Sewage Treatment Device and Method for Synchronously Recovering Water and Electric Energy

Abstract

The disclosure discloses a sewage treatment device and method for synchronously recovering water and electric energy, belonging to the field of sewage treatment. The method of the disclosure includes the following steps: enabling municipal sewage serving as influent water and a sludge and sewage mixed solution serving as a feed solution to enter a feed solution channel of a membrane component through a peristaltic pump, and enabling brine serving as a draw solution to enter a draw solution channel of the membrane component through a high pressure pump; enabling water to flow from the side of the feed solution to the side of the draw solution by means of the osmotic pressure difference between two sides of an FO membrane, and enabling the mixed draw solution with high pressure to push a turbine to rotate in an outflow process, so as to generate electric energy; and enabling the diluted draw solution to pass through a draw solution recovery system to obtain recycled water, and at the same time, enabling the concentrated draw solution to continue to be applied to the FO membrane.

Claims

1. A sewage treatment device for synchronously recovering water and electric energy, comprising an influent water pool, a bioreactor, a forward osmosis (FO) membrane component, a turbine, a draw solution pool and a draw solution recovery system, wherein the influent water pool is connected with the bioreactor, the FO membrane component comprises a draw solution channel, a feed solution channel and an FO membrane, the FO membrane separates the draw solution channel from the feed solution channel, both an inlet of the feed solution channel and an outlet of the feed solution channel are connected with the bioreactor, the draw solution pool is connected with an inlet of the draw solution channel, an outlet of the draw solution channel is connected with the draw solution pool through the turbine, and the draw solution pool is connected with the draw solution recovery system; a high pressure pump is installed on a pipeline where the draw solution pool is connected with the inlet of the draw solution channel; and the FO membrane comprises a support layer and an active layer, and the active layer faces a draw solution.

2. The sewage treatment device according to claim 1, wherein a pump is installed on a pipeline where the influent water pool is connected with the bioreactor.

3. The sewage treatment device according to claim 1, wherein a pump is installed on a pipeline where the bioreactor is connected with the inlet of the feed solution channel.

4. The sewage treatment device according to claim 1, wherein an aeration pipe is installed at a lower part of the bioreactor, and one end of an air pump is connected with the aeration pipe.

5. The sewage treatment device according to claim 1, wherein the draw solution recovery system comprises a conductivity meter, a high pressure pump and a reverse osmosis component, wherein the draw solution pool, the high pressure pump, the reverse osmosis component and the draw solution pool are sequentially connected to form a cycle, the conductivity meter is connected with the high pressure pump, and a detection end of the conductivity meter is located inside the draw solution pool.

6. The sewage treatment device according to claim 1, wherein the FO membrane component is made of stainless steel or an organic plastic material, and the FO membrane component further comprises gaskets positioned on two sides of the FO membrane.

7. The sewage treatment device according to claim 1, wherein the FO membrane is any one of a cellulose acetate membrane, a polyamide membrane, an aquaporin membrane or a polyether sulfone resin membrane.

8. A sewage treatment method for synchronously recovering water and electric energy, comprising using the sewage treatment device according to claim 1 to treat sewage.

9. The sewage treatment method according to claim 8, wherein the sewage is municipal sewage.

10. The sewage treatment method according to claim 9, wherein water quality indexes of the municipal sewage are as follows: COD: 200-500 mg/L, NH.sub.4.sup.+N: 20-50 mg/L, TN: 30-50 mg/L, and TP: 2-7 mg/L.

11. The sewage treatment method according to claim 8, wherein the using the sewage treatment device to treat sewage comprises the following steps: enabling municipal sewage serving as influent water to enter the bioreactor so as to be mixed with active sludge, pumping the sludge and sewage mixture obtained by mixing into the feed solution channel of the FO membrane through a pump, enabling the draw solution to enter the draw solution channel in the membrane component through the high pressure pump, and enabling water to flow from the feed solution channel to the draw solution channel by means of an osmotic pressure difference between two sides of the FO membrane; and at the same time, applying a certain pressure to a side of the draw solution channel, enabling a diluted draw solution to pass through the turbine and push the turbine to rotate, so as to generate electric energy, and when a concentration of the draw solution is too low, starting the draw solution recovery system, and concentrating and recovering the draw solution by a reverse osmosis component to obtain water.

12. The sewage treatment method according to claim 11, wherein a cycle rate of the sludge and sewage mixture is 0.1-0.5 L/min.

13. The sewage treatment method according to claim 11, wherein the active sludge has SS of 3-9 g/L.

14. The sewage treatment method according to claim 11, wherein the draw solution is a 0.5-4 M NaCl, MgCl.sub.2, KCl or CaCl.sub.2 solution.

15. The sewage treatment method according to claim 11, wherein the pressure applied to the side of the draw solution channel is less than an osmotic pressure on two sides of the FO membrane.

16. The sewage treatment method according to claim 11, wherein the pressure applied to the side of the draw solution channel is 4-8 bars.

17. The sewage treatment method according to claim 11, wherein when the concentration of the draw solution is too low, it means that the osmotic pressure difference of the FO membrane is less than the pressure applied to the side of the draw solution channel.

18. The sewage treatment method according to claim 8, wherein the using the sewage treatment device to treat sewage comprises the following steps: 1) enabling municipal sewage serving as influent water to enter the bioreactor so as to be mixed with active sludge, pumping the sludge and sewage mixture obtained by mixing into the feed solution channel of the FO membrane through a pump, enabling the draw solution to enter the draw solution channel in the membrane component through the high pressure pump, and enabling water to flow from the feed solution channel to the draw solution channel by means of an osmotic pressure difference between two sides of the FO membrane; and 2) at the same time, applying a certain pressure to a side of the draw solution channel, enabling a diluted draw solution to pass through the turbine and push the turbine to rotate, so as to generate electric energy, and when a concentration of the draw solution is too low, starting the draw solution recovery system, and concentrating and recovering the draw solution by a reverse osmosis component to obtain water, wherein the influent water is municipal sewage, and water quality indexes of the municipal sewage are as follows: COD: 35012.2 mg/L, NH.sub.4.sup.+N: 24.881.50 mg/L, TN: 38.241.68 mg/L, and TP: 2.080.13 mg/L; and in the bioreactor, the active sludge has SS of 3 g/L, the draw solution is 2 M NaCl, the pressure applied to the side of the draw solution is 6 bars, the active layer of the membrane faces the draw solution, and the operating time is 4 h.

Description

BRIEF DESCRIPTION OF FIGURES

[0032] FIG. 1 is a schematic structural diagram of an implementation of a sewage treatment device for synchronously recovering water and electric energy of the disclosure. In the figure, 1 denotes an influent water pool, 2 denotes a peristaltic pump, 3 denotes a bioreactor, 4 denotes an air pump, 5 denotes a peristaltic pump, 6 denotes an FO membrane component, 7 denotes a turbine, 8 denotes a high pressure pump, 9 denotes a draw solution pool, 10 denotes a conductivity meter, 11 denotes a high pressure pump, 12 denotes a reverse osmosis component, 17 denotes a draw solution recovery system.

[0033] FIG. 2 is a schematic structural diagram of an FO membrane component. In the figure, 13 denotes a feed solution channel, 14 denotes a draw solution channel, 15 denotes a gasket, 16 denotes an FO membrane.

DETAILED DESCRIPTION

[0034] The specific implementations of the disclosure are further described in detail below with reference to the examples. The following examples are intended to illustrate the disclosure but are not intended to limit the scope of the disclosure.

[0035] 1. Measurement method of COD: fast digestion spectrophotometry.

[0036] 2. Measurement method of NH.sub.4.sup.+N: Berthebt method.

[0037] 3. Measurement method of TN: potassium persulfate oxidation-ultraviolet spectrophotometry.

[0038] 4. Measurement method of TP: potassium persulfate digestion-molybdenum antimony anti-spectrophotometry.

[0039] 5. Measurement method of average water flux: expressed by the amount of water passing through a unit membrane area in a unit time.

[0040] 6. Measurement method of average electricity generation power density: expressed by the amount of electricity generated on a unit membrane area.

[0041] 7. Measurement method of membrane surface pollutants: all pollutants are put into a crucible and evaporated to a constant weight at 600 C. to obtain the total weight of the remaining solids.

Example 1

[0042] With reference to the FIG. 1 and the FIG. 2, a sewage treatment device for synchronously recovering water and electric energy of the disclosure will be described in detail. The device of the disclosure includes an influent water pool 1, a bioreactor 3, an FO membrane component 6, a turbine 7, a draw solution pool 9 and a draw solution recovery system 17. The influent water pool 1 is connected with the bioreactor 3 through a peristaltic pump 2. The FO membrane component 6 includes a draw solution channel 14, a feed solution channel 13, gaskets 15 and an FO membrane 16. The gaskets and the FO membrane are arranged in parallel and separate the draw solution channel from the feed solution channel. Both an inlet of the feed solution channel and an outlet of the feed solution channel are connected with the bioreactor 3. The draw solution pool 9 is connected with an inlet of the draw solution channel through a high pressure pump 8, and an outlet of the draw solution channel is connected with the draw solution pool 9 through the turbine 7. The draw solution recovery system 17 includes a conductivity meter 10, a high pressure pump 11 and a reverse osmosis component 12, and the draw solution pool 9, the high pressure pump 11, the reverse osmosis component 12 and the draw solution pool 9 are sequentially connected to form a cycle. The conductivity meter 10 is connected with the high pressure pump 11 and is configured to control the turning-on and turning-off of the high pressure pump. A detection end of the conductivity meter 10 is positioned inside the draw solution pool 9.

[0043] Further, an aeration pipe is installed at the lower part of the bioreactor 3, and one end of an air pump is connected with the aeration pipe.

[0044] Further, the membrane component is made of stainless steel or organic plastic materials, and the FO membrane is any one of a cellulose acetate (CTA) membrane, a polyamide (TFC) membrane, an aquaporin membrane or a polyether sulfone resin (PES) membrane.

[0045] It can be seen from the FIG. 2 that the FO membrane component includes a support layer and an active layer, and the active layer faces the draw solution.

[0046] The operating principle of the above-mentioned device is as follows: municipal sewage serving as influent water enters the bioreactor so as to be mixed with active sludge, the sludge and sewage mixture obtained by mixing is pumped into the feed solution channel of the FO membrane through a pump, a draw solution enters the draw solution channel in the membrane component through the high pressure pump, and water flows from the feed solution channel to the draw solution channel by means of the osmotic pressure difference between two sides of the FO membrane; at the same time, a certain pressure is applied to the side of the draw solution channel, and the diluted draw solution passes through the turbine and pushes the turbine to rotate, so as to generate electric energy; and when the concentration of the draw solution is too low, the draw solution recovery system is started, and the draw solution is concentrated and recovered by a reverse osmosis component to obtain water.

Example 2

[0047] The municipal sewage is treated by the device shown in FIG. 1.

[0048] In view of the structure of FO (one layer is an active layer having an interception effect, and the other layer is a support layer having a support effect. The active layer is relatively thin and dense and has a strong anti-pollution ability, and the support layer is relatively thick and porous and is prone to membrane pollution), and the condition that the FO membrane in the disclosure faces the active sludge containing various pollutants, in order to alleviate FO membrane pollution, when the OMBR of the present example operates, an AL-FS orientation is adopted (the active layer faces the feed solution).

[0049] The influent water is municipal sewage, and the water quality is as follows: COD: 35012.2 mg/L, NH.sub.4.sup.+N: 24.881.50 mg/L, TN: 38.241.68 mg/L, and TP: 2.080.13 mg/L. In the bioreactor, the SS (suspended solid) is 3 g/L active sludge, the draw solution is 2 M NaCl, the pressure applied to the side of the draw solution is 6 bars, the membrane orientation is AL-FS (the active layer faces the feed solution), and the operating time is 24 h.

[0050] The effluent water quality is as follows: COD: 102.45 mg/L, NH.sub.4.sup.+N: 4.410.40 mg/L, TN: 4.490.53 mg/L, and TP: 0. The average water flux is 7.79 LMH, and the average electricity generation power density is 1.4 W/m.sup.2.

[0051] It can be seen that, according to a conventional practice (that is, the FO membrane orientation is AL-FS), the finally obtained average water flux is only 7.79 LML, and the average electricity generation power density is only 1.4 W/m.sup.2.

Example 3

[0052] In order to further increase the average electricity generation power, the inventors try to adopt the unconventional FO membrane orientation, that is, AL-DS (the active layer faces the draw solution), to conduct experiments.

[0053] In the method of the present example, the influent water is municipal sewage, and the water quality is as follows: COD: 35012.2 mg/L, NH.sub.4.sup.+N: 24.881.50 mg/L, TN: 38.241.68 mg/L, and TP: 2.080.13 mg/L. In the bioreactor, the SS is 3 g/L active sludge, the draw solution is 2 M NaCl, the pressure applied to the side of the draw solution is 6 bars, the membrane orientation is AL-DS (the active layer faces the draw solution), and the operating time is 4 h.

[0054] The effluent water quality is as follows: COD: 101.51 mg/L, NH.sub.4.sup.+N: 5.120.90 mg/L, TN: 5.531.21 mg/L, and TP: 0. The average water flux is 12.19 LML, and the average electricity generation power density is 2.2 W/m.sup.2.

[0055] It can be found that when the active layer faces the draw solution (the membrane orientation is AL-DS), under the same conditions, the average water flux is 12.19 LMH and the average electricity generation power density is 2.2 W/m.sup.2 which are 1.57 times that of Example 2. In addition, during 24 h of operation, the water flux and power density are always higher than the membrane flux and power density of Example 2. Compared with the AL-FS, during operating in the AL-DS orientation, the pollution level of the FO membrane is similar to that in Example 2, and there is no obvious blockage. It can be seen that, when the membrane orientation is AL-DS, an optimal operating effect can be obtained.

Example 4

[0056] In the method of the present example, the influent water is municipal sewage, and the water quality is as follows: COD: 33010.1 mg/L, NH.sub.4.sup.+N: 24.881.50 mg/L, TN: 38.241.68 mg/L, and TP: 2.080.13 mg/L. In the bioreactor, the SS is 3 g/L active sludge, the draw solution is 2 M NaCl, the pressure applied to the side of the draw solution is 0 bar, the membrane orientation is AL-DS (the active layer faces the draw solution), and the operating time is 4 h.

[0057] The effluent water quality is as follows: COD: 122.45 mg/L, NH.sub.4.sup.+N: 5.110.30 mg/L, TN: 4.630.38 mg/L, and TP: 0. The average water flux is 13.54 LMH, and the average electricity generation power density is 0 W/m.sup.2.

[0058] It can be found that when no pressure is applied to the side of the draw solution, although the flux is also stable, no electricity is generated. By means of analysis of membrane surface pollutants, it is found that the membrane surface pollutants after pressurized operation are 0.78 g/m.sup.2, while the membrane surface pollutants without pressurized operation are 1.52 g/m.sup.2. It can be seen that, the membrane surface pollutants after pressurized operation are significantly reduced, which indicates that the membrane pollution after pressurized operation is lighter than the membrane pollution without pressurized operation.

Example 5

[0059] Referring to the method of Example 3, the difference is that the pressure applied to the side of the draw solution is changed, the pressure is 0, 4, 6, 8 and 12 bars respectively, the other conditions are the same as those in Example 3, and results are shown in Table 1. It can be seen from Table 1 that as the pressure increases, the average electricity generation power density is higher. However, when the pressure is 12 bars which is too high, the membrane is deformed, the membrane pollution is aggravated, and the system is unstable. Therefore, preferably, the pressure of the high pressure pump is 4-8 bars.

TABLE-US-00001 TABLE 1 Pres- Average sure Efflu- electricity applied ent Aver- gener- to side Effluent Effluent Effluent water age ation of draw water water water TP water power solution COD NH.sub.4.sup.+-N TN (mg/ flux density (bar) (mg/L) (mg/L) (mg/L) L) (LMH) (W/m.sup.2) 0 12 2.45 5.11 0.30 4.63 0.38 0 13.54 0 4 11.54 2.39 4.99 0.36 5.95 0.24 0 10.55 1.17 6 10 2.45 5.12 0.90 5.53 1.21 0 12.19 2.2 8 11.98 1.58 4.53 0.37 6.02 0.87 0 11.88 2.64