JP2008520428A - Filtration membrane cleaning method - Google Patents

Abstract

  The present invention relates to a filtration membrane cleaning method used for filtration of wastewater from a wastewater treatment plant, the method including at least one enzyme cleaning step using an enzyme cleaning solution.

Description

  The present invention relates to cleaning of filtration membranes used in wastewater treatment.

  The use of membrane filtration in high-performance treatment of wastewater for reuse or improved water quality is increasing due to water shortages in dry areas and the existence of laws that will become more severe in the near future. Many full-scale facilities around the world have been in operation for several years.

  During operation, the problem of membrane fouling has become more serious. These problems are not only seen in ultrafiltration of wastewater treatment plant wastewater, but also in other membrane filtration applications such as surface water treatment. However, the applied hydraulic and chemical cleaning methods are often not sufficiently effective and are often based on actual experience.

  Many attempts to apply cleaning strategies to maximize membrane flow recovery due to organic fouling have been studied. The effects of various chemicals such as NaOH, NaOCl, HCl, citric acid, and anionic surfactants are often studied by short-term filtration tests and possibly pilot-scale studies investigating irreversible soils. Has been. However, more mechanistic studies of cleaning strategies aimed at irreversible soil removal based on the physicochemical properties of wastewater treatment plant wastewater pollutants are relatively rare.

  Certain cleaning agents provide information on the nature and physicochemical properties of the contaminants. By using a cleaning agent that provides information on the type of binding between the contaminant and the membrane material, the interaction between the contaminant and the membrane material is interfered with or destroyed.

  According to the state of the art, the membrane is cleaned by water pressure or chemically. The hydraulic wash can be performed with water or a combination of water and air. Chemical cleaning can be performed with various cleaning chemicals.

  Chemical cleaning involves several steps that must be performed in a specific order. Initially, reverse flow (BF) or forward flow (FF) is provided to remove reversible soil. A chemical cleaning solution can be directed to the membrane surface by BF or FF. Thereafter, the membrane will often be immersed for a specific time. Mechanical energy can be introduced to pump the cleaning liquid along the membrane surface. The final step is to flush the membrane with permeate, tap water or ultrapure water.

  In general, four aspects of chemical cleaning are problematic: contact time, chemical reaction, temperature and mechanical energy. These parameters can be changed according to the soil and cleaning agent of the present invention. The effect of temperature in chemical cleaning can increase exponentially. Most chemical cleaning is performed at 30-50 ° C. depending on the limits of the membrane module.

  It is an object of the present invention to provide a method for cleaning a filtration membrane used for filtering wastewater from a wastewater treatment plant in order to reduce or remove such membrane fouling. Yet another object of the present invention is to clean such membranes in order to effectively ensure the initial wash water flow rate.

  According to the present invention, the object and other objects are a method for cleaning a filtration membrane used for filtering wastewater from a wastewater treatment plant, the filtration membrane comprising at least one enzyme cleaning step using an enzyme cleaning solution. This is achieved by the washing method.

  The enzyme washing process can advantageously reduce or eliminate irreversible soil, which occurs during ultrafiltration of wastewater treatment plant effluent and is one of the main components of extracellular polymeric substances. Such protein adsorption is considered to be the cause. Therefore, a novel enzyme cleaning protocol based on enzyme cleaning solution is applied according to the present invention.

  According to a preferred embodiment of the present invention, the washing step is carried out using an enzyme washing solution having a temperature of 10 ° C to 50 ° C, especially 25 ° C to 30 ° C.

  The method of the present invention may comprise flushing the membrane with water before, after, or both before and after the enzyme wash step. The water used for flushing can be, for example, tap water or permeate through a membrane in a wastewater treatment plant. Furthermore, the enzyme wash solution can be circulated throughout the membrane for a certain circulation time. This circulation time can preferably be 10 minutes to 1.5 hours, in particular 1 hour.

  Furthermore, the membrane can also be immersed in an enzyme cleaning solution for a certain immersion time, which is preferably 12 to 48 hours, in particular 24 hours.

According to one embodiment of the present invention, the enzyme washing step comprises:
A) Flushing the membrane in the forward direction with a cleaning liquid, preferably permeate (filtered water);
B) circulating the enzyme cleaning solution through the membrane for 1 hour;
C) soaking the membrane in the enzyme cleaning solution for 24 hours;
D) circulating the enzyme wash solution through the membrane for 1 hour; and E) flushing the membrane with water.

  The membrane that can be washed by the method of the present invention can be, for example, an ultrafiltration membrane, a microfiltration membrane, a nanofiltration membrane or a reverse osmosis membrane.

  According to one preferred embodiment of the invention, the enzyme wash solution contains an endo-type or exo-type proteolytic enzyme or a mixture thereof.

  According to one preferred embodiment of the invention, the enzyme cleaning solution contains a protease.

  The enzyme cleaning solution used in the method of the present invention preferably contains the enzyme at a concentration of 0.0125% to 0.1%. Preferably, the enzyme wash solution has a pH value of 8.5-10.

  Furthermore, the membrane cleaning method of the present invention can include an acidic cleaning step of cleaning the membrane using an acidic cleaning liquid. The acidic washing step can be performed both before the enzyme washing step, after the enzyme washing step, and before and after the enzyme washing step. Preferably, a weakly acidic prewash is performed prior to performing the enzyme wash protocol.

  The acidic cleaning liquid can contain at least one acid and at least one auxiliary cleaning agent. The at least one auxiliary cleaning agent may be selected from the group consisting of surfactants, chelating agents and sequestering agents.

  According to one preferred embodiment of the present application, the acidic cleaning solution has a pH value of less than 3.

  Furthermore, the film cleaning method of the present invention may include an alkali cleaning step of cleaning the film using an alkaline cleaning liquid.

  The alkaline cleaning liquid can contain at least one base and at least one auxiliary cleaning agent. The at least one auxiliary cleaning agent may be selected from the group consisting of surfactants, chelating agents and sequestering agents.

  According to one preferred embodiment of the invention, the alkaline cleaning liquid has a pH greater than 9, in particular a pH value of 9.3 to 12.5.

  In the method of the present invention, different cleaning steps can be carried out continuously. Each different washing step is preferably carried out with a time interval in the range of days or weeks. Each of the different cleaning steps can be performed sequentially without any significant time interval between them.

  The present invention is illustrated in the accompanying drawings. FIG. 1 shows a schematic diagram of the configuration of a pilot plant that can clean the membrane using the method of the present invention.

  According to FIG. 1, the wastewater treatment plant effluent 1 proceeds to a screen 2 from which it passes directly through a microfiltration device 3 or first through a multilayer filter 4 and then through a microfiltration device 3. Can do. The microfiltrate from the microfiltration device 3 enters the ultrafiltration device 5. The membrane 6 of the microfiltration device 3 and the membrane 7 of the ultrafiltration device 5 are exposed to dirt, and their washing water flow rate is reduced. In order to restore the washing water flow rate of these membranes to 100%, the method of the present invention can be applied to these membranes.

  The method according to the present invention was tested using a configuration as shown in FIG.

  A multi-layer filter 4 having one anthracite layer and one sand layer was operated on a 1.73 m filter bed with a predetermined amount of water. Before the feed water entered the filter, it was possible to administer the coagulant in-line to the feed pipe and mix with an electrostatic mixer. Aggregation was performed on or in the filter bed.

Microfiltration device 3 had three modules having a membrane surface area of 45 m ^2. The pore size of the membrane was 0.2 μm. The equipment was operated at a constant flow rate varying from 50 to 105 l / m ² · h with a production interval of 15 minutes and then backwashed. Chemical cleaning was performed once or twice a week depending on the filtration resistance.

The ultrafiltration device 5 contained an X-flow membrane having a capillary diameter of 0.8 mm and a pore diameter of 0.02 μm. The installed capacity is 10 m ³ / h and comprises two 8 inch modules, each 1.5 m long, providing a membrane area of 70 m ² . The equipment was operated at a constant flow rate. The coagulant was administered inline to the water supply.

  Several types of cleaning experiments were conducted during the pilot survey period at the wastewater treatment plant. Initially, an enzyme wash with a protease was compared to its basic alkaline wash to investigate the efficacy of the enzyme protease. Enzymatic washing with proteases indicates that protein adsorption is a fouling mechanism. The applied cleaning solution and protocol are shown in Table 1. The cleaning effect was determined by measuring the cleaning water flow rate (CWF) before and after cleaning. These washing experiments were performed twice. In the first wastewater treatment plant, these experiments were conducted 8 months after operation. In the second wastewater treatment plant, these experiments were conducted at the beginning of the pilot study period.

  At the end of the pilot study, the membrane was washed to continue the investigation at another wastewater treatment plant. Therefore, each different washing method was applied continuously based on enzyme washing with protease. Table 2 shows the applied cleaning methods.

  The Rosenberger method was modified and used to measure proteins in wastewater from wastewater treatment plants. This method is based on the Lowry method. The adsorption of the color formed is measured by a spectrograph Milton Roy spectral 401 in a 4 cm glass cuvette at 750 nm. The amount of protein is expressed in mg / l.

Table 3 shows the results of the first enzyme washing experiment and the basic alkali washing experiment in chronological order. The wash water flow rate (CWF) was normalized to 20 ° C. The CWF of the new membrane module is 4.00 × 10 ^{7 to} 5.00 × 10 ⁷ l / m ² · h · Pa (400 to 500 l / m ² · h · bar) at 20 ° C. Obtained by the product of the invention.

  The results clearly show that CWF returned to the original CWF of the new membrane module after performing the new enzyme wash protocol according to the present invention. In the first wastewater treatment plant, the effect of enzyme cleaning is significantly greater than the basic alkaline cleaning method. The effect of basic alkaline washing decreases with time, indicating that protein adsorption occurred as a fouling mechanism. In the second wastewater treatment plant, the CWF after enzyme cleaning shows similar results as after basic alkaline cleaning. Although the effect of enzyme washing is believed to be greater than that for basic alkaline washing, application of both washing methods resulted in 100% recovery of CWF.

FIGS. 2 and 3 show the results of these washing experiments in the first wastewater treatment plant and the second wastewater treatment plant, and the membrane contamination after washing, respectively, in the washing water normalized to 20 ° C. with respect to time. It shows as a relationship of flow volume (CWF). After the start of ultrafiltration of the microfiltrate, the CWF decreases rapidly, especially when the CWF begins to exceed 4.00 × 10 ⁷ l / m ² · h · Pa (400 l / m ² · h · bar). In the first wastewater treatment plant, CWF ranges from about 4.40 × 10 ⁷ l / m ² · h · Pa (440 l / m ² · h · bar) to 2.20 × 10 ⁷ l in about one day. / M ² · h · Pa (220 l / m ² · h · bar) and about 1.50 × 10 ⁷ l / m ² · h · Pa (150 l / m ² · h · bar). The CWF in the second wastewater treatment plant is about 4.30 × 10 ⁷ l / m ² · h · Pa (430 l / m ² · h · bar) to 3.05 × 10 ⁷ l / in about one day. It decreased to ^{m 2 · h · Pa (305l} / m 2 · h · bar), further, to about 2.60 × ¹⁰ 7 in about 3 days ^{l / m 2 · h · Pa} (260l / m 2 · h -It decreases to bar). The reduction in CWF after one day of ultrafiltration of the microfiltrate is about 50% in the first wastewater treatment plant, compared to about 30%, which is less than 40% in the second wastewater treatment plant. After about 3 days of filtration, the CWF becomes constant at 1.60 × 10 ⁷ l / m ² · h · Pa (160 l / m ² · h · bar) in the first wastewater treatment plant, whereas In a wastewater treatment plant of 2, this value is found around 2.60 × 10 ⁷ l / m ² · h · Pa (260 l / m ² · h · bar). That is, the contamination of the ultrafiltration membrane by the organic polymer is more serious in the first wastewater treatment plant than in the second wastewater treatment plant.

図２：第１の廃水処理プラントにおける精密濾過液の限外濾過による、洗浄された膜及び汚れた膜のＣＷＦ測定

Figure 2: CWF measurement of washed and dirty membranes by ultrafiltration of microfiltrate at the first wastewater treatment plant

図３：第２の廃水処理プラントにおける精密濾過液の限外濾過による、洗浄された膜及び汚れた膜のＣＷＦ測定

Figure 3: CWF measurement of washed and dirty membranes by ultrafiltration of microfiltrate at the second wastewater treatment plant

  The results show 100% recovery of the wash water flow rate relative to the original wash water flow rate of the membrane module itself after performing the enzyme wash protocol. Using this protocol, enzyme cleaning can be performed at a low temperature (25 to 30 ° C.), so that a low temperature resistance film can be used.

  If the metal complex is formed during the filtration of the wastewater of the (pre-filtered) wastewater treatment plant, it is suggested to carry out the acid wash prior to the enzyme wash.

FIG. 1 shows a schematic diagram of the configuration of a pilot plant that can clean the membrane using the method of the present invention.

Claims (24)

  A filtration membrane cleaning method used for filtering wastewater from a wastewater treatment plant, the method comprising at least one enzyme cleaning step using an enzyme cleaning solution.   The method according to claim 1, wherein the washing step is performed using an enzyme washing solution having a temperature of 10 to 50 ° C.   The method according to claim 1 or 2, comprising flushing the membrane with water before or after the enzyme washing step.   The method according to any one of claims 1 to 3, wherein the enzyme cleaning solution is circulated throughout the membrane for a certain circulation time.   The method according to claim 4, wherein the circulation time is 10 minutes to 1.5 hours.   The method according to claim 1, wherein the membrane is immersed in the enzyme cleaning solution for a certain immersion time.   The method according to claim 6, wherein the immersion time is 12 hours to 48 hours. The enzyme washing step
F) Flushing the membrane in the forward direction with a cleaning liquid;
G) circulating the enzyme cleaning solution through the membrane for 1 hour;
H) soaking the membrane in the enzyme cleaning solution for 24 hours;
The method according to any one of claims 1 to 7, comprising I) circulating the enzyme cleaning solution through the membrane for 1 hour; and J) flushing the membrane with water.   The method according to any one of claims 1 to 8, wherein the membrane is an ultrafiltration membrane, a microfiltration membrane, a nanofiltration membrane or a reverse osmosis membrane.   The method according to claim 1, wherein an enzyme cleaning solution containing a protease is used.   The method according to any one of claims 1 to 10, wherein the enzyme cleaning solution contains an endo-type or exo-type proteolytic enzyme or a mixture thereof.   The method according to claim 1, wherein the enzyme cleaning solution contains an enzyme at a concentration of 0.0125% to 0.1%.   The method according to any one of claims 1 to 12, wherein the enzyme cleaning solution has a pH value of 8.5 to 10.   The method according to claim 1, further comprising an acidic cleaning step of cleaning the film using an acidic cleaning solution.   The method according to claim 14, wherein the acidic washing step is performed before the enzyme washing step.   The method according to claim 14 or 15, wherein the acidic cleaning liquid contains at least one acid and at least one auxiliary cleaning agent.   The method according to claim 16, wherein the at least one auxiliary cleaning agent is selected from the group consisting of a surfactant, a chelating agent, and a sequestering agent.   The method according to any one of claims 14 to 17, wherein the acidic cleaning liquid has a pH value of less than 3.   The method for cleaning the filtration membrane according to any one of claims 1 to 18, further comprising an alkaline cleaning step of cleaning the membrane using an alkaline cleaning solution.   20. The method of claim 19, wherein the alkaline cleaning solution contains at least one base and at least one auxiliary cleaning agent.   21. The method of claim 20, wherein the at least one auxiliary cleaning agent is selected from the group consisting of surfactants, chelating agents and sequestering agents.   The method according to any one of claims 19 to 21, wherein the alkaline cleaning solution has a pH value of 9.3 to 12.5.   23. A method according to any one of the preceding claims, wherein each different washing step is carried out continuously.   23. A method according to any one of the preceding claims, wherein each different washing step is carried out with a time interval in the range of days or weeks in between.

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