Patent Application
20240294412
This application claims the priority benefit of China application serial no. 202310197343.0, filed on Mar. 1, 2023. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
The present invention relates to the technical field of environmental engineering, and specifically relates to a method and an apparatus for desalination of high-salt and high-concentration organic wastewater by coupling three membrane separation technologies.
A large amount of high-salt and high-concentration organic wastewater is produced by industrial activities, and high-concentration salt and organic matter contained in the wastewater will lead to salinization of soil, eutrophication of water, pollution of groundwater, safety hazards of drinking water and other serious water environmental pollution problems, which bring serious threats to life and health.
The high-salt and high-concentration organic wastewater contains a large number of total dissolved solids and high-concentration organic pollutants. Conventional wastewater treatment methods include biological methods, and a commonly used biological method is an activated sludge method, where sludge and organic matter are allowed to get in full contact by an aeration method, and then the organic matter is metabolized and decomposed in a large amount of dissolved oxygen. However, since salinity has a great influence on the activated sludge method, salt-tolerant microorganisms are required to be domesticated, which takes a long period of time.
Desalination is a most important step in treatment of the high-salt and high-concentration organic wastewater, and thermal desalination is a most commonly used method, in which distillation desalination is a most representative method. At present, most of distillation desalination technologies for wastewater treatment are developed from a seawater desalination technology. According to a multiple effect distillation (MED) technology, multiple evaporators are connected in series, heated high-salt wastewater is evaporated in a former evaporator to generate steam, the steam is used as a heat source for a next evaporator, and finally, the steam is condensed into fresh water. According to multi-stage flash evaporation (MSF), by controlling the pressure in flash chambers to be lower than the saturated vapor pressure corresponding to heated salt water, the hot salt water entering the flash chambers is quickly vaporized, and then steam is condensed to produce fresh water. The multi-stage flash evaporation finally achieves the purposes of concentrating salt water and producing fresh water by gradually reducing the pressure of steam passing through the multiple flash chambers. According to a mechanical vapor recompression (MVR) technology, heated salt water is introduced into an evaporator to produce steam, the steam is compressed with a compressor, and the compressed steam is used as a heat source for a heating side of the evaporator and finally condensed into water. Evaporation consumes a lot of heat, so that the operating cost is increased. During evaporation treatment of the high-salt and high-concentration organic wastewater, foam is easily produced due to excessive organic matter in the wastewater, and water produced by evaporation also contains too much organic matter.
Membrane separation is a new separation technology with separation membranes as the core, which can achieve wastewater treatment with high efficiency and low consumption by separating pollutants and water. Ultrafiltration, nanofiltration and other membrane separation technologies have been applied in wastewater treatment processes. According to the ultrafiltration, with a pressure difference of 0.1-0.5 MPa as a driving force, porous membranes are used for separating substances in solutions by a physical rejection method, so as to screen different components in the solutions, which require external pressure. Nanofiltration membranes have smaller pore sizes and dense structures, which can retain smaller particles. However, as the nanofiltration membranes have dense membrane pore structures, higher pressures are required to force liquid purification, which have higher energy consumption than the ultrafiltration. Meanwhile, the nanofiltration membranes are more sensitive to scaling problems, and the membranes are easily contaminated and destroyed. Therefore, the current membrane separation technologies require external pressure treatment, which are difficult to effectively separate and filter the high-salt and high-concentration organic wastewater, have a low water production rate, a long operating time and high energy consumption, and cannot achieve circular sustainable desalination. Therefore, it is urgent to develop new membrane processes that can operate continuously and have high energy efficiency.
The purposes of the present invention are to overcome the disadvantages of the prior art and provide a method and an apparatus for desalination of high-salt and high-concentration organic wastewater by coupling three membrane separation technologies.
The first purpose of the present invention is to provide a method for desalination of wastewater by coupling three membrane separation technologies.
The second purpose of the present invention is to provide an apparatus for desalination of wastewater by coupling three membrane separation technologies.
The three membrane separation technologies of the present invention refer to a diffusion membrane separation technology, a forward osmosis membrane separation technology and a reverse osmosis membrane separation technology, respectively. The diffusion membrane separation technology is used for desalination of wastewater, and forward osmosis is used for concentrating the organic wastewater after the desalination. By adopting the two methods, a driving force is generated only by concentration differences between liquids without external driving pressure. The diffusion membrane separation technology also reduces the membrane pollution degree. The reverse osmosis membrane separation technology is used for concentrating salt in water to obtain high-concentration salt water and pure water. On the one hand, a draw solution is provided for forward osmosis desalination. On the other hand, refined salt is recovered by evaporative crystallization, and pure water is also provided for diffusion desalination, so that circular sustainable desalination s achieved.
In order to achieve the above purposes, the present invention is implemented through the following schemes.
A method for desalination of wastewater by coupling three membrane separation technologies includes the following steps:
Preferably, in step S1, the wastewater is subjected to diffusion desalination after precise filtration.
Preferably, in step S1, the wastewater is subjected to diffusion desalination with pure water or diffusion desalination circulating water.
More preferably, in step S1, the wastewater is subjected to circular diffusion desalination with the pure water in step S2 and/or step S3.
Preferably, in step S3, the diffusion desalination wastewater is subjected to forward osmosis with the high-concentration salt water in step S2 or the forward osmosis circulating water in step S3.
Preferably, the high-concentration salt water in step S2 and/or step S3 is subjected to evaporative crystallization to obtain pure water and salt. The salt is refined and recycled.
Preferably, in step S2, the diffusion desalination circulating water is subjected to reverse osmosis when having a salt concentration of 20-25 g/L. The salt concentration of the diffusion desalination circulating water is controlled to further control the diffusion desalination rate, so that the diffusion desalination rate is maintained stable.
Preferably, in step S3, the forward osmosis circulating water is subjected to reverse osmosis when having a salt concentration of 15-25 g/L. The salt concentration of the forward osmosis circulating water is controlled to further control the forward osmosis rate, so that the forward osmosis rate is maintained stable.
Preferably, in step S3, the diffusion desalination wastewater is subjected to forward osmosis when having a salt concentration of 5-10 g/L. All the salt in the organic wastewater cannot be completely removed by the diffusion desalination to ensure that the wastewater after the desalination has a certain content of salt, which is used as an inorganic salt nutrient component required for subsequent biochemical treatment. The biochemical treatment cannot be performed when the salt content is low, and the biochemical treatment is difficult to perform when the salt content is high.
Preferably, the wastewater is high-salt and high-concentration organic wastewater.
An apparatus for desalination of wastewater by coupling three membrane separation technologies is provided. The wastewater treatment apparatus includes a pretreatment device, a diffusion desalination device, a forward osmosis device and a salt recovery device that are communicated with each other;
Preferably, a fluid switch valve is also arranged between the wastewater circulation storage device of the diffusion desalination device and the forward osmosis component of the forward osmosis device.
Preferably, a fluid switch valve is also arranged between the diffusion desalination circulating water storage device of the diffusion desalination device and the reverse osmosis circulating water storage device of the reverse osmosis device of the salt recovery device.
Preferably, a fluid switch valve is also arranged between the draw solution circulation storage device of the forward osmosis device and the reverse osmosis circulating water storage device of the reverse osmosis device of the salt recovery device.
Preferably, a fluid switch valve is also arranged between the reverse osmosis circulating water storage device of the reverse osmosis device of the salt recovery device and the mechanical vapor recompression (MVR) device of the salt recovery device.
Compared with the prior art, the present invention has the following beneficial effects.
In the present invention, by performing the diffusion desalination based on differences of the selectivity of a membrane to salt and organic matter and gradient differences of the salt concentration at an interface, salt in the high-salt and high-concentration organic wastewater is diffused to one side of water containing low concentration salt, so that the salinity of the wastewater is reduced or eliminated, and the membrane pollution degree is reduced without affecting a desalination process. Further, the forward osmosis, the reverse osmosis and the evaporative crystallization are performed to produce salt and recover pure water for recycling. According to the diffusion desalination and the forward osmosis treatment, a driving force is generated by concentration differences between liquids without external driving pressure. The diffusion desalination has a salt flux of 15-20 g/(m2·h), and the forward osmosis has a water flux of 15-25 L/(m2·h). Thus, the desalination and the forward osmosis are stable. The present invention has the advantages of high desalination efficiency, a low membrane pollution degree, stable operation and a low cost in treatment of the high-salt and high-concentration organic wastewater.
Callouts are as follows: 1, pretreatment device; 2, diffusion desalination device; 3, forward osmosis device; 4, salt recovery device; 5, wastewater storage device; 6, pretreatment device body; 7, pretreatment post-storage device; 8, wastewater circulation storage device; 9, diffusion desalination component; 10, diffusion desalination circulating water storage device; 11, pure water storage device; 12, to-be-treated wastewater storage device; 13, organic wastewater circulation storage device; 14, forward osmosis component; 15, draw solution circulation storage device; 16, reverse osmosis device; 17, reverse osmosis circulating water storage device; 18, reverse osmosis component; 19, mechanical vapor recompression (MVR) device.
The present invention is further illustrated in detail below in combination with drawings attached to the specification and specific embodiments. The embodiments are only used to explain the present invention and are not intended to limit the scope of the present invention. Unless otherwise specified, all test methods used in the following embodiments are conventional methods.
Unless otherwise specified, all used materials, reagents and the like are commercially available reagents and materials.
The pretreatment device 1 includes a wastewater storage device 5, a pretreatment device body 6 and a pretreatment post-storage device 7 that are sequentially communicated with each other through pipes and pumps. The pretreatment device body 6 is a precise filter and is used for filtering out solid particle impurities in organic wastewater with a high salt content.
The diffusion desalination device 2 includes a wastewater circulation storage device 8, a diffusion desalination component 9, a diffusion desalination circulating water storage device 10 and a pure water storage device 11 that are sequentially communicated with each other through pipes and pumps. The diffusion desalination component 9 is detachably connected with a diffusion desalination membrane, which is a spiral wound membrane or a hollow fiber membrane and has an effective area of 20 m2.
The pretreatment post-storage device 7 of the pretreatment device 1 is communicated with the wastewater circulation storage device 8 of the diffusion desalination device 2 through pipes and pumps.
The forward osmosis device 3 includes a to-be-treated wastewater storage device 12, an organic wastewater circulation storage device 13, a forward osmosis component 14 and a draw solution circulation storage device 15 that are sequentially communicated with each other through pipes and pumps. The forward osmosis component 14 is detachably connected with a forward osmosis membrane, which is a cellulose triacetate membrane and has an effective area of 25 m2.
The forward osmosis component 14 of the forward osmosis device 3 and the diffusion desalination component 9 of the diffusion desalination device 2 are communicated with the wastewater circulation storage device 8 of the diffusion desalination device 2 through pipes and pumps, respectively, and a fluid switch valve is also arranged between the pipes and used for controlling the flow direction of liquid.
The salt recovery device 4 includes a reverse osmosis device 16 and a mechanical vapor recompression (MVR) device 19 that are communicated with each other through pipes and pumps. The reverse osmosis device 16 includes a reverse osmosis circulating water storage device 17 and a reverse osmosis component 18 that are communicated with each other through pipes and pumps.
The diffusion desalination circulating water storage device 10 of the diffusion desalination device 2 is communicated with the reverse osmosis circulating water storage device 17 of the reverse osmosis device 16 of the salt recovery device 4 through pipes and pumps, and a fluid switch valve is also arranged between the pipes and used for controlling the flow direction of liquid.
The pure water storage device 11 of the diffusion desalination device 2 is communicated with the reverse osmosis component 18 of the reverse osmosis device 16 of the salt recovery device 4 through pipes and pumps. The pure water storage device 11 of the diffusion desalination device 2 is communicated with the mechanical vapor recompression (MVR) device 19 of the salt recovery device 4 through pipes and pumps.
The draw solution circulation storage device 15 of the forward osmosis device 3 and the mechanical vapor recompression (MVR) device 19 of the salt recovery device 4 are communicated with the reverse osmosis circulating water storage device 17 of the reverse osmosis device 16 of the salt recovery device 4 through pipes and pumps, respectively, and a fluid switch valve is also arranged between the pipes and used for controlling the flow direction of liquid.
The precisely filtered wastewater in the pretreatment post-storage device 7 is sequentially transported to the wastewater circulation storage device 8 and the diffusion desalination component 9 through pipes and pumps. By means of the diffusion desalination, the salt concentration of the precisely filtered wastewater is decreased, the salt concentration of the pure water is increased, and diffusion desalination wastewater is obtained.
Meanwhile, after the concentration of the pure water is increased, diffusion desalination circulating water is obtained, which is transported to the diffusion desalination circulating water storage device 10 through pipes and pumps and further transported to the diffusion desalination component 9 through pipes and pumps, so as to realize circular diffusion desalination.
Meanwhile, the pure water in the pure water storage device 11 is transported to the diffusion desalination circulating water storage device 10 through pipes and pumps to perform diffusion desalination continuously.
The organic wastewater with a low salt content needs to contain a certain amount of salt, which is used as an inorganic salt nutrient component required for subsequent biochemical treatment. The biochemical treatment cannot be performed when the salt content of the wastewater is too low, and the biochemical treatment is difficult to perform when the salt content is too high.
The salt water in the forward osmosis component 14 is used as a draw solution for forward osmosis. In a forward osmosis process, the salt concentration of the draw solution is decreased, and the draw solution stored in the draw solution circulation storage device 15 is transported to the forward osmosis component 14 through pipes and pumps so as to achieve circular forward osmosis.
When the draw solution has a salt concentration of 15-25 g/L, the fluid switch valve between the draw solution circulation storage device 15 and the reverse osmosis circulating water storage device 17 is turned on, and the draw solution is transported to the reverse osmosis circulating water storage device 17 through pipes and pumps and continuously transported to the reverse osmosis device 16 to produce high-concentration salt water and pure water.
The chemical oxygen demand (COD) is 10,000 mg/L, the NaCl content is 70 g/L, and the wastewater volume is 1 ton. The electrical conductivity is measured by an electrical conductivity meter, and then the salt concentration of the water is calculated.
The high-salt and high-concentration organic wastewater to be treated is subjected to desalination by using the device in Example 1.
The pure water used for the diffusion desalination is 0.5-0.6 of the weight of the pure water provided by the outside, the pure water is sufficient enough for the diffusion desalination, and the remaining pure water is spare for next use. The diffusion desalination is performed with a spiral wound membrane, the membrane has an effective area of 20 m2, and the diffusion desalting is performed at a rate of 15 g/(m2·h).
In a forward osmosis process, the volume of the high-concentration salt water is increased, the salt concentration is decreased, and the diffusion desalination wastewater, as forward osmosis circulating water, is subjected to forward osmosis continuously, so as to realize circular forward osmosis.
All the salt in the organic wastewater cannot be completely removed by the diffusion desalination to ensure that the wastewater after the desalination has a certain content of salt, which is used as an inorganic salt nutrient component required for subsequent biochemical treatment. The biochemical treatment cannot be performed when the salt content is low, and the biochemical treatment is difficult to perform when the salt content is high.
When the salt concentration of the forward osmosis circulating water is decreased to 15-25 g/L, 200 kg of the forward osmosis circulating water is subjected to reverse osmosis to produce high-concentration salt water and pure water continuously. The weight of the forward osmosis circulating water used for the reverse osmosis is 2-3 times of the weight of the high-concentration salt water produced by the reverse osmosis, which is used to control the concentration of the forward osmosis circulating water and ensure normal forward osmosis. The salt concentration of the forward osmosis circulating water is controlled to further control the forward osmosis rate, so that the forward osmosis rate is maintained stable.
The cellulose triacetate (CTA) membrane is used as a forward osmosis membrane, which has an effective area of 25 m2 and a water flux of 20 L/(m2·h).
The electrical conductivity is measured by an electrical conductivity meter, and then the salt concentration of the water is calculated. The salt flux is obtained based on changes of the salt content with time.
The finally desalted wastewater has a weight of 667.3 kg, the wastewater is reduced by 32%, the wastewater has a salt content of 8 g/L and a COD content of 14984.7 mg/L, and 61 kg of salt and 306 kg of pure water are finally produced.
I. Water quality of high-salt and high-concentration organic wastewater to be treated: The chemical oxygen demand (COD) is 15,000 mg/L, the NaCl content is 90 g/L, and the wastewater volume is 1 ton. The electrical conductivity is measured by an electrical conductivity meter, and then the salt concentration of the water is calculated.
The high-salt and high-concentration organic wastewater to be treated is subjected to desalination by using the device in Example 1.
The pure water used for the diffusion desalination is 0.5-0.6 of the weight of the pure water provided by the outside, the pure water is sufficient enough for the diffusion desalination, and the remaining pure water is spare for next use. The diffusion desalination is performed with a spiral wound membrane, the membrane has an effective area of 20 m2, and the diffusion desalting is performed at a rate of 15 g/(m2·h).
In a forward osmosis process, the volume of the high-concentration salt water is increased, the salt concentration is decreased, and the diffusion desalination wastewater, as forward osmosis circulating water, is subjected to forward osmosis continuously, so as to realize circular forward osmosis.
All the salt in the organic wastewater cannot be completely removed by the diffusion desalination to ensure that the wastewater after the desalination has a certain content of salt, which is used as an inorganic salt nutrient component required for subsequent biochemical treatment. The biochemical treatment cannot be performed when the salt content is low, and the biochemical treatment is difficult to perform when the salt content is high.
When the salt concentration of the forward osmosis circulating water is decreased to 15-25 g/L, 200 kg of the forward osmosis circulating water is subjected to reverse osmosis to produce high-concentration salt water and pure water continuously. The weight of the forward osmosis circulating water used for the reverse osmosis is 2-3 times of the weight of the high-concentration salt water produced by the reverse osmosis, which is used to control the concentration of the forward osmosis circulating water and ensure normal forward osmosis. The salt concentration of the forward osmosis circulating water is controlled to further control the forward osmosis rate, so that the forward osmosis rate is maintained stable.
The cellulose triacetate (CTA) membrane is used as a forward osmosis membrane, which has an effective area of 25 m2 and a water flux of 20 L/(m2·h).
The electrical conductivity is measured by an electrical conductivity meter, and then the salt concentration of the water is calculated. The salt flux is obtained based on changes of the salt content with time.
The finally desalted wastewater has a weight of 726.8 kg, the wastewater is reduced by 27%, the wastewater has a salt content of 10 g/L and a COD content of 20636.4 mg/L, and 76 kg of salt and 251 kg of pure water are produced.
The electrical conductivity is measured by an electrical conductivity meter, and then the salt concentration of the water is calculated. The salt flux is obtained based on changes of the salt content with time.
The desalted wastewater has a mass of 521.6 kg, the wastewater is reduced by 47.8%, the wastewater has a salt content of 72 g/L and a COD content of 18647.7 mg/L, and 32 kg of salt and 456 kg of pure water are finally produced.
Changes of the water flux with time during ultrafiltration are shown in
Finally, it is to be noted that the above embodiments are only used to illustrate the technical schemes of the present invention and are not intended to limit the scope of protection of the present invention. For persons of ordinary skill in the art, other changes or modifications in different forms can also be made on the basis of the above description and ideas, and it is not necessary or possible to illustrate all the embodiments herein. Any modifications, equivalent substitutions, improvements and the like made within the spirit and principles of the present invention shall be included in the scope of protection of the claims of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202310197343.0 | Mar 2023 | CN | national |
