JP2005279448A - Flocculant injection method in membrane separation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flocculant injection method in a membrane separation method capable of preventing clogging of a membrane surface while suppressing the use of the flocculant.
SOLUTION: When a mixed solution in a tank is supplied to the membrane surface of a membrane separator 12 immersed in a reaction tank 11 by crossflow and subjected to membrane separation, the upstream side immediately before flowing into the membrane separator 11 into the mixed solution in the tank The flocculant is supplied from the flocculant supply nozzle 17 at the position, and the flocculant is unreacted and present in a high concentration in the flow of the mixed liquid in the tank flowing in the cross flow on the film surface, thereby causing film contamination. The substance is separated from the film surface to suppress adhesion of film contaminants.
[Selection] Figure 1

Description

  The present invention relates to a flocculant injection method in a membrane separation method, and relates to a technique for preventing membrane surface blockage.

Conventionally, as a method for treating organic matter and nitrogen-containing sewage having a high nitrogen concentration, there is a submerged membrane separation activated sludge treatment method in which a membrane separator is used in combination to maintain a high activated sludge concentration in a reaction tank.
In this method, for example, as shown in FIG. 7, sewage from which impurities are removed in the pretreatment facility is stored in a first reaction tank (denitrification tank) 1, and the mixed liquid in the tank is transferred from the first reaction tank 1 at a constant flow rate. While supplying to the 2nd reaction tank (membrane separation tank) 2, it returns to the 1st reaction tank 1 from the 2nd reaction tank 2, and biologically denitrifies while circulating, The 2nd reaction tank In FIG. 2, the solid-liquid is separated by the membrane separation device 3, and the filtrate is discharged through a sterilization tank. In the second reaction tank 2, an upward flow is generated by the air diffused from the diffuser 4, and the mixed liquid in the tank is supplied by cross flow to the membrane surface of the membrane separation device 3 by this upward flow. By causing the upflow of the mixed phase to act as a sweep on the membrane surface, the membrane surface is prevented from being clogged due to adhesion of the separated solid content.
JP 2001-62471 A

  Conventionally, a flocculant is generally used to separate soluble substances (colloidal substances) contained in pollutants in sewage from water, but a large amount of flocculants is required to remove soluble substances. Thus, when the flocculant is injected at a high concentration, not only the flocculant itself is clogged into the pores of the membrane, but also the cost increases. In general, the flocculant is injected into raw water flowing into the treatment system or injected into a reaction tank (membrane separation tank).

  Membrane separation is effective for separating contaminants in sewage, but if there is not very little membrane contaminants (biofilm, etc.), membrane contaminants will clog the membrane pores as water permeates the membrane. It will be different. In other words, when separating sewage containing a lot of membrane contaminants, the membrane separation operation cannot be performed for a long period of time, and it is necessary to periodically perform a backwash operation to clean the membrane surface. When the frequency of operation increases, there is a problem that the operation rate decreases. The membrane is used by hydrophilizing the membrane surface that is inherently hydrophobic, but it becomes hydrophobic as dirt adheres. Most of the adhesion of dirt to the film surface is reversible adsorption, and in order to adhere the adhering substance to other substances, it is necessary to react the flocculant at a certain concentration (threshold) or more. The flocculant concentration and flocculant properties required for the reaction vary depending on the type of target water, and there is a problem of cost when the amount of flocculant used is increased.

  This invention solves the above-mentioned subject, and it aims at providing the flocculant injection method in the membrane separation method which can prevent obstruction | occlusion of a membrane surface, suppressing use of a flocculant.

  In order to solve the above-mentioned problem, the flocculant injection method in the membrane separation method of the present invention described in claim 1 is a method for supplying a liquid to be treated to the membrane surface of the membrane separation device by crossflow and performing membrane separation. The flocculant is supplied at the upstream position immediately before flowing into the membrane separator into the treatment liquid.

With the above-described configuration, the membrane separation apparatus separates the liquid to be processed while suppressing the adhesion of the solid substance that has been separated by applying a cleaning effect to the membrane surface by the liquid to be processed supplied by the cross flow.
Membrane contaminants such as biofilms derived from biological treatment of the liquid to be treated tend to increase over time on the membrane surface of the membrane separator. However, the flocculant supplied to the liquid to be processed at the upstream position immediately before flowing into the membrane separation device is present in a high concentration in the flow of the liquid to be processed flowing on the film surface in a cross flow, and the film adheres to the film surface. The flocculant comes into contact with the pollutant in a concentrated manner, and the adsorbing reaction separates the film pollutant from the film surface to suppress the adhesion of the film pollutant.

  The flocculant injection method in the membrane separation method of the present invention described in claim 2 is a method of immersing a membrane separation apparatus in which a plurality of flat membrane cartridges arranged in the vertical direction are arranged in parallel at a predetermined interval in a reaction tank. Then, the rising air is generated by the aeration air ejected from the diffuser arranged below the membrane separator, the flocculant is supplied at the upper position or the lower position of the diffuser, and the liquid to be treated with the flocculant is raised. The flow is supplied to the flow path between the membrane cartridges in a cross flow.

  With the configuration described above, the upward flow of the solid-gas / liquid mixed phase containing the liquid to be treated, the flocculant, and the aerated air flows into the flow path between the membrane cartridges of the membrane separation device in a cross flow and is washed on the membrane surface of the membrane separation device. Has an effect. At this time, in the laminar flow of the solid-gas-liquid mixed phase of the liquid to be processed flowing in a cross flow on the membrane surface, the flow is covered at the upper position or the lower position of the air diffuser, which is the upstream position immediately before flowing into the membrane separator. The flocculant supplied to the treatment liquid does not diffuse into the reaction tank area outside the membrane separation apparatus, and exists in a high concentration in a narrow area between the membrane cartridges. Are intensively contacted, and the adsorption reaction separates the membrane contaminants from the membrane surface to suppress the adhesion of the membrane contaminants.

  By the way, the flocculant flowing out together with the liquid to be treated from the membrane separation apparatus diffuses into the liquid to be treated in the reaction tank, and is consumed by causing an adsorption reaction on not only the membrane contaminants in the liquid to be treated but also sludge particles. Therefore, when the liquid to be treated that has circulated in the reaction tank flows into the membrane separation device again, the adsorption reaction caused by the coagulant that is associated with the circulation becomes weak. Further, the membrane contaminants generated due to biological treatment in the reaction tank are present at the highest concentration on the membrane surface by membrane separation.

  However, the flocculant supplied to the liquid to be treated at the upper position or the lower position of the air diffuser immediately before flowing into the membrane separation device is unreacted and in a high concentration on the membrane surface. Therefore, even if membrane contaminants are attached to the membrane surface at a high concentration, the flocculant can be maintained at the concentration threshold necessary to sufficiently remove the membrane contaminants and compete in the adsorption reaction. The unreacted fresh flocculant can be selectively concentrated on the membrane contaminants on the membrane surface without being inhibited by the sludge particles, and can exert an adsorption reaction.

  As described above, according to the present invention, the flocculant is not contained in the laminar flow of the liquid to be treated flowing in a cross flow on the membrane surface by supplying the flocculant to the liquid to be treated immediately before flowing into the membrane separation apparatus. The reaction can be present in a fresh state and at a high concentration, and the aggregating agent is selectively concentrated on the membrane contaminants adhering to the membrane surface to cause an adsorption reaction, thereby separating the membrane contaminants from the membrane surface. Thus, adhesion of film contaminants can be suppressed. Accordingly, stable operation can be realized by increasing the permeation rate of the membrane filtrate that permeates the membrane in the membrane separation device and suppressing the operation cost and suppressing the clogging of the membrane surface by the membrane contaminant with the flocculant. Moreover, the injection rate of the flocculant to be added can be minimized and the maximum effect can be exhibited.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Although this embodiment demonstrates the immersion type flat membrane activated sludge method which immerses a membrane separator in a reaction tank, this invention is applicable also when arrange | positioning a membrane separator outside a tank.

  In FIG. 1, a membrane separation device 12 is immersed in a reaction tank 11, the membrane separation device 12 has a membrane filling unit 13, and a suction pump that applies driving pressure (transmembrane differential pressure) to the membrane filling unit 13. 14 is connected. It is also possible to adopt a gravity filtration method instead of the suction pump 14. A diffuser tube 15 of an air diffuser is disposed below the membrane filling unit 13, and a blower 16 is connected to the diffuser tube 15.

  As shown in FIG. 2, the membrane filling unit 13 is composed of membrane cartridges 13a arranged in parallel with a predetermined gap, and each membrane cartridge 13a is formed by arranging organic flat membranes on both side surfaces of the filter plate. Are arranged along the vertical direction. A ceramic membrane or a tube-like membrane can be used for the membrane filling portion 13.

  A flocculant supply nozzle 17 is disposed above the air diffuser 15, and a flocculant tank 19 is connected to the flocculant supply nozzle 17 via a liquid feed pump 18. The flocculating agent to be used is preferably a cationic flocculating agent that does not clog the membrane, and more preferably an organic polymer flocculating agent having a high affinity with a membrane contaminant described later.

  The flocculant supply nozzle 17 can be disposed at a lower position of the air diffuser tube 15 and can be disposed at a plurality of locations. The supplied flocculant is subjected to a strong stirring action by turbulent flow due to the upward flow described later. It is preferable to provide it there. The reaction tank 11 is connected to a sewage supply system 20 that supplies sewage as a liquid to be treated, and a sludge discharge system 21 that discharges excess sludge.

  Hereinafter, the operation of the above-described configuration will be described. The air supplied by the blower 16 is diffused from the diffuser tube 15, and an upward flow is generated by the aerated air ejected from the diffuser tube 15. Further, the flocculant in the flocculant tank 19 is supplied to the flocculant supply nozzle 17 by the liquid feed pump, and the flocculant is in the upward flow at the upper position of the air diffuser 15 immediately before flowing into the membrane separation device 12. The flocculant is supplied from the supply nozzle 17.

  As shown in FIG. 3, the flocculant injected into the upward flow receives a strong stirring action due to the turbulent flow and is uniformly dispersed in the upward flow. As shown in FIG. 2, the upward flow of the solid-gas / liquid mixed phase of the mixed liquid in the tank containing sewage, activated sludge, and flocculant and aerated air is cross-flowed to the flow path between the membrane cartridges 13 a of the membrane separation device 12. And the cleaning effect is given to the membrane surface of the membrane separator 12. The membrane separation device 12 membrane-separates the sewage flowing in by cross flow, and suppresses adhesion of solid matter such as sludge particles separated by membrane by the cleaning effect by the upward flow.

Membrane contaminants such as biofilm derived from activated sludge treatment of sewage tend to increase over time on the membrane surface of each membrane cartridge 13a of the membrane separator 12.
At this time, since the membrane cartridge 13a is a flat membrane type, the solid-gas / liquid mixed-phase flow of the liquid mixture in the tank flowing in a cross flow on the membrane surface flows evenly in one direction. The flocculant supplied immediately before flowing in does not diffuse into the reaction tank internal region outside the membrane separation device 12 and exists in a high concentration in a narrow region between the membrane cartridges 13a.

  For this reason, as shown in FIG. 4 and FIG. 5, the unreacted and high-concentration flocculant 22 is selected with respect to the membrane contaminant 23 adhering to the membrane surface in preference to the sludge particles in the reaction tank. The membrane contaminants 23 are separated from the membrane surface by the adsorption reaction of the organic polymer flocculant 22 having a high affinity and the adhesion of the membrane contaminants 23 is suppressed.

  Therefore, stable operation is possible even if the sludge concentration is operated at a slightly high load, and by using a cationic system that does not easily clog the membrane surface as the flocculant, even if the concentration of the flocculant increases somewhat. Stable operation is possible.

  The flocculant flowing out together with the liquid to be treated from the membrane separation device 12 diffuses into the mixed liquid in the tank inside the reaction tank 11 and causes an adsorption reaction to the sludge particles as well as the membrane contaminants in the mixed liquid in the tank. Is done. Therefore, when the mixed liquid in the tank that has circulated through the reaction tank 11 flows into the membrane separation device 12 again, the adsorption reaction by the coagulant that is associated with the circulation becomes weak. Further, the membrane contaminant generated due to the activated sludge treatment in the reaction tank 11 is present at the highest concentration on the membrane surface by membrane separation.

  However, the flocculant 22 supplied to the mixed liquid in the tank at a position above the air diffuser 15 which is the upstream position immediately before flowing into the membrane separation device 12 is in an unreacted fresh state and at a high concentration on the membrane surface. Therefore, even if the membrane pollutant 23 adheres to the membrane surface at a high concentration, the electroadsorption reaction rate is increased by maintaining the flocculant 22 at a concentration threshold necessary for sufficiently removing the membrane contaminant. The flocculant 22 in an unreacted fresh state can be selectively concentrated on the membrane contaminants 23 on the membrane surface to exert an adsorption reaction.

  The reaction between the flocculant and the membrane contaminant will be described below. A flocculant that is not subject to biodegradation by activated sludge is added to sludge containing membrane pollutants and sludge particles. Immediately after the addition, 50 mL of sludge was sampled at appropriate time intervals, the sampled sludge was dead-end filtered with filter paper, and the amount of filtrate filtered for 5 minutes was measured. FIG. 6 shows the relationship between the elapsed time after adding this flocculant and the filtration rate.

  According to FIG. 6, the amount of filtrate is large immediately after the addition of the flocculant and shows a high filtration rate, but after 10 minutes after the addition of the flocculant, the amount of filtrate decreases and the filtration rate tends to decrease greatly. Further, the filtration rate gradually decreased during several hours.

  This suggests that immediately after the flocculant is added, the membrane pollutant, which has a fast reaction rate with the flocculant, is adsorbed in an instant, and the filter paper is less clogged by the membrane pollutant. The flocculant also reacts with large sludge particles with a slow reaction rate, and the adsorption reaction of the flocculant competes with the membrane pollutant and the sludge particles. Suggests more clogging.

  In the immersion flat membrane activated sludge method described above, the tank capacity / the internal circulation flow rate in the tank is several tens of minutes. For this reason, the method of uniformly injecting the flocculant into the reaction tank cannot obtain the effect of the present invention, and it is unique to the present invention by supplying the flocculant to the liquid to be treated immediately before flowing into the membrane separation device. An effect can be obtained. Also, the higher the concentration of membrane contaminants on the membrane surface, the more flocculant is required, but if the concentration of membrane contaminants is low, the concentration of the flocculant to be injected is lowered or intermittent injection It is also possible.

The schematic diagram which shows the immersion type flat membrane activated sludge method in embodiment of this invention Schematic diagram showing a membrane separator in the submerged flat membrane activated sludge process Schematic showing the spread of coagulant in the submerged flat membrane activated sludge process Schematic diagram showing the adsorption reaction of the flocculant in the submerged flat membrane activated sludge method Schematic diagram showing the adsorption reaction of the flocculant in the submerged flat membrane activated sludge method Graph showing the relationship between the elapsed time since the flocculant was added and the amount of filtrate Schematic diagram showing the conventional membrane separation activated sludge method

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Reaction tank 12 Membrane separator 13 Membrane filling part 13a Membrane cartridge 14 Suction pump 15 Air diffuser 16 Blower 17 Coagulant supply nozzle 18 Liquid feed pump 19 Coagulant tank 20 Sewage supply system 21 Sludge discharge system 22 Coagulant 23 Membrane contaminant

Claims (2)

Membrane separation, characterized in that a flocculant is supplied to the liquid to be treated at the upstream position immediately before flowing into the membrane separation apparatus when the liquid to be treated is supplied to the membrane surface of the membrane separation apparatus by crossflow. Method for injecting the flocculant. A membrane separation device in which a plurality of flat membrane cartridges arranged in the vertical direction are arranged in parallel at a predetermined interval is immersed in a reaction tank, and aerated air is ejected from an air diffuser arranged below the membrane separation device. An ascending flow is generated, the flocculant is supplied at an upper position or a lower position of the air diffuser, and the ascending flow of the liquid to be treated with the flocculant is supplied to the flow path between the membrane cartridges by a cross flow. The flocculant injection method in the membrane separation method according to claim 1.

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