CN111847692B

CN111847692B - Pollution-free integration method and device for recycling extracellular polymers with high additional values

Info

Publication number: CN111847692B
Application number: CN202010763794.2A
Authority: CN
Inventors: 曹达啟; 韩佳霖; 田锋; 郝晓地
Original assignee: Beijing University of Civil Engineering and Architecture
Current assignee: Beijing University of Civil Engineering and Architecture
Priority date: 2020-08-01
Filing date: 2020-08-01
Publication date: 2022-05-24
Anticipated expiration: 2040-08-01
Also published as: CN111847692A

Abstract

The invention relates to a pollution-free integrated method and device for recycling extracellular polymeric substances with high additional values. The method comprises the following steps: step S1: conveying the excess sludge into a cation exchange resin reactor, and extracting extracellular polymers in the excess sludge; step S2: intercepting microbial cells and residues thereof in the residual sludge through a microfiltration membrane component to obtain filtrate containing extracellular polymers; step S3: the multi-stage membrane component is used for filtering treatment, so that high molecular weight extracellular polymeric substances and low molecular weight extracellular polymeric substances can be concentrated and purified in sequence, and then extracellular polymeric substances in different molecular weight ranges can be separated; step S4: and (4) conveying the filtrate generated by filtering in the step S3 to a forward osmosis membrane assembly using the fertilizer as a driving agent for filtering to obtain a drawing liquid containing the fertilizer, wherein the drawing liquid can be directly used for water and fertilizer integrated irrigation or soilless culture. The invention has the characteristics of no damage to cells and no pollution.

Description

Pollution-free integration method and device for recycling extracellular polymers with high additional values

Technical Field

The invention relates to a pollution-free integrated method and device for recycling extracellular polymeric substances with high added values.

Background

Resource utilization has become an important direction and inevitable trend of future sewage treatment technology. Currently, the most common biological wastewater treatment technology is the activated sludge process, but this is followed by a large amount of excess sludge that is difficult to dispose of. Taking China as an example, according to data reported by the institute of E20 at the end of 2018, the yield of sludge (water content of 80%) in 2017 is as high as 4328 ten thousand tons/year. According to prediction, the annual output of sludge in China reaches 5075 million tons by 2020, so that the sludge needs to be stabilized, harmlessly treated and recycled.

Extracellular Polymeric Substances (EPS) are important components of activated sludge, accounting for about 10-40% of the dry weight of the sludge, usually from microorganisms, such as cell autolysis, cell secretion and cell surface shedding, and mainly comprise polysaccharides, proteins, nucleic acids, lipids, metal ions, etc. The substances form a compact and high-density net structure through the actions of electrostatic acting force, hydrogen bond combination, ion attraction, biochemistry and the like, can be used as a protective layer of microorganisms to resist the invasion of external heavy metals, toxic compounds and the like, have different complex structures due to different EPS combination modes, can be used as a water retention agent, a heavy metal adsorbent, a fireproof material, a biological flocculant and the like, and have extremely high utilization value.

In the treatment and disposal process of the excess sludge, the EPS percentage is also a key factor of sludge dewatering reduction, and the concentration and dewatering performance of the excess sludge after the EPS is removed can be greatly enhanced. Under the environment-friendly concept, the EPS recovery resource is taken as the primary target, so that the high-added-value utilization of resources can be realized, the problem of huge sludge amount can be solved from the source, and the sludge dewatering property is improved to be beneficial to subsequent sludge treatment.

However, recovery of EPS is facing two significant challenges. On one hand, regarding the recovery rate, the traditional EPS extraction method such as acid and alkali extraction method or organic solvent extraction method not only consumes a large amount of chemical agents and increases the extraction cost, but also may damage the cell structure and bring about secondary pollution. Although the cation exchange resin method (abbreviated as CER) has minimal damage to cells and can effectively adsorb heavy metal ions, the CER also has the problem of low treatment flux due to the limitations that the cation exchange resin needs to be frequently regenerated and the extraction effect of nonionic (neutral) polymers is not good. And the surfactant can increase the transfer of non-dissolved substances to dissolved substances and separate EPS in the sludge from cell bodies. Therefore, the surfactant and the like are used as pretreatment to solve the limitation of the CER method and improve the extraction rate of EPS in the sludge under the condition of zero pollution.

On the other hand, for recovery, the aerobic granular sludge, the activated sludge or the sludge generated in any stage of the sewage treatment process is theoretically a mixed microorganism system, and the extraction process also transfers most of the small molecular pollutants such as heavy metal ions and antibiotics from the residual sludge solid phase to EPS, which is ignored by all previous research institutes at home and abroad. The EPS mixture is not selectively separated after the traditional low-efficiency extraction, so that the recovered product contains a large amount of impurities, a specific high-added-value product is difficult to form, and the potential development and application are difficult to meet. In the field of bioengineering, multi-stage membrane (microfiltration and ultrafiltration) separation technology has been widely used in the research of separation, concentration and purification of polysaccharide and protein.

At present, the traditional method is difficult to improve the extraction rate of EPS and is easy to cause secondary pollution. The existing research only indiscriminately extracts EPS in sludge, and the extract contains a large amount of impurities and is difficult to apply. The residual sludge is generated in a municipal sewage mixed type microorganism treatment system, most of micromolecular pollutants such as heavy metal ions, antibiotics and the like can be transferred to EPS from the residual sludge solid phase in the EPS extraction process, so far, no research on toxic and harmful pollutant content detection of the recovered EPS is seen at home and abroad, and the removal of the toxic and harmful pollutants from the EPS is considered to be unhealthy. Meanwhile, the waste water generated in the EPS recovery process is used as a secondary pollution source, which is also a prominent problem to be solved.

Disclosure of Invention

In view of the above problems in the prior art, it is a primary object of the present invention to provide a non-pollution integration method and apparatus for recycling extracellular polymeric substances with high added value.

The technical scheme of the invention is as follows:

a pollution-free integrated method for recycling high value-added extracellular polymeric substances comprises the following steps:

step S1: conveying the residual sludge into a cation exchange resin reactor, and optimally extracting extracellular polymers by a surfactant reinforced cation exchange resin method so as to dissolve a large amount of extracellular polymers in water;

step S2: the sludge containing a large amount of extracellular polymeric substances in a dissolved state obtained in the step S1 enters a microfiltration membrane module for separation treatment, and suspended matters in the sludge are trapped and discharged to obtain extracellular polymeric substance filtrate containing the dissolved state;

step S3: conveying the extracellular polymer solution obtained in the step S2 to a multistage membrane module for filtration treatment, and concentrating and purifying a high molecular weight extracellular polymer and a low molecular weight extracellular polymer in sequence when the multistage membrane module adopts an ultrafiltration/ultrafiltration integrated membrane module, thereby separating extracellular polymers in different molecular weight ranges;

Step S4: and (4) conveying the filtrate generated by filtering in the step S3 to a forward osmosis membrane component using a fertilizer as a driving agent for filtering, intercepting and removing toxic and harmful pollutants in the filtrate, and obtaining a draw solution containing the fertilizer, wherein the draw solution can be directly used for water-fertilizer integrated irrigation or soilless culture.

In step S3, the multi-stage membrane module is a microfiltration/ultrafiltration integrated membrane module, and when the multi-stage membrane module adopts a microfiltration/ultrafiltration integrated membrane module, high-valence metal ions are added to the extracellular polymer solution to form a high-valence metal ion aqueous solution environment, so that the polysaccharide is converted from a dissolved state to a colloidal state, and the polysaccharide and the protein in the extracellular polymer solution are separated and recovered.

The high-valence metal ions are calcium ions, magnesium ions, iron ions and aluminum ions.

In step S4, the filtrate obtained from the filtration in step S3 is sent to a forward osmosis membrane module using fertilizer as a driving agent for filtration, and toxic and harmful pollutants in the filtrate are intercepted and removed, wherein the fertilizer is water-soluble fertilizer, and the toxic and harmful pollutants include heavy metal ions and antibiotics.

The substance in the extracellular polymeric substance comprises polysaccharide and protein.

The device comprises a cation exchange resin reactor, a microfiltration membrane component, a multistage membrane component and a forward osmosis membrane component, wherein the microfiltration membrane component is respectively communicated with the cation exchange resin reactor and the multistage membrane component, and the multistage membrane component is also connected with the forward osmosis membrane component.

The multistage membrane component is an ultrafiltration/ultrafiltration integrated membrane component, and the molecular weight cut-off of the ultrafiltration/ultrafiltration integrated membrane component is 1-500 kDa.

The ultrafiltration membrane in the ultrafiltration/ultrafiltration integrated membrane component is any one of a flat membrane or a hollow fiber membrane, and the filtration mode of the ultrafiltration membrane in the ultrafiltration/ultrafiltration integrated membrane component is a dead-end mode or a scavenging mode.

The multistage membrane component is a microfiltration/ultrafiltration integrated membrane component, wherein:

the microfiltration membrane in the microfiltration/ultrafiltration integrated membrane component is any one of a flat membrane or a hollow fiber membrane, and the filtration mode of the microfiltration membrane in the microfiltration/ultrafiltration integrated membrane component is a dead-end mode or a scavenging flow mode;

the ultrafiltration membrane in the microfiltration/ultrafiltration integrated membrane component is any one of a flat membrane or a hollow fiber membrane, and the filtration mode of the ultrafiltration membrane in the microfiltration/ultrafiltration integrated membrane component is a dead-end mode or a scavenging mode.

The microfiltration membrane in the microfiltration membrane component is a flat membrane or a hollow fiber membrane, the filtration mode of the microfiltration membrane in the microfiltration membrane component is a dead-end mode or a scavenging mode, and the membrane aperture of the microfiltration membrane in the microfiltration membrane component is 0.1-8 mu m.

The invention has the following advantages and beneficial effects:

1. the surfactant-reinforced cation exchange resin method optimizes the EPS extraction conditions and enhances the EPS extraction rate;

2. optimizing separation conditions by a multi-stage membrane, efficiently removing suspended matters such as cell bodies, heavy metal ions, antibiotics and other small molecular organic pollutants, and separating and purifying polysaccharide, protein and typical EPS with different molecular weights;

3. the forward osmosis purification and recovery of the EPS process waste water by using the water-soluble fertilizer as the driving agent can be directly used for water and fertilizer integrated irrigation or soilless culture, thereby realizing the purpose of pollution-free recovery.

Drawings

Fig. 1 is a process flow chart of an ultrafiltration/ultrafiltration integrated membrane module adopted in a pollution-free integrated method for recycling high value-added extracellular polymeric substances provided by an embodiment of the present invention.

Fig. 2 is a process flow chart of the microfiltration/ultrafiltration integrated membrane module adopted in the pollution-free integrated method for recycling the high value-added extracellular polymeric substances provided by the embodiment of the invention.

Fig. 3 is a schematic structural diagram of an ultrafiltration/ultrafiltration integrated membrane module as a multistage membrane module in the pollution-free integrated device for recycling the extracellular polymeric substances with high added values provided by the embodiment of the present invention.

Fig. 4 is a schematic structural diagram of a microfiltration/ultrafiltration integrated membrane module as a multistage membrane module in a pollution-free integrated device for recycling high value-added extracellular polymeric substances, provided by an embodiment of the present invention.

Detailed Description

The invention will be further described with reference to the drawings and specific examples.

As shown in fig. 1 to 2: the pollution-free integration method for recycling the extracellular polymeric substances with high additional values provided by the embodiment of the invention comprises the following steps:

step S1: conveying the residual sludge into a cation exchange resin reactor 1, and optimally extracting extracellular polymers by a surfactant reinforced cation exchange resin method so as to dissolve a large amount of extracellular polymers in water;

step S2: the sludge containing a large amount of extracellular polymeric substances in a dissolved state obtained in the step S1 enters a microfiltration membrane module 2 for separation treatment, and the separated suspended matters are discharged to obtain extracellular polymeric substance filtrate containing the dissolved state;

step S3: conveying the extracellular polymer solution obtained in the step S2 to a multi-stage membrane module for filtration treatment, and concentrating and purifying a high molecular weight extracellular polymer and a low molecular weight extracellular polymer in sequence when the multi-stage membrane module adopts an ultrafiltration/ultrafiltration integrated membrane module 3, thereby separating extracellular polymers in different molecular weight ranges;

Step S4: and (4) conveying the filtrate generated by filtering in the step S3 to a forward osmosis membrane component 4 which takes the fertilizer as a driving agent for filtering, intercepting and removing toxic and harmful pollutants in the filtrate, and obtaining a drawing liquid containing the fertilizer, wherein the drawing liquid can be directly used for water-fertilizer integrated irrigation or soilless culture.

The suspension includes a cell body and its remains.

The substance in the extracellular polymeric substance comprises high molecular substances such as polysaccharide, protein, nucleic acid, lipid and the like.

In step S3, the multi-stage membrane module is a microfiltration/ultrafiltration integrated membrane module 5, and when the multi-stage membrane module adopts the microfiltration/ultrafiltration integrated membrane module 5, calcium ions are added to the extracellular polymeric substance solution to form a calcium ion aqueous solution environment, the polysaccharide is converted from a dissolved state to a colloidal state, and then the polysaccharide and the protein in the extracellular polymeric substance solution are separated and recovered, that is, the polysaccharide and the protein are separated, concentrated and purified under the action of the calcium ions.

The toxic and harmful pollutants comprise heavy metal ions, antibiotics and the like.

In step S4, the filtrate obtained from the filtration in step S3 is sent to a forward osmosis membrane module using fertilizer as a driving agent for filtration, wherein the fertilizer is water-soluble fertilizer.

As shown in fig. 3 to 4, a pollution-free integrated device for recycling high value-added extracellular polymers is further provided for an embodiment of the present invention, and the device includes a cation exchange resin reactor 1, a microfiltration membrane module 2, a multi-stage membrane module, and a forward osmosis membrane module 4, wherein the microfiltration membrane module 2 is respectively communicated with the cation exchange resin reactor 1 and the multi-stage membrane module, and the multi-stage membrane module is further connected with the forward osmosis membrane module 4.

The multistage membrane component is an ultrafiltration/ultrafiltration integrated membrane component 3, and the molecular weight cutoff of an ultrafiltration membrane in the ultrafiltration/ultrafiltration integrated membrane component 3 is 1-500 kDa.

The ultrafiltration membrane in the ultrafiltration/ultrafiltration integrated membrane forming component 3 is any one of a flat membrane or a hollow fiber membrane, and the filtration mode of the ultrafiltration membrane in the ultrafiltration/ultrafiltration integrated membrane forming component 3 is a dead-end mode or a scavenging mode.

The multi-stage membrane component is a microfiltration/ultrafiltration integrated membrane component 5, wherein: the microfiltration membrane in the microfiltration/ultrafiltration integrated membrane component 5 is any one of a flat membrane or a hollow fiber membrane, and the filtration mode of the microfiltration membrane in the microfiltration/ultrafiltration integrated membrane component 5 is a dead-end mode or a scavenging mode;

the ultrafiltration membrane in the microfiltration/ultrafiltration integrated membrane component 5 is any one of a flat membrane or a hollow fiber membrane, and the filtration mode of the ultrafiltration membrane in the microfiltration/ultrafiltration integrated membrane component 5 is a dead-end mode or a scavenging mode.

The microfiltration membrane in the microfiltration membrane component 2 is a flat membrane or a hollow fiber membrane, the filtration mode of the microfiltration membrane in the microfiltration membrane component 2 is a dead-end mode or a scavenging mode, and the membrane aperture of the microfiltration membrane in the microfiltration membrane component 2 is 0.1-8 mu m.

The invention provides scientific design of membrane separation key parameters according to actual conditions such as specific cell types, biomacromolecule types, molecular weight and molecular weight distribution, and the like, determines an optimal multistage membrane (microfiltration and ultrafiltration) combination mode, and simultaneously realizes synchronous removal of heavy metal ions, antibiotics and other small molecules and efficient recovery of target EPS.

Meanwhile, the Forward Osmosis (FO) membrane separation technology which takes water-soluble fertilizer as a drawing agent is adopted to purify the wastewater generated in the EPS recovery process by a multistage membrane (microfiltration and ultrafiltration) combined process, and the drawing liquid is treated by the Forward Osmosis (FO) membrane separation technology to be directly used for agriculture, so that a pollution-free recovery integrated technology is really realized.

In step S1, important attention needs to be paid to the regeneration and reuse of the cation exchange resin and the selection of the biodegradable surfactant, and the degree of damage of the cells is analyzed and observed. Meanwhile, the content of high molecular substances such as soluble polysaccharide, protein and the like in EPS, the characteristic properties such as molecular weight, distribution, characteristic functional groups, viscoelasticity, hydrophilic and hydrophobic properties, particle size distribution, charge property and the like, and the aggregation state of the EPS on a micro scale such as the size, the dispersion uniformity of nanoscale phases and the like are analyzed, so that the high addition value of the high molecular substances is definitely extracted. Meanwhile, the interaction between EPS and toxic and harmful pollutants (heavy metal ions and antibiotics) and the microscopic action mechanism between the EPS and the toxic and harmful pollutants are clear, and further condition parameters are optimized to enable the EPS and the toxic and harmful pollutants to be mutually desorbed and free in water.

In step S2, the aperture of the microfiltration membrane is 0.1 to 8 μm, and the microfiltration membrane is mainly used for trapping suspended matters such as cell bodies and residues thereof to obtain a relatively pure EPS solution. Here, the important focus is: the EPS recovery rate and the retention rate of suspended particles such as cell bodies are used as indexes, and the type selection (membrane aperture) of the microfiltration membrane and environmental operating conditions such as pH, salt concentration, filtration pressure and other optimization parameters are adopted; the compressible deformed cell bodies accumulated on the surface of the micro-filtration membrane form the characteristics of a filter cake layer and the filtration resistance and the compression characteristics of a filter cake; the Zeta potential of the cell body, the viscosity of the EPS solution and the like have influence on the filtration impedance and the compression deformation of the cell body, and further a theoretical analytical formula of the filtration speed on the viscosity of the EPS solution, the compression coefficient of a filter cake and the filtration pressure is constructed to optimize the recovery method and the device design.

The EPS solution flows out of the microfiltration membrane component 2 and enters an ultrafiltration/ultrafiltration membrane component 3, and the cutoff molecular weight of the ultrafiltration membrane is 1-500 kDa. And (3) concentrating and purifying the high molecular weight EPS and the low molecular weight EPS in sequence by virtue of a multi-stage ultrafiltration membrane, and separating typical EPS with different molecular weight ranges. It should be noted that the ultrafiltration/ultrafiltration membrane module 3 can be replaced by a microfiltration/ultrafiltration membrane module 5 with the help of a specific aqueous environment (such as Ca) ²⁺) The physical phase state or aggregation state of the main components in the EPS is changed, so that substances with different characteristics (such as polysaccharide and protein) are separated from each other, the substances with specific structures in the EPS are intercepted or filtered through membrane filtration, the function of recovering the substances is enhanced, the concentration and purification of the polysaccharide and the typical EPS are sequentially obtained, and the quantitative relation between the molecular weight of the EPS and the molecular weight interception is established. Based on specific environmental conditions (such as pH, salt content and the like) and EPS characteristics, the membrane selection, the recovery rate, the concentration rate (EPS filter cake dehydration performance) and a membrane pollution mechanism and control strategy are clarified, and the macro morphology of the surface, the section morphology and the porous structure distribution condition of the concentrated and recovered EPS filter cake is analyzed. And (4) carrying out heavy point detection and evaluation on the content level of micromolecular pollutants such as heavy metal ions, antibiotics and the like in the recovered EPS to represent the EPS purification rate.

The target EPS is intercepted by the membrane, concentrated and recycled, and the possible micromolecules such as heavy metal ions, antibiotics and the like flow out along with the filtrate, and the wastewater containing the micromolecules such as the heavy metal ions, the antibiotics and the like generated in the recycling process of the multistage membrane module is filtered by the forward osmosis membrane module 4 uniformly. This patent uses water-soluble fertilizer as the driver, can overcome the selection of driver and reuse of reclaimed water problem simultaneously, makes the product water of drawing need not regeneration, recovery, but directly is used for water and fertilizer integration irrigation or soilless culture. The process focuses on: the rejection rate of heavy metal ions, antibiotics and other small molecular pollutants and the reverse permeability of a driving agent solute; the fertilizer is used as a driving agent, the optimal proportion of the fertilizer is determined according to the flux difference of forward osmosis water, and the quality of drawn product water is checked to meet the Standard of Water quality for Farmland irrigation (GB5084-2005), so that the fertilizer drawing solution can be used for agricultural irrigation or soilless culture. The whole process does not produce secondary pollution.

In addition, a forward osmosis separation mechanism research for simultaneously removing heavy metal ions, antibiotics and other small molecules is not seen, and the influence of the size, the charge property, the form distribution, the Stokes hydraulic radius, the valence state and the like of the antibiotic molecules on membrane pollution and water flux and the interaction between the antibiotic molecules and the forward osmosis membrane are analyzed, so that a trapping separation mechanism for synchronously removing the heavy metal ions, the antibiotics and other small molecules under the influence of environmental conditions such as pH, salt concentration and the like and the formation of membrane pollution are disclosed. The method is innovative and is also expected to be patented.

The pollution-free integration method for recovering the extracellular polymeric substances with high additional values, provided by the embodiment of the invention, has the following characteristics:

1) cell damage, EPS increment extraction: among the EPS extraction methods, the cation exchange resin method has the advantages of minimal damage to cells, no secondary pollution, enrichment and separation performance on heavy metal ions, and becomes the best choice for extracting EPS from sludge; meanwhile, the EPS extraction rate is enhanced by utilizing a surfactant-enhanced cation exchange resin method and optimizing extraction conditions such as the type and concentration of a surfactant, the addition amount of resin and the like.

2) Zero pollution, typical EPS recovery: the existing research does not selectively extract EPS in the sludge, and the content of toxic and harmful pollutants in the sludge is less concerned. The method is based on a microfiltration/ultrafiltration combined process, regulates the aggregation state of polysaccharide by virtue of calcium ions, and efficiently recovers the polysaccharide, protein and typical EPS (expandable polystyrene) with different molecular weights through multi-stage membrane filtration; meanwhile, in the membrane separation process, impurities of heavy metal ions, antibiotics and other small molecular pollutants are filtered out along with the filtrate, and the recovered typical EPS is purified.

3) Forward osmosis purification, process integration: the filtrate produced in the EPS recovery process by the microfiltration/ultrafiltration combined process (namely, an ultrafiltration/ultrafiltration membrane component or a microfiltration/ultrafiltration membrane component is adopted) is purified by adopting a fertilizer-driven forward osmosis technology, toxic and harmful pollutants are efficiently intercepted and removed, and product water is drawn to meet the Farmland irrigation Water quality Standard and is directly used for water and fertilizer integrated irrigation or soilless culture, so that the invention is a set of pollution-free integrated scheme for high value-added EPS recovery.

The pollution-free integrated method for recovering the extracellular polymeric substances with high added values provided by the embodiment of the patent can cover the recovery of all typical EPS, such as extracellular biomacromolecules secreted by polysaccharides, proteins, nucleic acids, lipids and the like.

The pollution-free integration method for recycling the extracellular polymeric substances with high added values, which is provided by the embodiment of the patent, improves the extraction rate of the sludge EPS by adding the surfactant to strengthen the cation exchange resin, and is also suitable for extracting extracellular polymeric substances in bioengineering and strengthening the extraction rate.

According to the pollution-free integration method for recycling the extracellular polymer with the high added value, provided by the embodiment of the invention, the forward osmosis technology which takes the fertilizer as the driving agent is adopted to efficiently remove the micromolecule technologies such as heavy metal ions, antibiotics and the like generated in the recycling process, so that the pollution-free integration method not only can be applied to the treatment and purification of wastewater generated in the process of recycling the high added value substances from sludge, but also can be applied to the sludge reduction purification or the wastewater generated in other fields such as medicines, foods, electrons and the like, and the method for purifying the wastewater by adopting the embodiment of the invention belongs to the protection range of the invention.

Finally, it should be noted that: the above-mentioned embodiments are only used for illustrating the technical solution of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A pollution-free integrated method for recycling high value-added extracellular polymeric substances is characterized by comprising the following steps:

step S3: conveying the extracellular polymeric substance solution obtained in the step S2 to a multistage membrane module for filtration treatment, and concentrating and purifying high molecular weight extracellular polymeric substances and low molecular weight extracellular polymeric substances in sequence when the multistage membrane module adopts an ultrafiltration/ultrafiltration integrated membrane module, thereby separating extracellular polymeric substances in different molecular weight ranges;

Step S4: and (4) conveying the filtrate generated by filtering in the step S3 to a forward osmosis membrane component using a fertilizer as a driving agent for filtering, intercepting and removing toxic and harmful pollutants in the filtrate, and obtaining a drawing solution containing the fertilizer, wherein the drawing solution can be directly used for water-fertilizer integrated irrigation or soilless culture.

2. The pollution-free integrated method for recycling high value-added extracellular polymeric substances according to claim 1, wherein the multi-stage membrane module in step S3 is a microfiltration/ultrafiltration integrated membrane module, and when the multi-stage membrane module adopts the microfiltration/ultrafiltration integrated membrane module, high-valence metal ions are added to the extracellular polymeric substance solution to form a high-valence metal ion aqueous solution environment, so that the polysaccharide is converted from a dissolved state to a colloidal state, and the polysaccharide and the protein in the extracellular polymeric substance solution are separated and recycled.

3. The pollution-free integrated method for recycling high value-added extracellular polymeric substances according to claim 2, wherein the high-valence metal ions are calcium ions, magnesium ions, iron ions and aluminum ions.

4. The integrated contaminant-free method for recycling high value-added extracellular polymeric substances according to claim 1, wherein in step S4, the filtrate obtained from the filtration in step S3 is sent to a forward osmosis membrane module using fertilizer as a driving agent for filtration, and toxic and harmful contaminants in the filtrate are retained and removed, wherein the fertilizer is water-soluble fertilizer, and the toxic and harmful contaminants include heavy metal ions and antibiotics.

5. The pollution-free integrated method for recycling high value-added extracellular polymeric substances according to claim 1, wherein the substances in the extracellular polymeric substances include polysaccharides and proteins.

6. The utility model provides a pollution-free integrated device of high added value extracellular polymeric substance recovery which characterized in that: the device comprises a cation exchange resin reactor, a microfiltration membrane component, a multi-stage membrane component and a forward osmosis membrane component, wherein the microfiltration membrane component is respectively communicated with the cation exchange resin reactor and the multi-stage membrane component, the multi-stage membrane component is also connected with the forward osmosis membrane component, and the multi-stage membrane component is an ultrafiltration/ultrafiltration integrated membrane component or a microfiltration/ultrafiltration integrated membrane component; conveying the residual sludge into the cation exchange resin reactor, and optimally extracting extracellular polymers by a surfactant-reinforced cation exchange resin method so as to dissolve a large amount of extracellular polymers in water; the sludge containing a large amount of extracellular polymeric substances in a dissolved state enters the microfiltration membrane component for separation treatment, and suspended matters in the sludge are intercepted and discharged to obtain extracellular polymeric substance filtrate containing the dissolved state; then conveying the extracellular polymeric substance solution into the multistage membrane component for filtration treatment, and when the multistage membrane component is an ultrafiltration/ultrafiltration integrated membrane component, concentrating and purifying the high molecular weight extracellular polymeric substance and the low molecular weight extracellular polymeric substance in sequence so as to separate the extracellular polymeric substances in different molecular weight ranges; and (3) conveying the filtrate generated by filtering to a forward osmosis membrane assembly which takes fertilizer as a driving agent for filtering, and intercepting and removing toxic and harmful pollutants in the filtrate.

7. The pollution-free integrated device for recycling the extracellular polymeric substances with high added values according to claim 6, wherein the multi-stage membrane module is an ultrafiltration/ultrafiltration integrated membrane module, and the molecular weight cutoff of an ultrafiltration membrane in the ultrafiltration/ultrafiltration integrated membrane module is 1-500 kDa.

8. The pollution-free integrated device for recycling high value-added extracellular polymeric substances according to claim 7, wherein the ultrafiltration membrane in the ultrafiltration/ultrafiltration integrated membrane module is a flat membrane or a hollow fiber membrane, and the filtration mode of the ultrafiltration membrane in the ultrafiltration/ultrafiltration integrated membrane module is a dead-end mode or a scavenging mode.

9. The integrated device of claim 6, wherein the multi-stage membrane module is an integrated microfiltration/ultrafiltration membrane module, wherein:

10. The pollution-free integrated device for recycling high value-added extracellular polymeric substances according to any one of claims 6 to 9, wherein the microfiltration membrane in the microfiltration membrane module is a flat membrane or a hollow fiber membrane, the filtration mode of the microfiltration membrane in the microfiltration membrane module is a dead-end mode or a cross-flow mode, and the membrane pore size of the microfiltration membrane in the microfiltration membrane module is 0.1 to 8 μm.