CN114195322A

CN114195322A - Ternary directional technical system for preparing fresh water by sewage recycling and application thereof

Info

Publication number: CN114195322A
Application number: CN202111386467.0A
Authority: CN
Inventors: 韩京龙; 王爱杰; 钱志敏; 王鸿程; 梁斌; 程浩毅; 孙移鹿; 刘文宗
Original assignee: Harbin Institute of Technology Shenzhen
Current assignee: Harbin Institute of Technology Shenzhen
Priority date: 2021-11-22
Filing date: 2021-11-22
Publication date: 2022-03-18

Abstract

The invention belongs to the field of sewage treatment, and particularly relates to a ternary directional technology system for preparing fresh water by sewage recycling and an application thereof. The system comprises: the device comprises a directional separation unit, a low-salt organic concentrated water purification unit and a reverse osmosis concentrated water nitrogen and phosphorus removal unit, wherein the directional separation unit is mainly used for directionally separating a loose nanofiltration section instead of ultrafiltration by arranging a wide flow channel before reverse osmosis, and the loose nanofiltration section contains organic pollutants, namely low-salt concentrated water and the reverse osmosis section low-organic matter and high-salt concentrated water which are separately treated, so that the difficulty of high-salt and high-organic matter concentrated water treatment is avoided; after the low-salt organic concentrated water purification unit adopts Fenton-like/ozone catalytic pretreatment, the low-salt organic concentrated water is finally mineralized by ozone activated carbon, and effluent water flows back or is discharged; the reverse osmosis concentrated water nitrogen and phosphorus removal unit adopts a denitrification filter tank to realize the deep purification of nitrogen and phosphorus in high-salt concentrated water, and the high-salt concentrated water is discharged or can be used as high-quality water for industrial recycling. The technology has good economic, environmental and social benefits and wide application prospect.

Description

Ternary directional technical system for preparing fresh water by sewage recycling and application thereof

Technical Field

The invention belongs to the field of sewage treatment, and particularly relates to a ternary directional technology system for preparing fresh water by sewage recycling and an application thereof.

Background

The resource utilization of the sewage can relieve the current situation of water resource shortage in water-deficient areas in China, reduce the amount of pollutants from the source and further relieve the problem of water pollution, provide more water resource space for the development of water-deficient areas in China, particularly the economic society of offshore cities, and reserve more ecological water surplus so as to better protect water resources and water environment.

At present, the traditional sewage recycling mode mainly adopts reverse osmosis, inorganic salt is removed after sewage is subjected to reverse osmosis, and high-quality recycling of reverse osmosis effluent can be realized. The reverse osmosis concentrated water is mixed with the inlet water of the nearby sewage plant or is directly discharged. The problem existing in the popularization and application of the system in China is the problem of concentrated water treatment, on one hand, reverse osmosis concentrated water is nondegradable sewage and directly enters a nearby sewage plant, the degradation of pollutants can not be realized in a secondary biochemical section of the reverse osmosis concentrated water, the amount of dilution and discharge of the reverse osmosis concentrated water mixed into an accessory sewage plant is limited and generally does not exceed 20%, so that the reuse amount of the sewage can not be increased; on the other hand, the concentrations of chloride ions and organic matters in the high-salinity concentrated water are in higher levels, the traditional Fenton catalytic oxidation and ozone catalytic oxidation processes are difficult to realize accurate and efficient pretreatment of organic matters difficult to degrade, and the concentrated water is difficult to treat; in addition, if a traditional zero-emission mode is adopted, concentrated water is further concentrated and then evaporated for salt separation, the yield of miscellaneous salt hazardous waste is too high due to the existence of organic matters difficult to degrade, and the landfill and disposal pressure is large and can not be sustained. Meanwhile, the evaporation salt separation process is a high energy consumption, high carbon emission process, and the use of evaporation salt separation is further limited under the pressure constraint of the "double carbon" target.

The pressure of double-carbon emission reduction is oriented, and aiming at the problems of water resource shortage and offshore area pollution, the development of a low-energy-consumption and high-efficiency sewage resource technology has important significance for reducing the emission of pollutants in offshore cities, relieving the pressure of water resource shortage and improving the water quality in offshore areas.

Disclosure of Invention

In view of the problems and the requirements in the prior art, the invention firstly provides a ternary directional technical system for preparing fresh water by recycling sewage, which comprises a directional separation unit, a low-salt organic concentrated water purification unit and a reverse osmosis concentrated water nitrogen and phosphorus removal unit; the directional separation unit is provided with a directional separation loose nanofiltration membrane, and the low-salt concentrated water and the high-salt concentrated water with low organic matters of organic pollutants are separately treated and respectively enter the low-salt organic concentrated water purification unit and the reverse osmosis concentrated water nitrogen and phosphorus removal unit.

As a preferable technical scheme of the invention, the front section of the directional separation unit is provided with a coagulation and high-density sedimentation tank, a multi-medium filter and a security filter.

As a preferred technical scheme of the invention, the directional separation loose nanofiltration membrane adopts a wide flow channel grid, and the width of the flow channel grid is 0.8-1.5 mm; the pipeline is made of a rigid polyvinyl chloride (UPVC), and the directional separation loose nanofiltration membrane is made of polyamide, polyether sulfone or graphene oxide.

As a preferred technical scheme of the invention, the low-salt organic concentrated water purification unit comprises a filter tank, which can adopt a manganese sand filter tank; or an ozone catalysis, ozone/ultraviolet or advanced reduction pretreatment device is adopted; further connecting with a biological activated carbon unit.

As a preferred technical scheme of the invention, the reverse osmosis concentrated water nitrogen and phosphorus removal unit comprises a reverse osmosis device, and is further connected with an energy recovery device; further connected with a denitrification unit.

The invention further provides a new method for preparing the fresh water by recycling the sewage, namely a new technology and a new method for preparing the fresh water by using the domestic sewage and the tail water of the industrial wastewater and sewage plant, and the system comprises the following steps:

1) removing certain hardness, suspended matters, organic pollutants and phosphorus through a pre-treatment section of a coagulation and high-density sedimentation tank, a multi-medium filter and a security filter;

2) removing most organic matters through a directional separation loosening nanofiltration section, and keeping low interception of inorganic nitrogen, inorganic phosphorus and other inorganic salts;

3) according to different properties of organic pollutants in the low-salt concentrated water of the organic pollutants filtered by the loosening and nanofiltration section, the catalytic pretreatment of the organic pollutants is realized through a Fenton-like or ultraviolet catalytic system, the biodegradability is improved, partial mineralization is realized, the low-salt concentrated water enters a filter tank or a filter tank to remove residual iron or other suspended matters, the low-salt concentrated water enters a biological activated carbon section to realize final mineralization, the outlet water is discharged or flows back to the system for water inlet, and the water yield of the whole system is improved;

4) and (3) carrying out reverse osmosis treatment on the low-organic-matter high-salinity concentrated water filtered by the loosening and nanofiltration section, and carrying out energy recovery on the reverse osmosis concentrated water by an energy recovery device, and then, treating the reverse osmosis concentrated water by a denitrification filter tank.

The reverse osmosis section realizes interception of most inorganic salts and organic matters, the effluent forms desalted fresh water, and the fresh water is reused as industrial or municipal high-quality reclaimed water; after the reverse osmosis concentrated water passes through the energy recovery device, the denitrification filter tank is adopted to remove inorganic nitrogen, partial phosphorus and organic pollutants, and the effluent reaches the discharge standard. According to the different distances between the new water plant and the coast, glass fiber reinforced plastic sand or high density polyethylene pipelines with different distances are arranged to discharge the sea or enter a water body suitable for discharging.

Preferably, all the working sections such as a coagulation working section, a high-density sedimentation tank, a multi-media filter, a cartridge filter and the like can be arranged in the pretreatment section in the step 1) according to different inlet water qualities, but one or more treatment working sections can be omitted if the inlet water qualities are good. If the device is arranged, according to different water qualities of inlet water, certain hardness, removal of suspended matters, organic pollutants and phosphorus and backflow of slurry in the high-density sedimentation tank can be realized by adding lime, sodium carbonate, polyaluminium, polyferric, polyacrylamide, powdered activated carbon and the like before coagulation or multi-medium filtration, and the optimal sedimentation effect is realized when the backflow ratio is 90%.

Preferably, the water inlet section in the step 1) controls the growth of microorganisms by adding certain hypochlorous acid, sodium hypochlorite, hydrogen peroxide and the like, wherein the adding amount is 0.1-2mg/L, and the formation of membrane pollution is controlled.

Preferably, the water inlet section in the step 1) controls the growth of microorganisms by adding certain hypochlorous acid, sodium hypochlorite, hydrogen peroxide, chlorine dioxide and the like, so that the organic pollution and the biological pollution of the membrane are effectively controlled.

Preferably, in the multi-medium filtering section in the step 1), a certain activated carbon layer is arranged, so that the deep removal of hydrophobic organic matters is realized, and the problem of membrane pollution is effectively controlled.

Preferably, the directional separation porous nanofiltration membrane used in the step 2) can be made of polyamide, polyether sulfone or graphene oxide, and preferably made of graphene oxide and polyether sulfone.

Preferably, according to different inlet water qualities, the molecular weight cut-off of the directional separation loose nanofiltration membrane used in the step 2) is different from 300 Da to 3000Da, and the apparent cut-off rate of the used medium salt is below 5 percent to 45 percent.

Preferably, the COD of the inlet water in the step 2) is about 30-200 mg/L, the retention rate of the directional separation membrane is preferably selected according to different COD of the inlet water, the retention rate of the preferred directional separation loose nanofiltration membrane on the COD is kept at 80-99%, and the concentration multiple of the inorganic salt is lower than 2 times.

Preferably, in the step 2), the membrane pollution is controlled by adding certain hydrogen peroxide, hypochlorous acid, ozone and iron-based catalytic particles in a controlled manner, wherein the adding amount is 0-5 mg/L.

Preferably, the operation pressure of the step 2) is 0.3-1.5 MPa.

Preferably, the design flux of the polyamide or polyether sulfone loose nanofiltration membrane in the step 2) is 9-17L/m²H is used as the reference value. The design flux of the graphene oxide membrane is 30-50L/m²/h。

Preferably, the design recovery rate of the directional separation loose nanofiltration membrane in the step 2) is 80-95%.

Preferably, the directional separation loose nanofiltration membrane in the step 2) adopts a wide flow channel grid, and the width of the flow channel grid is 0.8-1.5 mm.

Preferably, the material of the pipe in step 2) is a rigid polyvinyl chloride (UPVC).

Preferably, the catalytic pretreatment technology used in step 3) may be fenton, heterogeneous fenton, ultraviolet composite catalysis, ozone catalysis, advanced reduction, or the like, depending on the quality of the feed water.

Preferably, if the influent organic matter is mainly simple aromatic hydrocarbon compounds and the chloride ion concentration is less than 10000mg/L, the ozone catalysis or ultraviolet ozone catalysis is mainly adopted in the step 3), the adding amount of the ozone is 100-200 mg/L, and the ultraviolet dose is 600-2000 mJ/cm²The COD removal rate is controlled to be 40-65%.

Preferably, if the inlet water contains more halogenated organic matters or heterocyclic organic matters and the concentration of chloride ions is lower than 1000mg/L, Fenton or heterogeneous Fenton technology can be considered in the step 3), preferably heterogeneous Fenton-like technology, the adding amount of hydrogen peroxide is 50-300 mg/L, and the removal rate of COD is controlled to be 40-65%. If the incoming water chloride ion concentration is higher than 1000mg/L, the heterogeneous Fenton-like technique is preferably recommended.

Preferably, the water is mainly halogenated organic matters, the biological inhibition of the halogenated organic matters is dominant, and the step 3) can adopt advanced reduction technology or advanced reduction and ozone coupling technology, wherein the adding amount of sodium sulfite is 30-100 mg/L, and the ultraviolet dose is 600-2000 mJ/cm²And the adding amount of the subsequent coupling ozone is 60-150 mg/L.

Preferably, if the organic concentrated water in the step 3) is mainly pretreated by fenton or fenton-like technology, a manganese sand filter tank can be adopted as the filter tank in the step 3) to further remove iron ions and the like, and the filter tank can be omitted according to different water quality conditions.

If the organic concentrated water in the step 3) is mainly subjected to ozone catalysis, ozone/ultraviolet or advanced reduction pretreatment, the filter tank in the step 3) can be omitted or a sand filter device is adopted.

Preferably, the reverse osmosis membrane used in the step 4) is a polyamide membrane, and the designed flux is 17-25L/m²/h。

Preferably, the reverse osmosis membrane used in the step 4) has a salt rejection rate of 92-99%.

Preferably, the reverse osmosis membrane used in the step 4) has a micro-pollutant retention rate of more than 90% for water with molecular weight of more than 100Da,

preferably, in the reverse osmosis process in the step 4), two-stage reverse osmosis can be adopted to improve the recovery rate of water, the first-stage reverse osmosis concentrated water enters the second-stage reverse osmosis, the second-stage reverse osmosis process can adopt wide-runner reverse osmosis (STRO), the water inlet pressure of the second-stage reverse osmosis is 1-2 MPa, and the designed flux is-17L/m²And h, the width of the flow channel grid is 0.8-1.5 mm.

Preferably, a certain amount of hypochlorous acid is added into the reverse osmosis membrane in the step 4), so that membrane pollution is reduced, the rejection rate is improved, and the adding amount is 0.05-0.1 mg/L.

Preferably, the designed recovery rate of reverse osmosis in the step 4) is 75-90%.

Preferably, the concentrated water discharged from the reverse osmosis section in the step 4) is provided with an energy recovery device to further recover energy in the concentrated water, so that the pressure is increased for the first-stage or second-stage reverse osmosis, and the energy consumption is reduced.

Preferably, a certain amount of scale inhibitor and bactericide can be added before the reverse osmosis section in the step 4) according to the requirement to control inorganic scale and biological pollution.

Preferably, in the step 3), when a new water plant and a sewage treatment plant are jointly built, the loose nanofiltration concentrated water is preferentially subjected to catalytic pretreatment, and then the effluent water flows back to the biochemical section of the original sewage treatment plant, so that the final mineralization of the concentrated water is realized.

Preferably, in the step 3), when the outlet water of the loose nanofiltration concentrated water after being catalyzed is difficult to flow back to the biochemical section of the original sewage treatment plant, the organic concentrated water can be catalyzed and pretreated, and then the final mineralization of organic matters is realized by adopting a biological activated carbon technology formed by coupling organisms and activated carbon.

Preferably, the biological activated carbon canister in the step 3) adopts two-stage or three-stage arrangement, and the empty bed residence time of each stage of activated carbon layer is 1-3 h.

Preferably, the thickness of the activated carbon layer adopted by the biological activated carbon canister in the step 3) can be between 1.6m and 5 m.

Preferably, the activated carbon in the step 3) is coal-based irregular activated carbon, the iodine value is more than 950mg/g, the methylene blue value is more than 180mg/g, and the strength is more than 90%.

Preferably, in the step 3), in order to accelerate the start of the biological activated carbon, certain reinforced bacteria can be inoculated correspondingly according to the organic pollution type, so that the removal effect of the biological activated carbon is improved.

Preferably, a certain aeration device is arranged at the bottom of the biological activated carbon section in the step 3), and the dissolved oxygen in the clear water area is kept at 0.5-1.5 mg/L.

Preferably, the effluent mineralized by the biological activated carbon in the step 3) can be partially or completely refluxed to the water inlet end of the whole system or directly discharged, and if the effluent is refluxed, the reflux ratio is based on the standard that the final effluent of the loosening nanofiltration end does not exceed the standard, and the reverse osmosis effluent and the reverse osmosis concentrated water do not exceed the standard.

Preferably, the reverse osmosis concentrated water in the step 4) enters a denitrification filter tank after further recovering energy through an energy recovery device, and the denitrification filter tank can adopt an autotrophic denitrification filter tank or a heterotrophic denitrification filter tank, preferably an autotrophic denitrification filter tank.

Preferably, the residence time of the empty bed of the autotrophic denitrification filter in the step 4) is set to be 20-120 min according to the difference of the quality and salinity of the inlet water.

Preferably, the carbon source of the heterotrophic denitrification filter in the step 4) is preferably sodium acetate, and the adding amount is 30-60 mg/L.

Preferably, in the step 4), in order to reduce the start-up period of the heterotrophic or autotrophic denitrification filter, a certain amount of activated sludge or microbial strains can be inoculated, so that the system can be quickly started.

Preferably, inorganic nitrogen is removed through denitrification in the step 4), and part of the inorganic nitrogen is discharged to the sea or enters a proper water body (a salt water lake, a river, a lake and the like) by arranging corrosion-resistant and pressure-resistant pipelines at different distances according to the different distances between the new water plant and the coast, wherein the type of the pipeline is preferably glass fiber reinforced plastic sand or a high-density polyethylene pipeline.

Preferably, the pipelines in the step 4) can adopt self-flowing or pressure-bearing pipelines according to different terrain gradients, preferably pressure-bearing pipelines, and the flow velocity of the pressure-bearing pipelines is 0.6-2 m/s.

Preferably, the ocean dilution capacity and ocean current conditions should be calculated after the pipeline is discharged into the ocean in the step 4), so that the local salinity change is reduced, and the influence on the ocean is reduced.

Preferably, the pipeline in the step 4), such as a salt water lake or a pipeline directly entering the river and sea, can be directly discharged if the influence on the water ecosystem of the receiving water body is within an acceptable range by environmental evaluation.

Preferably, when the system is used in inland, if the system does not have any problem of receiving water body, the reverse osmosis concentrated water can be further concentrated by adopting wide-channel reverse osmosis (STRO) or disc tube type reverse osmosis (DTRO), and then evaporated into miscellaneous salt, and the miscellaneous salt is discharged in deep sea, so that the problem of miscellaneous salt is avoided.

The implementation principle and the solved problems of the invention comprise:

the directional separation unit is mainly characterized in that a wide-flow-channel directional separation loosening nanofiltration section is arranged before reverse osmosis to replace ultrafiltration, and low-salt concentrated water containing organic pollutants and high-salt concentrated water containing low organic matters in the loosening nanofiltration section are separately treated with high-salt concentrated water containing low organic matters in the reverse osmosis section, so that the difficulty of treating high-salt high-organic matter concentrated water is avoided; after the low-salt organic concentrated water purification unit adopts Fenton-like/ozone catalytic pretreatment, the low-salt organic concentrated water is finally mineralized by ozone activated carbon, and effluent water flows back or is discharged; the reverse osmosis concentrated water nitrogen and phosphorus removal unit adopts a denitrification filter tank to realize the deep purification of nitrogen and phosphorus in high-salinity concentrated water, finally the concentrated water is discharged into the sea or other suitable water systems through a glass fiber reinforced plastic sand adding pipeline, and reverse osmosis effluent (desalted fresh water) can be recycled as high-quality water industry.

Relates to a new technology and a method for preparing fresh water by utilizing the regeneration and the reuse of the tail water of a domestic sewage and industrial wastewater sewage plant aiming at the problems of water shortage and offshore water pollution in offshore areas, in particular to the new technology and the method for preparing the fresh water by the regeneration and the reuse of the domestic sewage and the industrial wastewater in the offshore and near salt lake areas. The invention provides a new water ternary directional preparation technology system for solving the problems of water shortage and offshore water pollution in offshore areas and the bottleneck problem of treatment of reverse osmosis regeneration concentrated water of sewage, and the core of the new water ternary directional preparation technology system is to explore a new way for sewage resource utilization and promote the development of a sewage regeneration technology and the like. The technology is suitable for recycling domestic sewage or industrial sewage plants, the operation cost per ton of water is lower than 4 yuan/ton, the selling price is higher than 5 yuan/ton, and the technology has good economic, environmental and social benefits and wide application prospect.

Based on the technical scheme, the novel technology and the method for preparing the fresh water by utilizing the domestic sewage and the tail water of the industrial wastewater and sewage plant have at least one of the following advantages:

1. the investment and the operation cost are low, and the method is suitable for the current economic, social and technical development levels;

2. the problem that concentrated water does not reach the standard in the traditional fresh water and reclaimed water process is solved;

3. the problems of high energy consumption and high carbon dioxide emission in the traditional concentrated water treatment and recycling process are avoided;

4. the generation and the discharge of miscellaneous salt hazardous waste are avoided;

5. the pollutant discharge is reduced, and the offshore pollution problem is relieved;

6. the system has the advantages of excellent effluent quality, convenient operation management, full automation of the operation process and wide application prospect.

Drawings

FIG. 1 is a conventional process for recycling sewage;

FIG. 2 is a flow chart of a process for producing fresh water abroad

FIG. 3 is a flow chart of the evaporation and salt separation process of the prior concentrated water treatment

FIG. 4 is a process flow diagram of the process of manufacturing fresh water according to the present invention;

FIG. 5 is a flow chart of the process of realizing deep mineralization of concentrated water by the directional separation coupling biochemical process in the implementation process of the invention;

table 1 shows the quality of the effluent after the directional separation according to the present invention;

in the above figures, the reference numerals have the following meanings:

abstract attached drawings and reference numeral 4 are as follows:

1-a directional separation loosening nanofiltration unit, which mainly realizes the separation of organic pollutants and salt and respectively generates salt-containing purified water and low-salt organic concentrated water of low organic matters; the 2-Fenton-like/ultraviolet catalytic unit can be one or a combination of UV, ozone and hydrogen peroxide or Fenton and Fenton-like, and mainly realizes the catalytic pretreatment of refractory organic matters to improve the biodegradability, thereby being beneficial to subsequent mineralization; 3-denitrification denitrogenation unit, mainly realize the denitrification of the nitrate in the concentrated water of high salt content of low organic matter and get rid of, can be heterotrophic denitrification, can also be autotrophic denitrification process, the concentrated water of high salt content after handling up to standard discharges the sea directly through the sand-adding pipeline of glass steel or PE pipeline, return river.

Detailed Description

In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.

In the traditional process of preparing fresh water by regenerating and recycling sewage, a synchronous concentration process of organic matters and inorganic salts is inevitably formed, so that high-salt and high-organic matter mixed concentrated water is generated (see figure 1), at present, the mixed concentrated water can only be diluted and discharged by other sewage plants, is directly discharged and the like, but the diluted discharge or the direct discharge faces the supervision and offshore pollution pressure. FIG. 2 is a typical process for preparing fresh water abroad, and after the concentrated water is generated, no good treatment method is available, and only sea drainage is available. At present, a salt separation recycling process shown in fig. 3 appears along with the development of technical economy, but the process has the problems that the investment and the operation cost are high, 10% -20% of miscellaneous salt is generated, the quality of the generated sodium chloride or sodium sulfate is not high, the generated sodium chloride or sodium sulfate cannot be recycled as high-quality industrial salt, the miscellaneous salt is mainly buried at present, but the burying is not an effective recycling means, and the risks of occupation and pollution to land and underground water exist. The invention provides a new technology and a method for preparing fresh water by utilizing domestic sewage and industrial wastewater and sewage plant tail water (figure 4). The invention provides a new raw water ternary directional preparation technical system aiming at the bottleneck problem of sewage reverse osmosis regeneration concentrated water treatment, and the core of the new raw water ternary directional preparation technical system is a directional separation unit, a low-salt organic concentrated water purification unit and a reverse osmosis concentrated water nitrogen and phosphorus removal unit. The directional separation unit is mainly characterized in that a wide-flow-channel directional separation loosening nanofiltration section is arranged before reverse osmosis to replace ultrafiltration, and low-salt concentrated water containing organic pollutants and high-salt concentrated water containing low organic matters in the loosening nanofiltration section are separately treated with high-salt concentrated water containing low organic matters in the reverse osmosis section, so that the difficulty of treating high-salt high-organic matter concentrated water is avoided; after the low-salt organic concentrated water purification unit adopts Fenton-like/ozone catalytic pretreatment, the low-salt organic concentrated water is finally mineralized by ozone activated carbon, and effluent water flows back or is discharged; the reverse osmosis concentrated water nitrogen and phosphorus removal unit adopts a denitrification filter tank to realize the deep purification of nitrogen and phosphorus in high-salinity concentrated water, finally the concentrated water is discharged into the sea or other suitable water systems through a glass fiber reinforced plastic sand adding pipeline, and reverse osmosis effluent (desalted fresh water) can be recycled as high-quality water industry. The new water ternary directional preparation technology system explores a new way for sewage resource utilization and promotes the development of sewage recycling technology and the like.

The technical solution of the present invention is further illustrated by the following specific embodiments in conjunction with the accompanying drawings. It should be noted that the following specific examples are given by way of illustration only and the scope of the present invention is not limited thereto.

The chemicals and raw materials used in the following examples were either commercially available or self-prepared by a known preparation method.

General example 1

The system comprises a sewage regeneration and fresh water preparation ternary directional technology system, a directional separation unit, a low-salt organic concentrated water purification unit and a reverse osmosis concentrated water nitrogen and phosphorus removal unit; the directional separation unit is provided with a directional separation loose nanofiltration membrane, and the low-salt concentrated water and the high-salt concentrated water with low organic matters of organic pollutants are separately treated and respectively enter the low-salt organic concentrated water purification unit and the reverse osmosis concentrated water nitrogen and phosphorus removal unit.

Wherein, the front section of the directional separation unit is provided with a coagulation and high-density sedimentation tank, a multi-medium filter and a security filter.

The directional separation loose nanofiltration membrane adopts a wide flow channel grid, and the width of the flow channel grid is 0.8-1.5 mm; the pipeline is made of a rigid polyvinyl chloride (UPVC), and the directional separation loose nanofiltration membrane is made of polyamide, polyether sulfone or graphene oxide.

Wherein, the low-salt organic concentrated water purification unit comprises a filter tank which can adopt manganese sand; or an ozone catalysis, ozone/ultraviolet or advanced reduction pretreatment device is adopted; further connecting with a biological activated carbon unit.

Wherein the reverse osmosis concentrated water nitrogen and phosphorus removal unit comprises a reverse osmosis device and is further connected with an energy recovery device; further connected with a denitrification unit.

General example 2

A method for preparing fresh water by sewage recycling, namely a new technology and a method for preparing fresh water by utilizing domestic sewage and tail water of industrial wastewater and sewage plants, adopts the system, and comprises the following steps:

Preferably, the operation pressure of the step 2) is 0.3-1.5 MPa.

Example 1

By adopting the system and the treatment method, serious water shortage problem exists in certain coastal areas of Shandong, effluent of sewage plants in industrial parks in the district is recycled by a double-membrane method (a new raw water plant, figure 1), and before modification, inflow of the new raw water plant is subjected to reverse osmosis concentration, and then reverse osmosis concentrated water COD is 120mg/L, total nitrogen is 25mg/L, total phosphorus is 1mg/L, TDS 23000mg & lt/EN & gtL, the concentration of chloride ion is 8000 mg/L. The concentrated water is directly subjected to Fenton, Fenton-like and ozone catalytic oxidation pretreatment without effect, if the concentrated water is doped into a sewage plant in a nearby industrial park for treatment, the impact on the sewage plant in the nearby industrial park is too large, the operation of the sewage plant in the nearby industrial park is influenced, and if the concentrated water is directly discharged into the sea, the excessive steal discharge and supervision risks exist. Based on the above situation, the process flow shown in FIG. 4 of the present invention is adopted to change ultrafiltration into a directional separation, loosening and nanofiltration system, and the designed flux is 15L/m²H, the membrane material is polyether sulfone, the molecular weight cut-off of the membrane is 800Da, the water inlet grid is 46mil, the pressure is 0.6Mpa, and the area of a single membrane is 26m²The recovery rate of directional loosening nanofiltration is 90%, an active carbon layer is added into a front-end multi-medium filter to remove hydrophobic organic pollutants, the active carbon is 2mm coal-based irregular particle active carbon, low-salt organic concentrated water produced by loosening nanofiltration enters a biological active carbon section after out-phase Fenton and is finally mineralized and then flows back to the water inlet end of a new water plant, the concentration of the out-phase Fenton catalyst is 6g/L, the retention time of a main reaction zone is 4h, and the reflux ratio of the catalyst is 10%. The reverse osmosis recovery rate is 80%, reverse osmosis concentrated water enters an autotrophic denitrification section after passing through an energy recovery device, the retention time of the autotrophic denitrification section is 2 hours, the height of a bed layer is 1m, the removal of nitrate in the high-salinity concentrated water is realized, finally, the concentrated water reaches the first-level A standard and is discharged in the sea, the operation cost of the improved system is lower than 3.5 yuan/ton (after the concentrated water is spread according to the yield of new water), the selling price of the new water reaches 7.5 yuan/ton, considerable economic benefit is obtained, the water shortage problem of an industrial park is effectively relieved, the pollution problem of coastal areas is controlled, and good economic, social and ecological environmental benefits are obtained.

Example 2

Recovery rate

By adopting the system and the treatment method, a certain coastal industrial park of Tianjin has a serious water shortage problem, the tail water of the municipal sewage plant is recycled by adopting a double-membrane method shown in figure 1 in the prior art (inlet water COD is 30mg/L, inlet ammonia nitrogen is less than 0.5mg/L, inlet water total nitrogen is 13mg/L, inlet water total phosphorus is 0.3mg/L, inlet water amount is 4 ten thousand tons, concentrated water is 1.2 ten thousand tons, and fresh water is 2.8 ten thousand tons), reverse osmosis concentrated water enters a nearby municipal sewage plant (treatment amount is 20 ten thousand tons/day) and is diluted and discharged at the inlet end, and the fresh water is diluted and discharged at the inlet end, so that the fresh water is dischargedThe factory hopes to further enlarge the scale and proportion of sewage reuse, but the factory receives the restriction that nearby municipal sewage plants can accept concentrated water, and the reuse rate is less than 20%. In view of the situation, after the technological process shown in the figure 4 of the invention is adopted for transformation, the original ultrafiltration section is replaced by the directional separation loose nanofiltration membrane, the membrane material adopts a graphene oxide and polyether sulfone composite membrane, the molecular weight cut-off adopts 1000Da, and the flux of the directional loose nanofiltration adopts 16L/m²The pressure is 0.5Mpa, the recovery rate is 92 percent, the COD of the effluent is reduced to 8mg/L, the effluent subjected to directional separation, loosening and nanofiltration enters a nearby municipal sewage plant after the biodegradability of the effluent is improved through ultraviolet composite catalysis, and the ultraviolet light intensity of an ultraviolet catalysis section is 600mJ/cm²320W of each dual-wavelength VUV lamp tube. Reverse osmosis flux 18L/m²And h, increasing the total nitrogen in the reverse osmosis concentrated water to 50mg/L, reducing the total nitrogen of the reverse osmosis concentrated water to below 13mg/L after active autotrophic denitrification, and realizing the discharge of the effluent after the autotrophic denitrification lasts for 1.5 h. After the improvement, the sewage reuse rate is improved to 70%, 14 ten thousand tons of fresh water is recycled every day, the problem of local water shortage is effectively relieved, the system operation cost is lower than 3.2 yuan/ton (according to the fresh water yield, after the fresh water is spread out), the fresh water selling price reaches 6.5 yuan/ton, considerable economic benefit is obtained, and good economic, social and ecological environmental benefits are obtained.

Example 3

By adopting the system and the treatment method, the problem of excessive squeezing of ecological water in a certain offshore pesticide park in Jiangsu, the water ecology cannot volatilize, the problem of serious pollution exists in the offshore area near the drainage port, the area of the offshore excellent sea area is reduced year by year, and the ecological environment protection pressure is huge. Based on the situation, the tail water of the park sewage plant in the industrial park is regenerated and recycled (2 ten thousand tons/day, the recycling scale is 73 percent, and 1.46 ten thousand tons per day), the high-salt-content concentrated water is treated by adopting activated carbon adsorption on the basis of the technical route shown in the figure 1, but the running cost of the activated carbon section is overhigh, the activated carbon section is leveled to the cost of 5 yuan of fresh water, the cost of preparing the ton water of the fresh water exceeds 7 yuan by adding the cost of reverse osmosis and pretreatment, the selling price of the tap water in the park is only 4.5 yuan, the preparation and running of the fresh water are uneconomical, and the fresh water is maintained by subsidyThe enthusiasm for preparing the fresh water is not high, and the stable operation of the project is influenced. On the basis, the technical route shown in FIG. 4 is adopted in the transformation scheme to transform and increase the loose nanofiltration section, the membrane material is polyether sulfone, and the flux is 14L/m²The water quality before and after loosening and nanofiltration is shown in table 1, an advanced reduction system is added before activated carbon adsorption to couple advanced oxidation, the addition of sodium sulfite in the advanced reduction process is 60mg/L, the water after the conventional loosening and nanofiltration organic concentrated water is pretreated by catalytic oxidation directly enters biochemical treatment and finally mineralized, and an activated carbon tank is only used for standby. The reverse osmosis flux is 20L/m²And/h, transmembrane pressure difference is 1.5Mpa, reverse osmosis concentrated water enters a denitrification section to remove nitrate, heterotrophic denitrification is adopted in the denitrification section, the dosage of sodium acetate is 50mg/L, and the standard-reaching concentrated water finally returns to the sea through a 20km glass fiber reinforced plastic sand adding pipeline (DN 600). The whole operation cost is 4.0 yuan/ton (after being flattened according to the yield of the new raw water), the operation cost is effectively reduced, the local ecological environment is protected, a good economic effect is achieved, and the mode is being popularized in other similar fine chemical industry parks.

TABLE 1

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The system is characterized by comprising a directional separation unit, a low-salt organic concentrated water purification unit and a reverse osmosis concentrated water nitrogen and phosphorus removal unit; the directional separation unit is provided with a directional separation loose nanofiltration membrane, and the low-salt concentrated water and the high-salt concentrated water with low organic matters of organic pollutants are separately treated and respectively enter the low-salt organic concentrated water purification unit and the reverse osmosis concentrated water nitrogen and phosphorus removal unit.

2. The ternary directional technical system for preparing fresh water by sewage recycling according to claim 1, wherein the front section of the directional separation unit is provided with a coagulation tank, a high-density sedimentation tank, a multi-media filter and a security filter.

3. The ternary directional technical system for preparing nanofiltration membranes according to claim 1, wherein the directional separation porous nanofiltration membranes are wide flow channel grids, and the width of the flow channel grids is 0.8-1.5 mm; the pipeline is made of a rigid polyvinyl chloride (UPVC), and the directional separation loose nanofiltration membrane is made of polyamide, polyether sulfone or graphene oxide.

4. The ternary directional technical system for preparing fresh water by sewage recycling according to claim 1, wherein the low-salt organic concentrated water purification unit comprises a filter tank, which can adopt a manganese sand filter tank; or an ozone catalysis, ozone/ultraviolet or advanced reduction pretreatment device is adopted; further connecting with a biological activated carbon unit.

5. The ternary directional technology system for preparing fresh water by sewage recycling according to claim 1, wherein the reverse osmosis concentrated water denitrification and dephosphorization unit comprises a reverse osmosis device, and is further connected with an energy recovery device; further connected with a denitrification unit.

6. A method for preparing fresh water for sewage recycling, which adopts the ternary directional technology system for preparing fresh water for sewage recycling of any one of claims 1 to 5, and comprises the following steps:

1) a pretreatment section comprising a coagulation section, a high-density sedimentation tank, a multi-media filter section and a security filter section;

2) loosening and nanofiltration sections through directional separation;

3) the organic pollutant low-salt concentrated water after filtration in the loosening nanofiltration section is subjected to catalytic pretreatment of the organic pollutants through a Fenton-like or ultraviolet catalytic system, then enters a filtration tank or a filter tank, and then enters a biological activated carbon section;

7. The method of claim 6,

in the step 1), certain hypochlorous acid, sodium hypochlorite and hydrogen peroxide are added into the water inlet section, and the adding amount is 0.1-2 mg/L; the multi-medium filtering section is provided with a certain activated carbon layer;

the directional separation loose nanofiltration membrane used in the step 2) can be made of polyamide, polyether sulfone or graphene oxide;

adding certain hydrogen peroxide, hypochlorous acid, ozone and iron-based catalytic particles into the feed water with COD of about 30-200 mg/L, wherein the adding amount is 0-5 mg/L;

the operating pressure is 0.3-1.5 MPa;

the design flux of the polyamide or polyether sulfone loose nanofiltration membrane is 9-17L/m²The design flux of the graphene oxide membrane is 30-50L/m²/h；

The directional separation loose nanofiltration membrane adopts a wide flow channel grid, and the width of the flow channel grid is 0.8-1.5 mm;

the material of the pipeline is rigid polyvinyl chloride (UPVC).

8. The method of claim 6,

the reverse osmosis membrane used in the step 3) is a polyamide membrane, and the designed flux is 17-25L/m²/h；

Two-stage reverse osmosis can be adopted, concentrated water of the first-stage reverse osmosis enters the second-stage reverse osmosis, the wide-runner reverse osmosis (STRO) can be adopted in the process of the second-stage reverse osmosis, the water inlet pressure of the second-stage reverse osmosis is 1-2 MPa, and the designed flux is 17L/m²The flow channel grid width is 0.8-1.5 mm;

a certain amount of scale inhibitor and bactericide can be added before the reverse osmosis section as required to control inorganic scale and biological pollution.

9. The method of claim 6,

the catalytic pretreatment technology used in the step 4) can adopt the technologies of Fenton, heterogeneous Fenton, ultraviolet composite catalysis, ozone catalysis, advanced reduction and the like according to different water quality of inlet water.

10. The method of claim 6,

and 5) the reverse osmosis concentrated water enters a denitrification filter tank after further recovering energy by an energy recovery device, the denitrification filter tank can adopt an autotrophic denitrification filter tank or a heterotrophic denitrification filter tank, and preferably the autotrophic denitrification filter tank.