A method for controlling reverse osmosis membrane pollution based on green biological scale inhibition

Abstract

The present application relates to a kind of reverse osmosis membrane pollution control method based on green biological scale inhibition, especially suitable for reverse osmosis membrane pollution treatment in industrial wastewater zero discharge system.The method comprises: regulating the composition of influent organic components by sand filter pretreatment unit, using the microbial community and its extracellular polymeric substance naturally enriched in sand filter process, without additional bacteria or chemical scale inhibitor, can directly interfere with the nucleation and crystallization process of inorganic scale on membrane surface, to form loose reversible pollution layer structure.The method effectively reduces the scale rate of inorganic salts such as calcium carbonate, inhibits membrane surface biological pollution, delays the densification of pollution layer, improves membrane flux retention rate, prolongs membrane operation cycle, reduces cleaning frequency.Compared with the existing conventional physical or chemical pretreatment method, the present application makes full use of the natural scale inhibition effect of the ecological system in sand filter unit, has the advantages of low operating cost, environmental friendly, strong adaptability and the like.

Description

Technical Field

[0001] This application relates to the fields of membrane separation technology and water treatment, and in particular to a green scale inhibition reverse osmosis membrane fouling control method based on microbial community construction. Background Technology

[0002] With increasing water scarcity and stringent environmental protection requirements, reverse osmosis membrane separation technology is widely used in industrial wastewater reuse and zero-discharge systems to achieve wastewater concentration, desalination, and resource recovery. However, high-salt, high-hardness wastewater typically contains high concentrations of hardness ions such as calcium and magnesium. During reverse osmosis concentration, these ions easily combine with anions such as carbonate and sulfate to form inorganic scale, including calcium carbonate and calcium sulfate. This is one of the most common and harmful types of fouling in reverse osmosis systems. Once these deposits cover the membrane surface, they cause a significant decrease in membrane flux, an increase in pressure differential, increased energy consumption, a shortened operating cycle, and an increased frequency of chemical cleaning, severely impacting the system's stability, economy, and service life.

[0003] Existing engineering methods typically control scaling risks by combining physical filtration methods such as sand filtration and ultrafiltration with chemical scale inhibitors (such as organophosphates and polycarboxylate salts). Chemical scale inhibitors delay the nucleation and growth of calcium carbonate crystals by complexing with calcium ions. However, these methods have the following drawbacks: (1) long-term use of chemical scale inhibitors increases operating costs and may introduce environmental risks; (2) under high-salt and high-hardness conditions, the dosage of scale inhibitors is large, and scale inhibition failure is easily caused by water quality fluctuations; (3) some scale inhibitors may form new deposits after reacting with impurities in the water, causing secondary pollution. Therefore, how to reduce chemical dependence and construct green, economical, and efficient pollution control technologies while ensuring the long-term stable operation of reverse osmosis systems has become a research focus.

[0004] To reduce reliance on chemical agents and improve the greenness of system operation, some studies have begun to explore "biological scale inhibition" technology. For example, Zhao Wei et al. (CN119979394A) disclosed a composite microbial scale inhibitor composed of *Lactobacillus plantarum*, *Pseudomonas*, and *Saccharomyces cerevisiae*. This microbial agent needs to be externally cultured before being added to the water treatment system, relying on the metabolically active products of the strains in the system to bind with scale ions to achieve the scale inhibition effect. This scheme constructs an exogenous composite microbial agent addition system, and its action process requires continuous maintenance of the activity and adaptability of the added microbial community, making operation and management relatively complex, and its stability is greatly affected by factors such as the source of the microbial strain and changes in water quality. Qu Qing et al. (CN110172489A) proposed a treatment method that uses artificially cultured Bacillus and extracts its extracellular polymers for use as a scale inhibitor. This method relies on the extracellular polymers produced by the metabolism of the bacteria in the external reaction system, which are then separated and concentrated and added to the water treatment system as a chemical additive to inhibit the formation of inorganic scale. This scheme constructs an indirect biological scale inhibition pathway of "exogenous cultivation - product separation - artificial addition," and its mechanism of action is similar to that of traditional chemical scale inhibitors, mainly relying on the complexation of functional polymers with scale ions. It lacks a continuous internal generation and transport mechanism, making it difficult to adapt to dynamic changes in water quality. Furthermore, the relevant disclosures do not provide verification of the bacterial stability and scale inhibition sustainability of this method in high-salt, high-osmotic-pressure wastewater systems over long periods. Zheng Shuaifei et al. (CN109437475A) disclosed a system for treating high-salt wastewater, whose process includes multiple treatment units such as "pretreatment - electrodialysis - oxidation - biochemistry - reverse osmosis," with a sand filtration unit included in the pretreatment. The disclosure indicates that this sand filtration unit is mainly used as a conventional physical filtration device to remove suspended particles and impurities; the technical description does not involve its microecological activity or microbial regulation mechanisms related to membrane scaling control. Zhang Wanyou et al. (Bulletin of the Chinese Ceramic Society, 2015, 34(9): 2543–2547) proposed adding screened bacterial strains to circulating cooling water systems to form a biofilm on the surface of metal heat exchangers to alleviate corrosion and scaling problems. This method constructs an indirect scale inhibition mechanism that relies on exogenous inoculated bacterial communities and nutrient regulation to form a protective layer on the metal surface, mainly used to control corrosion-scaling problems in low-salinity cooling water systems. Its control path relies on adjusting the pH of the water and the metabolic activity of the bacterial community to maintain ion balance, and the target is the metal surface of the equipment. Its application environment, control mechanism and target system are significantly different from the direction of reverse osmosis membrane fouling control, and no adaptive exploration or verification of membrane scaling control under high-salinity and high-hardness wastewater conditions has been found in the published content.

[0005] In summary, existing bioscale inhibition technologies generally have the following limitations: (1) They require the addition of artificial microbial agents or biological products, rely on external supply and stability adjustment, and increase the complexity of the system; (2) They are difficult to adapt to extreme working conditions such as high salt and high hardness, and have poor stability; (3) They lack targeted design in membrane fouling control pathways and fail to effectively integrate the synergistic scale inhibition mechanism between in-situ microorganisms and membrane systems.

[0006] Currently, although the combination of physical filtration and chemical antiscalants remains the mainstream method for controlling membrane scaling, it has gradually revealed problems such as limited efficiency, high operating costs, and poor environmental sustainability in the treatment of high-salt and high-hardness wastewater. The requirements for green and low-carbon water treatment processes are increasing, and the limitations of traditional antiscaling strategies in reducing reliance on chemical agents and improving long-term operational stability are becoming more prominent. Therefore, there is an urgent need to develop a green, efficient, low-cost, and environmentally friendly membrane scaling control method that can construct an in-situ stable antiscaling mechanism under complex high-salt and high-hardness wastewater conditions, reduce chemical additives, lower operating energy consumption, and achieve environmental protection and sustainable resource utilization goals while ensuring the long-term stable operation of the reverse osmosis system. Summary of the Invention

[0007] This invention aims to provide a green biological scale inhibition-based method for controlling reverse osmosis membrane fouling. Addressing the technical challenges of inorganic scaling during the reverse osmosis concentration of high-salt, high-hardness wastewater, the low stability of traditional scale inhibitors due to high dosage, and high environmental impact, this invention constructs a green control strategy that achieves long-term stable scale inhibition without the need for external bacterial agents or chemical reagents, relying on the in-situ microbial ecological function of the sand filter unit. By naturally enriching functional bacterial communities and generating extracellular polymers in the sand filter unit, a synergistic mechanism of "microecology-complexation-membrane control" is formed, continuously releasing and targeting the membrane surface. This achieves long-term, efficient, and green control of membrane fouling, reducing dependence on traditional chemical scale inhibitors and improving the system's economy, environmental friendliness, and stability.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] (1) High salinity and high hardness wastewater is introduced into a sand filter unit equipped with inert granular filter media, wherein the filter media has a particle size of 0.3–2 mm and the filtration speed is controlled within the range of 2.5–8.4 m / h.

[0010] (2) The sand filter unit in step (1) is run continuously for 7–20 days in the initial stage of operation, so that the background microorganisms in the influent attach and grow on the surface of the filter media, and establish the dominant bacterial community structure and extracellular polymer biofilm.

[0011] (3) No external bacterial agent is required. The composition of organic pollutants in the effluent is regulated by the microbial community established during the operation of the sand filter unit in step (2) and the extracellular polymers produced by its metabolism.

[0012] (4) Use the water effluent from the sand filter unit in step (3) as the feed water for the reverse osmosis membrane unit. By utilizing the complexation of the functional groups in the extracellular polymeric polymer with calcium and magnesium scale ions, the nucleation and crystallization process of calcium carbonate inorganic scale is interfered with, the densification of the reverse osmosis fouling layer is slowed down, and the membrane operation performance is optimized.

[0013] The inert particulate filter media of the sand filter unit in step (1) may include at least one of quartz sand, ceramsite, garnet sand, and anthracite, preferably quartz sand. The particle size of the filter media of the sand filter unit is preferably 0.5–1 mm, and the filtration rate is preferably 4.2 m / h, so as to ensure good interception and suitable hydraulic conditions, and promote the attachment and growth of microbial communities.

[0014] The microbial community enriched in the sand filtration unit in step (2) includes bacteria with the ability to produce extracellular polymers as the dominant flora.

[0015] In step (4), the sand filtration unit controls the operating parameters to ensure that the effluent is mainly composed of aliphatic and protein compounds, with a low proportion of aromatic and condensed aromatic compounds, and mainly derived from microbial metabolites and extracellular polymers. This effectively improves the feed water quality of the reverse osmosis membrane system and reduces the risk of organic pollutants contaminating the membrane.

[0016] This invention also provides a reverse osmosis membrane fouling control system based on green biological scale inhibition, comprising a sand filter unit and a reverse osmosis membrane unit connected by a connecting pipe. The sand filter unit is used to regulate the composition of organic components in the feed water through extracellular polymers formed by microbial metabolism, while the reverse osmosis membrane unit is used to perform deep purification treatment on the sand-filtered effluent. Preferably, this system does not add external chemical scale inhibitors during operation, and the backwashing interval of the sand filter unit is 20 days to ensure long-term, low-maintenance operation of the system, while maintaining stable growth of the microbial membrane and filter media permeability.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. By leveraging the ecological functions of the naturally enriched background microbial community and its extracellular polymers in the sand filter unit, an in-situ self-generating, continuously releasing, and non-artificially added green membrane pollution control mechanism is constructed, reducing operation and maintenance costs and improving environmental friendliness.

[0019] 2. The abundant functional groups in the extracellular polymeric material can effectively complex with scale ions such as calcium and magnesium, inhibiting the nucleation and growth of scale such as calcium carbonate, slowing down the densification of the fouling layer, delaying membrane flux decay, and significantly improving the antifouling performance of the membrane module and the system operating cycle.

[0020] 3. The effluent organic components are significantly adjusted, reducing the proportion of aromatics and nitrogen- and sulfur-containing organic matter, thus lowering the potential risk of subsequent membrane fouling. It is particularly suitable for reverse osmosis membrane systems under complex water quality conditions with high salinity and high hardness, and has good stability, adaptability, and application value. Attached Figure Description

[0021] The above and / or additional aspects and advantages of the present invention will become more apparent and readily understood from the following description of embodiments taken in conjunction with the accompanying drawings, wherein:

[0022] Figure 1 A comparative diagram of the organic composition of sand-filtered water under different filter media conditions;

[0023] Figure 2 A comparison chart of the effects of different sand filtration parameters on turbidity removal, where A is a comparison chart of filtration speed and B is a comparison chart of particle size parameters.

[0024] Figure 3 A comparison of three-dimensional fluorescence spectra of effluents from different pretreatment processes;

[0025] Figure 4 Distribution diagram of organic matter molecular composition in effluent from different pretreatment methods;

[0026] Figure 5 This is a comparison chart of the effects of different pretreatment methods on fouling control during the operation of a reverse osmosis membrane system. In the chart, A is a comparison chart of permeate flux, and B is a comparison chart of specific resistance of the fouling layer.

[0027] Figure 6 The bar charts show the comparison of pore structure parameters of the reverse osmosis membrane fouling layer under different pretreatment methods. A is a comparison chart of specific surface area (BET method) and micropore area, and B is a comparison chart of total pore volume and micropore volume. Detailed Implementation

[0028] The present invention will be further described below with reference to embodiments and accompanying drawings, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments are not intended to limit the present invention.

[0029] This invention provides a reverse osmosis membrane fouling control method based on green biological scale inhibition, the process flow of which is as follows: Figure 1 As shown, it includes the following steps:

[0030] S100, sand filter unit naturally enriches microbial communities

[0031] High-salinity, high-hardness wastewater is introduced into a sand filter unit using inert granular filter media. The unit is operated continuously for at least 7 days during the initial stage of operation, allowing microbial communities to naturally accumulate on the surface of the filter media and form a stable extracellular polymeric biofilm.

[0032] S200 sand filtration unit stabilizes the influent water sample.

[0033] After the microbial community has stabilized and attached, the sand filtration unit treats actual high-salinity and high-hardness wastewater. Through the extracellular polymers produced by microbial metabolism, the composition of organic pollutants in the sand filtration effluent is regulated, thus optimizing the influent conditions for the subsequent reverse osmosis membrane system.

[0034] S300, reverse osmosis membrane unit scale control

[0035] Using the effluent from the sand filter unit as the feed water for the reverse osmosis membrane unit, the abundant carboxyl and hydroxyl functional groups in the extracellular polymeric material can complex and adsorb scale ions such as calcium and magnesium in the water, interfering with the nucleation and crystallization process of inorganic salts such as calcium carbonate, slowing down the densification of the membrane fouling layer, and improving the antifouling performance and operating cycle of the membrane system.

[0036] Example 1

[0037] This embodiment optimizes the filtration speed and filter media particle size of the sand filter unit. Experimental results are as follows: Figure 2 As shown, regarding filtration velocity, a turbidity removal rate of 95.8% was achieved at a filtration rate of 4.2 m / h, which is superior to other velocity conditions. Regarding filter media particle size, a turbidity removal rate of 98.1% was achieved when the particle size was 0.5–1 mm, which is superior to the conditions for particle sizes of 0.3–0.5 mm and 1–2 mm. Combining these results, the preferred particle size range was determined to be 0.5–1 mm, and the preferred filtration velocity was determined to be 4.2 m / h. All subsequent experiments used this combination of conditions.

[0038] Example 2

[0039] In this embodiment, under the preferred conditions determined in Example 1, quartz sand was selected as the filter media. The sand filtration unit operated continuously for 21 days, and the properties of the effluent were recorded on days 5, 7, 9, 15, and 21. The three-dimensional fluorescence spectrum of the quartz sand-filtered water is shown below. Figure 3 As shown, during the initial 5 days of operation, peaks I and II corresponding to protein-like substances such as tyrosine and tryptophan in the effluent exhibited high fluorescence intensities, ranging from 0.5 to 0.75, indicating that the organic pollutants in the effluent mainly originated from microbial metabolites. With the operation time extended to 21 days, the fluorescence intensities of peaks IV and V gradually increased, eventually ranging from 0.75 to 1.0. The distribution of organic molecular composition in the quartz sand filtered water is shown below. Figure 4 As shown, the O / C and H / C values ​​are mainly concentrated in H / C 1.2–1.8 and O / C 0.2–0.6, dominated by aliphatic compounds, with some located in the high carbon region of H / C 0.7–1.2 and O / C 0.6–0.8, which are extracellular polymers and microbial metabolites.

[0040] Example 3

[0041] In this embodiment, under the preferred conditions determined in Example 1, anthracite was selected as the filter media. The sand filtration unit operated continuously for 21 days, and the properties of the effluent were recorded on days 5, 7, 9, 15, and 21. The three-dimensional fluorescence spectrum of the anthracite-filtered water is shown below. Figure 3 As shown, during the initial 5 days of operation, peaks I and II, corresponding to protein-like substances, exhibited high fluorescence intensities ranging from 0.5 to 0.75. As time progressed to day 21, the fluorescence intensities of peaks IV and V gradually increased, indicating a significant accumulation of humic acids and high-molecular-weight organic matter. This suggests that anthracite coal has a relatively weak ability to remove recalcitrant organic matter. The organic molecular composition of the anthracite-filtered water is as follows: Figure 4 As shown, the O / C value is mainly concentrated in 0.2–0.6, while the H / C value is relatively low in 0.7–1.2. It is dominated by complex aromatic compounds with high density and complex molecular structure, reflecting the release of aromatic organic matter from the anthracite filter, which increases the complexity of the effluent.

[0042] Example 4

[0043] This embodiment serves as a comparative example, using ultrafiltration membranes instead of sand filtration as a physical pretreatment process, operating under the same water quality conditions. The three-dimensional fluorescence spectrum of the ultrafiltration effluent is as follows: Figure 3 As shown, the proportion of aromatic compounds remains relatively high. Their organic molecular composition is as follows: Figure 4 As shown, the organic molecular composition of the ultrafiltration water is as follows: Figure 4 As shown, the H / C value is 1.0–1.8, the O / C value is 0.2–0.8, the density is low, the molecular composition is relatively simple, and the effluent contains more aromatic and condensed aromatic compounds, indicating that its effect on regulating organic components is not as good as that of sand filtration.

[0044] Example 5

[0045] In this embodiment, the quartz sand effluent determined in Example 2 was used as the feed water for the reverse osmosis membrane and operated continuously in the reverse osmosis membrane system for 20 days. The results are as follows: Figure 5 As shown, at the end of operation, the reverse osmosis membrane flux remained at 54.96% of the initial flux. The fouling layer specific resistance decreased from approximately 2 × 10⁻⁶ initially. 12 m -1 Increased to 2.78 × 10 13 m -1 The pore structure parameters of the membrane fouling layer are as follows: Figure 6 As shown, the specific surface area of ​​BET is 293.54 m². 2 / g, with a micropore area of ​​184.4 m². 2 / g, total pore volume 0.51 cm³ 3 / g, micropore volume 0.42 cm³ 3 / g. The membrane flux stability is high, the specific resistance of the fouling layer is low, and the pore structure of the membrane fouling layer is relatively loose, indicating that quartz sand filtration pretreatment can effectively mitigate reverse osmosis membrane fouling.

[0046] Example 6

[0047] In this embodiment, the anthracite effluent determined in Example 3 was used as the feed water for the reverse osmosis membrane and operated continuously in the reverse osmosis membrane system for 20 days. The results are as follows: Figure 5 As shown, at the end of operation, the reverse osmosis membrane flux remained at 42.34% of the initial flux. The fouling layer specific resistance decreased from approximately 2 × 10⁻⁶ initially. 12 m -1 Increased to 4.81×10 13 m -1 The pore structure parameters of the membrane fouling layer are as follows: Figure 6 As shown, the specific surface area of ​​BET is 72.37 m². 2 / g, with a micropore area of ​​67.27 m². 2 / g, total pore volume 0.11 cm³ 3 / g, micropore volume 0.09 cm³ 3 / g. The membrane flux stability was low, the specific resistance of the fouling layer was high, and the pore structure of the fouling layer was relatively dense, indicating that the anthracite pretreatment had a limited effect on mitigating membrane fouling.

[0048] Example 7

[0049] In this embodiment, as a comparative example, the ultrafiltration effluent determined in Example 4 was used as the feed water for the reverse osmosis membrane, and the system was continuously operated for 20 days. The results are as follows: Figure 5 As shown, at the end of operation, the reverse osmosis membrane flux remained at 32.36% of the initial flux. The specific resistance of the reverse osmosis membrane fouling layer decreased from approximately 2 × 10⁻⁶ initially. 12 m -1 Increased to 7.51 × 10 13 m -1 The pore structure parameters of the membrane fouling layer are as follows: Figure 6 As shown, the specific surface area of ​​BET is 31.16 m². 2 / g, micropore area 20.45 m² 2 / g, total pore volume 0.06 cm³ 3 / g, micropore volume 0.06 cm³ 3 / g. Membrane flux decreased significantly, the fouling layer had the highest specific resistance, and the fouling layer had the densest pore structure, indicating that ultrafiltration pretreatment is not effective in mitigating membrane fouling.

[0050] Example 8

[0051] This embodiment demonstrates the application effect of the reverse osmosis membrane fouling control method based on green biological scale inhibition described in this invention in a practical engineering project. The treatment target is a zero-discharge system for flue gas desulfurization wastewater from a coal-fired power plant, with a wastewater treatment capacity of approximately 110 m³. 3 / d. The system adopts the sand filtration unit combined with the reverse osmosis membrane unit process described in this invention. The sand filtration unit is filled with quartz sand filter media with a particle size of 0.5–1 mm, the filtration speed is controlled at 4.2 m / h, and the backwashing interval is 20 days.

[0052] In this engineering application, the naturally enriched microbial community and its extracellular polymeric substances in the sand filtration unit replace traditional high-dose chemical pretreatment. After the system is operational, the cost of chemicals is reduced by 65%, and the cost per ton of water treated is reduced by 5.80 yuan / m³. 3 This process saves approximately 705,000 yuan in reagent costs annually. Actual operation demonstrates that this technology can ensure the long-term, stable performance of reverse osmosis membrane systems, mitigate membrane fouling, extend the service life of membrane modules, and significantly improve overall operational economy and environmental friendliness.

[0053] The embodiments described in this invention are merely illustrative of preferred embodiments and are intended to aid in understanding the technical content; they are not intended to limit the scope of protection of the invention. Any obvious substitutions, modifications, or equivalent improvements made without departing from the spirit and scope of the claims are covered within the scope of protection of this invention.

Claims

1. A reverse osmosis membrane fouling control method based on green biological scale inhibition, comprising the following system, characterized in that: The system includes a sand filtration unit and a reverse osmosis membrane unit. The sand filtration unit is connected to the reverse osmosis membrane unit through a connecting pipe. The sand filtration unit is used to regulate the composition of organic components in the feed water through extracellular polymers formed by microbial metabolism. The reverse osmosis membrane unit is used to perform deep purification treatment on the sand filtration effluent. The method includes, High-salinity, high-hardness wastewater is introduced into a sand filtration unit equipped with inert granular filter media, the particle size of which is 0.3–2 mm, and the filtration rate is controlled at 2.5–8.4 m / h. The sand filter unit is operated continuously for 7–20 days in the initial stage of operation, allowing background microorganisms in the influent to attach and grow on the surface of the filter media, establishing a dominant bacterial community structure and an extracellular polymer biofilm. Without the need for external bacterial agents, the composition of organic pollutants in the effluent is regulated by the microbial community established during the operation of the sand filter unit and the extracellular polymers produced by its metabolism. Using the effluent from the sand filter unit as the feed water for the reverse osmosis membrane unit, the functional groups in the extracellular polymeric material are used to complex with calcium and magnesium scale ions, thereby interfering with the nucleation and crystallization process of inorganic calcium carbonate scale, slowing down the densification of the reverse osmosis fouling layer, and optimizing membrane operating performance. The inert particulate filter media includes at least one of quartz sand, ceramsite, garnet sand, and anthracite. The microbial community enriched in the sand filtration unit includes a dominant group of bacteria capable of producing extracellular polymers. The backwashing interval of the sand filter unit is 20 days to ensure long-term, low-maintenance operation of the system, while maintaining stable growth of the microbial membrane and filter media permeability. The system does not require the addition of external chemical scale inhibitors during operation.

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