Seawater pretreatment method and system for controlling reverse osmosis membrane biological pollution

Abstract

The invention discloses a seawater pretreatment system for controlling reverse osmosis membrane biological pollution, and the seawater pretreatment system comprises a raw water tank, a clarification tank, a sand filter, a security filter, a nanofiltration membrane filter and an ultraviolet disinfection tank which are connected in sequence. A slow flow cone, a steady flow plate and an anti-vortex plate are arranged in the disinfection tank, mixing of seawater in the tank is slowed down, the seawater needs 40-60 min from entering to flowing out, it is ensured that the seawater can be irradiated for 30 min or above, thorough ultraviolet sterilization and disinfection are completed, the seawater subjected to secondary disinfection is immediately subjected to reverse osmosis filtration, and the water quality is improved. Biological pollution is avoided as far as possible, and the service life of the reverse osmosis membrane is prolonged.

Description

Technical Field

[0001] The present invention relates to the field of seawater desalination treatment equipment, and particularly relates to a seawater pretreatment method and system for controlling biological fouling of reverse osmosis membranes. Background Art

[0002] Seawater membrane desalination mainly includes four steps: water intake, seawater pretreatment, reverse osmosis membrane desalination, and post-treatment of fresh water. Among them, the reverse osmosis membrane is a key component in the seawater membrane desalination process and is costly. Reverse osmosis membrane fouling can directly lead to an increase in the replacement frequency and operating cost of the reverse osmosis membrane. Therefore, seawater pretreatment is a key step in protecting the reverse osmosis membrane.

[0003] Reverse osmosis membrane fouling mainly includes three types: inorganic fouling, organic fouling, and biological fouling. Inorganic fouling and organic fouling can generally be removed by flushing or backwashing, while biological fouling is a sticky biofilm formed due to the deposition and growth of microorganisms on the surface of the reverse osmosis membrane. It is difficult to clean and requires chemical cleaning, and may even cause irreversible recovery of the performance of the reverse osmosis membrane.

[0004] Currently, oxidants such as liquid chlorine, sodium hypochlorite, and copper sulfate are usually added in seawater pretreatment to kill microorganisms. However, before entering the reverse osmosis system, a reducing agent needs to be added to reduce these oxidants to ensure that the content of oxidizing substances in the influent of the reverse osmosis system is less than 0.1 ppm (or ORP < 200 mV), so as to protect the reverse osmosis membrane from damage. However, after the oxidant is reduced, during the process of seawater passing through the security filter, ultrafilter, etc., microorganisms will regrow in a suitable environment and cause biological fouling to the reverse osmosis membrane. This is the existing problem. Summary of the Invention

[0005] In order to make up for the deficiencies of the prior art, the present invention provides a seawater pretreatment method and system for controlling biological fouling of reverse osmosis membranes. The seawater entering the reverse osmosis membrane module is disinfected twice by an ultraviolet disinfection tank without the need to stop the machine and wait, so as to improve the above problems.

[0006] The present invention is realized by the following technical solutions:

[0007] A seawater pretreatment system for controlling biological fouling of reverse osmosis membranes, characterized in that: the seawater pretreatment system includes a raw water tank, a clarifier, a sand filter, a security filter, a nanofiltration membrane filter, and an ultraviolet disinfection tank connected in sequence. A disinfectant dosing device and a coagulant dosing device are provided on the raw water tank. A mixing paddle is provided in the raw water tank. A scale inhibitor dosing device and a reducing agent dosing device are connected to the pipeline between the security filter and the sand filter. A plurality of mounting seats are evenly distributed circumferentially on the inner wall of the ultraviolet disinfection tank. Removable mirror panels are installed on the mounting seats. A vertical ultraviolet lamp post is provided at the central position in the ultraviolet disinfection tank. A plurality of layers of flow stabilizing plates are fixed on the ultraviolet lamp post. The water inlet of the ultraviolet disinfection tank is located at the upper part of the tank body, and the water outlet of the ultraviolet disinfection tank is located on one side of the lower part of the tank head.

[0008] Further optimized, a flow retardation cone is provided at the top of the ultraviolet lamp post, and a water inlet pipe is provided at the water inlet, and the water inlet pipe faces the flow retardation cone.

[0009] Further optimized, a water outlet pipe is fixed at the water outlet, and an anti-vortex plate is provided in the water outlet pipe.

[0010] Further optimized, a plurality of uniformly distributed through holes are formed in the flow stabilizing plate.

[0011] Further optimized, a transparent cover is fixed on the mounting seat. The bottom end of the transparent cover is closed, and a water blocking cover is provided at the upper end. The mirror panel is inserted into the transparent cover.

[0012] Further optimized, a branch exhaust pipe is communicated with the water blocking cover of each mounting seat transparent cover. The branch exhaust pipe is connected to a main exhaust pipe, and the main exhaust pipe is connected to an exhaust pump.

[0013] Further optimized, a scale inhibitor dosing device and a reducing agent dosing device are connected to the pipeline between the security filter and the sand filter. The reducing agent is sodium bisulfite.

[0014] Further optimized, the disinfectant is sodium hypochlorite, and the coagulant is ferric chloride.

[0015] Further optimized, the seawater pretreatment method for controlling the biological fouling of reverse osmosis membranes includes the following steps: a. Lift the seawater into the raw water tank, add disinfectant and coagulant, mix it through a large mixing paddle and enter the clarifier for sedimentation, and then filter it through a sand filter to obtain clear seawater; b. Continue to add scale inhibitor and reducing agent, and conduct further filtration through a security filter and a nanofiltration membrane filter; c. The reduced and filtered seawater slowly enters the ultraviolet disinfection tank through the inlet pipe and the flow-equalizing cone, and is disinfected in the tank for 40 minutes. There are a flow-equalizing cone, a flow-stabilizing plate and an anti-vortex plate in the tank to reduce the mixing of the water flow caused by the inlet and outlet water in the tank. The water inflow and outflow in the tank are kept consistent, and the seawater after secondary disinfection flows out from the outlet pipe; d. The seawater after secondary disinfection enters the reverse osmosis membrane module for the next step of reverse osmosis filtration to produce fresh water.

[0016] The beneficial effects of the present invention are:

[0017] In the pretreatment step of the present invention, an ultraviolet disinfection tank is provided before the reverse osmosis membrane to conduct secondary disinfection on the seawater entering the reverse osmosis membrane for desalination, ensuring the killing of microorganisms regrown after the reduction of oxidants. The seawater after secondary disinfection immediately undergoes reverse osmosis filtration to avoid biological fouling as much as possible and extend the service life of the reverse osmosis membrane.

[0018] In the ultraviolet disinfection tank of the present invention, there is an ultraviolet lamp post in the middle, and several mirror panels are provided on the inner wall of the tank. The ultraviolet light is combined with multiple reflections of the mirror surface to avoid the influence of occlusion and fully disinfect the seawater in the tank; there are a flow-equalizing cone, a flow-stabilizing plate and an anti-vortex ring in the tank to minimize the mixing of seawater caused by the inlet and outlet water in the tank. The water inlet is above and the water outlet is below, keeping the water inlet and outlet speeds consistent. It takes 40 - 60 minutes for the seawater to enter and exit, fully meeting the requirement that the ultraviolet disinfection time is higher than 30 minutes, and there is no need to stop the machine and wait during this process, avoiding the drawback of stopping the machine and waiting for 30 minutes for ultraviolet disinfection of the water body in the traditional method.

[0019] A transparent cover is provided outside the mirror panel of the present invention to prevent seawater from eroding the mirror surface. An exhaust pipe is connected to the lid of the transparent cover to exhaust gas regularly, avoid the generation of water mist, keep the inside of the transparent cover dry, make the reflection effect better and the disinfection more thorough. Description of the Drawings

[0020] Figure 1 It is a process schematic diagram of the present invention.

[0021] Figure 2 It is a cross-sectional schematic diagram of the present invention.

[0022] Figure 3 It is a longitudinal-sectional schematic diagram of the present invention.

[0023] In the figure: 1. Ultraviolet disinfection tank; 2. Mounting seat; 3. Mirror panel; 4. Transparent cover; 5. Water baffle; 51. Exhaust pipe; 6. Flow stabilizing plate; 61. Through hole; 7. Flow buffering cone; 8. Ultraviolet lamp column; 9. Water inlet pipe; 10. Water outlet pipe; 11. Anti-vortex plate. Specific implementation manner

[0024] To clearly illustrate the technical features of this solution, the present invention will be described in detail below through specific implementation manners and in conjunction with its accompanying drawings. In the description of the present invention, it should be noted that the orientation or positional relationship indicated by terms such as "left", "right", "front", "rear", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0025] As shown in Figures 1 - 3 the figure, the present invention provides a seawater pretreatment system for controlling biological fouling of reverse osmosis membranes. The seawater pretreatment system includes a raw water tank, a clarifier, a sand filter, a security filter, a nanofiltration membrane filter, and an ultraviolet disinfection tank 1 connected in sequence. A disinfectant dosing device and a coagulant dosing device are provided on the raw water tank, a mixing paddle is provided in the raw water tank, and a scale inhibitor dosing device and a reducing agent dosing device are connected to the pipeline between the security filter and the sand filter. The seawater is disinfected once by adding a disinfectant, and then the seawater passes through the clarifier and the sand filter for sedimentation and preliminary filtration. Then, a reducing agent is added to reduce the disinfectant. After passing through the security filter and the nanofiltration membrane filter for filtration, it is finally disinfected twice in the ultraviolet disinfection tank 1 to complete the pretreatment of seawater desalination and wait for reverse osmosis desalination filtration.

[0026] Among them, a number of mounting seats 2 evenly distributed circumferentially are provided on the inner wall of the ultraviolet disinfection tank 1. Removable mirror panels 3 are installed on the mounting seats. A vertical ultraviolet lamp column 8 is provided at the central position in the ultraviolet disinfection tank 1. A number of layers of flow stabilizing plates 6 are fixed on the ultraviolet lamp column. A number of evenly distributed through holes 61 are opened on the flow stabilizing plates. The water inlet of the ultraviolet disinfection tank is located at the upper part of the tank body, and the water outlet of the ultraviolet disinfection tank 1 is located on one side of the lower part of the tank head. The ultraviolet lamp column 8 disinfects the seawater in the tank, and the mirror panel 3 cooperates with the lamp column for light reflection to avoid blocking and enhance the disinfection effect of ultraviolet rays. The flow stabilizing plate 6 can slow down the mixing of seawater and make the disinfection more uniform.

[0027] As a preferred implementation manner, a flow buffering cone 7 is provided at the top of the ultraviolet lamp column 8, and a water inlet pipe 9 is provided on the water inlet. The water inlet pipe 9 faces the flow buffering cone 7 to reduce the potential energy when the water flow enters and avoid the mixing of seawater in the tank due to shaking.

[0028] As a preferred embodiment, a water outlet pipe 10 is fixed to the water outlet, and an anti-vortex plate 11 is arranged inside the water outlet pipe to prevent the generation of vortices in the tank during water discharge, which may cause the seawater to shake and mix.

[0029] It should be noted that the water inflow and outflow should be kept consistent. The purpose of the slow-flow cone, the steady-flow plate and the anti-vortex plate is to slow down the mixing of the seawater in the tank. It takes 40 - 60 minutes for the seawater to enter and then flow out, ensuring that the seawater can be irradiated for more than 30 minutes to complete thorough ultraviolet sterilization and disinfection. The traditional methods of disinfecting water bodies with ultraviolet rays all require shutting down the machine and waiting for 30 minutes for ultraviolet disinfection, and then proceeding to the next step. The setting of the ultraviolet disinfection tank in the present invention enables the seawater pretreatment process to work continuously without shutting down and waiting.

[0030] As a preferred embodiment, a transparent cover 4 is fixed to the mounting seat. The bottom end of the transparent cover is closed, and a water baffle 5 is arranged at the upper end. The mirror panel 3 is inserted into the transparent cover 4. Since the mirror is easily corroded by seawater, using a corrosion-resistant transparent cover can extend the service life of the mirror panel, such as tempered glass.

[0031] As a preferred embodiment, a branch exhaust pipe 51 is connected to the water baffle 5 of each transparent cover 4 of the mounting seat. The branch exhaust pipe is connected to a main exhaust pipe, and the main exhaust pipe is connected to an exhaust pump to regularly discharge the air in the cover and prevent the formation of water mist in the transparent cover, which may affect the light reflection effect.

[0032] As a preferred embodiment, the disinfectant is sodium hypochlorite to kill microorganisms in the water for primary disinfection. The coagulant is ferric chloride to coagulate the suspended substances in the seawater into large particles for precipitation. The reducing agent is sodium bisulfite to reduce the oxidants in the seawater and avoid damaging the reverse osmosis membrane.

[0033] As a preferred embodiment, the seawater pretreatment method for controlling the biofouling of the reverse osmosis membrane includes the following steps:

[0034] a. The seawater is lifted into the raw water tank, and a disinfectant and a coagulant are added. After being mixed by a large mixing paddle, it enters the clarification tank for precipitation, and then is filtered by a sand filter to obtain clear seawater;

[0035] b. A scale inhibitor and a reducing agent are continuously added to reduce the oxidants in the seawater. The scale inhibitor reduces the formation of scale on the re-filter membrane. After passing through a security filter and a nanofiltration membrane filter, it is further filtered;

[0036] c. The restored and filtered seawater slowly enters the ultraviolet disinfection tank through the water inlet pipe and the flow-slowing cone, and is disinfected in the tank for more than 30 minutes. The tank is provided with a flow-slowing cone, a flow-stabilizing plate and an anti-vortex plate to reduce the mixing of water flow caused by water inlet and outlet in the tank. The water inflow and outflow in the tank are kept consistent, and the seawater after secondary disinfection flows out from the water outlet pipe;

[0037] d. The seawater after secondary disinfection directly enters the reverse osmosis membrane module for the next step of reverse osmosis filtration to produce fresh water.

[0038] For those not detailed in the present invention, they are all well-known technologies to those skilled in the art. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A seawater pretreatment system for controlling biological fouling of reverse osmosis membranes, characterized in that: The seawater pretreatment system includes a raw water tank, a clarifier, a sand filter, a security filter, a nanofiltration membrane filter, and an ultraviolet disinfection tank connected in sequence. A disinfectant dosing device and a coagulant dosing device are provided on the raw water tank. A mixing paddle is provided inside the raw water tank. A scale inhibitor dosing device and a reducing agent dosing device are connected to the pipeline between the security filter and the sand filter. A number of mounting seats evenly distributed in the circumferential direction are provided on the inner wall of the ultraviolet disinfection tank. Removable mirror panels are installed on the mounting seats. A vertical ultraviolet lamp post is provided at the central position inside the ultraviolet disinfection tank. A number of layers of flow stabilizing plates are fixed on the ultraviolet lamp post. The water inlet of the ultraviolet disinfection tank is located at the upper part of the tank body, and the water outlet of the ultraviolet disinfection tank is located on one side of the lower part of the tank head.

2. The seawater pretreatment method and system for controlling biological fouling of reverse osmosis membranes according to claim 1, characterized in that: A flow retardation cone is provided at the top of the ultraviolet lamp post. A water inlet pipe is provided on the water inlet, and the water inlet pipe faces the flow retardation cone.

3. The seawater pretreatment method and system for controlling biological fouling of reverse osmosis membranes according to claim 1, characterized in that: A water outlet pipe is fixed on the water outlet, and an anti-vortex baffle is provided inside the water outlet pipe.

4. The seawater pretreatment method and system for controlling biological fouling of reverse osmosis membranes according to claim 1, wherein: A number of uniformly distributed through holes are formed on the flow stabilizing plates.

5. The seawater pretreatment method and system for controlling biological fouling of reverse osmosis membranes according to claim 1, characterized in that: A transparent cover is fixed on the mounting seat. The bottom end of the transparent cover is closed, and a water blocking cover is provided at the upper end. The mirror panel is inserted into the transparent cover.

6. The seawater pretreatment method and system for controlling biological fouling of reverse osmosis membranes according to claim 4, characterized in that: A branch exhaust pipe is communicated with the water blocking cover of the transparent cover of each mounting seat. The branch exhaust pipes are connected to a main exhaust pipe, and the main exhaust pipe is connected to an exhaust pump.

7. The seawater pretreatment method and system for controlling biological fouling of reverse osmosis membranes according to claim 1, characterized in that: The reducing agent is sodium bisulfite.

8. The seawater pretreatment method and system for controlling biological fouling of reverse osmosis membranes according to claim 1, characterized in that: The disinfectant is sodium hypochlorite, and the coagulant is ferric chloride.

9. A seawater pretreatment method for controlling biological fouling of a reverse osmosis membrane, characterized by the following steps: a. The seawater is lifted into the raw water tank, a disinfectant and a coagulant are added, and after being mixed by a large mixing paddle, it enters the clarifier for precipitation, and then is filtered by the sand filter to obtain clear seawater. b. The scale inhibitor and the reducing agent are continuously added, and further filtration is carried out through the security filter and the nanofiltration membrane filter. c. The reduced and filtered seawater slowly enters the ultraviolet disinfection tank through the water inlet pipe and the flow retardation cone, and is disinfected in the tank for 40-50 minutes. A flow retardation cone, a flow stabilizing plate, and an anti-vortex baffle are provided in the tank to reduce the mixing of the water flow caused by the inlet and outlet water in the tank. The water inflow and the water outflow in the tank are kept consistent, and the seawater after secondary disinfection flows out from the water outlet pipe. d. The seawater after secondary disinfection enters the reverse osmosis membrane module for the next step of reverse osmosis filtration to produce fresh water.

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