JP2008229613A - Wastewater treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of making the most of the application effect of a flocculant, that is, a technology which can maintain the differential pressure of a membrane stably for a longer time continuously with the same amount of flocculant and keep the risk of membrane function deterioration smaller and, to provide a technology which can reduce the adding amount of the flocculant if it is permissible to have the same degree of an operation risk. <P>SOLUTION: In a wastewater treatment method by a membrane-separation activated sludge method, the membrane is anionic, and a cationic polymetric flocculant is added to the activated sludge. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wastewater treatment method using a membrane separation activated sludge method.

  In recent years, from the viewpoint of improving the quality of treated water, ease of reusing water, and reducing the amount of excess sludge generated, as a method for treating organic wastewater generated at business sites such as municipal sewage, food, chemistry, and electrical / electronics Membrane separation activated sludge method is attracting attention. Here, as membranes for solid-liquid separation of activated sludge, microfiltration membranes and ultrafiltration membranes are mainly used, and they are used in the form of flat membranes, hollow fiber membranes or tubular membranes.

  Here, activated sludge contains a lot of organic gel-like substances composed of polymer polysaccharides, proteins, etc., so when filtering activated sludge with a membrane, the membrane is clogged, dirt adheres to the membrane surface, Alternatively, performance degradation is likely to occur due to sludge accumulation and retention between the membranes. For the purpose of preventing this, a method of performing a filtration with a diffuser provided below the membrane separation device while aeration of coarse bubbles (Patent Document 1) and a method of backwashing using a membrane permeate (Patent Document 2) ) And the like, and a method for efficiently performing the operation while cleaning the membrane surface has been proposed and widely adopted.

However, in the case of wastewater treatment, the treatment conditions are not constant, and there are fluctuations in the quality of the wastewater, the amount of water, the water temperature, and the like. Moreover, depending on conditions, such as when load fluctuation is large, the filterability of activated sludge may deteriorate. When the amount of water temporarily increases or the filterability of activated sludge deteriorates, the differential pressure increases in a relatively short operation even if only the above-mentioned physical membrane cleaning method is used. This leads to a situation where frequent chemical washing is required, and it becomes difficult to operate with high device efficiency. As an effective technique applicable to such a situation, a method (Patent Document 3) for improving the filterability by adding a flocculant to the activated sludge has been proposed, and when the filterability of the activated sludge deteriorates at low water temperature, It is used for peak flow countermeasures after rainfall.
: Japanese Patent Application Laid-Open No. 2001-212587 : JP-A-8-243577 : JP 2007-727 A

  The method of adding a flocculant to activated sludge is a very effective technology, but there are various limitations, and even if a flocculant is added, the differential pressure of the membrane rises in a short time, and it is not possible to prevent performance degradation There is. Moreover, since the addition of the flocculant directly leads to an increase in wastewater treatment cost, a technique that can further enhance the effect of adding the flocculant is desired.

  An object of the present invention is to provide a method for maximizing the application effect of a flocculant. That is, it is to provide a technique with which the differential pressure of the membrane can be stably maintained for a longer period of time with the same amount of the flocculant, and the risk of membrane performance degradation is reduced. When it is acceptable that the risk of film performance degradation is comparable, the object is to provide a technique capable of reducing the amount of flocculant added.

  The present invention is a wastewater treatment method using a membrane separation activated sludge method, wherein the membrane is anionic and a cationic polymer flocculant is added to the activated sludge.

  Although it is different from the wastewater treatment method by the membrane separation activated sludge method, it is known that when a cationic flocculant is added to an anionic crosslinked aromatic polyamide reverse osmosis membrane, the membrane causes chemical fouling. It is assumed that the addition of a cationic polymer flocculant to the activated sludge of the membrane separation activated sludge method using the above membrane causes the same harmful effect. Therefore, it is known to use an anionic membrane and to add a cationic polymer flocculant in the wastewater treatment method by the membrane separation activated sludge method, but it is attempted to combine these technologies. There was no.

  However, the inventors, in the wastewater treatment method by the membrane separation activated sludge method, the membrane is anionic, and even if a cationic polymer flocculant is added to the activated sludge, without causing the above-described adverse effects, It has been found that there is little risk of film performance degradation and the effect of application of the flocculant is maximized.

  When using an anionic membrane instead of a hydrophobic, neutral hydrophilic or cationic membrane as a membrane in a wastewater treatment method using a membrane separation activated sludge method, filtration is performed by using a cationic polymer flocculant. The mechanism that improves the performance is considered to be due to the following reason (FIG. 5). That is, when the activated sludge flocs, which are negatively charged, are increased in size by the addition of the cationic polymer flocculant, the negative charge of the part that has bound to the flocculant is neutralized, but the flocculant is still bound. There is a negative region that is not, and the amount of negative charge as a block of flocs is greatly increased. Along with this, the Coulomb repulsive force acting between the flocs with the anion groups of the membrane greatly increases, so that the flocs aggregated with the cationic flocculant are significantly less likely to adhere to the anion membrane than before the aggregation. The operation under the condition of low filtration resistance, that is, high flux becomes possible (FIG. 5).

  According to the present invention, it is possible to maximize the application effect of the cationic polymer flocculant. That is, with the same amount of the flocculant, the differential pressure of the membrane can be maintained stably for a longer period of time, and operation with less risk of membrane performance degradation is possible. In addition, when the operation risk can be allowed to be the same level, the amount of the cationic polymer flocculant used can be reduced, leading to cost reduction.

  As wastewater treated by the treatment method of the present invention, it can be suitably used for organic wastewater rich in organic matter discharged from municipal sewage, domestic wastewater, chemical factories, food factories and the like. In FIG. 1, an example of the apparatus conceptual diagram which employ | adopted the wastewater treatment method of this invention is shown.

  The treatment apparatus shown in FIG. 1 contains an aeration tank 1 that contains activated sludge and performs biological treatment, a stock solution supply pump 4 that supplies wastewater to the aeration tank 1, and membrane separation that separates the biologically treated treatment liquid into solid and liquid. The apparatus 2 includes a suction pump 3 that sucks a separation liquid during solid-liquid separation, a sludge extraction pump 7 that extracts excess sludge, and a cationic polymer flocculant supply line 8. The membrane separation device 2 is immersed in the liquid in the aeration tank 1, and oxygen is supplied below the membrane separation device 2 to advance the aerobic treatment and to the blower 6 for cleaning the membrane surface. A connected aeration device 5 is provided. In addition to the aeration tank 1 in which the membrane separation device 2 is accommodated, another biological treatment tank, for example, an anaerobic tank, an oxygen-free tank, an aerobic treatment tank, and the like may be provided independently.

  Here, the authors have found that when an anionic membrane is used as the membrane used in the membrane separation device 2, the filtration operation when the polymer cation flocculant is added becomes efficient.

  The anionic membrane in the present invention is a membrane containing an anionic resin. Although it does not specifically limit with anionic resin, Ethylene unsaturated carboxylic acid resin, ethylene unsaturated sulfonic acid resin, and ethylene unsaturated phosphonic acid resin are mention | raise | lifted.

  Here, it is thought that the higher the content of anionic resin in the membrane, the more clogging can be suppressed with respect to the cell suspension, but if it is too high, the anionic resin will elute into the water and the durability and removal performance of the membrane Decreases. Although the lower limit depends on the type of anionic resin, the performance of the present invention can be exhibited when the anionic resin is contained in the film in an amount of 1% by weight or more, preferably 1.5% by weight or more. The anionic resin content is calculated from the charged composition of the anionic resin component in the film after film formation. Solvents, surfactants and other solvents that are eluted during film formation are the values after film formation. It is not included in the film.

  Examples of the ethylenically unsaturated carboxylic acid resin include acrylic acid resin, methacrylic acid resin, crotonic acid resin, α-methylcrotonic acid resin, hexenoic acid resin, and itaconic acid resin. Examples of the ethylenically unsaturated sulfonic acid resin include styrene sulfonic acid resin, acrylic sulfonic acid resin, methacryl sulfonic acid resin, vinyl sulfonic acid resin, and 2-acrylamido-2-methylpropane sulfonic acid resin. Examples of the ethylenically unsaturated phosphonic acid resin include vinyl phosphonic acid resin and vinyl phenyl phosphonic acid resin. The porous membrane of the present invention may be a flat membrane or a hollow fiber membrane.

  The average pore diameter of the membrane is preferably 0.01 μm or more and less than 3 μm. If the average pore diameter is too small, the filtration resistance of the membrane itself is increased, and the water permeability is impaired. On the other hand, if the pore diameter is too large, the activated sludge cannot be completely separated, and the water quality of the permeate is deteriorated.

  The cationic polymer flocculant used in the present invention is not particularly limited, and the jar test is performed arbitrarily or from a preliminary test, etc., from among those commercially available as cationic polymer flocculants from the manufacturer. A material having excellent floc-forming ability may be selected and used. Representative cationic polymer flocculants include (meth) acrylic acid ester polymer flocculants.

  The addition amount of the cationic polymer flocculant is determined based on the solid content weight of the activated sludge, not the amount of waste water. Although the addition amount depends on the properties of the activated sludge, it is preferable to add 0.05 to 2 parts by weight with respect to 100 parts by weight of the total solid content of the aeration tank at the first addition. If the amount is less than 0.05 parts by weight, floc formation due to agglomeration of activated sludge is insufficient, and the effects of the present invention cannot be fully achieved. On the other hand, addition of 2 parts by weight or more is not preferable because it does not have much effect on the coagulation force of activated sludge and the use cost of the cationic polymer flocculant is high, and excessive cationic polymer flocculant is an anion. This may cause direct contamination of the membrane, which is not preferred. It is preferable that the optimum addition amount of the cationic polymer flocculant suitable for the activated sludge on site is periodically grasped based on an index such as filtration test or organic matter concentration or turbidity of the filtrate. For example, when the activated sludge of a certain amount (for example, 50 ml) is filtered using a filter paper, the amount of the cationic polymer flocculant added when the amount of the filtrate after a certain time (for example, after 5 minutes) becomes maximum is X weight. In the case of parts, 0.05X to 1.5X parts by weight can be mentioned as a guideline for suitable addition amount.

  When activated sludge is discharged from the aeration tank as surplus sludge, the solid content of activated sludge that increases until the next sludge discharge is calculated, and a suitable amount of cationic high sludge is added to 100 parts by weight of the solid content of activated sludge. A molecular flocculant may be added. In systems with a long sludge residence time, some cationic polymer flocculants are considered to be decomposed. In this case, in addition to the amount necessary for the increased amount of activated sludge, the decomposition amount of the flocculant added last time is taken into account for the weight part of the total solid content of the aeration tank at the time of addition. It is preferable to add an amount to which the amount to be replenished is added.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited thereby.
Example 1
The filterability in this example was measured as follows. A stirring cell (Amicon (registered trademark) 8010 manufactured by Millipore Corporation, 4.1 cm 2 effective membrane area) filled with a sample to be evaluated is pressurized with nitrogen gas, and permeation per unit time permeating through the membrane The amount of water was weighed with an electronic balance. (Chia-Chi Ho, AL Zydney, Journal of Colloid and Interface Science, 2002. 232 P389). The electronic balance was connected to a computer, and the flux that was the amount of water per membrane surface area was calculated from the change in weight over time. The membrane surface was given a membrane surface flux by the rotation of a magnetic stirrer attached to the stirring cell, the stirring speed of the stirring cell was adjusted to 1,000 rpm, the room temperature, and the evaluation pressure was 1 kPa. The activated sludge was collected from the aeration tank of the membrane separation activated sludge method, and the MLSS concentration was about 15,000 ppm.

  As the cationic polymer flocculant, Sanflock (registered trademark) C-109P (Sanyo Chemical Industries, Ltd.) was used.

  The anion membrane was prepared as follows.

  Polyvinylidene fluoride homopolymer (PVDF, weight average molecular weight 358,000), anionic resin copolymer of methyl methacrylate and methacrylic acid (P (MMA-MAA), polymerization average molecular weight 22,000, copolymerization mole Ratio 7: 3), N, N-dimethylformamide (DMF, manufactured by Mitsubishi Rayon Co., Ltd.), polyoxyethylene sorbidone monostearate (T-60V, manufactured by Sanyo Chemical Industries, Ltd.), ethylene glycol (EG, Wako Pure Chemical Industries, Ltd.), PVDF 16%, P (MMA-MAA) 1%, DMF 71%, T-60V8%, EG 4% with sufficient stirring at a temperature of 100 ° C. and mixed and dissolved. A film-forming stock solution was prepared.

Next, the film-forming stock solution is cooled to 40 ° C., applied to a nonwoven fabric made of polyester fiber having a density of 0.48 g / cm ³ and a thickness of 220 μm, and immediately immersed in a water coagulation bath at 25 ° C. for 5 minutes. A porous substrate on which a porous resin layer was formed was obtained.

This porous substrate was immersed in hot water at 95 ° C. for 2 minutes to wash out DMF, thereby obtaining a porous film. The separation membrane had a pure water permeability coefficient of 54 × 10 ⁻⁹ m ³ / m ² / s / Pa and an average pore diameter of 0.08 μm.

A membrane containing no comparative anionic resin was obtained in the same manner as in the production of the anionic membrane except that PVDF was changed to 17.0% by weight without adding P (MMA-MAA). The pure water permeability coefficient was 44 × 10 ⁻⁹ m ³ / m ² / s / Pa, and the average pore diameter was 0.08 μm.

  Based on the present invention, about 10 ml of a liquid obtained by adding 150 ppm equivalent of Sanflock (registered trademark) C-109P to activated sludge having an MLSS concentration of 15,000 ppm is charged into a stirring cell equipped with an anion membrane, and a flux when pressurized. This change is shown in (21) of FIG.

Comparative Example 1
About 10 ml of a liquid obtained by adding 150 ppm equivalent of Sanflock (registered trademark) C-109P to activated sludge with an MLSS concentration of 15,000 ppm was charged into a stirring cell equipped with a membrane containing no anionic monomer and prepared for comparison. The change of the flux when it is done is shown in (22) of FIG.

Comparative Example 2
FIG. 2 (23) shows changes in flux when charged with about 10 ml of activated sludge having an MLSS concentration of 15,000 ppm and charged in a stirring cell equipped with an anion membrane.

Comparative Example 3
Fig. 2 (24) shows the change in flux when an activated sludge with a MLSS concentration of 15,000 ppm is charged in a stirred cell equipped with a membrane containing no anionic monomer and prepared for comparison. Show.

From the above experimental results, when no anion membrane is used (Comparative Example 1) or when no cationic polymer flocculant is added (Comparative Example 2), no anionic membrane is used and no cationic polymer flocculant is added. Compared with the case (Comparative Example 3), it can be seen that the flux can be maximized in the present invention. When the operation is performed with a constant flux, it can be said that the operation is stable under the condition that the pressure difference across the membrane is the lowest.
Example 2
Acetic acid-based synthetic wastewater is prepared as an industrial wastewater with BOD removal type, and it is operated under the conditions of a TOD volumetric load of 1 g / L / day and a water residence time of 6 to 24 hours. ) Testing was performed using the apparatus. As the membrane, the anion membrane described in Example 1 and the PVDF membrane for comparison were used. Using these membranes, a 14 cm square mini-element was manufactured, and three anion membranes and three comparative membranes were alternately accommodated in a module with an interval of 8 mm, and used for filtration. The membrane module was placed at the top of the air diffuser, in the center of the water depth direction. The water collecting tubes of the three anion membranes and the three comparative membranes were combined into one and suction filtered with a pump, and the suction pressure in units of three elements was measured. As a polymer flocculant, Sunfloc (registered trademark) C-109P was used. The MBR was in a stable operation with a sludge concentration of about 30,000 ppm and a TOC removal rate of 95% or more.

Sun floc (registered trademark) C-109P is added in an amount equivalent to 1% of the sludge dry weight, and the flux is gradually changed to 0.1, 0.2, 0.3, 0.4, 0.6 m / d every 45 minutes. FIG. 3 (31) shows the result of the suction pressure of the anion membrane when the pressure is raised, and FIG. 3 (32) shows the result of the suction pressure of the comparative membrane. It can be seen that the anionic membrane has a lower differential pressure and can be operated with higher flux. It was confirmed that the influence of the permeated water was measured and was at a predetermined flow rate.
Example 3
In the same manner as in Example 2, the final suction pressure was measured when the flux was raised stepwise by 0.05 every 45 minutes, and the relationship between the flux and the suction pressure was plotted. The results of evaluating a certain critical flux are shown in Table 1. As the membrane, a chlorinated polyethylene membrane having a nominal pore diameter of 0.4 μm was used in addition to the anion membrane and PVDF membrane (Comparative membrane 1) described in Example 1 (Comparative membrane 2). From the table, according to the present invention, it is possible to maximize the application effect of the cationic polymer flocculant. That is, by using an anion membrane, it is possible to maintain the differential pressure of the membrane more stably with the same amount of the flocculant, and it is possible to operate with less risk of membrane performance degradation. Moreover, when it can accept | permit that a driving | running risk is comparable, it turns out that reduction of the usage-amount of a cationic polymer flocculant is attained, and it turns out that it leads to cost reduction.

Example 4
Using the evaluation system of Example 2, the flux is 0.8 m / d with MBR having a sludge concentration of about 30,000 ppm and a viscosity of 130 mPa · s (1 m / d during filtration, operation for 8 minutes, intermittent operation for 2 minutes break) FIG. 4 shows the result of comparing the transition of the differential pressure when). The change in the suction pressure of the anion membrane is shown in (41), and the change in the suction pressure of the comparative membrane is shown in (42). From the figure, it can be seen that the limit time for the increase in the differential pressure to increase compared to the initial stage of the operation is improved by about 2 times in the anion membrane, and it is possible to deal with a temporary increase in the amount of treated water with more margin.

It is a conceptual diagram which shows an example of the membrane separation activated sludge method concerning this invention. It is a graph which shows the time-dependent change of the flux in an Example and a comparative example. It is a graph which shows the time-dependent change of the suction pressure in an Example and a comparative example. It is a graph which shows the time-dependent change of the suction pressure in an Example and a comparative example. It is a schematic diagram which shows the presumed mechanism of the principle used as the foundation of this invention.

Explanation of symbols

1: Aeration tank 2: Membrane separation device 3: Suction pump 4: Stock solution supply pump 5: Air diffuser 6: Blower 7: Sludge extraction pump 8: Cationic polymer flocculant supply line 9: Organic waste liquid 10: Clarified liquid (Treated water)
11: surplus sludge 12: floc 13: floc associated with flocculant 14: negatively charged region 15: cationic polymer flocculant 16: Coulomb force (repulsive force)
17: Anion membrane

Claims (1)

  A wastewater treatment method using a membrane separation activated sludge method, wherein the membrane is anionic and a cationic polymer flocculant is added to the activated sludge.

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