Urban sewage recovery method

Abstract

The invention discloses an urban sewage recovery method which comprises the following steps: a, urban sewage and a draw solution are respectively fed into a raw material liquid side and a draw solution side of a forward osmosis membrane assembly for forward osmosis treatment, and the draw solution comprises a scale inhibitor; and b, feeding the effluent on the draw liquid side after the forward osmosis treatment into a nanofiltration membrane assembly, and carrying out nanofiltration treatment to obtain produced water. According to the urban sewage recycling method, the forward osmosis membrane and nanofiltration treatment processes are adopted, the scale inhibitor is adopted as the draw solution, efficient concentration is conducted on the domestic sewage, organic matter removal is achieved, and high-quality produced water is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to a method for recycling urban sewage. Background Art

[0002] With the continuous development of social economy and the continuous expansion of urban scale, the sewage treatment load continues to grow, and the shortage of urban water resources and water pollution have become important factors restricting the sustainable development of my country's economy. In recent years, sewage contains abundant water resources, organic matter, and nutrients such as nitrogen and phosphorus. It is a renewable resource, and the recovery of substances such as biogas and inorganic salts can be achieved through sewage energy and resource means.

[0003] The development of urban domestic sewage resource utilization can effectively improve the utilization rate of recycled water and alleviate the pressure on water resources. However, due to the low organic matter load of domestic sewage, it is difficult to achieve efficient recovery of biogas directly through the traditional anaerobic digestion process. Therefore, it is necessary to conduct in-depth research on this. Summary of the invention

[0004] The present invention is based on the inventor's discovery and understanding of the following facts and problems: At present, due to the low organic load of domestic sewage, it is necessary to concentrate domestic sewage before entering the anaerobic digestion process to achieve efficient utilization of resources. Forward osmosis is an efficient and pollution-resistant sewage concentration method, but it uses inorganic salts such as sodium sulfate and sodium chloride as the extraction liquid, and its regeneration cycle will cause salt loss, so that the produced water still needs subsequent membrane technology for deep desalination treatment. Therefore, it is necessary to develop a method for efficient recovery of domestic sewage resources and energy.

[0005] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, an embodiment of the present invention proposes a method for recycling urban sewage, which uses a forward osmosis membrane and a nanofiltration treatment process, and uses a scale inhibitor as an extraction liquid to efficiently concentrate domestic sewage, thereby removing organic matter and obtaining high-quality produced water.

[0006] The urban sewage recycling method according to the embodiment of the present invention comprises:

[0007] a. sending the municipal sewage and the drawn liquid to the raw liquid side and the drawn liquid side of the forward osmosis membrane module respectively for forward osmosis treatment, wherein the drawn liquid includes a scale inhibitor;

[0008] b. The effluent from the draw liquid side after the forward osmosis treatment is sent to the nanofiltration membrane assembly to obtain produced water after nanofiltration treatment.

[0009] Advantages and technical effects of the urban sewage recovery method of the embodiment of the present invention: 1. In the embodiment of the present invention, forward osmosis membrane components and nanofiltration membrane components are used to concentrate urban sewage. In the forward osmosis treatment, a scale inhibitor is used as the draw liquid. The scale inhibitor has a certain osmotic pressure. The scale inhibitor is used as the draw liquid in the forward osmosis process. After use, it does not need to be separated and treated, and can directly enter the circulating cooling water system to play a scale inhibition role, thereby saving regeneration energy consumption; 2. In the embodiment of the present invention, there is no need to use sodium chloride, sodium sulfate and other commonly used forward osmosis treatment draw liquids, and no subsequent membrane process is required for deep desalination treatment; 3. In the embodiment of the present invention, a scale inhibitor is used as the draw liquid. In the nanofiltration treatment process, it is the same as using commonly used sodium chloride and sulfuric acid. Compared with sodium, nanofiltration treatment has a higher interception rate for scale inhibitors, can more efficiently achieve the concentration of the drawn liquid, not only improves the sewage treatment effect, but also effectively reduces the conductivity of nanofiltration water, reduces the salt content in the produced water, and avoids the use of sodium chloride and sodium sulfate as the subsequent deep desalination treatment of nanofiltration water in the process of drawing liquid; 4. In the embodiment of the present invention, the water in the urban sewage passes through the forward osmosis membrane and enters the drawn liquid under the drive of the osmotic pressure difference, and the diluted drawn liquid realizes the regeneration of the drawn liquid and the regeneration and reuse of the water in the nanofiltration membrane. After the combined treatment of the forward osmosis membrane and nanofiltration, the urban sewage is efficiently concentrated, the organic matter is removed, and high-quality produced water is recovered. The produced water can be controlled below 25 mg / L, NH 4 + -N is controlled below 7mg / L, PO 4 3- -P is controlled below 1.2mg / L and the conductivity is controlled at 50μS / cm, which effectively improves the utilization rate of recycled water and alleviates the pressure on water resources.

[0010] In some embodiments, the scale inhibitor includes diethylenetriaminepenta-methylenephosphonic acid heptasodium (DTPMP-Na 7 ), hydrolyzed polymaleic anhydride (HPMA), sodium polyaspartate (PASP), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), aminotrimethylenesulfonic acid (ATMP), sodium hydroxyethylidene diphosphonate (HEDP-Na 4 ), polyepoxysuccinic acid (PESA), 2-phospho-1,2,4-tricarboxylic acid butane (PBTCA), sodium polymethacrylate (PMA-Na), sodium molybdate (Na 2 MoO 4 ) at least one of.

[0011] In some embodiments, the draw solution includes heptasodium diethylenetriamine penta (methylenephosphonic acid) and sodium polyaspartate.

[0012] In some embodiments, the concentration of the drawn liquid is 50-500 g / L. Preferably, the concentration of diethylenetriamine pentasodium methylene phosphonate is not less than 51 g / L; the concentration of sodium polyaspartate is not less than 93 g / L; the concentration of sodium molybdate is not less than 89 g / L; the concentration of sodium hydroxyethylidene diphosphonate is not less than 105 g / L; the concentration of polyepoxysuccinic acid is not less than 113 g / L; the concentration of 2-phospho-1,2,4-tricarboxylic acid butane is not less than 141 g / L; the concentration of aminotrimethylene sulfate is not less than 165 g / L; the concentration of sodium polymethacrylate is not less than 198 g / L; the concentration of hydrolyzed polymaleic anhydride is not less than 252 g / L; and the concentration of 2-acrylamide-2-methylpropane sulfonic acid is not less than 269 g / L.

[0013] In some embodiments, in step a, the osmotic pressure of the forward osmosis treatment is controlled to be 1-5 Osmol / kg.

[0014] In some embodiments, in step a, the urban sewage is sent to the feed liquid side of the forward osmosis membrane module after removing floating matter and / or suspended matter through a grid well.

[0015] In some embodiments, in step a, after the draw liquid is treated by forward osmosis, the effluent from the draw liquid side is used in a cooling circulating water system for scale inhibition.

[0016] In some embodiments, in step a, the effluent from the raw material liquid side after the forward osmosis treatment is sent to an anaerobic bioreactor for anaerobic digestion treatment, and the generated methane gas is recovered through a gas recovery device.

[0017] In some embodiments, the anaerobic bioreactor includes at least one of a fully mixed anaerobic reactor, an upflow anaerobic sludge blanket, an expanded granular sludge blanket, and an anaerobic baffled reactor.

[0018] In some embodiments, the effluent of the anaerobic bioreactor after anaerobic digestion treatment is sent to a struvite recovery reactor, and magnesium chloride and dipotassium hydrogen phosphate solution are added to the struvite recovery reactor to adjust the pH to form struvite precipitation.

[0019] In some embodiments, in step a, the forward osmosis membrane assembly comprises an active layer and a support layer, the active layer comprises cellulose triacetate, the support layer comprises polyester fiber, and the active layer faces the urban sewage side.

[0020] In some embodiments, in the step b, the concentrated water after the nanofiltration treatment is returned to the draw liquid tank and used as the draw liquid for the forward osmosis treatment in the step a. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1It is a schematic diagram of the process of the urban sewage recycling method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0023] The urban sewage recycling method according to the embodiment of the present invention comprises:

[0024] a. sending the municipal sewage and the drawn liquid to the raw liquid side and the drawn liquid side of the forward osmosis membrane module respectively for forward osmosis treatment, wherein the drawn liquid includes a scale inhibitor;

[0025] b. The effluent from the draw liquid side after the forward osmosis treatment is sent to the nanofiltration membrane assembly to obtain produced water after nanofiltration treatment.

[0026] In the urban sewage recovery method of the embodiment of the present invention, a forward osmosis membrane assembly and a nanofiltration membrane assembly are used to concentrate the urban sewage. In the forward osmosis treatment, a scale inhibitor is used as the drawing liquid. The scale inhibitor has a certain osmotic pressure. The scale inhibitor is used as the drawing liquid in the forward osmosis process. After use, it does not need to be separated and treated, and can directly enter the circulating cooling water system to play a scale inhibition role, thereby saving regeneration energy consumption.

[0027] In the embodiment of the present invention, there is no need to use sodium chloride, sodium sulfate or other commonly used forward osmosis treatment draw solution, and no subsequent membrane process is required for deep desalination treatment.

[0028] In the embodiment of the present invention, a scale inhibitor is used as the draw liquid. During the nanofiltration treatment process, compared with the use of commonly used sodium chloride and sodium sulfate, the nanofiltration treatment has a higher retention rate for the scale inhibitor, and can more efficiently achieve the concentration of the draw liquid, which not only improves the sewage treatment effect, but also effectively reduces the conductivity of the nanofiltration water, reduces the salt content in the water, and avoids the subsequent deep desalination treatment of the nanofiltration water in the process of using sodium chloride and sodium sulfate as the draw liquid.

[0029] In the embodiment of the present invention, water in the urban sewage is driven by the osmotic pressure difference to pass through the membrane into the draw liquid, and the diluted draw liquid is regenerated and the water is recycled in the nanofiltration membrane. After the combined treatment of the forward osmosis membrane and the nanofiltration, the urban sewage is efficiently concentrated, the organic matter is removed, and high-quality water is recovered. The water production can be controlled below 25 mg / L, and NH 4 + -N is controlled below 7mg / L, PO 4 3--P is controlled below 1.2mg / L and the conductivity is controlled at 50μS / cm, which effectively improves the utilization rate of recycled water and alleviates the pressure on water resources.

[0030] In some embodiments, the scale inhibitor includes diethylene triamine penta methylene phosphonate heptasodium (DT-PMP-Na 7 ), hydrolyzed polymaleic anhydride (HPMA), sodium polyaspartate (PASP), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), aminotrimethylenesulfonic acid (ATMP), sodium hydroxyethylidene diphosphonate (HEDP-Na 4 ), polyepoxysuccinic acid (PESA), 2-phospho-1,2,4-tricarboxylic acid butane (PBTCA), sodium polymethacrylate (PMA-Na), sodium molybdate (Na 2 MoO 4 In the embodiment of the present invention, the type of scale inhibitor is preferably selected, which can provide sufficient osmotic pressure in the forward osmosis treatment, so that the urban sewage can be efficiently concentrated, which is conducive to the full recycling of water resources.

[0031] In some embodiments, the draw liquid includes heptasodium diethylenetriaminepenta(methylenephosphonic acid) and sodium polyaspartate. In the embodiments of the present invention, the preferred scale inhibitor combination is used as the draw liquid, which further improves the concentration effect of the forward osmosis treatment and improves the quality of the produced water.

[0032] In some embodiments, the concentration of the draw liquid is 50-500 g / L. In the embodiments of the present invention, the preferred draw liquid concentration is adopted so that the osmotic pressure of the draw liquid can meet the osmotic pressure requirement of forward osmosis treatment, which is beneficial to the efficient concentration of urban sewage.

[0033] The minimum concentrations of the scale inhibitors used in the embodiments of the present invention and the commonly used scale inhibitors in the prior art when the osmotic pressure of forward osmosis is above 1.00 Osmol / kg are shown in Table 1.

[0034] Table 1

[0035] Extraction liquid Minimum concentration (g / L) NaCl 30 <![CDATA[Na 2 SO 4 ]]> 40 <![CDATA[DTPMP-Na 7 ]]> 51 PASP 93 <![CDATA[Na 2 MoO 4 ]]> 89 <![CDATA[HEDP-Na 4 ]]> 105 PESA 113 PBTCA 141 ATMP 165 PMA-Na 198 HPMA 252 AMPS 269

[0036] Preferably, the concentration of heptasodium diethylenetriamine penta (methylene phosphonate) is not less than 51 g / L; the concentration of sodium polyaspartate is not less than 93 g / L; the concentration of sodium molybdate is not less than 89 g / L; the concentration of sodium hydroxyethylidene diphosphonate is not less than 105 g / L; the concentration of polyepoxysuccinic acid is not less than 113 g / L; the concentration of 2-phospho-1,2,4-tricarboxylic acid butane is not less than 141 g / L; the concentration of aminotrimethylene sulfate is not less than 165 g / L; the concentration of sodium polymethacrylate is not less than 198 g / L; the concentration of hydrolyzed polymaleic anhydride is not less than 252 g / L; and the concentration of 2-acrylamide-2-methylpropane sulfonic acid is not less than 269 g / L.

[0037] In some embodiments, in step a, the osmotic pressure of the forward osmosis treatment is 1-5Osmol / kg, preferably not less than 4.5-5Osmol / kg. In the embodiment of the present invention, the use of a scale inhibitor as the draw liquid can make the concentration ratio of urban sewage reach more than 10 times after forward osmosis treatment at a higher osmotic pressure, which is beneficial to improving the sewage treatment effect.

[0038] In some embodiments, in step a, the urban sewage is sent to the feed liquid side of the forward osmosis membrane module after removing floating objects and / or suspended objects through the grid well. In the embodiment of the present invention, the urban sewage is first treated through the grid well to remove more than 85% of floating objects and larger suspended objects.

[0039] In some embodiments, in step a, after the draw liquid is treated by forward osmosis, the effluent from the draw liquid side is used in the cooling circulating water system for scale inhibition. In the embodiment of the present invention, after the forward osmosis treatment, the diluted draw liquid can be partially sent to the cooling circulating water system for use as a descaling agent.

[0040] In some embodiments, in step a, the effluent from the raw liquid side after the forward osmosis treatment is sent to an anaerobic bioreactor for anaerobic digestion treatment, and the generated methane gas is recovered by a gas recovery device. Preferably, the anaerobic bioreactor includes at least one of a fully mixed anaerobic reactor, an upflow anaerobic sludge bed, an expanded granular sludge bed, and an anaerobic baffle reactor. In the embodiment of the present invention, more than 95% of organic matter is effectively removed through the anaerobic digestion process, and at the same time, a gas recovery device is used to recover the methane gas (biogas) generated by anaerobic digestion in the anaerobic bioreactor. The organic matter-methane conversion rate can reach more than 30%, and the generated methane gas can be used as an alternative fuel.

[0041] In some embodiments, the effluent of the anaerobic bioreactor after anaerobic digestion is sent to a struvite recovery reactor, and magnesium chloride and dipotassium hydrogen phosphate solution are added to the struvite recovery reactor to adjust the pH to form struvite precipitation. In this embodiment, magnesium chloride and dipotassium hydrogen phosphate are added to the struvite recovery reactor using ammonia nitrogen and phosphate in the effluent of the anaerobic bioreactor to form struvite precipitated magnesium ammonium phosphate, so that nitrogen and phosphorus in urban sewage can be recycled as chemical fertilizers, realizing the synchronous recovery of nitrogen and phosphorus resources in domestic sewage.

[0042] In some embodiments, in step a, the forward osmosis membrane assembly comprises an active layer and a support layer, the active layer comprises cellulose triacetate, the support layer comprises polyester fiber, and the active layer faces the urban sewage side.

[0043] In some embodiments, in step b, the concentrated water after the nanofiltration treatment is returned to the draw liquid tank and used as the draw liquid for the forward osmosis treatment in step a. According to the loss of the draw liquid in the draw liquid tank, the scale inhibitor can be supplemented to ensure that the scale inhibitor concentration in the draw liquid tank remains relatively constant.

[0044] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0045] Example 1

[0046] The municipal sewage treated in this embodiment is: COD 260mg / L, NH 4 + -N 45mg / L,PO 4 3- -P 3.5mg / L.

[0047] In this embodiment, the forward osmosis membrane used in the forward osmosis membrane assembly has an asymmetric structure, which is composed of an active layer and a supporting layer. The active layer is made of cellulose triacetate (CTA), the supporting layer is made of polyester fiber, the total thickness of the membrane is 115 μm, and the membrane pore size range is 0.3-1.0 nm. Before use, the new membrane is soaked in ultrapure water 2-3 times, each time for 30 minutes, to completely remove the glycerol protective layer on the surface of the membrane, and then the membrane is immersed in ultrapure water and stored at 4 ° C. The configuration of the forward osmosis membrane assembly can be a flat membrane assembly, and the active layer of the membrane faces the side of the urban sewage, that is, the raw liquid side.

[0048] In this embodiment, the nanofiltration membrane assembly uses a nanofiltration membrane (model NF90-4040) produced by Dow Chemical Company of the United States. The nanofiltration membrane material is polyamide. The nanofiltration membrane assembly configuration can be a flat membrane assembly, and the active surface of the membrane faces the side of the drawn liquid.

[0049] like Figure 1 As shown, the urban sewage is sent to the grid well 1 to filter and remove floating objects and large suspended objects, and then sent to the sewage collection tank 2 for homogenization. The sewage in the sewage collection tank 2 is pumped into the raw liquid side of the forward osmosis membrane assembly 4 through the water inlet pump 3, and the draw liquid in the draw liquid tank 6 is pumped into the draw liquid side of the forward osmosis membrane assembly 4 through the draw liquid pump 5. The osmotic pressure of the draw liquid is controlled to be 4.78Osmol / kg. The draw liquid uses 200g / L DTPMP-Na 7(heptasodium diethylenetriamine penta (methylenephosphonate) solution. Under the action of the draw liquid on the draw liquid side, the water in the urban sewage pumped into the raw liquid side permeates into the draw liquid side, so that the draw liquid on the draw liquid side is diluted by the permeated water, and the water output of the draw liquid is pumped into the draw liquid tank 6. After the draw liquid is diluted, a part of the draw liquid can be sent to the circulating cooling system for scale prevention of cooling circulating water, and the remaining diluted draw liquid is pumped from the draw liquid tank 6 into the nanofiltration membrane assembly 8 through the booster pump 7. After nanofiltration treatment, the water passes through the nanofiltration membrane to obtain produced water. After the draw liquid is concentrated, it is returned to the draw liquid tank 6 through the concentrated water reflux pump 9. The concentrated draw liquid ensures the osmotic pressure difference between it and the urban sewage in the forward osmosis membrane assembly 4, so that the urban sewage can be forward osmosis concentrated and treated to remove organic matter. To ensure the stability of the osmotic pressure of the draw liquid during the forward osmosis process, a draw liquid concentration sensor is used in this embodiment. When the draw liquid is diluted, the draw liquid concentrated by nanofiltration is automatically added to maintain the stable concentration of the draw liquid in the forward osmosis membrane assembly 4. The conductivity of the sensor is within the range of ±1% of the set value.

[0050] The effluent of the raw liquid treated by the forward osmosis membrane module 4, i.e., the urban sewage concentrated by the forward osmosis membrane module 4, is sent to the anaerobic bioreactor 11 through the water inlet pump 10. The inlet water quality of the anaerobic bioreactor 11 is: COD2500mg / L, NH 4 + -N 400mg / L,PO 4 3- -P 34mg / L. The anaerobic bioreactor 11 is a UASB reactor with a height-to-diameter ratio of 8 and a hydraulic retention time controlled at 24 hours. The sludge taken from the anaerobic digestion tank of the sewage treatment plant is inoculated into the anaerobic bioreactor 11, and the initial sludge concentration is 3500mg / L. The concentrated urban sewage is anaerobic digested in the anaerobic bioreactor 11. A three-phase separator is provided on the anaerobic bioreactor 11 to achieve the separation of the three phases of mud, water and gas. A hole is opened on the top of the anaerobic bioreactor 11 to connect the reactor to the pH, conductivity and ORP probes, and an air hole that can pass through the wet gas flowmeter, and is connected to the gas recovery device 12 to achieve the recovery of methane gas. After anaerobic treatment, the effluent quality of the anaerobic bioreactor 11 is COD 80mg / L, NH 4 + -N 400mg / L,PO 4 3- -P 30mg / L, biogas recovery rate is 32%.

[0051] The effluent after anaerobic digestion in the anaerobic bioreactor 11 is pumped into the struvite recovery reactor 13, and dipotassium hydrogen phosphate and magnesium chloride are added to the struvite recovery reactor 13 to control the molar ratio of phosphate, ammonium salt and magnesium salt in the water to be 1.1:1.0:1.2. The pH in the struvite recovery reactor 13 is adjusted to 7.5 by adding sodium hydroxide solution, and the reaction and precipitation time is controlled to 4 hours. The amount of magnesium ammonium phosphate crystals generated reaches 33g / L·d, and the recovery rate of ammonia nitrogen in sewage is more than 98%.

[0052] The quality of the produced water after the nanofiltration membrane treatment in this embodiment is: COD 15mg / L, NH 4 + -N 4mg / L,PO 4 3- -P0.8mg / L, conductivity 40μS / cm 2 .

[0053] Example 2

[0054] The method is the same as that of Example 1, except that the draw solution used in the forward osmosis treatment is 150 g / L DT-PMP-Na 7 and 125 g / L of sodium polyaspartate to control the osmotic pressure of the drawn liquid to 4.78 Osmol / kg.

[0055] The water quality of the produced water after the nanofiltration membrane assembly in this embodiment is: COD 12mg / L, NH 4 + -N 3mg / L,PO 4 3- -P0.7mg / L, conductivity 38μS / cm.

[0056] The recovery rate of ammonia nitrogen in the sewage of this embodiment is above 98%, and the recovery rate of biogas is 34%.

[0057] Example 3

[0058] The method is the same as that of Example 1, except that the draw solution used in the forward osmosis treatment includes 300 g / L of sodium polyaspartate solution, so that the osmotic pressure of the draw solution is controlled to be 4.78 Osmol / kg.

[0059] The quality of the produced water after the nanofiltration membrane treatment in this example is: COD 18mg / L, NH 4 + -N 5mg / L,PO 4 3- -P0.9mg / L, conductivity 40μS / cm.

[0060] The recovery rate of ammonia nitrogen in the sewage of this embodiment is above 97%, and the recovery rate of biogas is 30%.

[0061] Example 4

[0062] The method is the same as that of Example 1, except that the draw solution used in the forward osmosis treatment includes 425 g / L of sodium molybdate, so that the osmotic pressure of the draw solution is controlled to be 4.78 Osmol / kg.

[0063] The quality of the produced water after the nanofiltration membrane treatment in this embodiment is: COD 25mg / L, NH 4 + -N7 mg / L,PO 4 3- -P1.2mg / L, conductivity 50μS / cm.

[0064] The recovery rate of ammonia nitrogen in the sewage of this embodiment is above 94%, and the recovery rate of biogas is 28%.

[0065] Comparative Example 1

[0066] The method is the same as that of Example 1, except that the draw solution used in the forward osmosis treatment includes 150 g / L of sodium chloride, so that the osmotic pressure of the draw solution is controlled to be 4.78 Osmol / kg.

[0067] The water quality of the produced water after the nanofiltration membrane treatment in this comparative example is: COD 25mg / L, NH 4 + -N 10mg / L,PO 4 3- -P1.5mg / L, conductivity 100μS / cm.

[0068] The recovery rate of ammonia nitrogen in the sewage of this embodiment is above 88%, and the recovery rate of biogas is 28%.

[0069] Comparative Example 2

[0070] The method is the same as that of Example 1, except that the draw solution used in the forward osmosis treatment includes 200 g / L of sodium sulfate, so that the osmotic pressure of the draw solution is controlled to be 4.78 Osmol / kg.

[0071] The water quality of the produced water after the nanofiltration membrane treatment in this comparative example is: COD 28mg / L, NH 4 + -N 9mg / L, PO 4 3- -P 1.4mg / L, conductivity 80μS / cm.

[0072] The recovery rate of ammonia nitrogen in the sewage of this embodiment is more than 89%, and the recovery rate of biogas is 27%.

[0073] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0074] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for recycling urban sewage, characterized in that: include: a. The municipal sewage and the draw liquid are respectively sent to the raw liquid side and the draw liquid side of the forward osmosis membrane module for forward osmosis treatment, wherein the draw liquid includes a scale inhibitor; b. The effluent from the draw liquid side after the forward osmosis treatment is sent to the nanofiltration membrane assembly to obtain produced water after nanofiltration treatment.

2. The method for recycling urban sewage according to claim 1, characterized in that: In the step a, the scale inhibitor includes at least one of diethylenetriaminepenta(methylenephosphonic acid)heptasodium, hydrolyzed polymaleic anhydride, sodium polyaspartate, 2-acrylamide-2-methylpropanesulfonic acid, aminotri(methylenesulfonic acid)sulfuric acid, sodium hydroxyethylidene diphosphonate, polyepoxysuccinic acid, 2-phospho-1,2,4-tricarboxylic acid butane, sodium polymethacrylate, and sodium molybdate.

3. The method for recycling urban sewage according to claim 2, characterized in that: The drawn liquid includes heptasodium diethylenetriamine penta (methylene phosphonate) and sodium polyaspartate; And / or, the concentration of the drawn liquid is 50-500 g / L, preferably, the concentration of diethylenetriamine pentasodium methylene phosphonate is not less than 51 g / L; the concentration of sodium polyaspartate is not less than 93 g / L; the concentration of sodium molybdate is not less than 89 g / L; the concentration of sodium hydroxyethylidene diphosphonate is not less than 105 g / L; the concentration of polyepoxysuccinic acid is not less than 113 g / L; the concentration of 2-phospho-1,2,4-tricarboxylic acid butane is not less than 141 g / L; the concentration of aminotrimethylene sulfate is not less than 165 g / L; the concentration of sodium polymethacrylate is not less than 198 g / L; the concentration of hydrolyzed polymaleic anhydride is not less than 252 g / L; and the concentration of 2-acrylamide-2-methylpropane sulfonic acid is not less than 269 g / L.

4. The method for recycling urban sewage according to claim 1, characterized in that: In the step a, the osmotic pressure of the forward osmosis treatment is controlled to be 1-5 Osmol / kg.

5. The method for recycling urban sewage according to claim 1, characterized in that: In the step a, the urban sewage is sent to the raw liquid side of the forward osmosis membrane module after removing floating matter and / or suspended matter through the grid well; And / or, after the draw liquid is treated by forward osmosis, the effluent from the draw liquid side is used in a cooling circulating water system for scale inhibition.

6. The method for recycling urban sewage according to claim 1, characterized in that: In the step a, the effluent from the raw material liquid side after the forward osmosis treatment is sent to an anaerobic bioreactor for anaerobic digestion treatment, and the generated methane gas is recovered through a gas recovery device.

7. The method for recycling urban sewage according to claim 6, characterized in that: The anaerobic bioreactor includes at least one of a fully mixed anaerobic reactor, an upflow anaerobic sludge blanket, an expanded granular sludge blanket, and an anaerobic baffle reactor.

8. The method for recycling urban sewage according to claim 6, characterized in that: The effluent of the anaerobic bioreactor after anaerobic digestion treatment is sent to a struvite recovery reactor, and magnesium chloride and dipotassium hydrogen phosphate solution are added to the struvite recovery reactor to adjust the pH to form struvite precipitation.

9. The method for recycling urban sewage according to claim 1, characterized in that: In the step a, the forward osmosis membrane assembly comprises an active layer and a supporting layer, the active layer comprises triacetyl cellulose, and the supporting layer comprises polyester fiber, wherein the active layer faces the side of the urban sewage.

10. The method for recycling urban sewage according to claim 1, characterized in that: In the step b, the concentrated water after the nanofiltration treatment is returned to the draw liquid tank and used as the draw liquid for the forward osmosis treatment in the step a.

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