CN103964619A - Advanced treatment and reuse method of pre-coated membrane of tail water of sewage plant - Google Patents

Abstract

The invention discloses an advanced treatment and reuse method of a pre-coated membrane of tail water of a sewage plant. The method comprises the following steps: firstly, feeding tail water into an adjusting pool so as to be homogenized, and then passing through a sand filter; passing through an ultrafiltration membrane by a solution containing a pre-coated membrane material and sand filtered effluent and effectively forming a dynamic membrane on the surface of the ultrafiltration membrane, wherein concentrated water of the ultrafiltration membrane returns to the adjusting pool while the effluent enters into a middle water tank; backwashing the ultrafiltration membrane through a pump by part of water in the middle water tank periodically, wherein the pre-coated membrane automatically falls and the sediment of the coating material is recycled to a pre-coated membrane material dosing device repeatedly, so that the operating cost is lowered; entering into reverse osmosis membrane treatment by water in the middle water tank, fresh reverse osmosis membrane is used as industrial water in the park to be returned, and the concentrated water is treated by an electrochemical reactor, and the effluent reaches the standard to be discharged. By adopting the pre-coated membrane method, the ultrafiltration backwashing frequency is low, and the water yield of the ultrafiltration membrane is improved. Loose filter cake layers with great holes can be formed to effectively relieve the rate of descent of membrane flux, improve the anti-pollution capacity of the membrane and improve the removal effect of the membrane on the water quality index at the same time.

Description

A method for advanced treatment and reuse of precoated film in tail water of sewage plant

technical field

The invention belongs to the field of sewage advanced treatment and reuse engineering, and relates to a method for advanced treatment and reuse of tail water of industrial park sewage plants.

Background technique

The increasingly tense water resource shortage and water environment pollution have attracted great attention both at home and abroad. Industrial sewage recycling is an effective way to alleviate the shortage of water resources, reduce the degree of water pollution, and improve the ecological environment. How to rationally and effectively comprehensively utilize sewage resources in the park has become the key to solving the problems of water resource utilization and water environment pollution in the park. . The main water quality indicators of the tail water of industrial park sewage plants, such as organic matter, ammonia nitrogen, and salinity, cannot meet the reuse standards and require further advanced treatment. Membrane separation technology has been highly valued in the world, and its biggest advantage is high separation efficiency, and the produced water can be reused in the production process. However, membrane fouling has become a bottleneck problem that restricts the further application of membrane separation technology.

The double-membrane method refers to a water treatment method that combines ultrafiltration membrane (UF) and reverse osmosis membrane (RO). Although the double-membrane method has many advantages, there are still these problems in actual operation, mainly in How to control membrane fouling to increase membrane flux for longer membrane lifetime. The ultrafiltration membrane can reduce the pollution of the subsequent reverse osmosis membrane, but after a certain period of operation of the ultrafiltration membrane, the surface of the membrane will intercept some organic matter, viruses, bacteria, algae and other substances, that is, the ultrafiltration membrane will inevitably be polluted. Regular backwashing is required for ultrafiltration during operation, which can take away part of the intercepted matter on the surface of the membrane and delay the attenuation of membrane flux. The frequency of backwashing is generally once every 20 minutes to 60 minutes, and the time for each backwashing is 20 minutes. seconds to 80 seconds, and high-frequency backwashing will significantly reduce the water production rate of the ultrafiltration membrane. In addition, membrane concentrated water has the characteristics of high salt content and poor biodegradability, so it is relatively difficult to treat. Therefore, how to effectively recover membrane backwash water and membrane concentrated water is also a problem that must be solved in the application of membrane technology in advanced sewage treatment.

Contents of the invention

Purpose of the invention: Aiming at the above-mentioned problems existing in the prior art in the double-membrane advanced treatment and reuse method of the tail water of the industrial park sewage plant, the present invention provides a method for the advanced treatment and reuse of the pre-coated film of the tail water of the sewage plant.

In order to solve the problems of the technologies described above, the technical scheme adopted in the present invention is as follows:

A method for advanced treatment and reuse of precoated film of tail water from a sewage plant, comprising the following steps:

(1) First send the tail water to the regulating tank for homogenization;

(2) After passing through the sand filter, the suspended impurities of larger particles in the wastewater are removed;

(3) The pre-coating material is added to the sand filter effluent through the coating material dosing device, and the sand filter effluent containing the pre-coating material solution passes through the ultrafiltration membrane to form a dynamic pre-coating on the surface of the ultrafiltration membrane. The water returns to the regulating tank, and the effluent enters the intermediate tank;

(4) The water in the middle tank enters the reverse osmosis membrane for treatment, the fresh water of the reverse osmosis membrane is reused, and the concentrated water enters the concentrated water tank;

(5) The concentrated pool water is then treated by an electrochemical reactor, and the effluent is discharged up to the standard.

As a further improvement of the present invention, a backwashing step is also included between steps (3) and (4), that is, part of the water in the intermediate pool is periodically backwashed by the pump to the ultrafiltration membrane, so that the pre-coating will automatically fall off and be removed. The backwash water is taken out and enters the coating material sedimentation tank. The coating material in the coating material sedimentation tank is deposited and recycled to the coating material dosing device for repeated use. The supernatant of the coating material sedimentation tank enters the concentrated water tank.

As a further improvement of the present invention, the ultrafiltration membrane is a hollow fiber membrane, and a precision filter is arranged in front of the membrane module with a filtration accuracy of 5-40 μm.

As a further improvement of the present invention, the concentrated water of the ultrafiltration membrane is refluxed, and the reflux ratio is 3% to 8%.

As a further improvement of the present invention, in the described coating material dosing device, the pre-coating material is zeolite powder and/or diatomaceous earth and/or activated carbon, the particle size is 400-2000 mesh, and the dosing amount is 50-2000 mesh. 400mg/L.

As a further improvement of the present invention, the ultrafiltration membrane is backwashed, the backwashing frequency is once every 1 hour to 3 hours, the backwashing time is 20 seconds to 80 seconds each time, and the backwashing flow rate is 100% of the ultrafiltration influent flow rate. 1.5 times to 3.0 times.

As a further improvement of the present invention, the coating material settling tank is divided into a reaction zone and a settling zone, and a polyacrylamide flocculant is added in the reaction zone at a dosage of 0.5-3 mg/L.

As a further improvement of the present invention, the electrochemical reactor is a two-dimensional electrode or three-dimensional electrode electrocatalytic reaction device, the current density is adjusted to 5-50 mA/cm ² , and the electrolysis residence time is 30-90 minutes.

Beneficial effects of the present invention:

The method of precoating the membrane of the present invention can form an effective "protective layer" on the surface of the ultrafiltration membrane to intercept the pollutants deposited on the membrane surface and reduce the direct contact between the pollutants and the membrane. The solid-liquid separation of pre-coating film ultrafiltration backwash water is carried out through the coating material sedimentation tank, and the coating film material is recycled in the pre-coating film material dosing device and reused in the pre-coating film ultrafiltration system, which can be effectively recovered Coating materials can realize resource utilization of backwash water and reduce operating costs.

The ultrafiltration and backwashing frequency of the pre-coating membrane method is low, which can increase the water production rate of the ultrafiltration membrane; and can form a loose filter cake layer with large pores, which is relatively loose and can absorb some organic matter and inorganic salts, and is easy to be reversed. Flushing can effectively alleviate the decline rate of the flux of the ultrafiltration membrane, delay the pollution of the membrane, strengthen the anti-pollution ability of the membrane, slow down the decline rate of the flux of the membrane by more than 30%, and improve the removal effect of the ultrafiltration membrane on water quality indicators, such as COD and TN The removal rate of UV254 and UV254 is increased by more than 25%, and the rate of subsequent reverse osmosis membrane flux decline is slowed down by more than 15%. Membrane backwash water and membrane concentrated water have high salt content and good conductivity. Electrochemical oxidation can achieve higher current density at a lower voltage, which helps to improve oxidation efficiency and can effectively treat membrane backwash water. And membrane concentrated water.

Description of drawings

Fig. 1 is a process flow diagram of the present invention;

Fig. 2 is the SEM figure of fresh ultrafiltration membrane;

Figure 3 is the SEM image of the precoated ultrafiltration membrane.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

The process flow of the method for advanced treatment and reuse of tail water pre-coating film of industrial park sewage plant tail water of the present invention is shown in Figure 1, and its steps are:

First, the tail water after the secondary biochemical treatment is sent to the regulating tank for homogenization, and then passed through the quartz sand filter to remove the suspended impurities of larger particles in the wastewater; the pre-coating film material is added through the dosing device, containing the pre-coating film material solution The sand filter effluent passes through the ultrafiltration membrane together, and a dynamic membrane is effectively formed on the surface of the ultrafiltration membrane. The concentrated water of the ultrafiltration membrane is returned to the regulating tank, and the effluent enters the intermediate pool; part of the water in the intermediate pool is periodically pumped to backwash the ultrafiltration membrane. , so that the pre-coating film falls off automatically, is taken out by the backwash water, and enters the coating material sedimentation tank, and the coating material is precipitated and reused to the pre-coating material dosing device for repeated use, and the supernatant of the sedimentation tank enters the concentrated water tank; The water in the pool enters the reverse osmosis membrane for treatment, the fresh water of the reverse osmosis membrane is reused as process water in the park, and the concentrated water enters the concentrated water tank; the concentrated water is then treated by the electrochemical reactor, and the effluent is discharged up to the standard.

Among them, the ultrafiltration membrane is a hollow fiber membrane, and a precision filter is installed in front of the membrane module, with a filtration accuracy of 5-40 μm. The structures of the fresh ultrafiltration membrane and the precoated ultrafiltration membrane are shown in Fig. 2 and Fig. 3, respectively.

Among them, the concentrated water of the ultrafiltration membrane is refluxed, and the reflux ratio is 3% to 8%.

Among them, in the dosing device, the pre-coating film material is zeolite powder, diatomaceous earth or activated carbon, the particle size is 400-2000 mesh, and the dosing amount is 50-400 mg/L.

Among them, the ultrafiltration membrane is backwashed, the backwashing frequency is once every 1 hour to 3 hours, the backwashing time is 20 seconds to 80 seconds each time, and the backwashing flow rate is 1.5 times to 3.0 times the ultrafiltration water flow rate.

Among them, the coating material sedimentation tank is divided into a reaction zone and a precipitation zone, and polyacrylamide flocculant is added in the reaction zone, and the dosing amount is 0.5~3 mg/L.

Among them, the electrochemical reactor is a two-dimensional electrode or three-dimensional electrode electrocatalytic reaction device, the current density is adjusted to 5-50mA/cm ² , and the electrolytic residence time is 30-90 minutes.

In the following, three cases of tail water treatment of a certain industrial park sewage treatment plant by the method of the present invention will be further described as examples.

Implementation case 1:

The water quality characteristics of the tail water of a sewage treatment plant in an industrial park are as follows: COD 55 mg/L, TN 17.3 mg/L, UV ₂₅₄ 0.232 cm ^-1 , turbidity 2.6, conductivity 5610μs/cm. The specific technological process of advanced treatment and reuse of tail water pre-coating film is shown in Figure 1. First, the tail water after secondary biochemical treatment is sent to the adjustment tank for homogenization, and then passes through the quartz sand filter to remove larger particles in the waste water. Suspended impurities; zeolite powder is added as a pre-coating film material through a dosing device, the particle size is 2000 mesh, and the dosing amount is 200 mg/L. The solution containing the pre-coating film material and sand filter water pass through the ultrafiltration membrane together It is a hollow fiber membrane, and a precision filter with a filtration accuracy of 10 μm is installed in front of the membrane module. The concentrated water of the ultrafiltration membrane is returned to the regulating tank with a reflux ratio of 5%, and the effluent enters the intermediate pool; part of the water in the intermediate pool is regularly pumped to the ultrafiltration tank. The membrane is backwashed, the backwashing frequency is once every 2 hours, and the backwashing time is 50 seconds each time. The backwashing flow rate is twice the ultrafiltration water flow rate. Add polyacrylamide flocculant, the dosing amount is 2mg/L, after the coating material in the sedimentation area is precipitated, it is reused in the pre-coating film material dosing device for repeated use, and the supernatant of the sedimentation tank enters the concentrated water tank; the water in the middle tank After entering the reverse osmosis membrane treatment, the fresh water of the reverse osmosis membrane is reused as process water in the park, and the concentrated water enters the concentrated water tank; the concentrated water is then treated by a two-dimensional electrode electrochemical reactor, and the current density is adjusted to 20mA/cm ² , and the electrolytic retention The time is 45 minutes, and the effluent reaches the discharge standard (GB 18918-2002 Class B standard). Under the same process parameters without the addition of pre-coating film materials, this pre-coating film advanced treatment and reuse method slows down the flux decline rate of the ultrafiltration membrane by 45%, and at the same time improves the removal effect of the ultrafiltration membrane on water quality indicators, such as COD, The removal rates of TN and UV ₂₅₄ were increased by 33%, 30% and 31% respectively, and the flux decline rate of the subsequent reverse osmosis membrane was slowed down by 20%. The removal efficiency of main pollutants is shown in Table 1.

Table 1 Removal efficiency table of process unit

Implementation case 2:

The water quality characteristics of the tail water of a sewage treatment plant in an industrial park are as follows: COD 42 mg/L, TN 13.6 mg/L, UV ₂₅₄ 0.207 cm ^-1 , turbidity 1.5, conductivity 3950μs/cm. The specific technological process of advanced treatment and reuse of tail water pre-coating film is shown in Figure 1. First, the tail water after secondary biochemical treatment is sent to the adjustment tank for homogenization, and then passes through the quartz sand filter to remove larger particles in the waste water. Suspended impurities; activated carbon is added through the dosing device as the pre-coating material, the particle size is 500 mesh, and the dosage is 100mg/L. The solution containing the pre-coating material and the sand filter water pass through the ultrafiltration membrane together, and the ultrafiltration membrane is hollow. Fiber membrane, a precision filter with a filtration accuracy of 30 μm is installed in front of the membrane module, the concentrated water of the ultrafiltration membrane is returned to the regulating tank, the reflux ratio is 3%, and the effluent enters the intermediate pool; part of the water in the intermediate pool is regularly pumped through the ultrafiltration membrane. Backwashing, the backwashing frequency is once every 3 hours, each backwashing time is 30 seconds, the backwashing flow rate is 1.5 times the ultrafiltration water flow rate, the backwashing water enters the coating material sedimentation tank, and is added in the reaction area Polyacrylamide flocculant, the dosing amount is 1mg/L. After the coating material in the sedimentation area is precipitated, it is reused in the pre-coating film material dosing device for repeated use. The supernatant of the sedimentation tank enters the concentrated water tank; the water in the middle pool enters the Reverse osmosis membrane treatment, the reverse osmosis membrane fresh water is reused as process water in the park, and the concentrated water enters the concentrated water tank; the concentrated water is treated by a two-dimensional electrode electrochemical reactor, and the current density is adjusted to 10mA/cm ² , and the electrolytic residence time is 30 Minutes, the effluent reaches the discharge standard (GB 18918-2002 Class A standard). Under the same process parameters without the addition of pre-coating membrane materials, this pre-coating membrane advanced treatment and reuse method slows down the flux decline rate of the ultrafiltration membrane by 30%, and at the same time improves the removal effect of the ultrafiltration membrane on water quality indicators, such as COD, The removal rates of TN and UV ₂₅₄ were increased by 29%, 25% and 27%, respectively, and the flux decline rate of the subsequent reverse osmosis membrane was slowed down by 15%. The removal efficiency of main pollutants is shown in Table 2.

Table 2 Removal efficiency table of process unit

Implementation case 3:

The water quality characteristics of the tail water of a sewage treatment plant in an industrial park are as follows: COD 60 mg/L, TN 19.5 mg/L, UV ₂₅₄ 0.271 cm ^-1 , turbidity 3.1, conductivity 6630μs/cm. The specific technological process of advanced treatment and reuse of tail water pre-coating film is shown in Figure 1. First, the tail water after secondary biochemical treatment is sent to the adjustment tank for homogenization, and then passes through the quartz sand filter to remove larger particles in the waste water. Suspended impurities; diatomaceous earth is added as a pre-coating film material through a dosing device, the particle size is 1000 mesh, and the dosing amount is 400 mg/L. The membrane is a hollow fiber membrane, and a precision filter with a filtration accuracy of 20 μm is installed in front of the membrane module. The filter membrane is backwashed. The backwashing frequency is once every 1.5 hours. The backwashing time is 80 seconds. Add polyacrylamide flocculant in the area, the dosing amount is 3mg/L, after the coating material in the sedimentation area is precipitated, it is reused to the pre-coating film material dosing device for repeated use, and the supernatant of the sedimentation tank enters the thick water tank; The water enters the reverse osmosis membrane for treatment, the fresh water of the reverse osmosis membrane is reused as process water in the park, and the concentrated water enters the concentrated water tank; the concentrated water is then treated by a two-dimensional electrode electrochemical reactor, and the current density is adjusted to 40mA/cm ² , electrolyzed The residence time is 60 minutes, and the effluent is discharged up to the standard (GB 18918-2002 Class B standard). Under the same process parameters without the addition of pre-coating film materials, this pre-coating film advanced treatment and reuse method slows down the flux decline rate of the ultrafiltration membrane by 35%, and at the same time improves the removal effect of the ultrafiltration membrane on water quality indicators, such as COD, The removal rates of TN and UV ₂₅₄ were increased by 27%, 25% and 26% respectively, and the flux decline rate of the subsequent reverse osmosis membrane was slowed down by 15%. The removal efficiency of main pollutants is shown in Table 3.

Table 3 Process unit removal efficiency table

In summary, the ultrafiltration and backwashing frequency of the pre-coating membrane method is low, which can increase the water production rate of the ultrafiltration membrane; and can form a loose and porous filter cake layer, which can effectively alleviate the decline rate of the membrane flux and strengthen the membrane. The anti-pollution ability of the membrane improves the removal effect of the water quality index at the same time.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (8)

1. a method for Sewage Plant tail water pre-coating film advanced treatment and reuse, it comprises the following steps:

(1) first tail water is sent into equalizing tank homogeneous;

(2) pass through again sand-bed filter, remove the suspended impurity of larger particles in waste water;

(3) pre-coating film material adds in sand-bed filter water outlet by class coating material chemicals dosing plant, passes through ultra-filtration membrane containing the sand-bed filter water outlet of pre-coating film material solution, forms dynamic precoated layer on ultra-filtration membrane surface, and ultra-filtration membrane concentrate recirculation is to equalizing tank, and water outlet enters intermediate pool;

(4) water of intermediate pool enters into reverse osmosis membrane processing, the reuse of reverse osmosis membrane fresh water, and dense water enters into dense pond;

(5) dense tank water is passed through electrochemical reactor processing again, water outlet qualified discharge.

2. the method for a kind of Sewage Plant tail water pre-coating film advanced treatment according to claim 1 and reuse, it is characterized in that: between step (3) and (4), also comprise backwash step,, the part water of intermediate pool regularly carries out back flushing by pump to ultra-filtration membrane, make precoated layer Automatic-falling, taken out of by backwash water, enter into class coating material settling tank, class coating material precipitation in class coating material settling tank is back to use class coating material chemicals dosing plant and recycles, and class coating material settling tank supernatant liquor enters into dense pond.

3. according to a kind of Sewage Plant tail water pre-coating film advanced treatment described in claim 1 or 2 and the method for reuse, it is characterized in that: described ultra-filtration membrane is hollow-fibre membrane, accurate filter is set before membrane module, filtering accuracy 5 ~ 40 μ m.

4. the method for a kind of Sewage Plant tail water pre-coating film advanced treatment according to claim 1 and 2 and reuse, is characterized in that: described ultra-filtration membrane concentrate recirculation, reflux ratio is 3% ~ 8%.

5. the method for a kind of Sewage Plant tail water pre-coating film advanced treatment according to claim 1 and 2 and reuse, it is characterized in that: in described class coating material chemicals dosing plant, pre-coating film material is zeolite powder and/or diatomite and/or gac, particle diameter is 400 ~ 2000 orders, and chemical feeding quantity is 50 ~ 400 mg/L.

6. the method for a kind of Sewage Plant tail water pre-coating film advanced treatment according to claim 2 and reuse, it is characterized in that: described ultra-filtration membrane backwash, backwash frequency be every 1 hour by 3 hours once, each backwash time is 20 seconds to 80 seconds, and backwash flow is 1.5 times to 3.0 times of ultrafiltration flooding velocity.

7. the method for a kind of Sewage Plant tail water pre-coating film advanced treatment according to claim 2 and reuse, it is characterized in that: described class coating material settling tank is divided into reaction zone and settling region, in reaction zone, add polyacrylamide flocculant, chemical feeding quantity is 0.5 ~ 3 mg/L.

8. the method for a kind of Sewage Plant tail water pre-coating film advanced treatment according to claim 1 and 2 and reuse, is characterized in that: described electrochemical reactor is two-dimensional electrode or three-diemsnional electrode catalytic reaction device, and adjusting current density is 5 ~ 50mA/cm ², 30 ~ 90 minutes electrolysis residence time.