WO2010021422A1

WO2010021422A1 - Apparatus and method for high flux membrane wastewater treatment using early stage control of membrane fouling

Info

Publication number: WO2010021422A1
Application number: PCT/KR2008/004984
Authority: WO
Inventors: Hyung Soo Kim; Uk Jae Lee; Kwan Yeop Kim; Eui Jong Lee; Yu Mee Na
Original assignee: Tae Young Construction Co., Ltd.; Taeyoungentec Co., Ltd.
Priority date: 2008-08-21
Filing date: 2008-08-26
Publication date: 2010-02-25
Also published as: KR20100023383A; KR101005422B1

Abstract

There are provided an apparatus and method for treating wastewater in a high flux membrane capable of performing high-flux filtrations by performing an agent backwashing operation under the automatic control of early fouling of the submerged membranes. The agent backwashing operation under the automatic control of the early fouling is performed by continuing to perform the filtration without an agent backwashing operation when a rate in pressure change calculated from the transmembrane pressure difference of the submerged membranes is maintained constantly, and is to perform an agent backwashing operation in order to remove contaminants from the initial membranes when the calculated rate in pressure change is increased suddenly. The apparatus and method according to the present invention may be useful to improve filtration performances of membranes 2 times by effectively controlling early fouling of the membrane, and to reduce the number of used membranes and used accessory equipments, which are required for membrane filtration, by 1/2.

Description

APPARATUS AND METHOD FOR HIGH FLUX MEMBRANE WASTEWATER TREATMENT USING EARLY STAGE CONTROL OF MEMBRANE FOULING

Technical Field

[1] The present invention relates to an apparatus and method for treating wastewater, and more particularly to an apparatus and method for treating wastewater in a high flux membrane capable of improving filtration performances by effectively controlling early fouling of the membranes. Background Art

[2] A membrane separation activated sludge process has advantages in that filtered water may be stably obtained by performing solid-liquid separation from membrane and maintaining a high concentration of microorganisms in a bioreactor, and the bioreactor may be significantly reduced in size and driven automatically.

[3] In spite of the various advantages, the membrane separation activated sludge process has problems in that the process is difficult to be commercialized. This is why excessive initial investment costs and energy costs are very high in the use of membranes, and the membranes should be washed or exchanged when they are fouled. Therefore, there has been attempts to enhance an amount (flux, 1/nf/h) of filtered water per membrane area in order to minimize the use of the membranes. However, because a fouling rate of the membranes is increased with the increase in flux, the membrane separation activated sludge process has a disadvantage in that it should be in operation under a suitable flux, so-called a critical flux. In order to maintain stable filtration performances, a flux of 201/nf/h has been used in most of the membrane separation activated sludge processes using a hollow fiber membrane of PVDF material.

[4] When the membrane filtration is performed under a critical flux, the fouling of separation membranes makes slow progress. Therefore, when the filtration performances of membranes are stably maintained but reach their uppermost limit, the membranes are rapidly fouled, which leads to the sudden deterioration in the filtration performances. Accordingly, maintenance cleaning of the membranes is periodically performed in order to prevent the sudden deterioration of the membranes by adding chemical agents during a backwash process. However, this maintenance cleaning process has problems in that it is necessary to use a separate agent backwashing pump. Even if maintenance cleaning is performed, the membrane filtration should not be performed at greater than a critical flux. Disclosure of Invention Technical Problem

[5] The present invention is designed to solve the problems of the prior art, and therefore an object of the present invention is related to an operation of filtering a high flux membrane at greater than a critical flux by effectively removing contaminants from membranes at an early stage of the fouling of the membrane.

[6] Also, another object of the present invention is related to reducing the number of used membranes and used accessory equipments (including a valve, a suction pump, a blower and the like that are required for membrane filtration) by 1/2 by performing the membrane filtration at a high flux of 401/nf/hr that is higher twice than the conventional membrane separation activated sludge process. Technical Solution

[7] According to an aspect of the present invention, there is provided an apparatus for treating wastewater through high flux membranes under the control of early fouling of the membranes, comprising a membrane separation activated sludge unit having submerged membranes installed therein and a filtration/backwash unit. In this case, the filtration/backwash unit comprises a filtered water storage tank, a backwash agent pump, automatic valves, a pressure gauge and an automatic control unit. Here, the filtered water storage tank may store water filtered through the submerged membranes during a filtration process. The backwash agent pump may supply a backwash agent through a backwash line in backwashing the backwash agent. The automatic valves may control a flow of the filtered water between the submerged membranes and the filtered water storage tank. The pressure gauge may measure the transmembrane pressure difference. And, the automatic control unit may calculate a rate in pressure change using the measured transmembrane pressure difference, continue to performing the filtration when the calculated a rate in pressure change is maintained constantly and supply the filtered water in the filtered water storage tank to the submerged membranes under the control of the automatic valve when the calculated a rate in pressure change is changed suddenly, wherein an agent backwashing process is performed by mixing the backwash agent in the filtered water and supplying the resulting mixture to the submerged membranes.

[8] According to another aspect of the present invention, there is provided a method for treating wastewater through high flux membranes. The method for treating wastewater may comprise: filtering contaminants through the submerged membranes; calculating a rate in pressure change calculated from the transmembrane pressure difference of the submerged membranes; performing the filtration when the calculated a rate in pressure change is maintained constantly; performing the backwash with filtered water that stored in filtered water storage tank when the calculated a rate in pressure change is increased suddenly, wherein the backwash agent is mixed in the filtered water to inject the resulting mixture to the submerged membranes and the injected mixture is settled stationarily for a predetermined period in order to dissolve contaminants in the submerged membranes and remove the dissolved contaminants from the submerged membranes.

Advantageous Effects

[9] The method for treating wastewater through high flux membranes under the control of early fouling of the high flux membranes according to one exemplary embodiment of the present may be useful to reduce the number of used membranes and used accessory equipments (including a valve, a suction pump, a blower and the like that are required for membrane filtration) by 1/2 since contaminants are removed from high flux membranes at an early stage through the filtrations.

[10] Also, the apparatus for treating wastewater according to one exemplary embodiment of the present may be useful to make the installation and maintenance more easy and economical since one pump is used for the both function without additional installation of a filter pump for sucMng in filtered water for filtrations and a backwash pump for supplying a backwash solution submerged membrane. Brief Description of the Drawings

[11] FIG. 1 is a diagram illustrating a schematic configuration of an apparatus for treating wastewater through high flux membrane under the control of early fouling of the membrane according to one exemplary embodiment of the present invention.

[12] FIG. 2 is a diagram illustrating filtration operations of the apparatus for treating wastewater through high flux membrane under the control of early fouling of the membrane according to one exemplary embodiment of the present invention.

[13] FIG. 3 is a diagram illustrating an agent backwashing operation of the apparatus for treating wastewater through high flux membrane under the control of early fouling of the membrane according to one exemplary embodiment of the present invention.

[14] FIG. 4 is a flowchart illustrating a method for treating wastewater through high flux membrane under the control of early fouling of the membrane according to one exemplary embodiment of the present invention.

Best Mode for Carrying Out the Invention

[15] Hereinafter, exemplary embodiment of the present invention will be described in more detail with reference to the accompanying drawings.

[16] FIG. 1 is a diagram illustrating a schematic configuration of an apparatus for treating wastewater through high flux membrane under the control of early fouling of the membrane according to one exemplary embodiment of the present invention. In this case, the apparatus for treating wastewater according to one exemplary embodiment of the present invention includes a submerged membrane separation activated sludge unit 100 and a filtration/backwash unit 200.

[17] The submerged membrane separation activated sludge unit 100 includes an anaerobic tank 111, an anoxic tank 112 and a membrane separation aerobic tank 113. Raw water flowing in the anaerobic tank 111 flows through the anoxic tank 112 into the membrane separation aerobic tank 113. Also, sludge in the membrane separation aerobic tank 113 is returned to the anoxic tank 112 by means of a first sludge return unit 130, and sludge in the anoxic tank 112 is returned to the anaerobic tank 111 by means of a second sludge return unit 140.

[18] Here, a phosphorus is discharged from microorganisms in the anaerobic tank 111.

Nitrate nitrogen is reduced into nitrogen gas in the anoxic tank 112, the nitrogen is then removed. And, ammonia nitrogen in intake water is oxidized into nitrate nitrogen, a phosphorus in the intake water is excessively fed by microorganisms, and organic matters in the intake water is oxidized and removed by the microorganisms in the membrane separation aerobic tank 113. The phosphorus excessively fed by the microorganisms in the membrane separation aerobic tank 113 is removed by removing the microorganisms in the sludge discharged by the sludge discharge pump 150. A sludge discharge pump 150 for intermittently discharging sludge is installed in an outer lower portion of the membrane separation aerobic tank 113. A submerged membrane 114 for filtering solids is installed inside the membrane separation aerobic tank 113. In order to prevent the filtered solids from being attached to the submerged membrane 114, a first air diffuser unit 115 is installed in a lower portion of the submerged membrane 114. A second air diffuser unit 116 is installed in order to supply oxygen required for growth of the microorganisms in the membrane separation aerobic tank 113. In order to supply air to the first air diffuser unit 115 and the second air diffuser unit 116, an air supply unit 120 is installed outside the membrane separation aerobic tank 113.

[19] The filtration/backwash unit 200 includes a filtration/backwash pump 430, a pressure gauge 260 and an automatic control unit 250. And, filtration/backwash unit 200 further includes automatic valves 210, 220, 230 and 240, a filtered water storage tank 310 and a backwash agent pump 420. Here, the automatic valves 210, 220, 230 and 240 functions to control filtration and agent backwashing directions, and a backwash agent is stored in a backwash agent tank 410.

[20] The filtration/backwash pump 430 sucks in filtered water during a filtering by the submerged membrane 114, and transfers the filtered water to the filtered water storage tank 310, and the filtered water in the filtered water storage tank 310 is injected into the submerged membrane 114 to backwash the submerged membrane 114 with a backwash agent. In the case of the conventional membrane separation activated sludge process, a filter pump for sucMng in filtered water for filtrations and a backwash pump for supplying a backwash solution in backwashing a submerged membrane with a backwash agent are additionally installed, but the filtration/backwash pump 430 is used together for the filtration and agent backwashing operations in the present invention.

[21] The pressure gauge 260 functions to measure a transmembrane pressure difference, and the automatic control unit 250 functions to receive the transmembrane pressure difference measured in the pressure gauge 260 to calculate rate in pressure change, and control the operations of the backwash agent pump 420 and the openings and closings of the automatic valves 210, 220, 230 and 240 during the filtration and agent backwashing operations. The automatic valves consist of four valves 210, 220, 230 and 240. The first automatic valve 210 controls a flow of filtered water so that the filtered water can be transferred to the filtration/backwash pump 430 during the filtration operation. The second automatic valve 220 controls a flow of filtered water so that the filtered water can be transferred to the filtered water storage tank 310 via the filtration/backwash pump 430 during the filtration operation. The third automatic valve 230 controls a flow of filtered water stored in the filtered water storage tank 310 so that the filtered water can be transferred to the filtration/backwash pump 430 during the agent backwashing operation. And, the fourth automatic valve 240 controls a flow of filtered water stored in the filtered water storage tank 310 so that the filtered water can be transferred to the submerged membrane 114 via the filtration/backwash pump 430 during the agent backwashing operation.

[22] Hereinafter, the method for treating wastewater through high flux membrane under the control of early fouling of the membrane according to one exemplary embodiment of the present invention will be described in more detail with reference to FIGS. 2 to 4.

[23] First, a wastewater is filtered by the submerged membrane 114 to produce filtered water (Sl 1). That is to say, FIG. 2 shows filtration operations of the apparatus for treating wastewater through high flux membrane under the control of early fouling of the membrane. Here, a filter line 300 is formed by opening the first automatic valve 210 and the second automatic valve 220 and closing the third automatic valve 230 and the fourth automatic valve 240.

[24] Raw water flowing in the anaerobic tank 111 of the submerged membrane separation activated sludge unit 100 is passed through the anoxic tank 112, and then flows in the membrane separation aerobic tank 113. Sludge in the membrane separation aerobic tank 113 is returned to the anoxic tank 112 by means of the first sludge return unit 130 and sludge in the anoxic tank 112 is returned to the anaerobic tank 111 by means of the second sludge return unit 140.

[25] Also, solids in the membrane separation aerobic tank 113 are filtered by a surface of the submerged membrane 114 during a filtration operation, and only the filtered water flows in the separation membrane. In this case, the solids attached to the surface of the submerged membrane 114 are removed off by rising up the air, which is supplied from the air supply unit 120, in the form of bubbles through the first air diffuser unit 115 installed in a lower portion of the submerged membrane 114.

[26] Next, a rate in pressure change calculated from the transmembrane pressure difference of the submerged membrane 114 is calculated (S 12).

[27] When the calculation result of operation S 12 shows that a rate in pressure change is maintained constantly, the filtration operation SI l continues to be performed.

[28] On the contrary, when the calculation result of operation S 12 shows that the rate in pressure change obtained from the transmembrane pressure difference is increased suddenly, the submerged membrane 114 is backwashed with a backwash agent (S 14). Here, the backwashing of the submerged membrane 114 with a backwash agent is performed by transferring a backwash solution including filtered water and a backwash agent to the submerged membrane 114 in an opposite direction to the filtration direction, wherein the automatic control unit 250 receives a transmembrane pressure detected by the pressure gauge 260 and calculates a rate in pressure change (ΔP/ΔT), i.e. a membrane fouling rate to control the openings and closings of the respective automatic valves 210, 220, 230 and 240, and determines which processes is performed, filtration of bachwash. [29] FIG. 3 shows an agent backwashing operation of the apparatus for treating wastewater through high flux membrane under the control of early fouling of the membrane according to one exemplary embodiment of the present invention. Here, a backwash line 400 is formed by closing the first automatic valve 210 and the second automatic valve 220 and opening the third automatic valve 230 and the fourth automatic valve 240.

[30] Filtered water in the filtered water storage tank 310 is supplied to the backwash line

400 by means of the filtration/backwash pump 430, and then mixed in a predetermined position with a backwash agent injected through the backwash agent pump 420. Reversible membrane contaminants attached to a surface or inside of the separation membrane are detached from the separation membrane by injecting the mixed backwash solution to the submerged membrane 114 for a predetermined time in order to backwash the submerged membrane 114. After the backwashing of the submerged membrane 114, all of the automatic valves 210, 220, 230 and 240 are closed by a signal of the automatic control unit 250, and an operation of the filtration/backwash pump 430 is suspended and settled stationarily for a predetermined period while the submerged membrane 114 is filled with the backwash solution. This is to dissolve and remove the reversible membrane contaminants from the backwash solution by their chemical reaction in the backwash solution.

[31] This agent backwashing process may be used to remove the membrane contaminants at a early fouling stage by treatment of the lower concentration agent than the conventional chemical detergents, and to sustain the stable membrane filtration even at a high flux (401/m²/hr).

[32] Any of backwash agents may be used if the backwash agents are effective in washing the submerged membrane 114. Preferably, sodium hypochlorite (NaOCl) is used as the backwash agent. This is why the sodium hypochlorite (NaOCl) is economical, and also effective in washing the submerged membrane 114 in the membrane separation activated sludge process.

[33] When a series of the backwashing operations are completed, the filtration performances of the submerged membrane 114 are recovered, and therefore the submerged membrane 114 is used again for another filtration operation (Sl 1).

[34] An amount of the filtered water used during the agent backwashing operation may be varied according to the shapes and sizes of the submerged membrane 114. In this case, the filtered water is used at an amount of 10 to 401 per membrane module, and sodium hypochlorite is used at a concentration of 0.01 to 0.06 % in the backwash solution including the filtered water and the backwash agent. When the concentration of the sodium hypochlorite in the backwash solution is less than 0.01 %, a washing effect is low, whereas the economic burden is high due to the increased amount of the sodium hypochlorite in the backwash solution when the concentration of the sodium hypochlorite in the backwash solution exceeds 0.06 %.

[35] In the case of the agent backwashing operation, the injection time of the backwash solution is set to 2 to 5 minutes, the backwash flux is set to 401/m²/hr that is identical to that in the filtration operation, and the settling time is set to 30 to 60 minutes, but the total time is adjustable according to the operation situations and the like.

[36] The exemplary embodiments of the present invention have been described in detail.

However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description. Industrial Applicability

[37] As described above, the apparatus according to one exemplary embodiment of the present invention may be useful to operate at a high flux of more than 401/m²/hr by backwashing a high flux membrane with a backwash agent at an early state of the fouling of the membrane to recover the high flux membrane into an initial state, thus to improve the filtration efficiency.

[38] Also, the apparatus according to one exemplary embodiment of the present invention may be useful to improve the economical efficiency since the filtration/backwash pump may be used together for the filtration and agent backwashing operations, and it is unnecessary to install a separate backwash solution tank by mixing the backwash agent and the filtered water in the backwash line.

Claims

[1] An apparatus for treating wastewater under the control of early fouling of a membrane, comprising a membrane separation activated sludge unit having submerged membranes installed therein and a filtration/backwash unit, wherein the filtration/backwash unit comprises: a filtered water storage tank storing a water filtered through the submerged membranes during a suction and filtration process; a backwash agent pump supplying a backwash agent through a backwash line in backwashing the backwash agent; an automatic valves controlling a flow of the filtered water between the submerged membranes and the filtered water storage tank; a pressure gauge measuring the transmembrane pressure difference between the submerged membranes; and an automatic control unit calculating a rate in pressure change using the measured transmembrane pressure difference, continuing to performing the filtration when the calculated rate in pressure change is maintained constantly and performing the backwash with the filtered water that is stored in the filtered water storage tank when the calculated a rate in pressure change is increased suddenly, wherein an agent backwashing process is performed by mixing the backwash agent in the filtered water and supplying the resulting mixture to the submerged membranes.

[2] The apparatus for treating wastewater according to claim 1, wherein a concentration of sodium hypochlorite (NaOCl) in a backwash solution including the filtered water and the backwash agent is in a range from 0.01 to 0.06 %.

[3] The apparatus for treating wastewater according to claim 1, wherein the filtration is performed at a high flux (401/nf/h) when the submerged membranes a hollow fiber membranes made of PVDF material.

[4] A method for treating wastewater in the apparatus according to any of claims 1 to 3, comprising: filtering contaminants through the submerged membranes; calculating a rate in pressure change calculated from the transmembrane pressure difference of the submerged membranes; performing the filtration when the calculated a rate in pressure change is maintained constantly; and performing the backwash with backwash solution when the calculated rate in pressure change is increased suddenly, wherein the backwash agent is mixed in the filtered water to inject the resulting mixture to the submerged membranes and the injected mixture is settled stationarily for a predetermined period in order to dissolve contaminants in the submerged membranes and remove the dissolved contaminants from the submerged membranes. [5] The method for treating wastewater according to claim 4, wherein the backwashing with the backwash agent comprises: mixing the backwash agent in the filtered water to inject the resulting mixture to the submerged membranes for 2 to 5 minutes at the same high flux as the filtration operation, and stationarily settling the injected mixture for 30 to 60 minutes in order to dissolve contaminants in the submerged membranes and remove the dissolved contaminants from the submerged membranes.