Method and system for completely recycling water for fermentation of polyhydroxyalkanoate
By treating the halophilic bacteria fermentation broth with nanofiltration and reverse osmosis membranes, the problem of high-salt wastewater treatment was solved, and the full reuse of water used for polyhydroxyalkanoate fermentation was achieved, reducing production costs and energy consumption and improving production efficiency.
Patent Information
- Application Number
- CN202410584436.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-11
- Publication Date
- 2025-11-11
AI Technical Summary
The high-salt wastewater produced by halophilic bacteria fermentation is costly to treat, and traditional methods such as evaporation waste water resources and increase energy consumption, which restricts the production cost of polyhydroxyalkanoates.
Nanofiltration and reverse osmosis membranes were used to treat the fermentation broth of halophilic bacteria, resulting in high-COD nanofiltration concentrate, high-salt-concentration retentate, and low-salt reverse osmosis permeate, respectively, achieving full water reuse and reducing the use of fresh water and raw material salt.
This technology enables the complete reuse of water used in the fermentation of polyhydroxyalkanoates, reducing production costs, wastewater treatment expenses and energy consumption, and improving production efficiency.
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Figure CN120922979A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of bio-fermentation technology, and in particular to a method and system for the complete reuse of water used in the fermentation of polyhydroxyalkanoates. Background Technology
[0002] Polyhydroxyalkanoates (PHAs) are biosynthesized high-molecular-weight polyester materials, synthesized by microorganisms under conditions of nutrient limitation and carbon source surplus. These are storage particles that act as both carbon and energy sources. The synthesis of this linear polymer involves the condensation polymerization of various types of hydroxyalkanoate monomers through enzymatic catalysis within cells. Due to their diverse structures, PHAs exhibit a wide range of properties, making them promising for various applications and gradually forming a PHA industry value chain. Because of their material properties, which are very similar to traditional plastics, they can potentially replace traditional plastics in many applications. Furthermore, PHAs possess unparalleled biodegradability and biocompatibility compared to traditional plastics, leading them to be considered "environmentally friendly plastics" that can address the increasingly serious problem of environmental pollution. However, the high production cost has consistently constrained the large-scale application and development of PHAs.
[0003] In recent years, researchers have focused on breeding high-quality, high-yield halophilic bacteria for PHA production. While this reduces production costs to some extent, halophilic bacteria require a high-concentration salt environment for fermentation. The use of large amounts of inorganic salts also increases production costs and downstream fermentation water treatment costs. If fermentation water can be recycled and reused, production costs can be further reduced, leading to increased yield and efficiency.
[0004] However, the high-salt wastewater produced by halophilic bacteria through PHA fermentation is a wastewater system with a mixture of COD and high salt content. The treatment cost of this type of wastewater is high. In particular, when treating high-salt wastewater, the only way to enrich the high salt content is usually by evaporation. As a result, water is wasted due to evaporation, and high treatment costs are incurred. It also increases energy consumption, which is both water-intensive and energy-intensive. Summary of the Invention
[0005] To address the problems existing in the prior art, this invention provides a method and system for the complete reuse of water used in the fermentation of polyhydroxyalkanoates.
[0006] In a first aspect, the present invention provides a method for the complete reuse of water used in the fermentation of polyhydroxyalkanoates, comprising: treating the water used in the fermentation of polyhydroxyalkanoates through a nanofiltration membrane to obtain a nanofiltration concentrate with increased COD content and the remaining saline solution; and then treating the saline solution through a reverse osmosis membrane to obtain reverse osmosis permeate and a retentate with increased salt concentration.
[0007] The nanofiltration membrane has a retention rate of over 95% for organic matter and a permeability of over 98% for monovalent and divalent salt ions.
[0008] The polyhydroxyalkanoate fermentation water described in this invention is the liquid obtained by centrifuging the fermentation broth after biological fermentation with halophilic bacteria. Further, the halophilic bacteria are *Haloxylon ammodendron* or its derivatives, or a combination thereof.
[0009] Halophiles are microorganisms that can grow in high-salt environments and have significant advantages and potential in the biosynthesis of polyhydroxyalkanoates (PHAs). Halophiles can achieve long-term, continuous, open fermentation processes, which improves production efficiency and reduces energy consumption. However, the treatment of high-salt wastewater also presents a challenge for the production of PHAs using halophiles.
[0010] This invention involves centrifuging the fermentation broth to separate the bacterial cells, preparing for subsequent PHA extraction and purification, while simultaneously yielding high-salt wastewater (i.e., water for polyhydroxyalkanoate fermentation). Centrifugation is a mechanical and physical process that does not introduce other substances, thus avoiding the introduction of contaminating bacteria and other unknown substances.
[0011] This invention employs a specific nanofiltration membrane to treat high-salinity wastewater, separating organic matter (COD) from salt. The resulting saline solution is then treated with a reverse osmosis membrane to concentrate the salt, yielding reverse osmosis permeate and a retentate with increased salt concentration, both of which can be reused. Since high-salinity wastewater contains a large amount of organic matter and suspended solids, the nanofiltration membrane selected in this invention must not only separate organic matter from salt but also possess good antifouling properties.
[0012] Specifically, in some embodiments of the present invention, the COD content in the nanofiltration concentrate is more than twice that in the polyhydroxyalkanoate fermentation water. The volume of the nanofiltration concentrate is about one-third of the original wastewater. Due to the significant increase in organic matter content, it has excellent biodegradability, but the salinity only increases slightly. Therefore, it can be used as a carbon source to supplement the carbon source of the biological system and improve nitrogen removal efficiency.
[0013] According to the method for complete reuse of polyhydroxyalkanoate fermentation water provided by the present invention, the salt ion rejection rate of the reverse osmosis membrane is not less than 98%.
[0014] Furthermore, the pressure applied during the operation of the reverse osmosis membrane is 2.0-5.2 MPa.
[0015] The remaining saline solution, approximately two-thirds the volume of the original wastewater, is further treated by the aforementioned reverse osmosis membrane, resulting in two parts of water. One part is a retentate with increased salt concentration, approximately two-ninths the volume of the original wastewater. Since the salinity meets reuse requirements, this retentate with increased salt concentration is reused in the production fermentation process of polyhydroxyalkanoates. This reduces the use of fresh water and raw material salt. It is understood that the high-salt, high-alkaline growth environment required by halophilic bacteria is primarily to ensure the osmotic pressure necessary for microbial growth; therefore, only the concentration of the reused brine needs to be maintained, without controlling the specific elements in the reused water. To obtain better fermentation results, additional nutrients such as glucose and urea can be added during reuse.
[0016] The other part of the water is reverse osmosis permeate, which is about four-ninths of the total volume of the original wastewater. This part of the water contains very few pollutants and has a low salt concentration. In some embodiments of the present invention, the salt concentration of the reverse osmosis permeate is less than 1200 mg / L, and in preferred embodiments it does not exceed 500 mg / L. It can be used as greywater for reuse.
[0017] Greywater, also known as reclaimed water or recycled water, refers to non-potable water that has been treated to meet certain water quality standards. The utilization of greywater is an important way to achieve sustainable water resource utilization and helps alleviate water shortages. Greywater can be specifically used for urban miscellaneous uses, industrial water use, and agricultural irrigation. To reduce transportation costs, factories can implement secondary utilization on-site, such as in cooling, washing, and dissolving processes.
[0018] In summary, the method of the present invention treats the water used for polyhydroxyalkanoate fermentation into three parts of water, which can be used separately, thus realizing the complete reuse of water used for polyhydroxyalkanoate fermentation.
[0019] Understandably, to prevent chemicals introduced from the membrane system from affecting the fermentation process of the recycled water, nanofiltration and reverse osmosis membranes employ methods such as water washing and top feeding during operation to ensure membrane flux, without adding scale inhibitors, reducing agents, bactericides, or other chemicals. Furthermore, after prolonged operation, when chemical cleaning (CIP cleaning) is performed, it is conducted separately. After chemical cleaning, a rinsing operation is performed to remove any chemical residues.
[0020] Secondly, the present invention also provides a polyhydroxyalkanoate fermentation water recycling system, including a nanofiltration unit and a reverse osmosis unit;
[0021] The nanofiltration unit is used to treat the polyhydroxyalkanoate fermentation water through a nanofiltration membrane to obtain a nanofiltration concentrate with increased COD content, as well as the remaining saline solution.
[0022] The reverse osmosis unit is used to treat the saline solution through a reverse osmosis membrane to obtain reverse osmosis permeate and a retentate with increased salt concentration.
[0023] The nanofiltration membrane has a retention rate of over 95% for organic matter and a permeability of over 98% for monovalent and divalent salt ions.
[0024] The polyhydroxyalkanoate fermentation water recycling system provided by this invention is compatible with the above-mentioned polyhydroxyalkanoate fermentation water recycling method, which can realize the complete recycling of polyhydroxyalkanoate fermentation water, solve the problem of high-salt wastewater treatment, and reduce production costs.
[0025] This invention provides a method and system for the complete reuse of water used in polyhydroxyalkanoate (PHA) fermentation. By using a specific nanofiltration membrane to treat high-salt wastewater, organic matter (COD) is separated from salt. The saline solution obtained after nanofiltration is then treated by a reverse osmosis membrane to concentrate the salt, thereby obtaining reverse osmosis permeate and a retentate with increased salt concentration. The three portions of water obtained can be reused in different scenarios, realizing the complete reuse of water used in PHA fermentation, reducing production costs, and showing broad application prospects. Attached Figure Description
[0026] Figure 1 This is a process flow diagram of the complete reuse of water for polyhydroxyalkanoate fermentation in an embodiment of the present invention. Detailed Implementation
[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.
[0028] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.
[0029] Example 1: PHA fermentation and high-salt wastewater treatment
[0030] Halophilic bacteria used for producing polyhydroxyalkanoates (PHA) are grown in a high-salt, high-alkaline environment with a salinity of 2.4% and a pH of 8.5. The microorganisms are supplied with the necessary environment and elements by adding substances such as glucose, alkali, and urea. After a certain growth period and reaching the desired yield, the material (containing PHA-containing bacterial cells) and high-salt wastewater are separated by centrifugation, producing high-salt wastewater with an average salinity of 1.3%. Each batch of fermentation broth has a volume of approximately 20 m³. 3 After centrifugation, 16m 3 The high-salinity wastewater is collected and then treated.
[0031] First, high-salinity wastewater is pumped to a nanofiltration treatment system via a centrifugal pump. The wastewater is then separated from the organic matter and salts using a highly fouling-resistant nanofiltration membrane (this membrane has directional selectivity, exhibiting excellent interception efficiency of over 95% for organic matter, but excellent permeability of monovalent and divalent salt ions, reaching over 98%; it also has excellent anti-fouling properties and a long service life). This process yields a high-COD nanofiltration concentrate (approximately one-third the volume of the original high-salinity wastewater) and the remaining saline solution (approximately two-thirds the volume of the original high-salinity wastewater). The high-COD nanofiltration concentrate can be reused as a carbon source in the biological treatment system.
[0032] To meet the salt concentration requirements for bio-fermentation, the saline solution produced by nanofiltration is passed through a reverse osmosis membrane (this membrane allows water molecules to pass through as much as possible, with a salt ion rejection rate of 98%, retaining most salt ions; the membrane has excellent anti-fouling properties, requiring no scale inhibitors or bactericides; in case of clogging, only routine maintenance with water washing is needed; in cases of high clogging, acid washing with citric acid is sufficient to restore membrane flux) to concentrate the salt concentration, resulting in a retentate with increased salt concentration (approximately two-ninths the volume of the original high-salt wastewater) and reverse osmosis permeate (approximately four-ninths the volume of the original high-salt wastewater). The retentate with increased salt concentration reaches the concentration required for brine reuse and can be recycled to the process of producing PHA by halophilic bacteria. The reverse osmosis permeate has a very low salt concentration and reduced pollutants, and can be used as greywater for reuse. The entire process flow of this embodiment is as follows: Figure 1 As shown.
[0033] The relevant data involved in the entire process are shown in Tables 1 to 5.
[0034] Table 1. Membrane system processing data
[0035]
[0036]
[0037] Table 2 Raw water (high-salinity wastewater) data (average values)
[0038] index COD ammonia nitrogen Total nitrogen Total phosphorus pH salinity Value (mg / L) 20749 45 80 15 8.05 12943
[0039] Table 3. Nanofiltration concentrate data (average values)
[0040] index COD ammonia nitrogen Total nitrogen Total phosphorus pH salinity Value (mg / L) 42300 120 180 20 7.15 17500
[0041] Table 4. Reverse osmosis membrane retentate data (average values)
[0042] index COD ammonia nitrogen Total nitrogen Total phosphorus pH salinity Value (mg / L) 9500 30 40 1 7.5 30700
[0043] Table 5. Reverse osmosis permeate data (average values)
[0044] index COD ammonia nitrogen Total nitrogen Total phosphorus pH salinity Value (mg / L) 450 4 5 0.5 8.05 500
[0045] Example 2
[0046] The reverse osmosis membrane retentate from Example 1 was reused in the fermentation process and compared with the use of a single water fermentation (a single water fermentation control was set up each time). The results are shown in Table 6.
[0047] Table 6
[0048]
[0049] Note: Fermentation OD (Optical Density) is one of the indicators for measuring cell density during microbial fermentation. During microbial fermentation, as the microorganisms grow, the number of cells in the culture medium increases, leading to an increase in the optical density of the medium. Cell density can be indirectly estimated by measuring the absorbance of the culture medium (typically at a wavelength of 600 nm).
[0050] The results above show that the high-salt wastewater produced by halophilic bacteria fermentation in this embodiment of the invention can be reused five times, greatly reducing the amount of salt used each time. After the high-salt wastewater in the fermentation broth is recovered, the salinity of the enzymatic hydrolysis and purification processes is significantly reduced, and the salinity of the batches discharged into the sewage treatment facility meets the national emission standards. The sewage treatment biochemical process does not have the function of desalination, and desalination can only be done through evaporation. Now that the salinity meets the national emission standards, there is no need to remove salt, saving a lot of steam and drying costs.
[0051] The nanofiltration concentrate with high organic matter obtained by this invention has good biochemical properties, which can supplement the carbon source required for denitrification in biological treatment, reduce the addition of carbon source, and reduce wastewater operation costs. The reverse osmosis permeate has good transparency and low pollutant concentration, and can be used as reclaimed water for primary cleaning of materials, membrane system flushing, and chemical dissolution, thereby reducing the amount of primary water used.
[0052] Statistics show that wastewater treatment costs (calculated by drying) account for approximately 10% of product production costs. After implementing brine reuse, wastewater treatment costs are significantly reduced by about 8%, and product competitiveness is improved by about 8%.
[0053] It should be noted that the endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0054] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "specific implementation," or "some specific implementations," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.
[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for the complete reuse of water used in the fermentation of polyhydroxyalkanoates, characterized in that, include: The fermentation water of the polyhydroxy fatty acid ester was treated with a nanofiltration membrane to obtain a nanofiltration concentrate with increased COD content, as well as the remaining brine. The saline solution is then treated through a reverse osmosis membrane to obtain reverse osmosis permeate and a retentate with increased salt concentration. The nanofiltration membrane has a retention rate of over 95% for organic matter and a permeability of over 98% for monovalent and divalent salt ions.
2. The method for complete reuse of water used in the fermentation of polyhydroxyalkanoates according to claim 1, characterized in that, The COD content in the nanofiltration concentrate is more than twice that in the polyhydroxyalkanoate fermentation water.
3. The method for complete reuse of water used in the fermentation of polyhydroxyalkanoates according to claim 2, characterized in that, The nanofiltration concentrate is reused as a carbon source.
4. The method for complete reuse of water used in the fermentation of polyhydroxyalkanoates according to claim 1, characterized in that, The salt ion rejection rate of the reverse osmosis membrane is not less than 98%.
5. The method for complete reuse of water used in the fermentation of polyhydroxyalkanoates according to claim 4, characterized in that, The pressure applied during the operation of the reverse osmosis membrane is 2.0-5.2 MPa.
6. The method for complete reuse of water used in the fermentation of polyhydroxyalkanoates according to claim 1, characterized in that, The retentate with increased salt concentration is reused in the fermentation process for the production of polyhydroxyalkanoates.
7. The method for complete reuse of water used in the fermentation of polyhydroxyalkanoates according to claim 1, characterized in that, The salt concentration of the reverse osmosis permeate is less than 1200 mg / L, and it is used as recycled water.
8. The method for complete reuse of water used in the fermentation of polyhydroxyalkanoates according to any one of claims 1-7, characterized in that, The water used for the fermentation of polyhydroxy fatty acid esters is the liquid obtained by centrifuging the fermentation broth after biological fermentation of halophilic bacteria.
9. The method for complete reuse of water used in the fermentation of polyhydroxyalkanoates according to claim 8, characterized in that, The halophilic bacteria are Halomonas or their derivatives or combinations thereof.
10. A system for the complete reuse of water used in the fermentation of polyhydroxyalkanoates, characterized in that, Includes nanofiltration units and reverse osmosis units; The nanofiltration unit is used to treat the polyhydroxyalkanoate fermentation water through a nanofiltration membrane to obtain a nanofiltration concentrate with increased COD content, as well as the remaining saline solution. The reverse osmosis unit is used to treat the saline solution through a reverse osmosis membrane to obtain reverse osmosis permeate and a retentate with increased salt concentration. The nanofiltration membrane has a retention rate of over 95% for organic matter and a permeability of over 98% for monovalent and divalent salt ions.