KR20240022274A - Operation method of bioreactor and water treatment system for controlling contamination of membrane in bioreactor - Google Patents

Abstract

The present invention relates to a method of operating a bioreactor in which a process of purifying waste water flows from the outside to the inside of a separation membrane immersed in the bioreactor and is continuously performed. The bioreactor includes rhamnolipid-producing microorganisms inside the bioreactor and an external By including the step of injecting a carrier coated with a polymer material, the produced rhamnolipid may have the effect of removing or inhibiting the production of biofilm on the surface of the separation membrane. In addition, the microorganisms contained in the carrier can continuously produce rhamnolipids, so a single injection can exhibit the effect of inhibiting or removing biofilm on the surface of the separation membrane, making it highly economical. Since the outside of the carrier is coated with a polymer material, the stability of the carrier increases and it has the advantage of being usable for a long period of time.

Description

Operating method and water treatment system of a biological reactor for controlling contamination of the membrane in the biological reactor {OPERATION METHOD OF BIOREACTOR AND WATER TREATMENT SYSTEM FOR CONTROLLING CONTAMINATION OF MEMBRANE IN BIOREACTOR}

The present invention relates to a method of operating a biological reactor and a water treatment system for controlling contamination of a membrane in a biological reactor.

A membrane bioreactor (MBR) is a process that integrates the separation of pollutants using a biological treatment facility and membrane to treat domestic sewage and industrial wastewater. Through this integration, MBR can produce a higher level of treated water than the commonly used activated sludge process (CASP). In addition, MBR has the advantage of being simple to operate and producing a small amount of sludge. In addition, since it requires less land, it has the advantage of being easy to drive even in places where space is limited and expensive, such as densely populated areas. In addition, the proportion of MBR in sewage and wastewater facilities is expected to gradually expand thanks to the continued decline in the price of membrane raw materials and an environment requiring increasingly higher levels of treated water.

Nevertheless, there is a major inevitable obstacle to the rapid development of MBR. This is membrane fouling, which occurs when microorganisms form a biofilm on the surface of the membrane (Figure 1). Membrane fouling not only has the disadvantage of lowering the quality of treated water, but also increases energy consumption and cleaning frequency. This leads to a shortened separator lifespan and increased operating costs. To solve these problems, research is continuing on methods for controlling and cleaning membrane contamination.

Among them, chemical cleaning is inevitable in cases such as MBR where extreme fouling occurs and permeability needs to be restored. Chemical cleaning is a method of cleaning a separator through a chemical reaction with contaminants attached to the separator using chemicals. Chemicals used for cleaning include acids, bases, oxidizing agents, and surfactants.

Among them, surfactants were confirmed to not only have less effect on membrane damage, but also bind with protein substances on the membrane surface to form micelles and reduce biofilm formation. They also made the membrane surface hydrophilic, forming a biofilm. It was confirmed that it inhibits adhesion of substances. SDS (sodium dodecyl sulfate) and Tween 20, a type of chemical surfactant commonly used in the past, have shown that chemical surfactants can control membrane contamination and significantly restore treated water flux. However, the cleaning efficiency is sometimes 30-50% and sometimes exceeds 90%, and the effectiveness is not constant, and biodegradation is difficult, so it was judged that industrial application in membrane pollution control is difficult. In addition, SDS has ecotoxicity, so when applied to MBR cleaning, it can cause protein deformation in the cytoplasm of microorganisms and have a negative effect on metabolism.

Accordingly, research on reducing membrane fouling using rhamnolipid, a type of biological surfactant, has emerged as a new membrane fouling control method. However, commercial production and application are difficult due to the high cost incurred during the purification process after biosynthesis of rhamnolipids. The process of obtaining purified rhamnolipids is still difficult and requires high costs. Because of the difficulties that arise in the process of purifying highly pure rhamnolipids, continuous injection of rhamnolipids into a bioreactor requires high costs.

Therefore, there is a need to develop a method that can exhibit excellent membrane fouling control effects at a lower cost than existing methods.

Korean Patent Publication No. 2014-0026116

The purpose of the present invention is to provide a method of operating a biological reactor for controlling contamination of a membrane in the biological reactor.

The purpose of the present invention is to provide a water treatment system for controlling contamination of a membrane in a biological reactor.

1. A method of operating the bioreactor in which the process of purifying waste water flows from the outside to the inside of the separation membrane immersed in the bioreactor and is continuously performed,

Comprising the step of injecting a carrier containing rhamnolipid-producing microorganisms into the bioreactor,

A method of operating a biological reactor, wherein the carrier is coated on the outside with a polymer material.

2. The method of operating a biological reactor according to 1 above, wherein the rhamnolipid-producing microorganism is Pseudomonas nitroreducens .

3. In 1 above, the polymer material is polysulfone, polyurethane, polyacetal, polyamide, polyamide elastomer, polyester, poly. ester elastomer, polypropylene, polyacrylonitrile, poly(methymethacrylate), polyolefin, poly(vinyl chloride), and A method of operating a biological reactor, one selected from the group consisting of silicon.

4. The method of operating a biological reactor according to 1 above, wherein the carrier is injected once into the biological reactor.

5. The method of operating a biological reactor according to 1 above, wherein the carrier is injected at a number density of 300/L or less per volume of the biological reactor.

6. Inlet pump for injecting waste water;

a bioreactor configured to allow wastewater injected by the inlet pump to pass through a separation membrane after being immersed in activated sludge; and

It communicates with the interior of the separation membrane and includes an outflow pump for discharging wastewater that has passed through the separation membrane to the outside of the bioreactor,

The biological reactor includes a carrier containing rhamnolipid-producing microorganisms,

A water treatment system wherein the carrier is coated on the outside with a polymer material.

7. The water treatment system of 6 above, wherein the rhamnolipid-producing microorganism is Pseudomonas nitroreducens .

8. In item 6 above, the polymer material is polysulfone, polyurethane, polyacetal, polyamide, polyamide elastomer, polyester, poly. ester elastomer, polypropylene, polyacrylonitrile, poly(methymethacrylate), polyolefin, poly(vinyl chloride), and A water treatment system selected from the group consisting of silicon.

The operating method of the biological reactor of the present invention can exhibit the effect of removing or inhibiting the production of biofilm on the surface of the separation membrane by injecting a carrier containing rhamnolipid-producing microorganisms inside the biological reactor and coated on the outside with a polymer material. In addition, the microorganisms contained in the carrier can continuously produce rhamnolipids, so a single injection can exhibit the effect of inhibiting or removing biofilm on the surface of the separation membrane, making it highly economical. Since the outside of the carrier is coated with a polymer material, the stability of the carrier increases and it has the advantage of being usable for a long period of time.

Figure 1 schematically illustrates the mechanism of membrane contamination due to biofilm formation.
Figure 2 shows the structure of rhamnolipid.
Figure 3 is a schematic diagram of the membrane fouling control mechanism according to the biofilm reduction effect due to the surface activity of rhamnolipid.
Figure 4 is a schematic diagram of the alginate bead manufacturing process used for fixation of microorganisms.
Figures 5 and 6 are a schematic diagram of the laboratory-scale biological reactor (MBR) used in the examples and a photograph of the actual MBR, respectively.
Figure 7 is a photograph of the water quality analysis device used in the examples. (Left: UV/vis spectrophotometer, Right: Hach kits)
Figure 8 is a schematic diagram of the dead end filtration process.
Figure 9 is a photograph of a field emission scanning electron microscope (FE-SEM) used in the examples.
Figure 10 shows the results of an experiment evaluating rhamnolipid production ability according to the medium, input strain, and input method confirmed in Example 3-1-(2).
11 to 13 show the COD concentration (FIG. 11), NH ₄ ⁺ -N concentration (FIG. 12), and NO of influent and treated water according to the type of membrane bioreactor (MBR) confirmed in Example 3-1-(4). ₃ -N concentration (Figure 13) and removal or production rate are shown. (Top: MBR1 without any carrier, middle: MBR2 with microorganism-immobilized alginate beads, bottom: MBR3 with alginate beads without immobilized microorganisms)
Figure 14 shows the change in transmembrane pressure (specific TMP) according to the type of MBR confirmed in Example 3-1-(5).
Figure 15 shows a linear regression equation for calculating the activated sludge specific resistance value (specific cake resistance, α) according to the MBR type identified in Example 3-1-(6). (Top: MBR1 without any carrier, Bottom: MBR2 with microorganism-immobilized alginate beads)
Figure 16 shows the results of measuring EPS (extracellular polymeric substance) carbohydrate components according to the type of MBR confirmed in Example 3-1-(7). (Left: LB-EPS (loosely bound EPS), Right: TB-EPS (tightly bound EPS))
Figure 17 shows the results of measuring EPS protein components according to the type of MBR confirmed in Example 3-1-(7). (Left: LB-EPS, Right: TB-EPS)
Figure 18 shows the change in carrier weight according to the type of carrier added to the MBR confirmed in Example 3-2-(2).
19 to 22 show the COD concentration (FIG. 19), NH ₄ ⁺ -N concentration (FIG. 20), and NO 3 -N concentration (FIG. 19) of the influent and treated water according to the type of MBR confirmed in Example 3-2-( ₃ ). Figure 21) and TN concentration (Figure 22) and removal or production rate are shown. (Top: MBR1 without any carrier, middle: MBR2 with microorganism-immobilized coated alginate beads, bottom: MBR3 with uncoated microorganism-immobilized alginate beads)
Figure 23 shows the change in transmembrane pressure (specific TMP) according to the type of MBR confirmed in Example 3-2-(4).
Figure 24 shows the results of measuring EPS carbohydrate components according to the type of MBR confirmed in Example 3-2-(5). (Left: LB-EPS, Right: TB-EPS)
Figure 25 shows the results of measuring EPS protein components according to the type of MBR confirmed in Example 3-2-(5). (Left: LB-EPS, Right: TB-EPS)
Figure 26 shows the cumulative sum of the EPS components according to the MBR type confirmed in Example 3-2-(5). (Top: EPS carbohydrate component, Bottom: EPS protein component)
Figure 27 is a photograph of the separator removed from each MBR confirmed in Example 3-2-(6). (Left: MBR1 without any carrier, Middle: MBR2 with microorganism-immobilized coated alginate beads, Right: MBR3 with microorganism-immobilized alginate beads)
Figures 28 and 29 are FE-SEM images at 1k times (Figure 28) or 10k times (Figure 29) of the separator removed from each MBR confirmed in Example 3-2-(6). (Top: MBR1 without any carrier, middle: MBR2 with microorganism-immobilized coated alginate beads, bottom: MBR3 with microorganism-immobilized alginate beads)
Figure 30 shows the results of an experiment evaluating rhamnolipid production ability according to the medium, input strain, input method, presence or absence of coating, and MBR input confirmed in Example 3-2-(7).
Figure 31 is a photograph of a laboratory-scale batch reactor used in Example 3-2-(8).
Figure 32 shows a linear regression equation for calculating the activated sludge specific resistance value (specific cake resistance, α) according to the type of MBR identified in Example 3-2-(8). (Top: first reaction tank without any carrier, bottom: second reaction tank with microbial immobilization coated alginate beads)

Hereinafter, the present invention will be described in detail.

The present invention provides a method of operating a bioreactor in which wastewater flows from the outside to the inside of a separation membrane immersed in the bioreactor and the purification process is continuously performed.

The method of operating a biological reactor of the present invention includes the step of injecting a carrier containing rhamnolipid-producing microorganisms into the biological reactor, and the carrier is coated on the outside with a polymer material.

The separation membrane is not limited as long as it can be used by immersing it in a biological reactor. For example, it may be a microfiltration (MF) membrane or an ultrafiltration (UF) membrane, and may be optionally used depending on the nature of the wastewater to be treated. can be selected

The form of the separation membrane may be a flat membrane or a hollow fiber membrane.

Rhamnolipid is a type of biological surfactant. Rhamnolipid is a type of glycolipid and is composed of the polysaccharide rhamnose and fatty acid, as shown in Figure 2. Rhamnolipids are highly biodegradable, have low toxicity, are compatible with various environments, and have relatively high surface activity. Rhamnolipids exhibit a biofilm reduction effect through surface activity. The membrane fouling control mechanism according to the biofilm reduction effect of rhamnolipid is shown in Figure 3.

Rhamnolipid-producing microorganism refers to any microorganism such as bacteria, and is not limited as long as it has the ability to synthesize or produce rhamnolipid under appropriate conditions. Rhamnolipid-producing microorganisms include, for example, Pseudomonas nitroreducens , Pseudomonas alcaligenes , Pseudomonas chlororaphis, Pseudomonas clemencia , and Pseudomonas collieria. collierea ), Pseudomonas fluorescens , Pseudomonas luteola , Pseudomonas putida, Pseudomonas stutzeri and Pseudomonas teessidea .

In one embodiment, the rhamnolipid-producing microorganism may be Pseudomonas nitroreducens .

In one embodiment, the rhamnolipid-producing microorganism may be Pseudomonas nitroreducens KCTC12325.

Rhamnolipid-producing microorganisms may be in the form of solids containing water, in which case they may be expressed by the term “wet cell.”

When a carrier containing rhamnolipid-producing microorganisms is injected into the membrane bioreactor, there is an effect of controlling membrane contamination due to the surface activity of rhamnolipids produced by the microorganisms. When using a carrier containing rhamnolipid-producing microorganisms, the rhamnolipid itself does not need to be injected multiple times into the bioreactor because the microorganisms contained in the carrier continuously produce rhamnolipids. Additionally, because the carrier collides with the separation membrane, there is also a physical membrane fouling control effect.

A carrier containing rhamnolipid-producing microorganisms may be injected once into the bioreactor. Since the microorganisms contained in the carrier continuously produce rhamnolipids, a single injection has an excellent membrane fouling control effect.

In one embodiment, the rhamnolipid-producing microorganism may be obtained by centrifuging the medium in which the rhamnolipid-producing microorganism was cultured and then removing the supernatant. The medium may be a liquid nutrient medium.

In one embodiment, rhamnolipid-producing microorganisms can be obtained from a pellet obtained after centrifuging the medium in which the rhamnolipid-producing microorganisms were cultured.

The centrifugation speed may be 5,000 g to 15,000 g, 6,000 g to 14,000 g, 7,000 g to 13,000 g, 8,000 g to 12,000 g, or 9,000 g to 11,000 g.

In one embodiment, the carrier may be alginate beads (eg, calcium alginate beads).

In one embodiment, a carrier containing rhamnolipid-producing microorganisms can be obtained from a mixture of a pellet obtained after centrifuging a medium in which rhamnolipid-producing microorganisms are cultured and an alginate solution. The pellet may be suspended in distilled water.

The carrier containing rhamnolipid-producing microorganisms is coated on the outside with a polymer material. Since a coating layer is formed on the outside of the carrier, the stability of the carrier increases and the shape and weight of the carrier can be maintained, allowing microorganisms contained therein to produce rhamnolipids for a long period of time. The present inventors have found that a carrier containing rhamnolipid-producing microorganisms and coated on the outside with a polymer material maintains its shape and weight stably even for a long period of 20 days or more, 30 days or more, or 40 days or more after being injected into a bioreactor, and I confirmed that the feed was being created.

The polymer materials that coat the outside of the carrier containing rhamnolipid-producing microorganisms include polysulfone, polyurethane, polyacetal, polyamide, polyamide elastomer, and polyester. ester, polyester elastomer, polypropylene, polyacrylonitrile, poly(methymethacrylate), polyolefin, polyvinyl chloride It may be any one selected from the group consisting of vinyl chloride), and silicon.

In one embodiment, the polymer material that coats the exterior of the carrier containing rhamnolipid-producing microorganisms may be polysulfone.

The number of carriers containing rhamnolipid-producing microorganisms is 300 or less, 250 or less, 200 or less, 180 or less, 170 or less, or 170 or less per volume of the biological reactor. It can be injected at a number density of . In other words, even with a small number of carriers, there is an excellent contamination control effect of the separation membrane in the biological reactor.

The average diameter of the carrier containing rhamnolipid-producing microorganisms may be 3.0 mm to 4.5 mm.

The average concentration of rhamnolipid-producing microorganisms contained in the carrier may be 20 mg/ml to 30 mg/ml, 21 mg/ml to 28 mg/ml, or 22 mg/ml to 26 mg/ml. The average concentration of the microorganisms is the ratio of the weight (mg) of the pellet to the volume (ml) of the pellet (or suspension of pellet) and alginate solution mixture obtained after centrifuging the medium in which rhamnolipid-producing microorganisms were cultured. It may have been calculated.

The operating method of the biological reactor of the present invention uses a carrier containing rhamnolipid-producing microorganisms, so a separate rhamnolipid purification process is not required. When rhamnolipids are used after biosynthesis, additional processes are required to separate and purify the rhamnolipids, which poses an environmental and economic burden on the industrial side. Therefore, the method of operating a biological reactor of the present invention has high industrial utility.

Additionally, the present invention provides a water treatment system.

The water treatment system of the present invention includes an inlet pump for injecting wastewater; a bioreactor configured to allow wastewater injected by the inlet pump to pass through a separation membrane after being immersed in activated sludge; and an outflow pump that communicates with the interior of the separation membrane and discharges wastewater that has passed through the separation membrane to the outside of the bioreactor.

The biological reactor includes a carrier containing rhamnolipid-producing microorganisms, and the exterior of the carrier is coated with a polymer material.

The water treatment system of the present invention may further include a carrier inlet through which rhamnolipid-producing microorganisms are introduced into the bioreactor. The carrier inlet may be connected to the inside of the biological reactor.

The inlet pump is a pump for transporting wastewater from the outside into the bioreactor, and the wastewater injected by the inlet pump is immersed in the activated sludge inside the bioreactor.

Activated sludge is sludge that has the ability to ingest or decompose substances in wastewater, and is composed of microorganisms such as bacteria, protozoa, and metazoans, as well as abiotic inorganic and organic substances. The wastewater injected by the inlet pump is immersed in activated sludge, and organic substances in the wastewater are adsorbed.

The separation membrane is immersed in activated sludge, and as wastewater immersed in activated sludge passes through the membrane, contaminants in the wastewater are removed. The type and shape of the separator may be within the above-mentioned range, but is not limited thereto. One or more separation membranes may be included inside the bioreactor.

The effluent pump is a pump for transporting treated water (i.e., treated wastewater) from the inside of the bioreactor to the outside. After being immersed in activated sludge, the treated wastewater that passes through the separation membrane is transported to the outside by the effluent pump.

The bioreactor contains a carrier containing rhamnolipid-producing microorganisms, so that the microorganisms contained in the carrier continuously produce rhamnolipids, so the membrane contamination control effect is achieved even if the rhamnolipid itself is not continuously injected into the bioreactor. great. Additionally, because the carrier collides with the separation membrane, there is also a physical membrane fouling control effect.

Rhamnolipids, rhamnolipid-producing microorganisms, carriers containing rhamnolipid-producing microorganisms, and polymer materials may be within the above-mentioned range, but are not limited thereto.

In one embodiment, the biological reactor may further include an oxygen generator that generates oxygen therein.

In one embodiment, the biological reactor may further include a water level control sensor that controls the water level inside the bioreactor.

In one embodiment, the biological reactor may further include an intermembrane differential pressure sensor therein that monitors the transmembrane differential pressure of the separation membrane.

Hereinafter, the present invention will be described in detail with reference to examples.

Example

1. Experimental Materials

1-1. Carrier (meida)

(1) Rhamnolipid-producing microorganisms and growth conditions

In this example, pseudomonas nitroreducens KCTC12325, purchased from the Biological Resources Center (KCTC), was used as a rhamnolipid-producing microorganism to be immobilized on the carrier. pseudomonas nitroreducens KCTC12325 is a microorganism that does not produce infectious substances but has a high rhamnolipid production rate.

KCTC12325, delivered in freeze-dried form, was first inoculated onto Nutrient Agar (NA) plate medium and then cultured in an incubator at a temperature of 30°C. When used for immobilization, one of the colonies cultured on a plate medium was inoculated into liquid nutrient salt medium (MSM) that had been autoclaved (121°C, 15 min). The carbon source of the nutrient medium was prepared from glucose (C ₆ H ₁₂ O ₆ ), the same as the carbon source of the artificial sewage used in this example, and the other nutritional components of the medium were determined under the conditions of this experiment with reference to previous literature (Onwosi and Odibo 2013). It was manufactured to suit (Table 1).

Ingredients Concentration (mg/L) carbon source C ₆ H ₁₂ O ₆ 20,000 macronutrients
(macro nutrient) KH ₂ PO ₄ 2,000 K ₂ HPO ₄ 5,000 (NH ₄ ) ₂ SO ₄ 3,000 NaNO ₃ 2,000 NaCl 100 MgSO ₄ ·7H ₂ O 200 _FeSO4 · _7H2O 10 CaCl ₂ 10 micronutrients
(micro nutrient) ZnSO ₄ ·7H ₂ O 5.25 MnSO _4· H ₂ O 140 CuSO ₄ ·5H ₂ O 70.5 NaMoO ₄ ·2H ₂ O 19.5 CoCl ₂ ·6H ₂ O 200 _{H3BO3 _} 15

All experiments related to microorganisms, such as microorganism inoculation and medium sampling, were conducted on a sterilized clean bench to prevent incorrect cultivation of other bacteria except KCTC12325, and all laboratory tools used in microorganism-related experiments were also sterilized for the same reason.

(2) Manufacturing of microorganism-immobilized alginate beads

Calcium alginate beads, which have low ecotoxicity and excellent biocompatibility, were used as a carrier for fixing microorganisms. In this example, since it was planned to be directly added to the activated sludge reaction tank, these calcium alginate beads, which have low ecological toxicity, were used as a microbial immobilization carrier.

The manufacturing method of calcium alginate beads is shown in Figure 4. KCTC12325, a rhamnolipid-producing microorganism cultivated on NA plate medium, was inoculated into MSM liquid medium and cultured in an incubator at 30°C at 180 rpm for 36 hours. The liquid medium in which KCTC12325 was cultured was centrifuged at a speed of 10,000 g for 15 minutes to remove the supernatant, and the remaining wet cells were resuspended in 10 mL of distilled water. 10 mL of KCTC12325 solution was mixed with 40 mL of 2% (w/v) sodium alginate solution to create a KCTC12325-alginate solution. The KCTC12325-alginate solution was dropped into a 4% (w/v) calcium chloride aqueous solution being stirred at a constant speed of 200 rpm through a nozzle with a diameter of 3 mm at a constant speed of 1.2 mL/min using a peristaltic pump. After dropping and curing for 10 hours, it was washed three times with distilled water.

(3) Coating of microorganism immobilized alginate beads

Non-solvent phase separation (NIPs) was used as a microbial immobilized alginate bead coating method. As a polymer material for coating the beads, polysulfone granules (SU346320) purchased from GoodFellow were used. N-Methyle-2-pyrrolidone was used as an organic solvent for dissolving the polymer material, and a homogeneous solution was created by stirring at 400 rpm at 60°C for 24 hours using a heating plate. The previously prepared microorganism-immobilized alginate beads were allowed to contain sufficient moisture, then submerged in a polysulfone solution and reacted for 10 seconds. During this process, the moisture contained in the alginate beads underwent a phase transition with the organic solvent through diffusion and convection, and as a result, polysulfone, a polymer material, precipitated on the surface of the alginate beads. First, the beads that formed a microporous layer were extracted from the polymer solution and soaked in distilled water for 1 hour to remove the polysulfone solution and secondarily create a microporous layer. Alginate beads with two layers of coating completed were washed three times with distilled water and stored in distilled water for more than 24 hours to prevent residual organic solvents before being used in the experiment.

1-2. Separator (membrane)

The separation membrane used in MBR operation was a MF (microfiltration) flat membrane manufactured by YUASA Co. (Japan). The membrane surface is hydrophilically coated and the effective area of the membrane is 0.1 m ² /module. The nominal pore diameter is 0.4 ㎛ and details are detailed in Table 2.

Parameter Property Material of the membrane PE (polyethylene) type of membrane Flat membrane Effective area of membrane (m ² ) 0.1 Nominal pore diameter (㎛) 0.4 Membrane size (mm) W240 × H340 × T7.5 Operating flux range (m/day) 0.3 - 0.5 Operating temperature range (℃) 2 - 38 Operating pressure range (kPa) -4.9 - 0 Operating pH range 3 - 10

1-3. activated sludge

Activated sludge was collected and used from the aerobic tank of the A20 process at J Water Reclamation Center in Seoul. The collected activated sludge was filtered three times using a 2 mm graduated sieve to remove unnecessary solids and then allowed to settle. Afterwards, other impurities and oil components were removed by removing the supernatant. The activated sludge that underwent pretreatment was maintained and stabilized by supplying air for more than 12 hours, and then seeded in a reaction tank with the MLSS (mixed liquor suspended solids) concentration adjusted to suit each experiment.

1-4. artificial waste water

Artificial sewage was used as the inflow water used in the MBR experiment. Glucose (C ₆ H ₁₂ O ₆ ) was used as a carbon source for artificial sewage, ammonium carbonate (NH ₄ HCO ₃ ) was used as a nitrogen source, and NaHCO ₃ was used to maintain alkalinity. In addition, the macro and micro nutrients added are detailed in Table 3.

Ingredients Concentration (mg/L) carbon source C ₆ H ₁₂ O ₆ 300 nitrogen source NH ₄ HCO ₃ 300 Maintain alkalinity NaHCO ₃ 211.6 macronutrients
(macro nutrient) _{NaH2PO4 _} 72 MgSO ₄ ·7H ₂ O 35 CaCl _{2 ·} 2H ₂ O 5 NaCl 180 KCl 30 yeast extraction One micronutrients
(micro nutrient) EDTA 10 FeCl ₃ 6H ₂ O 1.5 _{H3BO3 _} 0.15 CuSO ₄ ·5H ₂ O 0.06 KI 0.18 MnCl _{2 ·} 4H ₂ O 0.12 Na ₂ MoO ₄ ·2H ₂ O 0.06 ZnSO ₄ ·7H ₂ O 0.12 CoCl ₂ ·6H ₂ O 0.15

2. Experimental method

2-1. Rhamnolipid quantification

The orcinol test (Onwosi and Odibo 2013), which is widely used among spectrophotometric methods, was used to quantify rhamnolipids. The orcinol test is a method of quantifying the amount of rhamnolipid by directly measuring the amount of glycolipid in the sample to be measured. First, to quantify rhamnolipids, the collected samples were centrifuged (10000 g, 15 min) to separate only the supernatant. The separated supernatant was divided into three portions of 0.3 mL each for three repeated experiments. The divided samples were extracted twice with 1 mL diethyl ether. Distilled water was poured into the extracted glycolipid to make 1 mL of glycolipid solution, and 9 mL of orcinol solution in which orcinol was dissolved at a concentration of 0.19% in 53% H ₂ SO ₄ was injected. The final solution was heated to a temperature of 80°C for 30 minutes, cooled to room temperature for 15 minutes, and then OD421 was measured using a UV spectrophotometer. At the time of measurement, a standard curve was prepared with rhamnose (0, 10, 20, 30, 40, 50 mg/L), and the rhamnolipid was indirectly measured under the assumption that 1 μg of rhamnose corresponds to 2.5 μg of rhamnolipid. The concentration was obtained.

2-2. MBR (membrane bioreactor) device

The membrane bioreactor (MBR) was an immersion type, made of acrylic with three laboratory-scale reaction tanks with an effective volume of 6L (FIG. 5). The MBR device includes a peristaltic pump that injects and discharges influent and treated water, an aerator that injects air into the reaction tank, a water level sensor that controls the water level inside the reaction tank, and a separation membrane. It consists of a TMP (Transmembrane Pressure) sensor that monitors the differential pressure between membranes, and a flat membrane module immersed inside the bioreactor (Figure 6).

The operation method used a peristaltic pump to continuously inject influent water into the bioreactor, and connected another peristaltic pump to the flat module to continuously perform membrane filtration and produce treated water. In addition, a water level control sensor was connected to the influent pump to prevent accidents where sludge overflows inside the reaction tank due to continuous injection of influent water. When the water level rises above a certain level, the inlet pump is stopped to control the water level in the reaction tank. A submerged membrane bioreactor was operated by monitoring the transmembrane pressure applied to the internal membrane of the reactor using a TMP sensor.

2-3. water quality analysis

(1) MLSS, MLVSS

To maintain SRT (solid retention time), mixed liquor suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS) were measured using sludge removed from the reactor. Based on the process test method, MLSS was filtered with a 1.2㎛ GF/C filter (Whatman, U.K.), then dried at 105 ℃ for 2 hours to measure the weight of moisture removed, and then incinerated at 550 ℃ for 15 minutes to remove organic matter. MLVSS was measured as the difference between the solid weight remaining after combustion and the dry weight.

(2) COD, NH ₄ ⁺ -N,NO ₃ ⁺ -N,T-N

COD, NH ₄ ⁺ -N, NO ₃ ⁺ -N, and TN analyzes were conducted to confirm the organic matter and nitrogen treatment ability of MBR. The collected influent and treated water samples were analyzed using a UV/vis spectrophotometer (OPTIZEN POP, K LAB KISWIRE Co., Korea) using kits from Hach.

2-4. Transmembrane pressure (TMP) analysis

To indirectly determine the degree of fouling of each MBR used in the experiment, an electronic pressure gauge was installed in the treated water line to measure TMP. An electronic pressure gauge was connected to a laptop, and changes in TMP were observed every minute using a LabVIEW program in which Equation 1 was automatically entered.

[Equation 1]

(P ₁ = pressure entering the membrane (kPa), P ₀ = pressure being applied to the membrane (kPa))

To indirectly determine the degree of fouling of each MBR used in the experiment, an electronic pressure gauge was installed in the treated water line to measure TMP. An electronic pressure gauge was connected to a laptop, and changes in TMP were observed every minute using a LabVIEW program in which Equation 1 was automatically entered.

[Equation 1]

(P ₁ = pressure entering the membrane (kPa), P ₀ = pressure being applied to the membrane (kPa))

2-5. Sludge resistivity value analysis (specific cake resistance, α)

After operating the reactor, a dead end filtration test (Grenier, Meireles et al. 2008) was performed to analyze the effect of the carrier immobilizing rhamnolipid-producing microorganisms on the resistivity value of activated sludge. A PE (polyethylene) membrane with an area of 28.7 cm ² was installed in a 250 mL Amicon cell, 180 mL of sample was filled inside, and nitrogen gas was injected at a constant rate of 5 kPa (FIG. 8). Afterwards, the mass of the treated water passing through the membrane over time was continuously measured and recorded at 5-second intervals for 10 minutes using an electronic scale connected to a computer. The mass measured for 10 minutes was divided by the density of water according to the temperature at the time of measurement and expressed as volume (Vp), and the slope value was obtained through a linear regression equation between the indicated volume Vp and the time divided by volume t/Vp. . The sludge resistivity value (α) was obtained by substituting the obtained slope value into Equation 3 derived from the Vp and t/Vp correlation equation (Equation 2).

[Equation 2]

[Equation 3]

(△P = transmembrane differential pressure (Pa),

V _p = cumulative volume of effluent (m ³ ),

J = filtration rate of effluent (m/s),

μ = viscosity of effluent (Pa·sec),

R _m = internal pore resistance of the membrane (m ^-1 ), A = membrane area (m ² ),

C(t) = sludge concentration over time (kg/m ³ ),

t = elapsed time (s),

α=Sludge resistivity value (m/kg))

2-6. EPS (Extracellular polymeric substance) extraction and analysis

In order to determine the mechanism of inhibiting biofilm formation, we analyzed the effect of a carrier immobilizing rhamnolipid-producing microorganisms on EPS, one of the main causes of biofilm formation. As in the MLSS analysis, activated sludge removed from the reaction tank was used as a sample to maintain SRT (solids retention time). Loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) were extracted from the collected samples using the heat extraction method (Morgan, Forster et al. 1990). A 25 mL sample was centrifuged (4,000 g, 5 min), the supernatant was discarded, and the remaining solid was resuspended in 70°C PBS solution (phosphate buffered saline) to make the same volume of 25 mL. After mixing for 1 minute using a vortexing mixer, centrifugation was performed again (4,000 g, 10 min), and the supernatant was extracted as LB-EPS. The solid remaining after extraction was resuspended in 60°C PBS solution to make the same volume of 25 mL as before. After mixing for 1 minute using a vortexing mixer, the mixture was reacted at 60°C for 30 minutes, centrifuged again (4,000 g, 15 min), and the supernatant was extracted as TB-EPS. The extracted LB-EPS and TB-EPS were divided into protein and carbohydrate and analyzed for composition. Protein substances in EPS were analyzed using a UV/vis spectrophotometer using the Bio-Rad DC protein assay (Dreher, Modjtahedi et al. 2005), also known as the modified Lowry method, and carbohydrate substances were analyzed using The phenol-sulfuric acid method (Nielsen). 2017) was analyzed using a UV/vis spectrophotometer.

2-7. FE-SEM image analysis

Immediately after completing the MBR experiment, the separator was dried in a desiccator for more than 3 days, and then FE-SEM (field emission scanning electron microscope) image analysis was performed. The analysis device used was HITACHI's SU-8010 (Figure 9), and the membrane contamination status was visually compared and analyzed by magnifying and observing the membrane surface.

3. Experimental results

3-1. Evaluation of applicability of rhamnolipid-producing microorganism immobilization carrier

(1) Characteristics of microbial immobilized alginate beads

The pseudomonas nitroreducens KCTC12325 immobilized alginate beads prepared by the method of 1-1-(2) above have a turbid spherical shape with an average diameter of 3.0 to 4.0 mm, an average weight of 35 to 45 mg, and wet cells immobilized on the alginate beads. The concentration is characterized as 25.25 mg/mL (Table 4).

Parameters Properties Shape Unclear sphere Diameter (cm) 3.5 - 4.0 Weight (mg) 35 - 45 Wet cells/Beads (mg/mL) 25.25

(2) Evaluation of rhamnolipid production ability of microbial immobilized alginate beads

Before adding the prepared microbial immobilized alginate beads to MBR, an experiment was conducted to check the rhamnolipid production ability of the alginate beads. Different conditions were given to three 250 mL Erlenmeyer flasks. In Erlenmeyer flask No. 1, KCTC12325 was cultured in 50 mL of distilled water, and in Erlenmeyer flask No. 2, KCTC12325 was cultured in 50 mL of nutrient salt medium (MSM). Microorganism-immobilized alginate beads were added to 50 mL of MSM in flask 3 (Table 5). KCTC12325 added to Erlenmeyer flasks 1 and 2 was cultured in 50 mL of MSM at 30°C at 180 rpm for 36 hours to provide the same conditions as the microorganism-immobilized alginate beads added to flask 3. The supernatant was removed by centrifugation (10,000 g, 15 min) and used. The three flasks were incubated for 7 days at 180 rpm at a temperature of 30 °C. During the culture, 1 mL was collected from each flask at 24-hour intervals, and rhamnolipids were quantified using the orcinol test, and the obtained results were compared using cumulative sum.

As a result, flask No. 1, which cultured KCTC12325 in distilled water, showed the lowest rhamnolipid production ability, flask No. 2, which added microbial immobilized alginate beads to MSM, showed the next highest production ability, and flask No. 3, which cultured KCTC12325 in MSM, showed the lowest production ability. The flask showed the highest production capacity (Figure 10). As a result of the experiment, it was confirmed that rhamnolipids were produced in an environment with nutrients even when microorganisms were immobilized on alginate beads.

Flask No. 1 flask number 2 Flask No. 3 badge 50 mL distilled water 50 mL MSM 50 mL MSM Input strain pseudomonas nitroreducens KCTC12325 Input method wet cell wet cell Microorganism immobilized alginate beads

(3) Alginate bead injection and MBR reaction tank conditions

After confirming that the prepared alginate beads produced rhamnolipids in a nutrient environment, the MBR operation experiment was started. The experiment to evaluate the applicability of the carrier for immobilizing rhamnolipid-producing microorganisms performed in this example was conducted to determine not only whether the alginate beads immobilized with microorganisms showed an effect in controlling membrane contamination due to rhamnolipid production, but also whether the physical impact of the beads on the membrane was confirmed. We just checked to see if there was even a pollution control effect.

After a 3-day stabilization period in each reaction tank, MBR1 was operated as a control reaction tank without any carrier, and MBR2 was operated with alginate beads immobilized on KCTC12325. In addition, alginate beads that did not immobilize microorganisms were added to MBR3 to examine only the effect of controlling physical membrane contamination caused by the beads colliding with the membrane. The amount of beads added to MBR2 and MBR3 was set to 45 g, which is the amount produced when producing alginate beads using 100 mL of 2% (w/v) sodium alginate solution. In addition, the MBR reaction tank conditions were set to be the same for all three reactors and are described in detail in Table 6.

When checked on the 7th day of operation of the reactor, it was found that the alginate beads immobilized with microorganisms and the alginate beads without immobilized microorganisms added to MBR2 and MBR3, respectively, had all melted and disappeared. From a long-term perspective, it was judged that it was unlikely to apply microorganism-immobilized alginate beads. Accordingly, as described later in 3-2, microorganism-immobilized alginate beads were coated and applied to the experiment.

reaction tank MBR1 MBR2 MBR3 injection carrier - Microbial immobilized alginate beads alginate beads Injection amount (g) - 45 45 MLSS (mg/L) 5,000±500 HRT (hr) 4 SRT (days) 25 Flux (L/ ^m2 /hr) 15 Effective volume (L) 6 Reactor temperature (℃) 20 - 24 Reactor pH 6.8 - 7.4 Reactor aeration flow rate (L/min) 4 OLR
(kgCOD/m ³ /day) 1.5

(4) Water quality analysis

The COD and NH ₄ ⁺ -N analysis results are graphs showing the water quality analysis components and removal rate (%) of the influent and treated water for each reaction tank, and the NO ₃ ^― -N analysis results are the water quality analysis components of the influent and treated water for each reaction tank. and a graph showing the production rate (%) (Equation 4).

[Equation 4]

(C _F = concentration of influent components (mg/L),

C _P = concentration of treated water components (mg/L))

Figure 11 shows the COD influent concentration, treated water concentration, and removal rate of each reactor. All three reaction tanks, MBR1 without any carrier, MBR2 with microorganism-immobilized alginate beads, and MBR3 with alginate beads without immobilized microorganisms, all showed COD removal rates of about 95%, and the removal rates of the three reaction tanks were determined through two-way analysis of variance. It was confirmed that there was no significant difference ( p = 0.888). Figure 12 shows the NH ₄ ⁺ -N influent concentration, treated water concentration, and removal rate of each reaction tank. As a result, all three reaction tanks showed NH ₄ ⁺ -N removal rates of about 97%, and two-way analysis of variance confirmed that there was no significant difference in the removal rates of the three reaction tanks ( p = 0.176). Figure 13 shows the NO ₃ ^- -N influent concentration, treated water concentration, and production rate of each reaction tank. As a result, all three reaction tanks showed a NO ₃ ^- -N production rate of about 88%, and through two-way analysis of variance, it was confirmed that there was no significant difference in the production rates of the three reaction tanks ( p = 0.658).

As a result, it appears that the COD, NH ₄ ⁺ -N removal rates, and NO ₃ ^— -N production rates of the three reactors do not show significant differences ( p > 0.05), indicating that the input of carriers during MBR operation has a significant effect on the MBR's organic matter treatment ability or nitrogen treatment. It was confirmed that it did not have a significant effect on ability.

COD
Removal rate (%) _NH4 ⁺ -N
Removal rate (%) NO ₃ ^- -N
Creation rate (%) MBR1 94.96 97.18 88.57 MBR2 95.25 97.43 87.88 MBR3 95.23 96.36 88.38

(5) Transmembrane Pressure (TMP)

After stabilization, the change in transmembrane pressure in each reactor was observed for 7 days after the carrier was added to the MBR. Since the specific resistance value of the membrane used is different for each reaction tank, in order to compare the change in the transmembrane differential pressure, the value of the transmembrane differential pressure (specific TMP) normalized by dividing TMP by TMP ₀ was expressed in a graph (FIG. 14).

Looking at the graph, the transmembrane differential pressure of reactor MBR1, where nothing was added, rose the fastest. Next, the transmembrane differential pressure of MBR3, which contained alginate beads that did not immobilize microorganisms, rose quickly, and the transmembrane differential pressure of MBR2, which contained alginate beads that immobilized microorganisms, rose the slowest. When comparing MBR1, the reactor with the highest transmembrane differential pressure, and specific TMP, 7 days after the experimental operation, the transmembrane differential pressure was measured to be 3.21 times lower for MBR2 and 1.64 times lower for MBR3 compared to MBR 1.

As a result of the experiment, the rate of increase in transmembrane differential pressure of MBR3 with alginate beads that did not immobilize microorganisms was lower than that of MBR1 with no microorganisms added, and it was determined that there was an effect of reducing physical membrane contamination due to collision of the alginate beads themselves. In addition, the rate of increase in transmembrane differential pressure of MBR2 containing alginate beads immobilized with microorganisms was the lowest, indicating that not only the effect of reducing physical membrane contamination due to collision of the beads themselves, but also the production of rhamnolipids from alginate beads immobilized with microorganisms promotes the formation of biofilms. It was judged that it showed an effect in reducing membrane contamination by inhibiting formation.

(6) Sludge resistivity value analysis

A dead end filtration test was used to determine the effect of the microbial immobilization carrier on the specific cake resistance (α) of activated sludge. Immediately after the MBR experiment was completed, activated sludge samples were collected from MBR1 without any carrier and MBR2 with alginate beads immobilized on KCTC12325, and a dead end filtration test was performed. Using the activated sludge cake resistivity value equation mentioned in 2-5, a linear regression equation between V and t/V was obtained, and the slope value was used to calculate the activated sludge resistivity value (FIG. 15).

As a result, the activated sludge resistivity value of MBR1 was measured to be 1.44 times higher than that of MBR2. Based on this, it was determined that the alginate beads immobilized with KCTC12325 suppressed biofilm formation and reduced the resistivity value of activated sludge (Table 8). When correlated with the result in 3-1-(5) that the rate of rise in transmembrane differential pressure was the lowest for MBR2 in which microorganism-immobilized alginate beads were added, the microorganism-immobilized alginate beads inhibited biofilm formation and reduced the resistivity value of the activated sludge, resulting in a membrane It is believed that contamination was controlled and the rate of increase in transmembrane pressure was the lowest.

slope R ² α MBR1
(control) 9 × 10 ¹¹ 0.9949 3.43 × 10 ¹¹ MBR2
(KCTC12325 immobilized bead) 7 × 10 ¹¹ 0.9918 2.39 × 10 ¹¹

(7) EPS (extracellular polymeric substance)

By analyzing EPS, one of the biggest factors in biofilm formation in activated sludge, we analyzed how rhamnolipid-producing carriers affect EPS.

For the reactor MBR1 in which nothing was added and the reaction tank MBR2 in which alginate beads immobilizing KCTC12325 were added, the carbohydrate component (FIG. 16) and protein component (FIG. 16) of LB-EPS (loosely bound EPS) and TB-EPS (tightly bound EPS) Figure 17) was measured.

As a result, it was confirmed that the EPS value of MBR2 in which the carrier immobilizing KCTC 12325 was added showed a slight decrease in production compared to the reactor MBR1 in which nothing was added, but there was no significant difference.

Although rhamnolipids have an effect in reducing EPS production, the effect is small, so it is believed that the main membrane fouling control mechanism of rhamnolipids is not a reduction in biofilm formation through reduction of EPS production by the microorganism itself, such as quorum control (QQ). In addition, when correlated with the result in 3-1-(6) that the sludge resistivity value of MBR2 was the lowest, the generated rhamnolipid did not affect the growth of activated sludge microorganisms and biofilm was formed according to the surfactant activity of the rhamnolipid. It is believed that biofilm formation is suppressed by reducing contact between hydrophobic microorganisms that form .

3-2. Evaluation of long-term applicability of coated rhamnolipid-producing microorganism immobilization carrier

(1) Coated alginate bead characteristics

The alginate beads prepared and used in the experiment evaluating the applicability of the rhamnolipid-producing microorganism immobilization carrier conducted in 3-1 above completely melted and disappeared inside the reaction tank within 6 to 7 days of adding MBR. For long-term use of the beads, alginate beads immobilized with pseudomonas nitroreducens KCTC12325 were coated using the method previously mentioned in 1-1-(3). The manufactured microorganism-immobilized coated alginate beads have a white spherical shape with an average diameter of 3.5 to 4.5 mm and an average weight of 45 to 55 mg, and the concentration of wet cells immobilized on the coated alginate beads is 23.45 mg/mL. (Table 9).

Parameters Properties Shape white sphere Diameter (cm) 3.5 - 4.5 Weight (mg) 45 - 55 Wet cells/Beads (mg/mL) 23.45

(2) Coated alginate bead injection and MBR reaction tank conditions

The experiment to evaluate the long-term applicability of the coated microorganism-immobilized carrier performed in this example not only examined whether the coated alginate beads immobilized with microorganisms showed an effect in controlling membrane fouling by producing rhamnolipids, but also examined the possibility of long-term application of this. We proceeded to find out about it.

After a stabilization period in each reaction tank for 4 days, MBR1 was operated as a control reaction tank without any carrier, and MBR2 was operated by immobilizing KCTC12325 on alginate beads and then adding coated alginate beads. And uncoated alginate beads immobilizing KCTC12325 were added to MBR3. In the above-mentioned 3-1-(3), the amount of carrier input was determined by weight, but in this experiment, the weight varied greatly depending on the presence or absence of coating on the alginate beads, so the number of carriers input was specified according to the volume of the reaction tank rather than the weight. Accordingly, 170 ea/L of coated microorganism-immobilized alginate beads were added to MBR2, and 170 ea/L of uncoated microorganism-immobilized alginate beads was added to MBR3. In addition, the MBR reaction tank conditions were set to be the same for all three reactors and are described in detail in Table 10. In 3-1-(3), membrane fouling was induced in 7 days by operating the flux at 15 L/m ² /hr, but in this experiment, the initial flux was set to 10 to confirm the long-term applicability of the coated alginate beads. It was operated at L/m ² /hr. However, from the point when contamination began to occur in earnest, the flux was operated at 15 L/m ² /hr to see more rapid changes. Details related to this are mentioned in more detail in 3-2-(4) below.

The uncoated microorganism-immobilized alginate beads added to MBR3 gradually swelled and increased in weight after the beads were added, but when checked after 6 days, it was found that all of them had melted and disappeared. In contrast, the coated microorganism-immobilized alginate added to MBR2 was found to have melted and disappeared. The beads maintained their shape and weight during the 36-day application period, except for alginate beads that were lost due to incomplete coating. This could be determined by randomly selecting 10 of the accompanying carriers when disposing of sludge to maintain SRT, washing them three times with distilled water, removing the moisture, and averaging the measured weights. (Figure 18). In MBR3, where all the alginate beads initially dissolved and disappeared, membrane contamination progressed at a similar rate to MBR1, a reaction tank in which nothing was added, and in MBR2, where the coated alginate beads were maintained, membrane contamination was reduced. This is described in more detail along with the rate of increase in transmembrane pressure in 3-2-(4).

reaction tank MBR1 MBR2 MBR3 injection carrier - Microbial immobilization coated alginate beads Microbial immobilized alginate beads Injection volume (ea/L) - 170 170 MLSS (mg/L) 6,000±500 HRT (hr) 1 ^st : 6 / 2 ^nd : ４ SRT (days) 25 Flux (L/ ^m2 /hr) 1 ^st : 10 / 2 ^nd : 15 Effective volume (L) 6 Reactor temperature (℃) 20 - 24 Reactor pH 6.8 - 7.4 Reactor aeration flow rate (L/min) 4 OLR
(kgCOD/m ³ /day) ^1st : 1.2 / ^2nd : 1.5

(3) Water quality analysis

Figure 19 shows the COD influent concentration, treated water concentration, and removal rate of each reactor. MBR1 without any carrier, MBR2 with microorganism-immobilized coated alginate beads, and MBR3 with uncoated microorganism-immobilized alginate beads all showed a COD removal rate of about 97%. The removal rates of the three reaction tanks were determined through two-way analysis of variance. It was confirmed that there was no significant difference ( p = 0.351). Figure 20 shows the NH ₄ ⁺ -N influent concentration, treated water concentration, and removal rate of each reaction tank. As a result, all three reaction tanks showed NH ₄ ⁺ -N removal rates of about 99%, and two-way analysis of variance confirmed that there was no significant difference in the removal rates of the three reaction tanks ( p = 0.627). Figure 21 shows the NO ₃ ^- -N influent concentration, treated water concentration, and production rate of each reaction tank. As a result, all three reaction tanks showed a NO ₃ ^- -N production rate of about 92%, and through two-way analysis of variance, it was confirmed that there was no significant difference in the production rates of the three reaction tanks ( p = 0.531). Figure 22 shows the TN influent concentration and treated water concentration of each reaction tank. As a result, the treated water of the three reaction tanks all showed a TN concentration of about 27 mg/L, and through two-way analysis of variance, it was confirmed that there was no significant difference in the concentrations of the three reaction tanks ( p = 0.420). As a result, the COD and NH ₄ ⁺ -N removal rates, NO ₃ ⁻ -N production rates, and TN concentrations of the three reactors did not show significant differences ( p > 0.05), indicating that the input of coated alginate beads during MBR operation was a significant factor in MBR operation. It was confirmed that there was no significant effect on the organic matter treatment ability or nitrogen treatment ability.

COD
Removal rate (%) _NH4 ⁺ -N
Removal rate (%) NO ₃ ^- -N
Creation rate (%) Treated water T-N concentration (mg/L) MBR1 97.25 98.97 92.07 27.33 MBR2 97.24 98.83 92.08 27.89 MBR3 97.80 99.03 92.00 26.60

(4) Transmembrane Pressure (TMP)

Changes in transmembrane pressure in each reactor were observed for 40 days. Since the specific resistance value of the membrane used is different for each reaction tank, in order to compare the change in the transmembrane differential pressure, the specific TMP value normalized by dividing TMP by TMP ₀ was expressed in a graph (FIG. 23).

Looking at the graph, it was seen that the transmembrane differential pressure of reactor MBR1, in which nothing was added from day 22, and MBR3, in which uncoated microorganism-immobilized alginate beads were added, increased faster than that in MBR2, in which coated microorganism-immobilized alginate beads were added. Afterwards, the rate of change in transmembrane differential pressure decreased, and in order to see a more rapid change in transmembrane differential pressure, the flux was increased from the initially specified 10 L/m ² /hr to 15 L/m ² /hr on day 30, resulting in a more rapid change in transmembrane differential pressure. could be seen. Looking at the subsequent transmembrane pressure, it was seen that MBR1 and MBR3 rose noticeably faster than MBR2. When comparing specific TMP with MBR1, the reactor with the highest transmembrane differential pressure as of 40 days after the experimental operation, the transmembrane differential pressure was measured to be 3.24 times lower for MBR2 and 1.04 times lower for MBR3.

As a result, in the case of MBR3, the transmembrane differential pressure at the end of the experiment is not significantly different from that of MBR1. This is because, as shown in Figure 18 of 3-2-(2), the uncoated alginate beads added to MBR3 are 6 days after injection. It was judged that this was because everything melted and disappeared, so there was no significant difference from MBR1 in which nothing was added. In addition, considering that the rate of increase in transmembrane pressure of MBR2 was the lowest, as shown in the results of 3-1-(5), the coating alginate suppresses biofilm formation and maintains durability due to the continuous production of rhamnolipids in the microbial immobilization coated alginate beads. It was determined that the physical collision of the beads was effective in reducing contamination.

(5) EPS (extracellular polymeric substance)

In the above-mentioned 3-1-(7), it was confirmed that the rhamnolipid-producing microorganism immobilization carrier did not have a significant effect on EPS production. However, because the MBR operation period of 3-1 was not long, the EPS was analyzed in 3-2, which was operated for a relatively long period of time, to confirm once again the effect of the rhamnolipid-producing microorganism immobilization carrier on EPS.

LB-EPS (loosely bound EPS) and TB-EPS (tightly bound) for all three reactors: MBR1 without any carrier, MBR2 with coated microorganism-immobilized alginate beads, and MBR3 with uncoated microorganism-immobilized alginate beads. EPS) each carbohydrate component (Figure 24) and protein component (Figure 25) were measured.

As a result, like 3-1-(7), the amount of EPS produced tended to slightly decrease, but it was confirmed through two-way analysis of variance that there was no significant difference ( p >0.05). The decreasing trend was not clearly visible in Figures 24 and 25, so when this was expressed as a cumulative sum, it was confirmed that the EPS generation of MBR2 was slightly reduced compared to MBR1 even during long-term operation (Figure 26).

Accordingly, although rhamnolipids have an effect in reducing EPS production even during long-term operation, the degree is small, so it was determined that the main membrane fouling control mechanism of rhamnolipids is not reduction of biofilm formation through reduction of EPS production by microorganisms themselves. In addition, when correlated with the result in 3-2-(8) described later that the specific resistance value of activated sludge added with coated microorganism immobilized alginate beads was the lowest, the generated rhamnolipid did not affect the growth of activated sludge microorganisms. It is believed that biofilm formation is suppressed by reducing contact between hydrophobic microorganisms that form biofilms due to the surfactant activity of rhamnolipids.

(6) FE-SEM image observation results

After completing the experiment evaluating the long-term applicability of the coated microorganism immobilization carrier, the membrane immersed in the reaction tank was removed and the degree of activated sludge cake formation was observed with the naked eye. As a result, it was confirmed that the surface of MBR2 to which the microorganism immobilization coating alginate beads had been added had the least amount of cake formation and was relatively clean. was able to work (Figure 27). However, FE-SEM image analysis was performed to obtain more detailed visual information by enlarging. FE-SEM image analysis was divided into 1 k times image (Figure 28) and 10 k times image (Figure 29).

As a result, it was confirmed that the surfaces of MBR1 without any carrier and MBR3 with uncoated microorganism-immobilized alginate beads were both covered with cake. In contrast, in the case of MBR2 with microbial immobilization coated alginate beads, the surface was partially covered with a cake, but the thickness was observed to be thinner than the cakes covered with the other two films. Additionally, many membrane pores that were not visible in the other two membranes were observed. Based on the visual observation results and FE-SEM image observation results, the result is proportional to the increase in transmembrane differential pressure, suppressing biofilm formation by continuously producing rhamnolipids from the microbial immobilization coated alginate beads, and controlling membrane contamination by physical collision of the carrier. I was able to visually judge what had happened.

(7) Evaluation of the long-term rhamnolipid production ability of coated alginate beads

After completion of the experiment evaluating the long-term applicability of the coated microorganism immobilization carrier, all of the coated microorganism immobilization carriers that had been added to the MBR2 reactor were separated and washed at least three times with distilled water. Afterwards, the rhamnolipid production ability of these carriers used in the reaction tank for 36 days was compared with a new coated microbial immobilization carrier that was not used in the reaction tank and an uncoated microbial immobilization carrier. Add 100 mL of nutrient medium (mineral salt medium, MSM) to each of three 250 mL Erlenmeyer flasks, add a new coated microbial immobilization carrier to flask 1, a new uncoated microbial immobilization carrier to flask 2, and finally 3 flasks. The carriers used in the reaction tank for 36 days were added to the flask (Table 12). The amount of new carrier added to flasks 1 and 2 was the same as the amount initially added in the MBR experiment in 3.2. The three flasks were cultured at 30°C and 180 rpm for 8 days. During the culture, 1 mL was collected from each flask at 24-hour intervals, and rhamnolipids were quantified using the orcinol test in 2.2.1, and the obtained results were compared using cumulative sum.

As a result, the new coated microorganism-immobilized alginate beads and the new microorganism-immobilized alginate beads added to flasks 1 and 3 showed similar rhamnolipid production ability, and the carrier used in the reaction tank added to flask 2 had a lower yield than the new carriers. showed production ability (Figure 30). As a result of the experiment, it was found that the microorganism-immobilized alginate beads showed a similar amount of rhamnolipid production ability regardless of the presence or absence of coating, and the microorganism-immobilized coated alginate beads used in the reaction tank had beads lost due to incomplete coating film during MBR operation. Although it shows a lower ability to produce rhamnolipids, the possibility of long-term use of the coated microorganism immobilization carrier was determined as it continued to produce rhamnolipids even after 36 days of input into the reactor.

Flask No. 1 flask number 2 Flask No. 3 badge 50 mL MSM Input strain pseudomonas nitroreducens KCTC12325 Input method Microorganism immobilized alginate beads Coated or not coating No coating coating MBR
Input or not New carrier that was not used in MBR Carrier injected into MBR for 36 days

(8) Sludge resistivity value analysis

1) Batch reactor reaction tank conditions

After long-term operation for 40 days, it was confirmed that the transmembrane pressure difference between MBR1 with nothing added and MBR2 with coated alginate beads was more than three times different. As the operation period became longer, the difference in transmembrane pressure became larger, so it was determined that the treated water flux of MBR1 became smaller than that of MBR2. Because it is a continuous process, as the flux of treated water decreases, the flux of influent water also decreases, which means that the amount of substrate flowing in per hour also changes. Accordingly, it was judged to be unreliable to collect the sludge used in the 40-day experiment and analyze the sludge specific resistance value (specific cake resistance, α).

Therefore, new activated sludge of the same type was collected from the aerobic tank of the A2O process at J Water Reclamation Center in Seoul, and then seeded into two laboratory-scale batch reactors to conduct additional reactor operation experiments. A total of two reaction tanks were used in the experiment. The first reactor was operated as a control reaction tank in which no carrier was added, and the second reactor was operated with microbial immobilization coated alginate beads rescued after the experiment evaluating the long-term applicability of the coated microorganism immobilization carrier of 3-2-(2). Driving (Figure 31). Other than the input of carrier, the operating conditions of both reactors were set to be the same and are described in detail in Table 13. During the operation period, the influent was artificial sewage with the same composition as the influent used in the operation of the MBR reactor, adjusted to an organic loading rate (OLR) of 0.5 kgCOD/m ³ /day. It was operated for a total of 15 days, and the effect of the microbial immobilization coated alginate beads on activated sludge was analyzed through a dead end filtration test after operation.

reaction tank Reactor#1 Reactor#2 Injection carrier - Microorganism immobilization coated alginate beads MLSS (mg/L) 5000±500 F/M 0.1 SRT (days) 12 OLR
(kgCOD/m ³ /day) 0.5 Reactor effective volume (L) 3 Reactor temperature (℃) 20 - 24 Reactor pH 6.8 - 7.4 Reactor aeration flow rate (L/min) 2

2) Sludge resistivity value analysis

After operating the batch reactor for 15 days, a dead end filtration test was performed to determine the effect of the microbial immobilization coated alginate beads on the specific cake resistance (α) of the activated sludge. A dead end filtration test was performed immediately after samples were collected from the first reactor in which no carrier was added and the second reactor in which microbial immobilization coated alginate beads were added. Using the activated sludge cake resistivity value equation mentioned in 2-5, a linear regression equation was obtained between V and t/V, and the slope value was used to calculate the activated sludge resistivity value (FIG. 32).

As a result, the activated sludge value of the first reactor was measured to be 4.72 times higher than that of the second reactor. Judging from this, it was determined that the alginate beads immobilized with KCTC12325 showed the effect of reducing membrane contamination by reducing the resistivity value of activated sludge through biofilm fluorite suppression. (Table 14). When correlated with the result in 3-2-(4) that the rate of increase in transmembrane differential pressure was the lowest for MBR2 in which microorganism-immobilized coated alginate beads were added, the microorganism-immobilized coated alginate beads suppressed biofilm formation and reduced the resistivity value of the activated sludge. As a result, it was determined that membrane contamination was controlled and the rate of rise in differential pressure between membranes was the lowest.

slope R ² α MBR1
(control) 9 × 10 ¹¹ 0.9939 3.27 × 10 ¹³ MBR2
(KCTC12325 immobilized bead) 2 × 10 ¹¹ 0.9689 6.93 × 10 ¹²

Claims (8)

A method of operating the bioreactor in which the process of purifying wastewater flows from the outside to the inside of the separation membrane immersed in the bioreactor and is continuously performed,
Comprising the step of injecting a carrier containing rhamnolipid-producing microorganisms into the bioreactor,
A method of operating a biological reactor, wherein the carrier is coated on the outside with a polymer material.
The method of claim 1, wherein the rhamnolipid-producing microorganism is Pseudomonas nitroreducens .
The method of claim 1, wherein the polymer material is polysulfone, polyurethane, polyacetal, polyamide, polyamide elastomer, polyester, polyester elastomer. (polyester elastomer), polypropylene, polyacrylonitrile, poly(methymethacrylate), polyolefin, poly(vinyl chloride), and silicone ( A method of operating a biological reactor, which is any one selected from the group consisting of silicon).
The method of claim 1, wherein the carrier is injected once into the biological reactor.
The method of operating a biological reactor according to claim 1, wherein the carrier is injected at a number density of 300/L or less per volume of the biological reactor.
Inlet pump for injecting waste water;
a bioreactor configured to allow wastewater injected by the inlet pump to pass through a separation membrane after being immersed in activated sludge; and
It communicates with the interior of the separation membrane and includes an outflow pump for discharging wastewater that has passed through the separation membrane to the outside of the bioreactor,
The biological reactor includes a carrier containing rhamnolipid-producing microorganisms,
A water treatment system wherein the carrier is coated on the outside with a polymer material.
The water treatment system according to claim 6, wherein the rhamnolipid-producing microorganism is Pseudomonas nitroreducens .
The method of claim 6, wherein the polymer material is polysulfone, polyurethane, polyacetal, polyamide, polyamide elastomer, polyester, polyester elastomer. (polyester elastomer), polypropylene, polyacrylonitrile, poly(methymethacrylate), polyolefin, poly(vinyl chloride), and silicone ( A water treatment system selected from the group consisting of silicon.