TW201345842A - Method for treating fat-containing wastewater - Google Patents

Abstract

Provided is a method for treating fat-containing wastewater making it possible to purify fat-containing wastewater at high efficiency and efficiently recover energy from an organic component in the wastewater, and to stabilize a methane fermentation process, improve treatment efficiency, reduce the size of a methane fermentation tank, improve the efficiency of separating fat from the fat-containing wastewater, reduce the volume of sludge generated, and so forth. A method for treating fat-containing wastewater, the method being characterized in subjecting fat-containing wastewater to an acid generation reaction under alkaline conditions without having separated the fat and the wastewater, and next running a methane generation reaction while still under alkaline conditions. Also, a method for treating fat-containing wastewater, the method being characterized in running a methane generation reaction in a reaction tank packed with a fluidized bed carrier made of resin.

Description

Method for treating grease drainage

The present invention relates to a method for treating grease-containing drainage of food factory drainage or the like.

For example, in the food factory drainage (milk factory, deli factory, etc.), when the wastewater containing many fats and oils is subjected to biological treatment, since the oil adheres to the sludge microorganisms, the treatment capacity is lowered, so that the treatment is performed before the pressurized floating device or the like to remove the drainage. The oil and fat, the separation liquid after separating the oil and fat, is treated by microbial treatment such as the active sludge method, and the oily sludge is subjected to additional treatment. When a grease is drained from a grease-containing draining device by a pressurized floating device or the like, a large amount of a coagulant is required. Further, the separated fat-containing sludge is creamy and has poor workability. Therefore, the oil-containing sludge is treated with an adsorbent, and the oil is adsorbed to the adsorbent, and then dehydrated and discarded. At this time, since the fat-containing sludge contains undecomposed organic matter, generation of odor is also a problem. In addition, the dehydrated sludge produced is conventionally treated by burial or incineration, but the increase in waste cost is also a problem because of harmful substances generated during incineration or insufficient landfill.

As a grease that does not remove grease from the drain, it is directly treated as a drainage system. The method of the system treatment is a method in which a microbial preparation is added to an adjustment tank or an aeration tank, and oil is decomposed in an aeration tank.

For example, Japanese Laid-Open Patent Publication No. Hei 6-246295 discloses a method of performing an anaerobic treatment on a grease-containing drainage, adding a lipase, and decomposing the oil. Here, as a lipase, it is known that a fat enzyme is hydrolyzed into a glycerol and a higher fatty acid by a lipase, and the produced higher fatty acid is acidified into a lower fatty acid by high-efficiency β.

Methane fermentation, that is, Anaerobic digestive system, has the advantages of stable organic matter, reduced sludge, energy recovery, and aeration cost reduction. Therefore, it has been used in the treatment of grease-containing sludge separated by oily drainage or self-contained grease drainage. (Japanese Laid-Open Patent Publication No. SHO 57-117380, JP-A-2001-321792). In particular, JP-A-2001-321792 discloses a method of treating methane-fermented waste by mixing the remaining sludge generated from the aerobic treatment tank in the subsequent stage with the grease-containing drainage as an effective method for treating the grease-containing drainage. JP-A-2001-321792 discloses that in this treatment, by adding a lipase or introducing a microorganism-maintaining carrier, a microorganism for suppressing the relaxation of a higher fatty acid is added to improve the treatment performance. However, when the oil-repellent anaerobic treatment method is used to foam the oil and float, the oil adheres to the particles, the particles float, and the oil-containing drainage is difficult to be decomposed by the microorganisms, so that the microbial activity is inhibited. The biological treatment process is not decomposed and remains in the problem of treating water.

Prior technical literature Patent literature

Patent Document 1: Japanese Laid-Open Patent Publication No. Hei 6-246295

Patent Document 2: JP-A-57-117380

Patent Document 3: JP-A-2001-321792

The Anaerobic treatment method using grease drainage is foaming and floating. Further, the grease adheres to the particles, and the particles float. Further, it is difficult to decompose the oil itself.

The present invention provides a high-efficiency purification of oil-containing drainage, and efficiently recovers methane from organic components in the drainage, thereby achieving stabilization of methane fermentation treatment, improvement of treatment efficiency, miniaturization of methane fermentation tank, and self-contained grease drainage. The treatment method of the grease-containing drainage such as the improvement of the oil separation efficiency and the reduction of the amount of sludge is aimed at.

The method for treating a grease-containing drainage according to the present invention is characterized in that the oil-containing water is drained, the oil and fat are not separated from the drainage, the acid formation reaction is carried out under alkaline conditions, and then the methane formation reaction is carried out under the original alkaline conditions.

The anaerobic treatment can be performed efficiently by performing the acid formation directly under alkaline conditions without performing the acid separation under the alkaline conditions.

The best form for implementing the invention

The invention will be further described in detail below.

In the present invention, the oil-containing drainage system to be treated contains animal and vegetable oils and fats, and the concentration of the n-hexane extract is 100 mg/L or more, and the oil-containing drainage is preferably 100 to 1000 mg/L.

The oil and fat are not drained, the oil and fat are separated, and the oil is introduced into an acid generating tank, and the concentration of the n-hexane extract (hereinafter referred to as n-Hex) is 100 mg/L by reacting under an alkali condition of pH 8.0 or higher. Hereinafter, it is preferably 30 mg/L or less.

The pH of the acid generating tank is 8 to 12, especially 8 to 9, preferably 8.5 to 9.0. In order to promote the decomposition and emulsification of the oil and fat portion, although the pH value is high and the effect is high, in order to increase the cost of the medicine for raising the pH, it is economical to control the pH near 8.5 to 9.0.

The temperature of the acid generating tank is 20 to 40 ° C, preferably 25 to 35 ° C, and HRT is 2 to 24 hours, preferably 2 to 8 hours.

The BOD volume load of the acid generating tank is 1 kg/m ³ /d or more, for example, 1 to 20 kg/m ³ /d or more, and the HRT can be obtained by decomposing the oil component into an acid such as acetic acid. water. Further, by treating under a base condition, a part of the fat portion is solubilized, and the microbial reaction is easy to carry out.

As a method for maintaining the pH of the acid generating tank at such a pH value, it is preferred to continuously or intermittently measure the pH of the solution in the acid generating tank, and to add an alkali component such as sodium hydroxide, calcium hydroxide or calcium carbonate to correct the change. . Disgusted The treated water of the Anaerobic treatment is aerated, the pH is raised by the decarbonation reaction, and the water is returned to be used as a base.

Animal and vegetable fats and oils (triglycerides) are hydrolyzed into fatty acids and glycerol by in vitro enzymes (lipases) produced by bacteria originally present in the acid-forming tank.

Since the pKa of the fatty acid is about a weakly basic region of about 8, a free fatty acid which is not water-soluble is present in the neutral zone or the acidic zone, and the decomposability of the microorganism is deteriorated. Therefore, the light-weight fat component is accumulated close to the water surface, causing the foam mainly composed of a fatty acid.

However, in the present invention, by maintaining the pH of the acid-forming tank on the alkaline side of 8.0 or higher, the animal and vegetable oils can be hydrolyzed into a soluble fatty acid salt, so that the decomposition efficiency of the microorganism can be enhanced, and the occurrence of foam can be suppressed.

Even if the concentration of the oil having a low oil concentration (the concentration of the n-hexane extract is less than 100 mg/L), it is occupied by bacteria which are dominant in the alkaline region in the acid-producing bacteria by the treatment under such alkaline pH conditions.

In order to maintain the amount of microorganisms in the acid generating tank, a commercially available microbial preparation or a culture thereof or an activated sludge may be appropriately introduced.

In the acid formation tank, in order to further promote the decomposition of the oil and fat, for example, oil-decomposing bacteria, oil-decomposing fungi, lipolytic enzymes such as lipase, surfactants, and the like may be additionally added, and the oil and fat may be promoted by mechanical stirring or the like. By doing so, high-load processing with a BOD volume load of 5 kg/m ³ /d or more is also possible.

The polymer component in the acid generating tank is converted into an organic acid, and at this time, dispersed cells are formed. Dispersed cells even flow into anaerobic treatment tanks It does not accumulate, and the treated water flows out.

The treated water passing through the acid generating tank is preferably fed to an Anaerobic treatment tank without adjusting the pH.

This Anaerobic treatment tank performs oxidative decomposition and methane formation of residual organic components.

In addition, when the Anaerobic protozoa proliferates in the Anaerobic treatment tank, the dispersed cells are predators of the protozoa. In addition, protozoa are high-rise organisms in the food chain, and the amount of growth (= residual sludge) is very small, so there is no carrier adhesion and floating due to proliferation of protozoa.

When the anaerobic treatment tank is filled with a non-biological carrier, it is preferred to use a resin carrier which is easy to adjust the specific gravity and particle diameter. As the carrier, the size is 1.0~5.0mm, preferably 2.5~4.0mm, and the sedimentation speed is 200~500m/h. Further, as the Anaerobic treatment tank, a full-mixing type reaction tank using a stirrer or the like, an upflow type reaction tank by a water flow and a gas generating tank, or the like can be used.

In the present invention, Anaerobic treated water can also be subjected to aerobic treatment.

1‧‧‧acid generator tank

2‧‧‧Relay slot

3‧‧‧Anaerobic treatment tank

[Fig. 1] A flow chart of an embodiment.

Example

The present invention will be further specifically described below by way of examples and comparative examples.

[Example 1]

As shown in Fig. 1, an acid generating tank 1 having a capacity of 18 L, a relay tank 2, and an Anaerobic treatment tank 3 having a diameter of 15 cm, a height of 60 cm and a capacity of about 10 L were used, and treated with a water volume of 350 L/d. The following water quality contains grease drainage.

<Original water quality>

SS: 900mg/L

BOD: 2700mg/L

n-Hex: 400mg/L

CODcr: 4060mg/L

The water-passing conditions were an acid formation tank HRT for 6 hours and an Anaerobic treatment tank HRT for 1.5 hours. In the acid generation tank 1, NaOH of an alkali agent was added until pH = 9.0. In addition, the liquid in the tank is circulated and stirred by the crucible. The carrier is filled in an anaerobic treatment tank 3. The loading amount of the carrier was 40% with respect to the anaerobic treatment tank. In addition, 2 L of an Anaerobic sludge (10000 mg VSS/L) as a sludge was added. The treated water is taken out from the upper layer of the Anaerobic treatment tank 3 through the screen. In addition, a part of the treated water was returned to the relay tank 2 at 700 L/d. When the pH of the relay tank 2 is monitored and the alkali addition means of the acid generation tank 1 fails, an alkali is added to the relay tank 2. Acid generation tank and anaerobic The water quality of the treated water of the (Anaerobic) treatment tank is shown in Table 1.

As shown in Table 1, in the acid generation tank, the removal rates of BOD and n-Hex were 30% and 90%, respectively. In addition, the SS system is slightly increased depending on the production of the cells. The CODcr removal rate is approximately 26%. By reacting under alkaline conditions, although a little foam is visible, the foam does not accumulate on the surface of the water and can continue to operate without problems.

In the Anaerobic treatment tank, the removal rates of raw water by BOD and n-Hex were 93% and 95%, respectively. In addition, the SS system is slightly increased depending on the production of the cells. The CODcr removal rate was 82%.

[Comparative Example 1]

The same reaction was carried out by using the same reaction tank as in Example 1 and setting the pH of the acid generating tank to the neutral zone (7.0).

The water quality of the treated water in the acid formation tank and the Anaerobic treatment tank is shown in Table 2.

As shown in Table 2, in the acid generation tank, the removal rates of BOD and n-Hex were 21% and 23%, respectively. In addition, the SS system is slightly increased depending on the production of the cells. The CODcr removal rate is approximately 14%. Under neutral conditions, the oil portion becomes a foam, and foam is deposited on the water surface and adheres to the electrode, which is a cause of the problem.

In the Anaerobic treatment tank, the removal rates of raw water by BOD and n-Hex were 63% and 75%, respectively. Although the treatment of water can remove a certain degree of n-Hex composition, this is the reason why the oil component adheres to the surface of the carrier. In addition, the SS system is slightly increased depending on the production of the cells. The CODcr removal rate was 63%. Since the grease component adheres to the carrier groove, the carriers adhere to each other and cannot operate stably.

It is apparent from the following examples and comparative examples that according to the present invention, the oil is not separated from the drainage, the acid formation reaction is carried out under alkaline conditions (pH 8 to 9), and the methane formation reaction is carried out by the original alkaline conditions. It can efficiently process organic drainage containing grease.

Industrial use

The present invention will be described in detail using a specific type, but without departing from the present invention. The purpose and scope of the Ming, the relevant industry understands that various changes can be made.

In addition, this application is based on the Japanese Patent Application (Japanese Patent Application No. 2012-080519) filed on March 30, 2012, which is incorporated by reference.

1‧‧‧acid generator tank

2‧‧‧Relay slot

3‧‧‧Anaerobic treatment tank

Claims (4)

The invention relates to a method for treating oily drainage, characterized in that the oil and fat are drained, the oil is separated from the drainage, the acid formation reaction is carried out under alkaline conditions, and then the methane formation reaction is carried out under the original alkaline condition. The method for treating a grease-containing drainage according to the first aspect of the patent application is to carry out a methane formation reaction in an Anaerobic treatment tank filled with a resin-made fluidized bed carrier. For example, in the method for treating a grease-containing drainage according to the first aspect of the patent application, the treated water after the partial methane formation reaction is sent back to the acid formation tank. The method for treating a grease-containing drainage according to any one of claims 1 to 3, wherein after the methane formation treatment, a gas treatment is performed.