on the filler side decreases in a shallow treatment tank with a water depth of 3.0 m or less, and normal biodegradation does not occur. Problems such as deterioration of treated water quality and generation of odor occur. The treated water treated in the contact aeration tank 3 enters the discharge tank 5 through the intermediate tank 4 and is discharged by the pump P.

Oil content of 3 in an aeration tank with a water depth of 3.0 m or less
In order to reliably reduce the amount to 0 ppm or less, it is necessary to maintain the oil content capacity load in the contact aeration tank at 0.3 [kg-oil content / m ³ · day] or less. The volume loading of the oil filler in the contact aeration tank is also preferably 0.5 [kg-oil /
Filler amount m ³ · day] or less. Note that the oil capacity load O
L _V [kg-oil / m ³ · day] is OL _V = Q _S × C ₀
^Calculated from the formula of × 10 ^-3 / V. However, Q _S is the amount of water flowing into the aeration tank [m ³ / day], C ₀ is the average oil concentration [mg / l] of the water flowing into the aeration tank, and V is the volume of the aeration tank [ m ³ ].

As the filler (contact material) to be filled in the entire surface of the contact aeration tank, it is possible to prevent bubbles generated by blowing air or oxygen from gathering in the filler portion to form large bubbles and to cause clogging. In order to realize sufficient oxygen supply without the need for a spherical shape, a spherical shape with a large internal space is preferably used. The amount of air is 4 to 6m, which is the conventional effective water depth.
In the contact aeration tank of, 1 per 1 kg of loaded BOD
Although 20 m ³ of air is required, considering that the depth of water is shallow and the substance to be treated is oil in the present invention, 400 m ³ or more of air or 1 kg of oil is considered.
It is advisable to blow oxygen of 00 m ³ or more. Air volume 400
If it is less than m ³ and the amount of oxygen is less than 100 m ³ , the dissolved oxygen (D
O) decreases and becomes anaerobic, resulting in deterioration of processability and odor problem. As an air diffuser for blowing air, a special disc fuser having a ventilation hole diameter (ventilation gap) of 0.5 to 3 mm, preferably 1 to 2 mm is used.
The diameter of generated bubbles is maintained at 1 to 6 mm, preferably 2 to 4 mm. Commercially available perforated pipes, spargers, and disc fusers as air diffusers have a ventilation hole diameter of 4 mm or more, and therefore bubbles are large and not efficient. On the other hand, if the diameter of the ventilation hole is less than 0.5 mm, such as an air diffuser or an air diffuser, there is a problem that clogging easily occurs. If the generated bubbles exceed 6 mm, the oil removal effect tends to be insufficient.

In the present invention, based on the combination of the entire surface aeration by filling the entire surface of the contact material, the blowing of a predetermined amount of air or oxygen, the limited disc fuser gap, and the water depth of the contact aeration tank, Since bubbles generated by blowing oxygen do not grow greatly under the influence of water pressure when rising in the contact aeration tank, the properties of fine bubbles with a diameter of 1 to 6 mm are maintained regardless of the depth of the aeration tank. , The oxygen absorption rate is kept constant even in the upper part of the aeration tank. Therefore, the wastewater, to which sufficient oxygen has been given by the fine bubbles, comes into contact with the microbial membrane of the packing material while retaining sufficient oxygen to remove oil. The retention time of the waste water in the contact aeration tank is preferably 6 hours or less, and an efficient oil removal effect can be obtained by balancing with the oil content capacity load in a limited range.

[0012]

Since the wastewater treatment according to the present invention has the above constitution and functions, oil and other harmful substances can be effectively removed even in a small contact aeration tank with a water depth of 3.0 m or less, and particularly oil content of 30 ppm or less. Since the detoxification of sewage is surely achieved, a sufficiently satisfactory effect can be obtained as an intermediate treatment method before the discharge of sewer.

[0013]

EXAMPLES Examples of the present invention will be described below. Example 1 Wastewater treatment was performed by the apparatus configuration shown in FIG. The inflow rate of raw wastewater is 180m ³ / day (8 hours), the oil-water separation tank is 53m ^{3 and} it is a natural floating type, the contact aeration tank has a capacity of 62m ³ , the filling material (contact material) amount is 35m ³ , and the water depth is 1.2m. The amount of aeration air was 5 m ³ / min. The air diffuser used a special disc fuser with a ventilation hole diameter of 1 to 2 mm. The operating conditions in the aeration tank and the results of wastewater treatment are shown in Table 1 and Table 2, respectively.

[0014]

[Table 1]

[0015]

[Table 2]

As shown in Table 2, the treatment of the present invention surely removed harmful substances in the wastewater, especially oil, and it is recognized that the treated wastewater is below the standard for discharge into the sewer. .

[0017]

As described above, according to the wastewater treatment provided by the present invention, it is possible to effectively treat the oil content by using the small contact aeration tank, so that the problem of equipment cost and installation place is solved. It

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the apparatus configuration used in the wastewater treatment method of the present invention.

[Explanation of symbols]

 1 Oil-water separation tank 2 Flow rate adjustment tank 3 Contact aeration tank 4 Intermediate tank 5 Discharge tank 6 Contact material 7 Air piping 8 Partition plate 9 Floating oil

Claims (5)

[Claims] 1. In the wastewater treatment by a biological treatment method, the contact aeration tank is filled with a filling material on which microorganisms are adhered, and the oil volume load in the contact aeration tank is 0.3 [kg-
Oil content / m ³ · day] or less, air of 400 m ³ or more or oxygen of 100 m ³ or more is blown per 1 kg of inlet oil, and bubbles generated by blowing air or oxygen reach the water surface of the contact aeration tank. A method for treating wastewater, which comprises performing an intermediate treatment before discharging sewerage to reduce the oil concentration in treated water to 30 mg / l or less by making the diameter 1.5 times or less the diameter of generated bubbles. 2. The wastewater treatment method according to claim 1, wherein the residence time in the contact aeration tank is within 6 hours. 3. The gap of the disc fuser is 0.5 to 3 m.
The wastewater treatment method according to claim 1 or 2, wherein m is set to m and aeration is performed from the entire surface of the filler while maintaining the diameter of the generated bubbles at 1 to 6 mm. 4. The effective water depth range in the contact aeration tank is set to 0.8.
The wastewater treatment method according to claim 1 or claim 2 or claim 3, wherein the length is about 3.0 m. 5. The method according to claim 1 or claim 2 or claim 3 or claim 3, wherein the capacity load of the oil filler in the contact aeration tank is 0.5 [kg-oil / filler amount m ³ · day] or less. 4. The wastewater treatment method described in 4.