CN112777830A

CN112777830A - Process for sewage denitrification and phosphorus recycling combined seawater power generation

Info

Publication number: CN112777830A
Application number: CN202011546079.XA
Authority: CN
Inventors: 陈勇; 叶文馨; 胡从智; 唐冰琳; 黄隆隆; 陈小萱; 倪枨
Original assignee: Zhejiang Ocean University ZJOU
Current assignee: Zhejiang Ocean University ZJOU
Priority date: 2020-12-24
Filing date: 2020-12-24
Publication date: 2021-05-11
Anticipated expiration: 2040-12-24
Also published as: CN112777830B

Abstract

The invention provides a process for generating power by combining nitrogen, phosphorus and resource removal of sewage with seawater, belonging to the technical field of water treatment, comprising the steps of taking the sewage as a raw material solution, and taking concentrated brine obtained after seawater evaporation steam power generation as a driving solution to carry out forward osmosis; adding coagulant iron chloride, coagulant aid sodium abietate and sodium phosphate dodecahydrate into seawater, coagulating and precipitating, and decalcifying; carrying out nanofiltration on the obtained diluted forward osmosis driving liquid and the decalcified seawater to obtain the seawater after nanofiltration; the seawater after nanofiltration is used as a raw material, and evaporation steam power generation is carried out; and desalting the seawater subjected to nanofiltration by using waste heat and low-pressure steam generated after power generation to generate fresh water. The process for the combined seawater power generation by the nitrogen and phosphorus removal and recycling of the sewage has the advantages of simple process, high resource utilization rate, high water flux and low energy consumption.

Description

Process for sewage denitrification and phosphorus recycling combined seawater power generation

Technical Field

The invention belongs to the technical field of water treatment, and particularly relates to a process for generating power by combining nitrogen and phosphorus removal and recycling of sewage with seawater.

Background

Forward osmosis is a process of spontaneously achieving water transfer by driving water molecules from a low osmotic pressure feed solution side to a high osmotic pressure driving solution side through a permselective membrane at normal temperature and pressure using the osmotic pressure difference of the solutions on both sides of the membrane. With the osmosis, the driving liquid is continuously diluted by the permeated water, while the raw material liquid is continuously concentrated. Unlike membrane separation process driven by applied high pressure, forward osmosis technology has the obvious advantages of low power consumption, less membrane pollution, simple structure, convenient operation, low equipment cost, etc. In addition, the method also has the characteristics of good quality of permeating water, high water recovery rate, recoverable driving agent, no strong brine discharge and the like. Therefore, the forward osmosis has good application potential in various fields such as wastewater treatment, seawater and brackish water desalination, sludge digestion solution and landfill leachate treatment, food concentration and drug release, long-range exploration, field emergency rescue and the like. However, pure water cannot be directly obtained by a single forward osmosis process, and the diluted driving liquid needs to be subjected to subsequent treatment such as a reverse osmosis process to realize separation of the pure water and concentration and recycling of the driving liquid.

In the prior art, for example, a chinese patent with an issued publication number of CN 105753104B discloses a system and a process for simultaneously desalinating seawater and generating power by using geothermal resources, the system comprises a seawater taking unit, a raw water pretreatment unit located below the sea level, a geothermal heat taking unit, a raw water replenishing unit having a suitable head drop with the raw water pretreatment unit, a reverse osmosis unit, a fresh water lifting unit and a hydroelectric generation unit; a water conduit of the hydroelectric generation unit is communicated with a seawater taking unit, and a tail water conduit of the hydroelectric generation unit is respectively communicated with a raw water replenishing unit and a fresh water lifting unit; the geothermal heat taking unit outputs heat energy to the raw water replenishing unit and the fresh water lifting unit through heating pipelines respectively; the seawater is processed by the raw water pretreatment unit, and then is generated by means of water potential energy, the pressure of the tail water generated after power generation is supplemented by the raw water supplement unit, the seawater is desalted by reverse osmosis, the raw water is separated into fresh water and strong brine, the conversion of geothermal heat energy-water potential energy-electric energy is realized, and the social problems of shortage of fresh water and low-carbon power generation at present are solved.

Disclosure of Invention

The invention aims to provide a process for sewage nitrogen and phosphorus removal and resource utilization combined seawater power generation, which has the advantages of simple process, high resource utilization rate, high water flux and low energy consumption.

The technical scheme adopted by the invention for realizing the purpose is as follows:

the method for the combined seawater power generation by the nitrogen and phosphorus removal and resource utilization of the sewage comprises the following specific steps:

s1, taking sewage as a raw material liquid, entering a low-osmotic-pressure side of a pressure synergistic osmosis membrane module, taking strong brine obtained after seawater evaporation steam power generation as a driving liquid, entering the pressure synergistic osmosis membrane module, and promoting water in the raw material liquid to penetrate through a forward osmosis membrane to enter the strong brine by using the combined action of osmotic pressure difference and external pressure of the strong brine and the sewage as a driving force to obtain a diluted forward osmosis driving liquid;

s2, adding a coagulant of ferric chloride and a coagulant aid of sodium abietate and trisodium phosphate dodecahydrate into seawater, coagulating and precipitating, and then decalcifying to obtain decalcified seawater;

s3, performing nanofiltration on the diluted forward osmosis driving liquid obtained in the step S1 and the decalcified seawater obtained in the step S2 to obtain the seawater subjected to nanofiltration;

s4, taking high-temperature flue gas generated by burning natural gas as a heat source in a steam generator, taking seawater subjected to nanofiltration in the step S3 as a raw material, directly evaporating the processed seawater, feeding steam generated by evaporation in the steam generator into a power generation system, supplying the steam to a generator for power generation to generate electric energy, and feeding concentrated brine generated after evaporation into the step S1 as a driving liquid;

s5, enabling the low-pressure steam generated after power generation to enter a thermal method seawater desalination system to desalinate the seawater subjected to nanofiltration in the step S3, and generating fresh water. Under the coexistence of the sodium abietate and the trisodium phosphate dodecahydrate, the active site of the sodium abietate can efficiently adsorb colloidal particles and precipitate from the solution, and the sodium abietate and trisodium phosphate dodecahydrate can improve the turbidity removal effect of seawater during coagulation pretreatment, reduce the adhesion of pollutants on the surface of the nanofiltration membrane, reduce the pollution on the surface of the nanofiltration membrane and improve the water flux of the nanofiltration membrane.

In certain embodiments, the amount of ferric chloride added in step S2 is 2-8 mg/L.

In certain embodiments, the sodium rosinate is added in an amount of 0.08 to 0.16mg/L and the trisodium phosphate dodecahydrate is added in an amount of 0.17 to 0.26mg/L in the above step S2.

In certain embodiments, the concentration of calcium ions in the seawater after nanofiltration in the above step S3 is less than 50 mg/L.

In some embodiments, the temperature of the high temperature flue gas in the step S4 is 700-850 ℃.

In some embodiments, the steam generator generated in the step S4 has a steam pressure of 0.8-1.0MPa and a temperature of 160-175 ℃.

In certain embodiments, the generator power generation of step S4 is determined based on the steam amount.

In some embodiments, the temperature of the concentrated brine in the step S4 is 158-168 ℃, and the concentration is 58000-63000 mg/L.

In certain embodiments, the pressure of the residual heat low pressure steam generated after power generation in the above step of S5 is 0.1 to 0.2 MPa.

In certain embodiments, the seawater decalcification is performed using a chemical precipitation method.

Preferably, the chemical precipitation method is to perform the seawater decalcification by adding sodium carbonate.

In certain embodiments, the pressure-co-permeate membrane module described above is a plate-type pressure-co-permeate membrane module.

In certain embodiments, the pressure applied to the pressure-collaborative osmosis membrane module ranges from 0.2MPa to 1.0 MPa.

In some embodiments, the forward osmosis membrane comprises an active layer facing the wastewater side and a support layer facing the brine side.

In certain embodiments, the forward osmosis membrane in the pressure-collaborative osmosis membrane module is a polyamide thin layer composite forward osmosis membrane.

In certain embodiments, the active layer of the polyamide thin layer composite forward osmosis membrane is a polyamide material and the support layer is a polysulfone material.

In certain embodiments, the polyamide thin layer composite forward osmosis membrane described above is subjected to BaSO₄And (4) surface mineralization modification.

In certain embodiments, the fresh water recovery rate in step S5 is as high as 85.8% or more.

The invention adopts the method of sewage denitrification and phosphorus resource combined seawater power generation, thereby having the following beneficial effects: the strong brine generated after the seawater steam power generation is used as driving liquid for sewage treatment, and the waste heat low-pressure steam generated by the power generation is used for seawater desalination, so that three energy-consuming enterprises of sewage treatment, seawater power generation and desalination are closely combined, the energy is reasonably utilized, and the resource integration and circulation of the three industries are realized.

The invention adopts sodium abietate and trisodium phosphate dodecahydrate as coagulant aids, thereby having the following advantages: under coexisting, be favorable to the high-efficient micelle that adsorbs of active site of sodium abietate, precipitate from the solution for can improve the turbidity removal effect of sea water when coagulating the preliminary treatment, reduce the pollutant and receive the adhesion on filter membrane surface, alleviate the pollution that receives filter membrane surface, improve and receive filter membrane water flux.

Drawings

FIG. 1 is a graph showing the results of measurement of turbidity removal rate in test example 1 of the present invention;

FIG. 2 is a scanning electron microscope image of the nanofiltration membrane after the decalcified seawater is filtered in test example 1 of the present invention;

FIG. 3 shows the measurement results of the water flux of the nanofiltration membrane in test example 1 of the present invention;

FIG. 4 is the result of measurement of mineralization in test example 2 of the present invention;

FIG. 5 shows the results of measuring the contact angle in test example 2 of the present invention;

FIG. 6 is a scanning electron microscope surface view of a mineralized modified polyamide thin layer composite forward osmosis membrane in test example 2 according to the present invention;

FIG. 7 is a graph showing the results of measuring the water flux and the salt back-mixing flux of the forward osmosis membrane in test example 2 of the present invention;

FIG. 8 shows COD, TN, and NH of the wastewater before and after nanofiltration in test example 2 of the present invention₄ ⁺-N, TP determination of the removal rate.

Detailed Description

Unless otherwise indicated, all publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety as if set forth in their entirety.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.

Many embodiments are described herein in the context of a process for the denitrification and reclamation of sewage into phosphate and seawater power generation. Those of ordinary skill in the art will realize that the following detailed description of the embodiments is illustrative only and is not intended to be in any way limiting. Other embodiments will be readily suggested to those skilled in the art, given the benefit of this disclosure.

In the interest of clarity, not all of the routine features of the implementations or methods described herein are shown and described. It will of course be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions should be made to achieve the specific goals. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

When an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any larger range limit or preferred value and any smaller range limit or preferred value, regardless of whether ranges are separately disclosed. For example, when a range of "1-5" is described, the described range should be interpreted to include ranges of "1-4", "1-3", "1-2 and 4-5", "1-3 and 5", and the like. Where numerical ranges are described herein, unless otherwise stated, the stated ranges are intended to include the endpoints of the ranges and all integers and fractions within the ranges.

Embodiments of the present invention, including embodiments of the invention described in the summary section and any other embodiments described herein below, can be combined arbitrarily.

The present invention is described in detail below.

s4, taking high-temperature flue gas generated by burning natural gas in a steam generator as a heat source, taking seawater subjected to nanofiltration in the step S3 as a raw material, directly evaporating the processed seawater, feeding steam generated by evaporation in the steam generator into a power generation system, supplying the steam to a power generator for power generation to generate electric energy, and feeding concentrated brine generated after evaporation into the step S1 as a driving liquid.

In certain embodiments, the step S2 is performed by chemical precipitation to decalcify the seawater.

In certain embodiments, the pressure-assisted permeable membrane module described above applies a pressure in the range of 0.2 to 1.0 MPa.

In certain embodiments, the polyamide thin layer composite forward osmosis membrane described above is subjected to BaSO₄The specific steps of surface mineralization modification comprise:

a. putting polyamide thin layer composite forward osmosis membrane into 0.06-0.08mol/L BaCl₂Soaking the solution in 1.25-3.44g/L sesbania gum for 60-90s, and repeatedly washing with deionized water for 60-70 s;

b. adding 0.06-0.08mol/L Na₂SO₄Soaking in the solution for 60-90s, and repeatedly washing with deionized water for 60-70 s;

c. repeating the steps a and b for 5-8 times. Sesbania gum is favorable to Ba²⁺Is uniformly and firmly captured by carboxyl groups on the polyamide active layer, can improve the membrane mineralization degree and avoid BaSO₄The aggregation on the surface of the membrane can improve the hydrophilicity of the forward osmosis membrane, thereby improving the forward osmosis performance of the polyamide thin-layer composite forward osmosis membrane, promoting the interception of pollutants in sewage by the forward osmosis membrane and improving the sewage treatment effect.

The present invention is further described in detail with reference to the following examples:

example 1:

1. BaSO₄The method for preparing the surface mineralized modified polyamide thin layer composite forward osmosis membrane comprises the following steps:

1.1 test materials: the polyamide thin layer composite forward osmosis membrane is purchased from the Korea Sanxing group and has a three-layer structure, wherein a polyamide active layer, a polysulfone supporting layer and a polyester non-woven fabric bottom layer are respectively arranged from top to bottom,

1.2 putting the polyamide thin layer composite forward osmosis membrane into 0.08mol/L BaCl₂Immersion in solutionSoaking for 80s, and repeatedly washing for 70s by using deionized water;

1.3 charging 0.08mol/L of Na₂SO₄Soaking in the solution for 80s, and repeatedly washing with deionized water for 70 s;

1.4 repeat the steps 1.2 and 1.3 for 7 times.

2. A process for power generation by combining denitrification and phosphorus reclamation of sewage with seawater comprises the following steps:

2.1 test materials: the nanofiltration membrane is GE Uraslick membrane (NF 4040HS, USA), and the membrane material is polyamide.

TABLE 1 quality of wastewater

Index of water quality	Secondary sedimentation yielding water
		TP(mg/L)	1.84
COD(mg/L)	208
		pH	7.5
TN(mg/L)	34.5
		Conductivity (ms/cm)	2.37
NH₄ ⁺-N(mg/L)	29.4

TABLE 2 seawater composition and Properties

Project parameters	Numerical value
		Baume degree	3.5
TDS(mg/L)	3561
		pH	7.3
Conductivity (ms/cm)	45.2
		Turbidity (NTU)	49
Ca²⁺(mg/L)	422
		Mg²⁺(mg/L)	1254
SO₄ ^2-(mg/L)	2588
		Cl^-(mg/L)	17821
K⁺(mg/L)	354
		Na⁺(mg/L)	11665
HCO₃ ^-(mg/L)	145.3

2.2, sewage treatment: the domestic sewage is treated by standing and precipitation, and the actually used sewage quality is shown in table 1. The sea water composition and properties are shown in table 2. Sewage is used as a raw material liquid and enters a low-osmotic-pressure side of a pressure synergistic osmosis membrane component, strong brine obtained after seawater evaporation steam power generation is used as a driving liquid and enters the pressure synergistic osmosis membrane component, the volume ratio of the raw material liquid to the driving liquid is 3:1, the combined action of osmotic pressure difference of the strong brine and the sewage and external pressure is used as the driving force to promote moisture in the raw material liquid to penetrate through a forward osmosis membrane and enter the strong brine, so that diluted forward osmosis driving liquid is obtained, the pressure synergistic osmosis membrane component is a flat membrane component, and the forward osmosis membrane is BaSO prepared from the raw material liquid 1₄The surface mineralization modified polyamide thin layer composite forward osmosis membrane has the membrane operation mode that the active layer faces to the raw material liquid side, the supporting layer faces to the drawing liquid side, and the effective area of the membrane is 24cm²The pressure applied to the raw material liquid side was 0.6MPa, the raw material liquid flow rate was 1.4L/min, and the driving liquid flow rate was 0.6L/min.

2.3 seawater flocculation: flocculating the seawater, adding ferric trichloride according to 4mg/L, adding 0.08mg/L sodium abietate and 0.26mg/L trisodium phosphate dodecahydrate, stirring at 800r/min for 30s, and precipitating for 30min at each of the stirring speed of 5min, 150 min, 110 min and 60r/min to obtain a flocculated seawater clear solution.

2.4 sea water decalcification: adding Na into the clear liquid of the seawater after flocculation₂CO₃Stirring the powder with stirring paddle, controlling reaction pH value at 7.5, stirring for 25min at 450r/min, and allowing the reaction to proceed fullyStanding for 45min after precipitation to obtain supernatant as decalcified seawater.

2.5 seawater nanofiltration: respectively carrying out nanofiltration on the diluted forward osmosis driving liquid obtained in the step 2.1 and the decalcified seawater obtained in the step 2.4 to obtain the seawater subjected to nanofiltration, wherein the nanofiltration membrane component is a flat membrane component, and the effective area of the membrane is 0.32m²The operating pressure is 2.5 MPa.

2.6 seawater evaporation steam power generation: burning natural gas to generate high-temperature flue gas, wherein the temperature of the high-temperature flue gas is 750 ℃, and directly evaporating seawater (the water inflow is 70L/h, and the salinity of the seawater is 28000mg/L) subjected to nanofiltration in a steam generator; the decalcified seawater is evaporated to generate steam with the pressure of 0.82MPa and the steam quantity of 17L/h, the steam is supplied to a screw expander to generate electricity, the electricity is generated, the low-pressure steam pressure after the electricity is generated is 0.14MPa, and the electricity generation quantity of a screw expansion power machine is 0.75 kw/h; the decalcified seawater is evaporated to produce concentrated brine with the temperature of 162 ℃ and the concentration of 58000 mg/L.

2.7 seawater desalination: the waste heat and low-pressure steam with the pressure of 0.14MPa generated in the power generation process enters a thermal seawater desalination system (namely a high-temperature seawater desalination distillation device recorded in CN 201110253561.9), and the seawater subjected to nanofiltration is desalinated by a high-temperature multi-effect evaporator.

Example 2:

2.3 seawater flocculation: and flocculating the diluted seawater, adding ferric trichloride according to 4mg/L, adding 0.08mg/L sodium abietate at stirring speed of 800r/min for 30s, 5min for each of 150 r/min, 110 r/min and 60r/min, and precipitating for 30min to obtain a flocculated seawater clear solution. The rest of the process was identical to example 1.

Example 3:

2.3 seawater flocculation: and flocculating the diluted seawater, adding ferric trichloride according to 4mg/L, adding trisodium phosphate dodecahydrate of 0.26mg/L, stirring at 800r/min for 5min each for 30s, 150 r/min, 110 r/min and 60r/min, and precipitating for 30min to obtain a flocculated seawater clear solution. The rest of the process was identical to example 1.

Example 4:

2.3 seawater flocculation: and flocculating the diluted seawater, adding ferric trichloride at 4mg/L, stirring at 800r/min for 5min each at 30s, 150 r/min, 110 r/min and 60r/min, and precipitating for 30min to obtain a flocculated seawater clear solution. The rest of the process was identical to example 1.

Example 5:

1.2 putting the polyamide thin layer composite forward osmosis membrane into 0.08mol/L BaCl₂Soaking the solution in 2.25g/L sesbania gum for 80s, and repeatedly washing with deionized water for 70 s;

1.4 repeat the steps 1.2 and 1.3 for 7 times. The rest of the process was identical to example 1.

Test example 1:

1.1 the turbidity of the flocculated seawater is measured by a Hash portable turbidimeter 2100P, and the turbidity removal rate of the seawater is calculated. The results of the turbidity removal are shown in FIG. 1.

1.2 morphological analysis: and (3) observing a scanning electron microscope image of the nanofiltration membrane surface after the decalcified seawater is filtered. The scanning electron micrograph of the nanofiltration membrane after filtration of the decalcified seawater is shown in figure 2.

1.3 determine the nanofiltration membrane run water flux at 0, 10, 25, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300min, calculated as YYST-63 flow meter readings divided by membrane area. The water flux of the nanofiltration membrane was measured and shown in FIG. 3.

As can be seen from fig. 1, the turbidity removal rate of example 1 is significantly higher than that of examples 2, 3 and 4; as can be seen from fig. 2, the pollutants on the surface of the nanofiltration membrane after the decalcified seawater is filtered in example 1 are obviously less than those in examples 2, 3 and 4, and no obvious agglomeration phenomenon occurs; as can be seen from fig. 3, the water flux of the nanofiltration membrane is decreased with the increase of the nanofiltration operation time, but the decrease of the water flux of the nanofiltration membrane in example 1 is significantly slower than that in examples 2, 3, and 4, which indicates that the presence of sodium abietate and trisodium phosphate dodecahydrate is beneficial to the efficient adsorption of colloidal particles by the active sites of sodium abietate, and the colloidal particles are precipitated from the solution, so that the removal effect of the turbidity of seawater can be improved when the sodium abietate is used in the coagulation pretreatment, the adhesion of pollutants on the surface of the nanofiltration membrane is reduced, the pollution on the surface of the nanofiltration membrane is reduced, and the water flux of the nanofiltration membrane is improved.

Test example 2:

2.1 calculation of mineralization degree of the modified polyamide thin layer composite forward osmosis membrane:

the degree of mineralization of each modified membrane was calculated by measuring the increase in mass of each polyamide TFC membrane after surface mineralization modification. Before measuring the mass of each modified membrane before and after the surface mineralization, the membrane is repeatedly washed by deionized water and placed in a vacuum drying oven at 40 ℃ for drying until the weight is constant. The mineralization degree calculation formula is as follows:

MD(g/m²)＝(w₁-w₂)/A

in the formula: MD is degree of mineralization BaSO₄Deposition amount (g/m) on the surface of polyamide TFC film²)；

w₁Dry weight (g) of the TFC membrane after surface mineralization modification;

w₂dry weight (g) of TFC membrane before mineralization;

a is the surface area (m) of the TFC membrane²). The results of the mineralization measurement are shown in FIG. 4.

2.2 surface hydrophilicity analysis of the modified polyamide thin layer composite forward osmosis membrane: the contact angle of the film surface was measured herein using a DSA100 contact goniometer from Kruss, Germany. In the testing process, 2 microliters of ultrapure water is dripped on the surface of the film, the spreading condition of the liquid drops on the surface of the film is shot every 5 seconds, the top and bottom appearances of the liquid drops are analyzed through software to calculate the contact angle, each measurement lasts for 50 seconds, 3 films are measured on each type of sample, 5 test points are taken on each film, and the average value is taken. The results of the contact angle measurements are shown in FIG. 5.

2.3 morphological analysis: and observing the surface image of the mineralized modified polyamide thin layer composite forward osmosis membrane by using a scanning electron microscope. The scanning electron microscope surface image of the mineralized modified polyamide thin layer composite forward osmosis membrane is shown in figure 6.

2.4 the performance of the prepared forward osmosis membrane (mineralized modified polyamide thin layer composite forward osmosis membrane) is tested by using a self-made forward osmosis evaluation device, and the forward osmosis performance of the membrane in an AL-FS (active layer of the membrane facing to raw material liquid) mode is respectively tested under the following test conditions: the extraction solution is 1mol/L NaCl solution, the raw material solution is ultrapure water, and the flow rates of the extraction solution and the raw material solution are both set to be 15L/h; during the test, the test time is 1h, wherein the quality of the drawing liquid is recorded every 10min, and after the test is finished, Cl in the raw material liquid is measured by ion chromatography^-The content of (A); each film sample was repeatedly measured 3 times, and the test results were averaged; the whole measurement process is carried out in an environment of 25 ℃.

2.4.1 determination of Water flux: water flux J_wThe volume of water per unit time and per unit membrane area permeated from the feed liquid side to the driving liquid side. The calculation formula is as follows:

J_w＝△w/(ρ×A_m×△t)

in the formula: j. the design is a square_wIs the water flux, (L/m)²·h)；

Δ w is the change in mass of the drive fluid side before and after the test;

ρ is the density of water (kg/L) under the test conditions;

am is the effective surface area (m) of the membrane²)；

Δ t is the test time (h).

2.4.2 determination of salt back-mixing flux: the content of sodium chloride in the feed solution before and after forward osmosis was measured by using a dean ion chromatography (ICS-900). Calculating the content of sodium chloride in the feed solution after forward osmosis according to ion chromatography, and then calculating to obtain the salt back-mixing flux, wherein the calculation formula is as follows:

J_s-NaCl＝w/(A_m×△t)

J_s-NaClis the back-mixing flux (g/m) of the salt²·h)；

w is the mass (g) of sodium chloride in the raw material solution after the test;

A_mis the effective membrane area (m)²)；

Δ t is the test time (h). The results of measurements of water flux and salt back-mixing flux of the forward osmosis membrane are shown in FIG. 7.

2.5 respectively carrying out water quality determination on the diluted forward osmosis driving liquid before nanofiltration and the diluted forward osmosis driving liquid after nanofiltration: NH determination by Nashi reagent colorimetry₄ ⁺And (2) N, measuring TN by adopting a potassium persulfate oxidation-ultraviolet spectrophotometry method, measuring TP by adopting a potassium persulfate oxidation-molybdenum-antimony anti-spectrophotometry method, measuring COD by adopting a Hash fast digestion method, and calculating the removal rate of nitrogen, phosphorus and organic matters in the sewage. COD, TN, NH of the wastewater before and after nanofiltration₄ ⁺The results of the determination of the removal rate of-N, TP are shown in FIG. 8.

As can be seen from fig. 4, the mineralization degree of the modified polyamide thin layer composite forward osmosis membrane of example 5 is significantly greater than that of example 1; as can be seen from fig. 5, the contact angle of the modified polyamide thin layer composite forward osmosis membrane of example 5 is significantly smaller than that of example 1; as can be seen from fig. 6, compared with example 1, barium sulfate particles on the surface of the modified polyamide thin-layer composite forward osmosis membrane in example 5 are uniformly deposited on the surface of the membrane, and no agglomeration phenomenon occurs; as can be seen from fig. 7, compared with example 1, the modified polyamide thin-layer composite forward osmosis membrane of example 5 has higher water flux, lower salt back-mixing flux and better forward osmosis performance; as can be seen from fig. 8, the COD, TN, NH of the diluted forward osmosis draw solution of example 5 after forward osmosis before nanofiltration was compared to example 1₄ ⁺The removal rate of-N is obviously higher, and COD, TN and NH of the diluted forward osmosis driving liquid after nanofiltration₄ ⁺The removal rate of-N is also significantly higher, which indicates that sesbania gum is advantageous for Ba²⁺Is uniformly and firmly captured by carboxyl groups on the polyamide active layer, can improve the membrane mineralization degree and avoid BaSO₄The aggregation on the surface of the membrane can improve the hydrophilicity of the forward osmosis membrane, thereby improving the forward osmosis performance of the polyamide thin-layer composite forward osmosis membrane, promoting the interception of pollutants in sewage by the forward osmosis membrane and improving the sewage treatment effect.

Conventional techniques in the above embodiments are known to those skilled in the art, and therefore, will not be described in detail herein.

The above embodiments are merely illustrative, and not restrictive, and those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention, and the protection scope of the present invention should be defined by the claims.

Claims

1. A method for power generation by combining denitrification and phosphorus reclamation of sewage with seawater is characterized by comprising the following specific steps:

s4, taking high-temperature flue gas generated by burning natural gas as a heat source in a steam generator, taking seawater subjected to nanofiltration in the step S3 as a raw material, directly evaporating the processed seawater, feeding steam generated by evaporation in the steam generator into a power generation system, supplying the steam to a power generator for power generation to generate electric energy, and feeding concentrated brine generated after evaporation into the step S1 as a driving liquid;

s5, enabling the low-pressure steam generated after power generation to enter a thermal method seawater desalination system to desalinate the seawater subjected to nanofiltration in the step S3, and generating fresh water.

2. The method of claim 1, wherein: the dosage of the ferric chloride is 2-8 mg/L.

3. The method of claim 1, wherein: the dosage of the sodium abietate is 0.08-0.16mg/L, and the dosage of the trisodium phosphate dodecahydrate is 0.17-0.26 mg/L.

4. The method of claim 1, wherein: the concentration of calcium ions in the seawater subjected to nanofiltration in the step S3 is less than 50 mg/L.

5. The method of claim 1, wherein: the temperature of the high-temperature flue gas in the step S4 is 700-850 ℃.

6. The method of claim 1, wherein: and the pressure of the waste heat low-pressure steam generated after power generation in the step S5 is 0.1-0.2 MPa.

7. The method of claim 1, wherein: the applied pressure range of the pressure synergistic permeation membrane component is 0.2-1.0 MPa.

8. The method of claim 1, wherein: and the forward osmosis membrane in the pressure synergistic osmosis membrane component is a polyamide thin layer composite forward osmosis membrane.