CN100375648C - On-line chemical cleaning method for membrane-bioreactor - Google Patents

Abstract

The present invention discloses an on-line chemical cleaning method for control the membrane pollution of membrane-bioreactors, which belongs to the technical field of water and wastewater treatment and purification. The present invention uses alkali washing as a core accompanied with acid washing, and aiming at a small-scale membrane-bioreactor, a large-scale membrane-bioreactor and a medium-scale membrane-bioreactor, the present invention recommends two corresponding cleaning modes (a fixed cleaning period and a cleaning period controlled by a TMP development speed). The present invention can effectively clean membrane hole blockage and gel layer pollution which are formed from macromolecular organic matter and colloidal matter so as to restore membrane filtering capacity, and has the advantages of easy operation and low maintenance cost. The present invention can realize the long-term and stable operation of a membrane module, extend the service life of the membrane module and reduce the maintenance cost of the membrane module so as to ensure the long-term operating stability of the membrane-bioreactors in scale engineering application, and reduces the operation cost of the membrane-bioreactor.

Description

On-line chemical cleaning method for membrane-bioreactor

technical field

The invention belongs to the technical field of water and waste water treatment and purification, in particular to an online chemical cleaning method for membrane-bioreactors for controlling membrane pollution in membrane-bioreactors.

Background technique

Membrane-bioreactor is a new type of efficient sewage treatment and reuse technology that organically combines membrane separation technology with traditional biological treatment technology. Compared with the traditional wastewater treatment process, the membrane-bioreactor technology has outstanding advantages such as excellent and stable effluent quality, small footprint, and less residual sludge production due to the use of efficient membrane separation technology to replace the gravity sedimentation separation method, and The membrane-bioreactor device has a compact structure and is easy to realize automatic control. At the same time, it can also conveniently transform the traditional urban secondary sewage treatment plant so that the discharged water can meet the standard of reused water.

According to the location of the membrane module, the membrane-bioreactor can be divided into two categories: separate membrane-bioreactor and integrated membrane-bioreactor. Since the integrated membrane-bioreactor omits the mixed liquid circulation system and draws water out by negative pressure, the energy consumption is relatively low, and the occupied area is more compact than that of the separated membrane-bioreactor. Therefore, in recent years, integrated membrane-bioreactors have been used in the reuse of reclaimed water in large buildings and residential quarters, the treatment and reuse of urban sewage, the treatment of high-concentration organic wastewater, the treatment of refractory organic wastewater and the purification of slightly polluted source water. And other fields have initially started large-scale engineering applications. However, how to effectively control membrane fouling, reduce the cost of controlling membrane fouling, and prolong the service life of membrane modules is of great significance for the large-scale promotion and application of membrane-bioreactors.

As we all know, when the membrane-bioreactor is in operation, the membrane components will inevitably be polluted. The small molecular substances in the mud-water mixture will block the membrane pores, and the macromolecular substances and colloids will gradually adsorb to the membrane surface to form a gel layer. Such particulate matter will deposit on the surface of the membrane to form a mud cake layer, which will increase the filtration resistance of the membrane module, cause a significant decrease in the membrane flux or a significant increase in the transmembrane pressure difference, thereby affecting the long-term stability of the system. The mud cake layer pollution formed by bacterial micelles and other particulate matter can be improved by improving the hydrodynamic characteristics of membrane filtration (cross-flow filtration, air-water two-phase flow, hydraulic backwash or air backwash, etc.) and using appropriate working flux ( Subcritical flux) is well controlled, but the above-mentioned measures cannot remove the clogging of membrane pores and the contamination of the gel layer formed by organic matter and colloidal substances. Since alkaline cleaning (NaC10) has a strong oxidative decomposition and corrosion effect on organic matter and microorganisms, and pickling (citric acid, oxalic acid, hydrochloric acid) has a good dissolution and removal effect on inorganic precipitates, chemical cleaning is thorough. The most effective measure to remove membrane fouling and restore membrane filtration capacity is also necessary to maintain long-term stable operation of membrane modules.

Chemical cleaning is divided into immersion cleaning (in vivo or in vitro) and internal in-line cleaning. Generally speaking, the effect of immersion cleaning is better, but the damage to the membrane is relatively large, and the operation is also complicated. In vitro immersion cleaning requires not only the lifting and transfer system of the membrane module, but also a special cleaning tank and cleaning equipment, and there must be enough space. At the same time, there is also the problem of post-treatment of cleaning waste liquid; in vivo immersion cleaning requires the membrane module to be installed separately In the separation tank, there is also the problem of cleaning the waste liquid. On-line chemical cleaning not only has the advantages of better effect than other membrane fouling control measures, but also is simpler and easier than chemical immersion cleaning, and has less damage to the membrane, so it is an important membrane fouling control measure.

Although there are several patent documents on the application of membrane-bioreactors for sewage treatment at home and abroad, such as the domestic "suction built-in membrane-bioreactor (patent No. 97228698.5)", "through-flow membrane-bioreactor Water treatment process and its equipment (patent No. 99111514.7), "integrated membrane bioreaction equipment" (patent No. 98225338.9), "hollow fiber membrane bioreaction sewage processor" (patent No. 97228032.4), "membrane separation sewage Device" (Patent No. 00250653.X), "Membrane Bioreactor for Wastewater Treatment" (Patent No. 01212672.1), and foreign "Membrane bioreactor, process andaerator" (Pub.No.: US 2004/0108268 A1), " Apparatus and method forcleaning membrane filtration modules" (Pub.No.: WO 00/18498), "Chemicalcleaning backwash for immersed filtering membranes" (Pub.No.: WO01/08790 A1), "Filter device" (Pub.No.: JP 2001079362 A), "Separating membrane module and module assembly" (Pub.No.: JP 2003181248 A), "Method and apparatus for chemical cleaning of filter membrane module" (Pub.No.: JP 2003251159 A), but none of these patents It involves online chemical cleaning or is only mentioned in general without more detailed and clear operational parameters. Therefore, the present invention proposes relatively clear and highly operable operating rules about online chemical cleaning on the basis of experiments.

Contents of the invention

The object of the present invention is to provide an online chemical cleaning method for controlling membrane fouling in membrane-bioreactor wastewater treatment and reuse processes. The online chemical cleaning method is to use cleaning agents to clean and set corresponding devices:

1. Selection of cleaning agents

a) Alkaline washing

Alkali cleaning agent is mainly sodium hypochlorite (NaC10) solution: low concentration (available chlorine 50-200mg/L); high concentration (available chlorine 3000-6000mg/L). According to the membrane area, the amount of medicinal solution V = 5 ~ 20L medicinal solution/m ² ;

b) pickling

The acid cleaning agent is selected from citric acid, oxalic acid or hydrochloric acid solution (pH=1～2), and the dosage of the medicine solution according to the membrane area is V=5～20L medicine solution/m ² ;

The above-mentioned cleaning first uses alkali washing, and pickling is only used when the effect of alkali washing is not obvious or the content of inorganic substances in the feed liquid is high.

2. Judgment of cleaning cycle

a) Fixed cleaning cycle

For large and medium-scale membrane-bioreactors, wash with low-concentration alkali every 1 to 2 weeks, and wash with high-concentration alkali every 2 to 3 months. In this cleaning mode, the transmembrane pressure (TMP) of the membrane module is always maintained at a low level. This mode has more frequent cleaning and more complicated operation and management, so automatic control should be adopted.

b) Controlling the cleaning cycle with the rate of transmembrane pressure (TMP) development

For small-scale membrane-bioreactors, when TMP _t reaches the initial filtration value TMP ₀ plus 5-20kPa, it is used as a sign for cleaning, and high-concentration alkaline cleaning is used at this time. Under this cleaning mode, the TMP of the membrane module showed periodic changes, and the TMP showed a rising trend during the cycle, but after the online chemical cleaning, the TMP returned to close to the initial level. This mode has low cleaning frequency, simple operation and management, and can be operated manually in order to reduce costs.

3. The implementation steps of the online chemical cleaning method are as follows:

a) Prepare the cleaning liquid according to the membrane area and the type of liquid;

b) Stop the water in and out of the membrane module and aeration;

c) Stand still for 5 to 10 minutes, and complete the valve switching required for the cleaning operation;

d) Turn on the dosing pump, inject all the liquid medicine into the membrane module several times within 60-120 minutes in the opposite direction to the normal filtration direction, and then let it stand for 30-60 minutes;

e) Restart the aeration, complete the valve switching required for normal water inlet and outlet operations within 10 to 15 minutes, and then restart the water inlet and outlet for continuous operation.

4. To implement online chemical cleaning, it is necessary to set up a corresponding chemical cleaning system: liquid medicine storage tank, dosing pump, flow meter, chemical cleaning pipeline, and automatic control device. In addition, corresponding valves should be installed on the suction pipeline of the membrane module and the chemical cleaning pipeline to complete the online cleaning operation.

The beneficial effects of the present invention are: on-line chemical cleaning can always control the membrane fouling at a relatively low level, realize the long-term stable operation of the membrane module, prolong the service life of the membrane module, reduce the maintenance cost of the membrane module, thereby ensuring that the membrane-biological The long-term operation stability of the large-scale engineering application of the reactor and the reduction of its operation cost.

Description of drawings

Fig. 1 is a schematic diagram of a small-scale integrated membrane-bioreactor embodiment;

Fig. 2 is a schematic diagram of an embodiment of a large and medium scale integrated membrane-bioreactor;

Fig. 3 is the operating result of adopting TMP development rate to control the cleaning mode;

Figure 4 shows the running results of the cleaning mode with a fixed cleaning cycle.

Detailed ways

The invention is an online chemical cleaning method for controlling membrane fouling in a membrane-bioreactor. The online chemical cleaning method is to use cleaning agents to clean and install corresponding devices.

The present invention will be further described below in conjunction with the accompanying drawings.

Figure 1 is a schematic diagram of a small-scale integrated membrane-bioreactor using TMP development rate control on-line chemical cleaning mode. The system consists of water inlet pump 1 and water inlet pipeline, bioreactor 2, membrane module 3, blower 5 and aeration pipeline 6, suction/dosing pump 7 and water outlet pipeline, flow meter 10, clear water tank 9, pumping The suction/dosing pump 7, the medicine washing pipeline, the medicine liquid pool 8 and the corresponding valves 11, 12, 13, 14, the controller 15 and the liquid level gauge 17 are composed. The water inlet pump 1 is automatically controlled by the liquid level gauge 17 to ensure that the liquid level in the bioreactor 2 is basically stable. The bioreactor 2 is in the shape of a cuboid or cylinder with an upper opening. The deflector or the guide tube 4 divides the bioreactor 2 into two parts, the upflow zone and the downflow zone. The membrane module 3 (which can be an organic or inorganic hollow Fiber, plate, tubular microfiltration or ultrafiltration membranes) are placed in the upflow zone, and the aeration device 6 is located directly below the membrane module 3 . Pressure sensors 16 and 18 respectively measure the internal and external pressures of the membrane module to calculate TMP. The liquid medicine pool 8 and the clear water pool 9 are respectively used to store the medicine liquid for online chemical cleaning and treat the effluent. By switching the valves 11, 12, 13 and 14 accordingly, the suction pump and the dosing pump can be combined into one, which can reduce the investment cost. The flow meter 10 is used to measure the flow rate of treated water and chemical cleaning solution.

During normal filtration operation, the raw water enters the bioreactor 2 after being lifted by the inlet pump 1, and the organic matter in the raw water is fully degraded by the aerobic microorganisms in the reactor, and the treated water is sucked by the suction/dosing pump 7, Filtered by membrane module 3 to become system effluent. During normal operation, the valves 11 and 14 are closed, and the valves 12 and 13 are opened, so that the suction/dosing pump 7 can realize the function of pumping and discharging water. The suction/dosing pump 7 is controlled by the controller 15 to operate intermittently at certain time intervals to alleviate the continuous accumulation of pollutants.

When performing online chemical cleaning, first stop the water inlet pump 1 and the suction/dosing pump 7, then stop the blower 5, and then complete the valve switching required for online chemical cleaning: valves 11 and 14 are opened, and valves 12 and 13 are closed, so that The suction/dosing pump 7 can realize the reverse cleaning function. According to the type and dosage of the required liquid medicine, prepare the liquid medicine required for cleaning in the liquid medicine pool 8, then turn on the suction/dosing pump 7 to add medicine, and inject all the medicine liquid into the membrane several times within 60-120 minutes components (opposite to the normal filtering direction), and then stand for 30 to 60 minutes. Next, the blower 5 is turned on again for aeration, and the valve switching required for the normal water inlet operation is completed within 10 to 15 minutes: the valves 11 and 14 are closed, and the valves 12 and 13 are opened. Then, restart the water inlet pump 1 and the suction/dosing pump 7 to run continuously.

Figure 2 is a schematic diagram of a large and medium-scale integrated membrane-bioreactor adopting an online chemical cleaning mode with a fixed cleaning period. The system consists of water inlet pump 1 and water inlet pipeline, bioreactor 2, membrane module 3, blower 5 and aeration pipeline 6, suction pump 7 and water outlet pipeline, flow meter 10, clear water tank 9, and dosing pump 22 And medicine washing pipeline, medicine liquid pool 8, clear water pump 23 and corresponding valves 11, 12, 24, solenoid valve 20, solenoid valve 21 and PLC control device 19.

The water inlet pump 1 is automatically controlled by the PLC control device 19 to ensure that the liquid level in the bioreactor 2 is basically stable. The bioreactor 2 is in the shape of a cuboid or cylinder with an upper opening. The deflector or the guide tube 4 divides the bioreactor 2 into two parts, the upflow zone and the downflow zone. The membrane module 3 (which can be an organic or inorganic hollow Fiber, plate, tubular microfiltration or ultrafiltration membranes) are placed in the upflow zone, and the aeration device 6 is located directly below the membrane module 3 . Pressure sensors 16 and 18 respectively measure the internal and external pressures of the membrane module to calculate TMP. The liquid medicine pool 8 and the clear water pool 9 are respectively used to store the medicine liquid for online chemical cleaning and treat the effluent. Through the PLC control device 19, the automatic control of the water inlet pump 1, the blower 5, the suction pump 7, the dosing pump 22, the clean water pump 23, the solenoid valves 20 and 21, and the pressure sensors 16 and 18 in the system is completed, including normal filtering operation and online All operations of chemical cleaning. The three flowmeters 10 are respectively used to measure the flow rate of the concentrated solution of the chemical cleaning agent, the flow rate of the diluted water of the cleaning solution and the flow rate of the treated water.

During normal filtration operation, the raw water is lifted by the inlet pump 1 and then enters the reactor 2. After the organic matter in the raw water is fully degraded by the aerobic microorganisms in the reactor, the treated water passes through the membrane module 3 under the suction of the suction pump 7. Filtered to become system effluent. During normal operation, the solenoid valve 20 is closed, and the solenoid valve 21 is opened, so that the suction pump 7 can realize the function of sucking and discharging water. The suction pump 7 is intermittently operated by the PLC control device 19 at certain time intervals to reduce the continuous accumulation of pollutants.

When performing online chemical cleaning, the PLC control device 19 first automatically stops the water inlet pump 1 and the suction pump 7, then stops the blower 5, and then completes the valve switching required for online chemical cleaning: the solenoid valve 21 is closed, and the solenoid valve 20 is opened, so that The dosing pump 22 and the clean water pump 23 can realize the reverse cleaning function. According to the type and dosage of the required medicinal solution, the concentrated medicinal solution required for this cleaning is prepared in advance in the medicinal solution pool 8 . The PLC control device 19 automatically turns on the dosing pump 22 and the clear water pump 23 at the same time, and mixes the concentrated solution and the treated effluent in the pipeline at a certain flow ratio, so that the concentration of the mixed medicine solution reaches a predetermined value, which will save the medicine solution The volume of pool 8, and simplify the operating procedure of preparing cleaning liquid. All the liquid medicine is injected into the membrane module (opposite to the normal filtration direction) several times within 60-120 minutes, and then left to stand for 30-60 minutes. Next, the PLC control device 19 automatically turns on the blower 5 for aeration, and within 10 to 15 minutes, completes the valve switching required for normal water inlet and outlet operations: the solenoid valve 20 is closed, and the solenoid valve 21 is opened. Finally, the water inlet pump 1 and the suction pump 7 are automatically turned on to resume continuous operation.

Fig. 3 shows the operation results of the online chemical cleaning mode controlled by TMP development rate in a water reuse project of a one-piece membrane-bioreactor. The project has a treatment scale of 240m ³ /d and uses polyethylene hollow fiber membrane modules to treat bathing sewage from residential quarters. After treatment, it will be reused for community greening and landscape water. In the online chemical cleaning mode controlled by TMP development rate, the stable operation of the reclaimed water reuse project has been realized.

Figure 4 shows the test results of a certain integrated membrane-bioreactor pilot plant using a fixed-cycle online chemical cleaning mode. The device treats typical urban sewage, with a daily treatment capacity of Q _d =17m ³ /d, and adopts polyvinylidene fluoride hollow fiber membrane modules. Under the operation mode of regular on-line chemical washing (every 1-2 weeks with low-concentration alkali, and every 2-3 months with high-concentration alkali), it has achieved high-throughput (J=30L/m ² /h) conditions. Long-term stable operation.

Since alkaline cleaning (NaC10) has a strong oxidative decomposition and corrosion effect on organic matter and microorganisms, while pickling (citric acid, oxalic acid, hydrochloric acid) has a good dissolution and removal effect on inorganic precipitates, so on-line chemical cleaning ( Alkaline washing and pickling) are very effective and thorough for removing pollution caused by organic matter, colloid and inorganic matter precipitation, and restoring membrane filtration capacity.

Claims (1)

1. an on-line chemical cleaning method for controlling membrane-bioreactor membrane fouling, characterized in that: said on-line chemical cleaning method is to adopt cleaning agent to clean: 1) Selection of cleaning agents a) Alkali cleaning, the alkaline cleaning agent is mainly sodium hypochlorite NaClO solution: the low concentration of available chlorine is 50-200mg/L or the high concentration of available chlorine is 3000-6000mg/L; the dosage of the liquid medicine is V=5-20L liquid medicine /m ² membrane area; b) pickling, the acid cleaning agent is citric acid, oxalic acid or hydrochloric acid solution, pH = 1-2, the amount of liquid medicine is V = 5-20L liquid medicine/m ² membrane area; The above-mentioned cleaning first uses alkali washing, or first uses alkali washing and then pickling; 2) Judgment of cleaning cycle a) Fixed cleaning cycle, for large and medium-scale membrane-bioreactors, wash with low-concentration alkali every 1 to 2 weeks, and wash with high-concentration alkali every 2 to 3 months; b) The cleaning period is controlled by the TMP rate of the transmembrane pressure difference. For small-scale membrane-bioreactors, when TMP _t reaches the initial filtration value TMP ₀ plus 5-20kPa, it is used as a sign for cleaning. At this time, a high concentration is used. Alkaline cleaning: In this cleaning mode, the TMP of the membrane module shows a periodic change, and the TMP shows a rising trend during the cycle, but after the online chemical cleaning, the TMP returns to close to the initial level; 3) The implementation steps of the online chemical cleaning method are as follows: a) Prepare the cleaning liquid according to the area of the membrane and the type of the liquid; b) Stop the water in and out of the membrane module and aeration; c) Stand still for 5 to 10 minutes to complete the valve switching required for the cleaning operation; d) Turn on the dosing pump, inject all the liquid medicine into the membrane module several times within 60-120 minutes in the opposite direction to normal filtration, and then let it stand for 30-60 minutes; e) Restart the aeration, complete the valve switching required for normal water inlet and outlet operations within 10 to 15 minutes, and then restart the water inlet and outlet for continuous operation.

Images