JPS61230795A - Treatment of waste water - Google Patents

Abstract

PURPOSE:To perfectly separate activated sludge from treated water, by contacting a liquid to be treated with a pellet wherein bacteria or activated sludge is immobilized in a polymer carrier before performing membrane treatment. CONSTITUTION:Raw water is introduced into an immobilized bacteria treatment apparatus 15 to be contacted with immobilized bacteria. After a suspended substance such as diatomaceous earth is added to the treated water if necessary, said treated water is gathered to a storage tank 16. When a definite amount of water was gathered, a valve 1 is opened and a valve 2 is further opened to introduce treated water into an ultrafiltration module 17 to perform membrane treatment while treated water transmitted through a membrane is stored in a treated water tank 18 through a valve 9. Conc. water not transmitted through the membrane is again treated through valves 3, 4, 5. The conc. water flowing through the valve 5 is supplied to a microstrainer 20 to collect SS and returned to a biological treatment area from a valve 6 along with raw water.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater, particularly a method for treating organic wastewater.

Conventional methods for treating wastewater include biological treatment methods and physicochemical treatment methods. Since sewage, food processing industry wastewater, pharmaceutical industry wastewater, building wastewater, etc. contain a large amount of organic matter, biological treatment methods have become mainstream. Conventionally, the activated sludge method has been used for biological treatment, but since the activated sludge method has a high sludge conversion rate of 5 to 60%, this sludge has been extracted from the settling tank as surplus sludge. Moreover, it is difficult to completely separate activated sludge from treated water, and activated sludge tends to flow out into treated water. Therefore, when the activated sludge treatment liquid is reused, further physicochemical treatments such as flocculation and sedimentation and sand filtration are required.

In response to this, recently, a method has been proposed in which membrane treatment is performed to obtain regenerated liquid instead of subsequent treatments such as settling tanks, coagulation sedimentation, and sand filtration after activated sludge treatment, which saves space and labor. is being planned.

Membrane treatment is a treatment method in which a liquid to be treated is separated into a treated liquid and a concentrated liquid through a membrane using pressure as a driving force, and is classified into reverse osmosis, ultra-legal, and precision-legal.

However, in such membrane treatment, the amount of suspended solids in the liquid greatly affects membrane treatment performance. In other words, if membrane treatment is performed directly after activated sludge treatment, the amount of suspended solids in the membrane-treated liquid will be 20
00 to 20,000 .mu./l, this activated sludge accumulates on the membrane surface, clogging the membrane, reducing the amount of water passing through the membrane, and deteriorating the quality of the treated water.

To prevent this, membrane modules are used that create turbulent flow on the membrane surface, but this still does not solve the problem. In addition, the membrane module types used are the plate-and-frame type and tubular type, which are said to be resistant to contaminants, while the spiral type and hollow fiber type, which have a large throughput per unit volume of light, are unusual. Therefore, it is desired to downsize membrane processing equipment.

Therefore, an object of the present invention is to provide a treatment method that does not cause clogging even when membrane treatment is performed directly after biological treatment, and further allows the membrane treatment apparatus to be miniaturized.

The present invention solves the above problems by using immobilized microorganisms for biological treatment.

That is, in the wastewater treatment method according to the present invention, after the liquid to be treated is brought into contact with pellets in which microorganisms or activated sludge are immobilized inside a polymer carrier, membrane treatment is performed using pressure as a driving force, so that the membrane does not pass through the membrane. The concentrate is characterized in that it is returned to the treated liquid line through the SS separator.

When biological treatment of wastewater is performed using pellets with microorganisms immobilized inside a polymer carrier, the amount of suspended solids generated,
In other words, the amount of suspended solids required for membrane treatment is 1/100 of that when membrane treatment is performed without a sedimentation tank after conventional activated sludge treatment.
~1/1000, and since a compact spiral type or hollow fiber type module is used, the installation area of the membrane treatment device is about 1/20 of the conventional size.

In addition, since microorganisms are encapsulated inside the polymer carrier,
The residence time of the microorganisms themselves becomes longer, and the microorganisms self-digestion inside the polymer carrier. As a result, polymeric substances such as poly-β-hydroxybutyrate (PHB) inside the microorganism leak out of the polymer carrier. Furthermore, humic acids, fulvic acids, etc. due to the metabolism of microorganisms also leak out. Since these leaked materials have a flocculating effect, the suspended solids in the treated water that has been subjected to contact treatment with a polymeric carrier on which microorganisms or activated sludge are immobilized are the suspended solids obtained by the conventional activated sludge method. The particle size becomes larger. When such a liquid is treated with a membrane, the amount of water permeated through the membrane increases.

This can be explained as follows. The permeation flow rate through the membrane when a polluted layer is formed on the membrane surface is expressed by the following formula.

Jv= (ΔP−Δyr)/(Rn+ +Rg)
・ ・ (1) In formula c, Jv represents the permeation flow rate, and Δ
P represents the pressure difference between both sides of the membrane, and Δπ can be ignored because Δp>>Δπ when a polluted layer is formed on the membrane surface.

R- represents the resistance of the membrane, and Rg represents the resistance of the contaminated layer].

The transient resistance during membrane processing is expressed as the sum of Rm and Rg,
When a contamination layer is formed on the membrane surface, Rm<<Rg
Therefore, the following Kozeny Karmay (Kozeny
-Cars+an) can be replaced by the following equation: where, 5v=6/φC-dp [In the formula, 5v=6/φC-dp [In the formula, Sae is the transient average resistivity, and ε is the porosity of the polluted layer. , ρ
is the particle density, k is the Kozeni constant, Sv is the specific surface area of the particle, -0 is the shape coefficient, and dp is the representative diameter of the particle].

According to equation (2), it can be seen that the larger the particle size of the suspended solids, that is, dp, the smaller - becomes. That is, since the transient resistance during membrane processing is small, the transient flow rate in equation (1) increases.

Furthermore, as can be seen from equation (2), by increasing the particle size and increasing the porosity, the sharpness can be decreased. As a means for this purpose, in addition to suspended particles such as diatomaceous earth, kaolin, and fine plastic particles, which are generally used as temporary aids, it is also effective to add a polymer flocculant.

The amount of these suspended particles added is preferably 10% or more of the amount of suspended solids generated when wastewater is subjected to contact treatment with pellets on which microorganisms or activated sludge are immobilized.

The microorganisms used for wastewater treatment may be pure cultures of bacteria, molds, yeasts, actinomycetes, algae, etc., or mixed culture microorganisms, or activated sludge of sewage, industrial wastewater, etc.

Examples of polymer carriers include acrylic resins, epoxy resins, acrylamide resins, acrylimide resins, styrene resins, polyurethane resins, vinyl resins, polysaccharide derivatives, and inorganic materials such as alkylated porous glass. Any polymeric substance can be used as long as it solidifies when left at room temperature or at a temperature that does not kill microorganisms and does not release microorganisms into the liquid after solidification.

The membrane material used for membrane treatment is preferably a material to which suspended solids are difficult to adhere and which can be peeled off with a slight physical force.

The membrane material can be evaluated by its adhesion work to water in the air, and as a result of ultrasonic cleaning, as shown in Figure 1, it has a hydrophobicity of 80 taJ/ld or less, or 105 mJ.
/n? The above hydrophilic membrane materials are preferred. Preferred materials include, for example, Teflon-based, polycarbonate-based, polysulfone-based, cellulose acetate-based, polyvinyl alcohol-based, polysancharide-based, or modified products thereof.

The work of adhesion can be calculated from the following equation by measuring the contact angle of water droplets on the film surface.

WA=Kvo(cosθ+1)−−−・−(3)
[In the formula, WA is the contact work with respect to water in the air, Kv
o is the surface tension of water, 72.8 mJ/rs? (20℃)
and θ is the measured contact angle].

When suspended substances adhere to the membrane surface during membrane treatment, the effects of physical cleaning such as flushing and backwashing become clear by using these membrane materials.

For example, when sewage is treated with activated sludge and then subjected to direct membrane treatment to form a turbid layer and then flushed, a polyamide membrane with a contact work of 99.1 taJ/rd has a recovery rate of 5. %, whereas contact work? For the 0.4 taJ/rd polysulfone membrane, the recovery rate by washing was 35%.

Regarding the molecular weight cutoff of the membrane, since the BOD of recycled water needs to be 5 or less, the molecular weight cutoff is 100.000.
Preference is given to using the following membranes:

Next, the present invention will be explained in detail based on the drawings.

FIG. 2 is a flow sheet showing one embodiment of the method of the present invention, and mainly includes an immobilized microorganism treatment device 15, a storage tank 16
, an ultra-violet module 17, a treatment layer 18, a microstrainer 20, an ultrasonic oscillator 21 and a precipitation layer 22.

When treating wastewater in this device, raw water is first introduced into the immobilized microorganism treatment device 15, where it is brought into contact with the immobilized microorganisms, and then, if necessary, suspended solids such as diatoms are removed. After addition, it is collected in storage tank 16. When a certain amount of water has collected, open valve 1, then open valve 2.
, and pump 14 causes the limit? The sample is introduced into the filter module 17 and subjected to membrane treatment. l1ll! The treated water that has passed through passes through the valve 9 and is stored in the treated water 18. The retentate that does not pass through the membrane is reprocessed via valves 3.4 and 5. Concentrated water flowing through valve 5 has SS captured by a micro strainer 20 equipped with an ultrasonic oscillator 21, and then passes through valve 6.
The water is then returned to microbial treatment along with the raw water.

In this device, other flow paths than those described above can also be used. Hit, open valve 7, close valve 2, close valve 7
It is also possible to provide a flow path in which the water to be treated is introduced into the ultrafiltration module 17 and the concentrated water is discharged from the valve 8.

In this way, changing the flow path reverses the direction of water flowing into the module, thereby preventing blockage within the module. Therefore, it is preferable to switch and use these channels at regular time intervals.

After switching the flow path and operating for a certain period of time, close valves 1.4.6.8 and 9 to push out the raw water in the pump and lines, and then close valves 2.3.5.7, l0111 and 13.
is opened, and the treated water in the treated water tank 18 is allowed to flow using the valve 12 as an adjustment valve. At this time, a cartridge filter 19 is installed to prevent the treated water line from being contaminated.

Next, limit? The filter module 17 is backwashed. This backwashing is performed by closing the valve 7 following the raw water extrusion step described above. In this device, backwash water is introduced into the micro strainer 20 through valves 3 and 5, the ultrasonic oscillator 21 is turned on, the SS captured by the micro strainer 20 is cleaned with ultrasonic waves, and the sedimentation tank 22 is washed with ultrasonic waves.
SS is precipitated and separated, and recovered as sludge. The supernatant water is returned to the raw water line.

Such a device allows stable treatment over long periods of time using only one pump.

EXAMPLES Next, the present invention will be explained in detail based on Examples, but the present invention is not limited thereto.

Example 1 Raw water with ssso/l and BOD of 52/1 was treated with the apparatus shown in FIG.

At that time, the activated sludge was comprehensively fixed in a polyacrylamide gel using a conventional method, acclimatized, and the volume of the activated pellets was 5J! of immobilized microorganisms.

In addition, the ultra-violet module has a molecular weight cut-off of 5000.
A membrane made of polysulfone hollow fibers with an inner diameter of 1.1 m++m and an adhesion work of 70.4 mJ/rd was used with a membrane area of 610 d.

When raw water flows into an immobilized microorganism treatment device and is brought into contact with immobilized microorganisms within the device for a residence time of 3 hours, 5S19
Treated water with a BODI of ■/l and a BODI of O■/β was obtained. Diatom ±100■/It was added to this treated water, and the storage tank 16
After stirring at , membrane treatment is performed. First, membrane treatment was carried out for 15 minutes by introducing the ultrafiltration module through valve 2, and then switching to the flow path passing through valve 7, and doing the same for 15 minutes.
Separation membrane treatment was performed, and this switching was performed four times to perform normal operation for a total of 60 minutes. The concentrated water was returned to the raw water line via valves 4 and 5.

Thereafter, treated water was allowed to flow through valves 1011 and 7 for 10 seconds to push out the raw water in the pump and lines. Then, valves 2 and 7 are closed, and the treated water is pumped to a pressure of 3 kg/- for backwashing the ultrafiltration module.
Seconds passed. The backwash water was passed through a microstrainer with a mesh width of 100 μm. Furthermore, the microstrainer was cleaned using ultrasonic waves for 20 seconds.

By repeating the above cycle, the ss concentration is almost O and the treated water with a BOD of less than 2■/l is reduced to 30 f
/d processing efficiency.

Example 2 The following three types of treatment experiments were conducted using initial settling overflow water of sewage as raw water.

(A) Conventional activated sludge treatment (MLSS=2000■/l
), and then directly treated with a hollow fiber module made of polyamide membrane with an adhesion work of 99.1 mJ/ryl (
comparative example).

(B) The fixed activated sludge pellets used in Example 1 were used as a fluidized bed to treat sewage under aerobic conditions, and the resulting treated water with an amount of suspended solids of 20 μ/It was passed through the same module as in (A). In the case of membrane treatment (Invention 1) (C) In place of the membrane module of (B), a hollow fiber module of polysulfone membrane with an adhesion work of 70.4 mJ/rrl was used (Invention 2).

In addition, the conditions for membrane treatment are as follows in any case. Effective membrane area is 47ai1, molecular weight cutoff is 5000
0, operating pressure is l kg/ca, flow rate is 11/min,
Back pressure washing with overwater (pressure 3k) once every 15 minutes.
g/cm).

The treatment was carried out for 50 hours, and the change in the amount of permeated water over time was measured. The results are shown in FIG.

According to the present invention, it is possible to prevent clogging of the membrane due to SS, that is, a decrease in the amount of permeated water.

Example 3 A treatment device using initial settling overflow water of sewage as wastewater was as follows:
It consists of a biological treatment section at the front stage, a membrane treatment section at the rear stage, and a micro strainer in the membrane concentrate line.

In the first stage, pellets of activated sludge entrapping and fixing with polyacrylamide were filled into a 1.22 reaction tank so that the sludge concentration was 30,000 μ/l and the filling rate was 30%.

The amount of inflow water is 9.61/d, and lAl1 flows into the membrane treatment section.
Water was passed for 1 minute, and the concentrated liquid was circulated to the pre-processing section through a micro strainer.

The membrane processing section is composed of 10 polysulfone hollow fibers each having an inner diameter of 1.5 taya and a length of 10 cm.

Perform backwashing with temporary water once every 15 minutes, and
After operating for an hour, the amount of permeated water is 0.5rrr/1rid (
25°C).

In the above experiment, Celite 535 [trademark,
Johns-Manvi 11
e) Force-calcined diatomaceous earth particles] were added to account for 50% of the amount of suspended solids in the biologically treated water to form a layer of suspended solids on the membrane surface, and the same experiment as above was conducted. As a result, the amount of permeated water 50 hours after the start of operation increased by 1.22#d (25°C).

According to the present invention, by combining immobilized microorganism treatment and membrane treatment, clogging of the membrane due to SS can be prevented, and treatment can be carried out efficiently for a long time. That is, according to the present invention, a decrease in the amount of permeated water can be prevented. Furthermore, in the present invention, when a membrane made of a specific material is used for membrane treatment, the clogging prevention effect is significantly increased. Furthermore, if suspended particles such as kaolin are added to the water to be treated before membrane treatment, the effect of preventing clogging becomes significant.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between the adhesion work of the membrane and the peeling rate of SS, Fig. 2 is a flow sheet showing an embodiment of the method of the present invention, and Fig. 3 is a graph showing the results of Example 2 of the amount of permeated water over time. It is a graph showing changes.

Claims (3)

[Claims] (1) After the liquid to be treated is brought into contact with pellets in which microorganisms or activated sludge are immobilized inside a polymer carrier, membrane treatment is performed using pressure as the driving force, and the concentrated liquid that does not pass through the membrane is passed through an SS separator. , a method for treating wastewater characterized by returning it to a treated liquid line. (2) The contact work for water in the air is 80 mJ/
2. The processing method according to claim 1, wherein the membrane treatment is carried out using a membrane module made of a membrane of a material having a power of less than m^2 or more than 105 mJ/m^2. (3) The method according to claim 1 or 2, wherein suspended particles such as diatomaceous earth, kaolin, plastic particles, or a polymer flocculant are added before the membrane treatment.