A method and facility for photochemically degrading SDBS

Abstract

The present invention discloses a method and a facility for photochemically degrading SDBS, belonging to the technical field of sewage treatment. The method is as follows: biological film carriers are arranged in domestic wastewater to cultivate biological films. When the biological films are in the mature and shedding stage, a large amount of dissolved EPS that is free in the water body is secreted by the biological films, and the dissolved EPS degrades SDBS with photosensitive activity under light conditions. The facility includes a biological film tank (1), in which biological film carriers (2), a push-flow pump (3) and an aeration device (4) are installed. A sewage inlet is opened at the bottom of the biological film tank (1), and a treated water outlet is provided at the top. The technical effect of the present invention is that it can reduce the SDBS concentration with low energy consumption and quickly, and the SDBS concentration is reduced to less than 40%. It is applicable to areas with low pipe network penetration rates such as villages and towns and small sewage volumes.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and particularly relates to a method for photochemically degrading sodium dodecylbenzenesulfonate (SDBS) in greywater and a facility for implementing the method. Background Art

[0002] SDBS is one of the important components of anionic surfactants. Due to its hydrophilic and lipophilic group structures, SDBS is widely used in industries and daily life such as synthetic detergents and soaps. Therefore, SDBS has become an emerging pollutant that causes the increasingly serious pollution of the world's water resources. SDBS can cause eutrophication of water bodies (bloom outbreaks), thereby reducing the dissolved oxygen concentration, weakening the light transmission efficiency of water bodies, deteriorating the water quality, and affecting the natural ecosystem. Once SDBS enters natural water bodies, it will seriously affect the aquatic biological community, plant community and the self-purification process of the aquatic environment, reduce the water quality, and cause environmental pollution. If the concentration of SDBS surfactant is too high, it will produce toxic effects on organisms in the environment.

[0003] SDBS exists in the greywater part of domestic wastewater, including greywater generated during bathing and laundry. Although greywater is called low-pollution wastewater and the concentration of its conventional pollutants does not exceed the standard, the concentration of SDBS is higher than that in other domestic sewage. Considering that in some areas with low pipe network penetration rates such as rural areas, there is a phenomenon of direct discharge of wastewater, which will cause environmental problems that cannot be ignored.

[0004] Existing methods for removing SDBS mainly include physical and chemical methods, biological methods, and ecological methods. Physical and chemical methods include traditional foam separation methods, adsorption methods, membrane separation methods, coagulation methods, etc.; and emerging removal directions, including the photodegradation direction (photo-Fenton method, TiO2 photocatalysis method, ultraviolet radiation method), advanced oxidation direction (persulfate advanced oxidation), and electrochemical direction (direct electrochemical oxidation, solar-mediated electrochemical oxidation). Among them, the photocatalysis method in physical and chemical methods for degrading various pollutants is one of the research hotspots in recent years. The biological treatment method is a pilot experiment for constructing a reactor (such as FBR, EGSB, UASB). Based on the treatment of conventional pollutants by microorganisms, the treatment status of the reactor for SDBS and its homologues and other surfactants is mainly observed, and the dominant strains for degrading SDBS are searched for. The ecological treatment method is to establish horizontal flow constructed wetlands, vertical flow constructed wetlands, ecological filters and land infiltration systems for surfactants.

[0005] The above various methods for removing SDBS in greywater have problems such as high investment and construction costs, high energy consumption, slow treatment speed, and low efficiency, and are not suitable for decentralized greywater treatment in rural areas. Obtaining a SDBS degradation method with low cost, low energy consumption and fast treatment speed is a technical problem in this field. Summary of the Invention

[0006] In view of the problem of existing SDBS polluting water resources, the technical problem to be solved by the present invention is to provide a method for photocatalytic degradation of SDBS, which can rapidly reduce the concentration of SDBS with low energy consumption before wastewater discharge. The present invention also provides a facility for photocatalytic degradation of SDBS.

[0007] To solve the above technical problems, the technical solution of the present invention is as follows:

[0008] On the one hand, a method for photocatalytic degradation of SDBS provided by the present invention is: arranging biofilm carriers in domestic wastewater, culturing biofilms, the biofilms being in the mature and shedding stage, and the biofilms secreting a large amount of dissolved EPS (extracellular polymer) free in the water body, and the dissolved EPS photodegradating SDBS under light irradiation conditions.

[0009] On the other hand, a facility for photocatalytic degradation of SDBS provided by the present invention includes a biofilm pool, in which biofilm carriers, a pusher pump and an aeration device are installed. A sewage inlet is opened at the bottom of the biofilm pool, and a treated water outlet is provided at the top.

[0010] The technical effects of the present invention are as follows:

[0011] The method of the present invention can rapidly photodegrade SDBS, reduce the concentration of SDBS in domestic wastewater, with high efficiency, low implementation difficulty and low energy consumption. The reduction of organic pollutants such as SDBS can be completed through natural light irradiation, reducing the natural attenuation load of pollutants in the downstream basin, and is applicable to areas with low pipe network penetration rate and small sewage volume such as villages and towns.

[0012] The facility of the present invention can pre-collect rural direct discharge gray water, and utilize the photosensitization excitation of extracellular polymers in the water body to generate a series of reactive intermediates to indirectly photodegrade organic pollutants such as SDBS, rapidly reducing the content of SDBS in gray water, and effectively avoiding the impact of gray water direct discharge on the water quality of nearby drinking water sources. Description of the Drawings

[0013] The drawings of the present invention are described as follows:

[0014] Figure 1 It is the UV-vis spectrogram of SDBS (the ordinate ABS is the unit of ultraviolet absorbance);

[0015] Figure 2 It is the photocatalytic degradation effect diagram of SDBS under xenon lamp irradiation;

[0016] (a), SEPS (dissolved EPS); (b), LB-EPS (loosely bound EPS); (c), TB-EPS (tightly bound EPS);

[0017] Figure 3 It is a comparative graph of the photodegradation of SDBS under 8-hour irradiation of a xenon lamp;

[0018] (a), HA (humic acid); (b), FA (fulvic acid);

[0019] Figure 4 It is a schematic structural diagram of the facility of the present invention.

[0020] Figure 4 Among them: 1. Biofilm pool; 2. Biofilm carrier; 3. Pushing flow pump; 4. Aeration device; 5. Return pump; 6. Interception channel; 7. Sedimentation tank; 8. Pretreatment tank; 9. Effluent tank. Specific embodiments

[0021] The present invention will be further described below in conjunction with the drawings and embodiments:

[0022] In order to clearly describe the content of the invention, this patent application uses the sequential relationships "front" and "rear" for expression. The "front" and "rear" are determined along the sewage flow route. In the actual use of the present invention, if the sewage flow route changes, the "front" and "rear" relationships will change accordingly, which cannot be regarded as a limitation to the scope of patent protection.

[0023] A method for utilizing photochemical degradation of SDBS in the present invention is as follows: Biofilm carriers are arranged in domestic wastewater to cultivate biofilms. When the biofilms are in the mature and shedding stage, the biofilms secrete a large amount of dissolved EPS that is free in the water body, and under light conditions, the dissolved EPS degrades SDBS through photosensitizing activity. Dissolved extracellular polymer is also simply referred to as SEPS.

[0024] The principle of the present method invention: Most of the dissolved organic matter in surface water is extracellular polymer (EPS) secreted by biofilms. Under irradiation, the extracellular polymer EPS will absorb photons and be excited to generate photosensitizing active intermediates (Reactive Intermediates, RIs), and the RIs cause the migration and transformation of natural water pollutants. This process is called indirect photodegradation. Therefore, biofilms have a photodegradation effect on the water pollutant SDBS in the natural environment.

[0025] Degradation experiment on the photochemical effect of EPS secreted by biofilms on SDBS:

[0026] Under light irradiation, the dissolved organic pollutant SDBS in the water body may compete with dissolved organic matter (EPS, HA, FA) for photons. The situation where the pollutant SDBS absorbs photons and causes chemical bond cleavage or recombination to form products is direct photodegradation, while the process of generating reactive oxygen species (ROS) and other reactions with the pollutant SDBS to form products is indirect photodegradation.

[0027] Cultivation of biofilm: Water samples collected from a lake in Chongqing (106.462086E, 29.567711N, GCJ-02) were used to cultivate biofilm in the laboratory. The glass slides with carriers were placed in a transparent glass tank filled with natural water (50 cm × 30 cm × 25 cm), and a trace amount of mineral salt solution (Minimal Mineral Salts, MMS) was added. The glass slides were soaked in 3%-5% HNO3 for 24 h in advance, rinsed twice with deionized water, and then fixed in the glass tank. Mark the water level, add a heating rod to keep the water temperature at 25 ± 1 °C. Use an LED lamp (18 W) as the light source to simulate natural light in the laboratory for biofilm cultivation. A small power push-flow pump (2 W) was placed at the diagonal position in the glass tank to simulate water flow in the water body while avoiding the water flow rate in the glass tank being too fast, which would make it difficult for the biofilm to enrich on the carrier. The diagonal position of the submersible pump was changed every 3-5 days to change the direction of the water flow. A mini oxygen pump was placed in the glass tank to ensure sufficient dissolved oxygen in the culture medium. The cultivation method was the batch aeration method. Aeration was stopped every 3-4 days, and the mixture was allowed to settle for 1 h. One-fourth of the culture medium volume was replaced with newly collected natural water.

[0028] Extraction of extracellular polymeric substances EPS: Scrape the biofilm on the glass slide and place it in a centrifuge tube. Add water to 50 mL, and use the low-temperature water bath heating method to extract EPS step by step. The steps are as follows:

[0029] 1). Take 50 mL of biofilm sample, centrifuge (3000 g, 4 °C, 15 min). The above parameters are the centrifugal force, centrifugal temperature, and centrifugal time respectively. The same applies hereinafter. Filter the supernatant with a 0.45 μm filter membrane to obtain soluble extracellular polymeric substances (SEPS);

[0030] 2). Add deionized water to 50 mL, shake (100 r / min) in a constant temperature incubator (4 °C) for 1 h, and then centrifuge (5000 g, 4 °C, 15 min). Filter the supernatant with a 0.45 μm filter membrane to obtain loosely bound extracellular polymeric substances (LB-EPS);

[0031] 3). Add phosphate buffer PBS to 50 mL, perform water bath (80 °C, 30 min), centrifuge (10000 g, 4 °C, 15 min), and filter the supernatant with a 0.45 μm filter membrane to obtain tightly bound extracellular polymeric substances (TB-EPS).

[0032] Experimental conditions: Use a 500 W xenon lamp to simulate natural light irradiation for the photoreaction of SDBS. The reaction time is 8 h. The reaction is carried out in a 25 mL quartz test tube, and the SDBS concentration is 5 mg / L -1 Adjust the reaction system with phosphate buffer PBS (pH = 7.0). After placing a magnetic stirrer in the quartz test tube, place it in the test tube rack of the photoreactor.

[0033] Experimental grouping: ① Indirect photodegradation group: SDBS + EPS + light, with EPS concentrations set at 2, 6, and 10 mg / L. -1 ; ② Direct photodegradation group: SDBS + light, with EPS concentration set at 0.

[0034] Experimental procedure: The indirect and direct photodegradation groups were started after being placed in the dark for a period of time to determine the effect of light irradiation on the degradation of SDBS. For each EPS concentration value, three samples were taken, and equal amounts of the reaction solution were taken at equal time intervals for SDBS concentration measurement.

[0035] Experimental results:

[0036] The UV-vis (ultraviolet-visible absorption) spectrum of SDBS is as Figure 1 shown. SDBS has no obvious absorption peak in the visible light band. The spectral data indicate that SDBS has a weak ability to absorb photons in this band under natural light conditions, the direct photodegradation process is slow, and light is not the dominant factor leading to the decomposition and transformation of SDBS.

[0037] The photodegradation of SDBS by EPS is as Figure 2 shown. The removal rate and degradation rate of SDBS within 8 h are positively correlated with the EPS concentration. As the EPS concentration increases, the photosensitizers responsible for light excitation in the reaction system also increase, resulting in an increase in the content of RIs generated. The RIs targeting SDBS increase, leading to indirect photodegradation. Compared with the control group without adding EPS, it is found that the contribution rate of indirect photodegradation of SDBS is much higher than that of direct photodegradation at the laboratory level, and with the increase in the EPS concentration in the reaction system, the removal rate and degradation rate of SDBS can increase within a certain range. During the 8-h reaction process, the removal rate of the indirect photodegradation group shows a slowing trend over time. The first 2 - 3 h is the stage with higher reaction efficiency. It is inferred that as the reaction progresses, EPS in the system will be gradually consumed, the photosensitive activity will decrease, substances that are not easily obtained for photosensitive active intermediate RIs are generated, or the concentration of RIs precursors decreases, so the RIs yield decreases, and the photodegradation rate of SDBS tends to balance.

[0038] When different degrees of attached EPS are added to the reaction system as photosensitizers, SDBS will undergo different degrees of degradation. Among them, dissolved EPS has the best photodegradation removal rate for SDBS, and the removal rate reaches 62.1% at a concentration of 10 mg / L. The specific removal rates of the three different degrees of attached EPS are as follows: ① High concentration: SEPS > TB-EPS > LB-EPS; ② Medium and low concentrations: SEPS > LB-EPS > TB-EPS. Generally speaking, the SDBS degradation performance of dissolved EPS is significantly better than that of bound EPS (including loosely bound LB-EPS and tightly bound TB-EPS).

[0039] AsFigure 3 As shown, by adding purchased humic acid FA and fulvic acid HA and making comparisons, it is found that at the same concentration level, the removal efficiency of externally added natural organic matters HA and FA for SDBS is significantly inferior to that of EPS produced by the biofilm. Its highest removal rate appears at a low concentration (0.5 mg / L -1 ), the removal rate of the FA group is 36.3%, and the removal rate of the HA group is 32.8%, generally lower than the removal rate level of over 40% of the SEPS group. As the concentrations of HA and FA increase, the removal ability for SDBS shows a downward trend instead.

[0040] As Figure 4 shown, the facility of the present invention includes a biofilm tank 1, in which a biofilm carrier 2, a push-flow pump 3, and an aeration device 4 are installed. The bottom of the biofilm tank 1 is provided with a sewage inlet, and the top is provided with a treated water outlet.

[0041] The usage process of the facility of the present invention is as follows:

[0042] In the biofilm cultivation stage, sufficient sewage and surface water are introduced into the biofilm tank 1, and the biofilm is cultivated by the blanketing aeration method, that is, standing and sedimenting for 1 h every 3 - 4 days, discharging 1 / 4 of the volume of water, introducing 1 / 4 of the volume of sewage and surface water, controlling its total organic carbon TOC = 10 mg / L, and continuously aerating during this period until the biofilm growth enters the middle and late stages, that is, the phenomenon that the biofilm falls off from the biofilm carrier 2 appears.

[0043] In the greywater treatment stage, treatment can be carried out after meeting the following conditions: 1) The TOC reaches 10 mg / L, and if it is insufficient, it is adjusted by greywater, irrigation water, and return water; 2) There is sufficient sunlight during the day; 3) The SDBS concentration is above 10 mg / L, and a certain amount of defoaming agent is injected to avoid the generation of foam due to the water flow disturbance of SDBS. The push-flow pump 3 is used to keep the sewage in the tank homogeneous, and the aeration device 4 is for ensuring the growth of the biofilm. The sewage stays in the biofilm tank, and the SEPS in the water body undergoes photosensitization under natural irradiation to generate a series of reactive intermediates that can indirectly photodegrade pollutants such as SDBS, and is discharged into the effluent tank after a period of time.

[0044] The aeration device 4 adopts tube aeration or microporous aeration, both of which can ensure the growth of the biofilm. Continuous aeration enables the biofilm growth to enter the middle and late stages, secreting a large amount of EPS free in the water body, whose photosensitive activity is the best and the photodegradation efficiency for SDBS is the best.

[0045] At the front end of the sewage inlet of the biological membrane tank 1, a sewage interception channel 6, a sedimentation tank 7, and a pretreatment tank 8 are arranged in sequence. The sewage interception channel 6 is used to collect the greywater discharged from village and town laundry and bathing, and then collect the farmland irrigation water to adjust the optimal range of the greywater TOC, and the concentration is about equal to 10 mg / L. Usually, the laundry and bathing time in villages and towns mostly occurs after sunset. The sedimentation tank 7 is used to precipitate and remove substances such as sediment from the greywater collected in a timely manner. The pretreatment tank 8 is used to store the greywater and adjust the TOC concentration.

[0046] At the rear end of the water outlet of the biological membrane tank 1 for treating water flow, there is an outlet tank 9 connected. The outlet tank 9 is connected to the pretreatment tank 8 through a reflux pump 5. Part of the sewage discharged into the outlet tank 9 is refluxed through the reflux pump 5 to adjust the water quality of the pretreatment tank 8.

Claims

1. A method for photochemically degrading SDBS, characterized in that: A biofilm carrier is arranged in domestic wastewater to cultivate a biofilm. The biofilm is in the mature and shedding stage, and the biofilm secretes a large amount of dissolved EPS that is free in the water body. Under light conditions, the dissolved EPS degrades SDBS through photosensitized activity; Extract extracellular polymeric substances EPS: Scrape the biofilm on the glass slide and place it in a centrifuge tube. Add water to 50 mL, and use the low-temperature water bath heating method to extract EPS step by step. The steps are as follows: Step 1: Take 50 mL of the biofilm sample, centrifuge and separate it under the conditions of a centrifugal force of 3000 g, a centrifugation temperature of 4 °C, and a centrifugation time of 15 min. Filter the supernatant with a 0.45 μm filter membrane to obtain dissolved extracellular polymeric substances SEPS; Step 2: Add deionized water to 50 mL, shake it at 100 r / min in a constant temperature incubator at 4 °C for 1 h, then centrifuge and separate it under the conditions of a centrifugal force of 5000 g, a centrifugation temperature of 4 °C, and a centrifugation time of 15 min. Filter the supernatant with a 0.45 μm filter membrane to obtain loosely bound extracellular polymeric substances LB-EPS; Step 3: Add phosphate buffer PBS to 50 mL, heat it in a water bath at 80 °C for 30 min, then centrifuge and separate it under the conditions of a centrifugal force of 10000 g, a centrifugation temperature of 4 °C, and a centrifugation time of 15 min. Filter the supernatant with a 0.45 μm filter membrane to obtain tightly bound extracellular polymeric substances TB-EPS; Under irradiation, extracellular polymeric substances EPS will absorb photons and excite to generate photosensitized active intermediates RIs, and RIs cause the migration and transformation of natural water pollutants; The photodegradation removal rate of dissolved EPS for SDBS reaches 62.1% at a concentration of 10 mg / L. The SDBS degradation performance of dissolved EPS is better than that of loosely bound LB-EPS and tightly bound TB-EPS.

2. The method for photocatalytic degradation of SDBS according to claim 1, wherein: The concentration of dissolved EPS is 2 - 10 mg / L -1 .

3. The method for photochemically degrading SDBS according to claim 1, which uses a facility for photochemically degrading SDBS, includes a biofilm tank (1), and is characterized in that: A biofilm carrier (2), a push-flow pump (3) and an aeration device (4) are installed in the biofilm pond (1). A sewage inlet is opened at the bottom of the biofilm pond (1), and a treated water outlet is provided at the top.

4. The method for photocatalytic degradation of SDBS according to claim 3, characterized in that: A sewage interception channel (6), a sedimentation tank (7) and a pretreatment tank (8) are sequentially arranged at the front end of the sewage inlet of the biofilm pond (1).

5. The method for photocatalytic degradation of SDBS according to claim 4, characterized in that: A water outlet tank (9) is connected to the rear end of the treated water outlet of the biofilm pond (1), and the water outlet tank (9) is connected to the pretreatment tank (8) through a reflux pump (5).

6. The method for photocatalytic degradation of SDBS according to claim 3, 4 or 5, characterized in that: The aeration device (4) is a tube aeration or microporous aeration.

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