JP4602847B2 - Flock formation accelerator, activated sludge treatment method, and activated sludge treatment method - Google Patents

Description

  The present invention relates to a technique for promoting the formation of microbial flocs. More specifically, the present invention relates to a technique for promoting the formation of microbial floc in a biological reaction tank in an activated sludge treatment method or the like.

  An activated sludge method, which is a biological oxidation treatment method for organic wastewater, is known. This “activated sludge method” is a method of purifying wastewater using “activated sludge”, which is an aggregate of aerobic microorganisms such as bacteria, fungi, algae, protozoa, rotifers and nematodes. Currently, it is widely used for sewage treatment, industrial wastewater treatment, livestock sewage treatment and the like.

  The process of this activated sludge method is generally as follows. First, wastewater that has undergone pretreatment such as filtration and sedimentation is sent to a biological reaction tank (also referred to as “aeration tank”) and brought into contact with floc-like activated sludge while being aerated. The organic matter is aerobically oxidized and decomposed. Subsequently, the treated water is sent to a sedimentation tank (sedimentation basin) to separate and settle sludge (solid-liquid separation), and then the separated upper layer water is disinfected and discharged. Then, a part of the concentrated activated sludge generated in the sedimentation tank is sent to the biological reaction tank as a return sludge and used for the preparation of the microbial concentration of the sludge in the reaction tank, and in contact with a new influent wastewater (inflow substrate). Let

  The activated sludge, which is a floc-like microorganism aggregate, has strong organic matter oxidizing power and cohesive adsorption power, and is excellent in sedimentation separation. Microorganisms in the biological reaction tank form flocs with the polymer produced by the specific microorganisms, and the flocs increase the BOD treatment capacity of the microorganisms in the tank. Moreover, solid-liquid separation performance is improved by flocking, and a clear supernatant is obtained in the precipitation tank.

  However, once a phenomenon called “bulking” occurs in the biological reaction tank, the activated sludge swells and becomes lighter, so the sedimentation and compaction properties deteriorate, and the amount of separated upper water in the precipitation tank decreases. Such problems occur. This bulking occurs when microorganisms that form filaments in the activated sludge (filamentous bacteria) grow (filamentous bulking) or when substances such as highly viscous polysaccharides accumulate in the activated sludge (non-filamentous bulking). ). As the cause of the occurrence, changes in water temperature, inflow of wastewater containing a large amount of carbohydrates, inflow of a large amount of low-molecular soluble organic matter, decrease in inflow of SS, lack of nitrogen and phosphorus, and the like are known.

  As a general countermeasure against bulking, a method of improving the sedimentation property of sludge by adding a flocculant, a method of sterilizing filamentous bacteria by adding a bactericide, a method of suppressing filamentation of filamentous bacteria, etc. are adopted. ing.

  For example, Patent Document 1 discloses a bulking control agent containing a cationic polymer flocculant, an inorganic flocculant, and the like, and a bulking control method in which this is added to an aeration tank, a settling tank, and a return sludge. . Patent Document 2 discloses a bulking phenomenon inhibitor characterized by containing methylene dithiocyanate as an active ingredient and destroying specific filamentous bacteria with the active ingredient. Patent Document 3 discloses an anti-bulking agent that suppresses only filamentous bacterial filamentation with a pyrazolopyrimidine derivative. In addition, Patent Document 4 discloses an anti-bulking agent mainly composed of zeolite produced from natural raw materials.

Japanese Patent Laid-Open No. 10-244287. JP-A-6-206089. JP-A-5-309388. JP 2000-334483 A.

  However, a method for preventing or suppressing bulking by adding a flocculant or a disinfectant to an activated sludge tank or the like has a technical problem that microbial activity decreases. In addition, the conventional bulking inhibitor cannot sufficiently promote the formation of microbial flocs.

  Therefore, the present invention provides a liquid floc formation accelerator capable of promoting floc formation without reducing microbial activity, and also provides an activated sludge treatment method and a bulking prevention method using the floc formation accelerator. Main purpose.

  In the present invention, first, a floc formation promoter is provided. This floc formation promoter is a liquid agent useful for forming a microbial floc of activated sludge, a linear first polymer having a carboxyl group, and a cationic having an amino group hydrogen-bonded to the carboxyl group And a third polymer adsorbed on a composite polymer composed of the first polymer and the second polymer.

  The first polymer plays a role in forming a basic skeleton of the microbial floc, and the second polymer plays a role in forming a complex polymer having a branched structure by hydrogen bonding with the carboxyl group of the first polymer. The third polymer plays a role of firmly maintaining the structure of the composite polymer composed of the first polymer and the second polymer.

  The floc formation accelerator according to the present invention is useful as a microorganism-adsorbing carrier, and has a feature that it does not inhibit the activity of microorganisms once adsorbed, unlike conventional polymer flocculants. Conventional polymer flocculants form flocs so as to enclose microorganisms with a polymer film, which makes it difficult to inhabit aerobic bacteria and microaerobic bacteria. In the promoter, a phase of aerobic bacteria and phagocytic protozoa is formed on the outermost side of the floc, a phase of microaerobic bacteria is formed on the inside, and an anaerobic bacterial phase is formed on the core part of the floc. Phases are formed and these microbial flora are very stable. The phagocytic protozoa prey on bacteria in the flocs, and the predatory bacteria maintain their activity high by predatory stimulation, so this predation / predation relationship greatly contributes to flock stabilization and microbial activity maintenance. Contribute.

  Here, the polymer constituting the floc formation accelerator according to the present invention is not limited to a narrow one, but as the first polymer, for example, a polymer of sodium polyacrylate can be adopted, and the second polymer is, for example, Polyethyleneimine can be employed, and for example, polyglutamic acid can be suitably employed as the third polymer.

  When such a polymer configuration is employed, polyethyleneimine branches and hangs from the linear polymer of sodium polyacrylate by hydrogen bonding between the carboxyl group of sodium polyacrylate and the amino group of polyethyleneimine. A branched structure (crosslinked structure) is formed, and a net-like or lattice-like structure is formed as a whole. In addition, the ionized carboxyl group of polyglutamic acid is adsorbed on the network-like or lattice-like structure, thereby stabilizing and maintaining the branched structure. In addition, the cationic free amino group of polyethyleneimine (amino group not involved in hydrogen bonding) electrically attracts negatively charged microorganisms, and thus exerts an action of promoting the formation of microbial flocs.

  In the present invention, the activated sludge treatment method using the floc formation accelerator having the above-described structure, more specifically, this floc formation accelerator is added to the biological reaction tank to increase the activated sludge density, and further prevent the occurrence of bulking. An activated sludge treatment method is provided. Moreover, the bulking prevention method characterized by using the said floc formation promoter which concerns on this invention is provided.

  According to the present invention, floc formation can be promoted while activating microorganisms without reducing microbial activity. Moreover, since microbial flocs are firmly stabilized, the occurrence of bulking can be effectively prevented, solid-liquid separation is facilitated, and a clear supernatant can be obtained in the precipitation tank. Furthermore, the amount of sludge used can be reduced.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments for carrying out the invention will be described with reference to the accompanying drawings and chemical formulas. In addition, this embodiment shows an example of typical embodiment of this invention, and, thereby, the range of this invention is not interpreted narrowly.

  The floc formation accelerator according to the present invention is a liquid microbial adsorption carrier containing at least first to third polymers described below, and is added to a biological reaction tank (aeration tank) or the like in an activated sludge treatment method. This promotes the formation of microbial flocs, increases the activated sludge density (microorganism density), and effectively prevents the occurrence of bulking.

  In the present embodiment, linear sodium polyacrylate (hereinafter often abbreviated as “SPA”) having the following chemical structure is employed as the first polymer. Examples of other candidates for the first polymer include sodium polymaleate and a copolymer salt of acrylic acid and maleic acid.

  This sodium polyacrylate (SPA) forms a long chain polymer having a molecular weight of tens of millions to hundreds of millions, and exists in the state of a long thread entangled in water. The carboxyl group of this sodium polyacrylate serves to bind the cationic second polymer having the ability to adsorb microorganisms.

  As this second polymer, polyethyleneimine (hereinafter often abbreviated as “PEI”) whose molecular formula is shown in the following chemical formula 2 can be suitably employed. Since this PEI is positively charged in the solution, it plays a role of being electrically adsorbed between negatively charged microorganisms. Other candidates for the second polymer include alkyleneimine polymers other than polyethyleneimine, polyacrylamide, and polyamino acids (for example, polylysine and polyarginine).

  Furthermore, the third polymer is used in order to firmly bond the composite polymer state due to the hydrogen bond between a carboxyl group and an amino group in a solution of sodium polyacrylate (SPA) and polyethyleneimine (PEI).

  As the third polymer, polyglutamic acid (hereinafter, abbreviated as “PGA”) whose molecular formula is shown in the following chemical formula 3 is preferable. Other candidates for the third polymer include carboxymethyl cellulose, polyaspartic acid, alginic acid, and combinations of these substances.

  Here, three polymers of SPA, PEI, and PGA mixed at a high concentration exist as a highly alkaline solution having a pH of 12 in order not to interact with each other. If a high-concentration mixture of these polymers is added to, for example, a biological reaction tank (aeration tank) of an activated sludge treatment apparatus so as to be diluted and mixed about 10,000 to 100,000 times, the SPA has the following chemical formula 4. In addition, the PEI is ionized as shown in the following chemical formula 5.

The SPA carboxylated (—COO ⁻ ) and amino group (—NH ₂ ⁺ ) ionized in water form hydrogen bonds to form a composite polymer having a structure as shown in the following chemical formula 6.

  The ionized carboxyl group of PGA is sterically bonded to the above-described composite polymer to form a microbial adsorption carrier having a steric structure as shown in FIG. In this case, the cationic amino group part of PEI that is not bound to the carboxyl group of SPA functions as a part that electrically binds to negatively charged microorganisms, and the formation of microbial flocs in the biological reaction tank. It fulfills the function to promote.

  First, in order to verify the effect of the present invention, the following experiment was performed.

This experiment was carried out using the JARUS4 type (agricultural settlement wastewater treatment facility) in the Chinen West district sewage treatment facility in Shikiya, Chinen-mura, Shimajiri-gun, Okinawa. When this experiment was conducted, the activated sludge was in a bulking state. The aeration tank used in the experiment was a 200 m ³ batch aeration tank (two parallel tanks), and a single aeration tank and 150 m ³ daily wastewater were treated per day (a total of 300 m ³ because there are two tanks).

  The floc formation promoter according to the present invention was continuously added to the aeration tank at a rate of 1 kg / day (Example section). As a comparative example, no floc formation promoter was added to another batch aeration tank, and the other conditions were the same. The first polymer constituting the floc formation accelerator used in this experiment is sodium polyacrylate, the second polymer is polyethyleneimine, and the third polymer is alginic acid.

Experimental result.
The sludge interface water level after 8 days in the example section to which the floc formation accelerator was added was 2.64 m, and the sludge interface water level after 8 days in the one comparative example section was 3.64 m. The sludge interface water level correlates with the height of the sludge settled, and the smaller the value, the smaller the volume of the sludge and the greater the density. In addition, the state where the bulk volume of sludge is large and the density is small is called bulking. From the results of this experiment, it has been verified that the floc formation accelerator according to the present invention increases the density of activated sludge and is effective in preventing bulking.

  The following experiment was conducted at the wastewater treatment facility of the chemical factory. The waste water treatment machine used in this experiment is a test machine having a 10 L aeration tank and a 6 L settling tank. With this test machine, 14 L of factory effluent per day was treated. The COD concentration of raw water (factory wastewater) was 880 mg / L, and SS was 31 mg / L.

  The floc formation promoter according to the present invention is continuously added to the aeration tank at a pace of 56 mg / day (corresponding to 4 mg / L with respect to the raw water). Performed without addition. In addition, the floc formation promoter used for experiment is the same as that of Example 1.

Experimental result.
Regarding the water quality of treated water (water coming out of the precipitation tank) 10 days after the start of the experiment, COD was 38 mg / L and SS was 55 mg / L in the example section where the floc formation accelerator was added, and the floc formation accelerator was added. In Comparative Example, the COD was 45 mg / L and the SS was 76 mg / L. “COD” is a value of chemical oxygen demand, and is an indicator of water contamination. The smaller this value, the more the activated sludge worked, and the greater the amount of sludge and the greater the sludge activity. It is high. “SS” is a suspended matter value, which is also an indicator of water contamination. The smaller this value, the better the separation between sludge and water in the settling tank. Increases this value.

  From the results of this experiment, it was found that in the example section using the floc formation accelerator, the activity of the sludge is high and the separability between the sludge and water in the settling tank is good.

The following experiment was conducted at the wastewater treatment facility of the chemical factory. The treatment tank used in this experiment is a 3200 m ³ aeration tank and an 800 m ³ precipitation tank, and is a facility that performs 1500 m ³ factory wastewater treatment per day. The floc formation promoter according to the present invention was continuously added to the aeration tank at a pace of 25 kg / day. The floc formation accelerator used in this experiment is the same as in Example 1.

Experimental result.
The activated sludge concentration in the sedimentation tank 10 days after the start of the experiment was MLSS: 17500 mg / L, which was about 35% higher than the activated sludge concentration in the sedimentation tank before the experiment, MLSS: 13000 mg / L. In addition, MLSS is the density | concentration as a suspended substance of activated sludge, and the density of activated sludge is so high that this value is large.

  From the results of this experiment, it has been clarified that the floc formation accelerator according to the present invention contributes to the improvement of the density of activated sludge.

  The present invention relates to microbial floc formation technology, particularly wastewater treatment using an activated sludge treatment method, for example, floc formation promotion technology in a bioreactor tank (aeration tank) when processing wastewater from food factories that are prone to bulking. It can be used as a bulking prevention technology.

It is a figure which shows typically the three-dimensional structure of one Embodiment of the flock formation promoter which concerns on this invention.

Explanation of symbols

SPA Sodium polyacrylate PEI Polyethyleneimine PGA Polyglutamic acid

Claims (8)

A liquid agent for forming microbial flocs in activated sludge,
A linear first polymer having a carboxyl group;
A cationic second polymer having an amino group hydrogen-bonded to the carboxyl group;
A third polymer adsorbed on a composite polymer comprising the first polymer and the second polymer;
At least look at including the,
The third polymer is at least one of polyglutamic acid, carboxymethylcellulose, polyaspartic acid, and alginic acid .   The floc formation promoter according to claim 1, wherein the first polymer is a sodium polyacrylate polymer.   The floc formation promoter according to claim 1, wherein the second polymer is polyethyleneimine. The floc formation promoter according to any one of claims 1 to 3, wherein the third polymer is polyglutamic acid.   An activated sludge treatment method using the floc formation accelerator according to claim 1. 6. The activated sludge treatment method according to claim 5, wherein the floc formation accelerator is added to a biological reaction tank to increase the activated sludge density. 6. The activated sludge treatment method according to claim 5, wherein generation of bulking is prevented by adding the floc formation promoter to a biological reaction tank.   A bulking prevention method using the floc formation accelerator according to claim 1.