JPH05123694A - Treatment of organic waste water with nitrogen fixation bacterial - Google Patents

Abstract

(57) [Summary] [Purpose] Organic wastewater that does not substantially contain nitrogen has high treatment efficiency, reduces the amount of excess sludge produced, and reduces the amount of SS discharged into the treated water. Process aerobically. [Structure] Organic wastewater containing substantially no nitrogen is contacted with nitrogen-fixing bacteria immobilized on a carrier in the presence of nitrogen gas and oxygen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating organic wastewater, and more particularly to a method for treating organic wastewater containing substantially no nitrogen by a nitrogen-fixing bacterium immobilized on a carrier.

[0002]

2. Description of the Related Art Nitrogen-fixing bacteria can fix nitrogen gas in the air and convert it to ammonia when a nitrogen source such as ammonium ion does not exist in water, and from this, proteins can be synthesized via amino acids. Many kinds of nitrogen-fixing bacteria are known, but all of them are fixed with nitrogen by an enzyme called nitrogenase. Nitrogenase is very oxygen sensitive and its activity is halved within one minute when the purified nitrogenase is placed in air.

However, among the nitrogen-fixing bacteria, not only anaerobic bacteria but also aerobic bacteria such as Azotobacter are common. These aerobic nitrogen-fixing bacteria utilize oxygen to perform aerobic metabolism in order to generate energy. On the other hand, in order to activate nitrogenase, oxygen is removed from the nitrogen-fixing site with a high respiration rate. A mechanism called respiratory protection keeps the area around nitrogenase anaerobically. Therefore, a huge amount of carbon is consumed to remove oxygen, and from the viewpoint of the growth of nitrogen-fixing bacteria, a low cell yield can be achieved.
Therefore, when nitrogen-fixing bacteria are used for wastewater treatment, wastewater treatment that produces a small amount of excess sludge can be performed.

A method has been proposed in which organic wastewater substantially free of nitrogen is aerobically treated with nitrogen-fixing bacteria by taking advantage of such aerobic nitrogen-fixing bacteria. For example, JP-A-48-102453 discloses that a nitrogen-fixing bacterium is subjected to chemostat culture with a residence time of 3 to 12 hours using a dispersion growth system of a pure or semi-pure culture of an aerobic nitrogen-fixing bacterium. There has been proposed a method of treating organic wastewater by predominantly treating water in a tank.

However, according to this method, the amount of surplus sludge produced during the treatment can be reduced, but there are the following problems. 1) The processing time is as long as 3 to 12 hours and the processing efficiency is poor. 2) Microorganisms other than nitrogen-fixing bacteria easily grow, and it is difficult to make nitrogen-fixing bacteria dominant. When microorganisms other than nitrogen-fixing bacteria grow, the amount of excess sludge produced increases, which is not preferable. 3) Since nitrogen-fixing bacteria generally form a large amount of extracellular polysaccharides, they have poor aggregation properties and do not form flocs. For this reason, it is difficult to maintain the required amount of nitrogen-fixing bacteria in the treatment tank, the treatment efficiency deteriorates, and solid-liquid separation cannot be easily performed in a sedimentation tank or the like. 4) The SS concentration in the treated water becomes high.

A method of treating organic wastewater by keeping nitrogen-fixing bacteria in ordinary activated sludge has also been proposed. However, with this method, it is difficult to make the nitrogen-fixing bacteria dominate sufficiently, and since microorganisms other than the nitrogen-fixing bacteria grow,
There are problems such as a large amount of excess sludge produced.

[0007]

DISCLOSURE OF THE INVENTION The object of the present invention is to solve the above-mentioned problems. Therefore, the treatment efficiency is high, the amount of excess sludge produced is small, the SS concentration in the treated water is low, and the nitrogen-fixing bacteria are retained. It is to propose a method for treating organic wastewater with nitrogen-fixing bacteria that is easy to process.

[0008]

DISCLOSURE OF THE INVENTION The present invention relates to an organic wastewater produced by a nitrogen-fixing bacterium, which comprises contacting the organic wastewater containing substantially no nitrogen with a nitrogen-fixing bacterium immobilized on a carrier. It is a processing method.

The wastewater to be treated according to the present invention is organic wastewater which does not substantially contain nitrogen, and concrete examples thereof include food factory wastewater containing sugar, starch, ethanol and the like, chemical synthesis factory wastewater, etc. Can be illustrated. Here, the term "substantially free of nitrogen" means that the activity of nitrogen fixation by the nitrogen-fixing bacterium is not significantly inhibited, and the nitrogen-fixing activity by the nitrogen-fixing bacterium suitable for the purpose of the present invention is maintained to the extent that ammonium ion It means that it does not contain a nitrogen source such as.

If a nitrogen source such as ammonium ion is present in the waste water, the nitrogenase activity of nitrogen-fixing bacteria is inhibited, the cell yield does not decrease, and microorganisms other than nitrogen-fixing bacteria easily grow. Since nitrogen-fixing bacteria cannot be maintained predominantly, wastewater containing such a nitrogen source can be subjected to the treatment of the present invention after the nitrogen source is removed in advance.

The nitrogen-fixing bacterium used in the treatment of the present invention is a microorganism that fixes nitrogen gas in the air and converts it into ammonia, and then synthesizes a protein via an amino acid. As such nitrogen-fixing bacteria, both aerobic bacteria and anaerobic bacteria can be used, but the use of aerobic nitrogen-fixing bacteria enables treatment with a small amount of excess sludge. Those that can be treated aerobically, such as facultative anaerobes,
It can be used as it is like an aerobic bacterium.

As the nitrogen-fixing bacteria, there are some symbiotic nitrogen-fixing bacteria that grow by co-existing with the host, which can be used for treatment with the host, but generally, the non-cultivating bacteria that are self-sustaining grow. Symbiotic nitrogen-fixing bacteria are suitable for the treatment of the present invention.

Nitrogen-fixing bacteria suitable for the treatment of the present invention include the genus Azotobacter (Az) which is an organic nutrient aerobic bacterium.
motobacterium), genus Beijierinchia (Beij)
erlinkia), Achromobacter (Achrom)
and nitrogen-fixing bacteria belonging to photosynthetic bacteria, yeasts, algae and the like.

Among these, nitrogen-fixing bacteria belonging to the genus Azotobacter have a high nitrogen-fixing ability and are suitable for treatment. Nitrogen-fixing bacteria belonging to the genus Azotobacter include Azotobacter crococcum, Azotobacter vinelandii,
Azotobacter indicus, Azotobacter lacchycogenes, Azotobacter beigelinkki and the like.

The nitrogen-fixing bacterium used in the treatment of the present invention can be treated in a pure form by isolating these microorganisms, but can also be treated in the form of a mixture of many kinds. Nitrogen-fixing bacteria suitable for treatment can be obtained by performing integrated culture according to the growth conditions of the bacteria.

In the present invention, such nitrogen-fixing bacteria are immobilized on a carrier and used for treatment. Immobilization of nitrogen-fixing bacteria is preferably performed by encapsulating the nitrogen-fixing bacteria in a carrier so that the nitrogen-fixing bacteria are isolated from the outside world. Such immobilization methods include entrapping immobilization method of encapsulating nitrogen-fixing bacteria in a gel-like carrier, encapsulation method of encapsulating in a capsule, and nitrogen-immobilizing bacteria in a semipermeable membrane or a porous membrane. The method of encapsulation may be mentioned. Of these, the entrapping immobilization method is preferable.

The immobilization of nitrogen-fixing bacteria by the entrapping immobilization method is performed by gelling a mixture of nitrogen-fixing bacteria in an aqueous solution of a gel base and molding it into a predetermined shape. The immobilized nitrogen-fixing bacterium can be used in any shape such as a granular shape, a lumped shape, or a membrane shape, but it is preferably used in a granular shape. Molding into such a shape can be performed by cutting after gelling, but it is preferable to mold into a predetermined shape upon gelling. For example, in the case of granulation, the gelling agent solution may be stirred and the mixture of the gel base and the nitrogen-fixing bacterium may be dropped into the gelling agent solution to form the granulation and the granulation at the same time.

As the gel-like carrier used in the entrapping immobilization method, those capable of permeating BOD components, nitrogen and oxygen in the water to be treated and not inhibiting the activity of nitrogen-fixing bacteria can be used. Such gels include polyacrylamide,
In addition to synthetic gels such as polyacrylamide hydrazide, polyurethane, polyvinyl alcohol, etc., natural gels such as carrageenan and sodium alginate can be mentioned. Difficult synthetic gels are preferred.

In the case of polyacrylamide gel and polyacrylamide hydrazide gel, polyacrylamide or polyacrylamide hydrazide is used as a gel base and gelled by reacting with a nitrogen-fixing bacterium and a cross-linking agent such as glyoxal. You can In the case of a polyurethane gel, gelation is performed by using a polyurethane prepolymer as a gel base and polymerizing by heating or the like. In the case of polyvinyl alcohol, gelation is performed by heating or reaction with a crosslinking agent. Also, these can be gelated by polymerizing using a monomer or prepolymer as a gel base. When a polysaccharide such as carrageenan or sodium alginate is used as the gel base, gelation can be carried out by reaction with a gelling agent such as calcium chloride, magnesium chloride or potassium chloride.

The immobilized nitrogen-fixing bacterium obtained by gelation is preferably in a porous state so that the BOD component, nitrogen and oxygen in the water to be treated can easily permeate. For such porosity, a mixture of a plurality of gel bases and nitrogen-fixing bacteria is reacted with each gelling agent to form a gel, and one gel is eluted to form a porous material. can do. For example, using polyacrylamide hydrazide and sodium alginate as a gel base, mixing these with nitrogen-fixing bacteria, gelling each with a gelling agent such as dialdehyde and calcium chloride, and then using an aqueous solution of potassium phosphate or the like to form an alginate gel. By elution of, the nitrogen-fixing bacteria immobilized with porous polyacrylamide hydrazide gel can be obtained.

The immobilized nitrogen-fixing bacterium thus immobilized on the carrier is subjected to the treatment of the present invention by bringing it into contact with water to be treated which does not substantially contain nitrogen in the presence of nitrogen gas. The contact method varies depending on the shape of the immobilized nitrogen-fixing bacterium and may be a continuous type or a batch type, but a continuous type is preferable. For example, when the shape of the immobilized nitrogen-fixing bacteria is granular, it can be filled in the treatment tank and the water to be treated can be brought into contact with it by flowing in an upward flow or a downward flow. It is preferable to form and contact them. When aerobic nitrogen-fixing bacteria are used, oxygen is supplied by supplying air at the same time.

The amount of immobilized nitrogen-fixing bacteria used is 5 in the treatment tank.
-40%, preferably 10-30% by volume. The residence time of the water to be treated is 5 minutes to 10 hours, preferably 5 minutes to 3 hours. If the residence time exceeds 3 hours, other adherent microorganisms tend to adhere and grow on the surface of the carrier, so that the nitrogen-fixing bacteria may not be sufficiently dominated. Treatment temperature and pH are not particularly limited,
The treatment can be performed at room temperature and neutrality. The dissolved oxygen concentration is 1 to 10 mg / l, preferably 3 mg / l or more.

By carrying out the treatment as described above, the immobilized nitrogen-fixing bacteria pass through the carrier gel to form BO in the water to be treated.
It ingests component D and nitrogen and oxygen in the air to grow, and at the same time immobilizes nitrogen in the air. Since the growth of bacteria is performed inside the carrier, the amount of bacteria retained in the carrier can be increased,
The increased amount of sludge due to self-digestion is smaller than that in chemostat culture. As the growth of the bacterium progresses, a part thereof flows out from the thin portion of the carrier and flows out into the treated water, but the amount thereof is small. Other microorganisms that grow as the treatment progresses are present outside the carrier and do not affect the nitrogen-fixing bacteria inside the carrier. Other microorganisms attached to the surface of the carrier can be physically or chemically exfoliated if necessary.

By the above treatment, BOD in the water to be treated is removed, and the treated water flows out from the layer of the immobilized nitrogen-fixing bacteria to be easily solid-liquid separated and discharged as it is.
Since the increased amount of immobilized nitrogen-fixing bacteria is small, the treatment can be continued as it is for a long time. That is, since the increased amount is discharged outside the system as SS in the treated water, it is not necessary to treat the excess sludge. Further, as the treatment is continued, the carrier may be damaged and the nitrogen-fixing bacteria in the carrier may flow out, but the amount thereof is small.

When immobilized nitrogen-fixing bacteria are used, a large number of bacteria can be retained in the treatment tank as compared with the case of chemostat culture in a distributed growth system, so that the load of organic matter can be increased and efficient treatment can be achieved. It can be carried out. In chemostat culture, HRT (residence time) 3-5 hours (dilution rate 0.2
~ 0.33 hr ^-1 ) is desirable, and when HRT is made shorter than this, nitrogen-fixing bacteria flow out into treated water (wa
However, if immobilized nitrogen-fixing bacteria are used, the concentration of nitrogen-fixing bacteria in the treatment tank should be 10%.
It can be doubled and HRT can be processed for 5 to 30 minutes.

When immobilized nitrogen-fixing bacteria are used, the growth of microorganisms other than nitrogen-fixing bacteria can be reduced,
The nitrogen-fixing bacteria can be dominated, and the amount of excess sludge produced can be reduced. Even when treating organic wastewater that does not substantially contain nitrogen, nitrogen fixed by nitrogen-fixing bacteria can be used from the air, so that normal BOD-oxidizing microorganisms that do not fix nitrogen grow. Since the microorganisms other than the fixed bacteria are likely to become a dispersed growth system, the ratio of the colonization and retention becomes very small in the system treated with short HRT.

Nitrogen-fixing bacteria have poor flocculation properties and do not form flocs, but by immobilizing such nitrogen-fixing bacteria with a carrier, they can be easily retained in a treatment tank.
When the nitrogen-fixing bacteria are not immobilized, 5 to 15% of the treated water (raw water) BOD is converted into the bacteria in the dominant state of the nitrogen-fixing bacteria,
Although SS leaks into treated water, when nitrogen-fixing bacteria are immobilized, the retention amount of nitrogen-fixing bacteria in the tank can be set high, and the self-digestion amount of nitrogen-fixing bacteria is also high, which reduces the outflow of SS. .. Therefore, when the organic substance content in the water to be treated is small, the solid-liquid separation operation of the treated water may be unnecessary.

[0028]

As described above, according to the present invention, since the organic wastewater containing substantially no nitrogen and the nitrogen-fixing bacteria immobilized on the carrier are treated, the nitrogen-fixing bacteria can be retained. This facilitates the treatment of a large amount of nitrogen-fixing bacteria in the treatment tank and treats the organic wastewater with high treatment efficiency. In this case, since the yield of nitrogen-fixing bacteria is low, the amount of surplus sludge produced is small and the amount of SS discharged into the treated water is also small.

[0029]

EXAMPLES Next, examples of the present invention will be described.

Reference Example 1 Nitrogen-fixing bacteria were entrapped and fixed by the following method. First, 10 g (wet weight) of accumulated nitrogen-fixing bacteria was added to 100 ml of a solution A containing a gel base having the following composition and mixed sufficiently. This was dropped into 1 liter of an ice-cooled solution B containing a gelling agent having the following composition and dispersed in a granular form. In this state, the gel was allowed to stand for 1 hour, and then the granular gel was immersed in a solution C having the following composition for 30 minutes to dissolve only the alginic acid gel to make it porous. This was thoroughly washed with 1/50 M Tris buffer (pH 8) to obtain immobilized nitrogen-fixing bacteria, which was refrigerated and stored. Solution A Polyacrylamide hydrazide (average molecular weight 183):
3% by weight sodium alginate: 0.5% by weight 1 / 50M Tris buffer (pH 8) solution B CaCl ₂ .2H ₂ O: 2% by weight Glyoxal: 0.1% by weight 1 / 50M Tris buffer (pH 8) solution C K ₂ HPO ₄ : 1.46% by weight KH ₂ PO ₄ : 0.226% by weight 1/50 M Tris buffer (pH 8)

Examples 1-2, Comparative Examples 1-2 Orange juice production wastewater was chemostat-treated with a nitrogen-fixing bacteria dispersion-growing system (Comparative Examples 1-2), and comprehensive immobilization obtained in Reference Example 1. Table 1 shows the results of the case where the fluidized bed was formed by passing water upward through a packed bed of nitrogen-fixing bacteria and aerating with air or oxygen-rich air from below (Examples 1 to 3). The processing conditions are as follows.

Composition of water to be treated (raw water) COD _cr : 2300 ppm Kjeldahl nitrogen content: 3 mg / l Total phosphorus content: 12 mg / l Treatment conditions Dissolved oxygen: 5-7 ppm pH: 6.5-7 Temperature: 25-27 C HRT: 1-10 hours

[0033]

[Table 1]

As can be seen from Table 1, Examples 1 and 2
Although the solubility COD _cr of the treated water was about the same as that of Comparative Example 1, the treated water SS was about 1/2. Also, HRT is 10
Even in Example 3 where the time was set, the same water quality as in Comparative Example 1 was obtained. In Comparative Example 2 in which the HRT was 1 hour, the nitrogen-fixing bacteria flowed out into the treated water and could not be retained in the tank, so that the treatment became impossible.

Claims (1)

[Claims] 1. An organic wastewater containing substantially no nitrogen,
A method for treating organic wastewater with nitrogen-fixing bacteria, which comprises contacting the carrier with nitrogen-fixing bacteria.