CN112499728B

CN112499728B - Sewage treatment method for producing calcium alginate and synchronously recovering forward osmosis absorption liquid

Info

Publication number: CN112499728B
Application number: CN202011450392.3A
Authority: CN
Inventors: 王新华; 张若砺; 童兴明
Original assignee: Jiangnan University
Current assignee: Jiangnan University
Priority date: 2020-12-09
Filing date: 2020-12-09
Publication date: 2022-02-01
Anticipated expiration: 2040-12-09
Also published as: CN112499728A

Abstract

The invention discloses a sewage treatment method for producing calcium alginate and synchronously recovering forward osmosis drawing liquid, belonging to the technical field of sewage treatment. The method comprises the following steps: taking municipal sewage as a feed liquid, taking a calcium chloride solution as an extraction liquid, and making water flow from a feed liquid side to an extraction liquid side by using osmotic pressure difference at two sides of a forward osmosis membrane; the urban sewage can obtain a high-concentration concentrate which accords with economic benefits after forward osmosis concentration, and a by-product calcium alginate is obtained by adding a sodium alginate solution with a certain concentration into a drawing solution and separating the drawing solution from the solution in a gel form. The calcium alginate is widely used in food industry and medicine industry, and has important value. The water left after the calcium alginate separation can be directly recycled, such as urban landscape water and the like. The invention has scientific and reasonable technical design and has important significance for expanding the application of the forward osmosis membrane in sewage treatment.

Description

Sewage treatment method for producing calcium alginate and synchronously recovering forward osmosis absorption liquid

Technical Field

The invention relates to a sewage treatment method for producing calcium alginate and synchronously recovering forward osmosis drawing liquid, belonging to the technical field of sewage treatment.

Background

One of the most significant challenges of the 21 st century is to find an effective way to solve the human water use problem. In order to meet water demand, researchers are continually exploring low cost water treatment technologies. Forward Osmosis (FO) is receiving increasing attention as an emerging membrane separation technology. FO uses the osmotic pressure difference across the semipermeable membrane as a driving force to cause water molecules to flow from the low osmotic pressure feed solution side through the semipermeable membrane to the high osmotic pressure draw solution side. And after water molecules enter the drawing liquid, recovering water from the drawing liquid. Compared with other membrane process sewage treatment technologies, such as microfiltration, ultrafiltration, nanofiltration and reverse osmosis, FO has higher cost-benefit and energy efficiency. This is mainly due to the fact that FO requires neither high applied pressure nor high thermal energy and exhibits a low tendency to membrane fouling and reversible membrane fouling, while having a high contaminant rejection capacity. However, FO still presents some limiting factors in the actual wastewater treatment process. High performance FO membranes and draw solutions with high osmotic pressure and easy separation are two major challenges facing FO technology.

Draw solutes can be classified into volatile solutes, organic solutes, inorganic solutes, and nanoparticles. Researchers have conducted extensive research into the suitability of different types of draw solutes. Volatile solutes have the advantage of being easy to regenerate and separate, but the volatile solutes generally have low osmotic pressure, and in most cases, the product water needs to be heated and recovered, and gas residues are easy to exist after separation, thereby affecting the quality of the product water. The organic draw solution generally has a large molecular mass, so reverse salt permeation is not easy to occur, but the generated osmotic pressure is small, the flux is low, the organic solvent is difficult to synthesize, the cost is high, and the scale of commercial application cannot be achieved. The magnetic nanoparticles can generate large osmotic pressure, can improve surface hydrophilicity by modifying functional groups, and can be separated from product water by a magnetic field, but the application of the magnetic nanoparticles is limited because the magnetic nanoparticles can be coagulated. The traditional inorganic salt draw solution has high osmotic pressure, but the reverse osmosis of solute is serious, and the draw solution needs to be separated and recycled by reverse osmosis or nanofiltration, so that the energy consumption is high. The ideal draw solute for FO technology must meet the following criteria: (1) has higher osmotic pressure, (2) is highly soluble in water, (3) has chemical inertness, (4) is safe and nontoxic to human health and environment, (5) reduces reverse salt osmosis phenomenon to the maximum extent, and (6) is easy to separate from water.

Disclosure of Invention

[ problem ] to provide a method for producing a semiconductor device

Current FO technology lacks ideal draw solutions that have high osmotic pressures, low reverse salt permeation, and are easy to separate. The prior FO technology needs reverse osmosis, membrane distillation and other technologies to recover the drawn liquid during operation, so that the energy consumption is high, and the economic feasibility of the technology is influenced.

[ technical solution ] A

In order to solve the problems, the invention provides a novel sewage treatment method for synchronously recovering FO drawing liquid based on the production of calcium alginate by combining the production processes of FO and calcium alginate. On the basis of fully concentrating the sewage and even reaching the zero liquid discharge level, the drawing liquid is recovered by a chemical production method to obtain a byproduct calcium alginate, so that the post-treatment cost of the drawing liquid is greatly reduced. The calcium alginate can be applied to the food industry and the medicine industry and has important value. The water left after the calcium alginate separation can be directly recycled, such as urban landscape water.

A first object of the present invention is to provide a sewage treatment process for the production of calcium alginate with simultaneous recovery of FO draw solution, said process comprising:

1) pumping the municipal sewage in the feeding pool into the FO membrane component by taking the municipal sewage as the inlet water, and making the water in the municipal sewage flow to the drawing liquid and the concentrated liquid flow into the feeding pool by utilizing the osmotic pressure difference at two sides of the FO membrane;

2) the continuously increased drawing liquid flows into the intermediate pool through the overflow weir in the drawing liquid pool, when a certain volume is reached, the suction pump is started to pump the sodium alginate solution into the intermediate pool, and the CaCl in the drawing liquid flowing into the intermediate pool is stirred₂Forming calcium alginate gel, stopping stirring, allowing the calcium alginate gel to flow into a sedimentation tank, and separating to obtain sodium alginate and treated water.

In one embodiment of the invention, the process is carried out in an apparatus comprising a water inlet cell, a FO membrane module, a draw solution cell, a conductivity meter, a concentrated salt tank, and a draw solution recovery system; the FO membrane component comprises a drawing liquid channel, a feeding liquid channel and an FO membrane, the FO membrane separates the drawing liquid channel from the feeding liquid channel, the inlet of the feeding liquid channel and the outlet of the feeding liquid channel are both connected with a water inlet pool, the inlet of the drawing liquid channel and the outlet of the drawing liquid channel are both connected with the drawing liquid pool, the conductivity meter is connected with the strong salt pump, and the detection end of the conductivity meter is positioned inside the drawing liquid pool. The strong salt tank is connected with a draw solution pool through a strong salt pump, and the draw solution pool is connected with a draw solution recovery system;

draw liquid recovery system including middle pond, paddle agitator, ball-cock assembly, solenoid valve, suction pump, sodium alginate solution pond and sedimentation tank, wherein, draw liquid pond, middle pond, sedimentation tank and connect gradually, paddle agitator is located inside the middle pond, the ball-cock assembly is located middle pond inner wall, sodium alginate solution pond passes through the suction pump and links to each other with middle pond, the solenoid valve is located middle bottom of the pool, the sedimentation tank passes through the solenoid valve and links to each other with middle pond.

In one embodiment of the invention, a water inlet pump is installed on a pipeline connecting the water inlet tank and the inlet of the feed liquid channel. In one embodiment of the present invention, a draw solution circulating pump is installed on a pipeline connecting the draw solution tank and the inlet of the draw solution channel.

In one embodiment of the invention, the float valve is used to control the turning on and off of the paddle agitator and suction pump.

In one embodiment, the membrane module is fabricated from stainless steel or organic plastic material, and the FO membrane module further includes a gasket on one side of the FO membrane.

In one embodiment of the invention, the FO membrane comprises any of a cellulose acetate (CTA) membrane, a polyamide (TFC) membrane, a aquaporin membrane, or a polyethersulfone resin (PES) membrane.

In one embodiment of the present invention, the water quality index of the municipal sewage is: COD: 100 to 600mg/L, NH₄ ⁺-N：25～80mg/L，TP：2～10mg/L。

In one embodiment of the invention, the circulation rate of the feed liquid is 0.1-1L/min.

In one embodiment of the present invention, the draw solution is 0.2-0.6M CaCl₂And (3) solution.

In one embodiment of the invention, after the ball float valve of the intermediate tank is triggered, the paddle type stirrer is controlled to be started for 10-30 minutes.

In one embodiment of the invention, the concentration of the sodium alginate solution is 2-4%.

Compared with the prior art, the invention has the following beneficial technical effects:

(1) according to the invention, the production of calcium alginate is combined with the FO process, and the absorption liquid is recovered by a chemical production method while the sewage is intercepted and recovered by utilizing the FO membrane to obtain the byproduct calcium alginate, so that the novel sewage treatment device and method for synchronously recovering the FO absorption liquid in the production of calcium alginate are constructed, no extra energy consumption is needed in the separation process, and the post-treatment cost of the absorption liquid is greatly reduced; the calcium alginate is widely used in food industry and medicine industry, and has important value. The water left after the calcium alginate separation can be directly recycled, such as urban landscape water and the like.

(2) The novel sewage treatment device can fully concentrate sewage while treating the sewage, even reach zero liquid discharge level, and the FO membrane can provide high-concentration concentrate which accords with economic benefits and can directly recover energy in the form of methane through anaerobic digestion. The method solves the problem that the nutrient substances and energy can not be effectively recovered from the existing low-concentration domestic sewage, and is more economical and environment-friendly in treatment.

Drawings

FIG. 1 is a schematic structural diagram of a novel sewage treatment apparatus for producing calcium alginate and synchronously recovering FO draw solution according to the present invention; in the figure, 1-water inlet tank, 2-water inlet pump, 3-FO membrane component, 4-liquid drawing circulating pump, 5-liquid drawing tank, 6-conductivity meter, 7-concentrated salt pump, 8-concentrated salt tank, 9-intermediate tank, 10-paddle stirrer, 11-ball float valve, 12-electromagnetic valve, 13-suction pump, 14-sodium alginate solution tank, and 15-sedimentation tank.

Detailed Description

The following examples are given to further illustrate the embodiments of the present invention. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

Example 1

Referring to fig. 1, the sewage treatment apparatus of the present invention is specifically described, and the apparatus of the present invention includes a water inlet tank 1, an FO membrane module 3, a draw solution tank 5, a conductivity meter 6, a concentrated salt tank 8, and a draw solution recovery system. The water inlet tank 1 is connected with the FO membrane component 3 through a water inlet pump 2, and the drawing liquid tank 5 is connected with the FO membrane component 3 through a drawing liquid circulating pump 4. The FO membrane component 3 comprises a drawing liquid channel, a feeding liquid channel, a gasket and an FO membrane, wherein the gasket and the FO membrane are arranged in parallel and separate the drawing liquid channel from the feeding liquid channel, the inlet of the feeding liquid channel and the outlet of the feeding liquid channel are both connected with the water inlet pool 1, and the inlet of the drawing liquid channel and the outlet of the drawing liquid channel are both connected with the drawing liquid pool 5. The conductivity meter 6 is connected with the concentrated salt pump 7 and used for controlling the opening and closing of the peristaltic pump, and the detection end of the conductivity meter 6 is located inside the liquid drawing pool 5. The drawing liquid recovery system comprises a middle tank 9, a paddle type stirrer 10, a ball float valve 11, an electromagnetic valve 12, a suction pump 13, a sodium alginate solution tank 14 and a sedimentation tank 15. The device comprises a liquid drawing pool 5, an intermediate pool 9 and a sedimentation pool 15 which are sequentially connected, a paddle stirrer 10 is positioned inside the intermediate pool, a ball float valve 11 is positioned on the inner wall of the intermediate pool and controls the opening and closing of the paddle stirrer 10 and a suction pump 13, a sodium alginate solution pool 14 is connected with the intermediate pool 9 through the suction pump 13, an electromagnetic valve 12 is positioned at the bottom of the intermediate pool 9, and the sedimentation pool 15 is connected with the intermediate pool 9 through the electromagnetic valve 12.

The operation principle of the device is as follows: the method comprises the following steps of (1) pumping municipal sewage into a feed liquid channel of an FO membrane by using the municipal sewage as inlet water through a water inlet pump, enabling a drawing liquid to enter the drawing liquid channel in a membrane module through a drawing liquid circulating pump, and enabling water to flow from the feed liquid channel to the drawing liquid channel by utilizing osmotic pressure difference on two sides of the FO membrane; the conductivity meter controls the concentrated salt pump to keep the concentration of the drawing liquid at a certain concentration all the time. The constantly-increased solution that draws flows into middle pond through the overflow weir, and after the solution in middle pond reached a take the altitude, touch the ball-cock assembly, open paddle agitator and suction pump simultaneously, go into middle liquid pond with sodium alginate solution pump and form calcium alginate gel, automatic closing after the rotatory period of paddle agitator, the solenoid valve is automatic to be opened afterwards, and solution flows into the sedimentation tank, and the separation obtains calcium alginate and supernatant.

Example 2

Municipal sewage was treated using the apparatus shown in FIG. 1.

In view of the structure of FO (one layer is an active layer for interception, and the other layer is a supporting layer for supporting, the active layer is thinner and compact, the anti-pollution capability is stronger, and the supporting layer is thicker and porous, and is easy to generate membrane pollution), and the FO membrane of the invention adopts a cellulose acetate (CTA) membrane, the FO membrane faces to municipal sewage containing various pollutants, in order to research the concentration effect of common absorption liquid on domestic sewage, the FO of the embodiment adopts 0.3M NaCl as absorption liquid (0.3M NaCl and 0.2M NaCl) during operation₂The same theoretical osmotic pressure).

The water inflow is urban sewage, and the water quality is as follows: COD: 383.24 + -15.95 mg/L, NH₄ ⁺-N: 34.87 ± 3.54mg/L, TP: 3.03 +/-0.02 mg/L. The draw solution was 0.3M NaCl, the cross-flow rate was 1L/min, the membrane orientation was AL-FS (active layer towards feed solution), and the run was 31.5 h. And measuring the effluent quality of the concentrated solution and the drawing solution.

Water quality of the concentrated solution: COD: 260.8 + -56.74 mg/L, NH₄ ⁺-N：38.07±1.76mg/L，TP：2.75±0.32mg/L

Water quality of the drawing liquid: COD: 8.67. + -. 3.5mg/L, NH₄ ⁺-N: 3.76 ± 0.4mg/L, TP: 0.02 plus or minus 0.1 mg/L; the average water flux was 4.1LMH and the flux decay rate was 0.116 LMH/h.

Therefore, the common NaCl is used as the drawing liquid, the domestic sewage can be concentrated by two times, the drawing liquid needs to be recycled through reverse osmosis, and the required energy consumption is high.

Example 3

To address the high energy consumption problem in the draw solution recovery process, the inventors tried to use 0.2M CaCl₂As draw solution, draw solution recovery is combined with chemical production. And (3) dropwise adding a sodium alginate solution in a certain proportion into the diluted drawing solution, separating the solution in a gel form to obtain a byproduct calcium alginate, and performing a test.

The water inflow is urban sewage, and the water quality is as follows: COD: 383.24 + -15.95 mg/L, NH₄ ⁺-N: 34.87 ± 3.54mg/L, TP: 3.03 +/-0.02 mg/L. . The draw solution is 0.2M CaCl₂The cross flow rate was 1L/min, the FO membrane used a cellulose acetate (CTA) membrane oriented AL-FS (active layer towards feed solution), and the run was 35.9 h.

Water quality of the concentrated solution: COD: 213.44 + -88.56 mg/L, NH₄ ⁺-N：54.06±2.16mg/L，TP：3.43±0.57mg/L；。

Water quality of the drawing liquid: COD: 10 + -3 mg/L, NH₄ ⁺-N：4.98±0.6mg/L，TP：0.03±0.1mg/L

Water quality of supernatant after calcium alginate separation: COD: 34.75 +/-7.64 mg/L, NH₄ ⁺-N：4.42±0.37mg/L，TP: 0.08 +/-0.1 mg/L; the average water flux was 2.6LMH and the flux decay rate was 0.058 LMH/h.

It can be found that when CaCl is used₂And NaCl are respectively used as drawing liquid to concentrate the domestic sewage by two times, the concentrations of pollutants in the concentrated liquid and the drawing liquid are basically equivalent, and CaCl in example 3₂For NH as an extraction liquid₄ ⁺The concentration of-N is better and the flux decay rate is lower. Probably because even 0.3M NaCl and 0.2M CaCl₂The theoretical osmotic pressure is the same, but CaCl₂A more severe internal concentration polarization occurs, resulting in a lower initial flux, so the flux decay rate is slower during concentration.

By comparison with the national standard, the calcium alginate produced in example 3 meets the national standard for food safety, calcium alginate as food additive, and the supernatant after separation from calcium alginate meets the water quality for recycling landscape environment water from municipal sewage.

Example 4

In the method of the embodiment, the inlet water is urban sewage, and the water quality is as follows: COD: 383.24 + -15.95 mg/L, NH₄ ⁺-N: 34.87 ± 3.54mg/L, TP: 3.03 +/-0.02 mg/L. The draw solution is 0.6M CaCl₂The cross-flow rate was 0.5L/min, the FO membrane used a polyamide (TFC) membrane, the membrane orientation was AL-DS (active layer towards draw solution), and the run was 22 h.

Water quality of the concentrated solution: COD: 202.34 + -67.83 mg/L, NH₄ ⁺-N：48.12±3.52mg/L，TP：2.8±0.2mg/L；。

Water quality of the drawing liquid: COD: 8 +/-2.5 mg/L, NH₄ ⁺-N：3.2±0.4mg/L，TP：0.08±0.1mg/L。

Water quality of supernatant after calcium alginate separation: COD: 28.56. + -. 4.42mg/L, NH₄ ⁺-N: 2.8 ± 0.2mg/L, TP: 0.09 plus or minus 0.2 mg/L; the average water flux was 5.8LMH and the flux decay rate was 0.184 LMH/h.

By comparison with the national standard, the calcium alginate produced in example 4 meets the national standard for food safety, calcium alginate as food additive, and the supernatant after separation from calcium alginate meets the water quality for recycling landscape environment water from municipal sewage.

It can be seen that when different concentrations of the draw solution, cross flow speeds and FO membrane materials and membrane orientations are adopted, only the membrane flux of the concentration experiment is influenced, and the water quality of the supernatant after the separation of the concentrate, the draw solution and calcium alginate is hardly influenced. Therefore, according to different experimental requirements, proper operation parameters can be selected in parameter ranges in a targeted manner.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A sewage treatment method for producing calcium alginate and synchronously recovering FO draw solution, which is characterized by comprising the following steps:

2) the continuously increased drawing liquid flows into the intermediate pool through the overflow weir in the drawing liquid pool, when a certain volume is reached, the suction pump is started to pump the sodium alginate solution into the intermediate pool, and the CaCl in the drawing liquid flowing into the intermediate pool is stirred₂Forming calcium alginate gel, stopping stirring, allowing the calcium alginate gel to flow into a sedimentation tank, and separating to obtain calcium alginate and treated water;

the method is carried out in an apparatus comprising a water inlet tank, an FO membrane module, a draw solution tank, a conductivity meter, a concentrated salt tank and a draw solution recovery system; the FO membrane component comprises a drawing liquid channel, a feeding liquid channel and an FO membrane, the FO membrane separates the drawing liquid channel from the feeding liquid channel, the inlet of the feeding liquid channel and the outlet of the feeding liquid channel are both connected with a water inlet pool, the inlet of the drawing liquid channel and the outlet of the drawing liquid channel are both connected with the drawing liquid pool, the conductivity meter is connected with a strong salt pump, the detection end of the conductivity meter is positioned in the drawing liquid pool, the strong salt tank is connected with the drawing liquid pool through the strong salt pump, and the drawing liquid pool is connected with a drawing liquid recovery system;

the drawing liquid is 0.2-0.6M CaCl₂And (3) solution.

2. The method as claimed in claim 1, wherein the absorption liquid recovery system comprises an intermediate tank, a paddle stirrer, a ball float valve, a solenoid valve, a suction pump, a sodium alginate solution tank and a sedimentation tank, wherein the absorption liquid tank, the intermediate tank and the sedimentation tank are connected in sequence, the paddle stirrer is positioned in the intermediate tank, the ball float valve is positioned on the inner wall of the intermediate tank, the sodium alginate solution tank is connected with the intermediate tank through the suction pump, the solenoid valve is positioned at the bottom of the intermediate tank, and the sedimentation tank is connected with the intermediate tank through the solenoid valve.

3. The method of claim 1, wherein a feed pump is installed on a pipe connecting the feed tank and the inlet of the feed liquid channel; and a liquid-drawing circulating pump is arranged on a pipeline connecting the liquid-drawing pool and the inlet of the liquid-drawing channel.

4. The method according to claim 1, wherein the FO membrane in the FO membrane module comprises any of an acetate membrane, a polyamide membrane, a aquaporin membrane, or a polyethersulfone resin membrane.

5. The method according to claim 1, wherein the water quality index of the municipal sewage is as follows: COD: 100-600 mg/L, NH4⁺-N：25~80 mg/L， TP：2~10 mg/L。

6. The method of claim 1, wherein the feed liquid circulation rate is 0.1-1L/min.

7. The method as claimed in claim 1, wherein the paddle agitator is controlled to be turned on for 10 to 30 minutes after the ball float valve of the intermediate tank is activated.

8. The method as claimed in claim 1, wherein the concentration of the sodium alginate solution is 2-4%.

9. Use of the method of any one of claims 1 to 8 in water treatment.